Hello, I believe I have a crank position sensor problem after the research I’ve done on here & Google, but I’m looking for someone to weigh in with a second opinion. There’s one detail about it all that makes me second guess my diagnosis.

1989 ranger
2.3L fuel injected
manual w/4 wheel drive

new parts:
-In tank fuel pump
-fuel filter
-rebuilt trans
-driveline ujoint
-replaced bad wiring at coilpack, intake side
-recent spark plugs

short story:
-Starts/Runs great cold
-misfire when warm w/throttle open
-idles warm, but only for a minute & dies
-hard to start until cooled down


Long story:
Terrible misfire occurs with any throttle movement only when the engine has warmed up completely. Either going down the road or sitting in the driveway, given any throttle it will misfire heavily. It’s like I’m twisting a distributor by pressing the pedal (just a way to describe the problem, I know there’s no distributor). Even if I just let it idle, it will eventually putter out and die, given maybe 45 seconds. Once it’s that warm & giving me issues, it doesn’t want to start. It kicks & backfires (through the exhaust and intake), and won’t start until it’s sat for 20min.

What I find strange is that it will start up great if it’s cold. I was able to drive it 50 miles before it started the misfire, and now I can’t drive more than 10 minutes. I’ve read that a bad crank position sensor will cause a no-start situation. I don’t get that situation until the engine is hot. That led me to believe that the coil packs were bad, so I replaced them but the problem persisted. Had to return the new coil packs to save money.

My question is, is there something else that could cause this misfire if it’s only happening after it’s warmed up? Trying to not tear it apart just for that stupid crank sensor lol.

Any input is a big help, thank you

 

Check my thread I just posted titled “Recessed Exhaust Valve Seats”

 

Also check your coolant temp sensor. There are two separate ones. One for the gauge and one for the PCM. The gauge one could be working but the PCM one isn’t and the PCM is mixing the A/F incorrectly due to that.

 

Checked out your thread, man what a nightmare. Sounds like you’re having fun with that one. I think for now I can rule out recessed exhaust valve seats, as my truck (when it’s not acting up) runs perfect and has loads of power (something I did not expect from an 89 2.3L engine lol).

If my issue is just a coolant temp sensor, hallelujah. Thanks for the tip and I’ll go test for it. Do you happen to know which temp sensor is which? The dash gauge reads pretty normal but the problem I have really does sound like it could be wrong a/f ratio. Would be a lot nicer than replacing the crank position sensor for sure.

 

From what my parts system is telling me, the 1989 is a bit different than the 2000, which is to be expected. Looks like there is one with an electrical connector that has 2 pins and one that has one of those rubber push on connectors. The 2-pin is for the PCM and the rubber push on is for the gauge. On the 2000, they are both with electrical connectors and they are both in the thermostat housing right at the front of the engine. If yours does have different connectors, go for the 2-pin. If they are the same like mine, just warm the engine up and disconnect one. If the gauge stops working or jumps all the way up when you disconnect the first one, then the PCM one is the other one. If the engine changes its tune when you disconnect the first one, then that’s the one for the PCM. I know some people just replace both to be safe. But here are some pictures. The first should be for the PCM and the second should be for the gauge, at least according to my parts system.





However, my parts system has been wrong before so I would double check on that. There is also another sensor on the back driver side of the head on the 2000 but I believe that’s for the oil pressure gauge. I could be wrong though on that though. Some Ford’s had a “Cylinder Head Temperature” sensor as well that measured the temperature of the metal itself, so that may be what that back one is. I would honestly just unplug one with the engine at temperature and see what happens.

 

I’ve got one of the 2-pin sensors on order, ordered it through work first thing this morning. Trying not to get my hopes up but dang would it be nice if this was my issue. Could be the wiring too, already had to replace the intake side coil signal wiring.

I’ve gotta say, your info & help is above and beyond. I joined the forum with low expectations because of other forums in the past but it’s nice to see this place has a helpful person such as yourself, thank you.

 

I don’t want to get your hopes up too much but I am almost guaranteeing that CTS is your issue. The CTS means EVERYTHING to temperature related A/F ratio. Engines do what is called “warmup fuel enrichment” which is basically the EFI version of a choke on a carburetor. As the engine warms up, the PCM slowly leans the mixture until it reaches its programmed operating temperature at which time it enables the short term fuel trims. That is when the engine is running its optimum A/F ratio. That’s why a car with a thermostat that opens too early gets such poor fuel economy. It’s staying in the warmup fuel enrichment temperature. Well, it will continue to lean the mixture if the engine goes ABOVE the operating temperature. The mixture needs to be correct for the exact temperature the engine is running or it simply will NOT run right.

I had a turbo VW Jetta years ago that I had aftermarket ECU software so it would spike 22psi and slowly drop back to 15psi at redline. Well, one day it stopped making full boost when the engine was warmed up. If I shut it off and let it cool, boost would come back until it warmed up again. I kept scanning it for codes with nothing. Finally I borrowed a friend’s scanner and found a pending code for the CTS. This was before I had the understanding of cars that I do today. So, I replaced the CTS with one from the dealer because VW Bosch ECU’s are super picky about the data they receive, and the problem was fixed. That is a 4-wire sensor on that car. There are two thermal resistors in the one sensor. One is for the gauge and the other is for the ECU. The one for the ECU was reading improperly and throwing the mixture off as well as causing boost to be reduced because it thought it was overheating. Those cars have ECU controlled boost. They have the “N75” valve which is essentially an electronic boost controller but it’s controlled by the ECU rather than a standalone box. The ECU will reduce the requested boost if it senses the engine running hot.

I’ve seen many cars of many makes run like complete garbage because the CTS is reporting faulty data. It is probably the third most important sensor for A/F ratio control second to the MAF and the Upstream Oxygen sensors. It is HIGHLY important. Your truck is showing every symptom I have ever seen for a faulty CTS. I would be willing to lay money on the fact that the new one will fix your issue, as long as you bought the correct one. Did you try to unhook them like I suggested? You probably did order the correct one though. Usually the rubber push on connectors are for gauges on Fords. They don’t need to be as accurate as the ones for the PCM so the circuitry isn’t quite as advanced. The problem with the CTS and throwing a code is that there really isn’t anything to tell the computer it’s getting faulty data. There’s no other sensor telling the PCM temperature information and it really doesn’t know until the signal flat out becomes implausible to the PCM. The MAF gets confirmed with the oxygen sensor. The CTS makes the computer command a certain mixture and as long as the MAF and oxygen sensors are telling the computer that it’s getting the commanded mixture, it really doesn’t know there’s something wrong. It doesn’t know the reason it’s getting random misfires is because the CTS is lying to it. It doesn’t know those misfires are from it commanding the wrong mixture. That’s why some cars have 2 now. If it sees conflicting data between those sensors, it will mix the fuel on one sensor and look for misfires and then mix the fuel according to the other sensor and look for misfires. Whichever one causes misfires and other running issues, it throws a code for that sensor, ignores it, and listens to the sensor that is giving correct data. There’s no redundancy in your engine like that. It’s also an OBD-I vehicle which is even HARDER to diagnose until the computer throws a code. You can’t read live data out of your PCM. You can’t sit there and look at the actual data the PCM is seeing. That puts you even more in the dark. But I’m telling you, I’m like 95% sure it’s your CTS. Please report back when you get it installed. I’m curious to know the outcome!

 

It’ll be next week before I can get to it, it’s actually my dads truck I’m fixing while he’s out of town and work takes up a lot of my time. I’ll definitely come back with the result, I like that kind of closure too lol. Yeah it makes sense that the temp sensor for the computer side of things would cause this, funny I never thought of it. That’s exactly why it helps to ask for second opinions lol I’m glad I came here. This truck is right in that era of car I avoid due to the early computer & efi systems…much prefer carbs, or OBD-II if I have to deal with EFI at all hah. Which is ironic because I also own two late 80s Hondas…

 

In some aspects, OBD-I is easier, and in some aspects it’s harder. It’s easier because there are far less sensors and far less codes. It’s harder because you can’t read live data. You would be having full time issues if it was the CKP sensor. I honestly don’t know what the CKP sensor does on these other than tell the PCM if everything is in time. The CMP sensor judges when to fire the coils and/or injectors. I forget if the 89 had a distributor or if it had a coil pack. Either way, there is a CMP sensor either in the distributor or standalone to tell the PCM when to fire the injectors. The CKP wouldn’t tell the PCM anything like that because it doesn’t know which stroke the cam is on. That’s why they used the oil pump for the CMP. It has the same size sprocket as the Camshaft so it’s spinning at the same speed. That’s why you have to time it when you do the timing belt otherwise your ignition and/or fuel injection timing is way off. I guess it can use the CKP for RPM as well, but the CMP will also tell that. The CKP is MUCH more important on modern engines than it is older engines. Modern engine have variable cam timing which the PCM needs to know the Crank position as well as the Cam position because it has to compare the two. It tells the computer if everything is in time or if there is an issue with the timing belt/chain and also will know if it has advanced the intake cam and (if dual VCT) if it has retarded the exhaust cam far enough in relation to the crank. It can also use the CKP as a backup if the CMP fails. It might result in a longer crank time for start as the PCM figures out which stroke its on, but on a waste spark system like Ford uses, it doesn’t even matter which stroke it’s on. It’s mainly using it for injection timing as far as that goes. An engine will still fire if the fuel injection timing is off, it’s just going to run like complete poo if it has injected on the wrong stroke because the fuel won’t be getting sprayed into an air flow so it won’t atomize very well other than the injector nozzle but even then it’s just going to puddle on top of the intake valve until it opens. Then you have liquid fuel instead of atomized fuel so it’s REALLY going to run like poo since it won’t actually burn all the fuel. There’s no way it will have time to fully propagate the burn by just igniting a small amount of vapor and waiting for it to catch the rest of the fuel. That’s when you’ll get a rough start that eventually will smooth out because the computer realizes it has fired the fuel on the wrong stroke. Once it realizes this, it will correct itself and the engine will smooth out. It’s only going to have this issue if it knows the CMP has failed already. A lot of times a CMP can cause a no-start situation or at least a very hard start, again, until the PCM figures everything out.

The ONLY other thing I can really think of in your situation would be the fuel pump. I have seen A LOT of fuel pumps run like when they are cool and then either shut down or cause a low pressure when they heat up. Once they cool down, they will run normally again. I’ve seen it with pretty much all of the OEM brands of pumps, but mainly Delphi and Denso. The Bosch pumps just completely **** out without any warning at all. They will run just fine one second and then they are done the next second. They can even fail when they shut down when you turn the car off and then go to restart the car. It leaves you wondering WHAT DAFUQ JUST HAPPENED?!!!? A lot of times people think their timing belt failed because it’s that sudden. But here’s what I would suggest. I’m still totally thinking it’s your CTS. If it ends up not being that, go get one of those fuel pressure testers from AutoZone with their loan-a-tool program. There is a schrader valve on the front of the fuel rail or right next to the TBI, whichever one you have, with a black cap on it. Looks just like a tire valve stem. Hook your gauge to that and start the engine. Record what the idle fuel pressure is. Then wait until it starts to run like poo and then compare the reading to the reading you had when it was cold. The cold reading should ONLY be a COUPLE psi higher due to the higher cold start RPM and lower vacuum/higher manifold pressure, if it deviates at all. If you have a drop of anything more than about 5-6psi, your fuel pump and/or fuel filter are having problems. It should be about 40-44psi at idle. You’re going to start having problems around 30-35psi and it’s either going to run terrible or not at all below 30psi. It could also be an issue with the Fuel Pressure Regulator if you have low pressure. But, again, I DO NOT believe that is your issue.

When you go to change your CTS, make sure the engine has been sitting off for at least 8 hours. Remove the radiator cap to release any residual pressure, then reinstall it. This will draw a vacuum on the system to keep you from losing too much coolant. Remove the electrical connector and then take your ratchet with your deep well socket and remove the sensor. Have the new sensor ready to go immediately, preferably in your other hand. As soon as you pull the old sensor, get the new one in and started. The longer you have it open, the more coolant you’ll have to replace. If you do it quick enough, you’ll lose less than an ounce of coolant and you won’t have to top off at all. Reconnect your sensor wiring, and take it for a test drive. It should not take you more than 5 minutes to change the sensor.

 

Had a window of opportunity to replace the sensor today & I took it. Seemed okay at first but the problem persists. Going to test the fuel pressure next, like you described.

The previous owner said the fuel pump was replaced, but to my understanding there are two pumps, one in the tank and one out of it. From what I can tell, they replaced the pump that's in the tank, as I can see someone was recently moving things around on top of the tank. Trouble is, I have no idea where the other fuel pump is. From what I've read, it should be on the frame-rail, but all I can find is the fuel filter (also been replaced).

Also one last detail, this 89 Ranger has the coil packs, one for intake side and one for exhaust side spark plugs. I'll have to search for that Camshaft Position Sensor...granted there is one on this particular 1989 2.3L. Otherwise, all I can think of besides fuel & spark is air, which leads me to the Throttle Position Sensor, as I don't see a mass airflow sensor (I believe truck uses a MAP sensor). What I don't get is, if the problem was the TPS, I'd be experiencing a "dead zone" in pedal-travel. My sputtering happens at any throttle position. Gets worse as the engine gets warmer, and eventually gets so bad the engine dies & can only restart a few times before it just wont start at all, until it cools down. But it runs fantastic before it warms up...plenty of get up & go and very smooth.

Hoping to find some determining results with the fuel pressure test.

 

Where are you located? I’m in Columbus, Ohio. I’m actually very surprised the CTS didn’t fix the problem. I have seen fuel pumps fail prematurely and I’ve even had ones that made very weak pressure out of the box. A Jeep Liberty cost me 6 hours of troubleshooting one day because I replaced the fuel pump that the customer had JUST replaced with an Amazon part that failed in 3 days. I got a Spectra Premium pump from the Zone and it would only make 8psi right out of the box. Put ANOTHER Amazon pump in because NOBODY had one in stock and it fixed the problem. Personally, the ONLY pumps I trust are Delphi pumps. I’ve replaced over 100 pumps and I have only had ONE Delphi pump fail, and that was because my idiot assistant installed the fuel filter backward (it’s a directional filter on a 2000 Mustang), even after I told him like 10 times to make sure he had the filter in correctly. Luckily I was able to do that under warranty for the customer and I took my labor out of his pay since he couldn’t listen to me. He no longer works for me now. But that’s beside the point. If the previous owner used a low grade pump and/or filter, it very well may be a weak pump once it warms up. Also, when it starts to run like poo, see if you can get any codes to flash from the PCM. You don’t have to have a scanner. Google how to jump the OBD-I connector on a Ford and count the number of flashes from the Check Engine Light. A lot of times OBD-I will NOT store codes in the PCM. It’s all current-ignition-cycle diagnostics. What you can do to shut the engine off without switching off the ignition is to run the engine, wait until it runs like poo, pull the fuel pump fuse or relay, let the engine die, plug the fuse or relay back in, and then read the codes. That will ensure any codes will be present from that ignition cycle. When doing things like that, it’s not really a good thing to run the diagnostics with the engine actually running on OBD-I. Some cars are ok to do it, but I don’t do it as a general rule so I don’t mess something up. See if you can get any codes to come up and then report back.

 

Central Oregon. I’ll do the fuel pressure test and get any present codes next chance I get.

Was looking up fuel pumps on our parts website at work to try and see what the secondary one looks like, but the only ones that show up for this truck (looked it up by VIN) are the in-tank pumps. Maybe this truck doesn’t have the secondary ones like I read. So I wonder if the previous owner goofed their installation.

 

Currently checking fuel pressure, will update semi-live as I go.

Cold, engine off, three key-turns to prime fuel system: 38psi

Current reading as the engine warms up at idle: 29-31psi

Its looking like the problem lies within the fuel system.

 

After doing some more reading while this thing warms up, it looks like 28-30psi at idle is supposed to be normal for this engine. Thoughts?

 

Couldn’t get it to act up in the driveway, so with the pressure gauge still connected I backed out to go test drive it. Immediately started to act up, any throttle input combined with the load of any gear caused horrible stumble. Checked gauge, normal fuel pressure. Continued to drive so it could get bad enough to set codes, but magically the problem went away.

This has happened before, so I disconnected the gauge and went for a longer drive until it acted up again. Only it didn’t act up until after I gave up & parked in the driveway. After idling a few minutes (and some partial throttle input) it began the misfire issue. Again, idles perfect but any throttle input causes it to run like crap.

I let it do its thing, & eventually it died on its own. Installed the jump wire and tried to count the CEL flashes, but I admit it was a little quick for me. Seemed like I got a 418, a 348, and something something 88. Trying to repeat the process to get the codes again but I can’t get it to act up yet. Also, the chart I’m looking at doesn’t have some of these numbers, so I think they’re wrong. Here goes trying again.

 

Codes are

418

34

88

Going to look them up now on 6% phone battery lol

Edit: Oh also, as soon as I hook up the jumper wire, the CEL flashes “1” for a total of 5 times. So that’s one flash, with a large pause in between, 5 times. Then goes on to flash the above codes. It flashes them (418, 34, 88) twice, separated by one flash.

 

After watching the video I took, I think the codes are:

11 System OK

14 Ignition pickup (PIP) was erratic – Ignition Systems

18 Check base timing & advance function – Timing Tests

34 EVP – EGR did not respond properly during test – EVP

88 Throttle Kicker Solenoid – Solenoids


Is the throttle kicker solenoid the Throttle Position Sensor? Going to be researching these codes tonight..

Edit: Other websites list different descriptions for some of these codes, like 34 & 88. Not sure which OBDI list I'm supposed to use here...

 

Found this post by fefarms in this thread (https://www.ford-trucks.com/forums/2...p-voltage.html)

"Code 34 is one of the simpler EGR problems. The computer is telling you: I want (or wanted) the EGR valve to be shut. The position sensor says it is (or was) open. For this code, it does not matter if the diaphragm is shot, the vaccuum lines are off, or the EVR refuses to send vaccuum to the EGR valve.

If this is a KOEO code, it is a static, continuous problem and should be easy to track down. The only components implicated are the EGR pintle, the spring that is supposed to return the pintle to the closed position, the EVP position sensor, and the wiring between the EVP and the computer.

If you have a voltmeter, you can probe the EVP sense voltage with the key on and engine not running, and see what value it is. Normally it should be 0.41 volts or less, but the computer is complaining that it is not.

The most likely explanation is that the EGR valve is sticking due to carbon in the seat area. You can probably pull it off and clean it up."


This will be helpful. Trouble is, when I was hooking up the fuel pressure gauge, I had an easier time doing it by unplugging an electrical connector right under the EGR valve. The plastic clips broke off the connector, and I wonder if engine vibrations managed to wiggle it free. I will have to double check that tomorrow when I can get back to the truck (it's not at my house).

Onwards with the research.

 

Replaced ICM that's bolted to the intake manifold. Thought maybe it was fixed but no dice. Finally got the engine warm enough for the problem to return. Seems to really not like excessive heat (it's been 90+ for a few weeks now) and starts to have some sort of timing issue when the engine's hot. Dash gauge reads normal, and the ECT sensor is replaced like mentioned above. No idea what's going on.

After replacing the ICM I pulled the codes again, all the same (cleared them beforehand). Thinking about trying to clean the EGR valve next or something. It holds vacuum great and I can hear it shut when I release vacuum. So maybe it's dirty/getting stuck open.

Otherwise, I'm at a loss and could use some help.

 

Does it seem to be worse with ambient air temperature? There is an AIT sensor in the intake.

 

Yeah I mean today was much cooler and it took a lot more engine temp to recreate the problem. I noticed the AIT sensor when I was replacing the ECT. Think that could really cause this? Otherwise I’ve been wondering about the input that the ICM/DIS is supposed to receive for dual coil control & timing advance. I just can’t confirm where exactly it’s supposed to receive that input.

 

The ignition pickup is the Camshaft Position Sensor. It’s erratic and you’re also getting a code for the base timing and advance. How is your timing belt? If it has been replaced, are you SURE it’s in time? If it’s off a tooth, the engine may run fine when it’s rich during warmup and then crap out when the mixture goes to normal. An erratic ignition signal and a timing issue points to the CMP being good but having a dancing signal. The CMP is located behind the oil pump and reads off the oil pump. That’s why it’s important to have the oil pump in time with the crank and cam. Before going anywhere else, I would pull the timing cover, check the timing belt for proper tension/condition, and line up the timing marks to ensure that everything is in time. If anything seems amiss there, correct it and go from there. Oh, and I believe ignition timing also changes when operating temperature is reached. Say the oil pump is a tooth retarded. The ignition is more advanced during warm up because of the added fuel. When you reach operating temperature, the timing retards back to normal. If the oil pump/CMP sensor are retarded, then the ignition timing is going to be retarded more than normal as well.

 

I will certainly check these, as I wish to be thorough and solve this thing correctly, but I have to emphasize how well this thing runs & drives. I warm it up for 20 minutes, drive it 25 miles (HARD) with no issue whatsoever. Tons of power, throttle response, all is well.

As soon as it gets hot enough at idle (red lights, drive way) that the fan clutch engages a few times (aka, a couple cycles of the engine cooling itself at a standstill) the misfire starts. I’ll feel one little putt of a single misfire at idle, and from there if I add any open throttle input it will have a consistent misfire. Revving it higher (to a consistent RPM, not a stomp/snap of the throttle) will clear out the misfire and it will hold that higher rpm steady. If I hold it there & heat up the engine, the problem will get worse. As in, after closing the throttle and letting it idle, any open throttle position (even slightly) will cause the stumble. If I manage to get the engine warm enough (dash gauge barely reads higher than normal) it’ll eventually die if left to idle long enough.

Hopefully that wasn’t as confusing as it felt to type. Trying to be as thorough as possible with detail without over-explaining. Basically what I’m trying to say is, I’ve experienced engines that were a tooth-off on their timing belt. They didn’t feel like this engine. Maybe that’s because this engine is different - I just plain don’t know. Merely explaining what I’m experiencing.

 

With the codes you’re getting, I would DEFINITELY check that timing belt. It’s not going to cost you any money to pull that timing cover and check it. The only other thing temperature related would be the IAT (Intake Air Temperature) sensor. If I’m not mistaken, the 89 was a speed density engine and not a MAF engine. I could be wrong though. Now, it could be related to that EGR issue as well. I have mine blocked off. Just find yourself a scrap piece of metal. Grab your grinder and your drill. Cut it down to roughly the size of the EGR gasket and drill holes to match the gasket. Remove the EGR valve, install the block off plate between the manifold and the valve, putting a gasket between each side so you’re not leaking air and you’re not leaking exhaust. There are a million things it could be. With me being 2000+ miles away from you, it’s hard to diagnose it without seeing it in person. So, I can only offer you insights as to what COULD be hybrid problem. I would have put money on it that it was that CTS, but it wasn’t. Have you checked the cooling system for air? An air bubble near the sensor will throw off the reading. I would also take a dollar bill to the tailpipe as well just to rule out what I just got done dealing with. If that dollar bill gets sucked in AT ALL, you DO have at least ONE recessed valve seat.

And btw, my truck is running BEAUTIFULLY with the new head. It’s like a completely different truck. When I fired it up and it didn’t start shaking and putting like it used to, it was like the gates of Heaven opened up and let me in! The truck has more power with these 3.55’s now than it used to with the 4.10’s on the old head. I actually climbed a hill tonight WITHOUT having to floor it! I got in touch with Bo-Port and spoke to Bo himself about the old head. He said it’s trash and unrepairable. When the seat recess like that, especially as bad as mine, the head is cracked internally. He said they won’t use water or oil and the cracks won’t affect the way it runs, but they DO crack when the seats recess like that. So, off to the scrap yard it goes. I did pull my old cam out of that head though because I’m going to send it to Bo and have him regrind it to his Stage 1.5 N/A Ranger street cam. He said that yields 25 more wheel hp on the 2.3L. The 2.3L was 100hp at the crank and 75hp at the wheels stock. The cam brings it to 100hp at the wheels. So, mine should come up to about 114hp at the wheels if I am calculating correctly. I’m also going to add a header and an intake which should bring a total increase of 35-40hp at the wheels. That means I will be running about 124-129hp at the rear wheels or 165-172 hp at the crank. That’s actually a pretty decent increase. He told me if I send my cam in, he will give me a $75 credit toward the regrind since I supplied the core. $275 for a cam regrind is pretty damn good. Brings it to 0.436” lift at the valve. Not sure the duration. It has a lopey idle and it runs 2000-6000RPM. With the stock ports on the head, the head will run out of air at 5,000RPM so it’s not worth changing the springs yet to rev to 6,000RPM. Plus it’s an automatic so the transmission is going to shift at 5,000RPM anyway. I’m not building a race truck here. I just want a work truck that can get into traffic easier. It will sound pretty cool though with that lopey idle!

But back to you, sorry, I had to have my moment of victory, lol. If your EGR valve is leaking or whatever, maybe it’s causing exhaust gasses to get into the intake when they aren’t supposed to be. My dad has a 1995 Volvo 850 Turbo and I changed the turbo and replaced the exhaust with a performance turbo-back last year for him. Well, I had my idiot assistant (the one who no longer works for me. Hmm, I wonder why…) help me with it and he reversed the vacuum lines to the EGR control valve. Well, that was causing the idle vacuum to suck open the EGR control valve and therefore opening the EGR valve at idle. Now if you ran it hard and got the turbo spooled just before you let off the throttle, it wouldn’t do that. But if you were easy on it and let off the throttle, it would do it. You could smell unburnt fuel in the exhaust meaning it was running rich and it sounded like it was cammed. Well, of course it’s going to be rich when the intake manifold is filled with exhaust gasses at idle! There is VERY LITTLE oxygen in the exhaust gasses to burn the fuel! I figured it out by completely unplugging the EGR control valve vacuum line and plugging the source then going for a test drive. Cured the problem immediately. So, I reversed the way it was hooked up and VOILA, the problem went away. So, IF that EGR valve is opening at idle and allowing exhaust gasses into the intake at idle, it will run like complete poo. Block off the damn thing and drive it until you have the money to replace the EGR valve. I’m blessed here in Ohio with not having E-Checks. You aren’t so lucky. I can block it off and leave it. You have to fix it. But you can get away with it short term until your next E-check is due. Now, if your timing belt is loose or off as well, combining the two is REALLY going to cause issues. That EGR valve may not be leaking until it gets hot.

HOWEVER, with you stating that it happens AFTER you drive it HARD, THAT makes me wonder about the valve seats. The EARLY symptoms of that are dying after a high rev run, rough idle/misfire when coming to a traffic light or stop sign, and stalling after revving it. Mine was FAR more progressed than most of them are. Most people only experience the above symptoms. I had 1 completely dead cylinder and another about 75% dead. You can run a compression test all day long and never find it unless you run the engine with the compression tester installed, pull the fuel pump fuse, allow it to die, and then run the compression test with the lifters pumped up. The lifters will bleed down in about 5 minutes. The absolute QUICKEST way is to put a dollar bill at the exit of the tailpipe and see if it gets sucked in. If it just blows out, you’re good but if it gets sucked in at all while it’s misfiring, you have a recessed exhaust valve seat or a sticking exhaust valve. An exhaust valve CAN stick only when it’s hot and has expanded. Either way though, unfortunately, it’s head removal to fix it. If the seats are recessed, it’s head replacement. If it’s sticking valve, you can remove the valve, clean it, throw some assembly line on it, and put it back together, but it’s best to send it to the machine shop and have it repaired.

So, to recap, three things I would check would be the dollar bill test, check the timing belt, and block off the EGR for the test. You can probably do the EGR test without a gasket between the EGR valve and the plate but you definitely need one between the plate and the intake manifold. If it leaks a little exhaust for the test, it’s not the end of the world. Oh, ONE MORE thing. It could also be a plugged catalyst. You can check that by removing the oxygen sensor when it’s hot and see if it fixes the issue. If there is excessive back pressure from a plugged or partially plugged cat, removing the sensor will alleviate the back pressure and allow it to run better. Just unplug the sensor to make sure the computer runs open loop and doesn’t try to read the sensor with it in open air. That will cause a ton of fuel to get dumped it because the sensor is reading lean.

 

I’ll try those tests, I gotta get this truck figured out so my dad can get to rehab next week 3hrs south.

Thankfully we don’t have emissions tests in my region, but this truck won’t be staying here so maybe I do have to fix it lol (if it’s the EGR).

In regards to the performance upgrades you’re planning on doing, are you able to do all of that while still using the stock engine computer? I’m more familiar with my hondas where if I change the cam, intake or exhaust, I have to get a tune done to the ECU. Are these Fords able to compensate for mild performance modifications on their own? Because that would be awesome. Are there aftermarket headers/intakes available?

Anyways, I’ll probably end up replacing the IAT sensor (easy, cheap), blocking off/replacing the EGR valve, and in the very least doing the dollar bill exhaust test. And I’ll report back. Thank you for your thoughts & insight.