Won't start when warm, cold start OK

Bodog · March 5, 2005

1994 4.0 V6 Automatic. Cold starts OK and runs OK…until I shut it off and go into a store. It won’t start when warm. It tries to start and stumbles on 3 or 4 cylinders and then dies. After it cools for an hour or so it starts and runs normally.
What is used only on a cold start but not on a warm start? Or what is used on a warm start and not on a cold start?

Any suggestions as to what may cause something like this? It appears that we are getting spark and fuel since it will run briefly on just a few cylinders. My guess is that a sensor is sending incorrect information to the computer. But I don't know which sensors come into play here. Or which computer controls the warm start sequence or which components are involved in the warm start sequence. Any suggestions as to where to look or what to check?

Oh yes, the check engine light has not come on at all. Just in case, I had the local dealer check to see if there have been any codes set. None are there.

It's a mystery.

TPLYNCH · March 7, 2005

Crankshaft position sensor has been known to cause that problem.

Bodog · March 8, 2005

Thanks TPLYNCH. I'll check that out.

Another suggestion by a friend is the fuel pump relay. In Honda's this is a relatively frequent problem and is solved by replacing the relay that operates the fuel pump. Apparently the relay goes haywire when it gets warm and works normally when cool. The problem is that the failure is widely intermittent and because of that is very difficult to trouble shoot. That's the same problem I have. It works normally for days or weeks or even months and then it doesn't one time. Then you have to do the troubleshooting while the engine is warm because once it is cool the trouble goes away until the next time. I'll swap the fuel pump relay with one other others in the relay box and see what happens.

duckdog27 · March 8, 2005

I had the exact same problem with my 94XLT a couple months ago. I replaced basically every sensor on it and nothing worked, it would start fine cold and if I shut if off when warm/hot it would not start, but stumble. I had to wait at least an hour to let the car cool down. I had no idea what it was until I brought it to a Ford dealership. They ran tests and found that the fuel sender was burning itself out on the fuel pump the longer it ran. So when the it was warm I had really low fuel pressure at the rail. What I should have done was buy a fuel pressure gauge and I would of found the problem out sooner. They replaced the fuel pump sender and I haven't had the problem in over three months. By the way, my check engine light was on and I had a code for incorrect air/fuel ratio which makes since since the engine was being starved of fuel, why only a few cylinders were firing when it was warm. Hope this helps.

Bodog · March 8, 2005

Hi duckdog27,

Thanks for the info. Can you clairify what the fuel sender is? And, was your problem intermittent, hard starting sometimes months apart?

My gas gauge wasn't working so I had the fuel pump and the gas gauge sending unit replaced last summer but the problem didn't go away.

I'm coming to believe that the problem is in the fuel system. I guess I'd better get a fuel pressure gauge.

duckdog27 · March 8, 2005

I guess the fuel sender is basically the fuel pump. But I am not absolutely sure. It was only intermittent when it first started. The hesitation, stalling when warm got worse and worse to the point where when I stopped at a light the truck would sputter. Get a gauge and measure the pressure at the rail after you have driven it for over 10 miles. And another thing I just remembered at highway speeds the truck would misfire also b/c of the lack of fuel pressure. Should read around 40psi when warm.

TPLYNCH · March 8, 2005

Robert, when it happens, can you hear the fuel pump whining when you turn the key to on? If not, then the relay may very well be the issue. Since you mention the pump was replaced last summer, that being bad would be less likely.

Bodog · August 5, 2005

Update on warm start problem

I looked around and found the fuel pump relay in the fuse box on the right side of the engine on the fender. There are a bunch of identical relays so I swapped two of them. The warm start problem went away but another problem, a brake problem came up intermittently. I again moved the relay to the A/C location and the brake problem went away. So it was a bad relay that was causing the fuel pump to act up and not provide enough fuel for starting.

orcg · March 21, 2007

Hello, I'm here because I have a 94 xlt and I think the fuel sender (pump ?) is going out I've replaced the filter but still dying right after starting, or when it gets warm

Hello all

orcg

Bodog · March 22, 2007

Hi orcg,

I solved my starting problem by swaping the fuel pump relay with one of the relays next to it. I used the relay that cuts out the air conditioner during hard accelerating. When I made the swap the problem went away and has not returned. The relays are in the fuse box on the right front fender, passenger side.

Apparently the fuel pump relay would drop out from time to time and the fuel pump would stop. I had already replaced the fuel pump when I replaced the fuel sending unit so I felt strongly that the problem wasn't the fuel pump itself. Try swaping the relays and see what happens. They just upplug by pulling up on them. East to try.

bodog

bigsquirrelsdad · March 24, 2007

i have a 95 exp and have had the same problem. it is the fuel pump relay. the reason this happens is the soldered connection inside has come loose. when its hot under the hood or hot outside it will expand and seporate. when it cools down it contracts, causing it to touch the original soldered connection. i also am a sevice advisor for a honda car dealership and the relay for them is located under the dash. for them it will happen when its hot outside. if you open the doors or windows for a few min. it will cool off enough to touch and start. you can resolder the inside of the relay if you in a pinch and cant get a new relay.

scott

Baltoborn · September 12, 2016

Bodog said:
1994 4.0 V6 Automatic. Cold starts OK and runs OK…until I shut it off and go into a store. It won’t start when warm. It tries to start and stumbles on 3 or 4 cylinders and then dies. After it cools for an hour or so it starts and runs normally.
What is used only on a cold start but not on a warm start? Or what is used on a warm start and not on a cold start?

Any suggestions as to what may cause something like this? It appears that we are getting spark and fuel since it will run briefly on just a few cylinders. My guess is that a sensor is sending incorrect information to the computer. But I don't know which sensors come into play here. Or which computer controls the warm start sequence or which components are involved in the warm start sequence. Any suggestions as to where to look or what to check?

Oh yes, the check engine light has not come on at all. Just in case, I had the local dealer check to see if there have been any codes set. None are there.

It's a mystery.

I have had the same problem with my '03 explorer sport. It starts fine cold and runs fine. When I shut it off after a shirt or long drive it cranks and cranks but won't start until I let it sit for an hour+. Then it starts and runs fine. I replaced the fuel pump relay as suggested here with no luck. I took it to the dealer but without it acting up and with no check engine light/code to guide them, all they could suggest was the fuel filter. It was original so I had it done with no luck. I read on one of the sites that warm/hot starting problems could be caused by an overheating coil pack or fuel pump. I replaced the coil pack ($45 from online site) and have not had the problem in 4 weeks. I'm keeping my fingers crossed. Even though my problem occurred intermittently I've started, stopped, heated it up and cooled it off enough times that I think it's fixed. I hope this helps anybody having this problem with their Ford.

Won't start when warm, cold start OK

Bodog

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TPLYNCH

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