AW4 electrical problems, quick question

[Amund2]

I searched, found a lot, but I still have a question.

My AW4 won't always drop to 1st gear after stopping, i.e. stays in 4th or something. But sometimes it works perfectly. My question is - can it still be a solenoid, when it sometimes works and sometimes don't, or does it have to be a loose wire/bad connection/ground (i.e. will it NEVER work when a solenoid is bad, or will it work sometimes) ?

 

[jeeptime1]

I searched, found a lot, but I still have a question.

My AW4 won't always drop to 1st gear after stopping, i.e. stays in 4th or something. But sometimes it works perfectly. My question is - can it still be a solenoid, when it sometimes works and sometimes don't, or does it have to be a loose wire/bad connection/ground (i.e. will it NEVER work when a solenoid is bad, or will it work sometimes) ?

Are there any trouble codes stored? Sounds like it could be starting in limp mode intermittently. I don't know off hand which range the AW4 starts off in, when in limp mode (I'm at work right now - can't look it up) .

How often does this happen, when hot or cold, does it start in first after shutting the engine offf and restarting?

Bob

 

[DaveD in Canada]

Could be a flakey TPS.

 

[Amund2]

This happens all the time nowadays, and it's like that about 50% of the time I guess. I really can't see a pattern in when. Sometimes I start it up in the morning and it's fine the whole trip, and sometimes I start it up and it's bad from the beginning. And sometimes it switches between good and bad in one-second intervals (well not precisely, but something like that).

A while ago this thing only occured very seldom. Then it seemed that if I shut the ignition off and back on again it would work fine. Now I'm not sure, as it will come and go as it pleases, I can floor it from a stop and it may jump up and down between 1st and I don't know, 2nd, third or something, but when it picks up speed and gets to the higher gears it's all fine. So before when it started working again when "rebooting" the computer would make it seem like a limp mode, yes. But if it's limping now, wouldn't it stay in limp mode till I reboot (turn the key off)? Will a faulty TPS put the TCU in limp mode? Is the power to the TCU cut every time I turn off the ignition, unlike the PCM?

You say trouble codes, do you mean in the engine control computer, or the transmission computer? Because I don't know how to read fault codes from the transmission computer, if possible.

Yes, TPS sensor may also be it, but I'm definately not buying a new one unless I'm sure that's it.

All help to find what causes this is very well appreciated!

Maybe I should start off by checking the engine fault codes, I don't have the light hooked up yet, old XJ with a newer swapped-in engine. If it has a TPS error code - then that's probably it!

I've found an AW4 service manual, and I could check the solenoids, but I don't want to drop the pan and lose the oil unless I really have to.

I have also suspected the neutral start switch, it's a little buggy sometimes, occasionally it won't start unless I hold the key and wiggle the stick a little. I've noticed how that same switch connect different leads to the computer, so I was thinking maybe that could confuse the TCU.

 

[Amund2]

Checked the error codes, just something about the automatic shutdown relay having a short or open circuit, don't know what that is, but I think it's quite irrelevant to this case? So nothing about the TPS, but I guess an error code don't have to be triggered for it to make problems, I'll measure it tomorrow.

 

[Amund2]

Was at a Chrysler/Jeep dealer today, they ran a ODB3 thing on my computer, with an old card for the ODB1 in it, didn't work properly, and hung up on us when trying to enter transmission fault codes (everything else worked). I have also checked my TPS with a voltmeter, seems fine.

 

[Amund2]

I measured the solenoid resistance today, through the plug on the computer, I guess that will add some ohms, also I just used the body of the car as ground. I got about 14.5, 15.5 and 7.5 ohms for sol 3, 2 and 1 respectively. Number 1 is clearly out of spec, as the AW4 manual says it should be between 11 and 15 ohms.

What happens when these break? Is it just an internal short somewhere in the spool, giving lower ohm level, and reducing the magnetic force to a level where it sometimes work, sometimes don't perhaps? These solenoids are expensive, so I would like to make sure I have to change it before I do.

 

[old_man]

Was the computer disconnected when you checked the ohms? If not you can get flakey readings. 7.5 seems a bit low but the others are about right. Personally, 7.5 wouldn't scare me.

Tom Houston

I measured the solenoid resistance today, through the plug on the computer, I guess that will add some ohms, also I just used the body of the car as ground. I got about 14.5, 15.5 and 7.5 ohms for sol 3, 2 and 1 respectively. Number 1 is clearly out of spec, as the AW4 manual says it should be between 11 and 15 ohms.

What happens when these break? Is it just an internal short somewhere in the spool, giving lower ohm level, and reducing the magnetic force to a level where it sometimes work, sometimes don't perhaps? These solenoids are expensive, so I would like to make sure I have to change it before I do.

 

[Amund2]

Yes, I unplugged the TCU and measured into the plug...

I would guess the 7.5 is because that solenoid is shorted to itself somewhere in the middle, isn't that possible?

I also thought that measuring through the harness would cause higher ohm readings, but nothing (other than a shorted sol) could give lower ohms, right?

Maybe I'll have to drop the pan then, to measure them directly, if f.i. the wiring and grounding adds four ohms... then 7.5 is really low. Also, the manual does say to replace them if they are above or below spec... But if this is not what's causing it to misbehave then I don't want to change it... so any further help is appreciated (if you're certain that this isn't causing my troubles). However, it does seem to fit pretty well, I've studied the shifting patterns and I'd think sol1 would cause problems with the lowest gears. Also, a close-to-spec reading could maybe cause it to work sometimes, and sometimes don't, depending on ??? varying voltage, oil viscosity caused by temperature, pitching of the car and so on?

I'll have to investigate further, but does anyone know somewhere I can get that solenoid for cheap through the net?

Thanks for all the help so far.

 

[old_man]

The reason that measuring while the computer is installed is that there is +12v to the computer on at least one pin all the time. Don't know why they didn't do all the power switched, but if there is power to the circuit and you try and measure, it can effect the ohm's reading. I have been doing electronic test and design for too many years to count and have run up against this several times.

As for the ohms. I just did an AX-15 to AW-4 swap and had tranny problems due to a wiring issue on the computer. I measured the solenoids on my rig and the 1'st gear solenoid measured almost 20 ohms on mine while the others measured approx 15 ohms.

 

[Amund2]

Okay thanks. But I have a lower ohm reading. Won't that mean that the spool is somehow shorted between it's coilings, reducing it's magnetic field, probably to an extent where the solenoid won't send the oil where it's supposed to?

It's quick to disconnect the battery, if that helps my readings. Or I could drop the pan and measure the solenoids directly, but I'm a little lazy and a little broke, and the gearbox is full of quite new oil so I'd rather avoid doing that if I don't have to.

Still, if the solenoid is NOT the problem, then I don't know what is...