Hey guys! 5.7l Vortec plugs & Compression help needed

[kendogg]

Hey everybody! I found this forum searching for info on my '97 Cheyenne 2500 8600lbs GVWR 2wd that I just picked up the other day. Performancetrucks.net seems useless for anything thats not LS related, hopefully you guys can help.


Chassis has ~350k on it, unknown on engine. I just did a compression test and got the following results:

1 - 170
2 - 195
3 - 181
4 - 185
5 - 169
6 - 184
7 - 195
8 - 210


Numbers seem a little off, but not horrible if the motor really does have higher mileage. However, spec I found in Alldata was only 100PSI, which did seem suspect. Are these compression numbers normal, and what is the actual spec? Also, the plus look HORRIBLE. Most look rather white like the trucks been a wee bit lean, but 1 plug, #6 I think, looked particularly bad. Can anybody identify whats on this plug? Is it coolant, carbon, what?

[kendogg]

Well damn, looks like I can't post the pictures until I have 5 posts..... BRB!

[kendogg]

[AZRon]

A few specs from a factory 1998 manual for the 5.7 Vortec:

Disconnect power to the ignition coil
Disconnect Injector harness
Remove all spark plugs
Block throttle wide open
With gauge installed, crank engine through 4 compression cycles
Repeat on all cylinders

The manual doesn't give an exact compression spec, but states:

No cylinder shall be below 100 PSI
No cylinder shall be below 70% of the highest-reading cylinder

All of your readings are well above 100PSI
70% of 210 is 147. Your lowest is 169, meaning that it is well within specs.

Depending on mileage, your plugs don't look that bad to me. The white, fluffy accumulation is mostly caused by fuel additives that the refiners add.

If it were me, lacking any driveability complaints, I'd put in a new set of Delco plugs and retest it (see above) after 10 or 20 thousand miles.

[Quyonmob]

Plug deposits look like ash, likely a little blow-by.

How long were those plugs run?

[kendogg]

Plug deposits look like ash, likely a little blow-by.

How long were those plugs run?

No idea, I just bought the truck. They don't look THAT old though. I'll do a wet compression test this weekend and a leakdown and see what we get.

[Chevy53]

i suspect your going to have better numbers with wet tests your dry tests are fine doubt a wet is even needed deffinitly good numbers for a unknown miles engine

[kendogg]

i suspect your going to have better numbers with wet tests your dry tests are fine doubt a wet is even needed deffinitly good numbers for a unknown miles engine

These are good numbers??? . Seems I haven't spent enough time in Chevy land for this much variance (greater than 10%, let alone greater than 5% variation cylinder to cylinder) to be considered 'good' numbers. I'm wondering if I should just drop new plugs in it and Seafoam the hell out of it. I have a feeling it probably has a ton of carbon in it. Wish I could see inside those cylinders. Wonder if I can borrow my friends borescope..... :/