Need some help please
My 91ford f150 4.9l l6 with E4oD auto trans still has starting issues and I'm at ropes end here. It will start right up run perfect for 3-5 sec and then it sputters and dies. I can keep it running by fluttering the gas pedal a little and then it will smooth out and idle.
But just when you thing all is well out of nowhere it will stumble and die.
This is what I've done so far:

New part include:
Complete distributor (brand is WPS)
Plugs ,wires + new coil
New o2 sensor
New MAP sensor
Starter and solenoid
(Long story timing was a little off)

Also checked fuel pressure (koeo 49psi koer 50psi and for unhooked 60 psi
Checked for vacuum leaks with brake cleaner and check all vacuum lines as well

Hope someone can help me out Thanks for the help in advance.

 

Issue appear temperature related in anyway, only happens when its cold, hot? engine temperature makes no difference?

It will start right up run perfect for 3-5 sec and then it sputters and dies. I can keep it running by fluttering the gas pedal a little and then it will smooth out and idle.

If it only tends to die when starting it first time cold, how about if you slightly crack throttle open hold it there no "fluttering" the pedal, will it start and run smooth if you do so?
Improves after had been running long enough achieve full running temperature but requires excessive cranking time to get it and seams to idle rather slow/weak once its running?


Have a tach? what is its idle speed for that brief period of time its running right, seam normal or to slow?

Jumping the gun here little bit but sounds like it might be a IAC related issue but need more to go on.

 

check the idle air seems to be clean seems to be working but have doubts about throttle body gasket can't seem to find vacuum leak either

Thank for the help. Im a little slow at typing bear with me.

 

Just falls off as if ran out of fuel?

Idles to fast then too slow but no doesn't sound like can go by that, doesn't run for a long enough period of time to determine what its actual idle speed might settle in on.

Have you run the self test checking it for any stored codes in the process?

Ford Fuel Injection » How To Run a Self-Test

Perhaps returning one suggesting its seeing a rich or lean condition.

Exhaust system fully intact, if so what does the inside of its tail pipe look like. A light gray almost black coating, burnt white, heavy sooty black coating? Have you pulled a spark plug or two, if so how'd they look?

If get a system pass for KOEO and CM, run the KOER test see what if anything it flags having issue with.

 

kinda sounds like you've been down this road before

 

172 + white blistered spark plugs both equate to a lean condition rather than a simple sensor fault, 181 backing it up as well. Sounds like its starving for fuel.

See a fuel pressure test result in your OP as well as some other new parts tune up etc but nothing about a fuel filter, have you replaced the fuel filter recently?

 

https://cimg5.ibsrv.net/gimg/www.for...ff384a9eb4.jpg

 

sorry forgot to mention that did put a new fuel filter on about two and a half months ago old was plugged up with all kinds of nasty crap.

 

Maybe its plugged up again, you could have good pressure but little volume behind it, however that would tend to show up at speed/under load more than sitting at idle.

Have you watched the fuel pressure gauge for a period of time and also while trying to throttle it up, better yet observe pressure reading while running it down the road?

Fuel alone might not explain all your issues but sounds like its part of it, those couple codes and indicators accompany them are not likely to be due to the way it acts at idle speed.

181 is lean at richest adaptive limit part throttle, a continuous memory code so it happen at some point during a drive cycle. What I mean is its not a code thrown during a short test in the driveway at or near idle speed.

I'd check out that filter and if comes to it check volume see if its within spec, might be a problem with the system besides the filter.

'91 so you'd have low pressure pumps in each tank, a high pressure pump mounted to the frame.
Fairly safe at least for the moment based on pressure testing results to assume the high pressure pump is OK. The low pressure pump in the tanks should supply 6oz min in 5 seconds to pass a volume test.

 

I have a observed fuel pressure at idle and when trying to throttle. When trying to throttle pressure increases to mid 50s and at WOT it hits 60psi. Also this truck has dual tanks with only high pressure pumps in tank (FDM).
also back when the truck was running alright it seem to be lacking power when towing.
I will double check the fuel pressure tomorrow if weather holds.

also wanted to ask i check the computer because I seen a lot of posts about computers having fried compacitors and whatnot and found that the computer has already been replaced with a remanufactured one but can't find find out who makes it. it didn't seem to have any damage to PC board but I'm questioning its programming. could there be a problem with the programming in the computer causing this issue it just seems strange that it would run perfect for a little bit and then out of nowhere start to stumble and just stall out.

 

Ok wasn't sure if the 91s had the fmu yet.

You might have other issues reason its down on power while towing but lack of fuel, not enough volume would explain it too.

Thought this book listed volume spec for the FMU but if it does I can't find it now. I do know they'll push some fuel out at a stiff rate, was hoping to be more exacting that that though!

If possible set it up so you can watch the gauge during a road test, volume drops off enough it would effect pressure at some point to some degree especially under load.

 

okay I'll see if I can give that a try tomorrow after I get out of work I'll be back on here about 7:30pm or so. I'll keep you posted

I appreciate all the help sounds like you know quite a bit about these particular trucks.

hey just would like to know what your thoughts on computer causing this type of problem?

 

Couldn't rule it out naturally that said you stated you did have it out looked it over for signs of trouble didn't find any.

As far as it having the wrong programing for your truck, have you always had those problems, same issue/s and never been able to quite correct them from the moment you bought it?

If that is the case might feel differently but not seeing it as a computer issue at this point no, assuming everything else with the truck is unmolested in any way.

If it ran right when you first bought it for example but then over last couple few days it developed these issues, odds are pretty good the replacement has the correct programing for your truck.

 

the only problem I had with the truck when I bought it had a slight hesitation under light gas pedal that I never could fix. and that was about two and a half years ago

 

I'm going to jump off here for tonight
we'll pick this back up tomorrow after I do some more testing on the truck
Hope to hear form you tomorrow.