Complex A/C idle-up problem after tranny swap
09-22-2005, 06:30 PM
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Complex A/C idle-up problem after tranny swap
About 3 months ago, I ripped out the auto tranny in my '02 Double cab, and installed an R150F 5 speed. Everything is great. It runs great. Fuel consumption is superp. Lotsa power. No problems, except that the engine will stall when coming to a stop with the A/C on. This only happens when the airvent mode is set to either defrost or foot/defrost. In either one of these two modes, the A/C comes on automatically in the '02 Tacoma.
I have unplugged the A/C pump so the magnetic clutch doesn't engage and put a load on the engine, but interestingly enough it still stalls. This tells me that it is not as a result of the load, but rather an electrical circuit problem.
Some of the common things as mentioned in my FSM, like PCV hose, MAF sensor, O2 sensors seems fine, and besides this only started happening after the tranny swap. I have left the majority of the automatic transmission sensors unplugged, except for the park/ neutral switch and the back-up light switch. I have re-wired the park/ neutral switch somewhat, so that I used the stock oem clutch switch at the bottom of the clutch pedal and hooked it up to the park/ neutral switch's neutral position. So, when I depress the clutch, the ECM thinks the auto tranny is in neutral, and it allows me to start the truck. Thing is, it probably also thinks that I am shifting from drive to neutral when I come to a stop as I'm depressing the clutch. Also, if I still had the auto tranny and shifted manually from drive to neutral as I would come to a stop, I'm sure it wouldn't have stalled, though.
So, as I'm coming to a stop, which is the only time it will stall, the A/C is on, but does not cause a load on the engine, because it's unplugged, I depress the clutch, and hence puts it effectively in neutral, I depress the brakes which causes a load on the engine, the TPS is closed and the RPM drops. The computer does not know what my speed is, since I have no ABS and the VSS is not hooked up.
The idle-up that one would expect just before the A/C kicks in, works fine when the truck is idling, but doesn't seem to wanna do this as I'm stopping - but this is difficult to tell. The idle-up process happens whether the A/C pump is unplugged or not.
What is going on? Hopefully it is something really simple, and I am just to stupid to think of it. Please help.
I have unplugged the A/C pump so the magnetic clutch doesn't engage and put a load on the engine, but interestingly enough it still stalls. This tells me that it is not as a result of the load, but rather an electrical circuit problem.
Some of the common things as mentioned in my FSM, like PCV hose, MAF sensor, O2 sensors seems fine, and besides this only started happening after the tranny swap. I have left the majority of the automatic transmission sensors unplugged, except for the park/ neutral switch and the back-up light switch. I have re-wired the park/ neutral switch somewhat, so that I used the stock oem clutch switch at the bottom of the clutch pedal and hooked it up to the park/ neutral switch's neutral position. So, when I depress the clutch, the ECM thinks the auto tranny is in neutral, and it allows me to start the truck. Thing is, it probably also thinks that I am shifting from drive to neutral when I come to a stop as I'm depressing the clutch. Also, if I still had the auto tranny and shifted manually from drive to neutral as I would come to a stop, I'm sure it wouldn't have stalled, though.
So, as I'm coming to a stop, which is the only time it will stall, the A/C is on, but does not cause a load on the engine, because it's unplugged, I depress the clutch, and hence puts it effectively in neutral, I depress the brakes which causes a load on the engine, the TPS is closed and the RPM drops. The computer does not know what my speed is, since I have no ABS and the VSS is not hooked up.
The idle-up that one would expect just before the A/C kicks in, works fine when the truck is idling, but doesn't seem to wanna do this as I'm stopping - but this is difficult to tell. The idle-up process happens whether the A/C pump is unplugged or not.
What is going on? Hopefully it is something really simple, and I am just to stupid to think of it. Please help.
09-22-2005, 06:57 PM
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So what did you do with the Factory Auto tranny plugs? just leave them unplugged under the truck?? Did you seal them off at all? There are quite a few wires that have +12V on them, that could be shorting out..
According to the FSM there is only 1 wire that goes through the firewall from the Body wiring harness to the Engine/Tranny wiring harness. The wire that engages the AC compressor clutch. There are two wires that go from the AC control assembly to the engine ECU, but i doubt that those are the cause of your problem since i doubt that they were touched durring your swap.
Does this happen every time you come to a stop? what about if you have the AC on in any other mode...
Steve
According to the FSM there is only 1 wire that goes through the firewall from the Body wiring harness to the Engine/Tranny wiring harness. The wire that engages the AC compressor clutch. There are two wires that go from the AC control assembly to the engine ECU, but i doubt that those are the cause of your problem since i doubt that they were touched durring your swap.
Does this happen every time you come to a stop? what about if you have the AC on in any other mode...
Steve
09-23-2005, 04:30 PM
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Originally Posted by NorCalVP
So what did you do with the Factory Auto tranny plugs? just leave them unplugged under the truck?? Did you seal them off at all? There are quite a few wires that have +12V on them, that could be shorting out..
According to the FSM there is only 1 wire that goes through the firewall from the Body wiring harness to the Engine/Tranny wiring harness. The wire that engages the AC compressor clutch. There are two wires that go from the AC control assembly to the engine ECU, but i doubt that those are the cause of your problem since i doubt that they were touched durring your swap.
Does this happen every time you come to a stop? what about if you have the AC on in any other mode...
Steve
According to the FSM there is only 1 wire that goes through the firewall from the Body wiring harness to the Engine/Tranny wiring harness. The wire that engages the AC compressor clutch. There are two wires that go from the AC control assembly to the engine ECU, but i doubt that those are the cause of your problem since i doubt that they were touched durring your swap.
Does this happen every time you come to a stop? what about if you have the AC on in any other mode...
Steve
It doesn't happen all the time. You know how the A/C has a cycle. Well, I think it is when the A/C just so happen to be in the on cycle as I stop. Also, the truck has to be fully warmed up for this to happen, i.e. after the "auto choke" is off. A number of things have to happen simultaneously for this to occur: I have to be applying the brakes. The A/C has to be on. The revs have to be low, i.e. at idle, and the clutch has to be depressed, and as I explained before, when I depress the clutch the park/ neutral switch goes on, i.e. the ECU thinks it is being shifted from drive to neutral.
09-23-2005, 05:24 PM
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What kind of MIL codes are you getting when you plug in your OBD II scanner? I'd imagine you would have a few for the tranny, One for the speed sensor, But I'd bet that you have some other codes stored in there too...
Don't worry about the park/neutral switch. According to the FSM, The park/Neutral switch, and the clutch switch, are wired the same way. I wonder if your ECU is wondering which gear it's in... Since your selection switch is just open... I wonder if it would be benificial for you to try to trick the comp into thinking that the truck is in park all the time... That way it won't try to mess with shift points or torque converter lockup... (http://fsm.afraid.org/) Maybe try messing with that...
I am actually in the middle of a similar swap, but mine is a little different. I am taking a 97 3.4L 5 speed tranny and T-case, and putting an 04 D-cab body onto it. Since the D-cabs only come with the auto tranny i am having to deal with some of the same problems. But i am splicing the wiring harness from my 97 into the 04 Prerunner body harness. (TOTAL PAIN IN THE ASS)... I am also using the stock 97 ECU, which is totally different from the 04 ECU. So My ECU won't be looking for any input from the auto tranny, but I will have a ton of extra wiring in the cab.
I posted on TTORA, but you might want to look into Vacuum leaks.
Don't worry about the park/neutral switch. According to the FSM, The park/Neutral switch, and the clutch switch, are wired the same way. I wonder if your ECU is wondering which gear it's in... Since your selection switch is just open... I wonder if it would be benificial for you to try to trick the comp into thinking that the truck is in park all the time... That way it won't try to mess with shift points or torque converter lockup... (http://fsm.afraid.org/) Maybe try messing with that...
I am actually in the middle of a similar swap, but mine is a little different. I am taking a 97 3.4L 5 speed tranny and T-case, and putting an 04 D-cab body onto it. Since the D-cabs only come with the auto tranny i am having to deal with some of the same problems. But i am splicing the wiring harness from my 97 into the 04 Prerunner body harness. (TOTAL PAIN IN THE ASS)... I am also using the stock 97 ECU, which is totally different from the 04 ECU. So My ECU won't be looking for any input from the auto tranny, but I will have a ton of extra wiring in the cab.
I posted on TTORA, but you might want to look into Vacuum leaks.
Last edited by NorCalVP; 09-23-2005 at 05:28 PM.
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