M20 wont start all of a sudden

[ezlnh8u]

Hello, I have a 74 2002 withc a 91 m20 swap, over the weekend, the car stopped turning over, I never have had any issues with this motor. Have been driving it for about 2 years, currently 10k miles on the motor. I parked the car after my Sunday drive for about 2 hrs. Came back to it to leave home and the car wouldn't start. It will crank but does not turn over.

We checked the starter/Battery, fuel pump/main relay,coils, distro, Maf, crank sensor. And everything seems except for the ECU, it's not sending any power out. Any suggestions or how to's on how to check the ECU?

[Jaxx_]

How did you check parts like the fuel pump and coils?

[ezlnh8u]

Fur the fuel pump I can here it primer and by passed the relay.. Coils were tried on another car.

[Jaxx_]

I assume you have checked fuses, and that your harness is not modified for the swap.

confirm power at pin 27 at the ECU during start/run.
pin 36 on the ECU should be grounding, but from the wiring diagrams I am not sure on the conditions. Pin 36 is your main relay control. If it is hard to probe pin 36 on the ECU, probe pin 85 on the main relay.

[ezlnh8u]

Replaced the ECU and no change. I went back too the main relay, and swapped it it again with another new one. and the car finally turned on. But now a new problem started. There is black smoke from the exhaust and the smell of Fuel, seems as it is running rich.

Note that the car was running fine before this whole starting problem started. I am assuming I should check the plugs, FPR adn maybe the o2 sensor next? possibly leaking injector or injectors causing this now?

[Cayoncrusier93]

Replaced the ECU and no change. I went back too the main relay, and swapped it it again with another new one. and the car finally turned on. But now a new problem started. There is black smoke from the exhaust and the smell of Fuel, seems as it is running rich.

Note that the car was running fine before this whole starting problem started. I am assuming I should check the plugs, FPR adn maybe the o2 sensor next? possibly leaking injector or injectors causing this now?

When the battery died the memory of the ECU of the AFR’s got deleted. Once you put some miles on it that take it throughout the RPM range, it should fix itself.

[ezlnh8u]

When the battery died the memory of the ECU of the AFR’s got deleted. Once you put some miles on it that take it throughout the RPM range, it should fix itself.

I don't think a dead battery will wipe a DME to nothing? I could be wrong.

[Cayoncrusier93]

I don't think a dead battery will wipe a DME to nothing? I could be wrong.

Has happened to me multiple times.

[ezlnh8u]

Has happened to me multiple times.

It is literally impossible to drive down the street. Idle jumps and drops, almost as if it’s only working on 2-3 cylinders, I need to keep giving it gas to move slightly.

[Cayoncrusier93]

It is literally impossible to drive down the street. Idle jumps and drops, almost as if it’s only working on 2-3 cylinders, I need to keep giving it gas to move slightly.

If it’s that bad it might be another issue. It should be very driveable just rough.

[ezlnh8u]

I am assuming, check the wires and plugs 1st, than go from there?

[ezlnh8u]

Will do O2 sensor and check all the plugs and wires, before tackling any deeper issues, unless someone has any other suggestions?

[Jaxx_]

You are on the right track. Confirm plug wires are correct. I doubt that there is anything else wrong with the car. If it ran before you messed with it, and the only thing that has changed in the main relay to get it running again, it is something that you touched.

Generally the O2 sensor won't have enough authority to modify fueling so much that it will cause the car to run poorly. If you have so much extra fuel that you smell it, likely some cylinders aren't firing.

[george graves]

air, fuel , spark.

90% of the time it's spark. Pull a plug and see if you can see it spark.

Jaxx_ has a good point, if you smell fuel, it's not firing.

[ezlnh8u]

You are on the right track. Confirm plug wires are correct. I doubt that there is anything else wrong with the car. If it ran before you messed with it, and the only thing that has changed in the main relay to get it running again, it is something that you touched.

Generally the O2 sensor won't have enough authority to modify fueling so much that it will cause the car to run poorly. If you have so much extra fuel that you smell it, likely some cylinders aren't firing.

Thanks for the info, if there is no spark, that indicates to check, cap and r? Any.other relays?