Pinging at High RPM when Hot.

[oneblueyedog]

I just can't seem to remedy it. I've tried:

Reduced timing -2° from 5btdc
richened mixture (nearly stalls car with ac on)
lift plate tuning via Souk posts.
New WUR three years ago with a superceded PN.
All vacuum hoses replaced.
Oil return spring update.
O rings for the F injectors (Not the runner O rings)
Distributor cleaning and maintenance.

This car has always run hot during the summer. Temperatures up to 3/4 up scale with AC on. This is in +90° ambient temps. Never hit the Red band.

A shop couldn't duplicate my troubles.

It has had the same Pinging phenomenon before rebuild and after.

What seems to help:

Switching the WUR vac hoses from the way they are illustrated in the famous SC diagram. Car warms up like a junker. No pinging at 5K to redline.

Not driving it in the summer.

Suspect:

The WUR is incorrect for my '78. Vac leans the mix at high RPM. Since no vac seems to keep the pinging away.

Intake runners leak false air through the Phenolic sleeves.

Questions:

Should there be Vacuum at WOT at the lower port of the WUR? There is Vacuum there all of the time now.

My airbox had what looks like a line of tan glue where the two halves bolt together. Is this normal?

[tsuter]

Airbox glue on the line is normal.

Sometimes its just failing/arcing plug wires and its not pinging but missing when hot and under load.

[Mysterytrain]

The WUR for a 78 SC should be 0-438-140-045. It has a vacuum enrichment port on the bottom. With vacuum applied the WUR is lean. At WOT, loss of vacuum enrichens the mixture. What are your control pressures?

[bkreigsr]

does the ping go away with higher octane?

[dd74]

I've had this problem too for the duration of two engines, a CIS 3.0, and the other a Weber-carbed 2.7, and nothing that I tried remedied the "ping." On the 3.0, I changed plugs and wires, I retarded the timing, I ran a race gas/premium gas mixture; nothing worked.

With both engines, the pinging occurred on an uphill onramp between Hollywood and the San Fernando Valley during slow driving conditions on warm days. The noise occurs between 5-7,000 RPM respectively.

I've talked to countless people about it, and no one seemed able to replicate the problem, or solve it aside from the steps I already took. So, short of tearing down my engines to install lower compression pistons, I simply changed my driving style.

1) On hot days, in traffic, I avoid WOT acceleration from a near stand-still, which is when this occurs.

2) I find that if I don't accelerate quickly, but gradually take the engine up to redline, even on hot days, the pinging does not occur.

3) I also find that if I have been driving at a continual high RPM at a track event, the car does not ping.

Sometimes I wonder if it's pinging at all, or simply hot cylinder heads, fuel starvation, or just the nature of a flat 6 when "trounced" on after it has endured heavy stop-and-go driving.

I have been told that more traditional pinging occurs at low RPMs when the engine is being lugged in a high gear, which is not even the proper way of driving a Porsche. High RPM pinging seems to be something else, if it is at all a concern.

I say "if" only because a week ago at Willow Springs, I *****-slapped the daylights out of my 2.7 in 105-degree heat, several times hitting the rev-limiter at 7,300 in third gear. This was, btw, how the engine is supposed to be driven, even with temps up to 250-degrees, though I didn't let it go on for very long. All I'm saying is if the engine was going to blow apart from high-RPM pinging, I gave it more than enough opportunity to do so right then and there.

[oneblueyedog]

Originally posted by Mysterytrain
The WUR for a 78 SC should be 0-438-140-045. It has a vacuum enrichment port on the bottom. With vacuum applied the WUR is lean. At WOT, loss of vacuum enrichens the mixture. What are your control pressures?

I will set up my pressure tester and check the car.

WUR # 0 438 140 089 BOSCH bought new. Vac port on bottom sandwiched between the body and a cove plate. It's not on the very bottom.

I will also check the vacuum at 6000rpm.

That won't be the same as WOT though correct?

I hope to see a drop in vac. Just by holding my finger over the disconnected hose, it still has a strong vacuum.

Thanks

[oneblueyedog]

dd

This is the same phenomenon. I have actually backed off WOT to avoid the pinging at around 5K like you say.

Cold dense air days with a cold engine- awesome pull.

Thanks.

[oneblueyedog]

Vaccum test on the line to bottom of WUR:

13 static

Blip of throttle- zero initially and up over 20 when the RPMs catch up.

Top port O hg as specified.

[Mysterytrain]

Yep, thats the new replacement number. I guess I should have used on trottle rather then WOT. The enrichement works like old school vacuum powered wipers and perhaps the lower port is a better labeling of position vacuum port position. So basically it is still too lean when you are on it? Once you have the gauges set up to pressure test the WUR you can pull a vacuum on it and watch the control pressure drop. Maybe you aren't getting enough advance or the spark gets weak?

[oneblueyedog]

I'm suspecting ignition in the back of my brain. The CD box is a rebuild and has been running great for 5 years. I don't have the hottest wires. The distributor is from another SC of the exact same year. I have a spare with worn out bearings and field windings.

For FI the only thing left is replacing the injector sleeves and fuel distributor. If it ever comes to that. it's T-bitz.

I'll post pressures after the holiday weekend.
Thanks for the ideas,

Peace too,

Lee

[dd74]

Originally posted by oneblueyedog

For FI the only thing left is replacing the injector sleeves and fuel distributor. If it ever comes to that. it's T-bitz.

That would be my choice if I still had CIS.

[tom.langborg]

Hi
I just want to say that i have the same problem.

Next thing on my list is.
New ignitions wires.
Check valve adjustments
Check broken head studs
Check ignition rotor

What i have done.
new plugs
new distributer cap
check co level.
check ignition timing.
higher octane

[RoninLB]

Tyson posted that CIS may tend to run lean at high rpms. He didn't say what the reason was that I remember.

With carbs the E-tubes will richen or lean the mix as rpms increase depending on which tubes are used. My carbs are nowhere near detonation above 4k with only 135 mains, F11 tubes, and 34 vents. I don't know which tubes do which.

fwiw.. detonation will increase CHT. A single cylinder digital ga may be a heads up and a confirm if the detonation can be kept consistent long enough for a reading? Not that I would do that. It should show up on a plug reading.

[RoninLB]

E-tube selection info chart in

Weber Tech Manual by Bob Tomlinson p58

[tom.langborg]

Hi guy's my problem is partial solved

My pinging almost disappear when hot.
I change to new ignitions wires.
I have not check ignition timing yet but the car is running fine.

[RoninLB]

Do you think it was the Beru spark plug connector ?

[justinp71]

Has any one found a remedy to this?

I have a 75 2.7 with the same problem, it appeared to go away when I retarded my timing and ran good 91 gas.

But I re-timed my cams and the left side was retarded, then I re-timed the ignition and the car pulled like hel*, but as it go hotter it started to ping again.

Has anyone spotted a distributor with excessive endplay as the culprit?

I'm not sure what the endplay is exactly, but I would assume that it is the vertical distance that the distr shaft can move inside its housing. I know mine can move about 1mm, which I think is on the high side (if that is the end play).

[Gunter]

I strongly recommend to clean/lube the distributor first, it's easy:

Distributor service (Clean and lube) real easy without removing the pinion gear!

Then set the timing to maximum advance:

Maximum advance for SC 3.0 or ss 3.2

I suggest that you print out the instructions and follow exactly, especially the initial vac disconnect to get the 33 deg.

Justin: By end play, you mean up and down (Axial)? 1mm is no problem.
The radial play is the important one; there should be next to none.

[justinp71]

Okay I'll lube the distr.

I know I had the timing dialed in until I retarded to get away from the pinging.