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Topic: Poor drivability and stumbling idle (Read 578 times) |
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TonyS
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Scorpio Nutter - 12 years
Posts: 96
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Poor drivability and stumbling idle
« on: Jan 29th, 2005, 1:08pm » |
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To continue the saga ..
I've replaced the failed injector, bypassed the high resistance feed to the injector in the loom and checked what I can for failed insulation short of removing the whole loom to remake it.
But still I have an intermitent poor idle and hesitation in picking up (I think connected). The PCM seems to correct the idle by adding 50rpm as after about 30 seconds the idle problem disappears in a switch like fashion.
Logging the short/long term trims shows that the LTFT is drifting all over the place but tending to rich and under acceleration the short term trims hit the limit (25%).
Trim movements track across the banks so unlikely to be HO2S and these look to be switching ok (except it's logged a P0152 - Bank 2 Sensor 1 high voltage in the past 1000 miles).
The intermitant occurance has been pointing me to a loom fault and given the PCM can stablise the idle I don't think it's an air leak. Injector cleaner and Shell Optimax for two tanks to get any water out of the fuel, plus clean the injectors (although the one I took out was pristine apart from it's coil being open circuit).
I'm left thinking that the engine is operating well off the mapped conditions in the PCM which as both banks are similarly effected I'm left puzzled.
Apart from the MAF (load calculation looks ok and autobox works ok) , TPS (OBD shows sane information), and IAT (sane) there is nothing else electrical used in the PCM fuel calculation which it clearly is getting wrong.
Assuming the other 5 injectors are ok (no reason not to) and the replacement one matches flow rate (no reason not to, same colour top) then I'm left with only the fuel pressure being wrong.
Is there any easy way of testing the fuel pressure regulation?
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1996 Mk4 2.9 24v Estate
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waders
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Re: Poor drivability and stumbling idle
« Reply #1 on: Jan 29th, 2005, 2:12pm » |
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Hi tony,
I'm sure you have, but as it's not mentioned, have you checked the fuel filter isn't blocked, or the feed from the tank to the pump?
Logic says that if your trims are rich, to much air or not enough fuel for some reason, sounds like you have discounted to much air...............
The short term trims you say hit max under acceleration, sounds like it's running out of fuel fed to the injectors.
If youv'e checked already, sorry, but sometimes the simple things do get overlooked.
waders.
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TonyS
Junior Member
Scorpio Nutter - 12 years
Posts: 96
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Re: Poor drivability and stumbling idle
« Reply #2 on: Jan 29th, 2005, 2:42pm » |
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Here is the relevant part of the log showing the extreme trim during relatively mild acceleration. Before and after the LTFT's had been varying although at entry into the event is with both LTFTs at 0%
The log has missing data due to the polling design I used and relatively slow polling rate of the ELM based interface.
| Second | STFT1(%) | LTFT1(%) | STFT2(%) | LTFT2(%) | RPM | mph | ADV(Deg) | AF(gm/sec) | TP(%) | | 420 | 7.03 | 0.00 | 12.50 | 0.00 | 2557 | - | 20.5 | - | 58.03 | | 423 | 8.59 | 0.00 | 22.66 | 0.00 | 3135 | - | - | 86.18 | - | | 425 | 25.00 | 0.00 | 25.00 | 0.00 | 3609 | - | 27.5 | - | 43.13 | | 427 | 1.56 | 7.03 | 2.34 | 7.81 | 1802 | 47 | - | 18.29 | - | | 430 | 4.69 | 5.47 | 4.69 | 5.47 | 1853 | - | - | 44.31 | | 432 | 1.56 | 3.13 | 9.38 | 4.69 | 1934 | - | - | 34.17 | - | | 435 | 0.00 | 3.13 | 5.47 | 4.69 | 2003 | - | 20.5 | - | 32.94 | | 437 | 0.00 | 0.78 | 0.00 | 0.00 | 1603 | - | - | 5.62 | - |
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1996 Mk4 2.9 24v Estate
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TonyS
Junior Member
Scorpio Nutter - 12 years
Posts: 96
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Re: Poor drivability and stumbling idle
« Reply #4 on: Jan 29th, 2005, 4:19pm » |
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Thanks for the references.. and of course 'Finis is 7 334 684, cost about £40' is no longer stocked by FMD's or Ford UK 
Fortunately when sourcing the fuel injector I requested the whole rail which eventually arrived. The regulator looks a bit battered but it's worth ago.
I've just remembered that when I was first diagnosising the injector problem I pulled the existing regulator and found a small piece of aluminium foil in the well it fits into! It was big enough not to have travelled into the regulator but I'm wondering if there are more pieces inside.
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1996 Mk4 2.9 24v Estate
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