engine knock count

[danny tattersall]

I have had a code 26 problem for a couple of months now and have been having difficulty diagnosing the cause of the problem. Dermot O' Hare kindly offered to diagnose a free scan log that I had taken and he informed me that my engine knock count was vey worrying. In fact it contained over 250 counts in a ten minute drive and was registering 'knocks' at low rpm too. I have subsequently replaced the knock sensor (very awkward!) but to no avail. The counts are exactly the same as before. Therefore, the engine is either really knocking or something is resonating and causing the knock sensor to pick it up. The engine is in very good mechanical condition, quiet and the performance is as it should be. I am just wondering whether the ECU is not controlling the ignition timing etc properly. The exhaust is very sooty and this could possibly mean an over-rich mixture which has also caused a build up of carbon deposits in the combustion chamber / piston crowns. Any thoughts on this would be appreciated.

Thanks,

Danny '93 SE Highwing

[oharedm]

Danny,

I might be tempted to borrow an ECU next and change it over for a test. Just to double check it is real. The knock sensor basically a microphone, there is knock filter circuit in the memcal which processes this information and passes on to the ECU what it considers to be the characteristics of engine knock from this engine.


If it is real I bet it is related to fueling ....

Dermot

[lotusguy]

Hi,

A couple of thoughts on your issues... What octane gasoline are you running?... What condition is your air filter in (less air = richer mixture)... How well is your 0² sensor operating?... Are you using standard temperature range plugs?

Any or all of these things could produce the results you are seeing. Happy Motoring!... Jim'85TE

[danny tattersall]

Dermot, I hear what you are saying and agree with you entirely. The problem is finding somebody that would be willing to let me borrow one to try! Also, as you say it probably is fuel, although ignition could be to blame. Was the rest of the ECU plot ok in your opinion? Just wondering whether the spark advance etc seemed normal.

Jim,

I am running UK spec unleaded which is 95 RON. Air filter is a K & N which is only a few months old, plugs are standard NGK although they have been in a while. As for the O2 sensor, very infrequently I get an O2 sensor related fault that resets itself i.e. the light comes on under certain conditions for about 20 seconds then goes off. Apart from that I think it works fine and Dermot did not report any unusual readings. Hundreds of counts in a short drive is ludicrous though!!!!!!!

[igreenrover]

Danny

Sorry to hear you are still having trouble, and sorry I didn't reply to your text - I was very busy and then just plain forgot!

I still have my old ECU if you want to try it in yours and see if you get any knock faults?

Remember my old ECU was replaced because it wouldn't maintain the correct idle speed and 'intermittently' stopped working no. 2 and no. 3 injectors. If it’s working 2 and 3 injectors then otherwise it ‘s mostly ok.

I’m just not happy swapping my new ECU in case there is a fault on your system that will damage it! sorry.

Gareth

[danny tattersall]

Gareth, I don' t blame you for not wanting to swap your new ECU over! I think I would be exactly the same. It may be worth trying your old one though to just see whether it makes any difference to the knock counts. Fair enough the injectors might not work properly (but they might do)but if I do not get any knock counts it will point to a possible fault in that part of my ECU' s circuit. I am willing to give anything a try if you are up for it. I just don' t want to replace everything one at a time and find that it is the last thing that I fit that solves the problem. Thing is though that is probably what Lotus would do - and charge me a lot of cash for the labour and parts.

[oharedm]

Danny,

There is a spare ECU in circulation.
Try emailing Tony
[e-mail]


Running lean is a big cause of knock.
I have had a look again at your log, cannot see anything obvious, the ECU is triggering the injectors if they were blocked I could not tell.


D.

[danny tattersall]

Dermot, thanks for the e-mail address. I will have to wait until the weekend to e-mail him because my account at work will not send at the moment and will be out of action for a couple more weeks. I do not expect there to be any problem with the injectors though because the engine runs so smoothly. Poor flow and/or spray pattern would surely have a detrimental effect on this.