Lost compression in cylinder 3

[whoudi]

Hey guys, good afternoon. Newer member here and 87 Grand National owner since April of 2015. Bought the car with just over 30,000 miles. It was a near stock GN with the exception of an exhaust and an older Hypertech chip. It ran like a raped ape at WOT on the old chip but at idle and warmer temps (above 80*) it would stutter at lower RPMs especially slowing down to a stop. Fast forward to this spring, I upgrade the chip to a close to stock, mild TurboTweak chip. It really helped out the drivability throughout the rev range except now at WOT it would stutter which I chalked up to the 16-17 lb boost limiter. Odometer currently reads 36,340.

Now we get to the issue. One October drive while on a WOT rip I got the stutter up top followed by an immediate loss of boost and rough running engine. I limped the car home and got it into my local Buick dealership. I know, I know what the hell does a modern Buick dealership know about these cars. Long story short I know one of the managers who has had a couple of these and they have a tech who has 30 years there and has worked on these cars. Plug 3 was fouled out, new plugs and wires did not help. Compression test showed 5 cylinders at 90psi. Cylinder 3 had 0. So we buttoned it up and this is where I'm at.

I am by no means a mechanically inclined person who can diagnose this any further myself. I asked if they bore-scoped the cylinder which they did not as they do not have a scope. I thought that would be the next logical route without pulling the head off.

Just wondering if any of you more veteran GN guys had any thought as to what may have happened or what to look for. I live near Detroit at the Michigan/Ohio border and have a few places in mind one being Full Throttle Speed in Fraser, MI. If anyone can point me in the direction of a recommended engine specialist in the midwest I would appreciate it. Thanks for the help guys, I'm hoping to get her back up and running strong this spring! Here is a pic just for the hell of it.

 

[TurboBuRick]

More than likely you blew the head gasket into the valley.

There are a few places in Michigan area. Full throttle being one. Aggressive auto is another. Also White racing.

Other option is to find a fellow tb guy willing to help on the side.

Rick

 

[750H.P.V6]

I agree with Rick. I would advise you to replace both head gaskets while you're at it. The thought being that if one blew out more than likely the other gasket has been taking a beating too.

Neal

 

[84BuickGNYorkPA]

Also agree with Rick and Neal.
Fix your head gaskets and upgrade your fuel pump and regulator. You may have been going lean in the boost because the stock fuel pumps are weak brand new. Also think about backing that boost back a hair, do you have a scanmaster on this to monitor the engine?

Chuck

 

[Pronto]

You've got a long list of items not mentioned that would lead to gasket failure. As mentioned, Scanmaster, hot wire, fuel pump, filter should have been on there before even thinking of going wot. So you've got a head gasket job at the least ahead of you. Take it to a proven TB shop that will fix the car right and advise you to the future mods if you want to go faster.

 

[whoudi]

Also agree with Rick and Neal.
Fix your head gaskets and upgrade your fuel pump and regulator. You may have been going lean in the boost because the stock fuel pumps are weak brand new. Also think about backing that boost back a hair, do you have a scanmaster on this to monitor the engine?

Yes I do have a scanmaster in the car.

You've got a long list of items not mentioned that would lead to gasket failure. As mentioned, Scanmaster, hot wire, fuel pump, filter should have been on there before even thinking of going wot. So you've got a head gasket job at the least ahead of you. Take it to a proven TB shop that will fix the car right and advise you to the future mods if you want to go faster.

With some input and help from members on this site I know where to take the car next and what to look for in upgrades. For the time being I would like to keep the car as close to stock as possible. Thanks for the info.

 

[Pronto]

Regardless, you need the hotwire and pump upgrades. Low miles or not you are dealing with a marginal pump and wiring.

 

[Chuck Leeper]

90 psi?

 

[earlbrown]

AT 90PSI did you have the throttle open while doing the test? If so, I think rings are in your near future.

Also: what's a ''boost limiter', stock valve springs?

 

[1KWIKSIX]

I agree with both Chuck and Earl , I'd also be very concerned about such a low reading, to get the most accurate results a compression test should be performed on a warm engine with throttle blade wide open. "Just Sayin"