MSefi.com read only forum (Jan.15,2018)

I'm running an MS-II v3.0 with B&G code on a chevy v8 with TBI and a small cap HEI. I've been getting a minor fluctuation in the tach signal, it's not very severe but you can feel it under load as the timing bounces around. It's not a regular occurrence so I've been ignoring it but I decided to replace the module to see if it may be the culprit. I replaced it with a Delco D19443A, like is listed in the megamanual, and now I have no tach signal. I thought it was defective so I got another and still no signal so I swapped the old module back in a and it's running fine. I can't figure out why a cheap chinese module works but the ACDelco won't. I'm uploading a log that shows the fluctuation in case anyone has seen it before.

Thanks

Are you running an old version of B&G code? Can't seem to find battery volts in your log.

I'm running V2.88 B&G. The lack of voltage is my fault, I hadn't added it but I have now. I'll see if I can get a log when it does it again.

I don't have anything to compare it to but the vBatt looks like it's moving around way more than it should be. I'll start chasing wires this weekend. If ya'll see anything else out of the ordinary please point it out.

Thanks

Forgot to upload the tune.

I was wondering if you were running low impedance injectors. These can cause big spikes on the ground - but usually shows on the battery voltage trace. Not saying it would effect the tach signal, though. Just a possibility.

They are factory GM TBI and measure between 1.0 and 1.4 ohm. I'm not sure what they are supposed to be reading. It has blown the injector fuse once when it was in WUE and Accell enrich at the same time so I cranked the fuel pressure up but it will still hit 100% duty cycle.

They are definitely low impedance, then.

There is a mod to provide the injector drivers with a separate ground path, for use with low impedance injectors. My thinking being spikes from them may be interfering with the tach signal.
Bit of a long shot, though.

Thanks for all the assistance. I have an edelbrock mpi manifold so I think I'm going to quit messing around with the TBI, and I have high impedance injectors for it so that will save me having to mod the MS. Have you heard of anyone having problems with the Delco D1943A module? That has me more concerned than anything, because right now if the module dies I'm dead in the water.

I don't know if this has any relevance, but when I swap the BWD for Delco the module there is no tach signal. At least it doesn't show any rpm in Tunerstudio.

What tach input are you using? Minor variations in the tach signal from different makes of unit might just be 'go' on one and 'no go' with the other. It's the sort of thing a 'scope is useful for seeing.

I'm using the hall/optical input. I added the mod from DIYAutoTune's site that is supposed to give a stronger tach signal. I've been reading through the manual but the only adjustment I can find is for the VR circuit. Is there a way to tweak the optical circuit?

tx1572 wrote:I'm using the hall/optical input. I added the mod from DIYAutoTune's site that is supposed to give a stronger tach signal. I've been reading through the manual but the only adjustment I can find is for the VR circuit. Is there a way to tweak the optical circuit?

I'm not familiar with HEI, but reading the manual does suggest there can be problems getting a reliable tach signal from some versions. And gives a few mods. to the opto input to try.

http://www.megamanual.com/ms2/inputHEI.htm

Other than trying those, the alternative would be to use the VR input, which is designed to cope with a wider variety of input voltages and frequencies.

trakkies wrote:the alternative would be to use the VR input, which is designed to cope with a wider variety of input voltages and frequencies.

Absolutely agree with trakkies (as I normally do) on this!!

I have run HEI in the past and found the VR circuit to be much better! As I think back about it, I believe it was Dave who suggested running the VR circuit a long, long time ago, when I was having issues with HEI!

Ken

Sounds good, I'll get to work on that this weekend.

Thanks

I'm not sure if this related to my previous problem, but last weekend I was driving up to San Antonio which is about two hours away, and my engine started to randomly shut off. It happen two times on the way up and about 8 times on the way back. My laptop was dead so I couldn't get a log but it would start missing for a few seconds and the tach would drop to zero then come back up then it would die. It's a manual so the engine was still turning but the only way to get it restart was to cycle the power. Eventually it got so bad that I had to let it sit for several minutes before it would restart. It could be a coincidence but I removed the upper half of the MS encloser to check if anything was getting hot and after that it made it all the way home without any problems. The processor was hot but not so much that it burned my finger and the ambient temp. was around 85 deg.

Should I have pin G from the HEI module grounded at the MS with all the other sensor returns? That was the last thing I changed before this problem popped up, and it was running fine without it connected to ground but I thought maybe that was why the Delco module wouldnt work. I'm going to disconnect it and see what happens.

FYI, I haven't had a chance to switch to the VR circuit yet.

Thanks

I think I worked out what the problem is. It started idling like it had a bad vacuum leak, I had the air cleaner off and noticed that one of the injectors would stop pulsing when the rpm got low. I checked it and the coil is shorted, I think this is what has been causing the MS to shutdown and all the noise on the sensors. Here's a log of it shutting down.

I replaced the TBI with port injection and it seems that the shorted TBI injector was causing all the problems. The spikes in the sensor logs are gone and now the processor on the daughter card is barely warmer than ambient temp.. Still have to figure out why the new HEI modules aren't working, but I bought a scope for my laptop so hopefully that will be sorted soon.

Thanks for all the assistance