Vw 1990 t3 2.1 inj 5speed, bucking on deacceleration

[Steve Barnes]

Hi, I have bought a late vw 1990 t3 2.1 injection van with a DJ motor with an ottinger factory upgrade using a digifant ecu & distributor. It would have been fitted with a CAT, but at some time it looks like that has been removed & replaced with a straight pipe to the silencer.

It runs beautifully, economically & idles smoothly @ constant rpm but bucks on low rpm deacceleration especially in 2 nd gear but also in 1st & 3rd. This starts around 1,200 rpm.

Having checked & replaced so many parts including all engine/gearbox mounts(made no difference),refurbished throttle body ( cleaned /new bushes)& checked idle switch is working etc,tried adjusting AFM (tensioning spring as I thought the arm might be pulsating, then opposite to make richer running)/mixture settings, check for vac leaks, checked timing (10deg BTDC with ron99 petrol) replaced O2 sensor, fuel & air filters, checked ignition system, added forte fuel injection cleaner, checked Co (c.1.6%) it still bucks badly especially down hill in 2nd so my guess is that it’s probably running lean ? Spark plugs are a healthy light brown.

Now wondering if this could be idle control valve not letting enough air through on deacceleration ?(new one ordered to see if this might help) or wondering if this bucking could be caused by lack of the required exhaust back pressure with CAT removed??

Wondering if anyone has thoughts if a poor idle valve or lack of back pressure is likely to be the issue or something else? . I’ve run out of ideas!!

Thank you.

[silverbullet]

Did someone say Oettinger?

If your wbx has been ugraded or modified for increased capacity, it *should* have the engine size stamped on the flywheel end lifting eye of the crankcase.
Could be a 2.3 or a 2.5 litre

As to the overrun issues, it could be the so-called "vanagon syndrome" (not convinced that such a thing exists tbh as it could be caused by any number of things)

If the catalytic converter has veen removed it shoyld still have a lambda sensor in the exhust for the ecu to work properly.

My Oettinger 3.2 wbx6 has a variant of Digijet with lambda, so the distributor has vacuum connections. Is it possible that your van has the wrong distributor fitted?

It wont be the wrong ecu as they are not interchangeable.

[mark]

I would give each wheel a spin and check their tyres are not oval shaped. It feels just like a miss fire.
Good luck!!

[Aidan]

I'm confused

either it is a DJ 2.1, higher compression, vacuum advance and retard disi, no cat, 10' timing and 99Ron (or 5' and 95RON), ECU in engine bay in front of left rear lights, seperate TCi unit (which might be the issue if it has one, can lead to weak spark - see Ian Silverbullet's thread in Syncro), and electronic retard unit, both in engine bay

or it's a Digifant 2.1, lower compression, (MV, SS) no vacuum on disi, cat, lambda, 5' timing and can run anything from 91 RON upwards, ECU inside under rear seat, no TCi unit in engine bay, no electronic retard unit either, fuelling and timing controlled by ecu, informed by lambda in exhaust

Pics of ECU, position of ECU, pic of ECU plug to see the pin outs and some shots of engine bay wiring would be helpful. Pic of engine number on block or any other markings as described by Ian.
A pic of the M plate under left front seat and the white label if still present would also help, as would any Oettinger original paperwork - I'm wondering if you just told a bunch of bullshit by p.o. when you bought it ?

Oettingers can be weird though, but bodged together ones or messed with ones a complete nightmare

Just another idea, cause I don't know what you mean by bucking, but I do know what a misfire feels like in one of these when a lead breaks down, but which usually presents as lack of power, under load, uphill, so the opposite of what you are having by the sound of it and usually easy to diagnose so..

Could it be mechanical, ie gearbox, if pinion bearing is worn and pinion shaft is moving back and fro on / off load then pinion teeth can climb the crown wheel tooth - but you'd also notice the effect when reversing, especially reversing uphill (same as decelerating down hill), but if it was this bad then I'd expect symptoms in 1st gear, and debris on drain plug magnet. Also could it be worn CV joints ? Your 'runs beautifully' doesn't really suggest these mechanical issues but you do have a driving issue rather than an obvious engine when stationary one

[silverbullet]

Could just be an air leak of course. I've got an Audi with an iffy inlet idle air hose (it has a lot of them) which manifests itself as a "cough" at low rpm under engine braking below 1500rpm.

Pics of the engine bay please! What's its history? What does the blue Oettinger label in the engine cover say?

(use the black imgur button)