'94 Beretta Z26 trans problem
Posted: Thu Dec 05, 2013 7:43 pm
Hello all, occasional reader, first time poster.
I have a 1994 Beretta Z26, 3.1L V6, 4T60-E auto, 129000 miles. It was stored(though occasionally started and moved around) after previous owner died. I was told it only needed an intake gasket, figured I better start it up and verify this before I dove into the project, turns out the engine had a spun rod bearing.
I bought a 1997 Olds Cutlass Supreme with a rusted frame as a parts donor. I drove the car about 20 miles home, so I know everything functioned properly on the engine and trans. Coolant temp sensor setup was different, as was the rear exhaust manifold and engine motormount, but otherwise it bolted right in. Got it running, time for a test drive...bad news...trans shifted 1,2,4...no 3rd and no TCC lockup. After a few miles of cruising dirt roads, it downshifted to 2nd gear(computer was looking for 3rd, but that didn't work, so ended up in 2nd). Basically, after it warms up, the computer shuts off 4th gear. Since there is no 3rd gear, it went to 2nd. Park it for a couple hours, or till the next day...try it again...same thing. On cold start it shifts 1,2,4...all firm, no slippage, but no 3rd and no TCC lockup. After a few miles, it downshifts and won't go back to 4th till after it cools off.
I had saved the engine compartment wiring harness out of the parts car. I cut the trans connector off and added some solderless T connectors. I plugged this connector into the trans, from one side of the T I plugged into the trans connector on the Beretta's wiring harness. From the other leg of the T I ran wires into the car so I could check the ground circuits while driving. When the post-warmup downshift occurs, the computer is shutting off the ground circuit to shift solenoid A. I thought maybe it was the trans temp sensor, so I hit it with the multimeter, resistance readings were 12530 Ohms cold and about 800 Ohms hot. From what info I've found, this is within acceptable range.
Anyway, 3rd gear was still gone, so I pulled the trans and installed the one that came in the '97 parts car. All plugs, wiring and connections matched. I removed the side cover from the valve body to verify that wiring, solenoids, etc. were the same. I did change the differential, as the reluctor ring on the '97 trans had a 30 tooth count and the reluctor ring on the original '94 trans was a 29 tooth count. Got it all back together, new filter and fluid also, time for a test drive! Shifted 1,2,3,4, TCC lockup perfectly! Fantastic! But...only went a couple miles and it downshifts to 3rd gear again. Park it for a while, cold startup, everything works great. A few miles down the road and you're back to 3rd, won't go to 4th till it sits for a while. Same thing every time. Grrr!!!
I found a great technical paper that listed all the sensors that the computer reads to calculate shifting. It lists Coolant Temp Sensor, TPS, VSS, Vacuum Sensor, Park/Neutral switch, Temperature Sensor and Engine Speed sensor as inputs.
I have changed the Coolant Temp sensor and TPS with known good used ones. Vacuum Sensor I assume refers to the MAP sensor? Changed that today, didn't make any difference.
VSS I haven't checked or changed, speedometer works smoothly so I'm guessing there isn't a problem with that.
Park/Neutral switch I haven't checked or changed, but it does only start in P or N, backup lights come in on R, etc. so I'm guessing there isn't a problem there. I did read somewhere in researching this problem that it could be caused by a bad Range Switch? I haven't been able to locate a pinout and testing procedure for this yet.
Trans Temp Sensor I haven't checked or changed, as it worked flawlessly before I removed it from the parts car.
Engine Speed sensor I assume refers to the cam sensor? Tach works fine, so I haven't done anything with that.
Of course, my assumptions could be completely wrong.
Sevice Engine Soon light is not on. But...that doesn't necessarily mean there isn't a trans code stored because of mechanical failure in previous transmission?
ABS light is on. Wires to wheel sensor were broken on right lower control arm. Repaired the break but ABS light still on. But I don't think this would cause the shifting problem?
I was going to try jumping the A and B terminals in the OBD I connector, but there's no wire in the B hole. Can this be checked without using a scanner? It's a 12 pin connector, not a 16 pin. I don't have plates or insurance on it, as I wanted to make all repairs first, so I can't really run it to town for a scan.
So, in summation, it's a '94 Beretta with engine and trans from a '97 Cutlass Supreme, no 4th gear or TCC lockup after driving a few miles. On cold start, everything is great. Seems like the computer is interpreting the signal from the Trans Temp Sensor backwards.
Your opinions and suggestions are appreciated.
Thanks,
Anthony
Located just outside the huge town of Moscow, MI. Don't blink or you'll miss the whole thing.
I have a 1994 Beretta Z26, 3.1L V6, 4T60-E auto, 129000 miles. It was stored(though occasionally started and moved around) after previous owner died. I was told it only needed an intake gasket, figured I better start it up and verify this before I dove into the project, turns out the engine had a spun rod bearing.
I bought a 1997 Olds Cutlass Supreme with a rusted frame as a parts donor. I drove the car about 20 miles home, so I know everything functioned properly on the engine and trans. Coolant temp sensor setup was different, as was the rear exhaust manifold and engine motormount, but otherwise it bolted right in. Got it running, time for a test drive...bad news...trans shifted 1,2,4...no 3rd and no TCC lockup. After a few miles of cruising dirt roads, it downshifted to 2nd gear(computer was looking for 3rd, but that didn't work, so ended up in 2nd). Basically, after it warms up, the computer shuts off 4th gear. Since there is no 3rd gear, it went to 2nd. Park it for a couple hours, or till the next day...try it again...same thing. On cold start it shifts 1,2,4...all firm, no slippage, but no 3rd and no TCC lockup. After a few miles, it downshifts and won't go back to 4th till after it cools off.
I had saved the engine compartment wiring harness out of the parts car. I cut the trans connector off and added some solderless T connectors. I plugged this connector into the trans, from one side of the T I plugged into the trans connector on the Beretta's wiring harness. From the other leg of the T I ran wires into the car so I could check the ground circuits while driving. When the post-warmup downshift occurs, the computer is shutting off the ground circuit to shift solenoid A. I thought maybe it was the trans temp sensor, so I hit it with the multimeter, resistance readings were 12530 Ohms cold and about 800 Ohms hot. From what info I've found, this is within acceptable range.
Anyway, 3rd gear was still gone, so I pulled the trans and installed the one that came in the '97 parts car. All plugs, wiring and connections matched. I removed the side cover from the valve body to verify that wiring, solenoids, etc. were the same. I did change the differential, as the reluctor ring on the '97 trans had a 30 tooth count and the reluctor ring on the original '94 trans was a 29 tooth count. Got it all back together, new filter and fluid also, time for a test drive! Shifted 1,2,3,4, TCC lockup perfectly! Fantastic! But...only went a couple miles and it downshifts to 3rd gear again. Park it for a while, cold startup, everything works great. A few miles down the road and you're back to 3rd, won't go to 4th till it sits for a while. Same thing every time. Grrr!!!
I found a great technical paper that listed all the sensors that the computer reads to calculate shifting. It lists Coolant Temp Sensor, TPS, VSS, Vacuum Sensor, Park/Neutral switch, Temperature Sensor and Engine Speed sensor as inputs.
I have changed the Coolant Temp sensor and TPS with known good used ones. Vacuum Sensor I assume refers to the MAP sensor? Changed that today, didn't make any difference.
VSS I haven't checked or changed, speedometer works smoothly so I'm guessing there isn't a problem with that.
Park/Neutral switch I haven't checked or changed, but it does only start in P or N, backup lights come in on R, etc. so I'm guessing there isn't a problem there. I did read somewhere in researching this problem that it could be caused by a bad Range Switch? I haven't been able to locate a pinout and testing procedure for this yet.
Trans Temp Sensor I haven't checked or changed, as it worked flawlessly before I removed it from the parts car.
Engine Speed sensor I assume refers to the cam sensor? Tach works fine, so I haven't done anything with that.
Of course, my assumptions could be completely wrong.
Sevice Engine Soon light is not on. But...that doesn't necessarily mean there isn't a trans code stored because of mechanical failure in previous transmission?
ABS light is on. Wires to wheel sensor were broken on right lower control arm. Repaired the break but ABS light still on. But I don't think this would cause the shifting problem?
I was going to try jumping the A and B terminals in the OBD I connector, but there's no wire in the B hole. Can this be checked without using a scanner? It's a 12 pin connector, not a 16 pin. I don't have plates or insurance on it, as I wanted to make all repairs first, so I can't really run it to town for a scan.
So, in summation, it's a '94 Beretta with engine and trans from a '97 Cutlass Supreme, no 4th gear or TCC lockup after driving a few miles. On cold start, everything is great. Seems like the computer is interpreting the signal from the Trans Temp Sensor backwards.
Your opinions and suggestions are appreciated.
Thanks,
Anthony
Located just outside the huge town of Moscow, MI. Don't blink or you'll miss the whole thing.
But, let me add the few tidbits I have that might prove helpful, until a more educated or knowledgeable member can jump in. First, '94 is the beginning of GM's transition from OBD1 to OBD2, which didn't really come out until '96, so '94 and '95 are bastard years. You cannot read codes with a jumper wire, but you also cannot plug in an OBD2 scan-tool to access codes. You need special equipment, like a Tech 2 (IIRC) or similar. 
, basically, you are SOL on that.