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[omega2018]

this time its stalled while driving in traffic at about 2k revs

Were revs steady-ish at 2k rpm when the engine suddenly cut?

yes probably i normally drive at 2K and in 5th gear, even for roundabouts.  just took the car out again and it stalled at speed around 3K revs I think. switched off engine while rolling and re-started in neutral, fine.

now you've got me looking at LTFT here are the lastest at idle:


   07 - Long Term Fuel Trim - Bank 1    0.0    %    
   09 - Long Term Fuel Trim - Bank 2    -1.6    %    

compared to yesterday before I cleaned the bank 1 plugs:

   07 - Long Term Fuel Trim - Bank 1    2.3    %    
   09 - Long Term Fuel Trim - Bank 2    1.6    %    

so looks like just a small amount of oil in the plug wells 3 and 5 may have put the fuel trim out and maybe bank 2 is also in oil, will check when the new plugs arrive.

[TheBoy]

Lets clear the trims so we're starting at a known base.  So, assuming your reader lacks the direct capability (and unless its a genuine Tech2, or high quality generic one like the Span-off ones, then it probably won't have a reliable one), purposely put on a fault code (unplug maf, or a multiram or knock sensor), drive for 500yrs letting revs get up to 3k.  Then plug everything back in, and immediate clear all fault codes.

This *should* reset LTFT to 0%.  Which gives us a base to work from.


It will still be the crank sensor that's at fault, but I know you want to explore other options as well . Incidentally, when you last changed the crank sensor, where did you buy it from?

[omega2018]

It will still be the crank sensor that's at fault, but I know you want to explore other options as well . Incidentally, when you last changed the crank sensor, where did you buy it from?

you're going to hate this....

it was ebay.  however it was a genuine delphi sensor complete with hologrammed box.  I migth just swap it out if you think that is it i have a spare and will be off to france with the car next weekend if it is fixed.

[TheBoy]

It will still be the crank sensor that's at fault, but I know you want to explore other options as well . Incidentally, when you last changed the crank sensor, where did you buy it from?

you're going to hate this....

it was ebay.  however it was a genuine delphi sensor complete with hologrammed box.  I migth just swap it out if you think that is it i have a spare and will be off to france with the car next weekend if it is fixed.

Buy a genuine one from a dealer. Delphi is just pattern crap, and experience on OOF tells us pattern V6 crank sensors do not last long. Don't buy a genuine GM one from egay or amazon marketplace or the like.

[omega2018]

Lets clear the trims so we're starting at a known base.  So, assuming your reader lacks the direct capability (and unless its a genuine Tech2, or high quality generic one like the Span-off ones, then it probably won't have a reliable one), purposely put on a fault code (unplug maf, or a multiram or knock sensor), drive for 500yrs letting revs get up to 3k.  Then plug everything back in, and immediate clear all fault codes.

This *should* reset LTFT to 0%.  Which gives us a base to work from.

Seems my cheapo scanner can reset all fault codes and trims so no need to force an error.

changed the plugs today , all look normal for 30K miles.  1 and 2 completely dry, 3 and 5 tiny bit of oil, 4 and 6 just a trace of oil. 

took it for a run again, no faults this time.  idling doesn't seem as smooth as it was before all this but difficult to tell.

Here is a plot of the LTFTs and other items (revs divided by 1,000, speed by 10). Basically a 25 minute drive onto a motorway, steady 58mph then back onto a roads.

[omega2018]

should add my mention of oil and plugs was about the plug wells not the plugs themselves. the plug tips were all dry and tanned, no oil or soot.

[TheBoy]

Oil in the wells could affect spark, esp under load.


I'm thinking airleak, bank 1, is whats cause LTFT B1 to drift.  But I don't think that is the reason for the cutting out.

[omega2018]

here are the plugs at 29K miles

plug 4 does look a bit yellow... this is listed as "lead fouling" which seems unlikely nowadays.  especially on just one cylinder https://www.ngksparkplugs.com/about-ngk/faqs/spark-plug-faqs/how-do-i-read-a-spark-plug

some more info - bottom steel cover of bank 1 cat has gone awol and there was a tiny leak after the cat in the exhaust for bank 1.  I don't think that will affect much though.

[omega2018]

Oil in the wells could affect spark, esp under load.


I'm thinking airleak, bank 1, is whats cause LTFT B1 to drift.  But I don't think that is the reason for the cutting out.

on the graph the airflow figures seem to bounce around a lot given the steady revs at 58mph.  i wonder if it is a problem with the MAF after all?

[omega2018]

anyone think this could be the cam sensor?  i've still got chance to buy a spare before going to france at the weekend. i already have a spare crank sensor

[Kevin Wood]

I would be surprised. Cam sensor is only really vital to get the phase of the cams after engine start. It probably doesn't get used once the engine is running, so I doubt it would cause a stall.

Plus, they very rarely fail on a V6.

[TheBoy]

Oil in the wells could affect spark, esp under load.


I'm thinking airleak, bank 1, is whats cause LTFT B1 to drift.  But I don't think that is the reason for the cutting out.

on the graph the airflow figures seem to bounce around a lot given the steady revs at 58mph.  i wonder if it is a problem with the MAF after all?

Given the solvents you've sprayed on it, the MAF will soon be toast anyway....

...but if it was MAF, both LTFTs will go in the same direction, not one each way.

[omega2018]

i take the point that the MAF should affect both ltfts the same.

i still don't get this solvent issue.  solvents don't normally dissolve metal do they? surely not contact cleaner anyway.

short drive in town today,  behaved perfectly

spare cam sensor arrives tomorrow just in case, cheaper than european breakdown cover which i can't get anyway (car >12 years old). 

from what i've read no point carrying a spare MAF since i can just unplug it.

[omega2018]

actually looking at my graph again the ltfts did move together
. 
both ended up above zero

maybe the solvent cleaning of the MAF fixed it

[TheBoy]

If taking it abroad, esp without breakdown cover (which is crazy), take a crank sensor.


As said, the MAF may well be BF'd, but that's more likely a symptom of the solvent.  The engine cutting out is likely to be something else. And we all know what.  So take one.