Cold Start Problem

[kalmwill]

My 86 Vette won't start in the conventional (hands off the throttle and just turn the key) when it is cold. It will start quite easily if I blip the throttle and runs well thereafter. I think that the problem may be the cold start switch or cold start valve or both. My question is in two parts: 1. I can't find the cold start switch. It is supposed to be on the engine near the throttle body but I can't seem to locate it.
2. How does one remove the cold start valve? I wold like to take it out for inspection and cleaning but don't quite know how it comes out.
Any help or suggestions would be greatly

 

[vetteboy86]

I'm not sure if I know exactly what you are talking about, perhaps I do but call it something different. Your car should have a 9th injector which is the cold start injector. I know my car had it. I think it does exactly what the name implies, adds fuel for cold starts.

The valve you are talking about probably is the Idle Air Control (IAC) valve. This valve opens and closes per the computer control without moving the butter flies in the throttle body. This may be the valve you are mentioning. This valve should control idle speed and such. The valve is on the bottom side of the throttle body, and is removed by 8 or so star head screws. Careful though as they are probably old, and when i removed mine I snapped a few screws off.

 

[kalmwill]

I'm not sure if I know exactly what you are talking about, perhaps I do but call it something different. Your car should have a 9th injector which is the cold start injector. I know my car had it. I think it does exactly what the name implies, adds fuel for cold starts.

The valve you are talking about probably is the Idle Air Control (IAC) valve. This valve opens and closes per the computer control without moving the butter flies in the throttle body. This may be the valve you are mentioning. This valve should control idle speed and such. The valve is on the bottom side of the throttle body, and is removed by 8 or so star head screws. Careful though as they are probably old, and when i removed mine I snapped a few screws off.

Thank you for your response and input.
From my Vette manual the cold start system consists of two components, the cold start valve which is the 9th injector that you mentioned, and a switch that allows it to activate. The switch, when the temperature is below 35 degrees C, grounds the injector circuit and allows it to function. The switch is supposed to be somewhere near the throttle body. The IAC valve is part of the throttle body and is something separate. I don't know how to remove the cold start injector, nor can I find the switch. Can you shed any light on my dilemma. I much appreciate your taking the time to write. Thanks again

 

[vetteboy86]

I wonder if it is tied into the Manifold Air Temperature(MAT) sensor? That is screwed into the bottom side of the plenum. I can look into my service manual and find that circuit and/or determine operation.

 

[kalmwill]

I wonder if it is tied into the Manifold Air Temperature(MAT) sensor? That is screwed into the bottom side of the plenum. I can look into my service manual and find that circuit and/or determine operation.

Thank you for your input. Any light that you can shed would be quite helpful. My manual seems to indicate that the cold start switch works from the coolant temperature. It has a purple and tan wire coming out of it. Needless to say I can't find it.

Thanks again.

 

[vetteboy86]

I do see in my manual a diagram that includes a cold start valve. I have yet to find any information about it though. I don't have the original intake on my car, or I would go out and look, nor do I have the cold start injector. I will keep digging though.

 

[vetteboy86]

Looks as if the cold start valve is the injector itself, or at least that is what I will call it. It is located on the drivers side of the motor between injectors 1,3 and 5,7. So pretty much in the middle of the fuel rail. That valve then is secured to the intake. I would imagine if you found this, you could trace the wires to the source, if it operates in the manner you say it does.

What manual do you have?

 

[kalmwill]

Looks as if the cold start valve is the injector itself, or at least that is what I will call it. It is located on the drivers side of the motor between injectors 1,3 and 5,7. So pretty much in the middle of the fuel rail. That valve then is secured to the intake. I would imagine if you found this, you could trace the wires to the source, if it operates in the manner you say it does.

What manual do you have?

Thanks again for replying. I have a GM Corvette shop manual for an 86 Vette. I found the injector valve that you are referring to. The space is very tight for fingers and the manual doesn't exactly say how the valve is supposed to be removed. I am not an experienced mechanic, just a home hobbyist. I guess one is supposed to know these things. If the injector is the problem, I would like to take it out to clean it and then put it back. If the switch turns out to be the problem, I would like to replace it. It is a job I don't want to get into job unless I have some idea as to where I am heading and it is helpful to hear from someone who has been there before and experienced the pitfalls.

Thank you for your interest. I appreciate any further insight that you may have.

 

[vetteboy86]

My manual did show an exploded parts view diagram and I think had a procedure to clean it. I can look the page # up for you. Otherwise I think the injector will come out by removing the screws that go through its mounting plate and into the intake manifold.

 

[kalmwill]

My manual did show an exploded parts view diagram and I think had a procedure to clean it. I can look the page # up for you. Otherwise I think the injector will come out by removing the screws that go through its mounting plate and into the intake manifold.

Thank you for your assistance. I appreciate the time and effort that you have spent. I plan to have a go at it next week and will see what I get myself into. I like to plan for the worst and hope for the best.

Thanks again

Bill

 

[vetteboy86]

Bill,

Were you able to find the section in the manual that i was speaking about?

Craig

 

[kalmwill]

Bill,

Were you able to find the section in the manual that i was speaking about?

Craig

Hi Craig

I looked at a different GM manual and found where the thermo sensor for the cold start valve ( 9th injector) is located. It is in front of and slightly above the right valve cover. It must be tucked in underneath and behind the AC compressor. This would explain why I was unable to find it. At this point in time I don't want to be taking things apart to get at it. I'm thinking that the problem could be either the cold start valve or the sensor. There is a test procedure to test each of them. When I have time I will trouble shoot a little further. The sensor is important in that it allows the injector to operate when the temprerature is below 35 degrees C. It basically grounds the injector circuit and allows it to function. Above that temperature the sensor opens the ground and the injector circuit stops operating. Thus both components have to be tested to see if they work. I was looking for a simple diagnosis and fix but it looks like it is more than I want to tackle at the moment.

Thanks for your help Craig. I hope that we both learned something from our dialogue. I certainly did. Much appreciated.

Bill

 

[vetteboy86]

Bill, I am glad to hear some good came from this also. You will have to update me or this thread when you get around to working on it.Craig