Misfire - my turn!

[KKson]

Well set off bright and early in the fog to Shelsley this morning. Got about 10 miles when a intermittent misfire started. It seemed worst when in a higher gear/lower revs and felt as if the car was going to cut out. It felt almost as if there was complete power loss for a second of so and then it would clear. Managed to coax it home and started investigated. I did fit new HT leads last week so started by putting the old ones back in - no change. Took all connectors off from power resistor, ECU, AFM etc and gave the terminals a good clean - no change.

I next turned to the distributor and had a good look at all connections etc. The one obvious issue was the internal central contact that touches the rotor arm - the spring loaded contact in the center of the cap was only just showing out of its rebate. I tried to ease it out with a bit of WD40 but it is well and truly seized in its hole and barely, if at all, making contact with the rotor arm. I'm therefore assuming that this is the issue so a new cap is ordered.

The distributor and cap look very old and very original so I'm presuming that they do wear away eventually. Fingers crossed that this is indeed the issue. Has anyone ever had a similar problem? Thanks.

[rev-erend]

Check the carbon button in the dizzy ..

[mrzigazaga]

Hi Keith...I kept getting this, Sometimes it would cut out when I'm flooring it and then jump start itself which was horrendous...I have noticed that the carbon build up on the distributor points inside the cap need regular cleaning if you use the car a lot..The cap also needs regular cleaning as they can suffer from water ingress..Also make sure that the ECU plug is firmly clicked into place..I have a couple of cable ties around mine as it kept popping out every once in a while..Cheers..Ziga

[jmorgan]

Had a coil give me gip miles from home and drove as if it was missing one or two cylinders (never a feeling of stopping though!). Popped the spare in, that I cunningly left at home, and it worked.

[KKson]

Right, new dizzy cap fitted and car seems way more responsive however after 5 minutes on a run the misfire came back. It's not a single cylinder misfiring but more the whole power seems to die for a split second. Strange that it only happened when it had warmed up a little. it was the same on Sunday - all fine for the first few miles and then the problem appeared.

Any clues? Coil breaking down? I've read about the temperature sensor causing problems but would it cause such a big and occasional hiccup?

Any help appreciated. Thanks.

[mrzigazaga]

Hi mate..Could be an ignition amp...Although mine was a culmination of the king lead...The dizzy cap and the plug connector on the back of the ECU working loose and when i mean loose it was all of 2mm..Which you think wouldn't really matter...Trust me it does..And also the wires on the fuel pump coming loose...(Spade connectors)..Whats the plug connector like on the ballast resistor...I had to put two cable ties round mine as it vibrates loose....Cheers...Ziga

[KKson]

mrzigazaga said:

Hi mate..Could be an ignition amp...Although mine was a culmination of the king lead...The dizzy cap and the plug connector on the back of the ECU working loose and when i mean loose it was all of 2mm..Which you think wouldn't really matter...Trust me it does..And also the wires on the fuel pump coming loose...(Spade connectors)..Whats the plug connector like on the ballast resistor...I had to put two cable ties round mine as it vibrates loose....Cheers...Ziga

Mark, I've got a spare one of those in stock so I'll try that tomorrow night in order to rule it out. Any more ideas gents? Thanks.

[mrzigazaga]

Hi Keith...Thats the ballast resistor...Look on the dizzy on you will see a small plug on the side of it...See if you can see any white heat-sink paste on it, I think that this can cause similar symptoms....They are easy to replace and cost from around £15 for AM or £27 OEM...I will pop the part number up if i can't find where i put mine...Ziga

[ElvisWedgely]

From what you describe it sounds more like cutting out rather than a misfire. Though it could almost be failure of any of the electrical components already mentioned, my money is on the fuel pump overheating/cutting out, either because of faulty connections, blocked filter or simply knackered. The clue I think is in the fact that it occurs after running for a while. Just a guess mind you.

Tony. TCB.

[jase71]

Yes it does sound like the fuel pump . I had the same problem on my speed six cerb .changed the pump & now perfect .

[V8 Fettler]

OP, the cost of plugs/HT leads/Dizzy cap/rotor/coil/ignition amp is low compared to your time spent fettling, so if there's any uncertainty about age or condition then replace to avoid going round in circles.

A quick fix for a failing ignition amp when you're out and about can be to cool it with an aerosol freeze spray, it's exothermic y'know!

[KKson]

All, many thanks for the replies. I've ordered a new Lucas coil so will fit that tomorrow night to see if it's the problem, then ballast resistor, then amp. If they don't solve the problem then I'll get a gauge on the fuel line to see if a pressure drops coincides with the misfire. I had a new fuel filter fitted over the Christmas break so at least that bits new.

[celcius]

Hi keith i have a couple of s/h fuel pumps that are working fine.
Pm me if you want me to send to you one.
Cheers
Greg

[jmorgan]

Not sure how the pump works in the flapper system. On the hotwire it is on all time, so I spliced in a neon bulb holder to check the pump should I suspect it. I leave the bulb out normally but if I think something is iffy, pop the bulb in and it should light constantly. Not going to show blockages at the swirl pot feed etc. but will show the leccy is uninterrupted.

Put the connector at the last point I could reach in the run to the pump, behind the seat. It will not prove the last 14 inches or so of cable and the connectors on the pump.

[adam quantrill]

I had a similar problem over the last couple of days when it was warming up.

So this morning I disconnected and re-made the connections on: ECU multiplug, ignition amp, coil LT, CTS.

Now it's all running much better - so it probably all needs a further good clean and something to keep the water out. I suspect in my case a weak spark and/or dodgy mixture during warmup.

[rev-erend]

If it starts as a low rumble and builds to a scream - it's your other half in the passenger seat

[KKson]

celcius said:

Hi keith i have a couple of s/h fuel pumps that are working fine.
Pm me if you want me to send to you one.
Cheers
Greg

Greg many thanks for the offer. I may well take you up on your kind offer. Last night I swapped out the power resistor and also disconnected a shed load of old interference capacitors that were strapped to just about every electrical item under the bonnet. Just had another run out now and same issue - ran beautifully for about 2 miles then misfire started and got progressively worse as the engine warmed up. New coil is arriving tomorrow so I'll try that.

I did get on my knees near the fuel pump and listened to it. When the engine coughed for it's half second misbehave there did seem to be a matching drop in the pitch of the fuel pump. Not sure if that's cause its knackered or because the engine revs dropped right down so charge/power is not 100%?

Coil first, I'll swap all plugs second (even though I doubt all 8 could be misbehaving at the same time) and then if no joy then a loan of a fuel pump would be very much appreciated.

Cheers.

[mrzigazaga]

KKson said:

When the engine coughed for it's half second misbehave there did seem to be a matching drop in the pitch of the fuel pump. Not sure if that's cause its knackered or because the engine revs dropped right down so charge/power is not 100%?

Hi Keith...Doesn't sound like the coil..Now that you have said this i think it could well be the fuel pump..When you say that the rev's dropped down and so did the pump noise i should imagine the pump made it do that..

Im sure the pump feed is constant all the time the engine is running..Whether the rev's are at 2000rpm or 200rpm i think the pump would still pump the same volume and only the pressure would change as its determined by the vacuum.. The Fuel Pressure would drop from 36psi/2.5bar to 24psi/1.7 - 2 bar or there about's...
Have you looked at the condition of the spark plugs to see if they are burning a tad on the lean side..You might think that the cutting out was effected by a sudden drop and that it would not show on the plugs...However if the pump is failing then its possible for it to be happening from the moment you turn the key, Therefore the FP will be dropping in a gradient until the engine is getting too much air and not enough fuel..Then cuts out..Which could then be an electrical cut out or fault due to heat or power spike to the pump..Not sure what the steering relay..(Red) controls in that situation?...This would mean that the fuel/AFR would be lean most of the time prior to it cutting out.

Have you checked the fuel pump connections?...While its running give them a little wiggle if the car cuts out then theres your answer..A simple fix..Well kind of, You still have to jack the rear end up and remove the O/S wheel.....

Edited by mrzigazaga on Thursday 12th February 18:28

[V8 Fettler]

KKson said:

Greg many thanks for the offer. I may well take you up on your kind offer. Last night I swapped out the power resistor and also disconnected a shed load of old interference capacitors that were strapped to just about every electrical item under the bonnet. Just had another run out now and same issue - ran beautifully for about 2 miles then misfire started and got progressively worse as the engine warmed up. New coil is arriving tomorrow so I'll try that.

I did get on my knees near the fuel pump and listened to it. When the engine coughed for it's half second misbehave there did seem to be a matching drop in the pitch of the fuel pump. Not sure if that's cause its knackered or because the engine revs dropped right down so charge/power is not 100%?

Coil first, I'll swap all plugs second (even though I doubt all 8 could be misbehaving at the same time) and then if no joy then a loan of a fuel pump would be very much appreciated.

Cheers.

Can you connect a voltmeter to the pump?

[KKson]

mrzigazaga said:

Have you checked the fuel pump connections?...While its running give them a little wiggle if the car cuts out then theres your answer..A simple fix..Well kind of, You still have to jack the rear end up and remove the O/S wheel.....

Edited by mrzigazaga on Thursday 12th February 18:28

V8 Fettler said:

Can you connect a voltmeter to the pump?

I'm away tomorrow and Saturday but on Sunday I'll get the back of the car on the ramps once it's warmed up and misfiring and investigate both. Thanks for all the advice.