Ecu fault?

[colrich]

Does anyone in north west UK have a spare ecu that I could try on my car, had a mechanic look at it, but failed to diagnose, suggested swapping ecu first.
Engine runs fine until gets warm an fan cuts in, then revs drop and will not rev above around 1000 rpm is irractic and drops to around 500, it's like fuel starvation but no idea really, any help appreciated

 

[Christopher]

pm sent

 

[tochi]

I am no expert, but I would be surprised if your symptoms are solely due to a bum ECU. The list of possible culprits is finite and generally ends with the ECU - rather than beginning with it.

You superficially describe a problem that seems heat sensitive, so that poor operation only occurs when the engine reaches normal or above normal operating temperatures. This could easily be caused by a cold start system that is not fully disengaging, including disconnected or non-functioning temperature sensors, or a cold start injector that fails to completely shut off. One obvious scenario: if your vehicle has been sitting for a long period or it has seen limited maintenance, it is possible that coolant passages in which the bottom-most temp sensor and/or auxiliary air valve (14) sits, are clogged and not impacting the sensor or the air valve. The fuel injection system might function as though the engine is cold (despite it being warm or hot). Instead of fuel starvation, it would create a fuel rich or “flooding” situation. Neither scenario is a good one. This is not to say that there are other possible causes of your problem - given the limited information you provided.

Good luck


Note parts at center left containing auxiliary air valve

 

[colrich]

Thanks Tochi, the car has been standing for 10+ years so I'll look at taking the aux valve off an have a look .

 

[Midwestbike]

I had to replace my auxiliary air valve a few years ago. I could get it to start and run cold but not hot or I could get to run well hot but be almost impossible to start cold or I had to keep it at a ridiculously high idle rpm. I got mine from a guy in Norway that rebuilt them, but there is a Mercedes one that is angled the other direction.

 

[sandhu]

I had to replace my auxiliary air valve a few years ago. I could get it to start and run cold but not hot or I could get to run well hot but be almost impossible to start cold or I had to keep it at a ridiculously high idle rpm. I got mine from a guy in Norway that rebuilt them, but there is a Mercedes one that is angled the other direction.

Do you have the details of the guy that rebuilds them ???

 

[Midwestbike]

I can’t find my emails but quickly searching found this not too old write up about the MB version. https://www.benzworld.org/threads/auxiliary-air-valve-overhaul-aav.3029326/

plus there is a site that rebuilds yours for $200.

AAV Element for Bosch Auxiliary Slide Valve - Repair Your Valve and Save $$$$

WELCOME TO FUEL INJECTION PRODUCTS WE SPECIALIZE IN BOSCH FUEL INJECTION SYSTEMS Repair Your Own Auxiliary Air Valve With Our Thermo Heating Element Assembly. Will Work with: Bosch Valve 0280140013 For Volvo Bosch Valve 0280140017 For Mercedes-Benz Bosch Valve 0280140018 For BMW Bosch...

fuelinjectionproducts.com

 

[tochi]

I have seen a few amateur attempts at bypassing a poorly functioning auxiliary air valve, including the inclusion of what might have been a choke assembly from a small lawn mower. One suggestion from the Porsche crowd seems "slightly" promising: installing a a manually controlled heater valve to close off the air flow. In dealing with a different style of auxiliary air valve (electric) the source suggests using a Porsche 944 heater valve in conjunction with the cold start valve. Being unfamiliar with the inlet/outlet diameter of the heater valve, it is unknown whether this would be a direct or near-direct fit for the original rubber hose/tubing.

As they say, "necessity is the mother of invention."

A somewhat common mod on a lot of bosch l-jet cars is is delete the AAV and it its place put an early 944 heater valve and a cable in its place.

https://rennlist.com/forums/924-931-944-951-968-forum/691746-aux-air-valve-delete.html#post9454426

To do it you would need to fabricate a mount for the valve and then you would need some way to actuate it. My first thought was to go to aircraftspruce.com and I found this which I think would work really well.

http://www.aircraftspruce.com/catalog/appages/a730.php

https://rennlist.com/forums/924-931-944-951-968-forum/691746-aux-air-valve-delete.html#post9455005

 

[Frankie123]

Do you have the details of the guy that rebuilds them ???

@sfdon rebuilds these. He rebuilt mine about 3 years ago. Been perfect since

 

[sandhu]

Frankie 123… thanks for the info

 

[jvrenaudon]

I have a spare you can try (red spot). I am confident that it works fine. I am at CW3 9LQ and on 07860 515049. Best, John.

 

[sfdon]

Finish this week..

 

[sfdon]

Waiting for your core….

 

[boonies]

Waiting for your core….

And a new bucket of M&M’s…