neo964

Hi, any thoughts on this? I have a C4 1990 model, about 70k miles. Just changed the distributor belt, serviced etc.no signs of leak.
Pingging occasionally at low rev about 2000rpm, low gears. Thought it was the fuel mix, but always pumped her with highest grade gas. The pinging is not all the time. Definite coming from the engine.

Any ideas?

thanks

Bill Gregory

To elminate anything in the fuel path or valves, I would run a bottle of Techron, a Chevron product, through it. Wait until your tank is almost empty, add the large bottle of Techron (for a 20 gallon tank), and fill 'er up.

Jeff Curtis

You could also pull your alternator/fan assembly out and make sure your knock sensors are still torqued down...my friend, with a '93 had the same problem...the bolt holding down the knock sensor on the right bank had come loose. <img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />

Porschedude

You say that you get a knock that is audible. But do you get a “CHECK ENGINE” Light?

I have had several "1132" Error Codes appear and then disappear or I reset them. This “Check Engine” light comes on because of an inoperative sensor. Either the sensor has opened internally or one of the junctions/connections has a high resistance across the mate. Or I guess the cable could be shorted, which would bring the voltage to zero. If the sensor was loose or was really picking up an engine knock, the system would just retard the timing some 6 degrees of advance.

Repeat…If one of the knock sensors were loose, you would get an ignition retard but no knock. I don’t think one could hear or confuse the sound of a loose sensor for a ping or knock. I do believe that a loose sensor may retard the timing and give you a diminished performance condition.

I replaced my duct that runs from the fan shroud and the heater blower the other day, and I remember looking in at the knock sensors from this vantage point. I wonder if I can change or tighten the knock sensor mount, whichever is appropriate through the duct opening? Without removing the Alt/Fan?

I’m with Bill, run some Techron through the engine and see if helps. It sure sounds like carbon build up in the CC.

neo964

Hi , thanks for the advice..will try out the remedies and let you all knw.

tks again.
neo

Jeff Curtis

I in no way, shape, or form suggested that a loose knock sensor would cause the noise! (i.e. - rattling against the engine)

...a loose knock sensor would mean that the "tuning fork" principle that the unit uses would be diminished, therefore it would likely NOT be doing it's job.

I repeat: this happened to a friend's engine here locally, the bolt had completely fallen out and was resting between the cylinders on the right bank.

I'm not sure if you could tighten the knock sensor bolts, or check them through the opening that Porschedude cited, but I am sure you can access both sides with the half-moon cut-out removed then the alternator/fan assembly.

Porschedude

Jeff,

I didn't mean to sugest that you were confusing the noises. Sorry it came out sounding like that, but I see your point.

You think that if he was riding on the fringe of ping or detonation, the loose knock sensor may interpret that it was not pinging or knocking and be at full advance per the ignition map. After rethinking the matter, I would tend to agree with you. The loose sensor would most likely prevent the retarding of the ignition. The mass of the sensor itself is so small and the shock of a true ping would be much higher or sharper than a bouncing or vibrating sensor could experience.

I was looking through the new Bentley Technical Data Book and thought of another condition. I came across the Altitude Correction Pressure Switch (ACPS), which tells the DME that it is above 3,280 ft from sea level. The DME would then lean the fuel ratio some ½-1%. I went looking for the ACPS on my car and found the connector only, under the LH Seat. I guess this was an option or the factory or the dealer would install the ACPS if the car was destined or sold in high elevations. I guess the only way it could add to the pinging problem would be (1) the sensor would need to be installed, and (2) it would need to stick in the “At Altitude” position and (3) be operated at a lower altitude. It’s a long stretch and would most likely not happen.

I also found two other connectors under the seat that somehow condition the DME. They are the "MAP ALTERATION SWITCH" and the "VARIANT IDENTIFIKATION SWITCH"
Yes identification with a "K", that’s how they spell in the manual...

I wonder if there is any horsepower on tap here??? I found a coding plug in PET, but I’m unsure which, if either, it would mate to. The part number is 928.607.422.00.

Anyone know anything about these two or three devices?

Keith

Jeff Curtis

Keith (Porschedude) that's cool, email/discussion boards can be so darned impersonal and often people can get offended or misinterpret what another has to say. I'm glad you didn't misconstrue my response as hostile or me appearing that my intelligence had been insulted.

It's fun to "volley" back and forth between self-proclaimed "techies" on here, as in fact, I am just like the next person on here...a 964 owner who strives to find out more info. so I can save $$$$$ on maintenance and upgrades.

YES, with the knock-sensor loose, there is potential that it would NOT sense detonation, thus the program "map" going on about it's business in making max HP, with max advance under load.

Remember, the knock-sensor utilizes a "tuning fork" principle, so it doesn't necessarily sense "seizmic" waves/explosions, of sort, instead it picks up a spectrum of common frequency harmonics caused by pinging (detonation)...and goes to work.

As for your three "mystery" harness connection points...that's on YOU Luke, use the force and open up our eyes to more HP!! <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />