Over the last few months of this cold spell my mk2 has suffered what seems to be an intermittent misfire. I did a 2e/Pb conversion on my 1991 Digi Golf and every now and then it plays up. It usually does it when I'm sat around the 50-60mph area. The engine seems to splutter a bit making the whole car jerk and will sometimes carry on like this for miles. If i pull over and let it idle sometimes it will hunt then cut out or other times it will settle back down after a few seconds hunting. If i then leave it to idle for 5 mins it is ok for maybe 15-20mile and then may start to play up again. If while it is misfiring I accelerate it fires ok and pulls ok but then when eased off and brought back down to approx 3krpm it starts to misfire again. I can go for weeks without having any trouble at all with it then on the odd occasion it will start doing the above. It has happened about 7or8 times now and is getting a bit frustrating. I needed to change some service items such as; Fuel filter Spark plugs HT leads rotor arm Dizzy cap I checked the coil for arking and upon removal of the king lead found a piece of the plastic tube to be broken so i have also replace the coil. I thought it maybe the blue temp sender that had gone faulty so replaced that with a new one. All seemed to be fine until this morning when it played up again. I have a k&n cone filter on it, which when i cleaned it i made sure not to put too much oil in case it affected the hot wire in the air flow meter. Just before Christmas I took the front exhaust box out and replaced it with a straight piece of pipe but because it didn't really do much to the exhaust note i had piece made up that replaced the middle box just before the axle. So all i have now is a Jetex back box. I thought it maybe that there is not enough back pressure in the exhaust now and so this could be causing a fault somehow? I have also noticed that one of the tappets is a bit louder than the others and have wondered if it could be this that is sticking and not letting the valve open correctly, hence when left to idle the oil can pump the tappet up correctly again. Sorry for the long winded explanation but hopefully it will help with some diagnosis?? Cheers
I did used to get this and it turned out the mixture was too lean, has it been checked on proper garage equipment?
when i had it on the emissions tester just after i did the conversion it got 4.355% on the CO level and 203ppm on the HC. I know the CO level is a bit high but would the HC level being so low mean it is running lean as the test limit is 1200ppm? Would a colour-tune be the best way to set the mixture? Also would it be worth putting cream injectors in as i'm currently running the orange ones that was already on the car?
It certainly doesnt need to be that rich at idle....2% should be more than enough really. Stock injectors should be fine, unless the motor is a really high spec too. A sticky tappet should not be an issue when the engine is being revved and making plenty of oil pressure... If it only occurs in the midrange (light throttle?) & clears when accelerated I guess it could be something to do with the airflow meter. The spring might well be weak & allowing the flap to hunt about.....id certainly suspect it if your idle CO is so high
What did you do to cure the problem you had? Is there a resistance check that can be done on the air flow meter so as to see if it reads ok throughout the scale from idle to full throttle.
There are resistance tests for the AFM in the Haynes, and a graph for the built in air intake temp sensor (temp v resistance). If you've got a Haynes, have a look, otherwise I'll scan and send it to you. Rich at idle doesn't mean it's rich further up though - it'll depend on how the AFM and sensors are working. The next time it starts misbehaving, it would be good to switch off there and then, and whip the spark plugs out to see if that tells you anything. Is that my old Jetex system still on the car?
i did pull a plug out a while ago when it played up and it was a pale ash colour, so i guess from that it is running a bit lean. But next time it does it i will pull one again and double check. And yes Mike it is still your old Jetex system lol.
had similar prob a while back.. like you say mainly on motorway/part throttle. had already done all obvious stuff like yourself. few weeks later battery was struggling to turn engine over.. changed alternator for spare audi one i had (90A ) and its been fine ever since. might be coincidence but could be worth gettin multimeter on it
I put a new battery on just before Christmas and am sure I checked the alternator charging rate etc but it wont hurt to do it again. I have been thinking of getting the late mk3 setup so i can run a 120amp vr6 alternator so there is plenty of charge for my planned stereo install
Blimey - that must be about 8 years old now! My digi always used to leave the plugs a sandy sort of colour. Did you check the resistance on the AFM and temp sensor yet?
to fix mine i just got it set up to 1.8%, job done! the HC were thru the roof so even tho it was mega lean it smelt rich, purely due to all unburnt fuel bein chucked out the back! 4.8% is way to high, book figure is 1% +-0.5!
not had chance to check the resistance on my air flow meter yet Mike but i will get my haynes rooted out in a bit and find the graph you mean so i have it for reference. I'm going to try and have a look at my CO level etc tomorrow at work. Did just setting your car up properly cure the problem altogether then John?
just set my idle and co according to the faq. With the blue temp sender unplugged the co is approx 1.7 but when its plugged back in it goes to approx 2.5. Is this ok or do you set it with the temp sender plugged in?
was all the engine breather unplugged and capped off while you were setting it up? if not crank case fumes can give a false reading
I had exactly the same problem with my pb/agg. It used to jerk around the 70mph mark on steady throttle. It hasnt happen in around a year but no idea what it was. I think I may have had the co etc checked afterwards but not sure if it ever happened after that.
right it has been running ok for the last couple of days but this morning whilst sat waiting in traffic it started to misfire, which it did all the way throughout the rev range. Once i got going again it was missing for about half a mile. Got to work and started getting some tools out to investigate it a bit further when it cleared itself and reved ok. I'm going to try a spare set of injectors i have to see if this does anything? Another thing is, would it be worth replacing the lift pump and also maybe strip the pump out from under the car to see if the gauze is clogged?
