2G Low voltage in ECMLink but perfect at alt and batt???

[BrandonGST]

So I'm struggling to figure out this issue and can't quite find a thread that describes exactly whats going on with mine. I got my new motor built and dropped in. Now on first startup it was running weird and rough(very rich 10.4) so I checked on ECMLink. In link it was showing 6.4v for the battery! So I multimetered the battery with the car off, 12.6v. Car on the battery is at 14.7v, then I tested the alternator while idling around 1000-1300rpm and got 14.8v. I have double and triple checked all grounds, even added a ground from the alternator through bolt to the chassis. If I leave the car running to full operating temp, the battery voltage in link never gets above 8.2v, even with the alt putting out 14.8 and the battery sitting at 14.7. Does anyone have any ideas on what could cause this? Thanks in advance, this ones got me stumped

 

[DSMPT]

I don't know if this is your case but I had a similar case before with a customer's 2G. In ECMLink, it was reading the voltage way lower than the actual voltage at battery. It finally went 0.1v in ECMLink and got hard to start the engine. It was a bad ECU. Repaired the ECU and the issue was solved.

 

[dustyboner]

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[BrandonGST]

Thank you for the quick responses. DSMPT, That does sound pretty much like my issue, I have always had a lingering voltage issue with the car, but before this motor build the worst it got was 11v or so. It sat the last 6 months while I built the motor and now on first start this low voltage issue got worse. Thanks for the inspection procedure as well Dusty. I will most likely order the service from ECMTuning to get it all checked out. I will update the thread once I get a response from them on whats wrong with the ecu

 

[shinzon]

Sounds like you got a large amount of voltage drop between battery positive and and the ECU. I would first suspect those two white wires that run from the fuse box to the positive battery terminal, those love to corrode, even on my southern car. With the engine running, and the electrical system loaded, touch one end of your multimeter to battery positive, and the other to the terminal on the fusebox where the white wires connect. Basically, you're reading the difference in voltage between two ends of a wire. If the connection is good, you should read a couple hundred millivolts or less difference; if not, you should read 1-3v, or whatever amount of voltage you're missing. Repeat this procedure for any other suspect wires. The charge wire from alternator would be another suspect, also the wire to the MFI relay.

 

[steve]

Maybe I've missed some important data but it seem that there is a critical measurement missing. What does your multimeter say the voltage is at the ECU or at the MPI relay feeding the ECU.

If those are close to your battery voltages you clearly have an ECU issue. If it was a 1G I'd be looking at the CPU A2D reference voltage and the hybrid IC that buffers the input voltages. I don't remember ever seeing like problems on the 2G ECU's but the guys at ECMTuning would have more experience.

If the voltage is low at the ECU I'd measure the drop between the ECU and MPI and from the MPI to the battery to narrow won't the bad wiring segment.

 

[BrandonGST]

I already shipped it out to ECMTuning early this morning . But, if the ecu is not at fault I will definitely try these tests out

 

[BrandonGST]

Just to close this out, I just got the ecu back today. Turns out that some caps were leaking internally causing the low voltage at the ecu. They fixed the caps and now I am reading 14+v at the ecu

 

[DSMPT]

Just to close this out, I just got the ecu back today. Turns out that some caps were leaking internally causing the low voltage at the ecu. They fixed the caps and now I am reading 14+v at the ecu

Glad to hear that