'88 L98 compression check question.
Thread Starter
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
'88 L98 compression check question.
Before I do the siamese intake base mod I'm going to run a compression check to try and get a lead on cause of the "puff" of smoke at around the 1,000' mark.
I've read the instructions on how to do it but have no info on what pressure to expect from this engine. Since a "low" reading was mentioned I thought I should know what is "normal". I can only compute 14.7psi * 9.5 = 140psi.
Does this sound about right?
Oh, and since these are Al heads, should I realy be pulling the plugs from the hot engine so I can run the test with the engine at "normal operating temp>"?
[Modified by 65Z01, 3:57 PM 4/16/2002]
I've read the instructions on how to do it but have no info on what pressure to expect from this engine. Since a "low" reading was mentioned I thought I should know what is "normal". I can only compute 14.7psi * 9.5 = 140psi.
Does this sound about right?
Oh, and since these are Al heads, should I realy be pulling the plugs from the hot engine so I can run the test with the engine at "normal operating temp>"?
[Modified by 65Z01, 3:57 PM 4/16/2002]
Safety Car
Joined: Jun 2000
Posts: 4,870
Likes: 25
From: Long Island, NY
Re: '88 L98 compression check question. (65Z01)
Jim
I have done a Comp test on my other cars. I look at all the numbers from the 8 cylinders and compare them. If anyone of them is really low compared to the others then that cylinders could have a problem.
I think anywhere from 140 - 170 psi is ok.
Vic
I have done a Comp test on my other cars. I look at all the numbers from the 8 cylinders and compare them. If anyone of them is really low compared to the others then that cylinders could have a problem.
I think anywhere from 140 - 170 psi is ok.
Vic
Le Mans Master
Joined: Apr 2000
Posts: 5,589
Likes: 0
From: DrunkDefender
CI 1-2-3-4-5-6-7-8 Veteran
CI-IV AutoX Champ
CI-IV Burnout Champ
St. Jude Donor '07-'10
Re: '88 L98 compression check question. (65Z01)
When I put my plugs in I use a bit of antiseize. I can remove and re-install my plugs with the heads warm no problems. I did a cold and hot check and there wasnt alot of variance between the two. Mine when warm was 180psi +/- 5 psi all around. Keep in mind my mods plus I have a thinner head gasket 0.029 compressed thickness. I would think yours might be close to that but as long as all 8 cylinders are within 5% of each other I'd say your allright whatever the psi.
Thread Starter
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: '88 L98 compression check question. (Vic'89)
Vic,
Thanks much, the range numbers is what I was looking for.:cheers:
Now I can go see what ails "puff" the magic dragon.:cry
Thanks much, the range numbers is what I was looking for.:cheers:
Now I can go see what ails "puff" the magic dragon.:cry
Thread Starter
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: '88 L98 compression check question. (red90sixspeed)
red90sixspeed, thanks for that bit. Though I have anitseize on the plugs, I'd rather do the job with it cold since no real difference.
Thread Starter
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: '88 L98 compression check question. (65Z01)
Compression check didn't reveal anything unusual, after 4 cranks at each cylinder I got:
L.Bank=169 +/-7psi (1-7=168,175,170,162)
R.Bank=166 +/-4psi (2-8=165,162,165,170)
With these test numbers and after diagnosing the bad MAF today I'm beginning to suspect the "pufff of smoke" near the traps might have been due to the MAF causing a realy rich condition.
I'm very tempted to install a new MAF, clean up the spark plugs and take it to the strip to test that possibility (the oil leak was traced at least in part to the rear of the intake base gasket).
L.Bank=169 +/-7psi (1-7=168,175,170,162)
R.Bank=166 +/-4psi (2-8=165,162,165,170)
With these test numbers and after diagnosing the bad MAF today I'm beginning to suspect the "pufff of smoke" near the traps might have been due to the MAF causing a realy rich condition.
I'm very tempted to install a new MAF, clean up the spark plugs and take it to the strip to test that possibility (the oil leak was traced at least in part to the rear of the intake base gasket).
Thread Starter
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: '88 L98 compression check question. (Curtis629)
Diagnosing the bad MAF was a pita! The scanner wasn't much help and unplugging the MAF didn't change the symptom. Finally, after I eliminated other possibilities I swapped MAFs between the Vette and the '86 IROC. The Vette then started right up and idled smoother than ever; the IROC soon went into the surging idle mode. I now have a Wells MAF sitting on my desk, waiting for my injectors to come back from Rich.
A compression check is pretty easy to run. I pulled the panel from inside the right wheel well for better access to #2 & #4 plugs. Then I pulled all plugs, disconnected all injectors (the intake was comming off very soon after), and pulled the three connections to the dist cap. The compression tester (Sears) has a spark plug hole adapter that makes life easier. I screwed that into a hole, then screwed in the flex hose, clipped on the gauge body and cranked the engine. I watch the needle, taking note of the initial reading, the rate of increase and then recording the final value. Good instructions came with the unit.
A compression check is pretty easy to run. I pulled the panel from inside the right wheel well for better access to #2 & #4 plugs. Then I pulled all plugs, disconnected all injectors (the intake was comming off very soon after), and pulled the three connections to the dist cap. The compression tester (Sears) has a spark plug hole adapter that makes life easier. I screwed that into a hole, then screwed in the flex hose, clipped on the gauge body and cranked the engine. I watch the needle, taking note of the initial reading, the rate of increase and then recording the final value. Good instructions came with the unit.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
Thread Starter
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: '88 L98 compression check question. (Curtis629)
I didn't want fuel washing the cylinder walls so I did.
On an early L98 you could pull INJ 1 FUSE & INJ 2 FUSE on the main fuse block and CINJ/CLU FUSE on the aux fuse block, but I'd rather just unplug em.
On an early L98 you could pull INJ 1 FUSE & INJ 2 FUSE on the main fuse block and CINJ/CLU FUSE on the aux fuse block, but I'd rather just unplug em.
7th Gear
Joined: Jan 2023
Posts: 7
Likes: 0
From: Florida
Mines a 86 l98 and mine runs at 180psi with 95k for miles, just put new Bosch 3's and plugs n wires and she's running strong again I put a 3:83 rearend in it and a hyper chip I've had mine spin em doin 45mph, I see this is an older post but wanted to share that, imagine you got it figured out by now, take care
