96 Ranger 3.0
80k miles, I'm the second owner.
Shortly after buying, alternator issues, new alternator, battery, fusable link, tracked issues down to fuse box ground.
New starter, drive belt, and tensioner.
2 new front O2 sensors, rear one not connected due to previous owner modifying exhaust and not putting a bung in for it.
New plugs, wires, and coil.
New Battery cables
New Fuel pump, fuel filter, and new injectors.
New EGR valve.
New Fuel pressure regulator.
Cleaned MAF and Throttle body.
Runs rough at idle, sometimes 800 RPM, sometimes at 1200 RPM.
Timing advance jumps from 22 degrees to 11 degrees seemingly at random
At 1-5% throttle, truck stumbles, sputters, no power.
After that, little shakey but drivable.

CODES: p1443, Most likely a fuel filler neck issues, pretty sure it's cracked
P0136, O2 sensor, still hasn't gone away after replacing
P0141, Other O2 sensor
P0133, O2 sensor
P0306, cylinder 6 misfire, went away after replacing injectors
P0300, Random misfire, went away after replacing injectors
Had Codes for injector issues shortly after replacing injectors but they went away quickly
P0401, EGR tube
P0172 Running rich
P0175 Running rich

MAF sensor is 6.5-7 g/s at idle
I've seen this go as high as 80g/s but it's usually 30-40 driving
STFT1 is -10 to -15% at idle
This goes to -20% while driving, especially while coasting
Intake temp good

Recently took it to a shop, they replaced the throttle position sensor and called it fixed, did nothing
Took it back to the shop, they replaced the gasket that connects the EGR tube to the exhaust which quieted down the noise, so there was definitely an exhaust leak.
They are now saying that the cause of all my problems is that there is no rear O2 sensor plugged in, but everything I've read is that the rear sensor only measures the efficiency of the Catalytic converter, it doesn't actually change the fuel trim.
Now after the second shop trip, the truck will be set at -20% fuel trim at idle, then smooth out to + or - 5% at normal driving, then upon medium to hard acceleration go to +20% on the fuel trim.

Completely at a loss, I plan on taking it to an exhaust shop in a few days to weld in a bung, but I don't have high hopes.
Any help appreciated.

 

All 3 of these codes have 2 things in common, you either have bad wiring or an exhaust leak, which could be your EGR

P0401, EGR tube
These 2 are probably caused by the EGR/ DPFE (differential pressure feedback EGR)

So fixing your EGR problem should be your first concern.

 

The EGR valve has been replaced and there was a leak from the EGR tube to where it connects to the exhaust that has been fixed. Where else can it be leaking?

 

If you didn't need a part of the emission system, they wouldn't have put it in at the factory. They like to save as many pennies as they can.
I also suggest you clear the codes and see which ones return after you make any repairs.

 

Rear o2 sensor has been replaced, the exhaust shop said there wasn't one when they first looked at it which is why they didn't put one in but whatever. Still runs horrible, no low end power, sputtering when starting out.
Cleared codes, first one back is P0401 insufficient flow through EGR system. The valve is replaced, and the tube has been cleaned. Planning on buying a EGR pressure feedback sensor next payday.
Honestly feels like I have to rev it to like 1500 RPM to even get it to move. It's running rich at idle, and lean on acceleration.
Just for fun, took the air filter out of the box and now it's running extremely lean at idle. Drives like normal though, once it gets going.
Pulled the negative cable off the battery for the night to reset the computer, it'll go back to the shop soon, they seem pretty stumped as well. It seems obvious now this wasn't so much a fuel issues as it as an air issue. Hoping it's not something major like the throttle body.

 

When you changed the EGR valve, did you make sure the passages in the upper intake were clear? They can get carbon build up. What does your OBDII reader say the engine temp is at when its been ran for a while? Have you cleaned the IAC valve passage? It can get gummed up as well. Have you checked for vacuum leaks? Any cracks in the air cleaner tube to the throttle body or cracked vacuum lines?

 

Not sure, will check the upper intake tomorrow. Engine temp is good, maybe even a little low. 75-80, maybe creeps up to 85 on a very hot day idling forever. Cools down as soon as I start moving. Not sure what the IAC valve passage is, will do some research and check it tomorrow with the intake. Checked for vacuum leaks, but can go over it again. Other than checking with carb cleaner, any suggestions on finding vacuum leaks?

 

You may want to check voltage on the Throttle Position Sensor (TPS).

 

Just got the truck back from the shop, for the third time. They have no clue what is wrong, and would like to schedule to have the truck at their shop for a week to fully go through "everything". Don't have the time to be down a vehicle for a while, so back to tinkering on it myself.
Upper intake was clear, replaced the IAC valve, checked the voltage on the TPS, was good.
Removed the air filter again, the MAF reading went from 7ish g/s to 5 g/s, which is the lowest I've ever seen it. Still idles bad, no low end power.
Put it back because other than the reading being slightly lower, truck runs the same and I live on a pile of dirt so the filter is needed...
Takes forever to crank to start, at least 5 seconds. At least it always start.
The codes that keep coming back are P1443 and P0401, along with occasionally P0306 (misfire on cylinder 6) coming back now.
Replacing the EGR pressure feedback sensor tomorrow or the next day if it comes in.
It seems clear the issue is air related and most likely in the EGR system. Is there a diagram or video that goes through the entire system? Probably just need to work through everything again and hope to find something new.

 

https://www.troublecodes.net/p1codes/p1443/
https://www.fixdapp.com/blog/p0401-code

 

RonD explains the EGR system pretty concise in the following:

 

Replaced the Purge Flow Sensor and the Evap Canister Purge Valve today, no change. All the hoses look good, no cracks. Sprayed carb clean all over the truck, found no vacuum leaks anywhere.
So in total, that's a new EGR valve, new gasket between EGR tube and exhaust, new DPFE sensor, new purge flow sensor and new evap canister valve.
Truck still takes 3-5 seconds of cranking to start, still idles at 6-7 g/s on the MAF. Idles at 840-870 RPM, feels like it gets more and more shakey as the truck warms up now.
Seems to be running more rich than usual, basically pegged at -20% fuel trim, and rarely getting into the +% now, only on HEAVY acceleration
The hesitation from a stop seems a little better but didn't get to drive it too much today.
Checked the exhaust temps at each cylinder, all within range of each other so I'm not misfiring that badly I guess, it just is so shakey at idle.
On the drive, I disconnected the MAF, my sensor shows that the MAF quit reporting showing 0.4 g/s, but didn't change anything in the engine, still ran exactly the same. Plugged it back in, jumped back up to 6.5 g/s, still no change.

 

I know you put in a new fuel pump and such but was the fuel pressure verified within spec? Have you done a compression check? Is there a chance the previous owner reprogrammed the ecm to accommodate the lack of a rear O2 sensor? I'm assuming the removal of the rear O2 sensor also meant they removed the catalytic converter so I have to ask if there is a catalytic converter now?(sorry) Is the system going to closed loop after it warms up a bit? Just trying to get a better sense of what's going on. One issue can have several different causes.

 

Never verified the fuel pressure, I was changing the injectors due to the misfire code, since the truck was down might as well change the fuel pump. A buddy of mine has a few years older Ranger and all his problems stemmed from his fuel pump so I figured preventative maintenance. No compression check, I'll do that when I check fuel pressure. No clue about reprogramming, previous owner was an older woman who was tired of getting into "such a high vehicle". While at the shop, they said they reset the ECM a few times to reset fuel tables and try and relearn the system after we changed the fuel pump, not sure if that was a full reset or how that works. There is something on the exhaust, looks like an aftermarket catalytic converter before the muffler and rear O2 sensor. Even when there was no rear O2 sensor I never got a CEL about the cat though. How is the best way to test when it's in open loop or closed loop? I really enjoy all the questions, even though it isn't fixed yet this has been a lot of help trying to track down these issues.

 

An OBDII reader that shows live data, like the one I suspect you have been getting your info from, will show you whether you are in open or closed loop.

 

Well good news bad news. When I went to do the compression test, realized I didn't have the correct adapter. As I was putting it away, found my scope and thought might as well take a look at the cylinders. Cylinder 6 has oil on the top of the piston. Probably not valve cover cause no oil around the top of the plug, and it's on top of the piston so probably not rings. Looking like a bad valve seat or stem. Makes sense cause the idle and misfire and slow off the line gets worse throughout the day. If it sits for a few hours it barely wants to run cause the oil hasn't had time to go down past the rings, but by morning it's fine. Only question is why is the MAF is reading rich? Is that number effected by the o2 readings? I'm going to run some seafoam through it to see if it's possibly carbon build up but odds are the head is coming off in the next week or two.

 

Finally got the truck up and running again, with brand new heads.
It drives better, feels like it has more low end power and less hesitation on start up, the exhaust valve was definately leaking pretty bad lol
The issue is it's still running very rich at idle and deceleration.
While driving under normal conditions, STFT1 and STFT2 are anywhere from -5 to +5%, maybe +15% when I floor it up a hill
But when I let off the gas, it creeps up -5% -10% -15%, then pegs at -20.3% both banks.
They will flash ~.8% for a second, then creep up again
MAF is still reading 6 g/s at idle.
I checked MPG before I tore into the heads and was getting about 14 MPG, I'm guessing when I check in the next day or so it won't be much better.
At a loss again, really thought new heads would be the answer

 

Disregard most of that last post, truck is back to running like garbage.
I've noticed the MAF reading goes down when I turn off my ac, I'm in Texas so that doesn't happen to ofter lol
Cleaned the MAF yesterday, no change. Took the belt off and started the truck and it ran great, maf was like 3.8 g/s so something is putting a load on the engine, I think it's the power steering pump. Mine whines a little when turning at a stop and doesn't spin freely at all with the belt off. Ac condenser and alternator and tensioner is new. I have a power steering pump coming to my local parts store tomorrow so I can compare the two. I also plan on putting an electric fan on soon.
In other news, I upgraded my app that shows me all my fuel trim and such and my LTFT is pegged at - 25% anytime I'm not pushing the throttle. Driving, hard acceleration, normal conditions, no issues, drives great, anywhere from positive 5% to - 5%.The second I let off the gas, no matter what speed, all the fuel trims go to - 20.3% on short term, and - 25% on the long term

 

MAF sensor weighs the incoming air, not really a "flow" sensor as its named, lol
The computer "knows" its running a 3 LITER engine so it already "knows" exactly how much air is coming in at ANY RPM, its just math
Air at Sea level weighs more than air at 5,000ft elevation(i.e. Denver)
Gasoline's air/fuel mix is 14.7/1 and that is a WEIGHT RATIO
14.7 POUNDS of air needs to be mixed with 1 POUND of gasoline to get a good burn
OR
14.7 grams of air to 1 gram of gasoline, a weight ratio
That's why fuel injectors are rated in POUNDS per Hour of flow

The MAF reading is translated to grams per second for human consumption, most of us, me included, can't do math like a computer can
So MAF sensor will change with RPMs and engine load, i.e. no accessories(belt off) and AC on or OFF, that would be normal

Rich code(-20 fuel trims) on just one bank/side of an engine would usually come down to bad injector, bad O2 sensor or exhaust blockage on that ONE SIDE of the engine

Rich on Both banks/sides could be bad fuel pump regulator, 1996 computer expects 35psi fuel pressure, the fuel pump can do 80+ PSI, so the fuel pressure regulator needs to keep fuel pressure down under 45psi so computer can calculate correct OPEN TIME for each fuel injector
Fuel Trims ARE the open time for each injector
Computer calculates open time based on RPMs and Load and that's 0 Fuel Trim, "+2" trim means computer needed to keep injector open 2% longer than it calculated based on O2 sensor feedback
"-2" trim means computer had to close injector 2% earlier than it calculated based on O2 sensor feedback

Codes are usually set if Trims get to -20 or +20 repeatedly

Computer has a few assumptions, there is no fuel pressure sensor, so it assumes 35psi
It assumes injectors are 14lbs/hour(stock size), I think for 3.0l
It assumes O2 sensors are "the word of God", it has no way to know unless they fail outright
It assumes exhaust is flowing clear, no blockages
It assume "its always right", never makes a mistake, lol, like my wife, but computers do fail, not often but not never

Computer can compare MAF sensor and throttle sensor with RPMs to see if MAF or TPS is out of "known" range

General rule of thumb for MAF sensor and grams/second is 1gr/sc per Liter of displacement at 500RPM
So 3.0l engine at 500rpm would be 3gr/sc, but most idles are higher than 500 so 3.5gr/sec at 750rpm, the "flow" is not linear, it goes up with RPMs but its also load related so its a curve
To say XXX is correct for 3.0l engine at 1,000rpms at sea level with no load wouldn't be possible, there would be a Range that's correct and computer knows that range, so would set a code in most cases if it was out of range

 

Alright, thank you for the explanation on the MAF sensor, that makes a lot more sense now. The only codes it's showing is the P0172 and P0175, so rich on both sides. From what I've read about, the LTFT are supposed to change slowly and over time, while mine are snapping from -25% off the throttle to "normal" -3% to -7% on the throttle. I'll try and check fuel pressure and fuel pressure regulator. I got injectors from partsgeek that saidthey were the correct fitment, but they also say it works for similar year mustangs with a 5.0, so may have to go through those again. Injectors, all O2 sensors, and exhaust are all new, I can see the exhaust is good and the readings from the O2 sensors are correct, so I guess it is fuel related.

 

Yes, the 1996 Ranger 4.0l used 14lb/hr injectors as did 5.0l in some years, but 5.0l also used 19lb/hr injectors as well, which would cause Rich codes in your Ranger
Fitment is the same for most Ford injectors, the flow rate is what needs to match

So if you can look up the part number for the new injectors and see if you can find a flow rate

In the mean time rent or get a fuel pressure tester, test port is on the passenger side of engine on the fuel rail, its sandwiched between upper and lower intake
Test port looks like a tires air valve because that is what it is, a schrader valve, works the same way
Engine Running pressure should be 30-40psi

There are 2 fuel lines coming into engine bay from drivers side
One goes to drivers side fuel rail, that's the IN from fuel filter
The other one runs under upper intake at the front, and to the FPR, passenger side front of engine, this is the OUT back to gas tank fuel line

 

Turns out I have already replaced the fuel pressure regulator. Would too big injectors cause the LTFT issues? Because it drives fine once I get moving, it's just off throttle and at launch it's miserable.

 

I think you are reading too much into LTFT
It can change quickly if STFT is + or - by more than 10 either way

LTFT is there so computer doesn't have to calculate big changes in fuel trims constanly

0 STFT is computer's calculation of correct fuel trim for RPM and engine load at that moment

BUT............ 0 STFT is with LTFT added in

So if LTFT was -20, then 0 STFT is actually -20% injector open time to start off with
If STFT goes to -7 then STFT is actually -27%
LTFT + STFT = actual fuel trim

If you were to fix the Running Rich issue, then STFT would change to +20, because LTFT was still at -20, and then as you drove the LTFT would start to come down as the STFT stayed above +10 to +20 range

That's the "slow part" of LTFT, but still should come down within 20 to 30min to under -10%

But LTFT can go up really fast, it's coming back down closer to 0 that can take the time


High Fuel pressure is the most common reason for Rich fuel trims, only because people don't change injectors that often
If the problem came about after changing injectors then they would be the most likely issue

New means never EVER tested, now-a-days
So new FPR means even more likely to be the issue, lol, unless it was Motorcraft brand, Ford still requires all their parts to be tested before being boxed and shipped, which is why these parts can cost stupid amounts of money over 3rd party parts
I don't think Motorcraft parts are "better" in most case, but they are tested before you get them
I only use Motorcraft fuel pumps because of that, its a PITA to change a fuel pump, so don't want to do it again with 3rd party even with warranty

Test fuel pressure so you can take that off the table, or................find out it is the issue

 

Back with more bad news, or at least no good news. Fuel pressure is good, solid 35 PSI. Been working with a shop, lead mechanic is a friend of a friend, owned tons of rangers, and even brought his 94 with a 3.0 in so we could compare mine and his side by side. Turn out my new catalytic converter wasn't a catalytic converter at all, merely a test pipe. Replaced that, no change. Odd that after all the codes and issues, I never got a bad cat check engine light. Rechecked MAF, fuel pressure, IAC, intake temp sensor, coolant temp sensor, gaskets/vacuum leaks, coil, plugs and wires, airbox/air filter. This is the shop that replaced the heads, so those gaskets are new. Checked the injectors, those seem to be fine. Last thing we're thinking is computer, so ordered one, pre-programmed and updated. We reset the PCM which reset the LTFTs to zero. I drive a lot, so most "days" of driving is 80+ miles. First day or so, LTFTs stayed at -3 to -7 while the STFT stayed at -20.3 unless under heavy acceleration. The last few days the LTFTs have settled back to -25% at idle and no throttle, maybe reaching -15% during normal driving. Most times I get out of the truck I can smell gas it's running so rich, though no visible leaks or drips anywhere. Down to about 12 MPG or so. Something to note, under hard acceleration, truck gets really lean, flips all the fuel trims to +20-25%. I guess the next thought would be what causes rich at idle and lean under hard acceleration.

 

1996 3.0l Ranger

If fuel pressure is 30-40psi engine running
If Fuel Pressure Regulators Vacuum hose is dry(no gasoline inside)

And then you are getting negative, -15% or more, on LTFT then someone my have put in the wrong fuel injectors, or you have at least 2 leaking injectors
3.0l had different size injectors over the years, 1986 to 2008
The size of the injectors, the pounds per hour(lb/hr), is programmed into the computer just like fuel pressure is, so its part of computers 0 STFT calculation
3.0l used 14lb/hr, 19lb/hr and 24lb/hr over the years
Injectors are NOT the same as Jets on a carb, lol, bigger is not better it just causes Rich Codes and negative fuel trims not more power

1996 3.0l should use 14lb/hr injectors

The fact you smell gasoline after engine shut down would point me in the direction of leaking injectors, pull off the Air Plenum(big air hose from air filter) open throttle and see if it smells like gasoline, it shouldn't of course because injectors are shut off with Key Off, and engine then slows down to 0 RPMs so air flow would pull any residual fuel smell OUT of the intake
So any gasoline smell could only come from leaking injectors
OR
Fuel Pressure Regulators Vacuum line