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ignition problem possibility

Started by ergojack, April 03, 2016, 02:44:13 PM

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ergojack

April 03, 2016, 02:44:13 PM
I was riding my 84 FJ the other day and it suddenly starting missing. Got it home, removed the tank and hooked up a remove fuel can. While running at idle, I removed each plug wire. Significant RPM drop on all cylinders except plug wire #1, which had no change.  I pulled the plug, reconnected it to the plug wire and started the engine. Plug is firing well.  Don't have the adapter for my compression tester to fit these plug holes, but had compression when I put my finger over the hole while running.  I removed the air filter for #1 carb to make sure the slide is rising when the throttle is turned (it is).  It also starting spitting and popping through the carbs when this problem started.  Any ideas?

Pat Conlon

#1
April 03, 2016, 06:12:16 PM
1) How does #1 plug look compared to the others? Oil or gas fouled?

2) How does the brightness of the spark on #1 plug look, compared to #2? (Really need to do this in the dark)

3) To rule out the plug wire or plug boot, unplug #1 plug boot/wire and plug it into #4 and then move #4 over to #1 then retest. If the problem moves over to #4 then it's the plug boot or wire that's the problem. It's doubtful if the problem is the plug wire. The oem stainless core plug wires are damn near indestructible. There is a resistor boot that can (occasionally) give problems.
Look in the boot. See if there are any tracks or signs of arcing.

You sure it's electrical?
An improperly routed fuel line (pinched when hot) can cause a stumble.
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

ergojack

#2
April 06, 2016, 06:41:04 PM
The spark is nice and fat, however the idea about swapping plug wires 1 & 4 is good. I will try that. The plug looked good. It was not fouled, but I did switch them around when the issue 1st started. It can't be a general fuel supply problem since the issue is a dead miss on cyl. #1.  If it was that, it would show up in all cylinders. As fuel starvation issue feels completely different from a dead miss.

FJ_Hooligan

#3
April 12, 2016, 07:41:27 PM
The spitting and popping through the carbs could be a clogged idle jet or circuit.

Or, it could be a cracked plug.  Inspect the plug closely.
DavidR.
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