Bummer morning/dies at cruise
 

On the highway this morning, steady cruise @ 60 on flat ground, starts stumbling and backfires twice through exhaust. I get out, reset ECM, starts right back up. Go 1/4 mile feathering it and it does it again. Pull ECM, reseat Calpak and chip, reset ECM, starts back up. I limp it home (and I think it tried to do it once more maybe). Checked crank sensor, no scraping and balancer is tight. Checked cam sensor, tab is engaged and no visual problems. Pulled coil pack/module, ohm'd 12.1, 12.2, 12.4 across the terminals. The module has a one "crater" in the goo by the 2/5 wire. Everything else looks normal. I think it is the module so I plan to replace that unless someone has solved the same problem otherwise. I do have a separate ground wire on the module base so I don't think that's it. Got come good advice from Chuck and Lee, thanks.

Oh, coilpack/module is 3 years old and are OEM GM parts. I figure I'll have to replace at least one of these but looking to see if anyone has successful repaired a similar problem. It is not consistent.

FYI John,
Whenever these cars go into "LIMP HOME" mode don't forget the injectors are getting pulsed at 28# injectector rate.
With bigger than stock injectors (your 55# injectors) you can wash down the cylinders real fast.

My guesses are the ingition module or ecm.

Gary

Thanks Gary. When I said "limp home" I intended it to read that I drove it home gently (and afraid that it would crap out in the "hood" I was in at the time :eek: but this was 7am so not many people out yet).

EDIT: I just tested something. The coilpack is on the bench and had time to cool from the engine. Now cold, it ohms out at 11.6, 11.8 & 12.0. A consistent .5 ohm drop. I heated it back up by wafting a propane torch over it and the ohms went right back up to the original levels. This thing must be breaking down from heat, has to be.

Doesn't take much heat to change the resistance of a coil of copper wire. A set of injectors that measure .6 ohms at room temp, goes to .7 with just a couple mins at idle. Justa data point.

This would be one of those times to have a good spare ecm to drop in and just see what happens. The prices on used ones are about at an all time low.

That would be nice. I do have a spare unmodified stocker. I hear they will work with the low imp injectors for a while, how long I'm not sure.

Did the SES light come on? Did it throw a code?

No code, no light.

I went out again for a test run. I had installed a used replacement module only; the coil pack ohm'd to spec so only the module was replaced. Yesterday, went 5 miles out and back, no problems. I get up early this morning and head to the interstate. Take it about 10 minutes out. At the 8 - 9 mile mark, it starts the stumble. I'm in 4th, in lockup, 1800 rpms, 55mph. I pull off the upcoming exit and unplug Direct Scan to isolate it from the system. Get back on and make it about 2 miles; it starts stumbling again, this time worse with the backfiring and running really rough like it's pig rich. So I pull over and swap ECMs. I get back out and up to speed; starts stumbling again, the Scanmaster display won't illuminate either. It comes on and goes blank. So I drop back into 3rd gear to get it out of lockup; no difference. I slow to the shoulder with flashers on and cruise at 40mph, now it's running just fine. I make it home with no other hitches as long as I keep it under highway speeds and in 3rd gear.

Here's what it isn't:

Not ECM
Maybe still module (though I am going to take both somewhere and have them tested)
Not Direct Scan
Not TCC

If the modules test good, I will buy a new coil pack. I am stumped. I am wondering if the Scanmaster dying is a clue. When I swapped ECM back, the Scanmaster came back to life.

Note: One other odd thing happened first thing this morning. The Scanmaster displayed some parameters I had never seen before. Anyone ever see SP or PL show up? It was a first for me. After I unplugged DS, those never showed up again. I think they replaced some display but not sure.

Purely for the sake of the archives, here are the results of the module test at Autozone: they both failed. One failed on one test, the other was pretty much junk. I need a new module. This should solve the problem.

Moral of the story: have the module tested first. Lessons learned.....

Yep.. very similar symptoms as when my ign module failed, except mine would stall completely.. - I got one from John DiCarlo- all has been great since!

Well new coilpack/module allowed me to make it about 25 miles on interstate before the sputtering began. I pulled over, thought about it, and decided to unplug the MAF. Car was pig rich at the time. Suddenly, it drove almost perfect, for a little while; then it went into limp mode so I had to keep it under 30mph. Made it to Odell's and he let me borrow a MAF. Now it runs like new again. Oddly, the MAF would peg 255 and pass tap test no problem. I suppose the numbers don't always tell the story. Anyhow, it's fixed and I have to decide whether to go MAFless or buy a MAF.

good to hear you got it fixed-
just last night another turbo regal buddies car blew the top rad hose off the radiator and puked antifreeze into the airfilter and got into the MAF- by the end of the night, the MAF was toast and we are debating wether to get the lightning MAF and go with eric marshalls chip or just get another MAF.....

what to do.....

ps- we just unplugged the maf wires and took the uppipe off and ran it 25 miles home, car immediately woke up and drove as good as a NA 3.8 could :rolleyes:

which MAFLESS system were you thinking of doing?

BW

I bought a Max E two weeks ago. Haven't installed it yet due to the problems (trying to limit changes so I could isolate the immediate problem). So I suppose it only makes sense that I should use Steve's. Is there another other than FAST-type systems? Just wondering what you meant.....

i remember back someone made a computer chip for the track...
it was setup so you could delete the MAF and run about 2 tenths faster with that setup-

i was hoping you knew who did that, and was hoping someone improved it so we could run all the time without the MAF-


whatever happened with red armstrong running the lightning MAF and calling it the raptor???

The no-maf setup is Steve Yaklin's max-effort R. It's perfectly normal for the coils to go from 11.5K to 12 or 12.5K ohms, going from room temperature to underhood operating temp. If one is open it will be way higher, usually over 100K. You can try your luck with remanufactured mafs from NAPA or a TR vendor, but I recommend a tranlator and lt1/ls1 maf. It's more money up front but is very reliable.