'96 S'brbn Transmission "Slipping" ?

[stb100]

My '96 5.7 (4WD) w/ 171,000 is finally showing its age. Engine runs great and idles smooth, but lately, once up to speed it seems like there's a slip or momentary loss of drive. Motor sound doesn't change so don't think engine's the culprit -- could be wrong. Rolling along at an even speed, foot steady on gas is when it happens. Kind of a slip or hiccup...this will happen a couple times maybe, very sporadic. THANKS.

-- Steve in VA

PS - I recall thinking my old Isuzu Trooper had something major wrong about 12 yrs ago when it did a similar thing -- I thought clutch was slipping. So the shop gladly replaced clutch, master cylinder for $1200.00... and symptoms did NOT go away. Turned out to need new plugs. Replaced em -- ran great!

Whaddya think -- transmission issues or plugs?

[j cAT]

Originally Posted by stb100

My '96 5.7 (4WD) w/ 171,000 is finally showing its age. Engine runs great and idles smooth, but lately, once up to speed it seems like there's a slip or momentary loss of drive. Motor sound doesn't change so don't think engine's the culprit -- could be wrong. Rolling along at an even speed, foot steady on gas is when it happens. Kind of a slip or hiccup...this will happen a couple times maybe, very sporadic. THANKS.

-- Steve in VA

PS - I recall thinking my old Isuzu Trooper had something major wrong about 12 yrs ago when it did a similar thing -- I thought clutch was slipping. So the shop gladly replaced clutch, master cylinder for $1200.00... and symptoms did NOT go away. Turned out to need new plugs. Replaced em -- ran great!

Whaddya think -- transmission issues or plugs?

check fuel pressure its at this mileage for failure....

tranny will usually shift poorly if bad....sounds more like fuel,,,but could be the ignition...with NO DTC most likely fuel issues.....

[stb100]

THANKS
Any advice on that? How do you check it? Online manual says to replace it, remove upper manifold assbly. That a bear of job, as it sounds? May be above my pay grade.

[j cAT]

Originally Posted by stb100

THANKS
Any advice on that? How do you check it? Online manual says to replace it, remove upper manifold assbly. That a bear of job, as it sounds? May be above my pay grade.

first off get a repair manual for your vehicle...then with a pressure gauge measure for the correct fuel pressure...the pressure after the engine starts and then shut down should hold at what was indicated, and drop only 5psi over 15min...if it drops rapidly this usually indicates a bad pump..you should see pressures in the 50-60 psi range..off hand your exact spec I don't know..but the pressure is very important...

report back on your findings....as I stated before it could also be ignition,,,but testing for fuel is fast and cheap...then get into the other areas...

[1993Suburban]

How long does this little "slip" last? Also, how fast do you need to be going to notice it? Around 40 MPH the torque converter locks up, so you could be feeling either torque converter clutch shudder, or there may be a tiny miss or roughness in the engine. My '93 did it and occasionally so does my '96. Wasn't sure what it was on the '93 but the '96 seems to have a slight (very slight mind you) roughness or miss in the engine, so when the RPM's are brought down during torque converter lockup, you can feel the slight roughness which causes the transmission to act like it's slipping or "hicupping". However, it is hardly noticeable on my '96 and I don't know how noticeable it is on yours so it could be something different.

[stb100]

Trann'y seems to have gotten worse in last few days. "Slipping" had been short little blips of a second or less. Seemed to happen at little higher speed-- not sure, but maybe over 25-30 mph or more. Sporadic hiccups.
Now, accelerating into traffic on hiway, slip acts like stuck in lower gear, can't shift up. This happened once. Did shift up finally. But, not good, if something had been coming on fast.

[MT-2500]

Did you check out fuel pressure?
Get it on a good transmission/engine capable scanner and see what it tells you.
If any codes post back codes.

[j cAT]

Originally Posted by stb100

Trann'y seems to have gotten worse in last few days. "Slipping" had been short little blips of a second or less. Seemed to happen at little higher speed-- not sure, but maybe over 25-30 mph or more. Sporadic hiccups.
Now, accelerating into traffic on hiway, slip acts like stuck in lower gear, can't shift up. This happened once. Did shift up finally. But, not good, if something had been coming on fast.

as I stated before late shifting/shift problems would point to the transmission...with the fluid at the correct level and clean with a good clean tranny filter ...and this is occuring , bring to a tranny shop for diagnosis...

it [tranny] could be electrical or in need of componet replacement..

[stb100]

Thanks for input from all.

OK, I am guilty of not having this tranny serviced and will likely pay the piper...Took it to a mechanic I trust -- also drives an old Tahoe --and had him test drive. Checked fluid too, which was a little dirty and dark red.
His verdict -- bad news.

Said probably need to have clutch assbly rebuilt. $1500 plus... Thought b/c it ran smooth despite slippy shifts that other hardware probably intact. Said he'd seen 'em like this when they'd do a filter and fluid at this stage and that would kill a tranny that had been limping along...the dirt/crud/etc was all that kept it working...!

Any thoughts on that? Could the easiest and cheapest solution -- fluid/filter (or other miracle??)--save my guilty behind in this case or is the tranny mechanic recommended by my guy looking at a beach house payment courtesy of me.

THANKS

Steve in VA

[MT-2500]

Why did he not do some proper testing before say throw a transmission at it?

[j cAT]

when a tranny slips you must act quickly or it will be damaged . low pressures because of bad,dirty,and contaminated fluid also the filter plugged with debris...damages the transmission....all this debris/dirt gets into the torque converter ...then when fluid is changed and the pressures go to normal all this dirt gets flushed out and restricts the valves ...also the clutches are cooked with the slippage and heat generated...

when ever you have a large vehicle like this the tranny works much harder than a car...need to replace the fluid,and filter at 30,ooomi....

the new fluids used today are far better than the dexron III your vehicle had in it....the dexronIII is now gone as GM is now history as we know it..

scrap this dino , for a 22MPG vehicle and get 4500 dollars toward the new ride....that is a good deal you have one year to go for it...

as MT 2500 stated it should be properly tested ...to be sure its a total rebuild///

[stb100]

Thanks to all. Good input... FINALLY got back to this problem.

Took it to a local Trans shop -- mostly rebuilds racecars. Test drove, ran codes. Said he'd LOVE to sell me a tranny but not the prob-lame-o. Code was P 0161 (O2 heater circuit, bank 2, sensor 2)

Suggested replacing plugs, spark plug wires, fuel filter ( + O2 sensor).

Haven't done yet -- 1st two sound easy.
Filter-- how easy is that? (inside gas tank?) O2 sensor sounds pretty easy - true?

THANKS

[j cAT]

Originally Posted by stb100

Thanks to all. Good input... FINALLY got back to this problem.

Took it to a local Trans shop -- mostly rebuilds racecars. Test drove, ran codes. Said he'd LOVE to sell me a tranny but not the prob-lame-o. Code was P 0161 (O2 heater circuit, bank 2, sensor 2)

Suggested replacing plugs, spark plug wires, fuel filter ( + O2 sensor).

Haven't done yet -- 1st two sound easy.
Filter-- how easy is that? (inside gas tank?) O2 sensor sounds pretty easy - true?

THANKS

the p0161 code will not give you your issues you described here....so what if the down stream O2 sensor heater is not performing correctly....this is only used to check on cat converter operation/performance,,,not to control/change any PCM/COMPUTER engine controls..

you must get as MT 2500 stated a scanner that is capable of reading oem specific drivetrain codes,,,,most shops do not have a scanner that can read these codes///can you guess why ?????

[stb100]

Originally Posted by j cAT

the p0161 code will not give you your issues you described here....so what if the down stream O2 sensor heater is not performing correctly....this is only used to check on cat converter operation/performance,,,not to control/change any PCM/COMPUTER engine controls..

you must get as MT 2500 stated a scanner that is capable of reading oem specific drivetrain codes,,,,most shops do not have a scanner that can read these codes///can you guess why ?????

Well, j CAT, I don't rightly know. Assuming you mean only dealers have it. Thought guys I used, a seemingly reputable shop, would be able to diagnose it properly. Drove and scanned it, as I said though dunno if it was state of the art scanner.

HERE'S where I am now...The Sub will not start. Repeated cranks and nothing. Hearing no fuel pump hum at gas tank when someone else cranks it. Smell no gas/flooding at engine after repeated tries. Tried whacking tank hard during start attempt but no go. Replaced fuel pump relay. Noticed a bit of scorched plastic (from before?) on relay block where relay plugs into it. Had pump replaced 5 or more years ago when truck died on the road...

So...it's starting to look to my untrained eye like I need a fuel pump again. If so... is this related or unrelated to my "tranny" issue, which, as the shop guy said was more of a fuel/spark thing...

THANKS

[j cAT]

measure the fuel pressure if any with a guage,,,then check for proper voltage at the fuel pump, then check the fuel pump ground located at the frame rail next to the fuel tank//remove clean and re-install..then re-check fuel pressures.

If the fuel pump was not supplying correct pressure you should get DTC of random missfires...also it is common to get O2 excessive switching codes,,,as the engine is starved for fuel and the O2 see's this improper mixture...

perhaps your transmission slip/surge/shutter is the pump dropping out...

never just replace parts,,,testing takes time but saves unneeded expenses ..also you are sure why the damm thing died..