Bongo topping out at 30mph, no gear up

[bongovi]

Hello Bongo-heads,

After last year's epic cylinder head change thread, this year presents us with a new issue. Driving is normal up to 30mph, then it stops accelerating and the revs rise up to 3k-ish. It's not gearing up, if I've understood correctly.

After a look around here I found ref to the throttle position sensor, which seemed to fit the bill - maybe part of the potentiometer/resistor had gone for the upper gear parts? I also noted that mine didn't have the plastic connector between the top/bottom from the throttle to the TPS. For the last year. Given that we'd had another issue since that cylinder head fix, where it wouldn't go into top gear without dropping to 'S' mode, I thought this must have been what was wrong.

I picked up a 2nd hand TPS, with plastic bit, and installed - no change. It still maxes out at 30mph. In 'L' I can get a bit faster, but that's just the gearing, I think?

When installing the TPS I clipped the negative cable b/c there was no way I could get it out from behind the pump without dismantling everything. I soldered it onto the new/2nd hand TPS negative. This could be a factor, but I'm thinking it's more likely whatever was causing the issue initially still is.

Any idea what's causing this weird behaviour?

EDIT: It's a 1996 2.5 TD and it was this thread* that made me think electrical/TPS, and maybe this one for just changing the transmission fluid**

* https://igmaynard.co.uk/bongo/forum/vie ... 45#p697362
** https://igmaynard.co.uk/bongo/forum/vie ... 15#p694432

[cutlass]

"Driving is normal up to 30mph, then it stops" - may be you engine dont have more power?

[bongovi]

may be you engine dont have more power?

Yeah, you might be right, it could be that simple. Said something like that in the linked thread.

Have just ordered from Euro Car Parts:

502680198 - Crosland Air Filter
503690188 - Crosland Fuel Filter
522776291 - TRIPLE QX Multi Vehicle ATF-U - 5 ltr


There's 35% off this weekend so that lot was £50.

Should have changed air and fuel filter after cylinder head replacement last year. If this is all it takes, I'll report back. I'll also sell on my 'spare' throttle position sensor, as that doesn't seem to have been the problem.

Hoping there's a sump bolt under there, as I don't have a pump for the ATF change. Can anyone comment on the choice of fluid? All much of a muchness?

[cutlass]

"TRIPLE QX Multi Vehicle ATF-U - 5 ltr" - I use ATF from ZIC (Korean).......NOTE!!!!! for changing all volume ATF and clean system need aprx 13-15 l !!!!
I hope smoke have normal color? dont white or dark?

[bongovi]

"TRIPLE QX Multi Vehicle ATF-U - 5 ltr" - I use ATF from ZIC (Korean).......NOTE!!!!! for changing all volume ATF and clean system need aprx 13-15 l !!!!
I hope smoke have normal color? dont white or dark?

15 litres - is that for some kind of flushing method? I thought 4-6l was the capacity?

Plan is to:

a) replace fuel + air filters, see if that did anything, then if not;
b) drop the transmission oil/sump and clean the filter, refill with ATF

Order for filters/ATF hasn't arrived yet. Probably tomorrow.

Smoke is normal colour so far. Start has been lumpy at times, also perhaps pointing to potential fuel filter issue (in my limited experience).

[teenmal]

Firstly I would change the fuel filter, clean the small gauze filter on the injector pump and check that the Turbo System is sound. (you never know)

To Completely Drain and change the auto box fluid it will take approx.13-15 litres as has been said.

Take care

[bongovi]

Firstly I would change the fuel filter, clean the small gauze filter on the injector pump and check that the Turbo System is sound. (you never know)

To Completely Drain and change the auto box fluid it will take approx.13-15 litres as has been said.

Take care

Thanks teenmal. Is the small gauze the banjo filter I keep hearing about? I've had a good fish around with a hooked-long-thing before and there doesn't seem to be one in there, so I don't know if previous owner lost it, or if some models don't have it?

Will try the filter changes first, then consider buying a few more tubs of ATF. Kind of hoping I don't need to do that, but I have no idea if or when it was ever done before.

[g8dhe]

This is the Banjo filter, some people have been known to remove them .....

[bongovi]

This is the Banjo filter, some people have been known to remove them .....

Thank you. Can confirm with 90-something percent certainty that there's not one there. Had a right good root around this time last year. Worth buying one? Wouldn't want to gum up the pump. In the meantime, will report back after basic filter change.

[g8dhe]

I'm not an engine designer or mechanic in that sense, but designers don't add parts that aren't needed in a design - there are however people in the world that know better than the original designers, because they don't know any better, that love changing things

[cutlass]

"Will try the filter changes first, then consider buying" - it is wrong way...alltime need clean oil sistem and also you need disconnect tube at oil cooler and clean it use pressures air too...

[bongovi]

I'm not an engine designer or mechanic in that sense, but designers don't add parts that aren't needed in a design - there are however people in the world that know better than the original designers, because they don't know any better, that love changing things

Ah, thought that might be the way. OK, will see what I can find. Cheers!

[bongovi]

"Will try the filter changes first, then consider buying" - it is wrong way...alltime need clean oil sistem and also you need disconnect tube at oil cooler and clean it use pressures air too...

It may already be clean - I'm not sure it's the problem yet, haven't checked paperwork to see if TF was changed in last few years. Appreciate the thought though. Filters delivered this morning, will be in touch with results.

[cutlass]

" I'm not sure it's the problem" - YES!!! wery old ATF will only influence at moment of change step gear... It dont reason what you engine dont rotation more 3000....
but - in next time you will change ATF - and you throw out "5l new ATF" what you now try pour into gear box.....

[bongovi]

" I'm not sure it's the problem" - YES!!! wery old ATF will only influence at moment of change step gear... It dont reason what you engine dont rotation more 3000....
but - in next time you will change ATF - and you throw out "5l new ATF" what you now try pour into gear box.....

I know you're knowledgeable on these things, cutlass, appreciate your message, but struggling with your meaning here.

Are you saying ATF won't be the reason for the power loss (not going over 3000rpm), but will be useful anyway? Obviously putting in the full 15l and not 5 as I first thought...