MC2 running lean

Thu Mar 8 16:55:50 PST 2012

I sent this earlier but it never seemed to go through the listserver...maybe 
because of the hyperlinks to the ECU's I'd found on the web...so here it is 
again...hyperlinks removed...anyone wants the links, email me directly.
--------------------------------------------------
From: mboucher70 at hotmail.com
Sent: Thursday, March 08, 2012 9:15 AM
To: quattro at audifans.com
Subject: Re: MC2 running lean

Not familiar with MC2, but I have a 1990 where a single path of etching on 
the circuit board of the ECU had corroded.  I think that the etching of some 
of the electronics boards of that vintage was paper thin, and after 21+ 
years it just gave out.  Problems like that, or the infamous bobbing 
speedometer problem come to mind, and I've got to echo Huw's suggestions 
below about opening up the ECU.

In my case, 15 minutes with a multimeter had identified what contact was 
broken, and another 30minutes of micro soldering and the job was done.  That’s 
the short version but I'll go with that for now.

I did a quick search for the ECU for your car and turned this one up...not 
bad for $129.
(link removed)

or this one on ebay with the bid now at 56EUR ($74):
(link removed)

Worst case, its not the ECU, but you've eliminated it as the problem, and 
you've got a spare ECU for about $100, which is probably a good spare to 
have if you plan to keep the car .  Or resell it.

In my case, even after repairing the original ECU, I replaced it with a 
spare from Force5, with the logic that where there's one bad path on the 
circuit board, others might be developing.  I'm guessing you've already 
checked with Force5 and they didn't have your ECU, but if not, its worth 
checking.

Seems that you've traced all the failure points from the tank and fuel pump 
on forward.  So its either revisit those, or dive into the abyss of the ECU 
!

good luck
MC

--------------------------------------------------
From: "Huw Powell" <audi at humanspeakers.com>
Sent: Wednesday, March 07, 2012 9:52 PM
To: "Dag Bøsterud" <dag.boesterud at little-e.com>
Cc: "'Steve Buchholz'" <urq at pacbell.net>; <quattro at audifans.com>
Subject: Re: MC2 running lean

> It has been suggested that your ECU may be the fault, but you have no
> access to another one to swap.
>
> I would consider removing it, and bringing it to the bench, opening it
> up (how hard is that? easy? impossible?), and looking for corrosion,
> cold solder joints, signs of burnt components, etc.
>
> Also take a good look at the connection terminals on the ECU and on the
> cable that goes to it.
>
> On 3/7/2012 3:12 AM, Dag Bøsterud wrote:
>> New Bosch injectors with seals
>>
>> New Bosch 040 fuel pump. Measured voltage at pump at 13,76 V.
>>
>> Pump flows 790 ml (26,71 oz) / 30 seconds. This is within spesifications 
>> I think.
>>
>> New fuel filter
>>
>> All hoses in the engine compartment are new
>>
>> All sensors are new
>>
>> Replaced the fuel decel valve (fuel cut valve)
>>
>> Visually inspected the fuel pump relay. Looks good, but tested it with 
>> another one. No difference.
>>
>> Checked fuel, residual and control pressure. All good according to the 
>> Bentley Manual
>>
>> Tried running the car without the oxs connected. No difference.
>>
>> Visually inspected for vacuum leaks, and pressure tested the system at 
>> 1,5 bar. Plugged the ECU first not to damage the ECU. Can't find any 
>> leaks.
>>
>>
>>
>> The car runs lean on all cylinders, all spark plugs have the same color. 
>> Nearly white.
>>
>>
>>
>> So, this is what I've done that I can think of on top of my head.
>>
>> Remember that the car was working 100% with correct mixture/idle, and the 
>> problem startet gradually, then one day *boom*... undriveable. :/
>>
>>
>>
>> /Dag
>>
>>
>>
>>
>>
>> Fra: Steve Buchholz [mailto:urq at pacbell.net]
>> Sendt: 7. mars 2012 08:00
>> Til: Dag Bøsterud
>> Kopi: quattro at audifans.com
>> Emne: Re: MC2 running lean
>>
>>
>>
>> MC-2 is still based on CIS, there really isn't that much the ECU does to 
>> control mixture.  If you disconnect the OXS fueling is completely 
>> mechanical.
>>
>> You say that you tried everything, did that include checking the fuel and 
>> control pressures?
>>
>> Sometimes a problem in one cylinder can affect the operation of all. How 
>> do you know the whole engine is running lean? Have you checked spark 
>> plugs?
>>
>> I realize that you say that you have tried everything, but without a 
>> comprehensive list of tests and results anything any of us can recommend 
>> would not be much better than a shoot in the dark. That said, I think the 
>> likelihood that the ECU is causing a lean running condition is low.
>>
>> Steve Buchholz (mobile)
>>
>> ----- Reply message -----
>> From: "Dag Bøsterud"<dag.boesterud at little-e.com>
>> Date: Tue, Mar 6, 2012 2:35 pm
>> Subject: MC2 running lean
>> To: "'Mark Rosenkrantz'"<speedracer.mark at gmail.com>
>> Cc:<quattro at audifans.com>
>>
>>
>> Noo. Can't get hold of a MAC-14.
>> I can buy one off of eBay from Germany, but some seller will charge me 
>> like €425. I won't pay that.
>> That's way too expensive.
>>
>> Do you have a spare?
>>
>> /Dag
>>
>> -----Opprinnelig melding-----
>> Fra: Mark Rosenkrantz [mailto:speedracer.mark at gmail.com]
>> Sendt: 6. mars 2012 23:30
>> Til: Dag Bøsterud
>> Kopi:<quattro at audifans.com>
>> Emne: Re: MC2 running lean
>>
>> Yes, have you swapped it?  If all other reason fails, I often look at the 
>> ECU as the issue.... Sometimes, it is!
>>
>> Mark Rosenkrantz
>> Typos sent from my iPad
>>
>> On Mar 6, 2012, at 5:22 PM, Dag Bøsterud<dag.boesterud at little-e.com> 
>> wrote:
>>
>>> ECU like in Engine Control Unit :p
>>>
>>> /Dag
>>>
>>> 1990 Audi 100 Turbo Quattro Sport Exklusiv
>>>
>>>
>>> -----Opprinnelig melding-----
>>> Fra: Mark Rosenkrantz [mailto:speedracer.mark at gmail.com]
>>> Sendt: 6. mars 2012 23:11
>>> Til: Dag Bøsterud
>>> Kopi:<quattro at audifans.com>
>>> Emne: Re: MC2 running lean
>>>
>>> ECU?
>>>
>>> Mark Rosenkrantz
>>> Typos sent from my iPad
>>>
>>> On Mar 6, 2012, at 4:52 PM, Dag Bøsterud<dag.boesterud at little-e.com> 
>>> wrote:
>>>
>>>> I've for a long time been troubled with my 1990 Audi 100 TQ MC2-engine
>>>> running very lean. From June last year the car has been virtually
>>>> undriveable. You name it, I've replaced it, tested it and tried it. 
>>>> Hoses,
>>>> sensors, injectors, fuel pump, filters... brand new and double checked.
>>>>
>>>>
>>>>
>>>> I read on the SJM-page that if you disconnect the temp sensor for the 
>>>> ECU,
>>>> the car will run rich and pulse the cold start valve due to the fact 
>>>> that
>>>> this is an NTC-sensor.
>>>>
>>>> I disconnected the sensor in my car, and the car won't start. No way. 
>>>> Quite
>>>> the opposite of what it's supposed to do...
>>>>
>>>>
>>>>
>>>> ...how can this be???
>>>>
>>>>
>>>>
>>>> /Dag
>>>>
>>>> 1990 Audi 100 Turbo Quattro Sport Exklusiv
>>>>
>>>> _______________________________________________
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>>>
>>>
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