Transmission Problems - '97 Chevy 1500

[Gearheadtom]

So I've been having trouble with the transmission not shifting quite right on my truck. To start, the truck is a '97 chev 1500, 2wd, 305 vortec, and 4l60e trans I think. The trans works good under normal city driving, but if I get hard on the gas, or on long upgrades above about 80 km/hr, I start noticing that the truck won't shift right. Basically, if I get hard enough on the gas that it'll downshift, it won't upshift again until I let off the gas to about 1/4 throttle. It'll just keep accelerating until 4000 rpm, then stay there.
I'm thinking more an electrical problem rather than a mechanical problem with the trans. Only code that came up when I scanned it was for the maf sensor, but I've dealt with that.
Trans fluid it still a good red color, not burnt, and I have yet to do a fluid and filter change. The truck works perfect otherwise, only dash light on is abs, and that's because I pulled the fuse ( I hate abs).
Anything else to check before I start on trans specific issues?

[Scootertrash]

I believe you are correct that it's a 4L60E. You may want to run it to a shop so they can do a deeper scan on your computer. Are you just using one of those auto store home mechanic scanners?

[Gearheadtom]

I believe you are correct that it's a 4L60E. You may want to run it to a shop so they can do a deeper scan on your computer. Are you just using one of those auto store home mechanic scanners?

Ya, that's all I've been using, just to see if any codes come up. That's what I've been thinking about doing, taking it to a shop so they can use their scanners with it running and see what kind of reading each sensor and such is giving. I've been putting that off tho due to lack of money haha.

[Gearheadtom]

I did have some more codes come up again, the maf sensor one came back, two different 02 sensor codes, and an egr code that I dealt with a year ago came back.
I had replaced the maf sensor with a junkyard one, I'm guessing now I have a wiring problem, or an air leak. All of them came back within a week or two of me checking it last.

[Gearheadtom]

Got an email saying mts made a post, but now I can't see it... I'll answer the questions he asked tho...
The truck has about 180,000 km's on it, no shudder's or anything, at least not from the trans (I've got out of balance tires, and warped rotors haha).
It shifts perfectly normal if I drive it normal, but when the motor gets under a load either from climbing hills at highway speeds, or if I accelerate hard is when it hangs in gear. It does the same thing at lower speeds to, like if I hit it hard at about 40 km/hr it'll downshift, and rev like normal, but just keep accelerating and reving.

[Gearheadtom]

I've been doing some more reading on the problem and talking to a buddy of mine, and I guess the intake gaskets going are common on these vortec engines. So that would explain the maf sensor code coming back, and explain why the truck seems to run better with the maf sensor unplugged. Some people have reported having shifting problems as well with the intake leaking. Usually they either leak coolant out, or into the motor, and my truck has been doing neither.

[MTS]

sorry i deleted the post after re-reading yours a few times, The intakes are known to leak they will suck oil up the intake tract too, and air out the top depending on what gaskets are in there, and with 180km im sure they have been changed at least once. it could be the problem, throwing your maf,map, and tp sensor out causing it to not shift right under a load and a few otherthings. Just a fyi the dist gear wears out too and throw's the timing out several degrees causing poor running, somethin to look at. also your descrtiption sounds alot like my truck with a 700r4 i have to back out of it to upshift from 3rd to 4th when layed on but that's a complete differnt set up that im working on.

[Gearheadtom]

Okay, thanks. I thinking that an intake leak is the problem, that also explains the intermittent little shudder I feel at idle sometimes, just big enough that I notice it a bit. I've got another distributer here anyway in case the gears are worn, but like normal, where the screws go in for the cap is broke haha.

[max]

Most likely engine performance issue. Fix your engine problems first!!!

[Mosh]

It sounds to me as if the cats are plugged partially. This will cause the O2's to hang rich and not read correctly, force excess exhaust backpressure through the EGR system, and wig the m.a.f out since it can't draw air into the engine, due to the exhaust restriction. Remove the front O2's and rent a vacuum gauge and O2 port tester from a parts store. Install the tester into each 02 port and start the engine and let it idle. There should be no pressure on the gauge. If you have even 1/2 lb of pressure or more, say a 1lb or over, you cats are plugged. Also rev the engine while watching the gauge, it should not build any pressure. It is a classic symptom and problem for that vehicle with that mileage. If the tool is not available or testing is to complicated to do, drop the Y pipe and see if your symptoms go away. If so cats are clogged. When they clog up slightly, it causes the trans not to shift until you let off the throttle some.

[Gearheadtom]

I thinking I might have a look at the intake gaskets first, it would be the easiest to do considering everything underneath the truck is rusted to badly. Y-pipe bolts aren't recognizable, and the O2 sensors don't look much better.

[Gearheadtom]

I tried the carb cleaner trick to see if I had an external intake leak, and found nothing, but I didn't notice that before I even started, the intermittent slight shutter this has at idle was back, and after spraying carb cleaner around the idle got progressively worse, but that may or may not have been from the carb cleaner.

[EngineBob]

I work on a lot of these trucks and when they have a problem like this with multiple codes like O2 sensors I check fuel pressure and change the filter. They are very pick on the pressure.

[Gearheadtom]

I might have a look at that first then. I changed the fuel filter a few months ago, but I know my tank is getting rusty on the inside, and my last filter only lasted a year until it started to clog and the truck started acting up a bit, never had a shifting problem before tho, just rough idle and sometimes wouldn't start up as quick.

[Gearheadtom]

I've been noticing something else odd with this truck as well, if I unplug the maf sensor, the truck seems to have more power, and be sharper off the line.
I also tried to see if this truck would lay a patch of rubber as well as it did last summer, and now all it'll do it give just a few chirps if I hold to to the floor pulling out of somewhere.