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Got myself a misfire

M

Monkeythree

New member
Taxed the S2 today and celebrated by going out for a burn. Probably the hardest I've driven it since it went back on the road a couple of years ago. Pulled strongly though the gears as it always does but when I encountered a long uphill section that was, ahem, "fairly brisk" in 5th there was a definite hesitation, felt like a misfire. Slowed down, changed down, no problems. Pottered back through town, no problems. Got back close to the house where we have a nice long straight and gave it full potatos and it started missing again as it pushed through 4th at "fairly brisk" mph.

So it only seems to be when it is under severe loading. First thought is plug leads. Any other suggestions?
 
Same problem on my 3.2. Ran fine until I ragged it. Hard to diagnose ignition leads (which one)
so I changed the lot and problem solved. I do still have the old lead set and should test them I guess
but ....maybe one day? TBH, CBA

 
Interesting I had a misfire some time ago albeit at idle which turned out to be one of my magnecor leads.
 
A set of S2 plug leads is £120 which smarts a bit although that's what I will do if no one comes up with any other suggestions of probable causes. I might pop the distributor cap off for a look see first. It is only a couple of hundred miles old so should be perfect but might not be.....
 
Tom,

Leads or plugs. Change the plugs first for obvious reasons!

Or possibly AFM, if it hasn't been shown some love recently. If it is this then it'll be the old problem with the wiper track wearing out at a certain point, but this commonly happens lower in the rev range so less likely.

Weren't you trying to sell this car a while back? I guess you decided that a good S2 is a thing of beauty and kept hold of it .... [;)]


Oli.
 
Hi Oli,
Plugs are 250 miles old hence why I'm leaning towards leads. AFM was my other thought but they are SO expensive for a new one and I've not yet found a reconditioning service which I am convinced by. I have recently bought a spare AFM to have a play with as mine has a worn lower track. So I could try that under the same conditions as a comparator and see what happens.
I did make a degree of effort to sell the car last year but ended up putting it away for winter again. I am keeping it for now at least until someone comes along and makes me an offer I can't refuse!
Cheers,
Tom
 
May be a stupid question Tom but can't you just swop the leads with the Turbo to eliminate them?
Im assuming they're the same of course.
 
Good idea but I think they are different.

And the Turbo is a non runner which has done Starship Enterprise mileage so I wouldn't bank on the leads (or any other bit of it for that matter) being reliable. If you saw it you would understand.
 
Yes, turbo HT leads are quite different to S2 ones (and a bunch cheaper!)

Max Schenker sold me a rebuilt AFM a few years back and it seems fine to me. No objection and it was MUCH cheaper than a new one. I don't like the way it's been screwed together (you'd see what I mean if you looked at one) but it's offered faultless service. However I'm inclined to agree that the AFM probably isn't at fault on yours.

If you fancied an afternoon 'int city then you'd be more than welcome to come over and swap the relevant parts from my car to yours as a diagnostic procedure.


Oli.


 
Or ... one other thought .... if your S2 hasn't been used for a while I wonder if it could be something idiopathic arising from lack of use? They don't take kindly to being laid up and a few brisk trips around the rev counter may cure a number of minor ills.


Oli.


 
If it is happening at high rpm and high load, then maybe could also be fuel related (not enough)? what colour are the plugs - though my first thought was coil or leads too! How far can an s2 retard the timing for bad fuel?
 
Update on my misfire as I finally got some spannering time today for the first time in weeks.

Fitted new plug leads - no difference (Except to my bank balance which is significantly depleted)
Fitted new fuel pump - no difference (nothing left in the fuel system to replace as everything else has been done previously)
Fitted replacement (not new) AFM - no difference.

What is weird is that it revs cleanly to the upper limits of the rev range in 2nd and 3rd but in 4th it hesitates just as it hits 4000rpm. I was on a long enough straight today that I was able keep it floored through 4000rpm in 4th and it seemed to go through a sticky patch then clear again. I changed into 5th but only for a second or two as I was running out of road but I could feel it hesitating again.

The only other thing to report is that under hard acceleration there is quite a rattle which sounds like it might be coming from the catalytic converter. So I'm wondering if that might be flamingo'd and somehow upsetting the DME or making some strange backpressure pulses or something?

Any other ideas?
 
Tom,

Tricksy one. And thus far probably quite expensive for you. Apparently a broken valvespring on a cylinder head is not uncommon on an S2 and can cause similar symptoms but you have changed yours so it can't be this.

I guess the rattle from the exhaust is the best thing to pursue although it's not terribly indicative of anything other than that something is a bit loose. The observation about it only happening in 4th and 5th is interesting but surely can't be relevant as there is no link between the engine and the gearbox. (I write this to persuade myself as much as anyone else, I hasten to add). Could it be slight fuel starvation from a blocked fuel filter, or did you change this at the same time as the pump?

Monkeythree said:
flamingo'd
Click to expand...


Great word BTW - I need to use it more often in conversation. [:D]


Oli.
 
I did wonder about it possibly being a valve spring Oli but dismissed it on the basis of it being a refurbed head plus I can't hear anything untoward plus it seems fine when pulling hard through 2nd and 3rd.
Fuel filter was new when I replaced all the lines during the resto and it's since had a new FPR and the injectors serviced. So I'm pretty confident its not fuel related.
Think I will take the exhaust off and investigate the rattle as that is my only real lead at the moment and it's easy enough to do.
 
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