Sometimes it runs fine and then it will hardly idle and stalls?

Hi,

Are any codes present? Also, does this only happen when the engine is warm, or could it do it when the engine isn't warmed up?

Let me know if you have a live data scanner. If you do, check the short-term fuel trims when this is happening. Also, check the coolant temperature sensor's signal to the PCM.

Try this and let me know what you find.

Joe

shrt ft minus 15 to minus 18 coolant temp sensor 188 degree.

02 sensors now reading stuck on rich.

FTP is 33-34 pst

Hi,

The trims indicate the PCM is trying to lessen the amount of fuel entering the vehicle. As far as the fuel pressure is concerned, it's at the threshold of being low (KOEO), which is confusing. I would have suspected the opposite. (see pic below)

Is it possible to get the codes you found?

Joe

See pic below.

Key in on position 40 PSI when running 32-34 PSI.

IAT is 84 when warmed up.

p0451, p0172 0175, and p02196 2198.

see freeze frame.

Hi,

Where should we start? First, the fuel pressure appears to be good. There could be an injector issue. When you checked the pressure, did you take notice of how quickly it dropped when the key was turned off?

Next, have you checked for any restrictions on the air inlet system (air filter, inlet tube)? Have you replaced the oxygen sensors already? When was the last time spark plugs were replaced?

Don't laugh, but when this happens, does the transmission react differently?

Let me know. Sorry for so many questions. However, based on the codes, it could be something as simple as a plugged air filter and as extreme as the powertrain control module (PCM).

Let me know.

Joe

They are 2 months old. I put in new upstream 02 sensors and put in a new air filter. The fuel pressure when up a little when the key was turned off. I started it last night and it was ruff at first then it ran smoothly, but the ideal was a little low. Code 0451 appeared pending This morning I started it. Nothing but rough running and stalling no codes appeared.

I started it this evening and rev it up right away and got it to run smooth with now collection of codes.

Hi,

Do you mean there is a new collection of codes? If so, are they different? Let me know. Also, let me know what they are.

Take care,

Joe

I meant no collection of codes. I will keep an eye on things.

I changed the upstream 02 sensors and the fuel filter. I removed the fuel rail and injectors. I reached down behind the engine and removed and cleaned and reattached the vacuum lines. I cleaned and replaced 1 injector and reinstalled them and the fuel rail. Started it and it ran fine. Test drove around the block fine. When a little farther and it bogged down and stalled. Managed to get back to the house. It seemed to ideal fine but revved up a little from time to time. Pulling P0171 I tried to add an image of freeze frame data, but it will not except a Microsoft edge file.

Hi,

I went through the diagnostics again. Everything they indicate is related to either a coolant temperature sensor or an engine vacuum leak for this code.

I attached the diagnostics below specific to the code. It starts at step H17. Take a look through them and let me know if you are comfortable performing them or if you have already done what is suggested.

Take care,

Joe

See pics below.

Freeze frame data p0172 present SHRT FT1- 4.7 HHRT FT2- Minus25.3 LONG FT1 minus2.3 LONG FT2- minus 20.3 at 3600 rpm Live data at ideal SHRT FT1- between 0 and minus 7.0 SHRT FT2- between 0 and minus 4.7 LNG FT1- minus22.7 LNG FT2- minus 21.1 both set of data @ ECT-188F IAT- 71F Does this tell us anything? I do have a full freeze frame data set.

Hi,

the STFT bank 2 and crazy high. If that is a negative 25.3%, either we have a fuel injector leaking or a pressure issue. Am I reading that correctly?

Joe

Yes, that is correct. The fuel pressure at the rail is pretty steady around 33 PSI. Could a bad fuel driver module? Before I changed the upstream 02 sensor everything was stuck lean now it is stuck rich. The symptoms remain the same. running smooth and then it bogs down and won't idle.

Hi,

The fuel pressure sounds good. So, when you checked pressure, did you pay attention to pressure drop-off? In other words, did they stay steady for a while when the pump was off, or did it drop rather quickly? I ask because we may have a leaking injector. Also, and I think I asked this before, but do you have any exhaust leaks upstream from the oxygen sensors? Fords are notorious for manifold leaks.



Let me know.

Joe

The fuel pressure is around 40 PSI before starting the engine and runs steady around 33 PSI when running with no drop off. I am aware of the common leaking of the intake manifold. Have some testing. What testing do you like best for this?

I thought that intake leaks would cause it to run lean not rich?

Hi,

That is correct. The idea that it is showing a high positive number indicates the computer recognizes a lean condition and is trying to add fuel to make it richer. If the numbers were in the negatives, that would indicate the computer is trying to lean mixture.

Let me know.

Hi,

If I question if there is an intake leak, I usually use carb cleaner. See the attached link.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know.

Joe

I checked for vacuum leaks at idle with cab cleaner and did not see any difference in idle. I next tried putting water over the edges of the intake manifold and other vacuum tubes and electrical connection with no notable changes. For doing this check it took a while to get the engine to run from cold. It then runs pretty good. Should it be tested at higher RPMs. Presently it is not pulling any code but longft are still running -21 to -24.

Hi,

Are the short-term fuel trims still high?

Joe

shrtft 1 -1.5 to 4 shrtft 2 0 to 7 or 8.

Hi,

I'm not sure what is happening here. If the STFT are within spec, the LTFT should be a lot closer. I asked the site owner to take a look at this and see what he thinks.

Let's see what he says.

Joe

It sounds like one of the cats has fallen apart, here is a test to help confirm:

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

If these turns out okay, I would try swapping out the MAF sensor. Also, I have seen a bad PCM do weird things like this. Does the engine make any strange noises at idle?

I still need to test the cats. However today I checked the fuel pump drive module. It was in bad shape. It was being held on by one bolt and the housing had a hole in it that you could see the circuit board. I bypassed it and the engine idled better. The psi stayed around 42psi. After installing the new module it idled back at around 33psi and still stall out from time to time.

It sounds like the fuel pump is okay, I would still check the cats as well.

Key on, engine off .................... 240-310 kPa (35-45 psi)
Engine running .................... 193-310 kPa (28-55 psi)

Are there any codes? Can you clear them and re-run them?

So, I changed the fuel pump drive module and the MAF sensor. I checked the vacuum. I was between negative 15 and 16. When I revved the engine it snapped back to negative 15 and 16 in a mill a second. I drove to work today. No codes or check engine light. No freeze frame. The shortft and lngft trims at idle are very close to zero. The fuel PSI hovers at 39 to 41 PSI.

Hi,

That sounds great. It sounds like you found the issue. If anything changes, let us know.

Take care and feel free to come back anytime in the future.

Joe

Thank you, it seem to be a combo of the MAF and the pump drive. Keith