rebuilt a4ld no overdrive

[klein339]

I recently installed a rebuilt a4ld in my 94 explorer, but I'm having trouble with engine not starting( no signal is going to solenoid) and the tranny wont go into overdrive. Any sugguestions where to start

 

[MrShorty]

For the no start, check the starting circuit and the main ignition switch and wires.

Clarify the No overdrive. Does the transmission run fine through the first three gears, just not choosing to shift into 4th gear, or does the transmission not engage at all in the OD position?

 

[klein339]

tranny with shifter in od never goes above 3rd gear. I've tested on highway at 55 and changed shifter from od to d,

the no start happened the day after tranny install. when you turn key to start, you can hear a noise in engine compartment, but no juice through to firewall mounted solenoid. I can jumo the battery terminals on solenoid and it starts, and I can run a test lead from battery to the liitle wire to signal the solenoid to close( start) and it starts

I didn't know if somehow the two could be related if there is some kind of shift position sensor or something

 

[klein339]

a

 

[MrShorty]

There isn't a "shift position sensor" on the A4LD. There's a Park/Neutral position switch that prevents you from trying to start the engine in anything but park/neutral.

3/4 shift is computer controlled.

Did you get all of the electrical connectors hooked back up when you installed the transmission?

 

[BrooklynBay]

I was also thinking that it could be the neutral safety switch. Some models have 4 prongs while other ones have 5 prongs. A lack of overdrive could be the result of improper sensor inputs going into the PCM. This would prevent the 3-4 shift solenoid (overdrive) from getting a ground signal. The 3 prong harness has a 12 volt positive wire, and 2 wires which get grounded from the PCM to energize the solenoids. A snapped band, leaking servo, valve body malfunction or internal damage could cause a lack of overdrive as well.

 

[klein339]

we corrected the starting problem by removing an aftermarket alarm system that went bad. Didn't know it had one till started following the wiring. no problems starting now, but still need help to diagose why tranny won't shift into od ( 4th gear )
are there any external checks I can make??

 

[MrShorty]

Did you verify the wiring is all plugged in between the PCM and the transmission? Did you check to see if there is power to the transmission? Is the switch in the computer closing to signal the 3-4 shift solenoid to shift? Those are the main external checks. Get a wiring diagram if you don't have one, it's a pretty basic DC circuit.

 

[klein339]

I went thru wiring diagram and I do have positive current at the 3 prong plug that goes into tranny, but how do I check the 2 wires that connect to the computer that allow tc and od solenoid to function. I dont want to mess up computer

 

[BrooklynBay]

Check the wiring from the computer's connector. The computer sees the solenoids through this wiring harness.

 

[klein339]

I disconnected computer and ran hot thru hot and grounded the solenoid wire and got a clcik in the tranny. This is a fairly new computer so i'm not real sure where to go from here to find why computer is not telling to shift into overdrive

 

[MrShorty]

I know I've outlined this before, but here it is again:

1st) Pull codes from computer. Any number of faults in the engine management can prevent the computer from commanding 4th gear.
2nd) Put a voltmeter across the solenoid. Enter output state test (see my notes on pulling EEC-IV codes thread). You should be able to see the voltmeter "switch" from 12 V to 0 V. This will tell you if the computer can command 4th gear.
3rd) With voltmeter still measuring voltage drop across solenoid, test drive. You should be able to see the voltmeter switch from 12 V to 0 V (or 0 V to 12 V depending on exactly how you wire in the voltmeter) when the computer commands 4th gear. This will tell you if the computer is choosing to command 4th gear.

If the computer can and chooses to command 4th gear and the transmission doesn't respond, then the problem is in the transmission. If the computer can but never chooses to command 4th gear, then you have to work through the engine management system to figure out why (start with trouble codes).

 

[Hande]

Still no OD/engine braking

I have similar trouble with my A4LD. There's been no OD and no engine braking (in second manual) since we bought this '93 Explorer 4x4. First I changed everything that could be changed from the outside, then today I finally finished changing all things internal; bands, clutches, rings etc.
Still no change to 4th gear, no engine braking. So it seems the trouble is electrical or related to hydraulic pressure ? I'll get a pressure gauge and hook it up according to BrooklynBay's "most useful links", that's pretty straightforward, but if, as I suspect, that turns out to be another dead-end,
I'll be left with the electrical trouble alternative. The fault code reader shows nothing wrong with the system. As I understand the change into OD requires the coolant to be warm, the speed to be proper etc. My questions are: 1. Does anyone know the resistance values of the coolant sensor? 2. Has anyone tried to "manually" shift the tranny into OD by connecting "juice" to the OD solenoid? To completely rule out any fault in the tranny I thought I might try that. Any thoughts? Prior to trying this "manual" shift I would of course check whether the computer chooses to activate the solenoid. But if it doesn't choose to activate it, then I still won't know if the fault is in the tranny or if it is electrical, like a bad temperature sensor or the like. Or if the computer itself is faulty.

 

[klein339]

thanks guys. I'll be working on it and let you know. We did have some serious wiring problems from an aftermarket security system we pulled.

 

[MrShorty]

Hande:

1) I thought BrooklynBay had an ECT chart in his useful threads list.
2) Yes, but you've kind of got it backwards. The solenoid is always "hot", and the computer acts as a ground side switch to command the shift. Get a wiring diagram and visualize replacing the computer with a simple toggle switch.

 

[Hande]

Still no...

MrShorty
Thanks for your reply. I'll check again BrooklynBay's list. About the solenoid: Yes, I know the "hot" wire is always hot, but the solenoid is not activated untill the computer completes the circuit by connecting the solenoid ground wire to ground. I've checked the "hot" wire and it is "hot", so that part of the system is working. I'd sure like to get a wiring diagram (it would've been a great help in installing the car alarm) but haven't been able to find one. I bought the Chilton manual but it has no wiring diagram. Any suggestions as to where can I get one?
So you think if everything else fails, the "manual" shift experiment is doable?
BTW, I have already installed a vacuum gauge and a transmission oil temperature gauge under the dashboard, maybe I should install a hydraulic pressure meter and a OD light also. Would look kinda technical.

 

[MrShorty]

My Chilton's manual has several wiring diagrams in it for different years/engines. They put the wiring diagrams in the Chassis electrical section, so make sure you are looking in the right place. Unless they publish different editions that apply to a '93 Explorer, there should be wiring diagrams in there.

If not, check out the vehicle repair guides at autozone.com They have the exact same information as in Chiltons.

It is a doable experiment. It will answer the question "Can the transmission respond to the command to shift?" It won't necessarily help with "why won't the computer choose to command the shift?"

 

[BrooklynBay]

Check the VSS, and the TPS in addition to the ECT sensor. The ECT chart is # 25 in my list of useful threads:

 

[Hande]

MrShorty, I stand corrected. Yes, there are wiring diagrams in the Chilton manual. It was just something in the back of my head: "No usefull wiring diagrams!" I had trouble finding all the relevant wires when installing a car alarm system; had to use a magnifying glass, and still didn't find the wires I was looking for. I found the information I needed on some site in the web. So that's why I remembered there wasn't a wiring diagram in the manual.
BrooklynBay, thanks for the resistance value chart and I'll check your list.
I know I'm going at this backwards. I should have checked the electrical side and the pressures before tearing up the tranny, but this is a bit new to me. It's no fun carrying that greasy pig of tranny in a narrow grease pit with no help - and to what seems no avail! Well, at least now I know it's not the bands nor the clutches, it must(?) be electrical or hydraulic.
It's a life long process this learning thing; the longer you live the more you get to know - only the older you get the less your knowledge is appreciated.

 

[Hande]

Today I connected a lamp across the OD solenoid to see if the computer chooses to activate it. It does. But not exactly in the way I thought it would. I took off from practically cold (outside temp 15 C) and after a few hundred yards drive the lamp went on. No way the coolant temp would have been over 50 C. The lamp then stayed on untill a couple of miles further I dropped the speed to about 25 mph at which point the lamp went off. I tried various ways of accelerating and found out that the solenoid is activated at around 50 mph when accelerating medium hard, a bit higher than that if accelerating harder. Driving at a steady pace with the lamp on and then accelerating causes the lamp to go out, which I think it should do. But the main thing is: there's no shifting to OD. There are three sift points but the last in my opinion is the converter lock-up point. So it seems the fault lies in the hydraulic department. I haven't got a pressure gauge yet, so can't say anything about the pressures, but other than no OD and no engine braking the tranny works a dream. I'll try to get a gauge tomorrow and test the pressures over the week-end.