Cold vs. warm start

[htheduck]

Folks,

Just these couple of instanced in the past weekend have prompted me to ask the experts online here:

Car starts with no issues when cold: (overnight, 45min-2hrs of shutoff)
However, on a couple of instances when I would park, 30 minutes or less try and re-start the symptoms are:

-hesitation, erratic idle -> to stalling out. Naturally, the only thing I do once it "half" starts and hesitates, is to give it more throttle. This seems to clear it up and the rpms return to normal, and the car operates normal: does not stall during normal operations.

(GUESSING HERE: SINCE I DON'T KNOW WHAT TO LOOK FOR) It appears to have symptoms of a vacuum leak, but WHY only during WARM startup? Could a missing clamp cause a vacuum line to expand/contract - which is why my cold starts are 100% and my warm starts i worry about?

Please help since I don't know much about under the hood of this thing...THANKS in advance.

Details: 65k done at 85k, new auto transmission installed at 138K. 3.2 engine is stock w/KN panel filter:

 

[Phoenix]

sounds like a fuel pump , did you pull the codes?

 

[jayro]

I was thinking maybe a leaky injector. Next time it doesn't want to starts put the gas on the floor and see if it starts up.

 

[boat]

x2 on the bad fuel pump. I have had 2 go out like you are stating yours does. But definitely run your codes like Phoenix suggested.

 

[mhoffman1981]

#3 02-06-2010, 06:26 PM
hawkeye18
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Quote:
Originally Posted by kumba
I am having an issue where after driving my car around and it getting to normal operating temp it becomes rough starting and idling. Once I do get it started I usually have to rev it up to 1500-rpm or so for 10-15 seconds after which it usually starts to idle correctly. The problem does not happen if the car never reaches operating temp. The problem reminds me of a carb set-up where the fuel would percolate in the bowls under a hot engine bay.

Is there a most likely culprit I should be looking for?

This is actually a fairly normal condition in SHOs. Nobody's really figured out the exact cause of this (or if they have, they aren't sharing), but my best guess is that it has something to do with the metal intake getting hot with the rest of the engine. When you start it up, the air at the IAT is significantly cooler than the actual air in the intake as it's been heat soaking for a while. This makes the car dump waaaaaaay moree fuel than it needs into the air and makes it stumble until you get enough air through the intake that it cools down.

This has happened on all three of my SHOs, usually after not turning the car on for 10-15 minutes after letting it warm up all the way. Solution is just taking the engine RPM up to what should be about 2500 and just keep it there until the engine magically jumps up 700-900rpm.
__________________
Jason H ('95 ATX, '12 Mustang GT)

Quote:
Originally Posted by LJRuddy
Im still trying to figure out how to multiply "V" and a slice of pizza.


is it possible its just what hawkeye said here

 

[32MTX]

word I got the same shit. I've also heard some problems about faulty fuel pump assemblies causing this. My car will miss too when this is happening. Revving it up at higher rpm's will clear it up. Sometimes has hard starts and only will get running with WOT, sometimes its even worse then that.

my car has always done this, and throughout the years all these parts have been changed, but the problem persists.

ALL ignition components, engine, ecu, tps, maf, motor part of fuel pump only(155lph walbro I believe)- not entire assembly/level sender etc..., fpr, fuel rail, injectors, engine wiring harness, dis, cps, ckp..

pretty much only thing original is the car, chassis harness, o2 sensors, fuel pump assembly, and the CCRM.

I was really puzzled when most of that stuff was changed with the 3.2 swap and I still had same problem. Even with another intake manifold/couplers/gaskets/iac motor/secondary assemblies it does the same stuff. It is also worse when hot. At the drag strip or this passed weekend at the track it would get real bad after running it hard and getting hot as shit(heat soak type temp not operating temp of the coolant). I know another local member has same problem.

at this point I'm suspecting something to do with the fuel tank/lines/pump assembly. I'm still in investigation mode at this point but I think this is the right direction to go as far as solving this issue. what the **** else could it be... unless something I changed during the engine swap has the same exact problem as the original part.....

One thing I noticed after running my car and it warms up, pull off the gas cap and see how much pressure comes out, especially when the level is down far..... Some pressure is to be expected, but mine feels nothing like other cars I have, or other SHO's I've had in the past for that matter(which didn't have this problem BTW)


any of you other guys suffering from this, take off your gas cap if your cars been running like 30 minutes or real aggressive driving with under a 1/4 tank and see if you think it has excessive pressure built up. Mine will exhale a big volume for seconds.... its not just a quick little puff....