Looking for some help in solving an ongoing problem with my truck where it comes in and out of TCC lock-up at random times on flat surfaces. This problem has led to transmission failure and replacement three times in the past year. The problem shows itself most often at speeds of 60 mph or higher especially at 70 mph, where it should run 2000 rpm's, but it will kick up to 2200 or so every couple of minutes. It has been doing well at 55 mph, sitting right around 1600 rpm's, only occasionally kicking out of lock-up over the course of an hour or two of driving. The 55 mph range seemed to improve as the weather got above freezing here in the Midwest.

My family's transmission guy has been able to replicate the problem but can't solve it. A trusted mechanic in town could not either and neither could .... the Chevy dealership. The dealership said the truck tested out "beautifully," but they did not drive it at 70 mph where I said the problem is easily noticeable.

The brake switch was replaced this year. I replaced the TPS last year along with all other sensors when the Jasper engine was put in. The problem appears with cruise turned off and AC turned off. My transmission guy and the dealership both saw an engine misfire in the history.

Any thoughts here as to what else could cause a bad lock-up strategy? PCM and fuel inectors are original ... could they be the source of the mystery? I am wanting to continue down the road with this vehicle, but I can't trust it on the interstate while this lock-up issue continues. I greatly appreciate any suggestions you all might have to offer.

 

The only other thing I can think of is the harness. Not the entire harness but there's one in the trans that connects all the internal solenoids and TCC pulse module.

Then there's the outer one from the outside round plug of the trans to the rear of the motor. Now there can be a break in the insulation causing intermittent connections. You said you replaced the motor and these wires come up from the rear of the firewall down the center to the trans. They could've easily been pinched at the time of the swap.

One more harness/connector to look at would be to the brake switch. In all the harnesses inspect all the way to the connectors and verify continuity to the pins. Use Ohms to verify none of the wires are touching each other, to power or to ground. Other than that, I personally find it highly unlikely that the PCM or injectors have anything to do with it.

If you wanted to check the wiring all the way to the PCM the main 3 wires would be the 1 @Connecter1 TCC Brke sgnl switch pin# 33 Ppl to brake switch & 2 from the trans @Connector2 - TCC Sol Valve Cntrl pin# 42 tan/blk - TCC PWM Sol Valve Cntrl pin# 2 Brn - the pin #'s are at the PCM end to clarify.


So those are the 3 main wires that are directly connected to the TCC Pulse Module. Good Luck and let us know how it turns out

 

I appreciate your thoughts on this, very helpful. I was able to handle replacing most all of the sensors, since they are all in reach and doable for my skill level. Would checking the wires you mentioned be more a job for a pro, or could a regular joe like me get to them?

As a follow up -- I drove over 300 miles round trip today. Staying mostly on state roads and keeping it at 55 mph, it did really well and only came out of lockup once, and giving it a run on 20 miles of interstate, it only came out of lockup once there as well. However, there was some rumbling/vibrating in the back end when I was in 4th. On the way back, I decided to give it about a 60 mile run on the interstate, but it struggled, going in and out of lockup every 1-3 minutes at 70 mph. Once I got on the state roads, it did so-so at 55 mph. Halfway home, I lost 4th gear, then 3rd became an issue and about lost all gear. I limped home. It'll be another warranty job, but this mystery will have to get solved or it's bye bye to the Blazer era, sad to say.

 

Getting to the wire harness is not easy, but yes you could do it. Would require a continuity meter with either really long probes or 10' or so of additional wire, probably another person and a wiring diagram.

 

As a follow up: my transmission guy repaired various hard parts that were bad, as well as putting in a new torque converter. He followed the wiring back to the engine, and felt that it is fine. My first few drives with this have good -- all shifts are good, no random coming in and out of lock up at any speed. What the mechanic believes is that the warranty trannies were junkyard models -- not rebuilt.

I appreciate everyone's thoughts.

 

for me I had the exact problem, why has a tranny shop not gone a test and reproduced that problem with a scan tool hooked which would slow slippage value.. why have the not trigger the clutch on and off and tested that feature too? I mean they check it out as ok but don't even bother going into the speed range you say it happens at?


for me it was my torque converter but then again I didn't just replace the torque converter but my tranny was working flawlessly every other way. I choose to rebuilt it anyway when it was out.

 

+1^ IMO, That's the way to go if converter fails... almost always release metal when they fail mechanically.

Did you find much metal shaving in the case when you rebuilt?

 

I can say that with mine, the mechanic indicated a lot of metal shavings went into the pan, and I saw teeth shredded off and a great deal of scoring on one of the parts.

As a side note, I wonder if a rear differential can cause problems with the transmission, especially one with as many miles on it as this one.

 

Get a crankshaft sensor relearn procedure done. A phantom miss as incorrectly interpreted by the pcm will kick out the torque converter. The pcm think you'll need more torque because of a miss that's not there and disengages the torque converter. Usually won't set a code unless you really do have a miss. Been there on several of the vortec trucks. Usually happens if ckp sensor or timing comer have been replaced or moved at some time.

 

Lancealot - I went ahead and had a new crankshaft position sensor put in, along with the relearn. I road tested it at 70 mph, and it did not come out of lock-up. This seems to have fixed this nagging problem. As a side note, I had been having hard start issues when the engine is warm, and this seems to have solved that issue as well.

Thanks for everyone's advice.