Please help, unusual no-start condition on '97 Vortec 5.7L

[snydes]

I would appreciate any ideas here, because I'm out of them. I realize no one likes to get into these in depth problems, but here it goes...

'97 K1500 5.7L, 130K, truck began to start hard back in the summer, it has not been getting used much and will set for weeks at a time, finally one time it would not start at all, sounded like it wanted to but wouldn't. Pulled the plugs, all wet, checked spark at a few cylinders, spark looked good. Put a new set of plugs in, nothing this time, not even a cough, pulled them out, soaked again. Did some reading, read that the PCM coolant sensor might cause the truck to run too rich at start-up, figured that if that were the case then it might stand a better chance of starting when it was colder. Left the plugs out for a few days to make sure everything was dried out, put them back it, waited to a cold morning and tried it, sure enough it started, started hard, but started. It ran rough for 30 seconds or so and then cleared up and ran fine. Later that day I replaced that sensor figuring that was the problem. Started fine for the next few days. Parked the truck again for a week or two until I needed it again and went to start it up and now back to nothing, not even a cough. Checked fuel pressure, key on 62 psi when the pump runs and then 52 after it shuts off. Checked spark again at a few cylinders, looks good, plugs all wet again. Was getting real frustrated and tried giving it some ether (yes, I know that's a no-no but I'm getting mad now) and not even a cough. Oh, no codes are coming up either.

What in the world could this be? What else would determine air/fuel on start up?

Thanks for your time,
Steve

[J-Ri]

Intake air temp could also cause it to run too rich.

Incorrect barometric pressure reading could affect it a bit. It reads the MAP as soon as the key goes "on" (before any cranking) and uses that reading for the remainder of the ignition cycle.

What's the spark plug gap?

[snydes]

The plug gap is to spec, I can't remember what that spec is but off the top of my head I think it was .06". What sensors in particular are involved with the intake air temp/barometric pressure readings you are speaking of?

I appreciate the info...

[777stickman]

The IAT (Intake Air Temp) sensor is located in the inlet tube just as it comes out of the filter box. The MAP (Manifold Absolute Pressure ((AKA manifold vacuum)) ) is located between the throttle body and the dist.

Really should hook up a scanner that can read these sensors and see if they need to be replaced.

The IAT should read ambient temp and the MAP should read current barometric pressure (engine off-key on).

Also need to check the TPS (Throttle Position Sensor). With the throttle closed the voltage should not be more than 2.5 volts.

[snydes]

I guess you need a high end scanner that can read those sensors? I have one of those Actron code scanners, I just went through the manual and I don't think it can do that. This is the one I am using... http://www.actron.com/product_detail.php?pid=16298
Is there one that can do what you are referring, or are those type real expensive dealer type units? Thanks for the replies.

[2000CAYukon]

Originally Posted by snydes

I guess you need a high end scanner that can read those sensors? I have one of those Actron code scanners, I just went through the manual and I don't think it can do that. This is the one I am using... http://www.actron.com/product_detail.php?pid=16298
Is there one that can do what you are referring, or are those type real expensive dealer type units? Thanks for the replies.

That is a code reader not a scan tool. You do not need a real high end scanner to read the sensor values but the code reader is not going to do it.

//2000CAYukon

[snydes]

Ok, I see them now. I will have to see if I can find one to borrow.

[snydes]

Does anyone make any software for a laptop that can do the same thing?

[tempfixit]

Try www.autotap.com

or www.autoenginuity.com

[snydes]

Well, I got a PC type set-up on the way, I will report back with my findings, hopefully it will give some clues to the problem.

[bracketshark]

While your waiting for the software to arrive I'd check the Distributor cap and rotor button. I just finished a truck that showed good fire at the plugs but wouldn't run. When we opened the dist. it was obvious, found a dime sized hole in the rotor button and the metal was gone off of it. I don't think yours is this severe but it might be bad. Hope this helps.

[snydes]

I did take it off and look at it, it could use a new one, it didn't look like it was bad enough to be an issue, but I will replace anyhow to be sure. Thanks for the suggestion. Keep em' coming

[snydes]

Originally Posted by bracketshark

While your waiting for the software to arrive I'd check the Distributor cap and rotor button. I just finished a truck that showed good fire at the plugs but wouldn't run. When we opened the dist. it was obvious, found a dime sized hole in the rotor button and the metal was gone off of it. I don't think yours is this severe but it might be bad. Hope this helps.

Well, I got a new cap and rotor, put it on, put the spark plugs back in (I had left them out to dry out good), and it started. I'm not sure I understand why, it had good spark at the plugs, I had the cap off and looked at it, the contacts were showing their age, but I've seen much worse that had worked. When I pulled the rotor off and looked at it, it wasn't unusually bad either, but I did notice some condensation on it, which I suppose could have been a factor. I don't want to celebrate yet, as I had it running once before and it seemed fine, left it sit and it wouldn't start again, but I'm real glad it's at least running again. Thanks for the advice!

Steve

[maxwedge]

Good spark at the plugs can fool you, under cylinder pressure it may not be enough to fire the plugs.

[outofwaygreg]

have you tried the scanner tool that mentioned above?
well just bought 1 last month and it work all fine to me..

It cost me like almost $55 from this site http://actroncp9125.com