drummer0415

iTrader: (16)

Howdy guys, I haven't posted here in a looong while, but I'm having an issue that I need a little help on so I'm coning back to this knowledgeable group.

Symptom: first time the symptom popped up, my wife was driving the truck but she couldn't describe it well. She said she was slowing down for a red light, the light turned green, and when she got back on the gas it "freaked out for a second, then started going again". Ok not much info for me to go off of. So yesterday I'm driving it, I slow down because of a bus stopped in my lane (Metro bus, not school bus), then switch lanes, and get back on the gas to go around it. Instead of downshifting, it felt like the trans slipped hard, the engine free-revved, then it slams into gear and goes. It felt like a classic trans slip, but the weird part is everything electrical in the truck shuts off for about a second. The gauges go to zero, the radio shuts off, the AC shuts off, etc. Then very quickly it all turns back on, but the radio has switched to aux, the controls on the AC are all set differently etc.

So today I try messing around a bit to see if I can replicate the problem. This time I put the trans in manual mode, get to 2nd gear, get up to about 3000 rpms, and floor it. Immediately it slips, free revs, and everything electrical cuts out. So I tried it again with my camera rolling and it did the problem again. Here is the video link.






So the problem looks and feels to me like the trans is slipping, but the electrical cutting out is really throwing me off. I know a lot of stuff in the vehicle is controlled electronically including the transmission and all of the systems are tied together, but I can't figure out if it's a transmission problem and the electrical stuff is just a secondary symptom, or its an electrical problem and the transmission slipping is a secondary symptom.

I've done some basic troubleshooting to try and eliminate electrical possibilities. I checked ALL electrical connections. The battery, the alternator, the engine block, the grounds, everything is solid. The alternator is only a couple or 3 months old. The battery is 2 years old, but Vatozone says its fine. It's showing 12.4v engine off and 13.5v at idle.

So any advice here? Do I try changing battery and/or alternator? Do I try flushing trans fluid/filter? Do I just drop it at a shop and hope they figure it out?

Any insight is appreciated. Thanks.

wanablaze

iTrader: (3)

Why is the stability control light illuminated? Poor ground somewhere? Look as though the truck lost power/ground for a second as the instrument cluster appeared to reset. IMO, the transmission flare is a secondary issue.

Idryfly5

I had similiar issues, and I think I eliminated it. My truck would kick out of gear on acceleration, rev, then go back into gear like nothing happened, and the door locks would cycle. It *seemed* to be fixed after replacing the alternator. I borrowed my fathers radar detector and set it to voltage, and right before it would go haywire, I would get a low voltage warning. I assume the voltage regulator was on its way out, and when it dropped the truck went nuts. Here's a total list of what I replaced/added.

Cleaned all grounds
Additional ground from battery--->block
Additional ground from block---->frame
Replaced the mega fuse
Replaced the alternator
Replced the BCM fuse

drummer0415

iTrader: (16)

Well I replaced alternator just in case. Even stepped up from 145amp to 160amp model for the hell of it. Mega fuse looked fine but replaced it also. I haven't replaced battery yet, but two different stores tested it and said its good.

It is now having the symptom any time I floor it, whether in D or manual mode. I'm beginning to think more that it's the trans rather than electrical.

Chavette

iTrader: (6)

Some of the first NNBS trucks had a problem with the ground cable. Some of the problems were at either end of the cable and some was internal to the cable itself. I think there was even a TSB on the cable itself. You could try adding a temporary ground cable and then test drive just to verify there is no difference. I made my own from a cheap ground cable and clamps. I can then check most of the grounds when a problem occurs (battery, body, block).

I cant see the video at work but a failing fuel pump can result in a fuel cutoff.

Have you tried to pull codes? Some codes are not set to make your dash light illuminate.

This might be one of those times you need to find a buddy with a scanner (HPT, EFI, TechII, etc.) or even pay for somebody to scan it (paid diagnosis) so you can see what is happening with voltages, fuel, etc. when the event occurs. Its more difficult to chase everything statically in your driveway vs. scanning everything when the event actually happens. I hate to give up on a problem myself, but it could save you a lot of time and frustration.

drummer0415

iTrader: (16)

Small update. I happen to be acquaintences with a guy who is a tuner for a big name performance shop that's local to me, so I asked him if he would take a look at the truck and see what he thought. He said yeah sure so he rode along with me and monitored/logged everything on his laptop while I recreated the problem. His first reaction was "holy sheet that's weird", lol. After looking at all the wizardry and voodoo going on on his laptop, he said it is definitely 100% an electrical issue, but he has no clue what it is. His actual quote was "This is THE definition of an electrical gremlin".

So I guess it's good that the trans isn't bad, but now I'm going to be chasing an electrical gremlin. However, now that I'm pretty confident it's an electrical problem I have been doing a bunch of research on the issue. I found a bunch of other things I can try that fixed similar problems for other people. I will keep yall updated as I try different things.

01WS6/tamu

iTrader: (36)

Shake wiggle and stretch the wiring harness from the pcm to the drivers side valve cover and see if you can replicate the problem. I've had various wires break inside the insulation on NBS and NNBS trucks in this area and cause a myriad of problems. If you have access to gm scanner or matco snapon etc scan all of the modules and look for common codes this may give you a direction on which circuit to inspect or suspect and go from there.

Other than that unplug pcm and re plug it in. Check down on the transmission there is a metal clamp about 3 inches away from the harness electrical connector and see if it has rubbed through the harness. Another place is unplug the electrical connector out of the transmission and tug on each wire individually and see if any of the pins pull out. I've had a couple of these trucks have pins back out at that connector and cause problems as you describe. The next place to look is at the wiring harness under the dash near the emergency brake if you use it. Looks for any part of the harness contacting the the ebrake mechanism and then look for rub spots through the insulation.

This is one of those PITA epitomes of modern automobile intermittent hard to find electrical problems.

Trans problem is result of electrical problem.

Suburbazine

I would pull the underhood fuse panel out and check for loose/burnt connections on the connector grid underneath. Two grey arms rotate up and it's free.

01WS6/tamu

iTrader: (36)

Any luck? I forgot to add and the guy above is dead on I had forgot I had tons and tons of bad fuse blocks I changed on 07-08's for electrical gremlins of various nature also. Stinking new cars have so many glitchy problems now day's it's hard to remember them all especially after you quit seeing certain year models on a regular basis.

mjcotroneo

iTrader: (13)

Mine had a bad slip in it. Had my tuner change the on going and off going solenoid clutch parameters and fixed it