dsl4me

Did search but still have some questions.
Have a 1998 12V/auto that is shifting 1-2 <10mph and 2-3 around 17mph, regardless of throttle position. 4th and TCC seem normal. Test drove a stock '99 24V and 1-2 was ~20mph and 2-3 ~30mph, both with 3.54 gears.
Trans recently rebuilt with a dynamic billet converter(stock stall speed) and transgo kit. Early shifts happened before the rebuild as well.

Rebuilder thinks its a TCM controll issue. He has tried all kinds of TV adjustment, has the PR turned up and running higher than stock line pressure and swapped in a V10 V/B all with no luck. I have taken the T/V cable and unhooked from the pump and tied it all the way forward and did not change the shift timing.

Thinking about having the TCM reflashed from the local Dodge dealer($95). From what I read in the Dodge service manual there are 4 shift curves programmed into the TCM depending on temp/tps etc.
It's reliable, just did a 1700 mile road trip pulling a 22' enclosed trailer but did a lot of manual shifting. Truck has 180K+ on it.

Anyone else run into something like this?

mr T

yes u can have it flashed at the dealer i believe...i know i can get the 47RH reflshed there for TC lock-up speed

JKM

You can adjust the TPS on your truck fo different lock and unlock points too.

dsl4me

4th gear and TCC operation are ok. Issues are with 1-2 and 2-3 shifts, also does not down shift as soon as I think is should. Service manual does not show a flow chart for quick/early shift points.

dsl4me

Grabbed my brother in-laws matco scanner and looked at the limited data it has available. Gov voltage stays steady at 0.53V but I think that is due to a in-line resistor from the trans go kit??
Gov D/C starts at 40% and drops rapidly, actual Gov pressure is 80PSI+by 24mph.
Anyone have a manual handy to see what the specs are?

Dan

raychem

gov pressure shoulds increase 1 psi per mph(ex...0 mph 0 gov. pressure...30 mph 30 psi) where did you get the 80 psi from...the ecm scanner reading or the trans gov. port. The high gov pressure is causing you early shifts.


Richard

dsl4me

Yes, you are correct. IIRC the builder told me it was increasing 1psi/mph. Now it makes me wonder what he was looking at. The reading is from the scanner, I have not hooked up a gauge to this one yet.

Problem is I don't have a whole lot of time to screw with it, hence having someone else rebuild it. I am moving out of state this coming Saturday pulling a 20' enclosed car trailer.

Does the MT2500 snap-on scanner show line pressure readings?

Going out for a drive tonight and will CK the scanner again, pretty sure it shows 80psi by 30mph. Has a new Gov transducer and pressure switch installed. I'll check PSI @ 10mph increments if I remember while out.
If this trans has an adjustable pressure regulator and it is cranked up too high is it possible the TCM can't bleed enough pressure off and that is what is increasing the Gov pressure?

Will also try and whatch what is the desired Gov pressure at those mph readings.

Thanks, Dan

dsl4me

Ok, @ ~10mph there is 15-20psi gov pressure and it is erratic while holding 10mph. ~20mph and 45-50psi gov pressure. Interesting thing is the actual gov pressure matches the target gov pressure. So from what I see something is telling it to make that much gov pressure.

Speedometer reads steady and so does the mph on the scanner.
Question: Does the TCM use a different speed sensor than the speedo? If not then why is it asking for such high gov pressures??

Dan

dsl4me

Drove truck in 3rd with TCC locked up. Engine RPM and output RPM were within 20 of each other. The output was a more stable reading than the engine. Scanner mph matchs speedo reading.

Around 27 mph the target gov pressure jumps from 90s to 127 which appears to be a max request. At that point actual gov pressure can attain "only" 90 psi. Running in 3rd up to 50mph(2000rpm) can only hit 95 psi. It can't even attain what it is asking for, unless that is the max reading for the pressure sensor.

Why is it asking for such high gov pressures????

raychem

Your gov. pressure is the cause for the shift problems. You need to get the acctual pressure from the transmission b/c if the pressure senor that reads gov. pressure is bad them the ecm is not seeing the acctual pressure causing your erradic shift, hence why I ask for pressures from the trans direct. I also don't like shift kits and if there is a problem with it, it will effect everything( I AM NOT FLAMING HERE...LOL).

Richard

dsl4me

Going to try and dig out my pressure gauges and see what I can come up with.
The pressure sensor and transducer have both been replaced. The rebuilder never looked at it with a scanner before the work so I can't comment on what it was before but the shifts were early then as well.

Dan

dsl4me

Took reading from what I believe is the gov port, top rear facing right, and it is really close to what the scanner reads. 20mph 40+psi, 30mph 90 psi etc. 2nd port back from front facing slightly forward was ~90psi @2000 rpm. Check the port facing rear and it never went over 95psi, one to the front which is for a servo I didn't check.

So actual pressure is mirroring scanner pressure which is what the gov target pressure is. Any idea why it wants so much?

Dan

raychem

dsl4me,

Yeah you got the right port rear trans top on passenger side. I will only say that the trans shift kit that was installed might be the culprit. I know that many people have used transgo kits with good results and I would tell you to give them a call or find a stock vb for your truck to test and see if you still have the same problem(which you shouldn't). Ooh and one more thing, see if you trans guy has another gov pressure solenoid, I have see them bad from factory before but rarely. At least you know thats the problem though.

Richard

dsl4me

Well from all that I can find out my shift points are normal.
DTT says the 12V were the worst for early shifts, TransGo states in their instructions some vehicles are programed to shift at 4mph and 11mph which is earlier than mine.
Actual gov pressure is the same as target pressure.
DTT tech did say their valve bodies will help delay the shift points, to a point.
He did recommend having the TCM reflashed with the latest updates and then consider a V/B upgrade if still not happy.