Misfire...sometimes

Silverbullet · Post by **Silverbullet** » Sat Feb 25, 2012 1:54 pm

Ok I've given in and finally decided to make a thread about a problem I've had with this engine since day 1 of installing it months ago. It's always been there but recently has gotten worse. It's a misfire...sometimes.

Basically when it happens one or more cylinders don't fire and you notice it as a jump or jerk in the car, very uncomfortable and annoying. It comes and goes and is very intermittent at all rev ranges, any load condition hot or cold. Might not do it for a week then do it constantly for a day. Or might miss once in an hours drive. Mostly annoying only but sometimes it will stall the engine (if it happens at idle) or when trying to accelerate it will nearly throw my out of the seat if it's really bad.
I've never done anything about it because I knew as soon as I tried to show/tell someone it would go away, and it did! having anyone else in the car trying to tell them about it and it won't do it for love nor money. I also can't force the miss to happen.

Last night it was particularly bad, after driving nearly an hour home in 37 degrees then parking it in the sun for 2 hours I went out again and it stalled twice in 2 minutes. Driving for 15 minutes or so there wasn't a time where it wasn't mis-firing I thought I wasn't going to make my destination! then driving home at night it didn't happen once.

Anywhoo the only thing I can pin down that makes it happen is heat, happens worse when the engine is hot or weather is hot. Talked to an engineer friend last night and came up with possible ignition coil failing, as they can go intermittent and get worse in heat (This coil is also very old) so get a new coil today. Also looked at the dizzy rotor arm and the brass contact for that is pitted!

Also slightly sooted up as well as bit in the middle looks worn out, got a new rotor arm. Looking at the points without taking them out the contacts there looked sooty so get new points as well.

So I'm thinking I've done something wrong in the tune up, timing and/or setting dwell angle when I put the engine in, any ideas what would cause pitting of the rotor contact? Plugs are fine, not fouled and not running lean. Leads are fine as well.

Well there it is, I bet it won't misfire anymore now I've told you all but I'm replacing the coil, rotor and points anyway because they are an unknown quantity.

*Edit* I wish I could explain something without writing an essay

oh well

littlewhiteute · Post by **littlewhiteute** » Sat Feb 25, 2012 3:19 pm

Fit an electronic ignition.

Have seen ballast resistors go open intermittent which cuts the motor like a flat spot.

Coils don't come and go, when they fail that's it.

All distributors will get rotor contacts burning, a trade off for sparks jumping an airgap. Make sure your carbon brush is contacting the rotor, the spring should push the cap up lightly as you fit the cap.

Silverbullet · Post by **Silverbullet** » Sat Feb 25, 2012 8:31 pm

Elec ignition is coming on the twin carb engine, for now I just wanted a quicker fix since it is so bloody annoying. Coils don't go intermittent eh? Someone told me they do and get worse with hot weather/hot running.On the old rotor the contact in the middle didn't look very healthy, it wasn't brass colored any more rather a dull grey.

Installed the new coil (Bosch GT-40R) rotor and points and first start up I didn't hear it turn over it just fired right up

Only drove it round the block to see and I didn't get any mis-fires but I couldn't guarantee it would misfire anyway since it's such an intermittent problem. Will see over the week (driving 60k's every day) if it misses anymore and report back. Ballast resistor is next to be replaced if problem is still there. Describing it as a flat spot would make sense, when it misfired for a long period of time there was no chance of accelerating until it stopped.

Oh and as for the old coil, the metal inside the output (tube?) that contacts the HT lead was very chewed up and dark, not shiny metal at all.

Post by **yarney** » Sun Feb 26, 2012 8:41 am

One other thing you haven't mentioned is leads there might be a crack in one.

Jan

steptoe · Post by **steptoe** » Sun Feb 26, 2012 11:38 am

The age of your coil if original deserves to put out to the parts shed. I have had an original in my turbo L go just like yours is, intermittent, then the replacement Bosch tranformer style died in under 12 months same pogressive way - lucky I had my new genuine ready to fit and solved dilemma. The harder you work the coil like shty leads or plugs/plug gaps the more likely it is gonna let you down. It is a good idea to keep the sytem in good shape not see how far you get from plugs or leads etc

I love to find jap cars with 300,000km on them with original HT leads but understand that 50,000km is all they are warranted for on the aftermarket - if you get any more good luck. Good leads are affordable for your little EA81

Silverbullet · Post by **Silverbullet** » Sun Feb 26, 2012 12:15 pm

yarney wrote:One other thing you haven't mentioned is leads there might be a crack in one.

Jan

Possible since I've had 2 sets of leads crack in a few weeks in the past, if I still have the problem this week I'll change those as well. Although it's going to be a cool week this week, there won't be any heat to make this issue appear but we'll see. Also have had issues with plugs failing quickly but these ones look good, very healthy when I pulled them last night.

Johnno, put the old coil out to parts shed? more like rubbish bin! that thing was old, Dad can't remember it being changed but it was a Bosch so likely not original?

steptoe · Post by **steptoe** » Sun Feb 26, 2012 10:35 pm

No, not likely original as they were not Bosch, usually black with a big text number and Diamond may be the brand ? I can recommend Bosch leads and eagle performance

Silverbullet · Post by **Silverbullet** » Wed Feb 29, 2012 6:56 pm

Well so far so good; no more misfires

Hopefully all is well now with new coil and rotor.

What about operating temps affecting power though? today was a cool one and driving home in the wet today the temp gauge never got above 1/4 when it's usually just under half. Coming up the hill at the end it was down on power in 4th trying to do 70 up the hill when it usually could do 80 up there.

Silverbullet · Post by **Silverbullet** » Sun Mar 04, 2012 1:48 pm

Not a single issue since the new coil, looks like problem solved!

littlewhiteute · Post by **littlewhiteute** » Sun Mar 04, 2012 7:37 pm

Silverbullet wrote:Well so far so good; no more misfires Hopefully all is well now with new coil and rotor.

So you changed two parts at the same time?

Which one was faulty?

Could have been the rotor.

Silverbullet · Post by **Silverbullet** » Sun Mar 04, 2012 8:28 pm

Coil, rotor and points. I don't know which was bad since I changed them all at the same time, I'd have to put the old parts back one at a time to find out

My money is on Coil though since that was the oldest.

littlewhiteute · Post by **littlewhiteute** » Mon Mar 05, 2012 8:24 pm

Just for giggles, check the bottom of the rotor for burns marks and any cracking, then swap the rotor back.

Subaru88 · Post by **Subaru88** » Mon Apr 30, 2012 5:12 pm

Hey lads,

I am having similar problems with my 88 brumby. Bucking badly and sometimes stalling the car. esp when accelerating at first then it will have no power and will sometimes stall.

I have fitted new sparks plugs with the correct gap, rotor, rotor cap, leads, coil, battery terminals, both fuel filters. Was going grande again, then this avo it did it again. stalled, pulled over, then she started and I drove home wothout a problem?!?

Whats going on please:?

Thanks.

Venom · Post by **Venom** » Mon Apr 30, 2012 5:57 pm

Check for play in the carby acelerator/butterfly mechanism.

Bennie mentioned replacing the ignition unit in the electronic distributor of Sunnie the brumby, which cured some issues it was having.

Noticed on aviation forums about high power coils damaging the ignition module thingy in the dist. Someone sent the stock one to bosch who matched their Mec-713 as closest to factory, and hence what some fly guys use and recommend.

All i can think of right now. Although arcing from leads/faulty coil maybe?

Sent from my GT-I9100T using Tapatalk 2

steptoe · Post by **steptoe** » Mon Apr 30, 2012 6:47 pm

and sounds just like (gonna need to keep a link in my sig! ) the blockage I had in my fuel line between pump and tank. After doing everything else including carby rebuild - compressed air cleaned the crap out into the empty tank, claned out from the sender unit hole