MC2 running lean

[Dag Bøsterud]

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
>> 
>> _______________________________________________
>> quattro mailing list
>> http://www.audifans.com/mailman/listinfo/quattro
>> http://www.audifans.com/kb/List_information
> 
> 
> 
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