TheStock

Sorry if this has been gone over but I can't find anything.

1987 951 with a few extra mods, nothing dramatic.

I changed the spark plugs yesterday and let the car run. While it was running I felt each spark plug wire just to make sure none were grounding out and noticed a pulsing in one of them just as though it was grounding out. But the more I felt around I realized it wasn't coming from the wire, but actually from the fuel line it was sitting on right before the fuel rail. My fuel pressure gauge cycles between 35 and 38 psi at a fequency of maybe.... 10 cycles/second. Just guessing, it's fast enough that I have to read the needle as a blur. The pulsing in the line is about the same speed as one of the cylinders firing and speeds up proportionally when I increase the throttle.

Is this normal? Doesn't seem like it would be.

Any ideas or can someone point me in the right direction if this has already been discussed?

Thanks guys!

931guru

All the injectors on an 8 valve car fire at the same time, dropping the pressure down for a tenth of a second, then it repressurizes, resulting in a pulsing effect. Totally normal.

Different on 16 valve engines which have sequential injection.

TheStock

Really? Interesting... I would've thought they had the sequential injection as well.

Well thank you for the response. Good to know something else didn't fail.