quinnfiske

Where is this gizmo? How do you get to it? What happens when they go bad?

I plugged an LED into the test port (thank you Lindsey Racing web site) and it flashes like crazy, too fast to count the blinks. I think I might have a fried knock sensor. Could a bad one cause the KLR/DME to retard the timing at idle?

Perry 951

You need to try and get the codes from the KLR. If it outputs a mess of nothing, the KLR might be toast.

The knock sensor is under the intake, close to the center of the motor, mounted to the block where the head meets up with it.

A bad one could retard timing at idle, but that is not the usual failure.

With the car running, take a long screwdriver and rapidly tap on the intake a few times. (a pretty good thud) If it stumbles, the knock sensor is working. If it does nothing, there is either a problem with the sensor or the KLR.

RobNL

Not that tapping again. The last time m42racer almost killed me with his solution to check this.

See Another thread about tapping

What I learned from Danno is that the tapping only works under load. I haven't tried it, because I haven't mastered the driving and tapping at the same time (yet).

Perry 951

I have had Porsche Mechanics and several others tell me that the tap test works. I have not needed to do this myself, so I cannot comment if it works or not. Just passing along the info I got.

The knock sensor should have a resistance between 270K ohm and 330K ohm. Close variances are allowed, as per the manual.

quinnfiske

Thanks for the reply. I tried the tapping trick (a fairly hefty blow) and got no response from the engine.

My car stalls after a few minutes of running. I had a timing light hooked up to #1 cylinder and shined it at the marks in the inspection hole and the timing retards as the idle deteriorates. My thinking is the KLR is retarding it in response to a knock signal that is not really there.

I really appreciate this site. It has been invaluable in teaching me about my car.

David Floyd

Unbolt the knock sensor to see if anything changes.

Perry 951

Have you tried to bypass the air bypass valve and check for proper idle setting? Here is how you do it:
http://www.clarks-garage.com/shop-manual/fuel-08.htm

Blink codes:
http://members.rennlist.com/951_race...linkCodes.html

Does the car run fine until warm.. then stalls out? Can you keep it running? What exactly is it doing?

quinnfiske

It starts and runs OK for somewhere between 10 sec and 10 min and then it stumbles, sputters and dies. It is very difficult to restart. It is intermittant but has deteriorated to the point it won't run long at all. Lots of throttle and revs won't keep it running. Sometimes it will snap out of its crappy mode and be back to normal. Like some sort of electrical gremlin.

I have replaced the DME relay, fuel pressure regulator, TPS and speed and reference sensors at the flywheel. Distributor cap, rotor, wires and plugs are 5K miles old. Fuel pressure and delivery are good, there is spark.

tazman

Perry posted an ohm reading for the sensor would it be possible to unplug the knock sensor and put a resistor across the terminals to test the car to see if runs ok like that? Just figured this would be a cheap way to make sure it is the knock sensor!

Perry 951

When it starts to die, can you tell if it is getting rich or lean? It really sounds temperature dependant. I know you went through the fuel system, but if the DME is cutting back fuel, or adding fuel, it could be a temp sensor issue. You could try unplugging the coolant temp sensor and see if it defaults to a rich condition. If there is no change.. you may have found it.

Have you had a chance to run codes on it? You need to have the car running to pull them, so take a quick trip around the block, then pull the codes before it dies.

quinnfiske

I pulled the knock sensor and it tested OK. Resistance right in the window. Tried to run the car with it hanging there unbolted. No change.
I pulled the spark plugs and they have black soot (rich condition). I am going to look at the temp sensor on the block next.