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[TheBoy]

Hope this helps those learning diagnosis and fault finding, esp as its quite an easy one. I have Webby in mind, but hopefully useful to others.

Saw a 3.0l auto this evening, report was "EML on when accelerating a bit harder than normal".

Upon starting, the car had a distinct misfire, felt like it was only running on 4 or 5. Tech2 showed no fault codes. So, we are immediately suspicious of HT, aren't we, with it being a non OBDII car 

Before going further, always worth a quick look at the trims, as these can give a lot of info about the car. Motronic 2.8.x have 2 trim values per bank:
Idle
Partial Load
(No need for full load, as it will be open loop)

Bank 1 idle was trimmed to the endstop on Bank 1, trying to lean it off.

So, that makes us particularly interested in the HT on Bank1 (Cyl 1/3/5), as that side is too rich, as one pot is throwing unburnt fuel towards the lamda.

We now use the function to individually disable each injector one at a time,  to pinpoint the pot. Cyl 2/3/5/6 all showed a noticible decrease in revs when their injectors were disabled. Cyl 1 showed no difference, cyl 4 slight difference (remember 4 is 1's firing partner, and its wasted spark, hence the affect on 4)

So, its Cyl 1.

HT lead off, plug out, looks past its best, but OK. Look back to lead




And that is my idea of fault finding - methodical and logical. Not what you'd get from most garages, sadly.

[Entwood]

Nice one ...

So that's using fuel trims on the 3.0 (non - OBDII) ... but you never finished answering about the fuel trims on the 3.2 ...


http://www.omegaowners.com/forum/index.php?topic=113851.60

pretty please  ?? 

[dbug]

Hope this helps those learning diagnosis and fault finding, esp as its quite an easy one. I have Webby in mind, but hopefully useful to others.

Saw a 3.0l auto this evening, report was "EML on when accelerating a bit harder than normal".

Upon starting, the car had a distinct misfire, felt like it was only running on 4 or 5. Tech2 showed no fault codes. So, we are immediately suspicious of HT, aren't we, with it being a non OBDII car 

Before going further, always worth a quick look at the trims, as these can give a lot of info about the car. Motronic 2.8.x have 2 trim values per bank:
Idle
Partial Load
(No need for full load, as it will be open loop)

Bank 1 idle was trimmed to the endstop on Bank 1, trying to lean it off.

So, that makes us particularly interested in the HT on Bank1 (Cyl 1/3/5), as that side is too rich, as one pot is throwing unburnt fuel towards the lamda.

We now use the function to individually disable each injector one at a time,  to pinpoint the pot. Cyl 3/4/5/6 all showed a noticible decrease in revs when their injectors were disabled. Cyl 1 showed no difference, cyl 2 slight difference (remember 2 is 1's firing partner, and its wasted spark, hence the affect on 2)

So, its Cyl 1.

HT lead off, plug out, looks past its best, but OK. Look back to lead

And that is my idea of fault finding - methodical and logical. Not what you'd get from most garages, sadly.

 

[Kevin Wood]

I love it when a plan comes together.

.. only, isn't cylinder 1 paired with 4 rather than 2?

[TheBoy]

I love it when a plan comes together.

.. only, isn't cylinder 1 paired with 4 rather than 2?

Somebody was paying attention...  ...that trap was set for Mr DTM, I didn't think anyone else would spot it. Smart arse

[TheBoy]

Original post modified

[tunnie]

Thanks again for looking at it. I did ask her if it drove normally, she said yes 

[doz]

I find spraying a flammable liquid around the engine bay is good way to find a stray short on the ht side of things. Only downsides is eyebrow shortened life span and irate owners who don't share your sudden bout of hysterical giggles.


 


OK OK I'm shutting up no need to swear under your breath while sat at your keyboard

[Webby the Bear]

nice one TB. looks like a very logical way to go about it. I have a few questions re the fuel trim lol but ill ask tonight as i aint got the laptop :-)

[Webby the Bear]

Right now i'm on laptop 

just re-read the fault finding. excellent work and I wish i'd have been so astute when diagnosing my exhaust leak 

anyway, when you say about switching off injectors one by one I am presuming you do this via the techII?

Also, re the fuel trims. I understand that this is where the o2 sensor, on receiving the fuel/air ratio through the exhaust, will make the mixture richer if it detects its lean, and vice versa... and that's why on the techII youll constantly see the o2 readings changing from rich / lean and back constantly.

and also, in effect, what you were doing by switching off the injectors was cutting off the supply to that cylinder... if the sound changes then you've affected the cylinder.... no change meaning it wasn't doing anything to begin with ? 

[TheBoy]

anyway, when you say about switching off injectors one by one I am presuming you do this via the techII?

yup

Also, re the fuel trims. I understand that this is where the o2 sensor, on receiving the fuel/air ratio through the exhaust, will make the mixture richer if it detects its lean, and vice versa... and that's why on the techII youll constantly see the o2 readings changing from rich / lean and back constantly.

yup

and also, in effect, what you were doing by switching off the injectors was cutting off the supply to that cylinder... if the sound changes then you've affected the cylinder.... no change meaning it wasn't doing anything to begin with ? 

yup

[Webby the Bear]

I'm getting there 

[Andy B]

I'm getting there 

You just now need your own £thousands TechII to diagnose faults from a single manufacturer ..... 

[Webby the Bear]

I'm getting there 

You just now need your own £thousands TechII to diagnose faults from a single manufacturer ..... 

 

ill just take a trip to visit semi-naked TB in his pants 

[Andy B]

......
ill just take a trip to visit semi-naked TB in his pants 

Waaaaaaaaaaaaaaaaay waaaaaaaaaaaaaaaaaaaaaay too much information!!!!! 

To quote Jimbob ...... where's the mind bleach? !!!!!!!!!