1991 300TE-24V Intermittent Misfire
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1991 300TE-24V
1991 300TE-24V Intermittent Misfire
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)
- 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)
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Joined: Mar 2016
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From: SF Bay Area, CA
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
Non repeatable/random issues like this are almost always electrical. Most likely a relay is failing (could be part of a electronic control box not necessarily in the fuse box)
You have replaced quite a few parts with no success there. Some would have no involvement in this issue like the Camshafft sensor, AFM pot.
You will need some diagnostic testing on this.
What I can say is that it is never a good idea to only replace one fuel pump. If one failed the second is most likely right behind it.
I replace mine every 100K miles before they fail (like is 100K-150K miles)
I doubt the pumps are your issue though.
I did not see EZL on your list but that part hardly fails on these cars, particularly the Bosch one but Siemens is probably fine too.
Seems the foul state is random but once in that state, you should take measurements of the following:
(1) measure timing with a strobe light when it is running rough
(2) Measure duty cycle
(3) measure 0xygen sensor output
(4) measure voltage on the IACV as it is running by inserting probes in the connector
You have replaced quite a few parts with no success there. Some would have no involvement in this issue like the Camshafft sensor, AFM pot.
You will need some diagnostic testing on this.
What I can say is that it is never a good idea to only replace one fuel pump. If one failed the second is most likely right behind it.
I replace mine every 100K miles before they fail (like is 100K-150K miles)
I doubt the pumps are your issue though.
I did not see EZL on your list but that part hardly fails on these cars, particularly the Bosch one but Siemens is probably fine too.
Seems the foul state is random but once in that state, you should take measurements of the following:
(1) measure timing with a strobe light when it is running rough
(2) Measure duty cycle
(3) measure 0xygen sensor output
(4) measure voltage on the IACV as it is running by inserting probes in the connector
MBWorld Fanatic!
Joined: Mar 2016
Posts: 1,369
Likes: 195
From: SF Bay Area, CA
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
Sorry, I need to revise my advice. Did not pay attention to the fact that it is an M104. Those are known to have some EZL issues.
Unlike the M103 EZL's that are rock solid the M104 with KE-Jetronic are not so. I have read a lot of stories about the ever dying EZL.
Although they tend to cause a no start.
And the camshaft sensor that is just a diagnosic tool on the M103 must have an actual function for the M104. But you have already replaced it.
I would put the EZL on top of the list as item (0). See if the timing strobe light will tell you anything.
Unlike the M103 EZL's that are rock solid the M104 with KE-Jetronic are not so. I have read a lot of stories about the ever dying EZL.
Although they tend to cause a no start.
And the camshaft sensor that is just a diagnosic tool on the M103 must have an actual function for the M104. But you have already replaced it.
I would put the EZL on top of the list as item (0). See if the timing strobe light will tell you anything.
