Knock control test pulse

[ScottyWM]

This is for my daughter's E36, but the codes are the same and this forum gets so much more visibility I'm posting here.

I drove her '93 318iS to the store and got some gas in it. On the way back, the check engine light comes on as soon as I start it (after pumping the gas). I check the gas cap, no problem there. I do the stomp test and get 1286 - Knock Control Test Pulse.

What does that mean? There's no 1225,6,7,or 8 which is the knock sensors themselves.

[Jr ///M5]

Scotty,

I'm not putting you off or anything, but a quick Google on M42 knock sensor came up with some interesting results. The ones I read stated that replacing the sensor didn't do any good. Most of them were repaired by cleaning electrical connections, ranging from soldering the ECU (reflow) to cleaning the neg battery terminal under the hood while replacing the starter to fix a different problem.
I think investigating electrical connections for loose or corroded terminals would be the best place to start.
The knock sensor is located underneath the lower intake manifold, but the ECU picks up signals based on what it sees, maybe it's just a connector problem.
Just so you know, at least on the E30 M42, there's a plethera of vent hoses underneath the intake manifold that is integrated into the cooling system to prevent the throttle body from icing up in the winter time. This area is prone to heating and cooling cycles and the plastic connectors located in this area tend to get brittle and crack even after 40k mile replacement.
At least it's a place to start without throwing money and parts at the problem right away.

Hope this helps,
JR

[ScottyWM]

No worries, I wasn't planning to replace stuff willy-nilly. The only info in the Bentley says it may be in the ECU. But I agree with you, it's likely to be just a bad connection somewhere. Fun part is figuring out where. There's quite a few E36's being parted on Craigslist around here now, so even replacing the ECU shouldn't be too bad money-wise. Will the CE light go out as soon as the connecion (or ECU) is repaired? Then I could easily swap parts with a loaner and watch the results.

[Jr ///M5]

It depends. If I unplug a MAF sensor it will "set" the code in the ECU and trigger the light on until it is cleared with a reset tool or by disconnecting the battery. However, a lazy O2 sensor will cause the light to go on and off as will a leaking intake hose. A failed sensor or disconnected sensor cannot resend information to the computer and sets the code while it might not light the CE display, the code is still stored in the memory and can be read with a code reader.

[Ross]

If it turns out you need the knock sensor let me know. I junked an M42 recently but saved all the ancillary bits. Yours for the postage.

[ScottyWM]

Thanks Ross! It'll be a while before I know. I'm going to check the connections and grounds first. And with the lousy cold weather we've been having it may be a while before I even get around to doing that!

[Jr ///M5]

Ross is a standup guy, he's always there to lend a helping hand and has done so for me a couple of times in the past few years.

Kudos to Ross for again lending a helping hand to those of us here on the board. It just needed to be said, Ross, it just needed to be said...

If I remember right, I still owe you a 6 pack of your favourite brew. Maybe at this year's summer meet if we can arrange one!

Thanks for all you do bud,
Jr