[V8] Major Issue today w/V8

[Scott Justusson]

 3.6 Motronic is referred to as 'semi-sequential' fuel injection.  I suppose one could claim it's better than 'batch fire' in that it won't dump all fuel from the rail, but it still 'pools' fuel on the back of the intake valve just like batch fire does, and it does not use a potentiometer TPS. In 1992 Audi switch to the 4.2 Motronic platform, a true sequential injection system, 8 individual drivers and potentiometer TPS. The 3.6 Motroinc has 4 drivers that pair the injectors as follows:  1&5, 4&8, 6&3, and 7&2.  This means if you have a problem with one in the 'pair' you should have a problem with the other in the pair in your diagnostic tree (injector driver and/or wiring).  If it's truly only evident in one cylinder, the best diagnostic is to swap that injector in the rail, and see if the issue moves to the swapped position.  If it doesn't, likely an internal chamber problem, not electrical.  If the problem does move with the swap, it's likely a bad injector.

HTH

Scott J
92 v8 4.2 Auto ABT Chipped Sequential Injection
91 v8 3.6 Auto semi-sequential injection

 

-----Original Message-----
From: Tony and Lillie <tonyandlillie1 at earthlink.net>
To: Professor GT gmail <CavalloGT at gmail.com>; V8 <V8 at audifans.com>
Sent: Sun, Apr 15, 2012 7:08 pm
Subject: Re: [V8] Major Issue today w/V8


One thing of note, IIRC this is an early car (90 or 91) with the 3.6 
electronics. If that's the case, there are two injectors per driver, it's 
not a true sequential EFI. So, if one is held open, another will be as well.

To second what someone else stated, find someone who is either very 
knowledgable with the car, or someone who is very willing to spend a good 
deal of time with it. Might end up being both.

HTH,
Tony

----- Original Message ----- 
> Sounds like the injector is being electrically held wide open constantly, 
> either because of a shorted driver circuit in the ECU, or more likely the 
> harness is shorted to ground on that injector circuit. The injectors are 
> given power constantly and the ECU switches them on and off at a 
> particular duty cycle based upon engine load. It's time to break out a 
> noid light ($10 a set at Harbor Freight) and check to see if the light is 
> flashing with the engine running at idle or is on steady. 

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