Mefi1 guys please HELP! 502 efi GenV problems with Mefi1
 

Hi,
Long time Reader, first time I post here.
I just bought a GenV 502 EFI Mefi1 egnine. Tried to start and it ran, but only in idle. If you try to accelerate it will stall.
I read the codes, Code 33, Code 42.
On Code 33 MAP sensor, I did just replace MAP sensor but same Code. I started to measure all the references regarding to the Manual 23, Sensor works great, harness is ok, even the ECU shows the right voltage readings on the Rinda tester. Don't know why it always sets the code, maybe toast ECU?

Code 42 is more difficult. The Ignition doesn't change from Distributor Mode to ECU mode. I replaced the Ignition module in the distributor and the pickup coil. Same code. I started measuring all the voltages and Ohms referring to the Manual.
The manual says i shouls unplug J1 and J2 connectors from the ECU, ignition on. Measure Ohms on 423. should be over 3000. trigger 424 with positive, 423 should change from over 3000 ohms to unter 1000 ohms.
BUT: when i measure Ohms, I have unter 1000, and when i trigger 424, I get over 3000. So it does exact the opposite thing what it should do. replaced the ignition module a second time, no changes.
Later i found that when I unplug the ground wire connection from the mefi harness, it is as it should. same when i unplug the 2-pin connector between ignition module ion dist. and the ignition Coil.
Thought maybe bad Ign. coil,and replaced. Same. Checked harness completely, all grounds OK, no shorts, no opens in harness.
Problem is, I got the engine as is, I never seen it running properly and noone knows what happend to the engine and who meddes around with it.

Hopefully someone can help!

Thanks
Phillip

Is the ground a "good" ground? Have you checked for resistance between the location where that ground was connected, to the negative battery terminal?

Yes,
The ground is good, nearly 0 ohms. The ecm has also a reference ground to that sensor, wich is also 0 ohms from sensor to the ecm terminal.

the engine is on a crate, no battery is hooked up, it gets power from a power source.

Explain this power source. Thanks.

this is a 230V to 13.5V converter (230v because I'm in europe) wich is hooked up to the 10pin plug and to the engine battery + and - ports.

Being a MEFI 1 it might have a VST and should be using manual 16. Tell us more about the motor, VST or cool fuel, TB or EST ignition. With code 42 it should have EST

Yes it has the VST system. The distributor, I don't know what is what, so how can i identify? it is the distributor with the pick up coil and the ignition control module inside it. 2 connectors, the 4-pin is all for the ECU, Ref LOW, REF HI, BYPASS and IC. the 2-pin is + and "C" to the ignition coil.

Please don’t continue doing this.

Batteryless efi systems (motorcycle, snowmobile, etc) use a capacitor (my sled uses a 22,000uhf) in place of a battery.

Please install a battery. Also make sure alternator is charging. Your ECU and electrical system will thank you.

Okay thanks for the input!

Okay I just looked up in my Manual #16, it says the same. 423 should have over 3000 ohms to ground, and when i trigger 424, 423 should drop the ohms to under 1000. My module does it the opposite way. except when I remove the ground wire of the EFI harness. then it will do it the right way.

Merc Est / gm voyager / gm late model external coil hei / etc, etc. Has lots of names


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yes should be this one. replaced the pick up coil ant the module serveral times. always used heat paste under the module.

It has EST ignition
Are you getting 5V on pin J2-24 Bypass?
Is there 5V reference at the MAP pin C and at TPS pin C?


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I would not continue to troubleshoot anything until a battery and alternator is put into service and there are still issues. . My 02.

Agree

I have 5v on MAP and TPS. On J2-42 I have no 5V but let me check that twice.

Okay I first install a battery. Alternator is charging when engine runs.

Without 5V there, then the EST is not transferring timing to the ECM

When you say you have 5V on the others, is it exactly 5V or close to?

delete wrong post

okay yes I will check that right now. yes the ecm doesnt transfer it to rcm mode because the ohms on the j2-23 is not what the ecm needs. in distributor mode I should have over 3000 ohms at j2-23 but i have 1000. if i disconnect the ecu and give 5v to j2-24 , i have 5000 ohms on j2-23. just the opposite way what it should be like.

okay i hookes it up to a battery, didnt change something. on tps and map i have 4.99V from the ecu coming.

on j2-23 i have 5000 ohms and 1000 ohms when i trigger j2-24, but only with ignition off. referring to the manual i should test that with ignition ON, but then I have 1000 ohms on j2-23 and 5000 when i trigger j2-24. so with ignition on it doesnt do what it should do.

how do you have the ignition switch wired into the cannon plug ?
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the right hand cable is connected to the battery negative, together with the big ground cable off the engine block. the lefthand cable is connected to the battery + together with the big cable from starter motor.

4.99 is good enough
Circuit 423 should key ON = no more then 0.5V motor running = 1.2V
Circuit 424 should key ON = no more then 0.5V motor running = 4.5V

Did you get the module from GM or Merc?

key on 423 is 0.04v
key on 423 is 0.00v
on j2 connector without ecm hooked upstarting the engine isnt possible right now because i have disassembled the intake manofold to check the harness.

i have 2 modules, thought maybe the 1st was bad. both are merc

are you sure that gnd wire in the plug is in the correct pin ?

https://cimg1.ibsrv.net/gimg/www.off...5ae40259c4.jpg
refereing to this it should be right

did try everything. don't know what to do now with this. anyone?

Did you get the intake back ON, and if so what are the voltages with motor running

Okay something interesting happened to me. What I tried was, Igniton off, apply DVOM to 423, IGNITION ON. Measure ckt 423 to ground, should be over 3000 Ohms. apply + to ckt 424, Ohms on 423 should change to under 1000. It did the reverse thing. Ohms were unter 1000 and when i applied + to 424 it changes ohms on 423 to over 3000.

I have seen the manual says IGNITION ON in chapter "7.4mpi/8.2MPI MEFI1".
Inchapter "7.4MPI Mefi1" it says IGNITION OFF.

With the Ignition OFF, everything is okay, I have over 3000 Ohme in CKT 423 and under 1000 Ohms when i apply + on CKT 424.

Maybe i just had the wrong chapter in the manual? My Engine is a 502 EFI GenV F419717

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You should be using manual 16 for VST and MEFI 1
Manual 23 is for cool fuel and MEFI 3

Okay i just looked in the Manual 16. It says ignition ON. so my ignition does not work as it should.

Don't know what to do now.
3rd Ignition control module
2nd Ignition coil
2nd pick up coil
Harness has no opens or shorts

Why does my ignition module have under 1000 Ohms and changes to over 3000 ohms when i apply 12v+ on ckt 424? should be the opposite way, and it is when i have the ignition OFF.

Don't know if there is a misprint in the manual or not (its happened before), I've never checked the ohms readings. That said, being opposite could mean ECM issue
As I understand what you've said prior, is J2-24 is not seeing 4.5V

The ECM is not switching so I'm thinking the ECM issue

Yes I just want to double check if its the ECM. I have also a Code 33 everytime i switch ignition on. Map sensor is new, voltages are good, even the real time readings on the ecm are good, and it throws a code everytime. I think the ecm is shot. I try and put together the engine and read the voltages on the ignition system. Maybe its just the ECM.
But mefi1 ECM is hard to get, especially in germany. :(

Agree, a MEFI 1 is hard to find, and can see the extra issue being in Germany. I have my old one removed from my VST 502 when I repowered to MEFI 3 and cool fuel. OBDiagnostics has a listing for the M1 but don't know if Bob has any, and like John at Boats unlimited can test and maybe repair. A couple guys at iboats has contacted John about test/repair and he's told them he's so busy he doesn't have time right now. He may have freed up some time over the last couple weeks and may be worth contacting

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Question.
when at 424 is no voltage applied, 423 is grounded.
When at 424 voltage is applied, 423 goes to the transistor.

Why does the manual say i should have less resistance between 423 and ground when 424 is energized? should be the other way around, like it is on my engine. or am I wrong?

I don't fully get it either other then they are taking into account what resistance changes happen inside the ECM. I like test which verify the ECM is working correctly, like voltage measurements on the pins during start and run. If this is happening correctly and still getting code, then it has to be ECM