#2 cylinder misfiring on 74 2.0L

911buff · 911buff's Garage

The #2 cylinder on my '74 2.0 is misfiring. When the spark plug wire is attached, the engine back fires. When the wire is removed, the back firing stops. The injector is squirting and there is spark at the plug. Adjusting the valves did not reveal any apparent issues with the valve train. I am not really sure where to go from here. If anyone has an idea, I would love to hear it.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Are the spark plugs connected to the correct distributor cap towers?

--DD

911buff · 911buff's Garage

Yes,
The other three bog the engine down equally when disconnected. I have had some puzzling maladies with my 914s in the past but this one really has me stumped. I don't want to pull the engine down right now. I am planning on rebuilding later on this year. But I am afraid that there is something going on at the valves themselves. I can think of nothing else that could be happening.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Compression test is next, I think. Also, compare the volumes injected by the different injectors. And check for vacuum leaks, especially at the injector. And exhaust leaks.

And triple-check that #1 and #2 plug wires are not swapped.

--DD

911buff · 911buff's Garage

I will give it a shot. Thanks!

911buff · 911buff's Garage

I am really confused now. The compression on 2 was approx 100psi...number 1 was only 75-ish. After taking it out for a brisk drive, #2 was better but still when I removed the wire, it did not affect the engine as much as the other three. From the compression test, it will need a rebuild sooner than I expected, so I may find the Culprit then.
For some history, I just purchased the car a month ago and am in the process of sorting it out. I knew there was a mechanical problem with the engine when I bought it but with the condition of the car and the price, I could not pass it up. It is my 6th 914...I just can't get enough. I guess I will have to Rebuild the motor to fix my problem. Thanks for the advice.

911buff · 911buff's Garage

I finally tracked down the reason for the misfire. It only took about three hours of frustration (I was at my shop at work and had left my manual at home...so I was depending on my memory and expereince) but I finally won! I thought that the distributor was off 180 degrees so I went about fixing it. After 2 1/2 hours of not being able to get the car to start, I finally figured out that I had it on # 3...not #1 TDC. So once I got the distributor and crank aligned, it started right up and ran like a proper 2.0! With the distributor out 180 (wires were attached so it was sending spark to the right cylinders), the fuel injection points were out of phase. Hence the terrible running at low RPM and improved performance at higher RPMs. My Dad always did tell me to check the simple/obvious first, that is usually what it is. Now it is a blast to drive!
I feel guilty about "stealing" the car, now. The previous owner had given up and advertised that there was serious mechanical woes with the engine, when in fact it was an extremely simple fix. There is still some work to do to really make it sweet but I couldn't ask for a nicer 40 year old car for the price!
Thanks for the advice.