ECU removed once too often ?

[S2central.net]

Had some weird misfiring at idle immediately after swapping my ECU cable into a spare ECU - it was running some new AAN code, via emulator but nothing weird and I was a bit perplexed... Only when I squeezed / wiggled the ECU connector did the misfire disappear. Gets me wondering if this is related to my occasional suicidal idle behaviour. Anyway - I put it down as a once off in my head.

So the car drives fine - gently over some back roads to get fuel. A very slow learner driver is faffing about ahead with an 80TDi between me and the learner. He goes to overtake - its a long open straight with loads of room, so I proceed to try and overtake the 80 as well - and I get massively embarrassing splutters and coughs alongside the 80TDi - at which point my young passenger advises me its a neighbours car - oh ****ing great - what a way to let me down car. FFS - I cannot pass the TDi and have to fall back behind it. Thanks a lot S2 - after all these years of trusty overtaking and you choose NOW to let me down. Just great.........

It felt like fuel cuts you have with a big air leak, but the exact same setup was running perfectly only hours before this journey. It seems to drive OK as long as I stay off boost - weird, but in true mysterious ECU style - no fault codes declared (I have a MIL bulb).

So.... gently in for the planned fuel stop. I do nothing on the PC or the ECU... Just restart the car and off we go - still embarrassed (). Shortly into the drive home there is another momentary cutout whilst cruising in 4th - this time I briefly catch a red light blink on the dash - as if the ECU has lost power.

However - it drives fine after that burp - no issues at all on some acceleration tests.

I must have a gremlin in the 55-pin connector - or loom near that area. I have no idea how many times I have ever so carefully plugged / unplugged the ECU on my car - but clearly I must have some sort of intermittent bug in the wiring. Maybe Bosch tested it to sustain one thousand makes - breaks and I've just done 1001 !

Thats a right PITA and will probably take ages to find - even with my b.box - at least it will be good experience that can be documented for the next victim of any similar pain. Stupid clucking far - maybe its hinting to me that it wants a bit more TLC in its old age and is tired of being used for R&D.

[Sonic]

I had very similar symptoms when i re-plugged my ECU because id bent the vacuum hose over when pushing it behind the dash.

[S2central.net]

Good one Sonic... I've heard of that before alright... I don't have the hose kinked anywhere though and I could hear the misfire clear at idle when I squeezed the ECU connector. I'm not afraid of wiring but the thought of unwrapping that connector and picking my way thru 55 pins fills me with dread - its all untouched in there since Hans und Franz wired it all up 15 years ago... To be fair to them - it was never designed to cater for repetitive strain injury !

[shark_90]

Good luck with that Paul.. as you say they weren't really meant to be plugged in and unplugged regularly were they! Would it be worth splicing in some kind of other connector, such as 2 xPC motherboard connectors with a 55 pin ECU connector on the end? That way you could leave the ECU plug in your "normal" ECU and any time you're using the emulator or another ECU you could use a different fly-lead sort of thing?

Just brainfarting, hope it explained what I was thinking accurately because it doesn't scan very well!

[Rusty]

Good old wiring problems... I've got an intermittent with a crank sensor so it doesn't always start

Sacrificial connector sounds like a good plan... once you solve the current issue. Good luck!

[K7ERG]

I have had this similar fault on my Astra Turbo a few years ago. (C20 LET Motronic ECU) Found it was the shielded wire to the knock sensor (In the 55pin plug). Also i have seen the vac hose bent or air supply cut off which has been said above.

Craig

[Rusty]

I've bent the vac hose in the past when playing with ECUs and IIRC the car drove like crap from the get-go rather than having an intermittent fault.

[S2central.net]

After some late night tests I discovered that I have two issues --->

1. the dicky connector/cable which gives an audible misfire at idle if its not happy - but I didn't want to provoke that one just yet

2. fuel cutout was from the AAN chipset I was testing - it does WOT enrichment differently and I needed just a tad more fuel to cure the problem. It was weird... Hoofing round empty B roads last night and no issues with short blasts of full throttle, but on prolonged pulls deliberately up some steep hills I was getting horrible cutouts... Had to run an ABY stream to convince myself the problem wasnt ECU wiring. Now it remains to be seen whether the fault was caused as some safety routine in there was telling the engine to backoff as the calculated injector time would be 'unsafe' for the load point... or it was an extreme case of knock protection... happened reliably at 4500rpm - chanced it once with foot kept on the floor and got a second of boosting, then second of cutoff, then second of boosting. Its possible the extra fuel element cured the knock. I made no timing changes as I knew that was good from the ABY setup.