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94 e220 two cylinders down when warm

2K views 4 replies 3 participants last post by  john_tul 
#1 ·
Hi everyone,

I have a on-going mystery problem which doesn't appear to have been solved in any other forum.

I have a w124 1994 E220 7 seater, engine type m111.960 (HFM Sequential MultiPort Fuel injection System). The ECU on it is a VDO unit, merc number 016 545 96 32, current replacement Bosch part number 016 545 55 32.

Basically, what is happening is that once the engine is fully warmed up, the ECU shuts down fuel and spark to cylinders 1 and 4. So far, I have eliminated plugs, coils, harness, crankshaft position sensor, HT leads and Lamda sensor.

The problem appears to be purely temperature related because exactly the same problem arises when I am driving the car to operating temperature on the road or simply leave it idling at a standstill, in park, for about ten minutes or so, without even touching the accelerator.

I have read the error codes and I am getting only one error code, 21 which refers to "Ignition output 3 (or ignition coil cylinder 1 and 6)" but I have tried a new coil for cylinders 1/4 and this made no difference and I have checked the harness for open and short circuits.

The ECU specialists on the Isle Of Wight reckoned it was likely to be an ECU failure but I would appreciate knowing if anyone else has hit this problem before I opt for an expensive ECU repair which may not solve the problem.

Thanks:
 
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#2 ·
Hey,

Have you replaced the wiring harness? Or just checked the visible componentes?

My e220 had the ECU fried from the dreaded wiring harness problem, but it would still start and drive. Just had a bit of a high idle...

On my case the problem was in the harness and it was on a part that you cannot see: indise the main ECU plug. The wires were a complete mess, all cracked and shorting.

Something tells me that your ECU is gone... I'd start with the harness replace and then the ECU...

check Euromerc for a replacement ECU, I got mine from them for a good price.
 
#3 ·
Hi there, thanks for the reply, I have only done a visual check plus I have checked the leads for open and short circuits with the ECU connector disconnected and the coil and injector connectors disconnected.

But why does the car run perfect whilst it is running up to temperature ?

Still puzzled but thanks the thoughts. I guess I could try a harness repair kit.
 
#4 ·
because the engine starts off in open loop when it is cold, the engine is basically running without any feedback or control from any of its electronics. When it reaches operating temp it goes into closed loop and starts getting feedback and control from things like the 02 sensor, temp sensors, ECU, etc.
 
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