Rough Hot Starts

[WNP 2]

Hello

I have a 96 Limited with the OHV V6. It has had a replaced fuel pump, fuel pressure regulator, DPFE, fuel filter and IAC. Tune up was also done a year ago. The car sat for almost a year and now I am driving it again.

Cold it starts right away.

After it has been driven and sits for 20 minutes or so it will start right up but idle rough down to 500 rpm then smooth out.

I am perplexed as to what is wrong with this beast. The engine runs great otherwise.

Fuel pressure is great and does not bleed down.

Thanks,

Morgan

 

[2000StreetRod]

Check the ECT sensor

You may want to check the engine coolant temperature (ECT) sensor that sends data to the PCM. It may be telling the PCM the engine is cold when it's actually warm resulting in an excessively rich fuel mixture.

 

[WNP 2]

Sensor is within spec. Any other ideas?

 

[2000StreetRod]

DTCs?

Are any diagnostic trouble codes getting set?

Have you checked the compression when cold and warm and compared the readings?

One remote possibility is heat soak sensitive fuel injectors. A bottle of fuel injector cleaner might help.

 

[WNP 2]

Compression is good, also the I dumped in a bottle of EFI cleaner. No DTCs I am stumped, It never stalls it just starts idles rough for 20 seconds then smooths out. I wonder if this is a lean condition causing this? The car gets pretty good mpg 17 average half city/highway. I had another 96 it did 14 at best (same engine)

 

[WNP 2]

Also for what it is worth the car starts very fast, cold or hot, in fact cold it cranks over maybe two times, when hot no more than three.

 

[donaldspartan]

I've got the same engine in a 99 explorer sport 5 speed, 2wd. After doing a tune up (plugs, wires, IAC) it still had the problem. Turned out my Mass Air Flow sensor was gunked up, These range from $250 new on ebay to $50.00 used. Instead of buying a new one, I took it apart and cleaned it out with a can electrical component cleaner, and a can of compressed air- like you might use on a computer to clean the dust out. Cured the problem for me.

Hope this helps!

 

[WNP 2]

Thanks, I tried starting the car with this unplugged and it starts fine. My guess is you are right, or its an O2 sensor. Im gonna get a MAF off my moms 96 and try it.

 

[donaldspartan]

The engine would start fine with the MAF unplugged, because to my understanding, it sends information to the computer as to how much fuel to inject vs the air being sucked in the intake.

What I would do is run it for a while and get it warmed up, then unplug the MAF to see if it does the same thing.

Also, for what it's worth check out the rubber lines to the PCV valve. My truck burns through the shorter one of those at a rate of 1/year.

And to get the MAF sensor out of the intermediate tube I used a small pair of vice grips on those screws, because they took a special kind of allen key to twist out.

 

[WNP 2]

Okay I will check those. That is what I did got it hot, shut it off let it sit for 20 restarted it unplugged MAF and it didint lope. I will check the pcv anyway.

Thanks,

Morgan

 

[donaldspartan]

here's another thing you could check out, under your throttle body, there should be a rubber line. A few months ago I took my tb off and cleaned it, and when I put it on I forgot to put the rubber hose back on, the rig ran fine, but sounded like I had put a cam on it.

Sorry to blow up your original post, but thought I'd throw as much information at you as you may need.

 

[WNP 2]

No problem I need all I can get.