I've just joined the forums looking for help with my '95 Ranger with a 3.0L V6. The truck is an XLT with 4x4 and manual transmission. I was given the truck because it didn't run. The truck had sat in a field for about 10yrs and during that time rats got into it and had a bunch of fun. They chewed a bunch of wiring and made multiple large nests that had to be cleaned out (nest in the bell housing, HVAC plenum, front coil springs, etc). I have spent the past several months going through the truck and making repairs. I fixed all the known wiring damage (most were behind the dash, but some were under the hood too). I also installed a new clutch and radiator. Once I got the truck finally running and driving I started getting codes P0175 and P0172 which indicates that the engine is running too rich. I started reading up on these codes and basically, everyone said to check for vacuum leaks, leaking fuel injectors, too high fuel pressure, leaking fuel pressure regulator, leaking EGR valve, and dirty MAF. One by one I have gone through these and corrected issues that I found, but none have made a difference on the codes and the truck still runs a bit rough. The idle stays right around 1000rpm. It will sometimes drop into the high 900's, but never around 700-800rpm where I think it should be once it is warm. When cold the engine revs at around 1200rpm and drops down to around 1000rpm once it is warm.

What I don't know is why the truck was parked in the first place. I think the original owner got old and just parked it and once they died then the truck was sold to a friend who found out all the issues and gave it to me. The odometer shows it just over 50,000 miles and the truck looks like it hasn't driven that much for being a '95 so I think the odometer is accurate.

Let me run through some history to show you where I have been with this truck on making repairs.
When I first got the truck running I found it had a miss which I determined was cylinder #2. While doing some tests I found that cylinder #2 had a broken spark plug. Since I was replacing the one I decided it was a good idea to replace them all. Once this was done I still had a miss on cylinder #2 and I found that the injector solenoid was open and not working. I then replaced the injector with a new one and the truck ran better. The truck still had old gas in the tank (10yr old) so I filled it up with premium hoping the extra octane would balance out the old fuel. I drove it for about a day and the check engine light came on and the above codes so I started into those.

I checked the EGR valve and found it was leaking a bit so I replaced it with a new one. -No change, same codes.
I checked the fuel pressure and it holds steady at around 35psi when running.
I checked the fuel pressure regulator for leaks into the vacuum hose. - No leaks, but I change it anyway since I wasn't finding other issues. -No change, same codes.
I checked for vacuum leaks using carb clean and found nothing. I replaced a few sketchy hoses for good measure. I put a vacuum gauge on it and was getting around 19in Hg at sea level. -No change, same codes.
I checked the PCV valve. It seemed to not move freely, so I replaced it. -No change, same codes.
I checked the IAC valve and it seemed to be working fine. If you unplug it the engine will either die or almost die.
I removed the MAF and cleaned it. It seems to be operating fine, but possibly a bit high. My code reader doesn't read in grams per second like everyone talks about so I had to convert it from oz per min. I don't have the numbers offhand, but what I remember was that they seemed okay, but a bit high. However, the engine doesn't seem to be at a true idle since it runs at 1,000rpm so the numbers could be okay for 1,000rpm. After cleaning the MAF there was no change.
I finally removed the upper intake to remove all the fuel injectors and tested each one for leaks and found two that were leaking under pressure. I rigged up a test stand to apply 30psi fuel to the injectors while I checked for any leaks. I replaced the two injectors that I found to be leaking with new ones and resealed the others before reinstalling them. -No change, same codes
I did a complete engine compression test and found that cylinder #3 was only generating about 70psi pressure (a dead hole) and determined it was leaking valves. I removed both heads and had them repaired (the cylinders looked great with a good cross-hatch still showing). I reinstalled (with new head bolts) the heads and all new gaskets. -No change, same codes.

I checked the heater circuit to both O2 sensors and that seems to be working. I checked the resistance valve of both O2 sensors and that too checked out fine according to the specs I found online. When watching the live graph data on the scanner both sensors read the same at around 0.850-0.900V and both seem to go up and down together. When I create a large vacuum leak (remove the brake booster vacuum hose) I can make the O2 sensors read in the correct range so I think they are both working from what I can tell. All the wiring looks good too. I have not replaced the O2 sensors.

I am not one to just throw parts at something because I know that is generally a waste of money. I like to troubleshoot and find the root problem and fix it with good parts. I've been a professional heavy diesel mechanic for 15yrs and worked on cars for over 20yrs for fun, but this project has me scratching my head. I feel like I have chased down all the "normal" causes of this fault and not found the cure. I am starting to think that my MAF isn't reading correctly or I have a PCM issue, but I want to verify it before just buying expensive parts. My exhaust does have a smell when the truck is running. I wouldn't call it sulfur or rotten eggs, but there is definitely a funky smell coming from the truck exhaust. I have not checked for exhaust backpressure to see if I have a plugged CAT or muffler.

I have no smoke issues and the fuel mileage doesn't seem terrible (it was around 17mpg when I checked it), but I have only run a couple of tanks through the truck since I got it back on the road. I have okay power and she'll go down the highway at 60mph, but you can tell there is a bit of a stumble at times so I think there is still something not quite right.

What I am thinking now is that something electrical is causing the computer to add more fuel and then the O2 sensor "sees" the fuel and tries to trim it back. Or maybe my O2 sensors are coked up and reading funny and causing my fuel numbers to be bogus. My fuel trim numbers are a solid -20 on both banks. I also think the extra fuel is causing the engine to run a bit fast and so the engine won't idle all the way down. I have not messed with the little screw on the throttle body in case anyone is wondering.

I think this is about it. Hopefully, someone out there has some new ideas as I'm running out of them. Right now I've just been driving the truck and to see if running the truck more might help it out, but some far that doesn't seem to work either. If there are any points I am not clear on please let me know so I can clarify.

Thanks in advance for your advice.

 

I thought I'd post a quick update. After thinking about the issues more and doing some YouTube research I have circled back to my MAF having an issue. With the key on and engine off my MAF was putting out 0.041V on the signal wire back to the computer and not 0.010V like some of the videos were showing. The videos all showed the guys using their scan tool to read this voltage, but my scan tool doesn't do this so I just back probed the wire and used my multimeter. This is why I can read down to the thousandth of a volt, but the videos only show to the ten-thousandth place. My scan tool doesn't show all the data the computer can see, but my lbs per minute from the MAF were reading 0.06 with key on engine off. This converts to 0.453g/s which is what most people seem to talk about when talking MAF. From my understanding, this reading should be zero since there is no air movement happening with the engine off. So this has led me to believe that the calibration is off on the MAF for some reason so I have ordered a new one which should be here in a couple of days. Once I get it installed I'll update what I find, but I am thinking this will fix the problem since I have fixed all the mechanical problems I can find (leaking injectors, leaking exhaust valve, leaking EGR).

What I am thinking is happening is the computer thinks that more air is coming into the truck than what is actually happening because the MAF is starting from 0.4g/s instead of zero. The computer is then adding the proper amount of fuel to meet the air amount that the MAF is telling it. Then the O2 sensors see that things are running rich so they try to reduce the amount of fuel coming through by dropping the trim numbers, but they can only go to -20 so then it throws on the light and things are running a bit rich. Fixing the leaking injectors and leaking exhaust valve has helped, but still have not fixed the main problem of the computer thinking there is more air coming through than there really is.

Hopefully, this helps someone else, and like I said I'll update after I install the new MAF to let you know if it fixes the problem.

 

It has been a week since I installed the new MAF and I thought I'd give an update.

I still am getting P0172 and P0175 codes which is super frustrating. When I installed the new MAF I unhooked the battery for about 30 minutes to let the computer reset which it seemed like it did and then I took it out driving. I think the truck drove a bit better, but it is still throwing codes and my O2 sensor voltage seems to stay around 0.850-0.900V which means it is still running rich. I have driven the truck all week and driving the truck it seems to run better once it is up to operating temp and you're running down the road about 50mph with a load (like going up a slight hill). When I tested the new MAF it seems to be giving the same readings as the original Ford MAF I removed. The scan tool reads 0.06 lb/min KOEO and when I checked the voltage on the signal wire it read 0.041V KOEO

Here is the freeze frame data from the last code set during this week.

Code: P0172
Fuel Sys 1: Closed Loop
Fuel Sys 2 : N/A
Calculated Load: 69.4%
Engine Coolant Temp: 203F (I'm not overly worried about this because this is about the temp recorded when the thermostat opens, at which point the temp drops down and stays normally right around 195F)
STFT B1 -20.3%
LTFT B1 -24.2%
STFT B2 -20.3%
LTFT B2 -22.7%
RPM 1992
Spead 43mph

It also logged a P0175, but there is no freeze frame data, but I am assuming it would be similar since the Live Data seems to be consistent with the two banks.

I have been watched YouTube training videos about how fuel trims work to help make sure I fully understand them and what might cause a rich code. Almost every video that I watched said that vehicles throw lean codes 80% of the time and rich codes are rarer and thus there seemed to be less info about troubleshooting rich codes. However, I get the concept that the computer, via the O2 sensor, is reading too much fuel going through the exhaust and is trimming back fuel as much as it can do and then throws the code light because it is outside of its parameters. One video gave this list of possible causes for rich codes so I thought I would go through those and this is what I found or did.

• Coolant temp sensor issue - Generally this means that the sensor is telling the computer that the engine is cold when it is actually warm. My temp sensor seems to be working just fine and reading appropriate temps so I don't think that is a problem.
• Fuel Pump (pressure too high) - When I checked fuel pressure I was running at 35psi which I understand is proper pressure for this year of the truck so that should be fine.
• MAP/MAF sensor faulty - My truck only has MAF and replacing it gave me the same results as the original so I think that is okay. My replacement was a new (not reman) Blue Streak Elecectical which is supposed to be a good quality part.
• Fuel Pressure Regulator is leaking out the vacuum port - I checked this on the original and couldn't find a leak, but since the part was inexpensive I replaced it and there is no leak.
• EGR Valve slightly open - My original EGR was leaking a bit so I replaced it with a new one and no change in performance.
• Plugged Exhaust - This one I haven't really dived into, but I would think that plugged exhaust would cause other driveability issues like low power or sluggish power. The truck can go down the highway at 65mph without much issue. When I read up on this it seemed like people had a lot of low power complaints and I don't feel I have those types of issues. This truck did sit for a lot of years and had a rat infestation. It is possible that the muffler or tailpipe could be restricted with an old rat nest or something. I haven't found evidence of this, but it is possible. (As a total side note, I have a John Deere tractor torn down at the moment because it won't run and I found the whole exhaust manifold was filled with prune pits because the tractor was left sitting in a prune orchard. So strange things do happen. )
• Failed EVAP System - Allowing fuel tank fumes to be sucked straight into the engine from the charcoal canister. I had checked this and found no vacuum leaks where I thought fuel could be sucked in.
• Dirty Throttle Body - I've looked at this and I don't see anything that concerns me here. The TPS seems to be working just fine in its feedback to the computer.
• Leaking/Dripping fuel injector - I have gone through all six of the injectors. I replaced one because the coil was open internally and I replaced two others because they had slight leaks when bench tested. The other three are the original ones from the truck. I know there is a lot of talk about getting the wrong injector as in you could put a flex-fuel injector in a gasoline-only engine and they are a different calibrated injector and thus would cause a rich code. The aftermarket injectors were purchased for the year and engine of the truck and from all the data I could find on them they are correct. The one was a BWD from Advance Auto and the other two were Standard from Rock Auto (I bought them at different times). So mechanically I think my injectors are okay.

So this is the list and where I think I am at. I had done a compression test and found a leaking valve so I had removed the heads and repaired the leaking valve. Doing that has probably made the most improvement to the driveability of the truck as it fixed a cylinder misfire and I have seen the computer start operating in Closed Loop most of the time which makes the engine run smoother.

My next idea is that somehow the computer is getting bad data from somewhere. I have circled back to O2 sensors, but again nothing is jumping out to me as faulty there as they test out properly on internal resistance and they seem to respond instantly when viewing on the scan tool when you make snap throttle adjustments. The O2 sensor after the CAT seems to be slow in response and stays at 0.000V for a long time after the engine starts up but eventually, its voltage signal goes up to around 0.300V which from what I read is about normal. I would think that it would go up faster than it is, but really I don't know. I also checked all my engine grounds to make sure that I don't have a bad connection somewhere causing a fault, but those all checked out fine too after I shined up any that I had a question about. I did read that I could possibly have a ground short to ground on my injector ground wires. I have not checked this out yet, but I would think this would cause one bank to run rich and not both. I could have two wires that are shorted to ground, but I am doubtful. When I had the heads off I was able to look at all the harnesses and it all looked good and is still encased in the factory plastic wire loom.

Outside of this, I am running out of ideas for things to check. I am thinking about visiting a local shop and seeing if I can pick their brains a bit to see what they think. I've also thought about throwing a pair of O2 sensors at it to see what happens, but I am doubtful that is going to fix anything. It would seem strange to me that I would have two O2 sensors that test okay for resistance and response that were off in then reporting back to the computer. I could also have a bad ECM but I know that is rare and the only times I have seen bad computers is when I worked on big trucks and they would come in dead off the highway on a tow truck and had no response at all. Generally, computers are well made and don't just go partially bad.

So if there are any other ideas out there I'd love to hear them. I feel like I have chased down all the things that I can think of.

 

O2 sensors can wear out without throwing a code. They are chemical based and should be replaced after 100k miles or 10-12 yrs. Not saying this could be your problem, just saying it would take wondering off the table.

 

When the computer thinks the engine is not getting enough air the ecm tries to cut back on the amount of fuel delivered, which can reduce performance especially when the information is incorrect. I believe the ecm gets that info from the upstream O2 sensor.. all the other sensors give the ecm pre-fuel delivery information and the O2's give post-fuel delivery info. When any of the sensors lie to the ecm, you will have issues. The MAF and O2's are the most common deceivers in the system. Heck, a real dirty air filter can cause low air volume, but if the MAF doesn't tell the ecm correctly... well you get the point.

 

SOLVED - - Magically!?!

I know it has been a couple of months since I posted on this thread, but since I have a resolution, I wanted to come back and post what happened in case it helps someone else.

Shortly after Christmas I was in an accident with the Ranger and smashed up the front end pretty good (it was the other person's fault). I bought the truck back from insurance and made all the repairs to get it back on the road. Once I had it all fixed the issue with the check engine light and the engine running rich went away and it runs great now. As a mechanic this is weird to me, but I thought I'd share the things I replaced in case it helps someone else.

In the accident the air filter housing and EVAP charcoal canister were damaged and I had to replace them. I got a new-to-me air filter housing and EVAP canister from the junk yard and installed them. I reused my old MAF sensor from before the accident inside the new air filter box (I popped out the internal plastic part that the MAF fits into and stuck it into the new housing. I used the wiring and rubber plug that came with the housing to connect to the MAF). I also replaced the two sensors that sit in front of the radiator support that I believe work with the airbag system. They are two separate black boxes on brackets that have pigtails coming out of them. I don’t think they go to the engine control, but I thought I’d mention them since they were replaced if they are some sort of temp sensor.

These are the only parts that are electrical that I replaced that I think may have some bearing to the engine control/fuel systems. I also had to replace the hood, fenders and grill, plus I had to replace the passenger side inner fender and the radiator support. All this I got from a junk yard truck.

So, I’m not saying get in an accident to fix your truck, but it looks like something I replaced fixed the problem. I have several ideas of what might have fixed the problem, but if I were to guess which part did it, I’d say it was the EVAP canister but I’m not sure why. My other thoughts are that the rubber wire harness plug for the MAF sensor that goes into air filter looked better on the junk yard part than mine so I decided to use it instead. So maybe it had better seal and gives the MAF a better air flow reading. The only other thing is that my original air filter housing was set up to suck air through the fender, but inside the fender it had a plastic channel part that pulled air from just below the front headlight. That was not replaced after the accident and instead the junk yard air filter housing has a 90 degree rubber elbow that goes into the fender cavity and pulls air from inside the fender going back towards the drivers door. Maybe this is a better air spot.

Anyway the whole thing is kind of weird, but I’m glad that truck is running well now. Hopefully someone finds this helpful if they are stumped like I was.