95 Chevy k1500 goes in and out of limp mode at random times.

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#1
I have a 95 Z71, 5.7 with 4l60. I have had the same problem with the truck going into this "limp" mode just when ever.
The trans will work flawlessly one day or so then at any random time will jump into this mode when it would downshift from 4th or when I come to a stop and try going again.. If I turn the truck off for maybe 1 minute and start it back up it'll start off in 1st like it should but almost never go back into 4th. at this point i'm limited to 3rd gear and 2nd only by manual downshifting. At this point there is really no telling when it'll start working right again but always seems to at some point after sitting for awhile when I use the truck again. then it works fine but will repeat this at some unknown time. (the lockup on the converter seems to work as it should) I had this problem to start with which lead me to getting the trans rebuilt. The truck worked fine after the trans rebuild (less than 1500 miles on it) but then I let it set for many, many, months because of high gas prices. Now it has started to do this again. The rebuilder had said he replaced all the electronics in the trans cause of this shifting issue (the original problem I had with the trans), I'm really gun-shy of letting some of these repair shops even look at the truck cause I know they can smoke my trans with one trip around the block if it does this and it sticks in third.
My questions are about the extra computer grounding harness mentioned in another thread, is this something from the dealer? and might it be my problem
also about the grounds, I'm not sure I understand what to ground out
Do you think this could just be caused by corroded connection?
Thanks for any help you can give me in this issue, it's really begaining to drive me crazy. it's a really nice truck and I have put bunches of money into it, i'm begaining to grow tired of spending money on this truck and getting nothing in return.
Also I have replaced the neutral safety switch with no change and checked all fuses cleaned a but load of connections and have read many threads about related problems here on this forum.

edited more..... I didn't see this thread in the searches I made before but it's alot like my problem only the selection indicator and tack work fine on mine. http://www.batauto.com/Forums/index.php?topic=8110.0
I'm going to try the fuse testing next time it happends and see..... I'm guessing it's closely related to my problem. I'll keep adding to this thread till I get a fix, thanks for all the help so far guys. I you hadn't been answering all these question for others I believe I would be SOL.
 
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#2
Ok, been out running the truck and had it go into limp mode where I lost 1st and 4th. I pull over and check the trans fuse and have 14v going to the top side of the fuse, said .003 on the bottom side of it. Not sure if that's the meter or what. Checked this twice then turned the truck off, wait about 30 sec, start back up and it works fine stopping and running through the gears for awhile until at one stop sign it wouldn't drop back to 1st grear. drive a bit more with no 1st or 4th then pull over and check the trans fuse again, same results with 14. something volts at the top and .003 at the bottom. turn the truck off... wait a bit.... start up and it works fine right till I stop to pull in the driveway. test fuse with same results as before.
not sure what this means....... ???
 
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#3
I once had a Chevy Van that acted Sort of the same way. The van started fine but at terminal E at the trans connector It showed 12 V with a DVOM. but put a test light to it it lit very dim.As a last resort I cleaned the batt cables at the batt. The neg. connector (side Post) was co roded inside. after cleaning it my test light at terminal E on the trans connector lit my test light bright. The trans worked fine after. So make sure you batt. terminals are clean and tight and go for a road test. Good luck David
 
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#4
I have though it was a ground issue also so I did clean the battery cables ends put a 1000 cca battery in it. used studs and nuts on the battery instead of the cable bolts. new starter, ran extra ground wires on the frame, the bell housing, the cab. I did read about a computer ground issue in this thread http://www.batauto.com/Forums/index.php?topic=7511.0
quote transman "These vehicles also have a common problem with the "Range Mode" switch (neutral switch).
There is also a bulletin on '95 with a computer board breaking a ground inside, there is a repair kit (harness) so you don't have to replace the computer itself. With more info, we can go further. Post back, Transman"
I replaced the the neutral switch on the side of the trans but don't really have a clue about this repair kit harness or where to get it.

I'm now wondering if what this other guy did to fix his would work on mine but I can't even figure out what the alarm switch is he's talking about. any key will work on my truck and I don't think it has an alarm.
edshan said:
fixed

Hey all, just an update Upon replacement of the ignition module, and the alarm switch, all is fine, all my symptoms have been resolved, i would have replaced the key switch as well but my local locksmith messed up the cover for the tumblers and as soon as i installed it it locked up. well thanks to all the great advice and i will be recommending this site to all that i talk with. thanks
 
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#5
I thought I found the problem, pinched wires with broken insulation going to the speed sensor buffer. but after fixing the wires (I think), my problem now seems to be consistent.
It works fine when first started going through all the gears normal, then after running a 5-10 minutes it will not drop down to 1st gear going into limp mode when I come to a stop. I can turn the truck off, wait about 20 seconds, start it back up, and it'll work fine going through all the gears and into 4th until I come to a stop again and then it won't drop down to first and goes into limp mode again.
anyone have a clue what's going on, i'm kinda at a loss.
 

Transman

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#6
You have a problem at your fuse panel or a bad fuse itself. You cannot have 14 volts on one side of a fuse and .3 on the other if the fuse is good. The ground kit is available from the dealer. Where is your computer? Under the dash, no need for the kit/repair. Codes would be helpful here as the trans can be going into limp due to a ratio error also. Post back, Transman
 
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#7
Transman said:
You have a problem at your fuse panel or a bad fuse itself. You cannot have 14 volts on one side of a fuse and .3 on the other if the fuse is good. The ground kit is available from the dealer. Where is your computer? Under the dash, no need for the kit/repair. Codes would be helpful here as the trans can be going into limp due to a ratio error also. Post back, Transman
I was pulling the fuse out when testing those so it was my bad, I realized that after I posted but every time I checked it with the fuse in place it was in the high 13v range
The S/M at the chevy place said it was a bad torque converter lockup solenoid (when I was trying to find out about the ground thing) so I replaced that. no change..... The computer is behind the glove box, looked like a replacement unit so I kinda figured that wasn't the problem. I tried to get it scanned for codes today but the guy's scanning thing wouldn't work on the 95, only 96 and up.
I had noticed it working/not-working seem to co-inside with engine temp so I changed the thermostat (put in 195-deg) so now when it gets to where it's warmed up it will never go into 4th and goes into limp mode. when hot now...If I turn it off...wait a few seconds....start it back up... I takes off fine in 1st gear and runs through to 3rd but will not go into 4th. when it's cold after setting the night it'll work fine for a little while till it warms up. at least now I have it not working right constantly. I talked with the guy who rebuilt it and he said he'd figure out whats wrong with it tomorrow. we will see.... so the saga continues.....
 

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#8
I would be suspicious of the Temp sensor. This can make the engine burn more fuel also but to be sure you need to see the data as it is working. The computer is early enough to not need the TSB fix but still could be part of the problem. I would leave the ECM on the back burner for now but see if you can find someone who can read the data stream. Keep us posted, Transman
 
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#9
Ok, so the trans guy who has a wall full of diploma's from all the transmission classes/schools that he's been to, thinks he's figured out my problem. After 2 days of testing everything from the computer to all the electronics in the trans and consulting some transmission oracle, he has come to the conclusion that the valve body itself is the problem. They ordered a new one and are going to replace it hopefully today. It took them less time to pull and rebuild the trans than they have into just trying to figure out what's wrong with it.
I can't even begin to tell you how aggravating this whole issue has been for me, if anyone who's reading this is planning on having an old trans with shifting problems rebuilt think twice about it. IMO You'd be better off just getting a new one or a used one from a wrecked car/truck. This is the third vehicle I've had problems like this with. I have an explorer that my wife had to have, that lived 2 months in a transmission shop because of issues like this. I had a trans-am that has similar problems, my truck is just the icing on the cake. I figure it's cost me about the same as it would if I had a cab or a tow truck take me every where I went. At this point 100% of the things I've tried in order to fix this problem have failed, I now have about every part in and around the trans new.
So the saga continues........... maybe this vales body will finally appease the transmission gods and they will allow me to have a few years of trouble free service. I'll let you know.
 

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#10
Sigh, Bring it to Zoo Jersey when you want it fixed correctly. I hope the VB does the trick for you, keep in mind on this trans that the VB is not a mystery unit. If it is bad then you should be able to see the problem area. Unfortunately, a shop like this one can give you a bad taste for ALL Builders. I am not saying that we don't get problem trannys in the shop because we do but we DO get them solved without guesswork and the least possible inconvenience to our customers. Aside from my Diplomas and certs, I have been Building transmissions since I was 9 years old. I have even competed in blind man's competitions, building a tranny blindfolded against the clock. Although there are a lot of shysters out there, I do NOT believe I am the "exception to the rule". I still believe there are good builders out there and good shops, the trick is doing your homework before you pay the hard way by asking around, check the BBB, deli counter person, local parts store (NOT pep boys). Good luck, Transman