94Z28-MSTGKLR

iTrader: (20)

I will appoligize in advance for how long this will be but I want to put in as much detail as possible so I can get the best advice I can get from you guys.

So here is how it started: Driving down the road, got a bad misfire, started smoking really bad, and pooring oil out the exhaust. Got home and diagnosed it as a broken pushrod on the number 7 intake valve. All other pushrods were fine.

Pulled all the rockers and pushrods out.

Pulled the heads off and pulled out all the lifters.

Parts I purchased: New head gaskets, valve cover gaskets, ls2 lifter trays, and ARP head bolts.

Had a friend give me one good lifter and one good pushrod to replace the one lifter and the one pushrod.

I left all the parts sitting in a pan of fresh oil and it was covered to keep dirt and debris out.

While the car was down, I checked the valves and lapped them all. Valves looked good and lapping them put a nice clean face back on them.

Finally got all the lifters placed back in with the new trays, cleaned the block and heads, and put heads back on.

Torqued ARP bolts, 35-55-75 ft-lbs, then 25 ft-lbs on the smaller ones like recommended.

Put in all the pushrods and rockers.

Rolled each cylinder over until both valves were closed and torqued the rocker bolts to 22 ft-lbs like recommended.

Got the rest all put back together. Filled with fresh oil and new filter. Got new coolant mix in and no leaks anywhere. Reinstalled all the spark plugs that were originally in the motor except for the new on I purchased for the number 7 cylinder.

Fire it up and It has a horrible misfire. Setting a P0300.

I grabbed a can of carb cleaner and sprayed everywhere on the intake and all the vacuum lines to and from it and nothing made a difference. Double checked everything on the intake side and all looks good. I think I can safely rule out a vacuum issue.

Pulled all the plugs out. All seems okay except for the number 7 cylinder seems to have what appears to be a light film of oil on it along with having a lot of black residue on it. So I put all the plugs back in and placed the number 5 plug in the number 7 hole. Ran for a few minutes and removed. Now that plug appears the same as the new one I originally placed in that hole. When I scanned the car, it breifly set a p0307. I cleared it and it didn't come back though.

So I pulled all the plugs out. Pulled the valve covers off. I turned the motor over with the started to check to ensure the rockers and pushrods were traveling all in order. They seem to look okay however, only one pushrod is getting oil to the rocker. When I crank the motor, only cylinder 8's intake pushrod squirts oil out the top. All 15 of the other rockers are bone dry.

I need advice. I'm thinking I may need to do a leak down check on all the cylinders to ensure the head gaskets are good and that number 7 doesn't have anything broken. Or possibly all the lifters but the one have collapsed and went bad?

While the car was running, I had normal oil pressure and good coolant temperature. I drove the car to see if it would clear up. At low RPM the misfire would hit noticably hard. As you give it some gas, the miss seems to be masked over as it feels it comes and goes at that point but the car smokes a light blue under throttle.

Sorry for this being so long but I wanted to provide as much information as possible for you guys to help me out. Thanks for anything you guys got.

Chris,

vettenuts

iTrader: (4)

When you lapped the valves on the #7 where the broken pushrod was, how was the lap pattern? Nice and even? If it was then the next suspect would be the piston/rings. Did you happen to take any photos while you worked on the car? How was the piston in that hole, did it look OK?

If these are all OK, then I would not swap the plug, I would swap the wire and re-check. If that doesn't do it, listen to the injector to see if it is firing.

Start with the simple stuff first. Also, is the ground on the back of the head and block OK?

94Z28-MSTGKLR

iTrader: (20)

The lap pattern seemed to look just fine. I definantly didn't notice anything out of the ordinary when I did it in comparission to the others. It seemed smooth and even all the way around. I haven't performed a leak test yet. I'm currently looking into getting an air compressor and test kit along with a stethescope to continue my diagnosis with it. I have already swapped plugs and the plug wire to completely eliminate it. All the grounds are good and believe me I double checked those as well. I'm really starting to think that during the orginal damage a ring was damaged I just didn't notice it and there isn't enough visual evidence from what I can see to determine it as the cause. A leak down test should definantly tell the truth or stump me even more. When I had the heads off the car, the motor turned over very easily and nothing seemed out of the normal. There was no wear marks in the cylinders that would lead me to believe anything was wrong or broken. The bores were very smooth and the cross hatching was still very easily seen. I guess only time will tell. Thank you very much for the information and leading ideas to the cause.

RonSSNova

iTrader: (3)

I would do a simple compression test on #7. You said it was blowing oil smoke when you had the issue. For whatever reason, #7 seems to suffer the most piston failures.

Ron

94Z28-MSTGKLR

iTrader: (20)

What should I have looked for on the piston while I had it apart? It looked like all the others. Nothing stood out. Is it possible to be damaged and cause my issue but in a postion where you can't see it from simply having the heads pulled off?

RonSSNova

iTrader: (3)

Yes, the 2nd ring land can break, I remember seeing a photo here somewhere. Top of the piston looked fine.
I hope that's not your issue, but the smoke and the fouling plug are clues.

Ron

94Z28-MSTGKLR

iTrader: (20)

All the symptoms are there and I'm sure this is the issue. If it is, I guess the only other thing is deciding what to do with it.

RonSSNova

iTrader: (3)

Can you get the pan off the Camaro w/o pulling the engine? Sorry, I have a vette. Anyway, if you can, I'd just buy a piston and rod and replace them. Might find someone who has gone forged and has a spare lying around. Semi cheezy, but it would work.
Or is the engine too hidden under the cowl back where 7 is?

Ron

94Z28-MSTGKLR

iTrader: (20)

Ah, if the ring is broken I'm sure I'll completely rebuild the entire thing or just sell it. I'd probably have it resleeved and put a stroker crank in it. I just want to properly diagnose the issue before I go off pulling the motor for something simple I'm just not thinking of or overlooking. Would like to enjoy her this summer though but I don't think it's going to happen.

7beast

iTrader: (30)

let us know what the outcome is bud

vettenuts

iTrader: (4)

As an aside, there is someone on Corvetteforum experiencing the same issue. He had low/no compression on #7 and is in the process of pulling the piston. You may want to follow and see what he finds as he is close to having it apart. Link

94Z28-MSTGKLR

iTrader: (20)

^ Thank you for the link. It seems we have the same issue. I'll keep tabs on his as well as keep my updated.

94Z28-MSTGKLR

iTrader: (20)

Okay guys. I was able to get a compression test completed and found some rather interesting results. Here they are, keeping in mind I was only able to use a 100psi test on the cylinders.

Cylinder 1: 85/100
Cylinder 2: 85/100
Cylinder 3: 90/100
Cylinder 4: 90/100
Cylinder 5: 90/100
Cylinder 6: 85/100
Cylinder 7: 88/100
Cylinder 8: 40/100

Now keeping in mind that Cylinder 7 was my original problem cylinder I must say that I was quiet suprised and completely caught off guard. Now, for the intesting part. When I plugged in the tester to number 8, I instantly heard the air rushing out of the exhaust under the car.

So I took a step back and rethought through the process I took to ensure top dead center. Pulled out the tool and re center the piston on the compression stroke once again to ensure I was doint it right.

Plugged in the tester and yet again, right out the exhaust.

So while I was sitting there looking at it wondering what the issue possibilites could be, I noticed that the rocker looked like it was slightly opening the valve. Then it hit me! This was the rocker that was squirting oil over the fender.

So while it was top dead center on the compression stroke and with the gauge hooked up I grabbed a socket and ratchet and broke loose the rocker arm bolt. As soon as I got it backed out a few threads, the noise and bleed off through the exhaust stopped.

So I stopped the test, rolled the motor over through several cycles of that cylinder and brought it back up to top dead center on the compression stroke, re-torqued that rocker and plugged the tester back in.

Same result as the first time, bleed off through the exhaust valve. So once again, I backed off the rocker bolt and the bleed off quit.

So, whats my issue? Bad lifter? I'm thinking I may pull it back apart and put in some LS7 lifters, and TSP chromoly 7.400 pushrods along with reinstalling my new LS2 trays I just installed. What do you guys think? This possibly my issue? I first thought maybe a bent valve but once I loosen the rocker, the bleed off stops which leads me to believe it's not bent. Thanks again for all the help.

Chris,

LS1GM

Do a cranking compression check

94Z28-MSTGKLR

iTrader: (20)

What is that going to tell me?

gagliano7

Make sure you check proper spark and fuel on #7. Sounds like you are not getting spark on that cylinder since spark plug was black.

joecar

He found a problem with #8 exhaust valve not closing due to lifter.

garygnu

consider a valve job .

94Z28-MSTGKLR

iTrader: (20)

I would if these weren't 853 heads. I just want the car up and running for the very, very short summer up here in WA. This winter it will get a complete rebuild. As long as everything looks good with it I'll just get it back together. The valve wasn't open enough to make contact with the piston or at least I don't think it did. Never heard anything and defiantly didn't have issues turning it by hand.

LS1MCSS

iTrader: (18)

In an earlier post you said you changed one lifter and pushrod. Apparently that lifter is made different and will require a shorter pushrod, if you intend to keep using it. I would call TSP and get a complete set of lifters and good pushrods. Problem solved.