Bone stock LB9 T5 car, 188,000 on the clock. Bought the car as is. Seemed to have a miss at idle, no smoke on startup. Made some 1/8 mile passes, power is not there.

Pull plug wires one at a time- #8 was dead.

Pull #8 plug- covered with brown crap- cleaned, gapped plug.

Did compression test while plug was out- 125 psi cold and I forgot to hold the throttle pedal down.

Replace the plug, start engine- still no fire.

Removed plug again- Put the plug on the wire, crank engine, good spark- plugs and wires were just replaced prior to my ownership.

No coolant in the oil, no coolant visibly lost, no white smoke on startup that would indicate the intake gasket seeping coolant into the hole, "putting out the fire"

Plug gets slightly oily, but with no fire in the hole, that could be slight blowby.

Check injector harness with a test light, all good.

Pull connector off the injector while the engine is running- can hear a "slight" difference in sound.

Removed injectors, marked #8 separately- send to Cruizin performance.

Got a call today- bad news! #8 is GOOD.....all were gummy, and needed cleaning, but were only 3% off according to them.

OK, so what do I do now? I was positive there was a problem with #8!

I will also note that I checked fuel pressure, key on engine off, it goes to 42psi- but it does leak down when the engine is shut off, slowly. Has 38psi running at idle.

Any ideas in thirdgen land? I am going out now to drain some coolant and pull the lower intake, as is is leaking oil at the front and back anyway. I will look really closely for signs of coolant intrusion.

 

Pull the valve covers off and spin the motor and make sure all the rockers are doing their thing, I had a similiar condition with my '82,
one lobe on the cam was worn round, and a pushrod had broken through a rocker.

 

i had a similar problem with a tbi car i had it had a constant miss. i pulled the valve covers to find a broken pushrod.

 

The only thing I can think of would be a flat exhaust lobe- if it was an intake, I'd have no compression on that hole- if it was a broken pushrod or rocker, I'd have noise, and it's dead quiet.

Roller cams are not known to go flat though.

 

Well I pulled the lower intake, found the intake gasket between #6 and 8 to be torn- rolled the engine over by hand, and though I did not put a dial indicator on it the #8 lifters are traveling the same amount as the others, so no flat cam suspected.

I think the intake gasket was causing an internal vaccum leak if that makes sense, and the fuel charge not going into the cylinder directly.

I'll know more once it's back together- doing a gasket match on the lower intake and siamesing the runners while it's apart.

 

Well, the intake gasket was it. I went ahead and siamesed the runners, took some flash and the "wall" behind the throttle body out of the plenum, and gasket matched the base while it was apart.

Car runs 100% better now. Had a MAF sensor go bad, swapped with a spare I had.

NOW- I tried setting the base timing (est disconnected of course) to 10*, spec is 6*, to see how it ran. BAAAAD knock retard, over 20* on hard acceleration seen with auto-X ray.
Dropped back to 6* spec- less, but still too much.
Now at 0*. Still some, 6-8*.

I know this high mile (188,000) motor has some carbon buildup in the heads and chambers. Would running some seafoam or GM top engine cleaner through it (sucked in via a vacuum line) help?

Also- the pickup coil and pole piece in the distributor are really corroded, I cleaned them via a wire brush as well as I could, but they are still nasty. Last time I had the car out and shut it off hot, it would not restart right away, started a couple hours later no problem.

Could the carbon and the distributor be causing this problem?

I gtech timed the car at a 15.72@93.7 mph with it hot.

Keep in mind- stock LB9, right to the cat converter and manifolds, fresh injectors, fresh cap/rotor/wires, 5 speed and 3.08 gears.