1988 5.7 Engine Won't Start

cclay6482 · February 9, 2009

I'm usually not too bad at troubleshooting, but this one has me stumped.

1988 GMC K1500 5.7, 105,000 miles. A couple of weeks ago, I noticed the truck would have a distinct miss occasionally while driving. No issues otherwise. As time progressed, the miss got worse, then began to turn into a rough idle. Eventually, it got to where it would barely run unless it was getting a lot of accelerator pedal. I parked it in the driveway and it sat for a week.

I spent this weekend looking at it, trying to diagnose the issue. First of all, I did check for vacuum leaks around the engine, using both the carb spray/engine idle method, as well as a vacuum gage. The spray did not affect the idle at all. The vacuum gage needle fell just below the "good" range, ending up in the range that indicated an issue with engine timing. Since I had not touched the distributor, I discounted that and decided that it must not have that much of a vacuum leak (if any).

Fuel delivery has never seemed to be an issue, as it looks like it's getting plenty of spray from the injectors. In fact, it almost appears to be too much, and so I inspected and cleaned the pressure regulator. Also pulled and checked the fuel filter, which is fine. I've also pulled the plugs from both injectors and tried to start it, but that doesn't help either, so I don't think it's being flooded.

I replaced the map sensor, as my voltmeter checks seemed to indicate it was faulty. Did not fix the problem. I have also replaced the ignition module, as Autozone confirmed the original was bad. Before I replaced it, there was no spark at all. Also replaced the cap and rotor.

What I have now is this: fuel injectors are spraying fuel, ignition system is providing a spark (not the hottest blue spark I've ever seen, but it is sparking). When starting, the truck turns over easily, but never even tries to start at all. I've tried starting it with the fuel injectors disabled, thinking it could be very flooded, but still no luck. Doesn't start after priming the throttle body either.

Could it be that after all this cranking and no start, the spark plugs are so saturated with gas that it won't ignite at all? I've checked number one cylinder, and it's kind of wet but not too bad. What about the coil itself - could it need replaced? Will a less than stellar spark prevent the engine from starting? I could see it not starting up, but I'd at least expect it to hit on a cylinder every now and then. Any help would be appreciated.

Mike G · February 9, 2009

I would shoot for the coil next, and that is a relatively cheap and easy fix. You pretty much have run teh stadard stuff down too. Can you hear the fuel pump working when you turn on the ignition?

--Mike

Heavy Cruiser · February 10, 2009

Spark plugs are probably saturated.

With closed throttle plates during cranking, vacuum gauge should read at least 1 inch of vacuum.

With timing light, bypass ECM ignition control by unplugging the single wire at pass firewall - tan/white wire. Base timing should be 6° BTDC or what emissions sticker states, if less, procede to next step.

Disable the ign and perform a compression test, should be over 120 PSI. If not, I'd look for a stretched timing chain causing jumped timing low compression.

EFI engine should start with WOT at cranking to 'clean' it out, just like a carb flooded.

Most any engine will fire with a good squirt of WD40/starting fluid.

Externally charge the battery.

Hope this helps.

pennzoil29 · February 10, 2009

Spark plugs are probably saturated.
With closed throttle plates during cranking, vacuum gauge should read at least 1 inch of vacuum.

With timing light, bypass ECM ignition control by unplugging the single wire at pass firewall - tan/white wire. Base timing should be 6° BTDC or what emissions sticker states, if less, procede to next step.

Disable the ign and perform a compression test, should be over 120 PSI. If not, I'd look for a stretched timing chain causing jumped timing low compression.

EFI engine should start with WOT at cranking to 'clean' it out, just like a carb flooded.

Most any engine will fire with a good squirt of WD40/starting fluid.

Externally charge the battery.

Hope this helps.

This was my first thought.

Mike G · February 10, 2009

...., I'd look for a stretched timing chain causing jumped timing...

I would also suggest checking the distributor for wear.

--Mike

Axlshaft · February 10, 2009

I would check the plug wires. I had a similar problem with an '87 Suburban. It started out as a miss and eventually wound up not starting. Turns out the coil wire was intermitantly shorting on a bracket then just shorting all the time. I found the problem at night, you could see the arcing while cranking. The kicker was the wire set was about 1 yr old and not warn thru. That was the last cheap wire set I ever bought.

-Ken