BJ8 Engine Misfiring

[Frank C.]

It's been a while but I need some advice again! I was running my BJ8 yesterday and noticed that at high rpm (about 4,200) the engine would start to miss. It runs smooth and strong below there. The only problem I've had lately is the dreaded distributor rotor failure and the new one I put in (I found out later) is also subject to fail. I replaced the plugs earlier this year.

Any ideas?

Thanks as ususal!
Frank Custis

 

[Johnny]

Well Frank, at 4200 rpm in Overdrive that's about 85mph right?
If you have points, condenser etc. might be time to replace. Or if the valves haven't been set lately could be time to do that as well.
Let us know what you find, OK.

 

[Frank C.]

Thanks Johnny, I have Pertonic electronic points so I am thinking valves ... I just don't like doing them!!!

 

[healeynut]

Frank -

Before you start poking around your valves, I suspect you are having a fuel delivery problem. When your car starts misfiring, immediately shut off the motor and coast to a stop on the shoulder. Pull off the tops of the float chambers on the carbs and if you have a partially dry chamber this will be your problem.

You probably have either a plugged up fuel filter (if you are using one) or your fuel pump is starting to get clogged up.

Alan

 

[Frank C.]

Alan,
I do have a filter and haven't changed it so awhile ... I will try this before playing with the valves.

Thanks for the advice.

Frank

 

[Genos2]

Most misfires(in my 35+yrs exper)are due to electrical issues. I would check plug gap, .026",pts if equipped .o15",distributor bushing wear- will make pts misfire-particularly at high rpm.Also check resistance in ignition cables. Lack of fuel can cause a lean misfire-usually through rpm range or wide open throttle. Hope this helps. Genos2

 

[Patrick67BJ8]

Alan,
I do have a filter and haven't changed it so awhile ... I will try this before playing with the valves.

Thanks for the advice.

Frank

It would be a good time to disconnect the fuel lines and blow them out with a airhose. You won't believe how much stuff comes out if it has never been done before. Excess junk around the sump pickup in your tank will occassionaly plug up ot restrict the fuel flow and the tank will need to be removed and thoroughly cleaned out.
Patrick

 

[Cottontop]

I have Pertonic electronic points

If you have the Pertronix Igniter Module I or II in your distributor, check how it is wired.

The Pertronix module MUST be fed a full 12VDC or it is highly susceptible to a miss at high RPM.

I know that many Classic Mustangers try to wire the Pertronix to the + side of the Mustang coil. The older Mustangs used a resistor wire to absorb the current so that if the key was left ON with the points closed, the points wouldn't burn. The output of the Mustang coil wire was 8-9 VDC (under load) which the Pertronix doesn't like.

Check your wiring to see that you do not have a resistor wire or ballast resistor in the power line to the module.

Tim

 

[Frank C.]

I checked the filter and it definately needed replacement and I thought this worked. I took the car for a long drive to let it warm up and it seemed fine ... then, after it sat for about 1/2 hour we headed home and the same issue was back. This is the same way I noticed the problem originally, after the car was warmed up and then sat for awhile.

Good advice on the fuel lines and I will have to check the Pertonics wiring and voltage.

Any chance the timing could cause this?

To be continued.....

Frank

 

[zblu]

if its timing, it wont wait to happen now and again

 

[Frank C.]

Well, this is definately realed to temperature. Went for another ride (and it was HOT today) and all was well until I stopped and let the car sit again. Then it was very bad (comming in at about 3k RPM) until I ran for awhile and then it was fine again.

I am very suspicious of the the rotor. I had a failure a few months ago and the Moss replacement is the one that the latest Austin-Healey USA magazine shows as a sure failure. The metal rivit is already loose. I'm going to order a "premiun" replacement and see if it helps.

I'll let you know how or if it works.

Frank

 

[why]

Virtually identical problem, after umpteen fixes from new fuel pump to everything else imagineable it was simply the wire from the distributor to the coil, the actual conducting part, a weird black material (not metal) had burned itself a mm or two back into the insulation so presume upon getting very hot it would no longer somehow conduct to the coil terminal, after hundreds of $ and many hours, 2 minute fix no cost fix
Jay Glass, '65 3000

 

[Frank C.]

Sorry for the delay in responding but I needed to make sure of the fix. I was right (in my case) about the rotor. The standard Moss rotor (872-790) I got in the spring to replace the failed identical one failed again!!! I replaced it with the "premium" one (872-785) and all is well even after a 400 mile round trip this weekend. Moss is including the attached sheet with the new rotors and the part I highlighted in yellow defined my problem exactly.

My question is: why is Moss still selling the other part?

Thanks to everyone for their advice and help.

Frank

 

[Keoke]

All you have to do is remove the metal rivit and fill the void with JB weld as soon as you get that particular rotor. Then you will not be left on the side of the road. We discovered this and pointed it out here on the forum some time ago.--Fwiw--Keoke

 

[mjobrien]

Wanted to let you all know, I saw this and thought "I wonder if this is where I'm getting my 2500 RPM miss from".

Seemed that every time I got the 100 close to 2500 RPM's I would develop a slight miss which would start out with a slight ping and get worse quickly. It was only when the engine got to operating temp and under load. It would go away if I backed off the gas and slowed down to about 1500 RPM only to come back again. I noticed I could change when it came on by altering the timing so I thought must be ignition related.

So when I saw this post I thought that the rotor was about the easiest thing to change and the last thing I would have suspected so therefore it must be the issue! It was, after a nice run today, no miss, not a one!

Thanks for posting this Frank it really helped!

Michael.