Autobox gear changes

[corblimey]

Hi all

My Bongo seems to change down too easily or looking at it from the other point of view, it doesn't change up into top quickly enough.

I'm sure it was ok when I first got in December but after about a month I got what I initially would have described as gear hunting. I've taken it out on several occasions on a quiet road to replicated the problem and to decide what is actually going on. It would appear to hold third gear longer than it should and only change into forth when the engine load is not very high. Once in forth, if I increase the throttle very slightly it will drop back down into third. Ease off again very slightly and back it goes into forth. If it's in forth and I get to a hill it will drop back to third much sooner than I'd expect.


Here is a list of the symptoms/ relevant facts :

1) No hold light warnings
2) Every gear available (i.e. gearbox not dropped into safe mode)
3) Previous owner had gearbox solenoids replaced and oil changed 8 months ago by auto box specialist.
4) Speed converted fitted to speedo
5) No erratic behavior from the speedo or tacho needles
6) Can get the gearbox to change into top by easing of the throttle
7) Gear changes appear to be very sensitive to throttle position.
Symptoms appear when the gearbox has fully warmed up

My conclusion thus far is that it's some sort of fault in the gearbox feedback system or electrics, possibly the throttle position sensor.

Any thoughts would be appreciated.

[mikeonb4c]

I'm no expert corblimey but from all I've read on BF it sounds like an inspection by an auto gearbox specialist might be on the cards. It would be nice to find one who (a) is familiar with Bongo boxes (or at least the Nissan box that it actually is I think I read) and (b) will not lead you down the road to unnecessary spending if not needed (which it doesnt sound as though it is - feels like it ought to be realtively inexpensive to fix). I think there are one or two autobox specialists mentioned in the Members Area list of Bongo Friendly garages.

I'm sure someone else will come on BF with advice shortly, but good luck meanwhile.

Mike

[dandywarhol]

Is lockup selecting corblimey? It should lock in at around 37/40 mph, on the level and hot. This gives the impression of a "5th" gear.

[corblimey]

Cheers for the response Mike.

I've just read the ATF guide in the members area and it sounds like I've described the behavior of a gearbox that hasn't yet reached full operating temp.

I've just been out for a spin (about 15 miles) and not a sausage.

I think I've getting myself slightly confused here and perceiving something to be a problem when in fact it's not because I've become too suspicious.

There is definitely an intermittent problem but in retrospect what I described in my first post is not it.

I've also just read Owermoo's post and I think that sounds more like the problem I've experienced.

The facts from the previous post still stand but the gear change behavior
I previously described should be disregarded.

Hi Dandy you posted whilst I was typing; yes it does lock up.

[volamoose]

Hello I have been searching for over a week now to find a place to get a throttle position sensor. Anyway after speaking to bongo & Japanese car parts spcialist I thought I'd Google it and bugger me if it didn't come straight up. (I may be teaching people to suck eggs here but I thought if I couldn't get it from a specialist I'd had it) anyway I got one from Autolink , the fella orders them from Japan. Anyway I am in such a euphoric stat as I now don't have to pay over the odds for a fuel pump i thought I'd share the news. bingo bango......

[waycar8]

spooky..................i had the same problem today with the gear changes, had a funny feeling it may have been to do with the gear box/oil being cold. well i remember reading sumat about it a while ago anyway.

[dandywarhol]

Do you think the mesh filter was cleaned properly when the oil was changed?
Low 'box oil pressure would cause upshift problems.

[bigdaddycain]

Dunno if its relevent, but the late shifting/high revving probs sound very reminiscent of my old scorpio cosworth just before the torque converter packed up completely.

I also recall testing a bongo back in the day displaying these traits too...

I walked...

It would appear that the previous owner suspected something may be amiss too corblimey...

[corblimey]

Over the last couple of weeks my gearbox problem has become more regular to the point that every journey results in the behaviour. The good thing is that I've been able to observe the issue much better than before.

Since my wife is due anytime soon in the next few weeks I thought I'd better find some time to investigate in a bit more depth!

As I drive along at a constant speed, lets say 65mph, all of a sudden the gearbox with change up and down (usually up) erattically. I can still feather the throttle and force gear changes as normal but the throttle movents have to be more exagerated than usual. All the gears and lock up are achievable. The problem always seems to happen at the "normal" crusing throttle position i.e. the throttle position taht gets to most use.

All along I had a feeling it was electrical so I headed straight for the throttle position sensor (TPS). I took it off and the first thing I noted was that the little rubber boot had split into two halves. The TPS shaft was still very clean looking though. I measured the resistance at the throttle open and closed positions as stated in the workshop manual and the readings were correct.

For those who don't know what a TPS is, it's a potentiometer (variable resistor). The same thing used in a stereo to control the volume. As "pots" age the resistive carbon track and rotating contacts inside get dirty and in the case of a stereo causes that annoying crackling.

The symptoms would fit with a "crackling" pot causing erratic feedback to the ecu and causing the the random gear changes.

As the unit doesn't appear to come apart I took a can of switch contact cleaner and tried to fire loads of the stuff in down the shaft

My diag process was a bit arse about face since the next thing I did was to check the diag feedback from the flashing hold light. Sure enough I was getting error code 12 which means TPS feedback error.

I then connected up my multimeter to pin 2i on the ecu to check the feedback voltage at throttle open and closed positions. Again, they were fine according to the workshop manual.

I then went for a 30 mile spin (normally plenty enough to observe the fault) and all was fine.

Have I cured it? Well I'm not 100% convinced yet but I have a plan to confirm the fault if it happens again. I've left my multimeter connected and if it does happen I expect to see the erractic voltage readings which would confirm a TPS fault.

Anyone know where I can get a new rubber boot?

[pippin]

Glad you have had success, Servisol works wonders!

By the way, where has your wife been?

Since my wife is due anytime soon in the next few weeks

[corblimey]

I;m hoping Servisol does indeed work wonders.

Re: My wife, I hope shes only been with me else there's trouble

[dandywarhol]

Fingers crossed cor.......for both events

[corblimey]

Cheers Dandy.

The van's in for an MOT today so cross your fingers for that too please!

[bigdaddycain]

Good luck with the mot corblimey! Mine flew through a VERY thorough mot a couple of weeks back, ...no probs

From reading your posts i get the impression you are quite meticulous, (i had my leisure battery fitted per your instructions )so you shouldn't have any probs...

Post back later, and let us know how ya got on?

[corblimey]

Meticulous yes but lazy too especially where vehicle maintenance is concerned.

It failed but nothing untoward so I'm pretty pleased really

1) Headlamp alignment
2) Worn front pads

I also got an advisory on rear tyre wear and something else I can't remember right now.

So, over all, no drama.