Intermittent Misfire Diagnosis
Discussion
1998 VW Passat B5 1.8 20v (non turbo) 14 years old, 101,000. Just did filters, plugs & oil at 100,000.
Always had an occasional hesitation at 3000rpm
Now has an intermittent misfire below 3000rpm (had it before recent service)
E.g. accelerating in 4th, 5th from low revs
Occasionally stutters at motorway speeds on small throttle openings.
Occurrence of this increasing recently.
Currently car not being used as much, and only for short journeys. It has been getting quite difficult to start in the mornings. Starts but misfires really badly, need to keep trying and rev the b
ks off it then it will settle into a normal idle.
Was really bad one day so put it on a battery conditioner overnight and it was fine for a few days.
So... is this just a dead battery? (I've got a new one on order)
On my other cars I'd just replace coil pack, plugs leads because it was cheap... VW want £280 for a coil pack... cheapest online is £210 ish. So not going to change it for the sake of it.
Could be an injector, but doesn't seem to constantly drop onto 3 cyl... our old clio 182 did that and it was quite a constant, distinctive mis-fire.
Thoughts?
Always had an occasional hesitation at 3000rpm
Now has an intermittent misfire below 3000rpm (had it before recent service)
E.g. accelerating in 4th, 5th from low revs
Occasionally stutters at motorway speeds on small throttle openings.
Occurrence of this increasing recently.
Currently car not being used as much, and only for short journeys. It has been getting quite difficult to start in the mornings. Starts but misfires really badly, need to keep trying and rev the b
ks off it then it will settle into a normal idle.Was really bad one day so put it on a battery conditioner overnight and it was fine for a few days.
So... is this just a dead battery? (I've got a new one on order)
On my other cars I'd just replace coil pack, plugs leads because it was cheap... VW want £280 for a coil pack... cheapest online is £210 ish. So not going to change it for the sake of it.
Could be an injector, but doesn't seem to constantly drop onto 3 cyl... our old clio 182 did that and it was quite a constant, distinctive mis-fire.
Thoughts?
Ahhh the intermittent misfire. Possibly one of the simplest yet hardest things to diagnose.
I would ascertain what cylinder(s) are misfiring first. Then work from there.
Taking the plugs out and seeing what condition and colour they're in can help identify if a cylinder is running lean/rich etc.
If you can narrow it down to one cylinder, swap the coilpack over one from another cylinder and see if the misfire moves to there.
I would ascertain what cylinder(s) are misfiring first. Then work from there.
Taking the plugs out and seeing what condition and colour they're in can help identify if a cylinder is running lean/rich etc.
If you can narrow it down to one cylinder, swap the coilpack over one from another cylinder and see if the misfire moves to there.
Its a unit that sits above cyls 3 & 4 with connectors. There are two leads that come forward to cyls 1 & 2.
http://www.eurocarparts.com/ecp/c/Volkswagen_Passa...
http://www.eurocarparts.com/ecp/c/Volkswagen_Passa...
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