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4L80E TCC Unlocking defies logic

I am not clear if the scanner said the TCC actually was commanded on and off quickly causing your issue? (I may be a slow reader... :rolleyes5: )

I have seen the wiring harness by the speed sensors on the transmission have the insulation flake off and short out. This is between the connector on the trans and harness bundle especially at the harness bundle bend and tape and worse shape closer to the trans. These are separate 2 wire plugs one in front and one toward the rear. You can pull the speed sensors out and look for debris stuck to them that could degrade the signal. If you have 4x4 there may be a shifter switch for 4 low and another speed sensor in the transfer case. That sensor and switch can be checked as well. My thinking is a sudden RPM change from a short or bad signal could confuse the computer by showing sudden different speeds: say under 45 MPH TCC unlocked and then 60 MPH TCC locked from it's tables.

It would be interesting to run down wiring/fuses/grounds for the radio. Maybe the radio is bad or maybe there is a shared connection causing this issue.

Have you checked the fuel system? IE: lift pump pressure and flow, filter condition, fuel cap for excess vacuum... Maybe it is the engine surging/fish biting causing this.
 
I have only driven it once since I finished the IP install but the TCC issues seems to be gone. As soon as I have a chance to get that drain tube on the turbo I plan to drive it some more and adjust the timing. I will update you then.
 
The AM/FM/Cass/CD radio issue appears to be ground related, most likely the amplifier ground according to the wiring schematic, although the head unit does power on, take a cassette or CD fine and plays it (just with no sound coming out of the speakers) On really hot days, of when the heater has been on for a while, or occasionally when I hit a bump, the sound will come on briefly for a 1/2 second to up to a couple of seconds, then go back off. Once, it actually stayed on for about five minutes, then scratchily went back out. Either the ground point by the steering column, or the ground point above the heater blower on the firewall, both are part of the entertainment system.

The tranny shop real-world monitoring showed fine as far as pressures go, but that it was being told to unlock/lock when coasting by the ECM. The ECM was then subsequently reflashed with the latest GM OEM tune for the Burb, and the problem continued (but I did gain about 2mpg highway fuel mileage over the previous tune from '99 that was on it). Since then, the problem has continued, and seems to be getting worse, especially if I try to control the pedal vs. using cruise. I have also encountered a couple of times when the engine is cold (first start) and I'm idling that the throttle doesn't seem responsive to pedal input, ie: I try to lightly depress the throttle to fast idle it and idle speed doesn't increase, I'll do it a couple of times and nothing happens, then all of a sudden it will just take off up to 2,500 prm or thereabouts on its own then drop back down to idle. I'm leaning towards an IP on the way out, especially with 199,968 on the odometer and no knowledge of prior service history and four owners before me. That's why I'm awaiting DKA99Burb's results. Of course, if I'm going to put a new IP on, injectors are part of the package, too. Any thought's on the FuelMiser injectors that Walt sells at SSDieselSupply? I'm after max fuel mileage, not pulling houses off their foundations (that's what the tornadoes are for).
 
What was your APP% on the scanner? And, are you having trouble controlling the rev off idle when in N or P? Now that the IP is replaced it revs nicely and can be held at any RPM with ease.
 
dka99burb said:
What was your APP% on the scanner? And, are you having trouble controlling the rev off idle when in N or P? Now that the IP is replaced it revs nicely and can be held at any RPM with ease.
Click to expand...

Don't remember, the owner of the tranny shop was looking at the SnapOn Solus scanner on his lap while doing the test drive. I was riding shotgun. Yes I do to the second question, and also difficult to hold it at a certain rpm when cruising Interstate and hitting downhill stretches, thus I use the cruise even if I'm only on the freeway a couple of miles. Sounds like my IP may be about shot, but it hasn't thrown any codes yet, it's just internally wearing out.
 
I finally got to drive it today. The pedal response seems to be good. RPM is controllable and now it works on CC a lot better than before. I think the TCC issue was due to the IP. I'm going to drive it more tomorrow. If I find anything negative I will be sure to report.

I hate you drove from NE to NC to get troubles. I thought I was doing bad by driving 5-1/2 hours to buy mine last summer and then having issues. I went to Charleston, SC for my burb.
 
Yeah, some used car dealer in Mooresville had it on Ebay for a week, then took it down. I called the following Monday, then drove out of Lincoln that Saturday morning and got to Mooresville Sunday afternoon. Went to go look at it first thing Monday morning when they opened. Idiots at the dealership had fried out the glow plugs trying to start it off a commercial battery charger when the idiot lot boy couldn't get it started that 25*morning after I had specifically told them that I wanted to do the cold start on it when I got there. Kinda cursed from the git-go. Biggest reason I bought it is that it was originally a Florida vehicle, (did the Ebay history check on it) so there were NO cancer issues unlike anything bought out here or from the Northeast or Rust Belt. I'd rather put $1000 into an IP and new injectors than $1000 into trying to fix/stop the metal munching termites, which you can never really ever do once they set in. Hopefully if I can either find decent employment, or get the Work Comp Insurance company to finally settle with me for a reasonable amount instead of the insulting low-ball offer they made, I'll steam clean the underside and frame, then POR 15 everything, then Rhino Line or Line-X the underside and frame. I'll be gold for the next decade plus, with an engine I can still put another 300K on till rebuild. The motor's solid, how about I use about a pint of oil between changes, and most of that seems to be from the CDR oozing, and dripping from the filter adapter o-rings/cooler line fittings judging by the driveway spotting. Also I noticed today on the on ramp that it accelerated liked a raped ape and was smoking pretty good at WOT with the turbo spooled up, which I've been told is also a sign of the IP wearing out along with the erratic idling and rev runaway tendency when cold (like 20* out or less) too.
 
Yeah. Mine was doing the 'raped ape' runs too. We called it 'NASCAR mode'.
Sorry to hear about the issues with the insurance company. I havn't dealt with that type of insurance yet. Probably should have a couple times...
I can recommend staying away from Allstate for homeowners and car insurance!!!

Let me know if you find out anything good about injectors. I am thinking of doing that before too long since I think mine have about 100k on them.
 
dka99burb said:
Let me know if you find out anything good about injectors. I am thinking of doing that before too long since I think mine have about 100k on them.
Click to expand...

Yeah, took quiet the nasty spill at work in September of '08. F'ed me up pretty badly, messed up my left hip and had to have reconstructive surgery on my left shoulder twice, the last time in Jan '11 to repair the torn rotator cuff, after having surgery in April of '10 to repair the torn cartilage and biceps tendon in my left shoulder. July of '11 Work Comp kicked me off of weekly benefits after six months of PT following the surgery, before I was fully rehabbed. Surgeon gave me a disability rating and a permanent work restriction on how much I can lift (30lbs repetitively, no more than 40lbs max.). Can't find a job, I was an industrial maintenance mechanic, because I can't meet the job requirements for lifting which are usually 50 lbs minimum. I used to be able to lay on my back under a machine and with my left hand press up a 100+ lb 3hp 3 phase motor and hold it in place while I finger threaded the bolts into the gearbox with my right (I'm a lefty). Was a gym rat, could bench 225 15 times (better than some of those NFL prospects!), leg press 405 40 times three sets, etc. Not bad for a guy who was 47 at the time. Since the accident, I've gained as much as 48lbs up to 278 (dropped 20 of that so far), my blood pressure has skyrocketed and I'm now on seven BP meds a day. Under Nebraska Work comp Law, I'm entitled to vocational placement assistance since I'm unable to return to my old job, and if the placement counselor can't place me, vocational retraining. The company's Work Comp Insurance company is fighting the vocational placement because they know damn well a job won't be found and that they'll have to pay for a couple of years' tuition while I learn a new skill I can do and pay me weekly benefits while I'm retraining. So they "offered" me a really low-ball offer of $7,500 to settle the case. I laughed at the case manager on the phone when she offered me that and before I hung up, told her to do what the law requires they do, or I'll file the paperwork myself with the Workman's Compensation Court to make them get the court to appoint a vocational placement counselor. Now, if they offered me like $30K, I might consider it, as since I haven't worked for three years, I could get Pell Grants to go back to school for two years and get an Associates Degree as an RN and live off of the cash settlement just fine. Own my house free and clear, paid it off when I owned my construction company. Won't go into the back child support I owe the ex, but she's cool with that as she knows what the past five years have been like, and she's doing fine so far.

Anyway, about injectors. Since I had my '94, I was on pretty decent terms (and still am) with Walt at SSDieselSupply since he pretty much went into business. He's been pretty closed lipped about his FuelMiser injectors' specs, but they've been real world tested and do give improved fuel mileage. He did have a FuelMiser tune to go with the injectors that gave a 20-25% increase in fuel mileage and about 25hp additional- it was giving him 24mpg hwy on a '95 K2500 p/u, but he discontinued the tune because some people weren't getting the economy results with it (I suspect right foot leaditis). I don't know if they're the spec injectors off the 160hp fleet 6.5td like the Post Office and UPS used, or if they're standard nozzle with marine pop pressure or what. I want a high MPG Interstate cruiser that I can load my kids and the gear into and take a road trip with at least an 880 SAFE cruise range on a tank. I wonder if Bill Heath has an economy tune in his bag of tricks?
 
The spill was nasty. I was standing at the top of a wet steel staircase with a long 40lb machine part cradled in my arms when my foot slipped out from under me as I started to step down (no handrailings, either) and I went airborn and landed at the bottom of the staircase on my left side across the bottom step and on the lower platform. Imagine doing a WWF flying elbow drop off the top rope, but instead of a padded ring mat, I landed like a 230lb bag of cement at the bottom of the staircase without hitting any of the stairs between the top and bottom! OUCH!!:eek::eek:
 
The IP will go nuts if you have low fuel pressure, starving for fuel, or are giving it air. I would test lift pump pressure and flow. Then check for air via a clear return line on the IP. Cheap and free tests. Bad injectors can also be an issue.

You are on the right side of the grass after that one is all I can say. Make your PT therapist laugh is about the only way they will back off some painful procedures I have found. Aka funny noises. Only works once...
 
WarWagon said:
Have you checked the fuel system? IE: lift pump pressure and flow, filter condition, fuel cap for excess vacuum... Maybe it is the engine surging/fish biting causing this.
Click to expand...

Lift pump putting out plenty of pressure and flow from bleed on top of FFS, replaced the filter after I got the Burb home. New Diesel fuel cap on it. There is vacuum release when I remove the cap to fuel it up, If it was a surge/fishbite, it would be doing it all the time, on load upgrade, on the level and down hill. I'm pretty sure that it's a 200K worn out IP, that when the ECM is telling it to back off based on either TPS input or Cruise Control input, that instead of backing off on fueling just a hair, the sloppy IP is backing off a whole wooly mammoth, so to speak.

Radio ground is behind the glove box above the heater motor, the amplifier ground is adjacent the steering column. When I get the time and better weather, I will contort myself under the dash with my test light and multimeter and back probe the connectors and follow the diagnostic procedure in the factory shop manual to pinpoint the ground problem. Right now for tunes I have a 110V adapter plugged into a power port and then a cheap Magnavox AM/FM/CD miniboombox plugged into that and sitting on the custom center console.
 
FYI: I drove it about 60 miles today with about half of it highway. Drove pretty good. Have some new vibrations but TCC worked well. I think you are right. The PCM can't deal with the worn IP throwing so much fuel in when so little is requested.
NASCAR mode is gone...
 
dka99burb said:
FYI: I drove it about 60 miles today with about half of it highway. Drove pretty good. Have some new vibrations but TCC worked well. I think you are right. The PCM can't deal with the worn IP throwing so much fuel in when so little is requested.
NASCAR mode is gone...
Click to expand...

Bitchin'!! I'd rather spend the cheap cost of $500 on an IP (relatively speaking compared with a $2K+ tranny rebuild) to solve the problem and put off the inevitable transmission rebuild as long as possible. A set of new injectors (most likely originals in it now) will round it out, and all much cheaper and easier. Time to start saving up for the next several months. Let me know your final opinion after you get it on a Tech 2 and completely dialed in as to whether it solved your TCC unlock-lock cycling while downhill problem for good.
 
I got the IP timed by a local guy. It is honestly not as fun as before since 'NASCAR MODE' is now turned off. But the shifting seems normal and it is driveable. I have drove it a total of 320 miles since I got it running and it 'feels' fine. I don't have a TECH2.
The TCC phenomena is gone.
 
I had a bushing in my brake pedal worn on my 420,000 mile truck. It would allow the pedal to bounce and interrupt the brake switch. I kept replacing switches until I noticed it was a worn pedal isssue.
 
dka99burb said:
I got the IP timed by a local guy. It is honestly not as fun as before since 'NASCAR MODE' is now turned off. But the shifting seems normal and it is driveable. I have drove it a total of 320 miles since I got it running and it 'feels' fine. I don't have a TECH2.
The TCC phenomena is gone.
Click to expand...
Hot diggity dog!:thumbsup: $450 for a reman IP sounds a whole helluva lot better than $2000+ for a complete rebuild and upgrade of the 4L80E! Now, to save up the money (ha) and get an IP. How's Pennensular for IP's, or does anyone have a good recommendation for reliable, quality and relatively inexpensive source for reman IP's?
 
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