orignal message My 94 5.8L Fires up instantly in the morning. However, after the engine has warmed up, it starts very hard. Ford engine analyzer has found nothing wrong, but mechanic agrees something's amiss. New coil, wires, module. Nothing so far has alleviated the problem. Any ideas? I have the same problem on my 93 f150 351w . work as ford tech and still cant solve prob. Have ran all kinds of SBDS test, fuel inj flow, fuel pressure leak down, swaped part off other trucks pcm,ect,iat,map. Graph recording on hot start with SBDS cant see any thing bad out of spec except maybe fuel pw to high(dont remember reading right now i just live with it since it cost me ) i still think it maybe inj leak down, but fuel pressure dont drop during test. all grounds seem to be good . Have been meanning to try unplugging o2 sensor and see what happens on hot start. Remember something about a TSB stating acid migration through + batt cable can mess of o2 sensor readings (shouldnt effect start up due to open loop). battery cable has been replaced. tech hotline says it vapor lock due to fuel quality.(dont see how 30 psi fuel can vapor lock) (Have tried different brand & grades of gas). Stator,plugs, & wires (not module) have been changed at different times. Cycling the key several times before starting dont help. Starts perfect cold. Havent seen this prob on later modles 5.4 or 4.6 but it sounds like ckp on those.

 

Hmmm.... vapor lock,... I remember seeing somrthing with piston airplane motors where some folks wanted to save a bunch of money on gas and burn auto gas instead of av gas.
(100 octane low lead ) Seems that some of the motors could take the cheaper gas, but a big variable was in the formulation of auto gas that could cause vapor lock. In a plane this can be a real problem ( duhh ). I'll see if i can find the article and post it.
I use mostly Exxon Mobil because I have a company card from them. Just wondering if any of you with this hard to start when warm issue use mostly Exxon Mobil.

 

joefarmer,

i had an old subaru that was doing the same thing. started fine in the morning, but would not restart when it was warm. it had 75,000 miles on it when it started happening. the mechanic told me it was losing compression, through worn seals. the compression was fine when it was cold and i guess after it warmed up it was bypassing around the rings. i ended up having the engine rebuilt. don't know if this is what is happening with your truck or not (i hope not) but might be worth looking into.

 

OP,

I had the EXACT same problem as you on my 351. It would start fine in the morning but if I shut it off I couldnt get it to start unless it cooled down for 2 hours. My problem ended up being the Throttle position sensor. It was sending a signal like the throttle was wide open thus the computer would send lots of fuel making the mixture extremely rich, actually the oposite of what you would think would cause problems. It would start if I held the pedal to the floor when starting, because the mixture would be proper, but the mechanic showed me that just b4 he fixed it.

Although I would think it would send a code, you might want to check it out. I know at idle the tps is suppose to send >1 volt, if it is sending more the mixture will be rich.

 

No, I don't think it is the brand of the gas you use.
I have tried them all.
Chevron,Mobile,Texaco,76
It does the same thing.

It is brand of the truck that I should be changing.

 

Looking more and more like Joey time. I thought about trading it in on another brand but I really don't care for the competitions body style(s). :o

 

Don't put up with the dealers or ford if they are refusing to help you or if they can't duplicate. I've sucessfully won three lemon law suits, no I'm not an attorney. You don't need to have an attorney, you just have to know the processs. Most of the time it doesn't go to court because they will try to settle with you. If anyone is interested, I'd be happy to help them out just email me at eidaj2@hotmail.com

 

The PCM measures the engine cylinder head temp and sees a low value when it is cold and adds gobs of gas to allow for a cold start. When the engine is warm it sees a warm engine and deminishes the amount of gas to allow for a warm start.
When the truck cools off for a while it is still warm and should not have as much gas as a cold start.

Now here is my WAG. There is something amiss with the Engine Cylinder Head temp sensor. It might be giving too low a reading when the engine has cooled off for a while to make the PCM think it is in a cold start situation. This will cause a start proplem when the engine is luke warm. When the engine is still hot the sensor sees it and when the engine is cold it sees it. It Just doesn't see it when the engine is luke warm.

JMC

 

Good point JMC and well worded.

The exact same thing happens if the TPS is set wrong or putting out improper readings at start up. The PCM will signal excess fuel if it believes the throttle is open farther.

 

All of these are nice. What pisses me off is that Ford mechanics should be talking about this and try to fix something.
eidaj2 is right. Everyone is trying to fix the problem that Ford should be fixing.

I have been reading the forums and half of the people still have warranty left, but they can't get any help from the dealer so they turn to this site.

I will have my day in court on March 17th. Ford didn't want to settle out of court.

Everyone with remaining warranty should do the same.

 

Got the same problem, 1992 5.0 here. First start is no problem, just turn the key and it's lit. After it gets warm for the day it takes a few cranks to get going, but sometimes will start fine. I've already replaced a TPS for another reason (broken wire) and calibrated it, so I don't think that's it.

I'm guessing that since it is happening to a wide range of V8 engines, maybe it's a type of sensor (other than TPS) that is common to all V8's that is faulty or goes bad, or maybe something in the computer program.

The problem is only a slight annoyance for me, but I'd still like to solve it.

 

sounds like we all have a similar problem alright but i dont see it being the same causal part on the the 96 and back verses the 97 and up since they are totally different trucks. dont know how long before this post goes away but i will check it daily because every thing i have tried at my dealer hasnt worked yet. (havent tried TP because it appeared ok on my sbds recordings.

 

The system operates very similarly and uses many of the same type of sensors.

 

It hapened again yesterday. I pullled of the road to make a cell phone call ( we have a law on driving and talking on the phone)
I knew it would be a long one so i turned off the engine and haggled with my associate for 24 minutes. I know how long because the phone keeps track of it. Outside temperature was 34 degrees and no wind. Took 3 "tries" to get it started. Ended up using about 50% throttle to get it started. Real annoying

 

Two weeks before the trial Ford decided two settle my lemon law case.
Can’t wait to get rid of this beast out of my driveway.
Good luck for everyone else with the same problem.