[s-cars] Diagnosing misfire cause

Thu Jan 21 13:57:26 PST 2016

That's exactly what I did JC. Lots of troubleshooting and replacing parts (some of which were due, but weren't the cause of that issue, others that ended up being functional, if not old). It wasn't until I borrowed an ECU from Bob Myers (very grateful to him for shipping one to me) that confirmed my problem was indeed the ECU's internal ignition drivers.

I had read the same info re:Steve conducting a rather exhaustive search and thinking he may have found a suitable replacement, and even that a stock of NOS bits may have been located...but assume that never materialized.. 

Sent on the new Sprint Network

----- Reply message -----
From: "John Cunningham" <jc at j2c3.com>
To: "Tom Green" <trgreen at comcast.net>, <s-car-list at audifans.com>, <trodri69 at gmail.com>
Subject: [s-cars] Diagnosing misfire cause
Date: Thu, Jan 21, 2016 1:18 PM

(double-send - went from wrong email first time which generally means it 
would take a day to clear the spambot and hit the list - apols to those 
who get 2...)

Tom nails it as usual - the driver transistors DO crap out on these 
ECU's and that's well known, however it's gotta be like a 200 to 1 ratio 
of "other stuff" to "truly failed ECU's" in root cause analysis for 
incidents.  The best practical / easy way to prove this is to have a 
good UrS bud with a known-good with known-good chips in it do a quick 
swap with you and if it back-to-back runs perfectly and then reverts 
(showing it's not just that you effed w/ the connections) you are pretty 
sure it's truly the ECU.  You can scope the outputs as suggested but 
then you have to load them hard and hope that you're simulating running 
conditions etc.  Of course the quick swap depends on having hands on one...

To do my best Forgie UrS historical pendantry imitation, its well known 
Steve Eiche tried at length to find replacement semis for those 
transistors without success.  There were rumors a couple years ago that 
maybe he found a solution or that maybe somebody else had found 
something to drop in to repair them but I have yet to have that 
confirmed.  Then  again I'm outa the UrS loop these days so maybe 
advances have been made in modern ancient technology. Haven't talked to 
Swanson in ages, he'd probably know if there was something..

As Cody says it's not like they use some kind of majick transistor tech 
wit bipolar unicorn jizz and I believe they are straight up BJT 
(bipolarunicorn jizz tranzistorz? wait maybe they are... ) however it's 
often the physical format that gets to be tricky.  The ones in these 
ECUs line up against these heatsink tabs tightly so theres not a lot of 
slop for "just toss some other case in there and mod it to work". 
Steve did the read-the-part-number and look-for-drop-ins at length and 
has a pile of used ECU's he would "mine" for parts to repair, and so if 
he couldn't find new ones then it's prolly pretty sure it's not an easy 
task. But at same time could easily believe somebody had nutted it out 
by now or had found some source for a compatible item.

Lastly - I am very very close to a particular Ex-UrS weirdo with a very 
clean used ECU out of a '95 UrS6 that might be looking for a good home. 
He had it promised to another UrS guy but if said weirdo was plied 
with appropriate pleading and beverages, and if the first-call guy 
doesn't have cash immediately, I can assure you he'll be happy to see it 
go to good use.

--- TheGhostOfJC

On 1/21/2016 10:06, Tom Green wrote:
> Tom,
>
> Your problems with an intermittent misfire are typical of what other owners experience with ignition problems.  The others seem to be able to take the time to do the simple diagnostics to find if there is one cylinder that is misfiring so the repair efforts can be concentrated on that area.  Not much advice you can get online if you can’t do that simple part.
>
> Now you are stuck with a diagnosis of ECU death since the ignition module is not available for a repair of your ECU.
> This could be a valid diagnosis since ignition module failures do occur, but I would encourage you to investigate further since a shorting coil or wiring could initiate the failure.  The forum on Quattroworld.com has an extensive FAQ section as well as many current threads on problems with these vehicles.  You may need to sort through a lot of chaff, but the information is worth the effort, and you can likely find a source for a used ECU if needed.  Where do  you live?  You may find a repair shop that has extensive experience with this ECU in the FAQ or forum also.
>
> As far as Cody’s recommendation, I have never heard of Programma Inc ever completing a repair on the ECU for this vehicle.  Although they do list some vehicles with Motronic computers, they don’t include the UrS4/6 or any Audi vehicles in their expertise or inventory.
>
> For Cody:  Do these 30 repair jobs you mention in your recommendation include any 4A0 907 551 AA Motronic units
> that were successfully repaired at this shop?
>
> Tom
> ’95 S6, 95.5 S6 avant
>
>
>> On Jan 20, 2016, at 7:03 PM,  Cody Forbes <cody at 5000tq.com> wrote:
>>
>> PS. Several places can also repair them. I highly recommend Programma Inc in
>> Florida, they have done probably 30 of them for me.
>>
>> Cody Forbes
>> Black Forest Racing
>> (704) 489-0741
>> www.BlackForestRacing.com
>> Facebook | Instagram | YouTube
>>
>> -----Original Message-----
>> From: Tom Rodriguez
>> Sent: Wednesday, January 20, 2016 6:39 PM
>> To: s-car-list at audifans.com
>> Subject: Re: [s-cars] Diagnosing misfire cause
>>
>> Folks,
>> My shop has traced the misfire to a faulty DME Ignition Module.  This is a
>> Bosch Motronic unit, part no. 4A0907551AA.  Audi wants $2,500 for a new one.
>> Any suggestions on where to get this part for less money?
>> Thanks a bunch,
>> Tom
>> Tom Rodriguez
>> '95 S6, 267k miles
>>
>>
>>
>> From: Tom Rodriguez [mailto:trodri69 at gmail.com]
>> Sent: Wednesday, December 30, 2015 6:32 PM
>> To: s-car-list at audifans.com
>> Subject: Diagnosing misfire cause
>> Folks,
>>
>> My '95 S6 is misfiring intermittently and I am trying to determine the
>> cause.  When it misfires, it does so constantly at all engine speeds and
>> under all levels of acceleration & boost, including at idle.  On some days
>> the car starts well and runs well for a while, then begins misfiring once
>> warm.  On other days it misfires when cold, and then clears up once warm.
>> I've read the technical advice provided at SJM Autotechnik on this subject,
>> which points to either a bad ignition coil, a bad POS, or a bad fuel
>> injector.  They also mention dirty plugs but mine look fine.
>> My problem is that every time I try to diagnose the cause, the engine
>> refuses to misfire.  When it does misfire, I am not in a place where I can
>> do any diagnostics.  It's very frustrating.  I'm hesitant to drive the car
>> any long distances until I figure this out.
>>
>> Thanks for any advice,
>> Tom
>> Tom Rodriguez
>> '95 S6, 267k miles
>
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