Diagnose me this one!

[Prizam]

Driving steady, I get an intermittent ignition cut. Hesitation if you will.

Opening her up, at around 5k rpm she pops bangs and misfires. Sounds awesome. Like one of those old rally cars with the launch control turbo spoilers.

Any ideas? I have a feeling it is the ignition amp.

[bobfather]

poor or non ignition one one or more pot resulting in unsteadiness when holding a stable speed and when throttle is hard open you'll be pushing lots of unburned vapour into the headers causing ignition in the exhaust. Many things cause ignition failure, most common is the plug extenders followed by HT lead failure. Probably worth removing the extenders and adding heat protection to the leads where they encroach on the headers, also rene cap, rotor, leads and plugs

[Classic Chim]

In this heat I’d go for the ignition coil failing. Wait until it’s at ambient temp and see if it does it from cold, if it’s ok but starts missing again when hot I’d take a punt on coil/ ignition amp failing.

[WOO5IE]

I would go for the extenders as well as first suspects. It’s typical they fail when hot. Don’t just change the extenders as the new ones are all crap.
Heat Shrouds and new type plugs with the resistance built in . NGK 6 rather NGK 7 or other way round (can’t remember which way).
You can always try it with extenders removed and keep the plugs leads away from the exhaust as a temporary measure to try it. No cost involved.

[Prizam]

Everything was replaced around 2 years (1k miles) ago.

I'm running standard HT leads in heat socks and some fancy NGK iridium spark plugs. I forget what ones.


I had an issue with intermittent ignition and hesitation a week ago. It got quite bad, and at one point cut out for around 5 seconds. i put my foot to the floor, and a few seconds alter it kicked back in. Lighting up the rears in quite spectacular fashion.

I have replaced the ignition amplifier with an old one I had laying about, and it's better. but still have random ignition cut outs.

I also have an old coil i could test with too.

[QBee]

Once you have done those tests, which are probably the source of your problem, you could check that the king lead is making good contact both ends (total cut out), and then check for misfires.
You can do this by starting the car and, in the next three minutes, checking the temperature of the exhaust manifolds at each cylinder, about 1 inch from the cylinder heads.
Use a digital infra-red thermometer if you have one (about £15 off Ebay), any misfiring cylinders will show as 100 degrees cooler at the manifold. If you don't have a thermometer, then a cable tie touched onto the manifold will tell you where your misfire is - it will melt on working cylinders, not melt if there is no spark. The test won't work after about 5 minutes due to heat finding its way all along the manifolds.

[Prizam]

Thanks. I did check all my HT leads and the king lead. I have also replaced the distributor and rotor arm.

Here is one for you.... The bracket that holds the coil and ignition amp is bolted on to the plenum, via a bolt that is threaded and won't tighten down properly.

I'm going to take it all apart and Helicoil it properly... But, do you think that this could be being used as earth and thus, giving a bad/intermittent electrical connection?

[magpies]

Prizam said:

Thanks. I did check all my HT leads and the king lead. I have also replaced the distributor and rotor arm.

Here is one for you.... The bracket that holds the coil and ignition amp is bolted on to the plenum, via a bolt that is threaded and won't tighten down properly.

I'm going to take it all apart and Helicoil it properly... But, do you think that this could be being used as earth and thus, giving a bad/intermittent electrical connection?

I would not bother Helicoiling and relocate the coil away from the engine - above the passenger footwell? that will keep it cooler.

[O mage]

Prizam said:

Thanks. I did check all my HT leads and the king lead. I have also replaced the distributor and rotor arm.

Here is one for you.... The bracket that holds the coil and ignition amp is bolted on to the plenum, via a bolt that is threaded and won't tighten down properly.

I'm going to take it all apart and Helicoil it properly... But, do you think that this could be being used as earth and thus, giving a bad/intermittent electrical connection?

Yes especially if remote amp is on there aswell.

[blitzracing]

A test for amp failure is look at the rev counter as the engine dies. If the engine is still rotating as slow, you should still have an rpm reading but If the needle drops dead to 0 then you have lost your trigger pulse from the amp.

[Prizam]

blitzracing said:

A test for amp failure is look at the rev counter as the engine dies. If the engine is still rotating as slow, you should still have an rpm reading but If the needle drops dead to 0 then you have lost your trigger pulse from the amp.

Thats helpfull. I didnt look at the rev counter the one time i had an extended cut out. But when i have the "less than half a second" blips... the rev counter does jump about all over the place.