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| Knock sensor issues http://www.gt4dc.co.uk/forum/viewtopic.php?f=2&t=7639 |
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| Author: | Diceman [ Sat Aug 13, 2016 9:57 am ] |
| Post subject: | Knock sensor issues |
I'm trying to help someone diagnose some issues on a recently forged st205 running around 1.4-1.5 bar but progress has been hampered on checking a power fc map as the aem wideband is reading incorrectly by upto 1 integer on afr ratio (they all do that apparently!) but odd knock readings. Datalogging shows that a reading of "1" or an expected "no signal" is being recorded at all load/rpm cells other than 5k-7k under high load where readings were 45-50. This is not typically how the knock signal responds and I'd normally expect to see readings of around 4 at idle and upto 30 ish under various load/rpm points unless you have an old engine or actual detonation. High load/rpm may be a little higher and I've recorded circa 45 on my old tired standard engine without detonation. Does anyone have any thoughts as to why we are recording no signal then a sudden flurry of readings at high rpm/load? 2 theories have been put forward so far 1) the knock sensor has failed, suspected failure mode the piezo disc is broken and is now resonating at an unknown frequency. 2) corroded wiring that requires a very large signal to overcome the resistance (high levels of knock are actually present) Any thoughts before get someone to duck wiring and replace knock sensor? |
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| Author: | Nibbles [ Sun Aug 14, 2016 9:05 pm ] |
| Post subject: | Re: Knock sensor issues |
Most likely would be sensor IMO, although that is probably the most difficult / expensive to change so worth checking others first. If you have a spare ECU, it's worth a try just in case - especially if this one hasn't been used for a while. Another prime candidate would be a short to ground at the knock sensor end - especially likely as many people don't realise it's screened cable and re-make the end with screen and core all connected together. |
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| Author: | Diceman [ Sun Aug 14, 2016 10:15 pm ] |
| Post subject: | Re: Knock sensor issues |
Cheers Chris. I will be running a new wire to a spare knock sensor (bolted elsewhere!) as a test as we don't have a spare power fc. I read that the screen should only be connected at one end to either engine block earth or ecu Earth rather than both? Is that correct? It's different to my normal audio wiring if so which has the screen connected to chassis earth both ends. |
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| Author: | Nibbles [ Mon Aug 15, 2016 7:50 am ] |
| Post subject: | Re: Knock sensor issues |
The screen is normally connected at ecu and only. This is the best and as there's no electrical noise relative to ecu ground. |
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