Sporadic fault with automatic gearbox

nirmski · Post by **nirmski** » Thu Nov 22, 2007 6:22 pm

I have a bongo that seems to have an intermittent fault with the automatic box, most of the time it will change through the gears as it should do but then all on its own it will over rev and appear to change up and down on its own even when you keep your foot in exactly the same position.

I have cleaned the connections around the gearbox which don’t appear to be corroded . somebody also advised it could be to do with a Speedo conversion, but it doesn’t appear to have had a conversion on the Speedo just a face plate change, unless I am looking in the wrong place? I removed the Speedo and the only wires going in are from the original wiring loom.

Would be grateful if anybody else knows of a fault that can cause the auto box to rev up and down on its own occasionally.

dandywarhol · Post by **dandywarhol** » Thu Nov 22, 2007 6:32 pm

Could be off track here but if you're sitting on the level at around 37mph the box might be "hunting" between 4th and lockup. Otherwise have a look for blink code faults as per the fact sheet in the member's area.

Oh, and welcome

nirmski · Post by **nirmski** » Thu Nov 22, 2007 6:36 pm

Thanks for reply, it dosent seem to have a set speed that it happens but it does appear to hunt. ill check codes

corblimey · Post by **corblimey** » Fri Nov 23, 2007 12:25 am

I've been experienceing exactly the same symptons for the last 6 months.
No flashing hold light, speedo readings rock solid but gear hunting at random times , speeds, etc.

I connected a multimeter to the throttle position sensor input on the ECU and I could see the feedback readings jumping all over the place when the fault occured. I ordered a new throttle postion sensor from Autolink about 2-3 months agon and it finally arrived about 1 month back. SInce fitting it my van's been spot on.

I've posted before detailing which connector to test, search for "throttle AND position AND sensor"

If it is the sensor it may be worth asking Ian to source you one if the price is right. I'm sure he'll get it quicker than Autolink did. BTW I'm not slagging off Autolink, that chap there was really nice and helpful, it's just that the part took some time ot arrive.

HTH

nirmski · Post by **nirmski** » Fri Nov 23, 2007 10:09 am

That sounds promising, thanks for the advise ill try to find one, are they easy to fit & where are they located? Any idea what they cost.

Post by **Ian** » Fri Nov 23, 2007 10:29 am

It's £107.75 from Autolink. See here:

http://stores.ebay.co.uk/Autolink-UK-Ltd

Mazda price is unknown, I would need the part number to make an enquiry. But I expect it is far more expensive.

corblimey · Post by **corblimey** » Fri Nov 23, 2007 10:30 am

sort of, under your bum and yes

The actual sensor is dead easy to fit but there is one connector that is a real pig to get to. It's a threaded post on the fuel pump but there's not really enough room to turn a spanner. I resined myself to at least a hour simply to remove and refit that one connector. That was more metal preparation really cos I knew it was going to be one of those jobs. If I just dived in hoping to get the job done in 10 minutes I'd have got so frustrated I'd have broken something expensive

Make sure you have a pearl catcher, bubble gum on a stick or something similar just in case you drop the offending nut.

The sensor is located on top of the fuel pump. You need to open the drivers seat to get access to it. If you look up my other thread you'll see some photos of the offending part. Once you know what it looks like you'll easily spot it.

It part itself cost just over £100 which I found a little hard to stomach since it's only a potentiometer. Ask Ian how much he can get you one for. I tried to get one second hand but didn't have any luck.

The first thing I'd do before ordering one is to get a multimeter on it. You'll be able to see straight away if it's the TPS.

nirmski · Post by **nirmski** » Fri Nov 23, 2007 12:38 pm

Is it the top picture with the affending item having 466 written on it? im a novice with a muliti meter and would have to buy one which is fine im sure it will soon pay for its self, could you just give me a quick lesson regarding which wires to conect it to on the tps in order to check it and am i write in thinking it should read at 2.15v .

corblimey · Post by **corblimey** » Fri Nov 23, 2007 1:13 pm

Yes you're right, it is the item with 466 written on it. Yours may well have a different number on it so don't let that fox you.

You don't actually connect to the TPS itself. Behind the glove box is the engine control unit (ECU), you just need to connect the +ve lead (red) of your multimeter to the correct wire that goes into it and the -ve lead (black) to chassis earth. See the info below to identify the correct wire.

Set your multimeter to measure DC volts in an appropriate range (i.e. 0 - 30 volts) and then set off for a trip. A nice quiet road helps.

At stand still with your foot off the pedal you should get a reading of about 1.3v. As you press the throttle pedal you will see the voltage reading increase; this is expected. If you keep your pedal at a specific position you should get a steady voltage reading. If you find that it is jumping around significantly (> 0.5 volts) then the TPS is almost certainly the problem.

The open and closed voltages are not what you are trying to identify but they are certainly useful for reference. Yours may vary slightly so don't expect to get exactly the same values I'm mentioned.

You can pick up a simple digital multimeter for under £10 these days from places like Maplin so it won't take long to pay for itself.

Once you've hooked up your meter and got some readings post your findings.

If you would like to have a chat pm me and I've give you my phone number.

Here are the details from one of my other posts

The voltage readings for the TPS are as follows (approx):

Closed ~ 1.3v
Open ~ 4.2v

You can measure this from pin 2l on the ECU loom connector. I just shoved a bare wire into the back of the connector and connected that to +ve on my meter and then earthed -ve.

There are 3 loom connectors small, medium and large. It's the medium one (also happens to be the middle one of the three) you're interested in. Take it off and as you look at it face on with the keyed mouldings to the top, 2l is the third from the left on the bottom row.

mikeonb4c · Post by **mikeonb4c** » Fri Nov 23, 2007 2:17 pm

this corblimey blokes good innit eh?

corblimey · Post by **corblimey** » Fri Nov 23, 2007 2:28 pm

oh shut up Mike you'll make me blush

Seriously though, just doing my bit. What goes around comes around and all that. People are really great here and have helped me out with advice and freebies so you gotta put a little something back.

mikeonb4c · Post by **mikeonb4c** » Fri Nov 23, 2007 2:54 pm

100% dude 100%

nirmski · Post by **nirmski** » Fri Nov 23, 2007 3:20 pm

Thanks for all the advice very much appreciated. ill keep you posted.

dandywarhol · Post by **dandywarhol** » Fri Nov 23, 2007 6:31 pm

Have you ever dismantled the old TPS corblimey? It should be just a "sweeper" blade on a winding of wire in there.

Yamaha had a recall of 10s of thousands of these on their fuel injected bikes last year - the dust seal was faulty and allowing dust into the unit and making it misread. I'm wondering if it can be opened up and cleaned out with compressed air

corblimey · Post by **corblimey** » Fri Nov 23, 2007 6:47 pm

No I haven't.

I mean to when I get the time but that seems to be in short supply at the moment. If I can find 5 mins and remember where I put my hammer I may try gently dissecting it.

If you could mate a £1 pot to the end it would certainly save a few quid. Would be nice to find a simple fix for other bongonauts.

Over time the carbon tracks become prone to dirt and wear. It's the crackley radio volume knob syndrome. Switch cleaning solvent usually helps but in my experience it doesn't last for long.