Transmission shifting problem

[Falcon_LS]

I have a weird shifting issue with my Pajero/Montero. The transmission in question was supplied by Aisin-Warner to Mitsubishi at the time, until they started using their own transmissions in 2001 on these vehicles. Mileage is currently 336,000 km (210,000 miles) and apart from the issue I'm about to describe, the truck is as smooth as butter. I've always gone the extra mile maintaining and taking care of it.

Simply put, gear changes are delayed, and you have to either slightly release the gas pedal or depress it further (for it to speed up) to shift. As an example, you're doing 80 km/h (50 MPH), and should be in overdrive (4th gear). But you're in 3rd with the RPMs at 3,000 km. If you very slightly take your foot off the gas, the transmission shifts into 4th and the RPMs drop to 2,000. Alternatively, if you put your foot down further, the engine will rev higher as the vehicle accelerates and then you're in 4th gear. The shifts are also a bit hard and sudden, almost like a neutral drop. I don’t know what the cause is, although I was initially leaning towards the TPS.

Worth noting, apart from cooler line flushes, a couple of ARX runs and filter changes, nothing has been done to the transmission and it is all original.

A very knowledgeable person informed me that Mitsubishis of this era depend on the TPS, but also there may be a sensor/magnetic switch on the transmission that detects the shift. A web search reveals this "switch" to be an "Input/Output Pulse Generator":

So I went ahead and had a word with my parts guy at the Mitsubishi dealer, who told me there is something called an "A/T Inhibitor Switch" on my transmission:

So I did another couple of web searches, and it revealed that this is more or less a neutral safety switch. Some people have gone ahead and replaced it because the engine wouldn't crank in park or neutral.

Being ever so confused, I contacted the Service Manager at the dealership, who I'm on friendly terms with, and he said he would get their head tech to take a look at it. He takes the truck for a drive, and comes back to say it's perfectly normal. I've been driving this vehicle for the past 12 years and know straight up this is not normal. My fuel consumption even went up slight since this problem arose. So now I'm even more confused.

I just wanted to ask if someone in the know can tell me whether or not the "Inhibitor Switch" is a modern alternative to the "Input/Output Pulse Generator" and if this would cause the symptoms I'm experiencing. How likely would the chances be of a faulty TPS?

I don't want to play the guessing game, because a new TPS costs $120, whilst a new inhibitor switch costs $165. If I go ahead and replace both of them blindly, or replace one and then jump on the other one as being the "culprit", I'm just wasting time and money.

This is way over my head, as I know next to nothing when it comes to automatic transmissions.

Any input will be very much appreciated!

 

[The_Eric]

It could be a TPS, or maybe the vehicle speed sensor, or the pulse generator.

Without a scan tool to read their outputs, I think it will be hard to know for sure. If you have a scan tool that will at least give live data, you can check the TPS voltage at idle and see how it compares to spec. If you don't and don't mind being a bit more creative, you can do it with a multi meter. You can also check it's operation by reading the resistance as the throttle is opened. It should go in a nice smooth fashion.

 

[conor1326]

What is the transmission's code?

I also advise to read the fault codes, it might give some information whether it's an electrical problem or mechanical.

I don't think that the inhibitor switch has something to do with this.

Just an idea: maybe your end clutch packs are dent and worn, they often cause overdrive shifting problems.

 

[Falcon_LS]

Thanks for all the input!

I haven’t yet had time to check the TPS, although I will have to use a multmeter for that. Not being an American version, the vehicle is not OBD-II compliant, and one must use a Mitsubishi MUT-3 scan tool otherwise.

The transmission code is 4VAW2. Although one thing I just realized I didn’t make clear is that the problem isn’t just the 3 to overdrive shift. It also happens with the 1 to 2 shifts, and 2 to 3 shifts, so it’s throughout the band rather than just 3rd gear to overdrive.

Having said that, I did a bit of a search and found this on another forum:

Quote:
Inhibitor switch is a good place to start for shift problems. They are not too expensive new, so go for a new one. They are exposed to the elements on the outside of the gearbox and often suffer water damage.
A simple test which can indicate the state of the switch is to override the gearbox by manually changing gears. Often, if the switch is faulty, the gearbox will not change gear when manually changed.

Source


So I went and tried shifting manually, both up and down. During the 1 to 2 shift, I experienced the same delay that was there in Drive. The 2 to 3 was an immediate shift, whilst the 3 to 4 shift was also the same as drive. But downshifting from 4 to 3 was immediate, as was 3 to 2 and 2 to 1 (at sensible speeds of course). So I reckon that eliminates the inhibitor switch as being the culprit.

I’ll check the TPS next, and probably replace the VSS. If those two are alright, then I suppose I should suspect end clutch packs. I take it this is the sprag clutch?

 

[meep]

based on the gears involved I would suspect one of the solenoids is sludged, sticking, or beginning to fail. the AW4 unit I've seen had decent access to them IIRC.

M

 

[eljefino]

The inhibitor switch is a big problem on fords. Basically, hydraulically, you only have PRND and the lower gears are a computer function based on lever position. The switch is "resistive multiplexed" meaning, well, if there's slight extra resistance from corrosion it thinks it's in third or neutral instead of OD.

Anyway this does not sound like you. TPSs usually fail at 1% throttle from wear. If a Mitsubishi expert says TPS is a big part of the computer's decision making, that already is a huge clue. My 3T40 GM trans made all its shifting decisions based on throttle position, with the TV/kickdown cable. Since you have a third party transmission, it might be easier to meld it with your engine wiring with a simple TPS reading. I'm leaning toward this.

The hard shifting has me worried. You should get this at wide open throttle but that often doesn't wear out on the TPS. Even half throttle should shift somewhat softly. A great diagnostic, if you could find it, would be a transmission shop with dyno and ability to read line pressures under various conditions.

 

[Falcon_LS]

Thanks very much for all the input once again.

I'm about to go check the TPS voltage. Just needed a bit of help from someone to operate the throttle for me. I hope this is the culprit, as it is a very straightforward fix that isn't that expensive.

To expand a bit further, the hard shifts happen under light throttle. For example, if the shift does not happen from 1 to 2, and you release the gas, it shifts hard. But if you depress the pedal further and the engine revs higher for the same shift from 1 to 2, the shift is smooth.

 

[Falcon_LS]

Checked the TPS. Resistance should be between 3-5 ohms, and I have a flat spot at mid throttle. So I suppose the TPS is the problem.

 

[conor1326]

Yeah, it's more than suspicious...

After changing it, please refer back whether it solved the problem or not

 

[The_Eric]

Yes, please do.

edit: did you also check the voltage too?

 

[Nick R]

Strangely, I have kind of the same thing with TCC lockup in 4th gear.

 

[Falcon_LS]

Just wanted to post an update on this. I have not checked the voltage on the TPS, but I replaced it with an OE Hyundai part. The Hyundai Galloper was basically the same car as the Mitsubishi Pajero/Montero and quite a large number of parts are the same. Mitsubishi was asking $153.28 for their part, whilst Hyundai was asking $87 for theirs. Both parts are made in Japan, and even have the Mitsubishi logo on them.

Anyhow, after changing out the TPS, the engine ran considerably smoother and there was a noticible difference during downshifts. Fuel economy has definitely improved as well. But all that said, it did not entirely solve the transmission issue. The shifts got a bit softer, but they were still late and hard.

My next step was to clean the MAF sensor, which again resulted in an improvement but did not solve the problem. Noticed an improvment in fuel economy and engine idle, but that was about it.

Having done a web search, I read something about disabling overdrive to clear out 'gunk stuck in the hydraulics'. So I took the truck out for a 20 minute drive, and disabled overdrive afterwards. I drove it hard for another 20 minutes, ensuring it frequently shifted from first to second and into third, and that actually solved the problem. There's still a slight delay shifting to third, but other than that, it shifts like new. The shifts are now softer and on time, like before.

Had I known about this earlier, I would have done this before and saved myself the time and hassle. But I wouldn't entirely consider a new TPS and cleaning the MAF a waste of time.

I'm using Motorcraft Mercon V with a bottle of LubeGard Red in there at the moment, which has been there for about 2 months. I'm planning to change it out earlier (always done a cooler line flush every 25,000 miles since new), and installing a Magnefine inline filter.

 

[Jim Spahr]

Lube Gard is popular here in the USA with trans. rebuilders. I was wondering how you happened to hear of Lube Gard in Kuwait? Is it popular there with trans rebuilders and DIYers?

 

[Falcon_LS]

LubeGard is a popular product with transmission shops here as well, it's been around for many years, although they seem to be quite misinformed about the products and are not willing to change that. For example, when I went to get a bottle of LubeGard Red (Platinum wasn't available in stock) for my Grand Marquis, they tried to sell me LubeGard Green, which is to convert regular Dexron III/Mercon to Mercon V. They ask about your application to make a recommendation on which product to buy, but if I'm already using Motorcraft Mercon V, I don't need that. Unfortunately, a lot of people are wrongly advised by those guys to use that very product with Mercon V in Ford applications. They just believe LubeGard Green should be used in every Ford transmission. I went with LubeGard Red, against their advice, because I'm a BITOGer.

That said, I only started using LubeGard transmission additives after reading about their products here on BITOG.