Difficulty starting warm engine / Check Engine Light

[davem]

My 2001 Explorer (XLT, V-6) starts great when cold, including recent days when it was -10 F. But after driving awhile, its hard to restart. Turns over fine, but does start unless I pump the gas pedal.

My Check Engine Light has been on for a tank or 2 of gas. I thought I had gotten some bad fuel, but since I've used a couple tanks, I'm thinking it may be something else.

Engine seems to run fine. The gas mileage may be a little worse than normal (used to get about 15 MPG, might be closer to 10-12 MPG now).

Any suggestions ?

Thanks,
Dave

 

[dogfriend]

Try to get the codes read; you should be able to find an Autozone or other parts store to do this for you. Write down the codes (example P0171, etc) and post them here.

Its possible that you may have a sticking IAC valve, but I'm not positive based on the info given.

 

[ExplorerDMB]

FYI, pumping the gas pedal on a fuel injected vehicle doesn't do anything.

-Drew

 

[davem]

I had the code read at Autozone. The code is

PO306

Which the tech said indicates a problem with cylinder #6.

His code book said the problem could be:

ignition/wires/coil
vacuum leak
fuel injector
high/low fuel pressure

Given the info above, along with the symptons I reported (starts good when cold, difficult to start when engine is warm), do any of the above possible explanations seem more likely to be the problem than others ? Or any other suggestions ?

Thanks.

Dave

 

[dogfriend]

I'm posting the code below. I think that the reasons for the code he gave are correct, the one he left out would be low compression in that cylinder (hopefully not the problem, but a possibility).

I would check the ignition system first, replace spark plugs, inspect ignition wires, check coil pack resistance.

http://www.explorerforum.com/forums/showthread.php?t=61548&highlight=coil+pack

http://www.explorerforum.com/forums/showthread.php?t=108712&page=4&pp=20&highlight=coil+pack

 

[davem]

I took the Explorer to the local dealer. Told them the symptons and the code info from Autozone.

They detected the same code. Found no problem with cyl #6 (plug and wire were tested). Tested coil - OK. Checked injector - OK.

They reset the code and reflashed the PCM. And now all is well. (At least after about 20 minutes of my testing it seems OK.)

I have a hard time accepting this solution. I was sold on the theory that it was a bad sensor that was sending bad info, which caused the warm start problem (backed by the knowledge that a cold start does not use sensor input - assuming that is true).

Any thoughts ? Is it possible that the problem is intermittent and not really fixed ? (The warm start problem occured 100% of the time prior to this repair visit.)

Thanks
Dave

 

[dogfriend]

Hmmm....Interesting.....

Could you feel a miss or was the only symptom the difficult starting when warm?

Re: Sensor input vs cold/warm start. I haven't read this for some time now, but IIRC, when you start the engine, the PCM uses a set routine for ignition timing, injector pulse time, ect - but beginning with the first few cranks of the engine, the PCM starts to read and take data from the various engine sensors (i.e. Intake Air Temp, Engine Coolent Temp, Mass Air Flow, etc) and then starts to adjust the injector time (and possibly other parameters) to suit the conditions.

It is possible that they flashed the PCM with a new program that works better for your engine calibration. I think the only way you will know is after a couple of weeks. If the problem comes back, then you will know.

 

[davem]

After picking up the vehicle last Thursday (12/15), it drove fine on Thursday and Friday (I only drove about 20 miles). Vehicle was not used on Sat or Sun.
While driving to work on Monday (12/19), the CEL came on after about 3 miles of driving. I did not experience the warm start problem. Had the code read at Autozone - same PO306 as before. I had the code reset. The CEL has remained 'off' since. But on Tuesday, I drove about 1 mile, went into a store for about 10 minutes, and then experienced the warm start problem again. I could not recreate the warm start problem in the 24 hrs since then.

Any suggestions ? Would putting some additive in the fuel (inj cleaner, Sea Foam, other) be worthwhile ? Any suggestions ?

Thanks.

Dave

 

[dogfriend]

Seems most likely to be an ignition problem to me, but the dealer says everything tests ok. I had a problem similar to this on my Ranger and it turned out to be a bad coil. But it only caused a problem when the engine warmed up; it started fine when cold.

Also, can you actually feel it miss? If not, my other thought is that it could be a problem with the crankshaft sensor; the crankshaft sensor is involved in determining if the engine is missing, IIRC.

 

[davem]

Yes, when I have the warm start problem, I can feel/sense it missing.

Ever since I've had the "repair", I've been more focused on how its running. It could be my imagination, but when idling, it does seem to occasionally 'miss' - but in all honesty the slight idle imperfection may be 'normal' or may have been there before.

Does this support the coil theory ? Or rule anything out ?


Dave

 

[dogfriend]

If it is actually missing, then it will be for one of the following reasons:

ignition (coil pack, spark plug, spark plug wire)
injector (clogged or not opening)
low compression (valve leak or head gasket leak)

The dealer says the ignition is ok. I'm not sure they spent enough time though to replicate the problem. This is what makes intermittent issues a pain to diagnose. One trick that might help replicate the failure would be to use a heat gun or hair dryer to warm up the component that isn't working when the engine is warm. I would try this with the coil pack and possibly the crankshaft sensor to see if I could reproduce the problem.

For the injector, it is possible to listen to the injector to hear if it is working by using a mechanics stethoscope and placing it on the injector. You could listen to see if all the injectors sound the same, particularly the #6 injector.

For low compression, you should do a compression test or cylinder leak down test to determine if you have low compression in cylinder #6

 

[davem]

For what its worth, the CEL came back on today.

I'll keep monitoring.

Would a coil issue affect all cylinders ?

Is it possible that I am having problems with other cylinders, but just don't notice it because only 1 error code can be stored (and it always checks cyl #6 first) ?

Thanks.

Dave

 

[dogfriend]

Each coil fires two cylinders - the coil pack actually has 3 coils for a 6 cyl engine. So a problem with the coil pack may only affect one or two cylinders. You can test the coil pack for resistance. I was getting an intermittent missing problem at freeway speeds, especially going uphill or towing and it turned out to be high resistance in the coil pack.

The coil pack costs $120 aftermarket, so you want to test to be sure before replacing it.

In your situation, you might want to test the resistance when cold and then again with the engine warm (or after heating with a heat gun) to see if the resistance changes drastically when warm.

 

[davem]

Upon further review, I need to clarify some information about the symptoms.

On a cold start, like 1st start in the morning, it starts fine every time.
If I drive 10 miles, shut it off, then restart immediately, it starts OK.

But if I drive 10 miles, shut it off, then try to restart after like 10 minutes, I get the difficult start.

I don't know if this helps point this in a specific direction or not.


Dave

 

[dogfriend]

Same symptoms that I had with my Ranger when the coil was bad, but doesn't really change anything that I suggested above.

If you could reproduce the problem by heating up the coil or some other component, that might help confirm what is causing the problem.

 

[Nemesiszx2]

I am having a check engine light problem too. Just poped on tonight after starting and I was shifting from 1st, 2nd, into D. Popped on. I had a tranny leak a bit back. I am a novice so be gentle boys....if I am low on tranny fluid would it trip the light. My Voltmeter in the gauge cluster is reading low too. Just put in a new battery, still low, could it be that my alternator is on the outs and could that have tripped the check engine light. If those two aren't something to check....what are the intial things I can check on my own under the hood and such. Thanks Guys I really appreciate the help.

 

[Glacier991]

[Enjoying watching Dogfriend do his magic on this site once again. It is always impressive.]

No low trans fluid will not set a code.

 

[Nemesiszx2]

so that rules out one.....what should I inspect?

 

[dogfriend]

You need to scan for codes; there are many different things that could cause a Check Engine light. It may be related to the transmission shifting into D, or it could be a coincidence.

 

[dontexplode]

Dave your description sounds to me like you have an injector leaking down into the cylinder after you shut it off warm. I would put a fuel pressure gauge on it and run it until it's warm. Shut it off and see if the pressure drops off. There is a spec somewhere as to how much pressure can drop during a time frame. If it drops off, block the fuel pressure and return lines to verify that it's the injector. Please excuse if you guys have already discussed this.