Oddjob

Trouble shooting a possible igntion/timing/electrical problem - unplugged the knock sensor and test drove the car to see if power noticeably dropped - nothing dramatic, hard to tell any difference when doing 3rd gear runs on the street.

I originally believed that doing this would cause a KLR diagnostic fault and trip the "limp home" mode and blink codes - but it does not.

My belief is that the KLR will retard timing up to -6 deg when knock is detected, so I assume that the KLR will drop -6 deg timing if there is a faulty knock sensor or knock system problem (or if the knock sensor is unplugged). Any chip tuners or others know for certain?

On a basically stock car (chipped), ballpark how much horsepower would be lost? I would have guessed maybe 5-10%, maybe 10-20rwhp? 10 hp would be hard to feel when driving on the street, but 20 should be pretty obvious.


Also, reaching for straws here: if there is a voltage/current problem somewhere in the charging or ignition system - is there a way to measure low spark energy? And what symptoms could/would this cause? Missing and stumbling under load, or normal driveability but with slightly reduced power?

Van

Tough questions!

samluke

Jim,

Can you plug a spare knock sensor in and wrap it in foam/cloth to make sure its isolated so doesn't sense? See if it makes any difference. If your measuring knock count, it would be interesting to see what result you get. You shouldn't be getting any.

I've been chasing a similar problem as you, for years and effectively given up.

Mike Lindsey

If you un-plug the knock sensor can cannot tell any difference in performance, you have either a bad knock sensor, knock sensor harness, or KLR. The car would spool up slower with less "shove you in the seat" feeling. It may be hard to tell the top end difference between the two. More easy to distinguish the initial going into boost area.

I suppose how well your car is tuned down there could make it harder
or easier to detect.

Chris White

your EGT will go way up with that amount of timing retard, like dangerously high....

vette951s

I've had spark plugs in too cold a heat range 'flame out' under high boost conditions. Although this feels more like a complete shutdown rather than a stumble.

John

Oddjob

Thanks guys.

Richard, Im on the verge of completely giving up too. Yes, I think that would be a good test of actual knock. If the sensor itself is bad, and/or if the wiring is bad - the DME/KLR could still be retarding timing even with the sensor isolated. I still have the little curtis event counter and it does indicate a few knock counts every full boost run, even on the street. And as would be expected, when the knock sensor is unplugged it does not register any.


Mike, I am very close to swapping in one of your knock sensor harnesses as a last shot at troubleshooting the problem, and was hoping to get an absolute result with this test - but did not. I tested the car in question and could not say for certain that I could tell a difference; but it is difficult to be doing a lot of full throttle runs in a large metro area in a car with racing stripes & numbers and an open exhaust. I did the same test with my other street car, which is known to be good; and I also could not tell a dramatic difference with the knock sensor unplugged. But I was comparing the feel of top end pull, not the boost kick-in.

My next thought would be to put the car on a dyno and try a run with and without the knock sensor plugged in. And/or a dyno run with a timing light hooked up to measure full load timing. But would need to know the chip timing maps to compare. It would also be an issue of the timing light's accuracy, so may need to compare timing to another car running the same brand/make of chip.


Chris, I have an EGT in the track car, but did not pay close attention to that while testing/comparing. The numbers dont get that high when doing 3rd gear bursts on the street. I dont recall ever seeing much over 1300 on the street. On track, Im 300+ over that. So probably a dangerous test, but I could run the car on track for a lap or two with the sensor unplugged to see if the temps are noticeably higher. If no change in temp, then no change in timing. Could then use the FQS Pot to drop 3 deg timing and see what happens to temps in comparison with the unplugged knock sensor.

What numbers do you consider dangerously high? Over 1700? 1800? So at approx 15 psi, any idea what you might expect if dropping 6 deg timing? 100F, 200F increase?

John, "flame out" - meaning you blew/melted the tips off?


Anyone know of a diagnostic tool available that would allow tracking ingnition advance? Maybe a cheap or limited piggyback device - I dont need any signal modifying capabilities, just monitoring/logging the DME outputs.

hodmandod

I am interested in these comments. I found that when my knock sensor is unplugged, OR unbolted, I cannot start the engine. Is this normal?

Mike Lindsey

am interested in these comments. I found that when my knock sensor is unplugged, OR unbolted, I cannot start the engine. Is this normal?

No

Mike Lindsey

OddJob. You can tell just punching it in first or second gear.

TurboTommy

If the KLR is not getting a signal from the knock sensor, I understand that the system automatically goes into limp mode. This means that the KLR is reducing boost via the CV. Is it possible that when it goes into this mode the KLR doesn't even bother with cutting timing? I mean, Porsche wouldn't consider it to be beneficial to the engine to run reduced timing at low absolute manifold pressures for the limp home.
If that's the case and you run aftermarket boost control you might not experience reduced timing by disconnecting the knock sensor.

Oddjob

I used to think that too, but found that is not the case - it does not go into limp mode (even though there is a KLR diagnostic check/fault for a knock sensor failure; no blink code is generated with it disconnected and no limp mode). Boost is not cut as my cars run the stock cycling valve setup and boost was not reduced with knock sensor unplugged.

HIGHBOOST

What if the CV has been bypassed?

333pg333

I have had incidents of very high boost (30psi) due to malfunctions and had no discernible boost or timing pull. I have also experienced high pinging noise due to poor fuel. Again no retardation of anything.

JET951

not even your foot Patrick?
Hey Jim have you concidered hooking up a curtis counter to the KLR to see what the knock counts are?
you have a set of chips in the car, do you know what the timming is set for with these chips? do you know what the stock timing is meant to be?