Problem with gaining speed, been to several dealships

Discussion in 'Performance & Fuel' started by dalepre, May 19, 2013.

  1. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    But if it remained in a lower gear-it should accelerate-
    According to the OP-it jumps up to 3500 RPMs right away
    but the speed REMAINS at 55 mph
    so the RPMs double-speed stays the same
    power RPMs are being made at the crank-but it sure isn't getting to the driveshaft
    Eve if it IMMEDIATELY downshifted 2 gears-it wouldn't explain the no acceleration-since even at 3500 RPMs
    he has 2000 MORE RPMS on tap??
    Why the heck don't the RPMs KEEP going up??

    OP do you FEEL hear a downshift or two??
    Strange it doesn't increase RPMS- why "stuck at 3500 rpms and 55 mph??
    If nothing is slipping what gear gives 55 and 3500- 2nd gear??

    Maybe it is a strange fuel flow problem??
    Enough fuel flow to do 3500 RPMS and 55 mph in second gear or 3000 RPMS and 100 mph in 4th
    Maybe it is fuel flow
    STRANGE??
    If it was slipping-should slip all the way to the rev limiter or to 6000 RPMs if no limiter-guess probably no limiter on a 1995-
    so probably not slipping-maybe fuel flow??
     
  2. dobey

    dobey Rockstar 4 Years 100 Posts

    A drop from 4th to 2nd with a 3.08 rear, would keep the MPH exactly the same, if the RPM increased from 1500 RPM to 3500 RPM, and it stayed there. If the tach never goes above 3500 when mashing the gas at speed, and it stays at 55, then first place to look would be the kickdown.

    If it stays at 55 and the tach goes above 3500, then I'd look at the tach or the speedo being wrong.

    Take it back to the dealer, or your favorite mechanic, or someone who knows what they're looking for, and tell them to check the kickdown. Have them drive it on the highway, cruising at 55 MPH for a bit, and then mash the gas as if to pass, and see what happens. Have them do that at least 10 times.

    If you never go over 3500 when this happens, I guarantee the problem is the kickdown, or something related, forcing the trans to stay in 2nd gear. Or even if the RPMS do go higher, as the failure to shift could result in slipping clutches or converter, resulting in the engine RPM being higher than it should be, for the speed you're going.

    If you have a stretch of country road near you, go out there and put the truck in 1st, take off, and manually shift to 2nd. Stay there and see if you can go over 55 MPH in 2nd. You should be able to hit 80 MPH in 2nd, but you don't need to go that fast. Getting to 65 MPH is enough, as the RPM should be at about 4000 @ 65 in 2nd. What matters is that you're spinning the engine at more than 3500 RPM, and going faster than 55 MPH, in 2nd gear.

    Or if you can just get a reasonably good video (at least 480p with good sound, that means windows up), of this happening, it would certainly help. But my guess is you should be looking at the kickdown, and the TCC lockup.
     
  3. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    Dobey
    So 2nd gear is about 3500 RPMS 55mph and 1500 in 4th is same 55 mph?

    What is this kick down??
    It must be downshifting-kicking down to 2nd gear-but not doing ANYTHING after that?
    Not increasing RPMs or MPH
    AND not upshifting?
    What does the kickdown normally do
    and what do you figure it is doing on the OPs vehicle?
    Thanks
    Charlie
     
  4. dobey

    dobey Rockstar 4 Years 100 Posts

    Yes, 2nd is about 3500 at 55, and 4th is about 1500 at 55, with the 3.08 final drive gear, and factory diameter tires at proper inflation.

    The kickdown cable is a cable that connects between the throttle body and a valve on the transmission, so that when you mash the pedal to pass someone for example, the cable closes the valve which forces the transmission to shift down to a lower gear, so that you can apply more power to the wheels and gain speed quickly.

    There could be something wrong with the cable, the valve, or the TCC switch, most likely, which is causing the transmission to remain in 2nd (and not shift back up to 3rd and then 4th), and possibly causing the convertor to slip, or burning up the clutches in the transmission, causing them to slip. Though if the engine only ever remains at 3500 and 55, then something else could be wrong, but still I wouldn't suspect fuel, unless there was obvious misfire, or CEL indicating it.

    The engine can only spin as fast as the load being placed on it allows for. If it's spinning faster than that, something is slipping. If anything is slipping though, there should be a CEL come up, and a code may be stored in the ECM.
     
  5. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    Thanks
    Tricky problem-really curious what the answer turns out to be
    OP please keep us posted
    Charlie
     
  6. dalepre

    dalepre New Member

    Finally an end to the Nightmare

    Well Guys, after many trips to three dealerships, 3 or 4 other shops with no idea, myself not a bad wrencher (but..mostly my collection of T/As and Mustangs..ie no computers..lol) I myself found the ghost in the machine yesterday. By the way,, there is No kickdown cable on my truck from the TBI to the trans. all electronic. I dug out my original GM tech manual on this truck and dove in with a vengence. I first shot it on the lift again and wnt over every single wire from the trans, sensors, speed sensor, transfer case, etc under the truck and viewed every single inch and found no problems. Stop for a second to scratch head or butt and then let her down and pull the glove box out, verfiy version of ecm, flip to that unit and proceed to get the truck up to normal temp(took it for a 5 mile romp) pulled back in the shop, cut it off. Unplugged the ecm and pulled it out were I coud get a up close and personal look, plugged it it back up, start het back up and check every connection on the ecm with my fluke and a scope also and found most to be right on the money, couple measurements a little off. Turned truck off, unplugged ecm, got it in my lap for close inspection, removed the prom access panel and then when into a fit of cussing that made me blush...Of all things, the lock leveron the left side had became loose and the prom had rose up a wee bit on that end, the right side lock was still firmly enganged. Pressed the prom back down, push the lock VERY well into place and then placed a wire tie around the prom to ensure that wil never happen again. Started the truck back up, jumped into the driver seat, as soon as I hit the pedal rather hard in reverse, I knew then, all was going to be like old times again. Hit the highway, went WOT and be damm, she got up and went like a chevy should do. Shifting was a wee bit of as the ecm was a little stupid at this point. Went back to the shop, mounted the ecm correctly, hit the road for app 50 mile ride and by the time I got back, shifting was compeletly normal, perfect in every way. And NO, the ecm has NEVER been out of the truck, ever. I guess strange things happen. Hard to think 3 dealerships missed that, but so did I after several days of loosing hair. I hope this helps some other poor lost soul someday... Dale
     
  7. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    WOW

    GREAT STORY!!
    What is the PROM?? Some electronic bit on/in the ECM?? ROM read only memory??

    What is the PROM?? It is under the ECM cover-so I can't see it right??
    And it had become SLIGHTLY UNPLUGGED-?
    1)there is a locking lever on the left side that holds the PROM in place
    2)it was not fully locked down
    3)so the PROM lifted up a bit on that side-became SLIGHTLY UNPLUGGED
    4) and that made it RUN WEIRD?? not gain RPMS not upshift??



    WOW-GREAT FIND-and FREE- except for cerebral elbow grease -and whatever the shops charged you??
    Cover never removed-so heat vibration bumps caused to lever to unlock??
    Glad it worked out-great job!! REALLY GREAT JOB!!
    Charlie
     

Share This Page

Newest Gallery Photos