OverToyed

I did add a wire between the two battery grounds per some thing I read long ago and I added a dedicated ground wire from the driver's battery to a mounting bolts for the ECM. Is there more I should do?

You guys were correct. It was the ECM. Rebuilt one installed and seems to be working fine now. It made a suicide pact with the driver's side battery and that was further confusing me. Thanks very much for your help.

Thanks all - looks like my ECM is fried. Sent it to "Module Experts" in Florida and stupidly paid for diags in advance. They just called and said processor is fried so they want another 1.1k on top of the "diag fee" I already paid. I asked for it to be returned to me. Contacted Discount Diesel ECM in Davie FL and they say "Module Experts" is just a front for a junk yard with no actual ability to repair ECMs. Discount Diesel ECM says you can't reprogram one of these without an actual vehicle and he has a stable of vehicles just for this purpose. I, of course, haven't the foggiest. Is there a favorite place for ECM repairs?

ECM not booting..... Could that be why no codes are showing? No Check engine light either. I replaced the pcm about two years ago. That was an expensive one.

Hi all. Thanks in advance for your time and wisdom. Second gen 24 valve. Quadzilla tuner. No "wait" light and no grid heater in cold weather, but from the voltage drop I can tell the grid heaters do come on after starting, even if the IAT is reading over 100 degrees (I can see what it's reading through the Quadzilla). Doesn't always come on, but most of the time it does when when the engine is hot. Already replaced the IAT sensor and no change in symptoms. Throttle position sensor (already replaced and no change in symptoms) often forgets itself. Have to turn off, back on, press all the way down and release slowly and start. Then works fine. Something seems to be draining the batteries (already replaced alternator). If I don't run it every few of days it needs a jump. Possible ignition switch error? ECM?

Problem solved! Excessive corrosion on the positive battery terminal was blocking high power to the relay through the fuseable links. Apparently, no high power to relay = no little red "wait" light on the dash. Power was reaching all other systems so truck would start but nothing was going to the high amp posts on the relay. Than you all very much for your time and help. I really appreciate it. Mike One trick I did learn while troubleshooting this is that since it's a good idea to disconnect the main batteries before poking around the grid relay it's hard to test the relay with a safe power source. The two small terminals that trigger the relay, however, are exactly the right distance apart to test with a 9v battery. Just disconnect one of the high amp cables, put your ohm meter between the two high amp connectors and bridge the two small connectors with a 9v. Relay click, relay tested, zip zam done.

No check engine light - I'll pull codes this morning. I'm pretty sure that when I blew my grid relay a few years back the "Wait" light still functioned but nothing happened. I'm pondering what-ifs and wondering why it might think the heaters aren't needed even though the temp sensor knows its 40 degrees. Thanks all for your help, by the way.

But the "wait" light doesn't come on and the gross don't hear up when incoming air temp is over 60 degrees? So it's conditional?

It will start but runs awful with great smoke. Oversized injectors are probably pumping in too much fuel and it's burning in the exhaust.

1999 2500. Truck is getting fuel but without the grid heater it's running like crap. After market FASS lift pump. I've replaced the relays before but I think that even when the relays are broken the "wait" light still comes on. Seems odd that its not going through the motions and that's why I'm wondering if I'm missing something obvious. It's hard to troubleshoot when I can't turn the key and hold the voltmeter at the same time.

One thing to check. My truck (99 2500) has a rear ride height valve that controls how much the rear brakes are used. On the rear axle, left side. The lower the body sits in relation to the axle (heavy load in the bed) the more rear brakes are used. On mine, I was getting almost no rear brake wear/function so I put in a bypass. Really cut down on my front pad wear. I also went to cryo treated front rotors as I often heat warped them. Helped a lot.

Snow is forecast so of course the truck is on the fritz. It's about 40 degrees out. Turn the key, "wait to start" light doesn't come on and grid heaters obviously not working. I have a Quadzilla tuner and if I just leave the key on long enough I can see that the IAT is reading 40 degrees so I know the IAT is working. Even if the relays or grid is broke shouldn't I still see the "wait to start" light coming on for 10 seconds? Is there something obvious I'm missing?

No idea what you've just said but I thank you for the wisdom.

Excellent question Michael. I'd love to learn more. Same for PCM. Do those also route through the ODB2 in 1999?

Thanks for your help guys. New ScanTool LX device on order.