Hi guys, I haven't posted much at all on here but I'm a long time lurker. My '94 Favorit has developed a misfire that is proving almost impossible to sort. I've got a parts car that ran fine (before I starting taking vital bits off!) but has succumbed to rot, so everything I've fitted to the problem car has been either new or a known good part off the other one.

The misfire tends to get worse as the car warms up, there is a lot of fuel being unburnt getting into the exhaust so that would make me think it's an ignition problem. So far I've replaced the following:

Plugs

Leads

Complete dizzy with new rotor arm and cap

ECU

Coolant temp sensor

Crank position sensor

Coilpack

Fuel pump relay

Throttle body and injector

I'm really running out of ideas. I love Favorits and have never had any problems like this before, they've always been super reliable for me. Any help or ideas would be very much appreciated!

checked the valve clearances?

Yeah I've done the valve clearances, compression testing is good too. I tried a combustion leak detector and that passed so it's not the head gasket. It's such a bizarre and frustrating fault, I've put a lot of time into the car (it's on coilovers, has custom paint etc) but this is really testing my patience.

I know if anyone can sort it though, it'll be you guys.

head gasket would have been my next suggestion but you've already checked that....

lambda probe??

Let's try approaching this the other way - What have you not changed?

I make it the throttle body mounting/insulating block, the inlet manifold, the IM gasket, and the catalytic convertor. Failures in any of those except the cat will tend to cause the car to run lean, and then get shots of extra fuel when the Llambda sensor figures out the engine is lean. Does that match your symptoms at all? (presumes the car doesn't have CB points and a condensor; if it does, then if there's pit and pile on the points faces, change points and condensor)

Remember that even new parts can be faulty.

Worth checking that the alternator isn't overcharging, it's very common for the regulator to cause this to happen.

I've pretty much ruled out the lambda sensor and associated problems I think, I disconnected it to force the fuelling back to the basic ECU map and the problem was still there.

All the ignition is done by the ECU I presume, no points etc. I'd almost prefer there were, I like simpler older setups.

Are you saying swapping out the alternator (I guess the voltage regulator is internal?) will solve the problem? Definitely sounds worth trying!

servo pipe split? that was very common on the plastic pipe ones, the elbow used to split open and suck air..

have you tried spraying wd40 or similar all around the inlet manifold where it meets the head to check for air leaks there?

cat or exh blocked (get someone to rev it ahd feel how much comes out the end)

can you tell which cylinder it is missing on by pulling the ign leads off one by one?

Regulator on these cars can be changed separately from the alternator itself.

The only reason for mentioning points and condensor was that you mixed the terminology about ECU, dissie and "coilpack" in a way that made me uncertain as to exactly what the ignition system contained.

Actually, if you have a system that goes 1 coil -> dissie -> plugs, it's not unknown for coil insulation to break down at high temperatures and/or revs, but behave normally when cold and/or idling.

I just tried swapping the voltage regulator, no change in the misfire and there's 13.8v across the battery so I don't think the alternator is overcharging. Shame because it made a lot of sense for that to be the problem.

I also looked for air leaks and couldnt find any, and resealed the rubber block under the throttle body with gasket sealant. The exhaust isn't blocked and the car has the cat deleted.

I'm 99% sure it's an ignition problem, it smells strongly of fuel and will backfire. Annoyingly the car seems to idle and rev up fine, the misfire only happens when I try to hold revs at certain speeds or drive the car.

I borrowed Autodata off a friendly garage and tested the coilpack to the specs, despite it being off my parts car it is fine so that isn't the problem.

Thanks for all your help so far guys, there can't be much more left that can be wrong!

it smells strongly of fuel and will backfire. Annoyingly the car seems to idle and rev up fine, the misfire only happens when I try to hold revs at certain speeds or drive the car.

that is odd... you sure the valve timing is 100% correct?? you had the timing chain off at all?

have you checked that the rotor arm is pointing at the correct place inside the cap? there is a small dent/drilling on the lip of the dist housing that shows where no1 plug lead should be and the rotor arm should point at this when the timing mark is aligned on the crank pulley (will only align every 2 rotations tho as it will point to no 4 next rotation). if it is out by much you can adjust the dist to line it up.

also if it seems fine with no load are you certain the fuel filter is not blocked, I have known a few cars do this and sound fine untill load is applied

Is there any play in the distributor shaft? Try moving the rotor arm back and forth.

What about adjusting the timing by rotating the distributor in the extension tube after loosening the 10mm nut (this will be seized up if it hasn't been adjusted in its life so you may need a new o ring seal)?

I have a feeling the answer is with the distributor somewhere.

I've finally fixed it! Just as something to try I took the distributor stand out and put it back the other way round. I noticed that the distributor will only fit in the peg drive on the stand one way (the peg is offset), but the stand peg drive on the drive gear isn't offset. After putting it all back together it's spot on!

I don't know what caused the initial breakdown as that can't have been the distributor stand. Whatever it was though I must have resolved it along the way with one of the parts I replaced and the dizzy stand issue was stopping the car running properly again.

Thanks for all your help and input guys, I'll try to post more in future instead of lurking and give something back.

Edited 14 October, 201015 yr by Odin