Jim,

I just recalled that there was a technical service bulletin on switching [#6 & #8 - I think] spark plug wires in the square rubber loom at the back of the engine under the exhaust manifold [driver's side] to prevent "cross-firing" between those two cylinders.  I do not remember the specifics, nor do I have a copy to include here. Someone else please post if you have the drawing.

Regards, JLB

55 Ford Crown Victoria Steel Top

Thanks JLB. That's what I meant about the routing of the spark plug wires. I have the correct firing order. Sorry for any confusion in my question.
Jim  Yergin

Found this:

Jim.  Earlier in this thread you wrote:
                 'I have a T5 five speed in my car. The backfiring is worse when in 5th gear and revs are under 2000 rpm.'

I hope the spark plug wire routing of number 6 and 8 is responsible for your problem.  Finding that service bulletin was GreaT.  Another possibility to
consider . . . I had a late model Ford that had a miss only in overdrive.  The car had quality spark plugs which had less than half their 100,000 mile rating of use, BUT after checking out numerous other possibilities, the spark plugs were determined to be responsible!

Let us know what you find to be the problem.


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Jim,

THAT's the one [the TSB I was thinking about]!!!

Mentioning the O. D:  There's a "spark-kill" circuit involved with O. D. "kick-down" & Solenoid  I wonder if this may be involved due to O. D. relay points, solenoid points, other connections, chaffed primary spark wiring, etc.  Might be worth a look, too!

Hope it helps you and others.

55 Ford Crown Victoria Steel Top

I'm glad to hear about the induction misfiring bulletin. I never would have figured that one out.

JLB, can’t thank you enough for the tip. I repositioned the spark plug wires and there was a big improvement. However there is still occasional backfire so there must be another problem. There is no solenoid/spark cut out in the T5. Over drive is just a fifth gear.
Charlie, what brand of spark plugs solved your problem?
Jim Yergin

Jim, if crossfiring was happening between 6 and 8, it could also happen between 1 and 2, one follows 2 in the firing order.

John - "The Hoosier Hurricane"

Jim, a faulty spark plug could occur with any brand name.  Mine happened to be an original from the factory installed MotorCraft plug.  The miss only occurred in the overdrive gear, and only when under load and pulling at lower rpms.  Finally found the culprit with an oscilloscope mounted in the car out on the road duplicating the engine load condition.

John's suggestion is equally as possible as the one you found in the Service bulletin.  It's all about the parallel AND proximity routing of wires to plugs that fire in sequence.  You have to know how the cylinders are numbered on the particular make and model of engine you are working on, though.

Hope this helps! 


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

check your valve adjustment&valve train