Stumbling that feels like a bumpy road

I'm not sure if it is a torque converter lockup issue or if the engine is missing thanks to an electrical problem or what.

I first noticed the stumble in overdrive, 1500 rpm, about 50-55 mph with just enough throttle to maintain speed. It feels like the truck is going over heavy gravel, but the pavement is smooth. Downshifting and maintaining speed smooths it out, as does adding more throttle input. The engine feels like it has normal power except for the stumble.

The check engine light is not on (but does work). I have seen these codes:
P1229
P0700



On the way up the pass this afternoon it seemed worse: it occurred in a wider range of parameters (RPM, speed, gear, and throttle input).

Transmission fluid is clean and clear; it gets drained/filled with new screw on filter every 25K or so. The truck has about 253K miles on it. A few months ago I had some electrical issues that would drop the engine into limp mode, but some fresh wire loom and pinching injector pins seems to have cleared that up.

It's my work truck and sees daily use. The Benz is nice to drive around, but I'd rather not put all my tools in the back seat. The devil on my shoulder is telling me to start looking for a newer truck...

Thoughts?

The SES should be on, with the P1229 while it's still running rough, even if they are in recent history. You need to read the TCM to find out what's causing the P0700 (possibly caused by the stumbling engine). Look at connector blocks and harnesses (specifically the FICM), grounds between the block and chassis, and engine mounts. Worn out mounts allow the engine to move around in ways it wasn't designed (pushing and pulling on connectors, etc.). It could be related to your previous issue.

Or:
It's usually something simple.

Back in late August (about 3,000 miles ago) I drained/filled the transmission fluid, along with a new screw-on filter. I put in only 7 quarts of Dex 6, and remember thinking that I should check it sometime in the next few weeks...

Guess what I didn't do?

Yup, it was a quart low. Adding a quart today brought the level to about dead center of the cross hatching on the hot zone. A short test drive before the quart revealed a big stumble. After the quart, the stumble was gone. Hopefully I haven't taken much life away from the torque converter lock-up clutch, but I'm thinking that was all it was.:o

Used to be, I'd always suggest the simplest (and dumbest) things first. Funny how many folks get offended when suggesting to check the fuel level in the tank, or just smell the filler for gasoline. Oftentimes, that's the problem. Years go by, and we, who've been around here a long time, just assume someone else who seems knowledgeable would have already checked that stuff, you know, like fluid levels. As usual, the problem can often be tracked back to the last touch, such as in your case.

On the cautious side, you may not be done with this. One quart isn't much, to lose or to gain. Meaning, only one quart should not have caused that much of an issue. Still, check that P07xx code in history before it clears, or returns with a vengeance. Low fluid will usually trigger codes related to solenoid delays or main pressure, long before you see/feel any affects. Your trouble speed does correlate to converter lock-up, though.

Yeah, I've got a feeling that this isn't the end of it. In past years when the ATF has been low it has made itself known by not fully engaging gears or racing between gears when shifting. Tomorrow will tell the tale, and I may need to pick myself up an early Christmas present of a better code reader than and ELM adapter paired with Torque Pro. Been reading about the P0700 and it SHOULD have tripped the CEL but it didn't.

The ATF level should've been the first thing I checked after getting home on Friday...:o

Quote:

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Transmission fluid is clean and clear; it gets drained/filled with new screw on filter every 25K or so. The truck has about 253K miles on it.

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I had a P0700 appear once in Lil Red... due to too much power.. it slipped a little during an upshift. No other trans related codes appeared with the 700. So, it's possible to see a 700 without any other related codes.

Generally, the recommended first step in analyzing a transmission problem is to verify fluid level and then change the filter, if the fluid level/color wasn't a problem.

Fluid level... there was a torque converter "fluid drainback" condition with the Allison that caused fluid to leak out around the dipstick filler pipe seal when the truck sat for some period of time. An initial fix was offered that simply allowed owners to run their Allison a quart low. This wasn't a problem for trucks that were driven once or twice a week.

MP, that's some interesting info.

Drove the truck for work today and was 95% happy with how it went up and over the pass and around Jackson Hole. That other 5% is alarmed by what my butt dyno is telling me about the stumble still being there. I'll be talking to the local mechanic that does those things I can't do on the truck (not much, typically only the things that mean heavy lifting) to get it in to have a closer look at the wiring and put it on a proper scanner.

In the meantime, I've left it in JH at the Chevy dealer while I try on a new Silverado 1500:D

My Lil Red conversion truck has a TC that drains back, mostly because it sits for months - sometimes through the winter. If the fluid level is kept at the hot full mark, it'll leak fluid from around the dipstick pipe seal at the transmission during the winter as the TC drains back and the fluid level rises in the transmission. I just let it leak... till it stopped on its own. That's the way I run it - have run it for a long time.

By the way, how are the truck's U-joints?