ECU Temp sensor issue

[karabas 21]

Hi All,

I have an awkward situation with ECU temp sensor. Car runs normal when it is cold. After 3-5 mins, runs like 3 cylinder, misfires, rev can’t climb over 3000 rpm etc.

I suspected from ECU temp but couldn’t take it out. I connected a spare one to the plug and hung somewhere.

Took her out for a test drive and everything was fine. I tested a few times with 10-20min drives. No issues detected. Ordered a blue bosch sensor and changed.

Again after 3-5min same symptoms. Same solution, connected other one to the plug and hung again. This time I drove longer. Same symptoms after 40-50mins.

I think when engine compartment got hot and the sensor detects higher temp same ignition problems occurs.

Any idea, could it be ECU problem or any other part should I check?

 

Stay at Home...

[Tom Fenton 1,542]

I think you are masking another fault by making the engine run really rich with the temp sensor just reading ambient temp say 20degC. Effectively you are fooling the Ecu into running full cold start rich all the time.

If it’s actually running on 3 I’d start with a compression test.

[SRDT 182]

Your ECU is a Motronic right? You're not only running rich but the timing can also be altered. Do you have the "check engine" light on?

[karabas 21]

Tom, I did compression test already and they were all above 170. When cold (not actually) running really nice. 

 

SRDT, although its 1993, I have Jetronic car and no check light.

[SRDT 182]

Ok so you're just running rich, the thing is that a richer mixture can "solve" many problems.

Try to find if it's only one cylinder that's faulty, if so then it's not a problem with the ECU.

[karabas 21]

I will test tomorrow. Try to pull HT leads one by one, will see what happen.

Thanks a lot.

 

[karabas 21]

After trying known AFM, 2 new coils, new fuel pump, 4 new ign amps, 2 set of new spark plugs, known ECU, new tachy relay, refurbished injectors and many many hours, nothing changed.
Borrowed a fuel rail fitted a Tomei regulator and a gauge on it. Pressure was below 2 bars. Since the fuel pump changed with a brand new one before, I didn't give any chance to that. Then I suspected on fuel filter. I put a new Bosch one but pressure was same.
Anyway, desperately I changed the fuel pump with the old one (thanks God I didn't throw away).
Instantly pressure rose up and all problems gone away.
Thanks a lot to everyone who help me.