Douglas Sorrells

I was driving my 87 951 this weekend and everything seemed fine. I briefly hit the gas at about 60 mph, downshifted to 3rd and took the car upto about 80, all seemed fine. Once I slowed back down to about 60 mph I noticed the car was running funny. It seemed like I may have fouled a plug and it was only running on 3 cylinders. I limped the car home and checked the plugs, all looked fine except the the plug in #4 cylinder, it was fouled. I replaced all the plugs with some new Bosch Supers and there was no change - Still not running on #4. I pulled that plug again and checked it, it was wet. The plug is sparking & getting fuel to that cylinder, but still not running on it. Plug wires, distributor, rotor & coil are all new. I've spent some time searching on this and didn't find much. Any ideas and thanks in advance! Doug

travisgreen

If the plug is wet then it's not firing.....check your plug wires, a good thing to remember when diagnosing a problem like this is not to let the fact that you may have recently replaced something keep you from checking the obvious first. Pull your car in a garage, turn the lights out while it's running and see if they are arcing anywhere.

Voith

Swap injector to another cylinder and try again. Than check injector connector and wire..

Douglas Sorrells

The reason I feel the #4 plug is firing is that when I disconnect the fuel pump relay and leave the plug laying on top of the engine and crank it, it is sparking.

eman930

Well the 3 basics, Spark, Fuel. Compression.... seems you have spark and fuel.... time for a compression test on cyl 4

audisport

This....

Douglas Sorrells

Thanks Fast 924S, Good suggestion, will try that this evening.

Douglas Sorrells

Well, just checked the compression in the #4 Cylinder, sure enough, zero compression. One of my Porshche buddies suggested I either burnt an exhaust valve or have a hole in that piston. Any other ideas before I start on pulling the head? Thanks. D (PS, there is no evidence of a blown head gasket or any oil in the cooling system)

carlege

possibly broken valve spring.

black944 turbo

As carlege said valve springs are not uncommon and do not require head removal, but will require cam box removal. I have seen this on several 944 s.

eman930

Perfect time for "upgrades"

Black51

And with Christmas coming around the corner...

Douglas Sorrells

Well, pulled the head this past weekend to see why number 4 cylinder had no compression. Valve springs were all fine, but valves for #4 cylinder are shown here & cylinders 1 & 4 looking like this.

This motor is looking done to me.

mahoney944

I would ask yourself how much you value this motor. Fix the valve cheaply run it until it dies. Start building up a new motor in the mean time for when it ****s the bed. Suprisingly even with the scoring you have the motor will probably run for many more miles as it has been up until now, whose to say how long the motor was running with the scoring and you didnt even know it.

audisport

Yup. Probably be just fine. And fix the tune that bunt the valve of course.