3blackbirds

Hello Guys,

I need some help with my 964. I have a backfiring/misfiring issue. Sounds like the intake filter box is going to pop off. Even trying to open the throttle yields no difference. My distributor belt is intact and my DME relay is fine. I replaced the DME with the 993 unit 3 years ago. Could it be an ISV or vacuum issue? I have done some searching but it that points me to DME and dist belts...

I recently did a clutch and tune up myself. I replaced the flywheel, pressure plate, clutch disk, etc. I put in new plugs and wires, dist caps and rotors. etc. It has been running great for the past two weeks (about 200 miles).

I ran some errands today with it. Then all of a sudden, this out of the blue.

Here's a short video of it.
http://www.youtube.com/watch?v=kWwlsjyeoTw

Thanks in advance!
Jamie

darth

Hi Jaime

Sounds like a misfire. What kind of spark plug wires did you install? How did the engine run prior to the tuneup? I'd double check all the work done relating to the wires, rotors, etc. and anything in the general viscinity of the installed components such as vacume lines, sensors near the flywheel etc..

Bill

ian89C4

+1 for checking all of the connections and that it is a misfire.

Could it possibly be a coil?

3blackbirds

The engine ran well before the tune up. It was one of those "while it's out" projects I wanted to do since the car just turned 65k miles. The clutch and fly needed to be replaced, so why not tune it as well. Anyway, I used the bosch plugs from pelican PN:999-170-183-90-M14 and I rebuilt the wire sets using new beru wires from a fellow rennlister with the original ends. Old plugs looked normal and old wires were in decent shape.

I rechecked a lot of the connections on top of the motor around the throttle and pulled the dist caps and rotors. I haven't checked the flywheel speed sensor or the plugs on the bottom of the car which will be tomorrows project. Would coils just crap out like this?

Indycam

Does it back fire out the intake or out the exhaust ?
I can't tell from the video .

Indycam

Will it run on one spark ?
Will it run on just the other spark ?

3blackbirds

Out of the intake. Small puffs of black smoke come out when it misfires, which I know is fuel. Nothing else comes from the exhaust.

I haven't pulled plugs and ran it yet.

bwoodry

coils....

or incorrect plug wire to spark plug

3blackbirds

I ran the plug wires one at a time as I replaced. Ran perfectly for a good number of miles.

I'll troubleshoot the coils tomorrow as well.

Indycam

How would coils make backfire in the intake ?
I can see how crossed wires might , but he said the wires went on and the car ran OK for two weeks .

I'm thinking an intake valve is leaking fire into the intake system .
I would do a quick test of removing the two sparks to one cylinder at a time to try and find what cylinder is sending fire into the intake system and then check the valve clearance for that cylinder . Or I might try a quick/dirty "leak down" to try and find a leaky intake valve .

Another thing might be cross talk between wire causing a spark to show up at a time when an intake valve is off its seat .

Indycam

I can't imagine any way a bad coil could cause an intake system backfire ,
unless its an exhaust system backfire going past an open exhaust and intake valve and then into the intake system . The duration of the overlap is so short I guess that's only theoretically possible .

Broken exhaust valve system ?
Cylinder fires off half *** and then exhausts via the intake valve ?

Plugged up exhaust system / cat ?

springer3

+1 on the possible bad intake valve. When were the valves adjusted last?

Always run a compression or leak-down test if the easy troubleshooting items do not identify the problem.

Indycam

Yeah , if the intake valve lash is gone and the intake valve is just hovering just a millionth off the seat ...

3blackbirds

The valves were adjusted late '08 around 5k miles ago by a good shop. Maybe he didn't tighten an intake valve correctly or it let loose.

Indycam

Try to not run your car at all with an intake backfire .