98 Montana transmission issue

[jaded13640]

I got a call today on a 98 Montana that needs a transmission.

So I picked it up and drove it to the shop and here's what it's doing...

You put it in drive and it takes off like nothings wrong. When it's time to shift to second it acts as though it goes into neutral and will not shift until you lift on the throttle. It's not a typical slipping between gears. When you lift on the throttle it shifts normally until it's time to go into the next gear. I did notice that if you are really babying it from a take off it'll shift without slippage sometimes. For the most part even when going really easy on it it'll do the same thing.

It will not shift no matter how long you wait. Until you lift on the throttle, it won't shift.

Also, it will do this when you step on the throttle hard enough to engage the passing gear. It downshifts, then acts like it goes into neutral, you lift, it shifts. Or, it just stays in the lower gear until you lift. I think it did that once. I didn't drive it far, about maybe 10 miles.

The check engine light is on so I scanned it to see if there were any powertrain related codes.

Mostly missfire, lean on one bank intermittent, and catalyst.

But one code is P0122 which is the Throttle Position Sesnor code.

That's the only one that made me question anything.

Is there any possibility that the TPS issue could made the transmission not shift like that?
I wouldn't think so but you never know.

I have no problem dropping the trans and swapping it for him. I just don't want to get done and find out it's doing the same thing because of some non transmission related issue.

Or, if it's something external that can be replaced, that's fine too. I'd just assume not have to go through all the hassle of changing the trans if I can avoid it.

Any help would be greatly appreciated,

Wayne

 

[melsg5]

It sounds like you have a shop but dont have any diagnostic equipment to check the transmission? If so, just a guess would be the transmission solenoid is causing the issue and below is a link to the procedure.

http://www.justanswer.com/pontiac/1v1yn-replace-pressure-control-solenoid-99-pontiac.html

 

[jaded13640]

I didn't see anything about diagnostics there. It talked about being able to change the solenoid in vehicle.

What diagnostics lead up to that part being bad?

I have diagnostic tools. Gauges, multi meter, etc.

The question is where to start. If it was slipping between shifts I would assume warn frictions and drop the pan and look for friction goo to confirm. But that's not what it's doing.

I could test line pressure but it's dropping right into gear. If there was a long delay or very slow engagement I'd be thinking pressure.

I've never had one act like this and wondered if it was common issue with this particular transmission.

Again, it drops right into gear. It engages right away. It does shift and shift solid but not until you lift off the throttle.

I don't know a lot about these transmissions but this seems more likely to be electronic than mechanical.

How would you go about diagnosing that on this particular transmission/vehicle?

The customer is more than willing to just have me swap the transmission and I'm willing to do so but I don't want to just pull it and swap it if can be avoided. If it saves the customer some money, great.

Thanks,

Wayne

 

[sergeimoskva]

Hi!
These symptoms appear most likely because the throttle position sensor (TPS).
TPS is definitely used in transmission control. The TPS takes the place of the TV cable from the older transmissions. The more you push down on the accelerator the more line pressure is increased through the EPC. So, yes the TPS can cause harsh shifting.
I recommend to clean the throttle cleaner. If this does not help - maybe replace the TPS.

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[jaded13640]

Thanks. That's what I was looking for. Someone with some direct exprience with these vehicles willing to assist.

I'm a mechanic more in a general sense. When things are broke I know how to fix them. From symptoms I can make some inference but I'm not a trained diagnostition. I have no certifications. I've just been working on cars for 38 years.

With everything being so interrelated on cars any more you can't just go by the symptoms. These symptoms on a car 20 years go would have meant that it was a given that the trans was worn out. With pretty much ZERO doubt about it.

When someone comes to a forum as specific as "Pontiac Montana" there should be the assumption that the original poster has pretty much never worked on one. I know I never have. I've done brakes and stuff like that on an aztek which I believe is about the same vehicle.

When the people reply by saying, "it appears you have a shop, don't you have any diagnostic equipment at this shop?" they weren't actually interested in helping you in the first place. It's like I came to his house asking for a free meal or something LOL.

Yes, I have a shop. It's a pole building behind the house with a hoist and tools. No sign, no parking lot, no waiting area with coffee and a bathroom, no 2 ASE masters, 4 techs with multiple certs and 3 guys with a couple. Just a guy fixing cars as best he can to keep food on the table. I have diagnostic equipment but A. I often don't see the same model of car twice unless it's a really common problem to that model. And B, most of my work is like brake jobs, engine swaps, AC work, that sort of thing. I've spent much of my "career" in cars building race engines. The pay is great but times are tough. People just don't have 8 to 25k to build a new engine this season every season anymore. Most people are done with drag racing because of that.

I see those sort of responses all the time so I guess I should have just not repled to it but it's starting to get on my nerves. These do it yourself forms are here for a reason and it's not for the forum veterans to stroke their egos.

I really appreciate the suggestion. I had a hunch about that but again, I have little knowlege or experience with these vechles and transmissions. Give me an old 727 any day. I'll have it appart and better than new in flash. Wanna run in 9s? No problem, it's just a matter of quality parts selection. What a 500 inch 440? At this point I can do it blindfolded. But a god awful pos van that was crap out of the gate? No, sorry, I don't have the answers to those questions. So I ask them.

Again,

Thanks and have a great day.

Wayne

 

[Zimgxp]

Start with the TPS. As stated, it controls line pressure.

 

[sergeimoskva]

Hi Wayne !
Try to clear TPS , and test TPS (see picture)

 

[jaded13640]

I hopped in it this morning when it was really cold, like 6 below, and it wouldn't even move initially. After it warmed up gradually went into gear.

I told the guy to get a trans for it.

The TPS may also be an issue...but this trans is dead in my opinion.

Wayne

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[Steelcity]

whatever does fix it , tell us .

 

[sergeimoskva]

HI !

but this trans is dead in my opinion.

This opinion As well interesting is......

 

[jaded13640]

Sergie, I'm sorry I didn't understand your comment.

 

[sergeimoskva]

Hi!
I wanted to say ...... I'm sure you'll be able to repair the engine.

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