No compression!! after intake gasket change

"Vernon1252" wrote

Don't do anything until you keep cranking it over. It will run like shit for a few minutes, but it will straighten itself out. This is assuming that you did get the pushrods back in correctly, but you did mention that you kept them in order.

This is very normal for these engines. Almost every one that I do, either appears to have no compression on the initial crank, or just runs really bad for a few minutes. I suspect that the lifters come up to the top of their travel, and because of the constant coolant contamination in these motors, the lifters are slow to return to their 'zero lash' position.

If you didn't change the oil after you completed the repair....do it now. And then just keep cranking.

Ian

ok.. Ian.. & thanks for your fast relay..i ;am checking the pushrods out right now to double check they r right..& yes i did change the oil & filter after the intake change.. , so i should just keep cranking it until the lifters pump back up if the push rods r in right?...thanks alot for your help!

"Vernon1252" wrote

Sounds like you've done everything right. The lifters actually will be bleeding 'down', but you have the right idea. Once it's running ok, just drop a line to let us know how it worked out.

Ian

thanks for your help Ian.. you were right on the money..after a few extended crank sessions.. it roared to life..& it still ran like rough for a few minetes then it smoothed right out.. thanks again for your help

"Vernon1252" wrote

Good stuff!! You don't know how may tech's I've seen tear back into those engines believing that they have done something wrong. It scared the bejesus out of me when I first encountered it, but now it's common place. One little thing that I do now....I will leave the injectors unplugged (you don't want them squirting away while you crank the engine) and then just crank the engine over for about

20-30 seconds. Then let the engine sit for a couple of minutes, connect the injector harness back up and she usually fires up and runs quite well.

Ian

This is very good info to have Ian. I'm curious, on the 3.4 while the intake is off can you see the lifters? If so would dumping oil over them just B4 dropping the manifold into place possibly help? Kinda like soaking new lifters B4 assembling an engine. GW

shiden_kai wrote:

I am glad Vernon got the beast settled down! That's great! This might explain why my "Mr Goodwrench" said my Montana ran like crap after the gasket change and insisted on replacing the O2 sensor. I refused saying that the O2 sensor was fine up until the time it rolled into the service bay. To make a long story short, they said they replaced it....free.

I'm glad we have techs like you on this board Ian! Thanks.

"Geoff Welsh" wrote

You can see the lifters when the intake is off. No, I don't believe that just dumping oil over them would do anything. I've never soaked new lifters before installing them, other then applying whatever pre-lube was required on the base of the lifter. Any engine that I do major work on gets cranked over without any fuel supply until I have good oil pressure. I've found that this works fine.

Ian

Normally what pre-lube (name/make) are used when you replace the lifter?

"Sam Kaan" wrote

I've always used a GM product called EOS (Engine oil supplement). There were some years in the 80's and 90's when GM put out a special pre-lube for non-roller lifters, but I couldn't tell you what the part number is now. It was a dark blue/green color and came along after GM had so many problems with small block camshafts in the 80's. Lifter and cam problems are almost non-existent now that the vast majority of GM engines have gone to roller lifters/rocker arms.

Ian

Ian... have you considered that maybe the rough running is caused by a vacuum leak at one of the intake ports? After the engine warms up enough, the manifold gasket finally seats into position. I did my 4.3 V6 lower gasket and after starting and running like crap for about 20 seconds the check engine light came on. I immediately shut it off fearing that I had installed the distributor incorrectly and that it might case engine damage I had a scanner at the time but I was too lazy to hook it up and read the code. I just assumed that I had installed the distributor incorrectly and it was causing the error.

The next morning I took out the distributor and painstakingly reinstalled it at TDC. it took me about and hour to get it lined up perfectly. Surely this would correct the check engine light. I started it up and sure enough it ran like shit and the light came on again after about 20 seconds. After several explitives I pulled out the scanner and it was showing a P303 ( misfire in No. 3 cylinder). I cranked it over and let it run for about 4 or 5 minutes until the idle finally smoothed out. The misfire counter on no. 3 I think was up to about 900 misfires before I cleared it.

"Rob" wrote

Rob, I'm not sure what the problem was with your gasket installation. Probably nothing. But, no....I don't think that your vacuum scenario is what causes the problem. If an intake gasket were to "seat" into position only after the engine warmed up....that would be a serious problem. I know of no gasket that by design needs to "seat" into position after an engine is warmed up. This would make no sense as engines have to operate in all sorts of different temperature conditions. A gasket either seals, or it doesn't.

I'm sure that the problem stems from the lifters taking a bit of time to bleed down to their 'zero' lash positions. The second generation of GM 60 degree v-6's didn't exhibit this problem as badly, but due to the gasket design on those engines, you only had to remove the (I think) exhaust valve push rods. As a result, you only had half of the lifters that could "pump up" as opposed to the 3rd gen 60 degree v-6 which (due to the intake gasket design) require that you remove all of the pushrods.

Ian