car misfiring or spluttering high revs only

[shemar]

dear all,

went for ride yesterday all good and car pulled fine under normal load but

under hard accelaration above appx 4k the car started to hold back and hic up

put car in next gear pulls good again .

I have elecronic ingnition via powerspark and uprated coil can I assume this is fuel stavation

[wilf]

Not sure you can totally discount that, but it could well be fuel starvation.

[mattsay]

dear all,

went for ride yesterday all good and car pulled fine under normal load but

under hard accelaration above appx 4k the car started to hold back and hic up

put car in next gear pulls good again .

I have elecronic ingnition via powerspark and uprated coil can I assume this is fuel stavation

Hi,

I had this exactly (holding back / spluttering at 4k revs and above) . Mine turned out to be ignition timing. I needed much more advance than the timing plate suggested (almost off the scale needed). If it's a sudden change to your car, this may not be any help though.

Matt.

[shemar]

Hi,

I had this exactly (holding back / spluttering at 4k revs and above) . Mine turned out to be ignition timing. I needed much more advance than the timing plate suggested (almost off the scale needed). If it's a sudden change to your car, this may not be any help though.

Matt.

matt, I have fitted a new vacum advance unit but the timing is as it was perhaps the vacum unit has altered it at high revs but I thought it did not work at full throttle as no vacum .

regards

Mark

[V Mad]

Could be fuel starvation, but eliminate possibility of timing problems by checking ignition advance (above 4k) with a strobe lamp (on a Mk2 you should get about 12-16 deg max plus static advance). I assume it does not happen under load at low revs?

[mattsay]

matt, I have fitted a new vacum advance unit but the timing is as it was perhaps the vacum unit has altered it at high revs but I thought it did not work at full throttle as no vacum .

regards

Mark

Hi Mark,

My ignition timing was out - I had to advance about 6 or 8 degrees to get mine pulling properly at full poke. The engine stripdown and rebuild showed that I had issues with timing chains incorrectly fitted and also distributor problems, so things were not right with my car full stop. Just my experience but this (timing) should be easy enough to check if you have a strobe light as Chris (Vmad) has said - might need to disconnect and plug the vacuum advance pipe. Good luck with it, anyway.

Matt.

[shemar]

many thanks for replys so I need to raise the engine speed up to above 4k and see the timing at this speed then neigbours will like that !!

you are correct in saying under normal load and low sppeds no misfires at all infact just done cornwall run and put over a 1000 miles in 6 days but it did the same when aceelarating on to motorways change up misfire went .

[Firept]

Just had a similar problem.
Car OK at low revs and fine at high revs except when pulling hard it would hesitate (99% certain it was not fuel related).
Recently fitted new inductive ignition and coil (powerspark) now the solution perhaps. At the same time I have just fitted a Cobra immobiliser as required by the club insurance so was looking around for suitable connections...to cut a long story short found that the ballast resistor was not being switched out when starting( contacts on the solenoid!) so to get round it, and as it was raining, and due for its MOT today so just for the moment I bypassed the ballast resistor direct to new coil and hey presto the car now performs well with no miss fire checked the resistance of the new coil and it came in at about 2.2Ohms which is right in the middle for it being a ballasted coil or not. may be worth a try this is on a Mk1 just don't overload the coil if it gets too hot stop the test!
Oh and it passed the MOT only one advisory and that was for a weep on the new power steering hose so good for another year.

Take care

Paul.

[Richard Saunders]

I had a similar problem which turned out to be the chopper in the distributor. One of the blades was nicked. Swapped it out and no problem since...

[flying farmer]

Best way to check if it is ignition or fuel is to hold 4000rpm on a light throttle, then floor it.
If it is ignition it will misfire straight away, if it is a fuel problem it will take a few seconds to empty the float chambers.
Since you say it goes away when you change up it is almost certainly ignition as the float chambers would still be empty
I would hazard a guess that the coil is weak, but check your plug gaps as I spent ages and a lot of money chasing a high rev misfire, only to find the new set of plugs I bought were still in the shed, not in the engine. The gaps had opened to nearly 35 thou which was too much for the spark to jump at high revs.
Neil

[ChasR]

When I had this issue it was down to a new coil gone bad. If I very carefully drove it above 4k (held in gear down a hill!) it would go past. If not, it would misfire (you could feel it in the car) in addition to hearing a 'spitting' out of the exhausts from the rear. Reinstating the old Bosch Red coil had the car revving quite happily again .

[V Mad]

It is difficult to decide between ignition and fuelling sometimes, but at least its easy to test fuel delivery and eliminate that first. Much more difficult to test for this kind of ignition fault though. Best you can do is first check the obvious, plugs, dissy cap, leads, then start replacing stuff.

[Drewy01]

Hi guys, had the same issue and ended up being a coil after replacing leads, plugs, dizzy cap, rotor button, fuel and air filter, never run better, u can guess that coil was last thing replaced, oh well, worth it

[shemar]

tried the timing at 4000 rpm and it is differcult to determine advnce settings due to the timing mark going offf the pulley marker

but it did seem to be only slightly off the marks so would assume this is quite good .when re connecting the vacum again the marks further advance so all hpoefully ok

However I still have the misfire in all gears at high revs . so new coil ordered today so will see if this helps but the coil fitted is a non ballast coiul fitted 1 year ago .

[wilf]

Clue there - if your car needs a 6V coil (i.e. it has a ballast) then with a 12V (non ballast) coil fitted you will get a very weak spark, especially at high revs..........also I'm not sure the ignition timing should go off the pulley marker assuming you have the std one fitted..........sounds like too much advance to me.