Stuck in 3rd Gear

[ugandaburb]

I've got an automatic transmission ('96 2500 6.5L Burb). When I manually drop it down, it will go into second gear. Otherwise the car stays in 3rd. . . can't get it into 4th either.

The car slowly builds up to 30mph and tops out at 50mph (with my rpms racked it blows black smoke). I have to put the car in neutral to push the 4WD button, but it doesn't engage until dropping into drive.

I don't have a diagnostics tool to check the codes (I live in Uganda), but one will be here in two weeks.

So far I have:

1. Replaced the fuel filter (and turned the small plastic bit on top allowing fuel to run for a bit)

2. Replaced the transmission fluid and filter. No particles in the pan and I cleaned all the connections for pressure switch, solenoids, etc.

3. Removed the catalytic converter (thinking it may be clogged)

4. Cleaned and replaced the air filter.

5. Checked fuse boxes.

6. Kicked myself repeatedly for not joining the dieselpage sooner. I have searched the forums several times, trying not to duplicate this process. Forgive me if I'm doubling your efforts.

[Wing Nut OOA]

i remember reading somewhere that the Band in the transmission for 2nd and 4th are the same, but that doesnt explain why it stays in 3rd.

most of the time i would say it would start in first and then shift to 3rd but you'd have to rev the snot out of it to get it there. and then you wouldn't be able to get past there.

automatic trannys are weird sometimes.

[ugandaburb]

i remember reading somewhere that the Band in the transmission for 2nd and 4th are the same, but that doesnt explain why it stays in 3rd.

most of the time i would say it would start in first and then shift to 3rd but you'd have to rev the snot out of it to get it there. and then you wouldn't be able to get past there.


The 1-2 solenoid is "ON" for 1st and 4th gear, and it is "OFF" for 2nd and 3rd gears. I was kinda wondering if it was just stuck to OFF and I need to get another one. I looked at the solenoid and it seemed okay, but I didn't test it or anything.

I don't know much about band movements. No matter how much I rev the thing. . . no fourth gear.

[JohnC]

Any strange behavior of the speedometer, tach or gear indicator light? Shifting problems are often traced to low voltage on the trans/instrument circuit, often caused by a failing ignition switch. Once it senses a problem it'll stop shifting.

[ugandaburb]

Any strange behavior of the speedometer, tach or gear indicator light? Shifting problems are often traced to low voltage on the trans/instrument circuit, often caused by a failing ignition switch. Once it senses a problem it'll stop shifting.

The fuel gauge needle has been acting erratically but the rest are fine. How could I check this voltage?

[DmaxMaverick]

Is the "Service Engine Soon" or "Check Engine" lamp on? It should be.

Sounds like you are in "Limp Mode". You need to read the DTC's (PCM codes) to determine what the PCM is seeing, and why it's acting this way. You'll need a Tech II or OBD II code reader.

It could be a transmission issue, but the tranny will only do what's commanded by the PCM, if it can. You really can't proceed with diagnosis until the codes are read, short of guessing, trial and error, or just getting lucky.

[ugandaburb]

Is the "Service Engine Soon" or "Check Engine" lamp on? It should be.

Sounds like you are in "Limp Mode".

That's what is strange. . . the "Service Engine Soon" light is NOT on!

[ugandaburb]

I just removed the factory fuel filter unit (in order to install a fuel/water separator). After removing it, I found about 3/4 inch of sludge in the bottom! Is this common?

If this is a clue to my problem, what else would you guys suggest? Fuel pump cleaning/replacement? Clean the tank?

[DmaxMaverick]

That'll do it. Every time.

You should clean/flush the entire system, drop/clean the tank, then treat with a heavy dose of a biocide for the first couple tankfuls. Change the filter often (and keep several handy) until you are certain the system is completely clean. If you don't clean the whole system, it can take several weeks/months and many thousands of miles to clear it. All the while, filters will plug regularly, as the algae dies and becomes a particulate contaminant. Unless you can identify the source of the sludge (being other than biological), assume that is what it is, and treat it as such. It won't go away on its own, but will continue to grow.

[ugandaburb]

Well. . . the filter cleanout didn't solve it. Any other ideas? (that don't include a code reader)

[DmaxMaverick]

You should clean/flush the entire system, drop/clean the tank, then treat with a heavy dose of a biocide for the first couple tankfuls. Change the filter often (and keep several handy) until you are certain the system is completely clean. If you don't clean the whole system, it can take several weeks/months and many thousands of miles to clear it. All the while, filters will plug regularly, as the algae dies and becomes a particulate contaminant. Unless you can identify the source of the sludge (being other than biological), assume that is what it is, and treat it as such. It won't go away on its own, but will continue to grow.


Anything short of this probably won't help you much. The fuel line uptake sock is probably as bad as your filter was, and the pump and lines are likely fouled. Just a filter change won't do what you need done. Kinda' like searching for something where you know it isn't, because the light is better. It may make you feel good at the time, but it does not solve the problem.

You could test your system downstream of the filter by supplying fuel from another source, like a fuel can, from above (gravity supply), connected directly to the filter inlet. Remember, if you don't re-plumb the return line, most of the fuel you feed through the IP will get returned to the tank. A return line to your "new" fuel source will eliminate that issue.

[midniteplowboyy]

Unplug the big round connector on the side of the trans. Go for a short drive with shifter in OD position, trans will actually be in second gear, if trans is working correctly.

If still in third, its prolly a bad solenoid or stuck valve in valve body.

If it goes to second, unplug both the PCM and big trans connector, ohm the 2-3 shift solenoid wire to ground(it should be open, no continuity).

Tell us what you find.

[ugandaburb]

midniteplowboyy, great advice! I unplugged and went for a spin. . . still in 3rd. I'll order new solenoids and a valve body kit. (unless you've got ideas for tinkering with the old ones)

DmaxMaverick, I'm pulling the tank in the morning. . . it'll get a good scrub down.

[JohnC]

Are you sure it's not second? Second is the normal "fail safe" behavior. If you can't go more than 55, it's probably 2nd.

These electronic devils have a lot of built in troubleshooting. You really need to get a code reader. I would not order any parts until you do.

See if you can find a fuse labeled "trans" or something similar. Or, find a fuse which, when pulled, makes the gear indicator light go out. Put a volt meter on that circuit. It should power on anytime the key is not in the lock position. If the power on that circuit ever gets below 8 or 9 volts the PCM will default to second gear.

[ugandaburb]

JohnC, there's a reason that "Newbie" is under my name and "Moderator" is under yours! I'm not sure of ANYTHING! :D

The car putters up to 30mph before offering any decent acceleration, then the car tops out at 50mph. I'm just guessin' 3rd. I ordered a code reader (we'll see how long it takes to get here, but I've never gotten a package in less than 3 weeks). I just hate waitin'!

I tested the "trans" circuit just now. . . it's clocking 11.8V. The fuse panel calls for a 10A fuse, but I found a 25A in place.

[JohnC]

11.8 is suspicious. When running it should be close to battery voltage, 14 volts or so. The ignition switch has a separate contact for that circuit and it is a known problem, at least in the earlier trucks. Pay attention to the voltage immediately after turning the key from lock. This powers up the trans circuits as well as the tach and speedometer. The PCM tests the current on the solenoid circuits and if it doesn't see what it's looking for it locks the trans in second.

The 25 amp fuse is a little suspicious, too. Maybe something on the circuit is pulling it down, enough to blow the 10 amp fuse...

You might try running a wire from a good power source (unswitched - it has to be powered before the self test) to that fuse and trying it that way.

[midniteplowboyy]

Check to see if your getting 12v @ the trans connector. If you want to rule out some things manually, I'd clear the codes first and see what it does.

Find a pinout diagram on the net of the trans connector, and pcm connector. Tie two extra wires that you can can ground while driving, one to the 1-2 shift solenoid and the other to the 2-3 shift solenoid.

Ground the 1-2 wire will give you first. Ground the 2-3 wire will give you third. Ground both gives you OD. This is a simple way to rule out solenoids and valve body when no scanner is available.

Also with the key on have somebody listen to the valve body while you ground each solenoid, you should hear a click, if no click first ohm the solenoid through the trans connector, if no click and your vehicle wiring checks out and the solenoid ohms ok it could have trash in it. If you have a click but still wont shift, I'd still suspect trash in solenoid or stuck valve behind solenoid first(see if valve will move before removing valve body).

If you can manually shift it by grounding, check your trans input speed sensor first(I'd ohm both though).

See what you find and maybe I can help, its kinda hard to do without seeing the truck in person and a good scanner would help also(but not entirely needed most of the time, just alot easier with one). Keep working at it and you'll figure it out.

Clear the codes again, after doing the mentioned above, your computer will kinda flip out(wont hurt it, just set codes)

If you'll be doing other serious work to the truck in the next year, I'd suggest an alldata subscription for your truck, think its like $30 a year. Just save it all to your computer and you'll be set after the subscription runs out.

Good luck,