[Kim]

Hi guys - just back from a trip to Toronto to pick up my 92 cabriolet. Drove it 1800 km in 18 hours back home and now I know what a car feels like that doesn't ping (#$%#@ amazing, that's what!!). Nonetheless, this car is a tip and it just doesn't cut it acceleration-wise compared to the 92 coupe 6-speed (until 3500 rpm, of course!). Still a hoot to drive.



This pinging is driving me nuts (and broke).



Some other info that might be helpful after I thought about it at some length.



When I bought this car 33,000 km ago I don't remember it doing this. It was using some oil and I had a number of leaks repaired as well as the cam and balance belt (and too much other stuff to mention without crying) replaced at a Nissan dealer. It my insistence they checked these belts three times becuase I though the car was vibrating above 3000 rpm. It has since been to the local Porsche shop for additional oil leak repairs and replacement of exhaust hangers. I will ask them to CONFIRM that the timing is EXACTLY correct.



The car does seem to be still using oil, about 0.3 litres per 800 km. There are still some leaks so, to date, I haven't really been excited about this. Maybe I will be. I don't think that 1 litre of oil in 2500 km is acceptable. I had a 1986 944 that used about 1 litre in 12,000 km at 340,000 km.



I want to have the compression checked because I seem to recall that the NISSAN place said the compression was 145/145/145/185. Someone on this site thought that I should keep an eye on the high one (ie the supposition was that carbon buildup was raising the compression) but now I think that maybe three cylinders are too low. That would explain oil consumption.



I fear that I am looking at rings for sure and what else?



Fortunately, the 92 cab is fun to drive (I learned today that when you have long hair that is a bit fuzzy you really ought to wear a cap if you drive with the top down (never was even in a cab of any make before today!).

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[Greimann]

Those compression numbers on the 3 are way low. Compression numbers of a tight motor are around 185, 195 consistently.



That and the oil consumption could be telling of the pinging problem too. When oil gets into the combustion charge, the oil mixes with the gasoline and reduces the octane rating for that moment. It is kind of like blending in some diesel fuel with your premium gas.



Your knock sensors should be kicking in too and controlling that. Do you get error codes?



Anyway, if the compression numbers can be verified, you may be looking at a either a head rebuild or a ring job, or both.

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[Kim]

when I run the engine up past about 4000 and keep it there rpm I will get a knock sensor code (one or both).



With trepidation I humbly ask - is that as expensive as it sounds?

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[Greimann]

I guess the first thing would be to verify the wiring and connectors to the knock sensors are in good shape. If the problem persists, replce the knock sensors. Then perhaps something more involved is required. I would hesitate to say absolutely that major surgery is required by only reading your description of the issue. That should be made by a trusted mechanic who can put his hands on the situation.

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[Kim]

I had two interesting comments today from PCA members regarding possible pinging problems.

1. is the chip an aftermarket one installed for racing and optimized for racing gas (I don't know the answer but want to try to find out).

2. is the car drawing too much hot air - I understand that there is a "flap" that allows heated air to enter the intake to help warm the car (I am going to also have this checked in addition to all the other things suggested by all of you).

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[Greimann]

On your #1, you will have to open the computer box to find out. If it is aftermarket, it will have a logo on it.



On your #2, NO. There is no preheat flap, so don't pay anyone to have that checked.

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[Kim]

Update as of today.



Compression is 185/185/185/155, no significant improvement after wet test.

No vacuum leaks.

Flushed with MotoVac system with no improvement.

Knock sensors are both working.

Oil on plug for cylinder 4.

No other obvious problem noted.



Suspicion that oil leaking into cylinder 4 is causing low octane and knocking. Car uses about 1 litre per 2500 km. Am getting upper and lower range of costs to do rings only or to do complete project.

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