Julian

Who feels like playing detective?

History:-
Car: UK MY99
ECU: AE800
Mods: itg panel filter, ScoobySport decat centre and back box
Fuel: OptiMax
Knock Sensor: Standard Subaru part
Knock Position: 1 On gear box cover! (dealer moved two services ago - no explanation provided). 2: On block nearest number 4 cylinder (where knock link is usually fitted, I believe)
DeltaDash: Monitoring since August 15th
Problem: Not one single knock noticed at all - including rolling road runs with sensor in both positions


That doesn't sound like a problem I hear you say, but my ECU is not attempting to modify the ignition timing (advance or retard) in the slightest under any conditions. So although there is no knock activity (good) there is no attempt by the ECU to try and get a bit more from the engine (bad).

Assumption 1: I was under the impression that the ECU was adaptive and should try to advance ignition and then back off at the slightest knock. Correct?

At PE today we tried two knock sensors. These were checked with a volt meter and both gave similar responses when the block was gently tapped. i.e. not a consistent output.

Assumption 2: Knock sensors react to a very specific frequency and simply tapping the block is not a sure fire way to generate the correct type of frequency to trigger a big (mV) reaction. Correct?

Question 1: Anyone have the specifications of the standard knock sensor and/or is able to explain exactly what it's listening for and what type of output to expect?

Next step we checked the connector from the knock sensor into the loom. Again two were tried and both OK. Original unit connector had two wires at sensor end going into one by the time it reached the loom end connector. Second connector kit tried only had a single wire straight through.

Question 2: Anyone explain the two into one wire?

Next Step was to check from the loom connector back to the ECU side connector at the other end of the loom. Again all OK.

By this pint it was looking like the ECU was not responding correctly, so we swapped to a TEK1 mapped AE801 ECU. Exactly the same behaviour!

So we’ve now tried two sensors, two connectors and two ECUs. All combinations exhibit the same behaviour. No knock correction applied to ignition timing at all.

I can’t believe that my engine runs so smoothly that there is never any form of knock registered. If its running so smoothly, why doesn’t the ECU advance the ignition?

If anyone has any ideas or explanations to any or all of this I’d be very happy to hear.

Thanks,

Julian.

Knock Knock. Who’s there? No one - apparently!

PS. We also did a back to back run of my standard ECU against a Standard TEK2 mapping (i.e. not optimised for my mods). Very impressed +30lbft from 2000 to 5000 and +10 to +25bhp across the same range too.

john banks

I have seen a "dead zone" with timing where it stays on zero knock correction all the time. You need to advance the ignition until it knocks and then see if the ECU does anything to know if it is working. Some with exhaust manifolds running pretty high boost have found similar, maybe changes the frequency of the knock.

Ken E

Is the ignition as far advanced as it can go ? I thought a UK car would run OK on normal unleaded, so running on optimax it is less likely to knock ?

Julian

Ignition seems to be at or near 42 degrees most of the time when under way - does drop sometimes. I'll need to do a few more specific runs checking this. What's the max advance I should expect to see?

Does any one have some Delta Dash figures under known conditions, from a well running UK car that I could take a peek at Please?