Club 80-90 Forums

Hi - looking for some diagnostic advice before I take the major step of pulling the engine to bits...

This is a 1989 vanagon 2.1 DJ which I bought about 5 years ago. The engine sounds good - no rattles etc and ran fine until about a year ago, since when it's been running rough and losing power under load. It's high mileage but sounds and pulls very well when it's firing on all four cylinders.

The only bit of history is - about 3 years ago No. 1 cylinder blew a plug in France and I got a helicoil put in. Didn't seem to be any valve/piston damage (at least it ran fine afterwards and has done a few thousand miles since!). Helicoil is still there.

Now the symptoms are:

1. At idle, No 3 cylinder is missing, but cuts in at about 2000rpm i.e.if revving under no load all 4 cylinders are firing. No 1 was also missing at idle but that's improved after adjusting tappets. So no problam as long as you don't need the engine to do any actual work!

2. MAIN PROBLEM - When driving under load the engine will only fire on 4 cylinders if I use minimal accelerator. Opening the throttle cuts out one or both of the problem cylinders. I can coax it back to firing on four by closing the throttle again. Problem is worse the higher the load on the engine (i.e. uphill). Problem appears after 5-10 minutes running from cold, then stays stable.

Now I've checked all the obvious things many times and it now has me stumped. Here's what I've eliminated as culprits so far...

1. Fuel supply - injectors and fuel compression are checked and fine. New injector in No. 1 didn't help problem either.

2. Fuel delivery is fine (nearly 1L per min). New tank with the large bore pipe for injection engines. Fuel pump and filter recently replaced.

3. Spark is fine. HT coil about 2 years old. Earthed OK.

4. Compression is good and within limits on all four cylinders, warm and cold.

5. No sign of leaking head gaskets, no water in oil etc.


So I had a specialist take a look. He's adjusted the tappets again, which improved things a bit, but not much - the problem is still there and he suspects either the hydraulic lifters or the camshaft or both.

But why is the problem so dependant on throttle position while driving?? I can make 1 or 2 cylinders cut out reliably just by pressing the accelerator down a bit.

Any ideas? As far as I can see it has to be valves/tappets/cam but it behaves just like fuel starvation.

Next thing is to take off the heads and have a look, replace the lifters in the problem cylinders and check the valves are sealing. Does anyone know if it's possible to check cam wear properly without splitting the case?

I wanted to take the van to France in a couple of weeks but obviously won't be able to if I have to do an engine rebuild, so any suggestions very welcome indeed.

Thanks

Paul

Couple of thoughts.

You say spark is fine, have you changed the plugs and or leads? Misfire under load is often associated with the HT circuit breaking down when it is under strain, it will look like its ok on static tests as you will see a spark but under load the spark fails.

You say it doesn't happen when cold - does that mean doesn't happen even under load when cold? The difference when cold is mainly mixture which would lead you down the fueling route, but could also be air leak.

HTH

MM

Hi
I am not farmiliar with the injection system so I can not comment on it, however I run a 1.9 DG and I had similar problems recently. After a lot of head scratching it turned out to be a new distributor cap that wasnt sitting correctly on to the dizzy, the clips were on and it was located in the right position but it still wasnt completely full down. Tell tail signs is the chips out of the ceramic near the electrodes inside the cap were the rotar arm had been catching. It still took me several attempts to get it sitting right and with each time I thought it was on OK it turned out to be not. Might be worth a check

how do you know it's one and 2 struggling under load ?
I'd bet on either TCI unit or more likely HT leads arcing out from metal covers - the new leads aren't very good imho even the beru and bosch ones which I think are now made in china, I've had several instances of insulation breakdown on almost new leads which check out ok for resistance end to end but arc out via the shroud - genuine VW ones though are £150 a set new - so I've gone back to old VW leads no problems
a leakdown test would check the valves out wouldn't it ?

Hey thanks for all the replies!

MM - have changed plugs but not HT leads - will try with new leads as per Aidan's reply too. But how does the HT system know whether the engine's under load or not?? And how could that be dependent on throttle position?

Re: second question: When starting off driving from cold the engine behaves MUCH better for a few minutes even under load, but then as soon as it warms up the old problem is back. PS Your WBX rebuild thread is very much appreciated thanks!

Nicbeese - I'll re-check the distributor today

Aidan - I don't know for certain, sorry I wasn't clear - shd have said 'I can make one or more cylinders cut out reliably just by pressing the accelerator down a bit'. Numbers 1 & 3 are the ones firing intermittently if at all on idle, so can only assume that those are the ones cutting out on the road.

Anyway I hope you're right. Like I say, I'll change the HT leads to see if that makes a difference. I'll check the TCI unit as well. Can you explain how that could cause the above problems even at high revs? I hope it can!

Finally, I'm trying to figure out if or how the cam/lifter system could be causing this. Even if a lifter is full of air or seized in one position, could that stop a valve opening? I guess it could stop one closing if the tappets are adjusted tight - maybe I should back off the tappets on each suspect cylinder temporarily and adjust as if they were solid ones to see if there's a difference... if someone can clarify this I'd be grateful.

But it''s the throttle position that affects whether it's firing on 4 under load or not, not engine speed or anything else. That's what makes me keep thinking fuel - but fuel system seems to check out...

Thanks

Paul

the only thing the throttle body affects is switching the idle system on and off, ensuring full fuel at high revs under load, and the mass of air coming in which is measured by the AFM so maybe the AFM has some drop outs and that's what's causing the issue ?
Much easier to see the drop outs with an analogue meter than with a digital one

Ah - now I get what you mean. I'll test throttle switch and investigate AFM as far as I can without a CO tester. Also there should be a way of cutting out the idle system temporarily so it's off, and see if that makes a difference driving...

There is a deeply technical reason why full throttle/ load puts and extra strain on the ignition system but I can't remember all of it, to do with compression and spark etc. Basic story is the spark has to work harder under load so it shows up any weaknesses in the HT circuit.

PS I would be surprised if it was lifters from what you describe, pull the valve covers and rotate the engine by had and check all the rocker arms are going up and down ok and that you have consistent heights when valves are closed. You can check pre -load (~1 1/2 turns) as well, but if there is a real problem inside the heads you will need a compression or leak down test.

I would work through ignition first then fuel/fuelling then air (leaks) which is pretty much what it sounds like you are doing



MM

Damn! The main problem was the HT leads...

Hadn't suspected them because they were fairly new and I'd already tried swapping them in various combinations with another old set I had.

Here's what I did first last week which improved things a bit - took distributor to bits, checked and reassembled it, replaced distributor cap, checked throttle body switch was operating by checking resistance across the terminals at idle and full, readjusted idle speed with ICU disconnected, re-made all the earth connections from engine and HT coil.

Then I put in a new set of HT leads and it's now running like new! So an obvious fuel problem turned out to be electrical...

Thanks Aidan and thanks MM

Quick update - I've just driven it to South West France and back. Did about 2000km and no engine problems at all...

Thanks again for the advice

Paul