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Engine misfiring??

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Hi guys I need some mk1 wisdom my car after running spot on has developed a cough or misfire it sounds like a backfire near the carburettor and sure enough I pulled the ramair filter of.and its slightly melted above the carburettor area and blackened .its worse when it's under load .its intermittent and worse going up a hill .if I'm at full throttle it very rarely does it .it does it mostly when I'm set off. Worse after it's hot. And doesn't seem to do it when my choke is on in the morning for the first run .its bothering me as it completely loses power for that second then Carrie's on .I did have a split in the carburettor to manifold flange. Which I thought was the issue. I've fixed that with a brand new flange and it's still the same and appears to be getting worse.
Please help guys the sun is out and my cabriolet needs some cruising
Regards Dean

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Misfires to me were always;
Bad plugs,
Bad Wires, Cap or rotor, and
Timing.

What do Divorces, Great Coffee, and Car Electrics all have in common?

They all start with GOOD Grounds.

Where are my DIY Links?

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hi agree with all apart from the timing issue
mate

Do not know a lot but willing to help if possible

1989 Sapphire Blue Mk1 Cabriolet KR
1985 Atlas Grey Mk2 GTI 2.0 ABF

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Engine misfiring??

Ok guys it's got a new coil new distributor including fizzy cap and new rotor arm .new 8mm silicone leads and plugs are less than 6 months old .the timing has been set when I had it dynod and it was running fine then .its happened over the last 2 weeks .my go to guy who dynod it has been too busy to look at it. He thought it might have needed re-jetting so we did that as it's on a ramair foam filter and was running a little lean .we changed main primary from 117 to 120 and main secondary from 120 to 140. As per a Weber guide to jetting .its made no difference.its backfiring through the inlet as that's the area of foam that's scorched. It was suggested it had water in the system? But again brand new mechanical fuel pump brand new Weber 32/34dtml carburettor. Brand new stainless braided fuel lines throughout .only thing I haven't done is the new tank .but shone a torch in the circle bit under the back seat. And saw no debris or anything. My inline fuel filter is changed every 2 months regardless of weather it needs it or not .???? I ran 500ml of methylated spirits in the tank of fuel to remove the water .made no difference. It's worse on hills and under load ???? I'm stumped

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How long has the foam air filter been fitted?  Does it still have any sort of air intake heating?  I used to get terrible problems with carb icing due to running a K&N filter without the heat deflector plate and warm air pipe to the inlet.

I also had a misfire on my GTi which many years ago which turned out to be a dodgy plug lead (which was only a few months old).  Might be worth swapping leads with a spare set just to rule this out.

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Engine misfiring??

Thanks mate .its been on since the start of the year with no issues. I pulled all the plugs today checked them looked good .checked all the leads. I dont have a spare set I had them made up .so I'd have to have a set made .checked the rotor arm coil dizzy cap .cant see anything at all its driving me nuts .if I feather the throttle gently and build up the speed slowly it wont do it .but if I put my foot down it does it constantly until I lift again and gently accelerate. Any help would be great .its my daily driver and only car .I'm stuck without it

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Check your diz advance, sounds like your diz if vacuum advanced has a leak or that you have a vacuum leak somewhere.

I had a misfire caused by a bad wire, but it took a spare set to find it, as the Plug Sets I bought (bosch triple plats) had 1 bad plug in the first set, and 3 bad ones in the second, add to that a bad wire in the mix I had the original bad wire, and 2 bad plugs so I made it progressively worsen.  I got my Ohm meter out and found that 2 of the Plugs were open. Still was doggy, and even the Switch to NGK plugs caused me an intermittent miss….  When my Daughter got home with the other car I swapped Caps and Leads and presto…it was a race car…. I then swapped leads over one at a time and found the bad one….

Another thing to look for is Carbon Tracking, that can cause a miss.  Take a Blanket (dark one or do this after dark) and with all lights around the engine off.  Start the car and see if you have sparking fairies dancing about…

I have seen it on Wire Sets that the metal plug end was shorting out to the head, as well as cracks in the diz that had gotten water soaked.


What do Divorces, Great Coffee, and Car Electrics all have in common?

They all start with GOOD Grounds.

Where are my DIY Links?

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Re:

Briano1234 said

Check your diz advance, sounds like your diz if vacuum advanced has a leak or that you have a vacuum leak somewhere.

I had a misfire caused by a bad wire, but it took a spare set to find it, as the Plug Sets I bought (bosch triple plats) had 1 bad plug in the first set, and 3 bad ones in the second, add to that a bad wire in the mix I had the original bad wire, and 2 bad plugs so I made it progressively worsen.  I got my Ohm meter out and found that 2 of the Plugs were open. Still was doggy, and even the Switch to NGK plugs caused me an intermittent miss….  When my Daughter got home with the other car I swapped Caps and Leads and presto…it was a race car…. I then swapped leads over one at a time and found the bad one….

Another thing to look for is Carbon Tracking, that can cause a miss.  Take a Blanket (dark one or do this after dark) and with all lights around the engine off.  Start the car and see if you have sparking fairies dancing about…

I have seen it on Wire Sets that the metal plug end was shorting out to the head, as well as cracks in the diz that had gotten water soaked.

Thanks briano for your reply I really appreciate you taking time out to council me .it appears to be getting worse but then seems to get a bit better ?? Very strange. Can you educate me .I had the timing set to the right degrees by my tuner .if you recall I was boasting how I got 106.9bhp on the dyno .he set it then and it's not been touched since then ? So how could it be that .? As it was running well after the dyno then developed this fault? I'm not doubting your expertise mate .I know that you know your stuff .I'm just trying to understand how it could have "moved" timing ? I am hearing you about the leads but dont have a spare set unfortunately. So would have to buy a new set .including plugs etc .so il have to do that .could it be a fueling issue? As foot down its worse at set off but as the rev range rises it happens less and less until almost nothing at the top of the rev range ???? Such a royal pain in the bum, as it's just passed its mot only failed on 1 ball joint, which I thought was brilliant for a 29 year old car. I got both done obviously with new wishbones ball joints the lot ….

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Do you have a timing light? That would be needed to diagnose if the vacuum advance is working properly. I guess there is a diaphram of some kind within the vacuum mechanism of the dizzy, and if this were leaking, possibly by being rotten over time, it could just fail and produce these symptoms.

I have a similar issue, never really gotten to the bottom of it. I recently took the chance to refurb (paint) the pulleys when the water pump was replaced, I painted them black and highlighted the timing marks, and also painted on degree markings at 10 deg, 20 deg, 30 deg etc so at least I can check it better now.

                                

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Engine misfiring??

Yes thanks paul the timing has been set by my tuner guy .with a snap on one so set to the exact degrees .the distributor is brand new so no diaphragm issues. But I will double check that tomorrow. As the first distributor that I bought fro. Classic vw had a split diaphragm and was pulling no vac .so il check mate thankyou for your time Regards Dean

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Sorry just to clarify, are you trying to fix this yourself or do you have a mechanic looking at it? I'm confused.

                                

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Engine misfiring??

I have a very good specialist tuner .but unfortunately hes too busy right now to have a look at it .so hes suggested things by text .but it's me doing it .Regards Dean

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Engine misfiring??

He set the timing back when it was dynod a couple of months ago. And it's not been touched since .so with timing set and running well .its then developed this issue paul .hope that makes sense

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Engine misfiring??

Just a quick update .I've just done a good run to drop my little girl of a at dancing .I've a manual choke .I kept it out about a quarter and it never backfired at all .ran great sounded good lots of power ???? Any ideas

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Ok so the requirement for a timing light still holds true. If it were timed properly, it ran good, but then subsequently went bad, then it needs checking.

The choke would richen the mixture. It might be that's slipped too, except they don't really "drift" that much over time unless there is a fault with the carburettor. In any case, my tool of choice to check mixture is a wideband lambda probe. A garage/mechanic will probably have this kit.

                                

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Engine misfiring??

Ok paul thankyou il check that. Not sure what you mean by moved .? Does the fact the choke makes it run well .not suggest it's running lean?
Il get it checked regardless mate

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Deano777 said

 Does the fact the choke makes it run well .not suggest it's running lean?

Yes but the question is, if it were professionally set up, then something has changed and its now running lean, what's broken?

There isn't a single fixed point at which the mixture, or timing, MUST be set. There's an acceptable band, within which the car will run without misfiring or other issues, and outside, it will be noticeable. Within the band, you won't be able to tell from your own senses but it will show on instruments eg timing light, mixture (gas analyser, lambda sensor) or power output on a rolling road.

Its quite possible to measure the relevant stuff and put the car "in the middle" of that sweet spot, or (deliberately) on the rich side, or on the lean side, etc. If your car was set up nicely but on the lean side - quite appropriate to do for a daily driver - then a small change could make it misfire.

Also bear in mind, a Mk1 Golf is old-school compared to a modern car. The ignition and mixture isn't controlled by a computer with a map, its all done with mechanical physical things which wear out over time. And there's no monitoring or feedback available from the car eg you can't read off misfire events or knock sensor events, fuel trim, etc etc. And definitely no "closed loop"!

                                

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Engine misfiring??

Ok mate thankyou il check it all as you have said .much appreciated paul

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Engine misfiring??

To those who told me the engine misfire is plugs or leads i salute you ,,,i changed carburettor jets. No joy, new fuel filter no joy ,new plugs slight improvement, new rotor arm no joy, new leads voila lead number 1 was disintegrated at the distributor end ,no idea why all others were fine and the leads are less than 12 months old !! So i now have no misfire ,awesome,,almost  as now its cutting out completely whilst im driving just no power dies ,then starts but wont rev at all wont even tick over ,left me in the middle of a busy roundabout last night. Hazards on left it a few minutes started up revs fine drove all the way home ? Could it be something in the tank ??

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Engine misfiring??

Voila

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