95 lost overdrive after vac work and supercharger gasket

My 95 riv has been having some problems. For the past few months it has been surging when in overdrive, it seems like it is trying to downshift but then it jumps back in to overdrive. Took it to the shop, they suggested it was vacuum leaking from the gasket under the supercharger. We bought a gasket and put that in, the old one definitely was leaking a bit. Replaced a few vacuum lines during the process. Took it out for a drive today and it wont shift into overdrive. Idle seems better than it was previously and it runs well, just no overdrive, and perhaps no 4th gear although i'm not sure. If anybody has any ideas it would be greatly appreciated! Thanks.

Mason wrote:: My 95 riv has been having some problems. For the past few months it has been surging when in overdrive, it seems like it is trying to downshift but then it jumps back in to overdrive. Took it to the shop, they suggested it was vacuum leaking from the gasket under the supercharger. We bought a gasket and put that in, the old one definitely was leaking a bit. Replaced a few vacuum lines during the process. Took it out for a drive today and it wont shift into overdrive. Idle seems better than it was previously and it runs well, just no overdrive, and perhaps no 4th gear although i'm not sure. If anybody has any ideas it would be greatly appreciated! Thanks.

check if your front brakes are dragging - need to be on jackstands or on a lift in neutral to check. Also, it may be the brakes will only drag after several actuations.

Make sure you have the vacuum line connected to the modulator.

I will check the brakes but I am doubtful. I started it up when it was 30 degrees out and the first chance it had to get into 4th it didn't. To my understanding the tranny goes into limp mode when it heats up too much, and it definitely didn't have a chance to heat up. I'm hoping it's electrical or vacuum, because i went from mostly working 4th to no 4th at all. I will check that the line goes to the modulator! Thanks

Vacuum gauges are among the cheapest gauges you can buy. Better yet, install a vacuum/boost gauge. Fully warmed up, the engine should pull a solid 20" of vacuum at idle, in Park.

_________________
98 Riviera SC3800 All stock except gutted air box.
1970 Buick GS455 Stage1, TSP built 470BBB, 602HP/589TQ
Best MPH, 116.06 MPH, Best ET, 11.54
https://www.youtube.com/watch?v=UHCda-t_Jls
https://www.youtube.com/watch?v=sfT2tEO4XcU

https://i.imgur.com/XYTUK.jpg

It's got a strong vacuum just using my finger, maybe I should get a guage. I've noticed that the idle has gotten higher since we took the supercharger off and on, maybe this has something to do with it. It idles at around 1200, much higher than it was before we did the work

Mason wrote:: https://i.imgur.com/XYTUK.jpg

It's got a strong vacuum just using my finger, maybe I should get a guage. I've noticed that the idle has gotten higher since we took the supercharger off and on, maybe this has something to do with it. It idles at around 1200, much higher than it was before we did the work

You have to get a gauge on it, unless you have a calibrated finger smile

_________________
98 Riviera SC3800 All stock except gutted air box.
1970 Buick GS455 Stage1, TSP built 470BBB, 602HP/589TQ
Best MPH, 116.06 MPH, Best ET, 11.54
https://www.youtube.com/watch?v=UHCda-t_Jls
https://www.youtube.com/watch?v=sfT2tEO4XcU

Smells like the TPS to me. my old SSEi did something similar.

Maybe important to note - before we did the upper intake redo we took it to the shop and they got these codes -

P0131 Oxygen Sensor Signal Is Too Low
P0171 Fuel Trim Sensor Signal Lean
P0321
P1361 Ignition Control (IC) Circuit Low Voltage

Mason wrote:: Maybe important to note - before we did the upper intake redo we took it to the shop and they got these codes -

P0131 Oxygen Sensor Signal Is Too Low
P0171 Fuel Trim Sensor Signal Lean
P0321
P1361 Ignition Control (IC) Circuit Low Voltage

first thing to do is clear the codes and see if they come back after 20 miles of driving, or so.

found out the TPS was one of the issues! the arm of the TPS was on the wrong side of the throttle pin... rookie mistake. Now we are pretty much back where we started, it feels like it is misfiring in 3rd and 4th gear at low rpms, 1500ish on the highway. The shop said it may have to do with p0321 which is something to do with the crankshaft sensor

Last edited by albertj on Fri Dec 28, 2012 4:17 pm; edited 1 time in total

With a proper scan tool you can read the crank sensor output and calculate/reckon if it is sensible. Scan tool is tricky on a 95 they are basically OBD I with OBD II connector. I think there is an Actron scanner that will work, hopefully someone will post the model #.

I've never seen a crank sensor cause a misfire. They usually cause a total shutdown. I would start checking ICM or wiring, coils, or plugs and wires. A remote possibility is an injector. Most quality scan tools have the capability to read either system, you just have to find a serious tech that has spent the money on one. Hang in there, you'll get it figured out.

I appreciate all of the help, took it to the shop again and he couldn't scan it, but he says based on the description it's probably the plug wires. We just replaced the plugs so it's probably not them. They are Delco, I'll have a look at them next, thanks!

EDIT EDIT- The wires have 20k miles on them.

Replaced the wires. This seemed to improve it but not fix it. Still dealing with misfires in the low revs especially when lugging along in overdrive and 3rd. Running some injector cleaner through it tomorrow and getting my codes checked. SES light is on occasionally

Suggest you consider getting your own code reader/scanner.

Suggest you read stored codes (did you clear them last time?)

Suggest you consider to remove coils and swap in known good ignition module.