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1969 Pontiac GTO Backfires and misses

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Anonymous Poster

Jun 30, 2008, 5:28 PM

Post #1 of 8 (2437 views)
1969 Pontiac GTO Backfires and misses Sign In

I recently had my 1969 GTO 400 CID 4-speed 4-barrel-carburetor tuned up. The garage said they used all new correct parts (and I believe this is true), including new wires, distributor cap, condenser points and plugs. However the car backfires and misses all the time. The dwell is set at 30 degrees and the timing is set at 12 degrees. Do you have any ideas why the car is 'missing' and backfiring, even when accelerating. Thanks for your help. Ron

Double J
Veteran / Moderator

Jun 30, 2008, 8:00 PM

Post #2 of 8 (2433 views)
Re: 1969 Pontiac GTO Backfires and misses [In reply to] Sign In

Couple a crossed spark plug wires perhaps?
Recheck the firing order?
Take a compression test?
Was this something that arose after the parts were installed or were the parts installed in an attempt to correct this concern?

Timing chain /gear issue possibly..These use a nylon timing gear ,unless it been replaced before with a steel gear..

Hit back with some info and one of us should be able to help you!


Tom Greenleaf
Ultimate Carjunky / Moderator

Jun 30, 2008, 11:15 PM

Post #3 of 8 (2429 views)
Re: 1969 Pontiac GTO Backfires and misses [In reply to] Sign In

Everthing Jim mentioned and to add: Timing chain even if replaced with an all metal one can go again in these. They eat those right up. Take off dist cap and look at rotor. Turn engine by crankshaft bolt either way when at timing marks till rotor moves and stop. Turn the other way and see how many degrees it turns crank before rotor moves. 5 or more - toss that chain after ruling out a distributor problem perhaps.

At idle put on your dwell meter and find it at 30 as you said it was. Rev up engine a bit and watch dwell. 5 degrees change (usually would go lower #s) is too much and shaft bearings are worn.

Still nothing found - check points for resistance. new or not they may not line up right flush to each contact,

Long retired now

Anonymous Poster

Jul 18, 2008, 10:37 AM

Post #4 of 8 (2384 views)
Re: 1969 Pontiac GTO Backfires and misses [In reply to] Sign In

I'm the GTO owner who had the problem. I took GTO back to garage and a more experienced mechanic put in new platinum plugs. Also ran a compression test to be sure no valves were burnt. Everything checked out fine. The car ran great for a couple of days, but then it developed a small miss. It turns out that the #8 spark plug wire popped off because it apparently needs a 45 degree angle 'bend' because the steering wheel mechanism 'catches' on the wire and pulls it off the plug. I've manually maneuvered the wire so it doesn't touch the steering column, and the car runs great again! But due to vibrations this spark plug wire might get snagged again by the steering column. Did the GTO's originally have a bent #8 rubber connector. Do you know where I can obtain a bent rubber connector from the wire to the spark plug? Thanks!

Tom Greenleaf
Ultimate Carjunky / Moderator

Jul 18, 2008, 3:36 PM

Post #5 of 8 (2377 views)
Re: 1969 Pontiac GTO Backfires and misses [In reply to] Sign In

If you have trouble finding right angle plug wire ends send me a PM as I have tons of them for regular plug wires. The correct wire set should have had one or more for the application. Back when you could buy plug wire and make up your own and I still do for certain things. No kidding - these should still be available - specifically at NAPA if not others. You can also buy just one pre made up wire but you probably want to match as much as possible for your current set.

I'll actually go look now and see if I have any and what colors for 7mm or 8mm wire and hit back if not just black,

Here come da Judge!

Long retired now

Tom Greenleaf
Ultimate Carjunky / Moderator

Jul 18, 2008, 4:03 PM

Post #6 of 8 (2374 views)
Re: 1969 Pontiac GTO Backfires and misses [In reply to] Sign In

Looking right at three, black 7 or 8mm compatible right angles, one for a fatter porcelained plug, and one 45* gray one (used but as new) plus a new right angle metal plug grabbing end peice which crimps to wire insulation - yours for the postage,

Long retired now

Anonymous Poster

Oct 16, 2008, 9:53 AM

Post #7 of 8 (2288 views)
Re: 1969 Pontiac GTO Backfires and misses [In reply to] Sign In

Sorry it's taken me so long to get back to you. Appreciate all your help. First of all, the GTO is running great now. I replaced the shorter wire with a longer one. Hard to believe GTO is 40 years old coming up! Everyone amazed that I'm the original owner, and everything is original - no restoration. Yellow maize color with black interior and top (also original).

Have gone to many car cruises this summer and have had no problems.

For future tuneups, I would be interested in having the correct angled wire that you kindly said you would send for the price of postage. Please advise cost and how to send payment.

Since I'm on this 'thread', I'd like to ask a quick question about my 1995 Dodge Caravan if i may.
I have a 3.3 liter V-6 engine, 4-speed auto tran. After running for awhile, after stopping for lights, etc., it doesn't shift into 4th gear automatically - stays in 3rd gear. I've replaced fuse in fusebox with another fuse and it doesn't make any difference. Can you suggest anything else I can try. Dealer replaced fluid in vehicle about 6,000 miles ago as maintenance item, but started not shifting just recently. Thanks very much for your time!

Tom Greenleaf
Ultimate Carjunky / Moderator

Oct 16, 2008, 1:40 PM

Post #8 of 8 (2281 views)
Re: 1969 Pontiac GTO Backfires and misses [In reply to] Sign In

Ok: Tell me if you wanted right angles or the 45 degree and how many in a PM (private message) {click on my user name will link to that option} so the world doesn't know your address and I'll send what I have that you need. Guess is $5 postage +/- ??

Know that they make spay dye that will color them to match what you want too for restoration and OE appearance.


Mopar trans issue - you should make a new post for that. I think there's a TCC (torque converter control) switch that may need replacing or migh be a bad torque converter.....

Long retired now

1969 Pontiac GTO Backfires and misses

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