1994 TBI 5.7 - Crank, no start, stumped

[The Macinist]

I have a few questions for you, and they may or may not solve your problem. First, how long ago did you replace your plugs. If you don't mind me asking, which brand and part number did you use?

If I were you, I would use only AC Delco plugs. It's also recommended to run plugs that are 1 heat range colder than stock to avoid detonation. I'm currently running AC Delco R42TS (stock would be R43TS, the second number indicates heat range).

I replaced the plugs in September, maybe 1000 miles ago. I am running AC Delco. Don't remember the number, but it is whatever is spec'd stock.

Second, do you know if the truck had a custom tune installed with the supercharger? You said it was installed when new, so how long has this thing been on?

Canepa design did the installation when it was new. They had a system where people would bring them a new Suburban, check the boxes for the upgrades they wanted, and they would build it. I'm sure they tuned it. They are a high-end tuner. They build race cars and such.

Third, sounds to me like you have some other serious issues going on. Oil on your plugs, burning through oil pretty fast, smoking under throttle. I'd say it's time for a rebuild. At the very least, I would do a compression test to see if your valves/piston rings are still good.

I know. That was disappointing. I will get there. The truck doesn't get driven much.

And just curious, how much boost are you currently putting through the motor? How many miles are on it?

I have no idea how much boost. 105k miles.

OH, and I almost forgot, is your coil currently mounted to the intake manifold kind of underneath the throttle body? That's where my kit had mine relocated, and I found that it was overheating the coil and giving me a starting issue. I know you said you swapped coils, but just something that I had an issue with that may or may not help.

That's where the coil is. Pretty much under the throttle body, slightly off to the driver side. The throttle body is mounted sideways behind the supercharger, almost up against the firewall.

Thanks for everybody's help here. I talked to the mechanic who works next to my shop today. He said the pickup coil is a common problem on these too.

I just took the Burb out for a test drive and it is running strong. Still blowing a fair amount of smoke though.

 

[gmcyukondriver]

Glad it's running better. You might want to consider mounting that coil to the firewall one of these days. I don't know why it was mounted in that cramped little space, there's no airflow, and it's easy to overheat.

You also might want to consider buying a vac/boost gauge and a wideband air:fuel ratio gauge sometime. Those are kind of important when running a vehicle with boost. That's just my thoughts, though.

I have pretty much the same setup, sounds like. Do you also have the fuel pressure regulator that came with the kit? Is it running SUPER rich? I only ask because my regulator poked a hole in the diaphragm, so the truck was sucking fuel through the vacuum line at idle, and it was really drowning the engine down. Just another thing you might want to keep in mind or take a look at. It wouldn't take too long to pop that open and check the diaphragm.

 

[The Macinist]

Thanks for the tips. The coil mounting does seem to be less than ideal. For some reason mine is loose. The firewall would be a better spot.

Gauges are in order for this setup. I don't know why they weren't included in the original build.

The fuel pressure regulator looks like it is probably the original. It might not be in the best shape. It makes more noise than I think it should. Kind of a whining sound. The truck does run super rich. There is a lot of unburnt gas. I'm not a mechanic, but my research makes me want to replace the distributor to get a hotter spark.

One more thing about spark plugs and the tune. There is a label on the gas door that says 92 octane is required. That makes me think that it must be tuned for colder plugs. I should probably get that figured out. The bummer is that the Borla headers make some of the plugs REALLY hard to get to.

 

[thunderstruck]

Does it make sense that I get nothing, even with starter fluid, when there is at least some spark?

Makes me think ignition timing is way off, or timing chain is done.

 

[dr_goodwrench66]

A simple vacuum gauge reading at idle will tell you alot of the mechanical condition...

 

[The Macinist]

Makes me think ignition timing is way off, or timing chain is done.

That's what I was afraid of. I need to check it correctly. As soon as I got it started it was about 10-12° advanced. That was with a cold engine and I hadn't disconnected the advance connector.

 

[The Macinist]

A simple vacuum gauge reading at idle will tell you alot of the mechanical condition...

Will the supercharger mess with that? I just replaced the PCV valve and installed a check valve between the PCV and the throttle body.

 

[dr_goodwrench66]

If you can use the brake booster port to measure manifold vacuum then no. If you used a port on the throttle body then yes.