1974 911, Pinging badly, 4-5000rpm...

Hi everyone…

I’ve got a bit of a problem. My daily driver is a 1974 911 2.7. It runs fine, albeit with the occasional hiccup – nothing serious – but I’ve got a new problem that I would like some advice on.

It pings at around 4000-5000 rpm when I romp on it. First thing I thought was timing – checked and OK. I replaced the distributor last year with a brand new unit – the mechanical advance in the old one grenaded – and the points ignition with a pertonics unit. New plugs, cap, rotor and wires at the same time as well. So I think I can rule out the ignition system.

So I went through the archives on the list – found one that referred to pinging based on a lean mixture condition at a similar rpm. How the heck do you check for this? Now, it also happens that I replaced the fuel filter and accumulator last year as well…but I have a related problem that has been nagging me for some time and I wonder if it’s related to the pining problem. In the morning, I have to leave the ignition in the on position – let the fuel pump run for 30 seconds or so – before the car will successfully start. You can definitely hear the hum of the fuel pump and I suspect the check valve in the pump has failed. Question is – could low fuel pump pressure and/or low pump volume cause pinging?

Thanks for your advice!!

Mike

Mike,

Have your mechanic check the tension of the heads -- before you go fussing over possible fuel-related causes, first rule out pulled head studs.

Trust me!

I had that same problem with my 74 911, and changed my gasoline for a higher octane, and solved the problem, if I am not mistaken, I´m using 91 or 92 octane

I'm running "super" now. Checking the head studs is somthing that's been on my mind - perhaps now is the time. Thanks!

I had a loose head stud on the '77 that made a sound that could be confused with pinging.

It got louder very quickly. I looked at all the typical adjustments and everything was fine. I even suspected the muffler based on the sound.

I ended up taking it to my mechanic who diagnosed the stud. Lucky for me it wasn't pulled, just loosed.

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'86 Cab, '77 Targa, Family Truckster

If it sounds like glass marbles in a tin can, it's pinging.

I had the same problem--2nd and 3rd gear the car would ping like nuts when I got on it at 4-5k. Especially when warm.

Checked the timing, checked the studs. Added octane enhancer to already "premium" gas.

Final fix? Had my wrench run "Dr. Bob's Magic Decarbonizer" (or whatever) through the engine a few times. Cleaned all the crap out.

Now I can floor it up to 6k when it's 105 degrees out and the A/C's on. No pinging.

Remember--today's gas is absolute garbage.



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blue
'81 SC Targa

It’s defiantly pinging. Under full throttle between 4-5000 rpm. If I back off on the throttle the pinging goes away. Any suggestions on a specific brand of “de-carbonizer”?

What is your timing settings at these RPMS?

Even though you have the distributor replaced, rebuilt it sounds like it is going to full advance before it should.

Does yours have a vacuum advance or retard?

Just curious.

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Nick Hromyak
'85 Carrera 7 & 9 Fuchs
Havin' Fun in Sacramento

Timing at that RPM - I'll have to check that tonight - that's a really good question. It was a "new" unit. Vacume advance - yes.

Thanks!!

Mike

I had a 73.5 T 2.7 CIS. That thing pinged like there was no tomorrow. My dad and I rebuilt it, spent almost two years. FAST as heck THOUGH! I found the cams were too advanced. I never knew about ignition timing, other than static, until I started to work on my SBC.

Do you know if your vacuum advance is plugged into the correct port? In other words, should it be ported vacuum or always vaccum?

In either case what should your total vacuum advance be? Perhaps you have the right year distributor but the wrong model?
Just spewing my thoughts.

Of course none of this applies to my '85 (DME)!

Good luck.


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Nick Hromyak
'85 Carrera 7 & 9 Fuchs
Havin' Fun in Sacramento

Ok - I checked the timing tonight...

At 4000 RPM I'm about 3/16" away from the 30 degree mark.

Does this sound reasonable?

Thanks!

Mike