99 Blazer Hesitation

[mikendeb1202]

I have a 99 S10 Blazer with 4.3W.
I guess it might be hard to describe, but it has a hesitation under acceleration in first gear. on take off it will start going then fall on it's face for a second then go the fall again. It will do it up to about 25-30MPH after that it is fine. It does it cold, warm, hot.
First thing I tried is a new fuel filter and air filter.
Now, I started checking for problems at the intake, found an antifreeze leak in the rf corner of the manifold(common), only to discover the manifold was cracked!!! Figured while doing the work I replaced plugs, wires, cap, & rotor.
So, now I get this all done, and it still ran exactly the same.
My next step, I check fuel pressure, with KOEO, had just over 60 PSI.
KOER, had just under 60 PSI. Now, unfortunatley after a conversation with one of the guys at my employers tech line, I find myself suspecting the fuel pump.
So, as my luck has been, I put in a new DELPHI fuel pump assembly, and still runs the same.
Now, here is where I think I might be looking, correct me if I'm wrong, but possible torque converter or solenoid?
When I am trying a take off, while lightly holding the brake pedal it seems like the problem is gone. If I try without touching the brake, as soon as it starts to fall I tap the brake and it jumps right back up.
Does this sound like a possibility.
I have been a technician for about 20 years and I have never had so much trouble trying to diagnose a problem, this one has got me baffled.

Thanks for lookin'
Mike n Deb

[mikendeb1202]

Ok, now I took it into the shop today. I dropped the tranny pan and installed a new TCC solenoid, filter, and gasket. Plus we have a wynns transmission flush machine, so I also did a flush.
Guess what? It still did the same thing.
A friend of mine who owns his own shop stopped by and we shared some thoughts on the issue.
I have a OTC Genesis scanner with pathfinder 2003 software installed. We hooked up and went into data stream for transmission.
Now here is where it gets interesting. From take off it is showing me to be in 4th gear by the time I'm going 30 mph!!
Now I'm not a tranny specialist, but I don't think it should be in 4th by 30mph.
Now the next thing we noticed, once up to 4th, stomp the gas to the floor and it will not downshift???
If there is anyone who has seen or heard of a problem like this PLEASE HELP.
I have a breakdown of the solenoids and DTC diagnostics, but there are no DTC's.

[maxwedge]

If you manually shift 123, does it do this? With a bi-directional scanner for transmission diagnostics you can command all your up shifts and determine what is going on here. Usually if a shift soleniod fails it would set a trans code. The tapping the brake issue is the key here, that would kick out tcc, but this can be seen on a road test with the trans scanner. Try unplugging the main connector at the trans and make sure it is not corroded and making good contact.

[whitetrash982]

does it have a lock up tq converter? i know the full size chevy , at speed , the converter locks up , and if you just tap the brake , it un locks , perhaps it could even be some sort of computer issue. thought that tid bit of info cuold be a bit useful

[mikendeb1202]

It will shift through all the gears manually without any hesitation or slipping. I even put in a new TCC solenoid, filter kit, and ran a flush on the tranny.
I read this article on these trannys that has me thinking, but I can not come up with a definite answer.

Here is a part of the article:

CM/VCM receives signals from various transmission sensors.
Sensors include engine speed and throttle position, transmission
speed, hydraulic pressure and transmission fluid temperature. PCM/VCM
has on-board self-diagnostics to help identify any parts or circuits
which may need further testing.
Shift solenoid holds hydraulic pressure (solenoid on) or
releases hydraulic pressure (solenoid off). This action controls shift
valves inside valve body. By switching one or both solenoids on or
off, different combinations of clutches, sprags and bands are
operated. See SHIFT SOLENOID OPERATION table under SOLENOIDS.
Line pressure control system compensates for normal wear of
transmission components during upshifts in order to maintain optimal
shift quality during life of transmission. PCM/VCM uses "adaptive
learning" to maintain acceptable upshift times by adjusting line
pressure. PCM/VCM compares actual "acceptable" shift time to
calibrated desired shift time and calculates difference. An
"acceptable" shift is considered valid if no inconsistent vehicle
operations (A/C compressor cycling or extreme throttle changes)
occurred during upshift. Line pressure is either increased or
decreased depending on duration of time for upshift.
ABC123
PCM/VCM
Passenger cars and light trucks with 2.2L, 4.8L and 5.3L
engines are equipped with a Powertrain Control Module (PCM). All other
light trucks and vans are equipped with a Vehicle Control Module
(VCM). For PCM/VCM locations, see PCM/VCM LOCATIONS table.
PCM/VCM controls TCC, pressure control solenoid (hydraulic
pressure), PWM solenoid and shift solenoids 1-2 and 2-3. In addition,
PCM/VCM also controls ignition, fuel and emission devices related to
engine.
PCM/VCM receives electronic input signals from sensors and
switches. These signals help PCM/VCM determine when to operate various
relays and solenoids related to engine and transmission components.
NOTE: PCM/VCM is also referred to as "control module" throughout
this article.

[mikendeb1202]

The part about "Adaptive Learning" is where I start burning brain cells!!

[maxwedge]

Again, a scan with a full trans capable scanner will reveal if this is trans related, used by someone who is familiar with what to look for of course.