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Doesnt wanna run when the engine is hot

k20

k20

3/4 ton status
Joined
Sep 9, 2001
Posts
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Location
Mineral Springs, NC
Hey all, truck starts and runs fine when its cold, a little rich till it heats up but runs ok. Once heats up, all is right w/ the world. Prob is that if i shut it down once it gets warm, for any period between 5 mins and an hr. It will refire ok, but then wants to choke down. You have to feather the throttle to keep it runnin, and it does that until its been runnin long enoguh that you have had time to run it up through the gears. I mean get goin fast enough the tranny shifted into all the gears, and then it will run fine. Any ideas? Thanks. Chris.
 
ttt anyone? Doubt its vapor lock, fuel lines arent that close to exhaust. BTW for anyone who doesnt know its mpfi not carb.
 
its helpful to post what you are working on, many times people post a problem and get replies based on whats in their profile only to find out thats not the vehicle thats broke. /forums/images/graemlins/thumb.gif
 
ah true, only vehicle i have is one in profile lol. Anyway, 87 V20, now has 496 w/ edelbrock mpfi/tbi conversion on it. Has msd ignition system, did this b4 ignition too, so that aint the prob. Timing is correct. Ideas?
 
sounds like a very cool engine. off the top of my head I'd guess some sort of lean condition possibly caused by vapor lock........I also wonder if the fuel pump is weak??? Anyone??
 
it definately aint lean lol. It runs rich until it gets warm, its fuel injected, but I already had a 180 t-stat so I put that in. Would I be better off putting in a 195?
 
see i thought vacuum leak too since it runs richer on the pass side, but i cant find one anywhere, tightened all manifold bolts, checked all the hoses, sprayed soap/water everywhere i could think of lookin for change in idle which would equal vac leak, and I couldnt find anything.
 
Try starting fluid or carb cleaner instead of soap and water.

A vacuum leak will suck the fluid in, which is kinda hard to see with soapy water...it's not like a tire leak. /forums/images/graemlins/smile.gif
 
may try that, i thought purpose of soap/water was to temporarily plug the leak, which would change running characteristics, and let you know leak is there.
 
[ QUOTE ]
Try starting fluid or carb cleaner instead of soap and water.

A vacuum leak will suck the fluid in, which is kinda hard to see with soapy water...it's not like a tire leak. /forums/images/graemlins/smile.gif

[/ QUOTE ]

Carb cleaner doesn't work on TBI, anyways it's too easy to ignite and start fires, thats nasty when that happens, finding vacuum leaks on TBI try using WD-40 or the water trick does work. (it seals up the leak causing the engine to idle up to normal range)

I'm curious if it's a TBI setup, does it have a throttle position sensor (TPS) on it? and if it's working correctly.

Also the Idle Air Control (IAC) valve inside the TBI unit could be dirty or damaged.
 
IAC is new and works, tps is new, but i put the one i took off back on and no diff. the one i put back on was good when i took it off.
 
How's about the EGR setup? the EGR vacuum switch? vacuum hose going to that switch. HMMM. /forums/images/graemlins/thinking.gif
 
Does the ECM coolant temp sensor match the actual engine temperature?

Kind of hard to "guess" what it SHOULD be reading, but if it says 32* when the engine should be at 195*, or some other equally wacky reading, then the temp sensor isn't working right.

Not real likely IMO from your explanation, but engine temp does play a big part in how the EFI vehicles run, and with it being a "hot only" issue, a temp sender is a possible culprit.
 
The coolant temp sensor, if i remember correctly, is just another sensor that tells the computer when it's warmed up and adjusts fuels mixtures, or idle speed, somethin like that, back when i had problems with the way mine was runnin, i was checking all the sensors, if again i remember correctly, you are supposed to check the voltage coming from one of the wires with the key off, and also with the key turned on. There is a specific reading you are to look for, if it is not within the perimeters of a good working unit, it's probably bad, but then again, it's only a $7.00 sensor, i just changed it anyways.
 
Since the computer can TELL you what the temperature is, I don't see the point in A)replacing a part that might be bad or good, and B)wasting time trying to determine voltage/resistance readings that correlate to X engine temperature.

Maybe it's just me, but I see WAY too much parts replacing on this board trying to solve problems, and probably 7 times out of 10, the wasted money didn't fix anything. Sure, new parts, but I'd rather have a known good part in place than a questionable (new) part that I had to pay for.
 
I totally understand what you are saying about the replacing of parts, but if you really want to find out exactly what the problem is then, you are at the wrong place for this info,(this website) where you need to be then is at the shop with a computer plugged into it that can tell you exactly what sensor is faulty. /forums/images/graemlins/deal.gif But then again you are going to pay around $50 /forums/images/graemlins/yikes.gif or so for the time and computer usage, so i guess pick your price???? /forums/images/graemlins/dunno.gif

Good luck with it,, /forums/images/graemlins/waytogo.gif

Actually after i reread your post, i think you were misunderstanding what i was saying about the temp sensor, there are two of them, one is for the temp gauge, and the other is for the computer, the one for the computer i believe is on the front top of the intake, the gauge sender unit is in one of the heads i believe. Is this what we are trying to finger out about the computer telling you the engine temp,,,by the gauge?? I guess i'm confuzzed /forums/images/graemlins/doah.gif
 
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