Calling All GM Mechanics!

[Broker57]

I have a 1997 GMC 1500 extended cab 4X4 with the 5.7L Vortec. It just rolled over 200,000 miles a few weeks ago. Aside from some minor drive train repairs I have had to do recently, it has been running without incident until today.

It started and drove fine this morning until a few miles from home when I stopped to gas up. I started away from the station and the truck started to lug under load. It would idle fine and I could rev the engine, but when I put it in drive and accelerated it would choke to the point of stalling. I made it into a large, empty chain store parking lot and I could get it up to about 30 mph, but then it would stall out again. It soon reached the point where it wouldn't even start. I had it towed home and started in on it.

As an aside, last September I replaced the fuel tank sending unit, fuel pump and filter. Just the same, I pulled the fuel filter to confirm that it wasn't plugged, and I could hear the fuel pump cycle on when the key was turned. I hooked a gauge up to the fuel rail and confirmed that there was good pressure there as well.

I pulled a spark plug and the spark was thin, weak and yellow. All of my local sources agreed that the ignition coil was a good place to start, so I spent this afternoon and evening replacing it. Let me tell you, that was a treat! The coil was still riveted to the mounting bracket, so it would appear that this was the factory original and probably due to be changed anyway.

Upon completing the installation I tried to fire it up. Engine turned over fast and strong with no indication that it wanted to catch. Two observations:

I pulled the #1 plug again and this time the spark was fat and orange instead of thin and yellow. However, there was no blue and I take it that this might not be a good sign.

The plug itself was bone dry and did not smell like gas. I would have thought that with all of the attempts I had made to start it before I changed the coil that the plug would have been wet or at least smelled like fresh gas.

So – with an orange spark, am I still not getting proper ignition? Is there still a fuel delivery issue past where the pressure readings are taken on the fuel rail? I assume that tomorrow when I am more fully awake and the skeeters aren't thick enough to carry me off that I should pull the cover to the throttle body and check to see if I am getting fuel there.

Any other diagnostic steps and possible solutions would be much appreciated – thanks in advance for your help!

 

[dynamike]

you said you had good psi? what was the psi on the gauge? should be minimum 50 psi. also, did it hold psi after the initial 2 second prime? should hold psi for a good long while. also, you need to check injector pulse. kinda tough to do without hte proper gm tool on that engine

 

[29aholic]

PM member 66tas....he's a mechanic

 

[mikelain]

Have you pulled off the distributor cap and checked it and the rotor? If not do so. It might be worn out and not distributing the spark correctly. It could be wet. Mine had been acting up with all the rain this spring. Good luck

 

[2Loud4You]

What Dynamike said, Vortecs need a lot of fuel pressure. To test if it's fuel starvation spray some carb clean into the intake while someone starts it. If it runs off of carb clean then you're looking at a fuel issue. I recently had to replace a fuel pump on a '97 Tahoe that my shop had done just 6 months prior. Sometimes they just crap out.

 

[shooboy]

You need a hot, crisp, blue spark for ignition under compression. If the spark is still yellow then you still have a problem there. Not to say you don't have other problems also. Might have to take it into a dealer unfortunately, Shoo

 

[66TAS]

Is your throttle body injection or multi port? You could have an issue with the pick up coil in the distributor, what is your fuel pressure??

PM me and I'll see if I can help.

 

[m1gunner]

On the GM fuel injection systems, the ignition system is also used to fire the injectors. I had a 1500 in the shop last summer doing exactly what yours is doing. It turned out to be the ignition module (located on the passenger side of the engine). If you end up replacing this module, do not buy one of the cheapie Chinese made clones, get a Delco or other name brand replacement.

As mentioned above, if you aren't holding 50 or so psi, the GM fuel injection system won't work. The gasahol they are selling these days really wrecks those intank fuel pumps.

 

[Broker57]

Thanks for all of the input and offers of help. Unfortunately I can't recheck the fuel pressure because my buddy with the gauge is at work right now, but as soon as he gets home I'll try to get some new readings. The other problem is that I haven't been able to check fuel pressure with the engine running. I just picked up a can of ether and I'm going to pull the snorkel and see if the engine catches after a healthy whiff.

As for the orange spark, I was reminded that I've been cranking the engine with no results so battery power could be low.

66TAS, I'll PM you as soon as I have more info to go on.

M1, thanks for the reminder on gasahol. I belonged to the Farm Bureau in Michigan until last year because they had the best group insurance rates. One of the newsletters I received back then was touting the victory in the Michigan legislature whereby gas stations are no longer required to post on the pumps that their gasoline contains ethanol. One of my friends used to swear by Mobil as being the best and purest gas until I told him about my trip to St. Louis last year where the Mobil station I stopped at had a 10% ethanol sticker. I suspect that it is in every brand here now, and without the labeling requirement we are all clueless. The havoc it can wreak on a vehicle's entire fuel system far outweighs the cost savings as far as I am concerned. I work for a Florida marine dealership, and ethanol has become a big marine industry concern as well.

Thanks again, everyone. I knew I could rely on the S&W forum for knowledgeable advice.

 

[2Loud4You]

You don't really need a running fuel pressure test to determine if you have the proper initial fuel pressure. Do make sure your battery is charged though.

 

[Broker57]

Sorry to resurrect an old thread, but I needed to give credit where credit is due.

Thanks to 66TAS and his patient tutelage over the phone with diagnostics, I was able to pinpoint and confirm that the fuel pump was definitely the problem.

Replacing it in this instance got a little ugly, but when it was all said and done the pressure with the new pump was 66 psi and the truck fired right up on the first turn of the key.

Thanks to all for the input, and especially to 66TAS for taking the time to walk me through all of the various troubleshooting steps.

 

[Firehouse]

Thanks for bringing it back up. I have a 1999 Chevy K1500 with the 5.7 Vortec in it. I will keep this in mind if/when I start to have trouble.