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Dr. Bob, Wally, docmirror,

Thanks all for the information. Its a bit over my level of knowledge, but that's mostly b/c I haven't spent much time looking at the ignition system in these cars. I'll have to sit down, bring myself up to speed, and swing back around with any questions.

One quick one though: If you ground the wires on the block, I presume you want to keep well clear of anything that has the electrical charge flowing through it. Yes?

Much appreciated,
Dave

docmirror

Ya see, this is why I try to keep it simple. I've seen guys told to 'ground the coil wire' and so sure enough, there's the 'coil wire' hanging out of the dizzy cap faithfully 'grounded' to the engine. Sigh,,,,,,

Easy compression testing. Tools: Spark plug socket, various 3/8 extensions, ratchet. Warm engine.

A. Pull plug wire caps off each individual plug hole.
B. Using socket, ext as needed, and ratchet, remove spark plugs.
C. Put plugs back on loose ign wires, and lay plugs on the valve cover, so that the plug metal base is touching a metal engine surface(ground).
D. Screw comp gauge into head in place of a plug.
E. Remove fuse for fuel pump.
F. Hold gas pedal to floor, and crank engine for 6-9 seconds. Record reading.
G. Lather, rinse, repeat step F for each cylinder.
H. Replace plugs in heads using socket, snap wires back in place.
I. Replace fuse.

Jeff777

Hi All

My compression tester says to use a remote switch, something about triggering fuel injectors using ignition? So, I would like to try using a remote start sw from the start relay and out of car battery ( normal battery out for storage).
Can anyone confirm which post on my 14 pin is the correct connection? And the other lead to positive external battery? My car is 73 911.

Thanks

Mrmerlin

I work on 928s but I will fathom a guess it will be that fat yellow wire that runs to the starter solenoid,
use a multi meter to find power.

NOTE to make sure I told you the correct info ,
find the yellow wire at the starter and see if it has continuity to the 14 pin connector.

UKKid35

I'm due to do another compression test one day soon

A couple of years ago the test resulted in one cylinder being 50% of the others, which is considered damning

However the car still maxed out at 164mph gps with roof open, lights up, and no belly pan (in fact it was still accelerating but I ran out of road/*****/whatever)

So the engine is probably doing OK, even at approx 250k miles

FredR

Compression test results tell you something but they are not necessarily a harbinger of doom. A healthy S4 should generate cranking compression pressures of around 185 psig and the time to worry as if and when several cylinders have low results. If you were genuinely developing 90 psig on one cylinder then the motor should feel pretty sick. It is very easy when testing to do something silly like forget to open the throttle fully. Similarly a small sliver of carbon can wreck the reading.

If the motor is running well, oil consumption is normal, no chronic smoking etc chances are it was a glitsch and an Italian tune up will take care of it.

928FIXER

NO. Spark plugs making a spark can be a recipe for disaster.

Jeff777

So, I've studied the wiring diagram and hooked up a new remote starter switch from OTC to the pin 14 connecter, last pin, bottom. Start sw shows red light indicator hot as does voltmeter. Press the button and nothing. Tried the pin above but this wasn't a hot connection. Guess I can do it the old fashioned way from the cockpit but really liked the idea of spinning the motor with ignition sw off. Frustrating because I know I'm doing something wrong but can't figure out what. Suggestions?