North American Turbocoupe Organization

thinking of bad head gasket?
bprewit Offline
Junior Member
I have a '88 coupe and it has been in the hands of my wife for the last year as a daily driver. Runs great just crusin but if the boost gets over 10lbs then it starts to jump and buck pretty bad until the boost pressure drops back a bit. Intercooler hoses were replaced, lots of items replaced actually! Vacuum gauge needle bounces really bad at idle which tells me vacuum leak, burnt valves, or head gasket right? 160K miles on the car and fixing to replace the clutch so ordered head gasket set figuring pulling the head for a valve job isnt a bad idea. Will probably throw rod and main bearings in as well for prevenative maint down the road. Any ideas on the stall/buck/jumping problem? Sound like head gasket problem? Oh no oil in radiator fluid and no water in oil, no steamy glycol smelling exhaust either. Also no codes on this car, live in a very deserted place, no way to pull codes at this time. Appreciate any suggestions or ideas and sorry for the long post.

CougarXR7 Offline
When I blew the head gasket between #1 and #2 cylinders, my car did the same thing only it was all the time. It barely ran at idle, and I had to keep on the throttle to make the car move. It was because of the "cross compression" between those cylinders.
I'm not sure if you're having the same problem.
Perhaps a compression test would tell you more about the condition of the head gasket.
1986 Mercury Cougar XR-7
5-Speed - Leather - Dual Manual Seats - Vent Windows - Smokin' T3

gregpro50 Offline
Quote: Will probably throw rod and main bearings in as well for prevenative maint down the road.
Dont do that unless you will be putting in a re-surfaced crank too.
'79 Indy pace car T-top
'81 Cobra
'81 Cobra T-top
'82 GT T-top
'85 ascMcLaren coupe
'86 SVO
'98 Lincoln Mark VIII LSC

Sluggo Offline
Posting Freak
My opinion would be to get a valve job, ranger roller cam and followers, new HLA's/lifters, and MOTORCRAFT tune up.

The jumpy vacumm leads to the valves and cam. The boost problem sound like ignition parts or a vacumm leak. As for the pulling the oil pan, I wouldn't do it. I would put a rear seal in while doing the clutch though. Nothing you mentioned points to the head gasket in my opinion, but you will be replacing it when the head comes off anyway.

Welcome to the board. Other opinions to follow.
88 TC / T5,4.56,Log,SC60,NPR,2277,MegaSquirt

Pete D Offline
Welcome to the board. I agree with Doug, nothing you have said nails it as a head gasket when in the boost. That could be a bad plug wire or other ignition component, perhaps a deficient injector. What brand of wires and plugs you using?

Tell us more about exactly how the vacuum gauge is behaving at warm idle. That could tell more specifics on what is going on.

Since you have an 88 you can pull the codes "in the car" See

Be sure to replace the valve springs when you do the head.
Pete Dunham


trashline Offline
Posting Freak
the vacuum could be anything from a bad leak to the cam. Since it is kinda bouncy Id guess cam as long as it is in a pattern. how much vacuum are you pulling? should be up around 20 " Hg. Pressurizing the intake system is a good idea to help find bad leaks fast. This way you can hear them and fix the problem.

I wouldnt even take the head off. Pull the valve cover and inspect your cam lobes for real serious wear. As long as you kept up on oil changes and good maintiance i think you will be fine.

I do agree on the rear main seal for good measure there onyl around 20 dollars.

I would also take a look at your fuel system. Use the diagnostics in the tech section.

06 Cobalt SS
66 mustang 289 C4 handfully modded

Stingers IC install and tbird photos

charles88tc Offline
Senior Member
Get a compression test done that should answer your h/g question.
88 tc 5sp, Gillis, K&N on vam, Redneck cat back exaust (nothing from the cat back) 220,000 mile short block. Rebuilt 86 head and cam.

bprewit Offline
Junior Member
Sorry so long to reply, work is busy and thanks for the replies!
I replaced the plugs and wires not long ago but this problem has been with the car since I bought it, and used motorcraft wires, NGK plugs, and it has a new cap/rotor. I thought the boost problem was the intercooler hoses or intake hose but after replacing them it still has the same old problem, also replaced the fuel pump and regulator. The jumpy vacuum bounces between 15 and 20"hg when warm and the gauge has a constant flutter. I went through and replaced most vacuum lines early on and checked for vacuum leaks. I thought maybe it was the head gasket but from your replies im leaning more toward a burnt or sticking valve though had not thought about a flat cam lobe or other cam problem. I will tear into it this weekend as have to replace the clutch, rack and pinion, all heater hoses as they are starting to spring leaks one by one. Also will mention that the cam belt was replaced not long ago and ignition timing has been set and checked. I found a ranger roller cam, rockers, and lifters on Ebay for $100 buy it now price and nabbed it so sent payment off today. I will start with checking the cam and if nothing obvious shows will pull the head and have a valve job done and install new springs. Thanks for the help!

bprewit Offline
Junior Member
sorry double post

bprewit Offline
Junior Member
finally got around to pulling the head off tonight. 8 of the head bolts were no problem to get off, very tight but nothing unexpected for head bolts. 2 of the suckers made me scream and cuss and broke 2 good ratchets. When the finally came out I found the problem...lots of rust. Seems the head gasket was leaking between the number 2 cylinder and one of the coolant passages also seeping around the head bolts I am guessing. Head has a small "warranty void if removed" washer glued to the freeze plug so now I know the head was replaced at one point. Valves and piston crowns look excellent with very little carbon buildup. Am going to install ranger roller cam and bolt this thing back up. Wish me luck

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