R129 M119 Misfire when hot, no ideas left!

[Rogerkuala]

Hi, 1995 R129 in overall excellent condition. Runs great when it's cold (although I live in Malaysia where 28c is cold!) but after 15 mins starts to misfire on one or two cyls. On full throttle accelaration feels like cutout or backfire, big hiccup but recovers. On crank sometimes when hot, kicks back like a motorcycle if that makes sense, firing out of sequence. Had new dist. cap, leads, coils, plugs, swapped out the EZT to test, STAR says knock sensors faulty but seems strange one to me. Plus the sensors are NLA here Am I missing something?

 

[neilrr]

EZT = EZL?

 

[Rogerkuala]

EZT = EZL?

Lol yes, doh, sorry. Star Wars impending movie fever I must have E.T. on the brain or something. EZL

 

[ivan1983]

1995 falls within the period for biodegradable wiring looms.
Have both of yours been changed /checked?

 

[Flyinspanner]

If knock sensor is breaking down when hot, it will back off the timing as it is defaulting to sensing pre det, so you get a sudden slight timing change which you may experience as jerkiness/misfire.

Change the sensor, clear codes and see how it goes.

 

[Rogerkuala]

If knock sensor is breaking down when hot, it will back off the timing as it is defaulting to sensing pre det, so you get a sudden slight timing change which you may experience as jerkiness/misfire.

Change the sensor, clear codes and see how it goes.

Ah OK, thanks. Sensors are NLA here but they seem to be pretty universal. The odd thing is it's a regular misfire, like the car runs on 6 cylinders. The exhaust note gets a definite rhythmic "pop" and power drops, and it runs with vibration. More than a timing change but that would explain the jerk on full throttle for sure. It may of course be a combination of things since the car stood for 2 years before I bought it and it's always done this (2 months) but getting worse

1995 falls within the period for biodegradable wiring looms.
Have both of yours been changed /checked?

Not as such, the car was seen by a brand specialist who looks after maybe 10 R129's in the club here. I'm going back in the morning and I will ask him. Thanks for the pointer!

 

[grober]

I imagine your engine electronics will be very similar to the W140 described here.
K6JRF Auto Page
Specifically
K6JRF Auto Page

There's no sign of head gasket failure is there?

 

[alabbasi]

Distributor insulators , common issue

 

[Rogerkuala]

I imagine your engine electronics will be very similar to the W140 described here.
K6JRF Auto Page
Specifically
K6JRF Auto Page

There's no sign of head gasket failure is there?

No thank goodness. Just had it up on a lift and physically inspected the knock sensors, one has the wires hanging out of it Culprit found I think. It matches the DTC error code 5. That article was really useful, thank you very much!