JohnnyCamaro91

I am having an issue. First, I did use the option, and had no luck. If there is anyone who knows of another post about this issue it would be appreciated.

The problem seems to be whenever I am driving and trying to maintain a speed around 50mph the trans jumps back and forth between gears like it cant make its darn mind up.

The speedometer also doesn't work. You might ask how I know I am going 50. Haha, I have been using my garmin as a speedo. And the speedometer works sometimes, after i drive it for a while. But it's like 10mph under, and bounces around.

I am assuming this is the trans speed sensor/ vehicle speed sensor, which I plan on replacing this week.

My question is, could the speed sensor be whats making the trans jump back and forth, or is likely being caused by something else?

camaronewbie

Speedo - is electronic - check the wires/connector at the tranny tailshaft to make sure they are all good.

The tranny is 'hunting' at that speed - can't make up it's mind between 3rd and 4th. THis is common - depends alot on the grade of the road and the load on the car. Simplist answer is, when it does this, change from OVERDrive to Drive - this will keep 4th gear from being available as an option. Also, sometimes this happens when the torque converter can't seem to make up it's mind - and thus it's locking and unlocking - but rarely do we ever actually feel that - more than likely just hunting between 3rd and 4th. It happen with all our automatics, and is normal (assuming your fluid level is good - remember to check tranny fluid hot, while car running in park).

JohnnyCamaro91

Hmm, I have the automatic overdrive there is only one drive position. I do however have a third gear should I just shift down to that? Also would the torque converter make it jump when I put it in drive?

Project 3.4 Camaro

3rd=drive, it still shifts up and down at will as it would in OD(overdrive) with the exception that it will not shift into 4th(which is the OD gear)

JohnnyCamaro91

Kool, thanks. So in other words theres not really a fix for this? Somebody told me that their car was doing this and it was solved by new sparkl plugs... dunno if this makes sense...

Project 3.4 Camaro

Like he said, its just trying to figure out which gear to be in, putting it in drive(3rd) takes away the option of shifting into 4th, and voila, problem solved.

JohnnyCamaro91

Ok, sounds good. And as far as the speedo problem, I'm gonna check the wires tomorrow. If those are all sound, am I correct to assume speed sensor? There appears to be a bit of trans fluid leaking around the unit.

Project 3.4 Camaro

Can't help with the speedo without knowing whether or not its mechanical or vss, what year car is it?

JohnnyCamaro91

its a 91 3.1 700r4

Project 3.4 Camaro

might be the vss or speedo is bad, or possibly a loose connection would explain why it works sometimes, now why its 10 mph off though. But the 10 mph off and bouncing around and only working sometimes makes me lean towards bad speedo. But idk for sure.

Maverick H1L

iTrader: (8)

Problem with the 90-92 730 cars is that the speedo is actually run off of the ECM... VSS wires feed directly into the ECM, no buffer box, no nothing. If you're having a problem with the VSS, yes, the trans will act funny.

I don't think it's your trans skipping gears but the torque converter clutch locking and unlocking. If the engine speed doesn't shoot up to about 2300 RPM when you're at 50 but jumps to about 1700-2000 or so due to the TC slip, you're still in 4th (using the tech calculator on the TGO Tech Articles page, 3.23:1 rear ratio and 1:1/.70:1 3rd and 4th trans gears and a stock 13" tire radius). It's most noticeable when going about 70 or so as the TCC will unlock and the engine speed will shoot to about 2900 or so when trying to hold 70 from about 2300 RPM. If you were to drop a gear at that speed, you'd be at over 3500 RPM with the TCC unlocked (very rarely does the TCC lock in 3rd).

I'd bet on a problem with the trans mounted VSS first, and second, you're traveling at such a low speed when in 4th gear that the TCC may not even lock (ECM's primary job is to keep the engine running, after all, and those low speeds with the TCC locked can possibly stall the engine).

Could also be an issue with either the throttle valve or shifter/manual valve cables being out of adjustment is causing the "jumping gear" issues, but I'd start with the VSS for the speedo head.

JohnnyCamaro91

OK, I ordered the VSS. It should be in around 5:30. I will be back on around 6 with the results. There is another problem though, the tach also doesnt work. Might this also be a result of this sensor?

JohnnyCamaro91

OK. Installed VSS. Speedo now works like brand new. Very happy thanks for all the info guys, I really appreciate it. Now for the tach...

Maverick H1L

iTrader: (8)

Camaro tachs are notorious for being inaccurate... I believe Project 3.4 has a thread running on how to fix it. Problem with our tachs is that they are based on a Toshiba chip that's WAAAAY outmoded and nobody can get datasheets for as a result, so nobody other than pro shops can fix them properly.

Project 3.4 Camaro

Pretty much, I gave up on fixing mine, it will be cheaper to get an aftermarket unit, or at least about the same, just bugs me because I would prefer all my gauges match and it will be a very long time before I can do full aftermarket gauges considering it costs like ~$700, which is a set of forged pistons and total seal rings...maybe I will happen across a v6 tach for sale on ebay but I am not counting on it.

Btw Maverick, I think I have an oil pressure problem, anyway to discern whether its the pump or bearings without pulling the crank? I narrowed down my valve lash problem to my lifters going flat, I could push the plungers down on like 4 or 6 of them with my hand, and the car hasn't sat long enough for them to go flat just from sitting, or is there any chance a bad oil filter housing gasket could cause an oil pressure problem?

JohnnyCamaro91

Its not that its inaccurate, it just plain doesnt work. Havnt seen it budge since i got the car lol

regal301

i fixed the tach in the 91 rs i had , it was a bad resistor,search for tach fix. it took me 15 minutes to fix.

regal301

Maverick H1L

iTrader: (8)

Best I can say is to look for a white wire in a gray connector coming out of the harness near the ignition coil's gray connector (that has the pink ignition switch wire coming out of it). This connector will only have the white wire in it and is designed similar to the EST bypass connector which is used for setting the timing, except it's used for checking the ignition system. If the wire is broken in this connector or if the connector has come apart, the tach won't work as it won't be getting a signal.

Project, yes, the oil filter adaptor gasket can be giving you oil pressure problems. Also, did you pull the pan off of the 3.4 to make sure there were no metal shavings in the bottom or in the oil pump pickup? Oh, and get an external mechanical gauge and hook it into the pressure test port down there. Yes, there should be an extra port, if you're using the 3.4's oil pressure unit. If not, remove the gauge sender and hook the gauge up there. You should have 70 PSI when cold (and possibly at about 2K RPM) and no less than about 20 PSI hot.

Project 3.4 Camaro

Yeah well you're lucky enough to have a v8 and thus a lot more resources, I have searched plenty of times for a fix for a v6 tach and the info isn't there, because no one knows the details on the part needed as its different than a v8.