flywheel

iTrader: (2)

Got car going and took to tuner (6.0l 4l60e) tuner said it seemed like the tranny was slipping. Got car home and tranny went out...pulled, took to tranny shop, rebuilt, put back in and within 5 miles it burnt up again..took whole car to shop and they pulled and rebuilt, but said converter looked burnt, sent back to Revmax, they rebuilt and sent back, put tranny back in but they couldn't get enough line pressure to make it work..........called tuner and had him talk to tranny guy, he told them it was tuned by speed density NOT thru the maf...so tranny guy pulled pan an adjusted line pressure thru valve body to 150psi....BUT the tranny still doesn't shift right, doesn't seem to go into 4th/overdrv...nor does seem to shift very firm....

Whats the advantages/cons of tuning with speed density vs thru the MAF?
ANY help would be REALLY appreciated.
Rick

mrvedit

When I recently changed my engine from MAF to Speed-density, I obviously had to make major changes to my engine tuning, but I DID NOT change anything related to trans tuning. The trans worked and shifted exactly the same. I do all my own tuning with HP Tuners.

The PCM will change the pressure in the trans (via the pressure control solenoid) based on "engine load". The PCM calculates this from some combination of the MAF, MAP, TPS and other parameters which are part of GM's secret sauce. When the MAF is disconnected, it is correctly calculated from the remaining parameters.

IMHO, at least one or two things in your trans and engine are seriously wrong. As a guess, it doesn't sound like your trans has enough line pressure and whoever has been rebuilding it hasn't checked it. When the tranny guy set your line pressure to 150psi, did he hook up a gauge or did he just make a hack and say that sets it to 150?
(He probably made this hack because he didn't trust the tuner.)

You can buy a trans pressure gauge on ebay for $45. It comes with a long 6ft hose. You can tie-wrap it to your outside mirror and drive around while monitoring pressure.

On the engine side, either the tune is way off, or there is a sensor problem.
Have you scanned the PCM for codes?

You may need to find someone that can log the PCM parameter while the car is driven, and of course monitor the real trans pressure. (The logged trans pressure is not real - it is what the PCM is requesting, not what you are actually getting.)

James@ShorTuning

Depends on the tune... The only difference is the torque would be changed due to different airflow from mods in a calibration. Alot of stock OS's set the max line pressure code when the MAF fails but any experienced tuner should know what to do to disable that!

mrvedit

Good points. I should have added that when I switched from MAF to speed-density, I was nowhere near a stock tune.

flywheel

iTrader: (2)

Thanx guys,
this in no way a stock tune, cam has .615 lift and .223/.239 duration....lq4. in my 66 chevelle, headers, ls3 heads, n intake... Right now has 2.73 gears, revmax 3200 stall. I have ordered new 3.42 gears and will be changing next week so that will help make things more like normal if I can get it to shift right...

Tranny shop did have a guage in it. I saw it when I took it for test drive.. This a shop that's been around since the 70's owned by the same guy....BUT, they usually work on stock stuff so some of this perf. stuff maybe out of there relm...
Talked to shop where tuner works, he's going to re-look at it week from saturday...henss, getting in the lower gears b-4 hand. Thanx...anymore thoughts?
Rick

mrvedit

I would have preferred to see the line pressure before the 150psi hack was made.
I suspect the trans guy turned the shaft in the pressure control solenoid; not sure that can be undone accurately without buying another one.

If you don't mind the $45 for a trans gauge, I would recommend that. Search ebay for "trans pressure gauge 5550". Hook it up for driving when you take it to the tuner.
The tuner should then be able to hook up his scanner and force any desired pressure. This assumes of course that the 150psi hack is removed.

You are correct that even very experienced trans guys who mostly work on stock setups can be confused by custom mods and tunes. As James@ShorTuning pointed out, a failed MAF often results in max line pressure, but that is not the case if the MAF is simply tuned out.

joecar

If the IFR is undervalued then the resulting corrected VE will be undervalued...

the PCM commands line pressure based on the engine torque value it calculates from the VE table...

if the VE table is low then calculated engine torque is low causing line pressure to be low...

scantool can monitor engine torque (TRQENG) and commanded PCS pressure (TFMPRS, see note below for range of values)... look at these in addition to hydraulic line pressure (as said above) to see what is happening.

[ note: the PCM commands Torque Signal pressure (see Figure 44 on Page 47 of the HMTG) which ranges 0-96 psi, and pushes on the end of Boost Valve to increase regulated line pressure into the range 50-220 psi. ]

edit: corrected.

mrvedit

Joecar obviously knows the "secret sauce" better than I do.

And now I have learned why the trans pressure tuning table has a range of 0-96. Thanks for the explanation.
(Although I thought stock line pressure can be as low as 50 psi.)

flywheel: keep us posted.

joecar

You're right... I corrected my post above.

joecar

[ also note that the pressure tuning tables you see are the shift pressure tables... i.e. they do not control the running pressure (i.e. they control pressure during shifts) ]

flywheel

iTrader: (2)

Boy, I wish I understood all that stuff. IFR, VE sounds like greek...but I'll suggest this to the tuner....Thanx.

mrvedit

IFR - Injector Flow Rate
Unless you changed the injectors, the IFR should be right
VE - Volumetric Efficiency
This is the primary table tuned for almost any engine changes, especially different cams.

I believe Joecar is saying that strangely tuned engine parameters could lead to low transmission line pressure, leading to failure. The engine might even be working perfectly.

01ssreda4

iTrader: (96)

With a correctly failed MAF, a SD tune has no effect on the transmission. Something else is amiss here.

flywheel

iTrader: (2)

Well, it's not a stock 6.0l, it has an ls3 intake on it with the stock injectors in..The tuner never asked about any of that...Maybe he assumed it's an ls1 or something else. We've just had 10" of snow so things are on hold for awhile... working on the paint part of the project now.... stay tuned.
Rick