Sprint Misfire - Yes, We've Heard It Before, But Humour Me

[howardearl]

There are a lot of posts about ignition coils, misfires etc. but none seem to relate to what is going on with my Sprint.

I have Newtronic ignition (predecessor to Pirana I think) installed 1996. I have a misfire on cylinder no. 3, pulling the plug lead makes no difference. I have ruled out blown gasket because I changed distributor cap and rotor arm and normal service was resumed with the car pulling like a train for 6 or 7 miles before losing the plot again. Still No. 3 cylinder. There is a non ballasted coil with feed from fusebox recently installed (system previously running happily on ballasted coil for years). This new coil (Bosch blue) gets VERY hot whereas the ballasted one didn't. The HT leads are new, as are the plugs. In short the whole HT circuit is new. The contact for No. 4 inside the new distributor cap is scored, the others are OK.

Any ideas? All suggestions welcomed.

Howard
1980 Magenta Sprint owned since 1987, mileage now 64,000

[ham204]

I'm not sure if this applies to your car but I had a similar problem on my stag and after changing everything bu the distributor, I added a new earth to the module. Misfire gone!

[MIG Wielder]

I don't think an ignition coil should run hot. I think this could be a bad sign. For instance after a long run my 1850 with a Lumenition Optronic set-up it is just vaguely warm. Now I have a Newtronic set-up on my MGB and it has been reliable for 20 odd years. Can you tell us what the writing is on the coil please ? I've always reckonned on Bosch ignition coils as being good. The reason I like Newtronic and Optronic ignition is because the electronic box can be mounted away from sources of heat to increase reliability, rather than being inside the distributor.
One other possibility is a sticky exhaust valve. I had this on MPD ( an early 1850 ) when they look the lead out of petrol years ago, and the fault was very intermittent. A decoke cured it. I could see vast amounts of carbon building up the valve stems
HTH,
Tony.

[Mahesh]

I had a coil go very hot due to the timing being ATC as opposed to BTDC,
was holding the chart up the wrong way round.

[Carledo]

The usual suspects seem to have had a bad batch of dizzy caps doing the rounds lately, it's possible your first one failed from old age and it's replacement from bad manufacture.
But a cylinder specific electrical missfire can only be caused by one of 3 parts, ie dizzy cap, lead or plug. so should be fairly easy to trace (he said, famous last words and all that!)

Steve

[James467]

The usual suspects seem to have had a bad batch of dizzy caps doing the rounds lately, it's possible your first one failed from old age and it's replacement from bad manufacture.
But a cylinder specific electrical missfire can only be caused by one of 3 parts, ie dizzy cap, lead or plug. so should be fairly easy to trace (he said, famous last words and all that!)

Steve

I agree, I have a bad cap on NWL, the bottom wasn't machined properly so it sat off at an angle.

[howardearl]

The usual suspects seem to have had a bad batch of dizzy caps doing the rounds lately, it's possible your first one failed from old age and it's replacement from bad manufacture.
But a cylinder specific electrical missfire can only be caused by one of 3 parts, ie dizzy cap, lead or plug. so should be fairly easy to trace (he said, famous last words and all that!)

Steve

Interesting to hear about bad batch of caps. Certainly new one not as well made as original Lucas I took off. Will pursue that as a line of enquiry. Thanks Steve

[series111]

Hi
I have the same setup as you on my Sprint Blue Bosch coil and pirana ignition and guess what my coil is hot as well, I have tried everything rewiring from fuse box to ballast and to starter from coil to dissy checked plug gaps plug leads rotor arm but it still gets hot. one thing someone did say to me about a year ago was try fixing the coil in the upright position???? is the Bosch coil oil filled does this have some affect.