From: aussierob (aussierob@odyssey.net)
Date: Tue Feb 05 2002 - 21:59:55 PST
Tony Hello ut's Rob here;
It's hard at times, to pin point a miss !
However, here's a trick that always helps greatly to at least, "eliminate"
some sections of the electrics ???.
1]
Get a cheap water mister ...a simple type that you or the lil' lady might
use to mist your clothes when ironing .
Go out at dark... START the engine, all house, garage & vehicle lights
off... really dark !
Lift the hood.
Now spray / mist lightly the Dist. cap and along the complete length of each
wire.right to the plugs. If you have any insulation breakdown problems, the
"light water misting" will cause an even greater misfire.
Possibly, you will see a spark track across the moisture at "absolutely
any weak point" in the insulation.
If there's an "external" electrical reason in the high tension circuit for
the misfire, it will show up with this light misting test.
2]
Check that the rotor button is totally clean all over. No grubby oil finger
prints. Especially, look on the underside when it was last grasped to remove
it.
Wipe spotless.
No fine electrical dust whatsoever, inside the dist. cap either
3]
If the plugs are reasonably low mileage, then they are probably fine.
However, I have seen a plug fire in open air... but misfire under
compression. I once took a set of plugs to a plug tester. Amazingly, one of
the plugs misfired erratically as the pressure was increased to around 125
lbs. I must admit, I have not seen one of these testers, in some time now !
Probably because spark plugs are "so cheap" at Walmart and AutoZone etc..
4]
Next , you mention a upgraded ignition system ? Then, I would "hardwire" a
short piece of electrical wire from the supply voltage input to the ignition
system, and run that wire directly to the battery. This will completely
"isolate" the "ignition" wire harness under the dash and all associated
low tension ignition switch wiring. If you have a loose connection under
the dash this "temporary" wire will give you a good solid low tension
circuit. Take it for a test run.
5]
Good grounding Woes !
I once had an English '51 Morris Minor, after an engine change, it misfired
badly. In a rush to get the thing running, I did not have any "good" ground
for the low tension ignition circuit. So, against all odds, when I needed
several hundred amps to operate the starter motor, everything seemed fine.
It turned over nicely. No Problem,
However, as I drove down the road the engine misfired, and always
imtermittently.
I did not have a ground strap to the engine. I "did have" a ground strap to
the body/firewall.
Now This vehcile, like most, had complete rubber engine and tranny
mounts... good insulation.
It seems, that the low voltage and current somehow "found" its way back to
the firewall and the Neg of the battery.
So, the following is a somewhat educated guess !
For the Ignition circuit, the current return, at first, passed through the
distributor case into the engine block, then into the engine bearings and
crank, then the flywheel & spigot bearing, through the transmission input
shaft, then out the back of the tranny splines, through into the drive
shaft and U Joints, into the rear axles & out through the axle ball
bearings, then into the axle housing, into U-bolts, the springs and
shackles, into rear sub-frame and body metal and through the body back to
the firewall Neg. strap !!!
I also, imagine, that you could probably get some back flow through the
generator's Field and Armature wire, then into the voltage reglator, and
back to the ground that the voltage regulator was screwed onto. As well,
there was the metal to metal contact of the clutch linkage and too, the
accelarator cable.
This Morris was my second frame up rebuild.
I had installed an "warmed" MG B engine. The Original small sidevalve 4
cylinder engine, developed a whopping lousy 27 BHP You could skate faster !
So, with over a hundred horsepower, this vehicle moved along quite nicely..
However, quite frustrated, I drove the car for a few days before I got the
ground strap to the engine block. re-installed.
Remember now, I "did have" a ground strap to the body of the car. And the
high starting current flowed nicely too !
The moral here is simple !
Be sure you have "No" rust or corrosion in the ground strap/s I, would
make sure I had decent grounds to the Tub, Chassis & Engine block.
If it still misfires, drive it to the crusher.
However, make sure you put duck tape over the mother-in-laws mouth before
you bundle her into the back under a ratty tarp. Then off to the crusher .
Be in touch with your solution.
Rob P.
Upstate Ny area near Syracuse.
'42 MB Been to #ell and back
'46 CJ2A Fully Rebuilt Eng. not yet intsalled
'47 CJ2As Really Rusty one Runs (two jeeps)
Two CJ5s great engines - bad tubs
1, Surrey jeep. soon to have Toyota Celica eng. + Tranny
----- Original Message -----
From: "Tony Castagno" >
As some of you might remember I am starting to restore my m151a1
I've pulled the spark plugs, they are all firing, but it (seems to me) that
they are not firing consistently; I
> played with the timing of the distributor, but no real change.
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