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Poor running on a DX engine - help.

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Hello,

I recently bought a 1990 GTI Cabriolet. It has a DX engine. When I got it it was running very badly – it felt like it had a misfire and the acceleration was slightly juddery, especially at low revs. It felt like the power wasn't coming through smoothly.

The car has since had new NGK spark plugs and Bosch distributor cap, rotor arm, and HT leads. The timing belt was changed and the timing set up properly (it was completely off, apparently). The oil and filter were changed and a K&N fitted.

But, although it is now running a lot better, it still doesn't feel right. At low speeds or low revs, or when it's cold, if I stamp on the throttle it seems to take a short while before the power comes on. It's like there's a block, then it goes away.

My guess is it's a vacuum leak and/or the injector seals. Could it be anything else?

Thanks!
 

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Could be numerous things with the mechanical fuel injection system but without the proper pressure testers its a bit of trial and error.
Does it start from hot OK?
Had the car been stood for a while before you bought it?

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Poor running on a DX engine - help.

It starts from hot fine, from cold it takes a little while to fire into action.

It just feels kind of hesitant on the acceleration.

I don't think it's been standing. The previous owners had had it since new and used it as a local runabout in good weather. I don't think they realised/cared that it wasn't running quite right.

It's going to the garage for some other bits and pieces tomorrow. I just wondered if there was anything I could ask them to check while it's there.

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If its hesitant when the throttle is snapped open and the timing is all good it sounds like fuel and could be as simple as the CO is weak. Its a simple test for the garage to check.
If its not starting straight away from cold it could be that its got an aftermarket fuel pump relay which doesn't activate a pump prime when ignition is on. When you turn to ign on you should hear the pump run for a couple of seconds. If it doesn't then just flick the ignition momentarily - enough to send a signal to the pump relay from the dizzy. Do that a couple of times to build system pressure and then see if it starts easier. If it is priming then it could be many things from a sticky plunger in the metering head or possibly the gauze filter is blocked in the wur (warm up regulator) bolted to the front of the block next to the dizzy. Fifth injectors can fail or as you say a vacuum leak.

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Ah, right – thanks for the pointers. I'll try them out and see if we can get it sorted tomorrow.

With the throttle hesitation, it's mainly when it's under about 3500rpm. After that it seems to pick up. Plus it's only when the throttle more open; when I'm driving more gently it's not as noticeable.

The start thing is only when it hasn't been started for a little while. I'll do as you say and see if it makes a difference.

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My genuine VW fuel pump relay does not prime before starting the car and the has never primed the fuel pump since I've owned the car (20 years) and I've never had a problem starting it.
Have a look at what replay is fitted, you can easily spot a aftermarket relay.
Is the fuel filler neck OK.
Any recipes etc for new injectors, they don't last forever and my poor running and starting problems have been injectors but check other stuff first as injectors are expensive and you can check the spray pattern and any leaking fuel on the injectors you have.
What fuel are you using, super unleaded or normal unleaded as the timing is set up differently for each fuel?

1988 Mk1 Golf GTi Cabriolet 1.8cc DX, K-jet. Daily drive. 317,000 miles and counting
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.

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i had similar on mine, but it was hesitant at higher revs.

i changed all the pumps , filters ,plugs, leads, dizzy cap\arm, still the same.

in the end it was the injectors, get some beer bottles mounted on some wood and test the output.

Alps 1992 Rivage Green, 1991 Rivage Blue (SOLD), 1986 GTI convertible White (SOLD) 

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I had a similar problem just last week on a 1.6 gti. If the dizzy has a vacuum advance it may be seized and would effect the car when driven on. 

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Well, it's been to the garage. They replaced and reconnected some of the vacuum hoses and seem to think it's now OK. They did mention something about the vacuum advance. I didn't have chance to really drive it though so I'll see over the weekend. I still think it might be the injectors…

It's got a tank of Shell V-Power Nitro+ in it at the moment. My mk2 GTI seems to run better on that and I assumed it'd be the same. I'll test it with regular unleaded when I next fill it up.

The problem is that I don't have the tools or space to do very much myself, so I have to rely on the mechanics at the garage to figure it out. It's a costly business! They're an old school VW garage, but is there anyone in the London area who could set up the injection system properly?



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Stick with super unleaded as I found mine runs best on the stuff.
VW did fit a sticker saying min 98 RON petrol so I'd stick to super unleaded as normal unleaded is 95 RON.

1988 Mk1 Golf GTi Cabriolet 1.8cc DX, K-jet. Daily drive. 317,000 miles and counting
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.

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Poor running on a DX engine - help.

OK - thanks - I'll stick with that. My mk2 definitely runs better on the expensive stuff.

I'm driving the mk1 to France on Saturday so that should shake out any remaining running issues. I just hope it stops raining.

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Poor running on a DX engine - help.

I'm still having minor issues with this: a slight hesitation at low revs and what I think is pinking when I accelerate. I've tried it on UK (97) and French (98) premium unleaded and it doesn't make much difference.

I'm going to ask the garage to check the injectors and replace the rubber seals, and also to check the timing. Haynes says it should be at 0 degrees (TDC). Is that right?

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Timing, mark the dissy shaft where it is now loosen the bolt holding the dissy camp start the car and advance the timing (turn the dissy clockwise) you may need to a adjust the idle speed a little 7mm spanner needed. Drive the car and listen for any pinking, advance it a little more till you can hear the pinking then retard it a little (turn dissy anti-clockwise) till the pinking stops.
You need a quite road to do this as you need to keep stopping and adjusting the timing and idle but you only need a 13mm and 7mm spanner to do this, also be carful of the fan if it starts when working on the dissy.
If it all goes wrong you can just turn the dissy back to where is now and then take it to a garage.
I always set my timing this way.

1988 Mk1 Golf GTi Cabriolet 1.8cc DX, K-jet. Daily drive. 317,000 miles and counting
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.

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Just a quick update.

The guy at the garage took a brief look at it for me. He adjusted the mixture because he thought it was running too rich. The timing is a 0 tdc. It's got Shell V-Power Nitro+ petrol in it and it seems to be pinking whenever I give it any throttle. Should it be moved to 6 btdc?

The hesitation remains to be tackled…

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1.8 base timing is 6 degrees BTDC with the vacuum line on the dizzy disconnected and plugged, there is a big 6 degree diamond mark on the flywheel you use as a reference point if you have a basic timing light with no advance dial

Hello my name is John and I'm a dub addict.



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rubjonny said

1.8 base timing is 6 degrees BTDC with the vacuum line on the dizzy disconnected and plugged, there is a big 6 degree diamond mark on the flywheel you use as a reference point if you have a basic timing light with no advance dial


I've had the timing checked with a stroboscope and it's on 6 BTDC.

The tank is full of Shell V-Power Nitro+, into which I've poured a bottle of Redex octane booster and some Redex cleaner in the hope that this might be an easy way to solve the hesitancy without having to remove anything.

I've just spent a couple of hours ragging it round central London. No high speeds, but lots of revs and lots of stopping and starting. The hesitancy doesn't seem as bad, but it's still pinking. Less than it was, but it's still doing it. Is it possible that the timing just needs to be fine-tuned?

If it's not that, I guess I start fiddling with WURs and stuff. Any suggestions?

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Check the cam belt timing marks are in the right place, It's really easy to be a tooth out, they car will still run but not at it's best.

Pictures.




There is a pointer on the cam belt cover as well for a quick check as you don't have to remove the cover.

1988 Mk1 Golf GTi Cabriolet 1.8cc DX, K-jet. Daily drive. 317,000 miles and counting
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.

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if you're on 97+ fuel with timing at 6 degrees it shouldnt pink, the timing isnt your issue. but while you're looking check the VW part number on that dizzy and post it on here perhaps someone has fitted a carb one by accident.

But it might be a bit coked up, as you run it now its setup better the carbon gradually burning it off hence the pinking getting better. a way to speed up the process is get the engine to suck in a little water, steam cleans the bores. its tricky to do on a kjet though, for a carb you would just trickle water in the choke flap :lol:

one way is pop a vacuum hose to the throttle body off and submerge it in water, give it some revs and it'll gradually drink it all up :) pull the hose out if the engien starts to bog, hold the revs till it clears then put it back in the water. half a litre should be more than enough!

Hello my name is John and I'm a dub addict.



My wiring diagrams and other documents have moved here:

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Thank you for all the advice, guys. Much appreciated.

I gave it a blast again this morning. It's waaaaay more responsive and the engine seems really eager (I guess because of the Nitro petrol and the octane booster!), so that's good. It doesn't seem as hesitant as it was. I have my fingers crossed that it was just a gunked up injector or something. It is still pinking, but nowhere near as badly as before.

I've noticed that the engine smells really bad at the moment - kind of the smell you get when from burning oil and grime. Presumably that's the Redex cleaner doing its work and some of the build-up inside being burnt off?

I'll check the timing and the distributor number later. I'd be very surprised if it had been changed. The previous owner (there has only been one) didn't say anything about it being replaced, only that they'd had it set up to run on unleaded. I guess that's why it'd been set at TDC. The mechanic at my garage said that when the switchover took place VW issued a directive to put back the timing by 6 degrees to cope – at least that's what he says. I'll have a look though.

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yeah you would need to knock the timing back to cope with regular, so what he says sounds correct! Worth a double check just to be sure though regardless :)

Hello my name is John and I'm a dub addict.



My wiring diagrams and other documents have moved here:

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You'll need to sign into google/gmail for the link to work! (its free!)
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