1991 300TE-24V Intermittent Misfire

[kevinnathanael]

I have a 1991 300 TE–24V M104 engine with the following symptoms:

• Use the vehicle up to warm (doesn’t have to reach 80 degrees C), sometimes only a 15 min drive
• Leave the vehicle for 30 mins – 1 hr (this is vital since if I restart the car immediately, there is no issue)
• Upon restart, sometimes the car would misfire, but not all the time
• Sometimes switching the car off then starting it back up immediately would make it normal
• Other times it may have difficulty starting, or misfire would continue and car would have no power with low idle rpm and rough running. (Some times I would restart 20+ times and misfire still continues, I would have to wait a longer time to let it sit till it goes normal again)

Parts that have been changed since I owned the car:

• 8 spark plugs (correct Bosch non-resistance)
• One of the two fuel pumps (since the other is normal)
• Fuel accumulator
• Idle control valve (Bosch)
• Air flow Potentiometer
• Distributor cap and rotor (both Bosch)
• Bosch coil
• Camshaft Position Sensor
• ECU switched to another used unit
• OVP Relay switched to another used unit
• MAS Relay switched to another used unit
• Crankshaft position sensor cable switched to another used unit
• HT Leads seem to be new (Beru)

Can anyone help guide me as to where else to look for? I’ve tried going to several mechanics without any results since they have difficulty in replicating the misfire issue, since sometimes just by restarting the car immediately it becomes normal.

 

[grober]

These cars are notorious for suffering from condensation in the distributor body---especially in humid conditions. OK when the engine is cold but then engine heat evaporates any moisture deep in the distributor body whicch migrates into the cap area causing HT shorting across the cap interior surface--try using a hair drier to really dry out the inside of distributor metal body to affect a cure.

 

[kevinnathanael]

I’ve recently changed the distributor cap and rotor with Bosch. Is there anything else I can do to mitigate this moisture issue?

 

[neilrr]

ECU switched to another used unit

ECU = EZL?

 

[kevinnathanael]

Yes ECU switched, the one near by the battery, not the EZL ignition control module. I haven’t changed that

 

[ray_hennig]

EZL ignition control module. I haven’t changed that

Unlikely I think. My experience is that these either work or not. But do buy a spare as they are increasingly rare.

As said in 2 other places, I had something similar and it was the injectors dribbling fuel while the warm engine sat for half an hour. On start-up it would misfire for a while and then clear. A morning's work, new injectors, guides and seals and normal service returned. Costly but satisfying.

As for HT, these engines demand the best. In 2020, I replaced the entire HT system, from coil to plugs, with MB original parts, leads included. I am more confident now than I have been for years.

Before the refit, I had a 9 month old Bosch distributor cap (fitted by cowboys in Toulouse) that was cracking around the centre electrode, but still working. That came out in favour of the new Bosch MB one and that, after 2 years still looks like new.

Is there really such a difference between Bosch MB and Bosch aftermarket??? They look similar when new.

The shield behind the rotor arm should also be in good nick so if it's old, get a new one.

Good hunting.

RayH

 

[ray_hennig]

These cars are notorious for suffering from condensation in the distributor body---especially in humid conditions.

So often this is said and I'm not disagreeing. But I have never had that problem despite the car living outside 27/7 in temperatures from -5 to 40+ and loads of rainfall and fog.

Alwyas prompt cold starts unless I'd fried the EZL!!!

RayH

 

[ray_hennig]

ECU = EZL?

I assume not. I think he refers to the KE controller:

R

 

[Bellow]

Along with moisture in the distributor,

injectors dribbling fuel while the warm engine sat for half an hour.

the above is where I'd look. Pressure bled from leaking injectors can create fuel vaporisation which compromises hot starts. Especially so in warmer climates.

 

[ALFAitalia]

So often this is said and I'm not disagreeing. But I have never had that problem despite the car living outside 27/7 in temperatures from -5 to 40+ and loads of rainfall and fog.

Long days where you live......!

 

[ray_hennig]

Long days where you live......!

Haha. Drunk again. Another product of where I live.

R