Misfire...

**silverswedemachine** · Friday 2nd October 2015, 19:31

The old girl has got the monk on and developed a misfire/shudder over night. Ive searched through misfire threads and everybody seems to have high RPM problems or WOT problems... Firstly most of the ignition is new or very good condition, only old parts are the leads n coil...

The problem is a very noticeable shudder/misfire under half plus throttle openings starting at around 2.5k'ish and only upto 4k revs, (I say shudder hoping its not the autobox), its does this till 4k then smoothes out and gets on with business as normal. It drives fine on normal driving and lightish acceleration, kick down is a problem, it does it in more than 1 gear as well... I have very little experience on autoboxes, even less when it comes to problems with them but don't think it would create that kind of feeling... Will check oil level though as a precaution...

Will check the obvious, comments always welcome...

Mark

**Doingitsideways** · Friday 2nd October 2015, 20:26

My best guess would be a vacuum leak somewhere, hence runnng better at higher revs when it comes on boost.
Start it up and let it idle, then spray around all the hoses and inlet manifold with carb cleaner, if it runs worse, you've found a leak.

Wouldn't do you any harm to change the leads and coil though.
PFV are doing a good deal on Bougicord leads (OE) at the min, just got myself a set.

**stribo** · Friday 2nd October 2015, 20:54

Originally Posted by Doingitsideways

My best guess would be a vacuum leak somewhere, hence runnng better at higher revs when it comes on boost.
Start it up and let it idle, then spray around all the hoses and inlet manifold with carb cleaner, if it runs worse, you've found a leak.

Wouldn't do you any harm to change the leads and coil though.
PFV are doing a good deal on Bougicord leads (OE) at the min, just got myself a set.

It'll actually run better if there's a leak, as carb cleaner's highly flammable.

**Doingitsideways** · Friday 2nd October 2015, 21:11

Originally Posted by stribo

It'll actually run better if there's a leak, as carb cleaner's highly flammable.

Yeah, maybe in small doses I suppose, like with a small vac leak.

In high doses, like spraying it straight up your intake, it'll run really rough and try to stall.

So, if engine note changes, you have a leak!

**Shinsplintz 101** · Saturday 3rd October 2015, 13:05

As above, I'd be changing the leads & coil so that you can be sure you've got good spark throughout the rpm range.

If that doesn't cure it then start searching for vac leaks.

Good luck, Morgan

**silverswedemachine** · Saturday 3rd October 2015, 21:20

cheers people, I will inspect all vac hoses tomorrow... Will also check out the deal on leads as well...

Mark

**silverswedemachine** · Sunday 4th October 2015, 18:47

Hi all, just a quick update..

Fired her up tonight from cold after standing since Friday night and its starts fine, idles normal but blips of the throttle has it missing plenty, definitely a ignition issue, dead plug maybe... Will have the plugs out Tuesday evening for inspection...

Comments welcome

Mark

**Shinsplintz 101** · Sunday 4th October 2015, 19:48

My money is still on a dodgy lead or coil, especially as you mentioned the rest of the ignition system.had been renewed - I assume including new plugs?

Old ht leads can arc & a dodgy could won't give you the same crank , both likely sources of a miss fire.

**silverswedemachine** · Sunday 4th October 2015, 20:06

^ Yeah the plugs are only a 1000 mile old, gen' Volvo ones. Think I have another set of HT's lying around somewhere, ill swap um over then get a new set when im sure the old set are shot...

Will inspect the ignition system Tuesday...

Mark

**silverswedemachine** · Tuesday 6th October 2015, 19:57

Had the car running for 5 minutes tonight before stripping it down for inspection, purely so im not working on a cold engine, any way whipped the plugs out and checked the dizzy and rotor. Dizzy and rotor are as good as can be, all plugs look to be running the same colour but... No.1 was wet through... Less than a 1000 mile on these, and one is goosed already...

Cant find my spare set of HT leads so for the time being put the knacked plug back in a different cylinder to see if the problem follows it, have no new parts as yet so its been put back together to see what happens...

Comments welcome

Mark

**silverswedemachine** · Tuesday 6th October 2015, 19:59

Forgot to add, did a compression check with 5 minute run warmish engine. 150 psi across all...

Mark

**Doingitsideways** · Tuesday 6th October 2015, 20:18

If No.1 HT lead is shagged, no spark on that cylinder would give you a wet plug as it's not firing properly

**silverswedemachine** · Friday 16th October 2015, 20:20

Hi all, quick update...

Car is still mis-behaving, although sometimes it does seem to run fine and rev cleanly on blipping. I have put new plugs and tried another coil. Next purchase will be a set of HT leads. After that.....?

Comments welcome

Mark

**bunka T5** · Tuesday 27th October 2015, 20:20

Ive been having this issue on my 96 t5 auto , used to be really bad till I changed the leads, rotor cap and arm, but still apparent .. Then I started using that Lucas injector cleaner (100ml every half tank) and the hesitant acceleration has declined a LOT.. rarely I get a bit of hesitation on kickdown, then it backfires and takes off.. I think thats now down to old plugs (probably ancient .. )

**silverswedemachine** · Tuesday 27th October 2015, 21:25

Hi people, sorry forgot to update this...

I bought a set of new HT leads for it and all seems well...

Now the engine is fine, it needs more power, but the inconsistent boost levels need sorting first, weak actuator I think...

cheers

Mark

**merc85** · Thursday 29th October 2015, 19:06

Inconsistent boost is usually Maf, New bosch/volvo unit id have thought would sort it out.

**Doingitsideways** · Friday 30th October 2015, 13:41

Originally Posted by merc85

Inconsistent boost is usually Maf, New bosch/volvo unit id have thought would sort it out.

Or BCV.

**silverswedemachine** · Saturday 31st October 2015, 18:57

its inconsistent with levels at different times, its steady as a rock when pulling, its just next time you floor it might be less boost, but still stable, time after more boost. The boost also seems to creep up with high revs over 4k, wastegate is adjusted up a lot though so might not clearing more gas, hence the weak actuator...