Hi folks

First post
UK CAR

944 1984
Copenhagen Blue
2.5 N/A
42k miles

The vehicle only runs with the DME sensor plug removed
With it attached it ticks over for a few seconds then the DME sends a signal to cut the engine out.
I purchased the car as a none runner and after throwing a few parts at it decided to pull off sensor lugs to see if anything would change and hey presto DME sensor plug it was.

NEW PARTS FITTED:
DME Relay
DME sensor
Fuel pump and filter
Distributor Cap
HT Leads
Rotor arm
Fuel pressure regulator
Fuel Damper (used part)
Oil /Filter/Plugs

I have bypassed the DME relay but the car still cuts out after a few seconds
The spark plugs get really black sooty deposits after running for a few mins
Fuel presure is 35 psi approx

Even though it ticks over like new there is bogging when i apply revs.
If i slowly apply the throttle it will increase rpm well up to about 4k then bog out. But Im aware this may be another issue like (AFM etc)

I have a spare AFM TPS and DME relay but nothing changes if i change them.

I took the inlet manifold off today and changed breather pipes just to try to cure the flat spot but nothing changed.

i am handy with spanners so can complete anything myself
any ideas would be appreciated.

Thank you!

 

By DME sensor, I assume you are referring to the temperature sensor.
I had an 84 BMW e24, essentially the same motronic system, that exhibited this exact symptom. It was remedied by having the DME rebuilt.

 

Removing the plug to the temperature sensor makes the ECU think the coolant is at -40C or some extremely cold temperature. It tries to compensate by dumping a ton of extra fuel to richen the mixture. That could explain the black plugs.

 

If it's the temp sensor you are referring to, I had the same problem when getting my car running after about two decades off the road. I ended up turning the wheel in the AFM 3 or 4 teeth in whichever direction made it richer.

 

I just had the ecu rebuilt but nothing changed. After swappig the afm, the car started with the dme sensor plugged in but ran really rough until warm then picked up a bit but tics over like its misfiring. When i apply pedal it revs ok. reckon the icv could be the issue?

 

Did you test the DME temp sensor to make sure its actually good? There could be some other component that is bad, or a vacuum leak causing it to run only when its ultra rich (ie: DME temp sensor unplugged).

I would first start looking for unmetered air getting in, through a vacuum leak, issue with ICV or perhaps bad AFM. Unmetered air entering the system would cause an overly lean condition, perhaps not allowing the car to run. Unplugging the DME temp sensor causes it to run overly rich, balancing out the unmetered air. Just a theory.

Testing sequences for the DME temp sensor, AFM and ICV are on Clarks Garage. Start testing components, dont guess or start replacing random parts.
https://www.clarks-garage.com/shop-manual/ts-01.htm

 

Hi just an update. I replaced the 2nd AFM with another and it runs with the DME sensor plugged in now. It idles like a bag of crap and wont rev correctly until its warm/ Its struggling to tick over ar 450 rpm but is very rough indeed. Even when its warm the tick over is terrible. Would the afm cause this or would the Idle control valve be culprit?

thanks In Advance

 

Have have checked that TPS is adjusted properly? It should click audibly(car not running) when throttle closes and click again when throttle is opened again. You can also verify by measuring the circuit.
http://www.clarks-garage.com/pdf-manual/ign-03.pdf

If that's ok then I would try if adjusting the throttle bypass srew makes it better. Someone might have messed with it.
http://www.clarks-garage.com/shop-manual/fuel-08.htm

 

HI DME TS is new and vacuums are all good?

 

UPDATE
I have had the afm rebuilt and bench tested all good.
the TPS is now working fine
DME has been refurbed

The car has decided not to run more than a few seconds before it cuts out again with the dme sensor plugged in!!
With the DME temp sensor removed it will tick over fine but only when i very slowly press the throttle will it rev.
If i press the throttle with any speed with the sensor removed it cuts out .

The DME relay is new.

Its really driving me nuts as ive eliminated more or less everything at this point

Soooo frustrating......