Yes I searched;)

After many hours and $$$, I discovered that my low power issue (E36 M3 S50) was coming from bad knock sensors/false knock readings. Ignition timing under full load is only 16 degrees, and when I let off the throttle, it momentarily jumps to 38. My car is fully race-prepped, with solid engine and tranny mounts, lightweight clutch/flywheel, etc. In other words, the knock sensors are bound to get false detonation readings from all of the vibrations.

I'll be replacing the sensors today. My shop, which specializes in Rally race prep, suggested their rally car solution. Instead of replacing them to the stock position, I should bolt them to each other, wrap them in foam, and put them in a separate, isolated box. Obviously this bypasses the sensors, and I'll risk engine damage if there is a real problem. Any thoughts or other solutions?

Hmmm, ... very interesting. False readings from solid motor mounts, ... I could see this happening. Anyone else with this issue?

I may be chasing a similar problem. Can you tell me how you finally discovered the problem?

Thanks - Jay

Jay,

$2K and 5 dyno sessions!!!

The knock sensors were my last resort. I had already replaced the:

MAF
Speed Sensor
VANOS Unit
VANOS Solenoid
TPS
ICV
Plugs
Crank Sensor

I did a compression, leakdown, swapped DME's, swapped another MAF, checked coil resistance, readjusted throttle plate, etc. There wasn't much more I could check!

Part of the problem is that we can't drive my car on the street (ie. under load) to get a code to come up (tried that, and got pulled over by Richmond's finest. You should've seen the look on his face!). And there's usually not a $10K scan tool at the track (and who said that OBD1 was better than OBD2?).

But yesterday my mechanic came with me to the dyno, and brought his scan tool. He got codes for the knock sensors, the ignition timing was low, and the car ran rich from 5-7K rpms, all of which point to the knock sensors retarding the timing. Christ, this better be the problem, or I'm just going to add ballast and run in GTS-2!

Jay we did not get knock sensor codes from your car and the mixture values were in line. IU am willing to bring my Autologic box the the next that we will both be at to double check.

maxxfish - NICE car...

When Turner built my car they said the solid motor mounts would disrupt the knock sensors. No place for knock sensors in a race car anyway. Tuning should be correct and the fuel hopefully better than weak/suspect pump gas.

Jay we did not get knock sensor codes from your car and the mixture values were in line. IU am willing to bring my Autologic box the the next that we will both be at to double check.

maxxfish - NICE car...

Walter-

We need to talk. I don't fully understand what you guys looked at and/or checked out. I don't want to be on a goose chase or look for things that have been eliminated as a possible problem. I'll try to give you a call next week. AFAIK, I've gotten no CELs. Ever. But I don't know if there'd be an indication I would see.

I've got to get it on a dyno. Just to see what's what.

Jay

Many thanks - Jay

Jay,

$2K and 5 dyno sessions!!!

The knock sensors were my last resort. I had already replaced the:

MAF
Speed Sensor
VANOS Unit
VANOS Solenoid
TPS
ICV
Plugs
Crank Sensor

I did a compression, leakdown, swapped DME's, swapped another MAF, checked coil resistance, readjusted throttle plate, etc. There wasn't much more I could check!

Part of the problem is that we can't drive my car on the street (ie. under load) to get a code to come up (tried that, and got pulled over by Richmond's finest. You should've seen the look on his face!). And there's usually not a $10K scan tool at the track (and who said that OBD1 was better than OBD2?).

But yesterday my mechanic came with me to the dyno, and brought his scan tool. He got codes for the knock sensors, the ignition timing was low, and the car ran rich from 5-7K rpms, all of which point to the knock sensors retarding the timing. Christ, this better be the problem, or I'm just going to add ballast and run in GTS-2!

I'm at my shop, my mechanic just removed the old sensors from the block, and the mounting surface had been painted! I'm not going to say who built my engine, but the Bently Manual specifically states that this surface needs to be perfectly clean. Grrr. Update to follow...

I'm at my shop, my mechanic just removed the old sensors from the block, and the mounting surface had been painted! I'm not going to say who built my engine, but the Bently Manual specifically states that this surface needs to be perfectly clean. Grrr. Update to follow...




What have y'all decided to do with the sensors...keep installed as stock, isolate or eliminate?

Anyone know if the euro engine knock sensors would have the same issues using solid mounts?

maxxfish, I see you're from Richmond, VA. I was born and raised there. Where are you located?

Good luck, glad you found the issue.

OK. We installed the new sensors, but didn't mount them (a la isolation technique). We got fault codes for both sensors. Then we mounted the new sensors on CLEAN surface (we scraped the paint off) and voila! Ignition timing at 39 degrees. I'll be at the track next week and test out the butt dyno.

OK. We installed the new sensors, but didn't mount them (a la isolation technique). We got fault codes for both sensors. Then we mounted the new sensors on CLEAN surface (we scraped the paint off) and voila! Ignition timing at 39 degrees. I'll be at the track next week and test out the butt dyno.

Here's hopin' that'll solve the problem. Seems like it's usually the simple, small things.

Jay

I belive they need to be grounded.. You might try isolating and grounding..

i have a 95 325i, not at all race prepped, but I am having the same knock sensor issues. I tried the isolation technique and had marginal success with that, but I still have a rich running condition due to the timing being retarded. What would be the best way to eliminate the sensors? I've thought of installing a resistor in the setup, but I'm unsure of what ohm to use. I've also been looking for someone in my area (Southwest Florida) to remap the ECU and trick it to think the knock sensors always read normal, but I can't find anyone around who can tune the OBD1 chips. Any suggestions would be greatly appreciated.