Taking advantage of the good weather to Locost to work, 5 miles in to my 30 mile trip I developed an occasional mis-fire. Well a back fire really when under medium load. Noticed that the rev counter reading drops dramatically at the same time. I’m running a 1986 pinto with standard carb and Ford ESCII ignition. Anyone want to offer an arm chair diagnosis? Only recent change is a new plug on No3 cylinder to replace one with a cracked insulator. As the rev counter picks up from the coil my initial thoughts are problems with either the coil itself or the LT power to the coil. Just hope it doesn’t get any worse on the way home, in my enthusiasm to get in the car this morning I forgot my mobile phone, could be a long walk if it packs in altogether!

Is the problem there when you rev it up is Ie not driving ?

Vacume advance ( if fitted ) tube on ok ?

Is it always there at the same RPM or intermittent ?

regards

Agriv8

Is the ECSII the early pinto electronic ignition set up with the ignition amplifier? Dizzy with 3 wires and black plug on the end? Is the coil the correct one for electronic ignition?

Did the car run well for a period of time or is all new on the road?

What carb are you using? Is it the one that came with engine? Im just trying to determine what has changed and if it all would have run OK before.

I had an issue with mine ages ago when i used an aftermarket amp (Intermotor). I suspected fuel vaporisation when hot and all sorts of strange things. The mis-fire got steadily worse until car stopped. Cause was the amp, changing to second hand Motorcraft amp (OE) fixed it. Not sure if your experience is the same though.

Backfire sounds like unburnt fuel getting into exhaust, maybe this suggests one cylinder isnt firing A1.

What timing settings are you using?

I have also experienced a dizzy cap failure. I fitted a new one and the carbon brush disappeared after very few miles. I bet youve checked that already though.

I dont suppose you know someone with spare amp and coil that you could try cheaply to rule those out do you? I have a spare amp that was tested on another car. Not sure what condition my coil is in, you are welcome to borrow but not exactly local.

Your rev counter takes feed from coil - i wonder if its starting to break down hence revs dropping off. My ignition stopped again recently but as i was almost ready to convert to MJLJ i bit the bullet and did the change, been OK since.

Thanks for the suggestions Guys.

ESCII is the large silver box about 4” x 5” with a 20+ wire multiplug. Car has run 1700 miles with few problems on the standard webber carb. A part from new rotor, dizzy cap, leads and plugs the engine is straight out of the donor. Timing is standard as per Haynes, can’t remember if its 10 or 12 degs.

Doesn’t seem to miss when rev’ed when not driving. Seems more related to engine load rather than speed. Seems OK on the over run and when accelerating hard.

I do think it is unburnt fuel getting into the exhaust because one (or more) cylinders are not firing. It is very intermittent (once or twice per mile), but when it happens the power drop is worse that the other week when the plug failed and I was running on 3 cylinders most of the time (but only for about 3 miles before I fixed it).

Do you have any oil on the plugs?

A leaking valve stem oil seal will cause a miss fire when under light load or overrun.

Have you replaced all the plugs? I had a set of Champion in my Pinto, they lasted 300 miles I've been using NGK since then with no more trouble.

Alarm bells are ringing when you describe the large silver box.

Sierras used 2 distinct types of electronic ignition. Hall effect and inductive. Hall effect needs the ECU to control advance etc (i think). Inductive gets its signal from a black ignition amp that is mounted onto a heat sink. It is more normal for kit car builders to use the inductive as its easier to transplant and get working. From memory i think the later hall effect needs a crank trigger input.

The easiest way to identify the dizzy's is by how the plug arrangement is. Hall effect has a built in plug with 2 connections. Inductive dizzy has a plug on the end of short leads - 3 wires into the plug (one is for connection to earth).

When i did all of the investigation a while back i came to the conclusion that the hall effect set up could get the car running but not very well and that the only way to get it running well on electronic was to use the earlier inductive (fitted up to 85 / 86 i think).

Im now wondering if your problems are down to the fundamental way the ignition is working but of course i dont know how you have connected it all up. It may be you have the later hall effect and have fitted the sensors etc. If this is the case and you did it right then the diabnosis may be along a different path.

Suggest you keep it simple, at least until you get home. If the rev counter drops dramatically without a corresponding drop in engine speed it sounds like a poor electrical connection. Check tightness of connectors.

Good luck

Darren W - I'm assuming the basic set-up is OK as I pulled everything across from the donor sierra, but you are right if the gremlin is in the electronics its going to be a devil to find.

It will be interesting to see if it starts straight away on the way home or if it takes a while before it appears. In the past I have had coils mis-behave when warm but fine when cold.

Not enough tools at work to have serious look at anything so I'm just going to have to strike out and hope for the best.

A thought that did occur is that it given the slight movement of the engine dependant on how much of a load it is under I could have a chafed wire that is shorting out in certain positions, like the wire going from the coil to the rev counter.

Not much time to investigate this week but would like it fixed for the 250mile trip to Stoneleigh and back if this weather holds.