Just poking around on Ludis' site regarding my 730. Something beyond my logical explanation happened and before I swap out the ECM, I want peace of mind that it is really faulty.

Drove fine. Next morn, started it up, had MAP, CTS, and MAT codes. Thought it was a problem with either pin B5 or B6 or both in the ECM. Hardwired these sensor grounds to the plenum and codes disappeared. Didn't drive quite right though. Rang the wires and had no probs there.

Looked at http://www.cruzers.com/~ludis/1227749schematic.html and clicked on connectors on the right. B5 and B6 get tied directly to the ECM foil ground strip. Ok...so there is no signal buffering that I can see directly. They should be at the same low that the case is at.

If anyone has info regarding

1) Test resistances

-or-

2) Theory of how I got those 3 codes at the same time and the only remedy was hardwiring the ground on them to the plenum, but noted a loss in performance/drivability, but the pins show common with the foil on the DMM.

...I would appreciate the help. Thanks, -85Y

BTW, I have done my best to eliminate ground loops and all my chassis grounds have been gone through, sandpapered, and star-washered...including the elusive ground near the t-stat. Fuses all ok. It was fine one day, not the next. Not really any more info I can provide.

 

Disclaimer, I'm not an EE.

I've rewired several cars for EFI, and early on took to wiring the grounds EXACTLY as GM did. For the same odd coding reasons.

What seems to be working for me know is testing for any VOLTAGE drop across a ground connection. Any voltage being too much.

 

I've seen you mention destructive testing of inj drivers in other threads...have any info on just what it takes to blow them/it? Actually, to be more specific, have you seen what it would take for saturated injectors to blow the driver?

Reason I ask, I think I might have stumbled across the problem a while ago but didn't put 2 and 2 together.

1) With Inj fuse plugged in, all connectors off ECM, injector clip off of the inj...Inj Clip A to ground...44 ohms. Inj clip B to ground...39 ohms. Inj Clip A to B...5 ohms.

2) With Inj fuse UNplugged, all connectors off ECM, injector clip off of the inj...Inj Clip A to ground...infinite. Inj clip B to ground...infinite. Inj Clip A to B...5 ohms.

Just so no one has to look at the manual, for the 730, one side of the inj harness goes directly to the ECM...with the ECM unplugged, that line should always read nothing, regardless, unless the connector itself has a 5 ohm resistor hidden in the housing...and if it does, someone better stop me quick.

Seems that something under my hushpanel, not related to the CTS,MAT, or MAP got pinched and thus, is why the wires I was ringing were A-ok.

If that circuit had an extra 5 ohms of resistance in it, I would think that the driver would still be fine. FWIR when I blew one in my 870, it was because it got shorted. Yeah/nay? Could likely be the cause of the performance suffering I think.

I'll probably find a wire pinched to the dash skeleton when I pull the hush pad.

I hope I do--It'll be the first problem on my car that I actually caused

 

Disregard that. The 5 ohms was the other 3 injectors in parallel.