M20 Misfire (Please help....)

[quikveedb2]

fuel pump relay & coolant temp sensor did not fix the problem for me...

[DTMbimmer07]

i just replaced the two sensors ontop of the thermostat and my car started right up and is running good now.

[quikveedb2]

i just replaced the two sensors on top of the thermostat and my car started right up and is running good now.

which ones?

[iamsam]

i just replaced the two sensors ontop of the thermostat and my car started right up and is running good now.

wait what? as in no misfire? this worked for you?? please post a pic of these sensors.

[quikveedb2]

2nd!

[DTMbimmer07]

alight ill take pictures tommorow morning.

[sticksdaman]

He's talking about the water temp and coolant temp sensors. I've already done those, along with a valve adjustment and a good cleaning on the connections of my distributor.

I've followed the troubleshooting list in the bentley and the only other thing that stands out to me would be vacuum hoses.

Maybe you guys will have better luck than I did. The sensors are worth changing out in any event, I've noticed significantly lower engine temps since.

Best of luck with a solution, I'll try and keep you updated with my findings.

[quikveedb2]

i ran through the bentley's motronic control unit electrical tests today and could not get the main relay, fuel pump relay control, or any of the fuel injectors to click as the bentley indicates they should when tested. wtf? the voltage to the control unit, main grounds, throttle switch, reference sensor, temp sensor, icv, and airflow sensors all had the correct test values. i dunno what the hell is going on. i'm wondering if the main relay is bad but wouldn't the car just not run at all? i don't plan to replace the cps now, since it tested within specs for resistance both at the control unit and at the connection to the harness...

i"m gonna start runniging ignition diasgnostics this afternoon...

[Quailane]

i ran through the bentley's motronic control unit electrical tests today and could not get the main relay, fuel pump relay control, or any of the fuel injectors to click as the bentley indicates they should when tested. wtf? the voltage to the control unit, main grounds, throttle switch, reference sensor, temp sensor, icv, and airflow sensors all had the correct test values. i dunno what the hell is going on. i'm wondering if the main relay is bad but wouldn't the car just not run at all? i don't plan to replace the cps now, since it tested within specs for resistance both at the control unit and at the connection to the harness...

i"m gonna start runniging ignition diasgnostics this afternoon...

You need to short pin 36 to ground for the main relay to "click." With that still in there short the other pins to ground to get the other things to work. I actually was just doing this today.

I actually have the same problem. Cold the engine runs great. The car becomes almost undriveable when warm and will take a while to start when warm. The car idles perfectly fine when warm though. When driving along for no rhyme or reason the entire engine will misfire and I have to baby it along. I am talking in 5th gear going 35mph barely touching the throttle or else the engine misfires. I have checked almost all the electrical things in the bentley but no dice. Everything reads fine at the harness.

[iamsam]

wow this sounds like a really common problem with the M20. wonder why there is no DIY out there to fix this problem. I am beginning to like M20s less and less.....

[nando]

it's common because of how poorly maintained most 20 year old cars are, not because the M20 is a bad motor.

Motronic 1.3 is really simple, it's just not easy to diagnose problems like this over the internet.

[iamsam]

it's common because of how poorly maintained most 20 year old cars are, not because the M20 is a bad motor.

Motronic 1.3 is really simple, it's just not easy to diagnose problems like this over the internet.

siiiigh...... too true...

[Quailane]

wow this sounds like a really common problem with the M20. wonder why there is no DIY out there to fix this problem. I am beginning to like M20s less and less.....

Yeah, I miss my M50 sooo bad. All I ever did to it was change the air filter and the oil. This M20 leaks oil all over, gets worse mileage, and has tons of problems, and it only has 100k on it opposed to the 180k of the M50, both of which were made in '92!

it's common because of how poorly maintained most 20 year old cars are, not because the M20 is a bad motor.

Motronic 1.3 is really simple, it's just not easy to diagnose problems like this over the internet.

It isn't exactly easy in person when everything checks out within specs. Also maintenance isn't really an issue here as none of the parts that cause these problems have any sort of maintenance schedule.

[iamsam]

Yeah, I miss my M50 sooo bad. All I ever did to it was change the air filter and the oil. This M20 leaks oil all over, gets worse mileage, and has tons of problems, and it only has 100k on it opposed to the 180k of the M50, both of which were made in '92!

+1 to this.


The M50 in my wife's car has about 240k miles, and runs without a flaw, and doesn't leak anything. Because the M50 has dual over head cams, and 24 valves, it is much more efficient than the 12 valve M20 with one cam and rockers. From what i hear, an M50 swapped E30 gets better gas mileage than the stock M20. It seems like a win-win situation if you can successfully do the swap.

[Quailane]

Right now I have a hunch that I'm going to try out later. When at WOT or idle, the engine runs in open loop mode. If after getting the symptoms I give it WOT and the engine doesn't completely misfire, I know there is a problem with one of the sensors and/or its path to the DME. It should make it easier to narrow down.