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cruise control and vapor lock

J

joshkbomb

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Location
Lafayette, CO
So I am having a couple problems:

1. Here in the Denver area we've been having 100+ weather and like last year when the temperature was this high my truck acts like it's vapor locked when I try to get going from it sitting in the heat for a while already warm from driving. The rpm's will go up and down when it's idling and when I hit the gas I may have to wait a few seconds for the engine to go.
Like I said this happened to me last year when the weather was 100+ but happens at no other time. As a matter of fact, if the car gets going it's able to cool off enough to not have problems until I stop and it heats up again. The reason I'm going into so much detail about this is because my truck is fuel injected (87 blazer 350). I was told that fuel injected cars can't get vapor lock, is this true? If it isn't vapor lock what could it be? If it is vapor lock, what can I do?

(sorry for the long post, too much explaination is better than not enough)

2. My cruise control seems to be not working. I had my mechanic look at it and he told me that the computer was bad. I got a couple from the junk yard (one with the same part number, one from an 89 suburban) and neither does anything. I know it's possible that all 3 computers are bad, but highly unlikely. Today I tried hooking up one of them again, I engaged the cruise control and it pulsed the engine and cut out. I wasn't able to repeat this. I'm thinking it just may not be getting power, but I'm not sure.
The cruise control is pretty complicated and it's probably not trivial to diagnose. I just wanted to see if anybody else had this or something similar happen to them and what they did to fix it.

Thanks
 
Vapor lock with EFI isn't likely at all of being a problem. Could be the pump just getting hot/old though. More fuel in the tank would solve the problem if it were vapor lock. (fuel is recirculated through the system so the tank and lines are how it is kept cool)

Here's the cruise diagrams:

http://coloradok5.com/forums/showthread.php?t=38669&highlight=cruise+troubleshooting

There is a separate "ECM" for the cruise FYI. Blaming the ECM right off the bat is the sign of a poor mechanic, sorry. Unless of course he went through the diagnostic checks, sounds like not though.
 
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I don't know if GM is similar to Ford in EFI respect but my 90 Bronco would do the same thing. I had to replace the air bypass valve twice to get it to stop. The RPM's would surge, then drop, surge, then drop.
 
Sorry I wasn't clear enough, the "computer" I was talking about is the cruise control computer.

I talked with my mechanic today about it and he said that since the "vapor lock" problem can't be vapor lock, it might be some electronics getting too hot and malfunctioning. He mentioned that the ignition module might be the problem.
 
My problem is a little different. It doesn't surge, it does the opposite. The rpm's will drop then come back to normal. This is what got me thinking that it was being starved for fuel. The rpm's even dropped so low as to kill the engine a couple times.
 
Well, I could see how you would think maybe fuel pump. EFI has to be under constant pressure. But, usually the pumps just plain fail, not go out slow. If it is cyclical, then I would say something else. If it is sporadic, maybe you have some gunk in the lines restricting flow.
 
being a gm tech, i have run into this before. check your vapor canister and purge solenoid under the hood. if they are bad it will cause that. it happened on my 91 jimmy also
 
Like a moron, a while back I did a gas tank swap. I ended up switching the vapor return line to the carbon canister with the fuel return line. That caused a similar problem. I would get decent acceleration out of the hole, but it would drop off if I got on it. I ended up causing all kinds of problems. Situation rectified now though. I didn't know EFI rigs had a vapor canister...
 
But would a bad vapor canister or purge solenoid only cause this problem in extreme heat (95+) and run fine the rest of the time? That for me is the weird thing about this problem and may be key to fixing it.

I don't have a vacuum pump so I can't fully test these guys, but I did notice some leakage coming out of the hoses from the pcv valve. It dripped down and was damp beneath the canister.
 
yep, that's exactly when it happened on mine

joshkbomb said:
But would a bad vapor canister or purge solenoid only cause this problem in extreme heat (95+) and run fine the rest of the time? That for me is the weird thing about this problem and may be key to fixing it.

I don't have a vacuum pump so I can't fully test these guys, but I did notice some leakage coming out of the hoses from the pcv valve. It dripped down and was damp beneath the canister.
Click to expand...
 
I guess I'll go ahead and replace the vapor canister and purge solenoid.

I wonder what it is happening in the heat with these parts to cause this problem. Anyone know?
 
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