1969 GTO - a few questions - Pontiac GTO Forum
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post #1 of 10 (permalink) Old 04-13-2017, 11:38 PM Thread Starter
 
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1969 GTO - a few questions

Hi, I looked all over and dis not see this mentioned elsewhere, so.....

1. I have the order sheet from the Dealer and the the car was built in October 1968. The heads are 48, i assume all 48 heads are "D" port, right? The date code is H208. H is the 10th letter, so does that mean the heads are October 20, 1968? Seems odd that the heads would not predate the car since I would expect those would be an inventories sub-assembly.

2. The car is trim code 250 which is blue. Does anyone make a paint that would match interior trim colors. Also, the softer parts (Seats and door panels) are noticably a darker blue than the harder parts (console, dash and kick panels) which are brighter. Was that normal?

3. I have a popping sound that is present every 5 to ten seconds or so at idle (kinda sounds like a fart) and on deceleration sounds more like a 'pop' almost like a backfire. Probably not a question for here because it can be anything. I am chasing it down, but I figured since I was here.....

Thanks all!
Mike

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post #2 of 10 (permalink) Old 04-14-2017, 12:54 AM
 
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I think H is August so your heads were cast in Aug 20th 1968.
Not sure about the blue colors.....hopefully someone else can offer some help with that part.
How do your spark plugs look?
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post #3 of 10 (permalink) Old 04-14-2017, 09:30 AM
 
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Hi, I looked all over and dis not see this mentioned elsewhere, so.....

1. I have the order sheet from the Dealer and the the car was built in October 1968. The heads are 48, i assume all 48 heads are "D" port, right? The date code is H208. H is the 10th letter, so does that mean the heads are October 20, 1968? Seems odd that the heads would not predate the car since I would expect those would be an inventories sub-assembly.

2. The car is trim code 250 which is blue. Does anyone make a paint that would match interior trim colors. Also, the softer parts (Seats and door panels) are noticably a darker blue than the harder parts (console, dash and kick panels) which are brighter. Was that normal?

3. I have a popping sound that is present every 5 to ten seconds or so at idle (kinda sounds like a fart) and on deceleration sounds more like a 'pop' almost like a backfire. Probably not a question for here because it can be anything. I am chasing it down, but I figured since I was here.....

Thanks all!
Mike

Popping sound & backfiring could be a couple things. Bad timing. Sloppy timing chain causing bad timing. Plug wires crossed. Needs a complete tune-up. Bad exhaust leak/gasket. Improper adjustment of the valves. Cam lobe worn off. Burned valves. Weak valve springs.

Check your timing, do a compression check and put a vacuum gauge on it and see what you get. Then go from there with your findings. Kinda a generic question and hard to give a solid answer.
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post #4 of 10 (permalink) Old 04-14-2017, 10:14 AM Thread Starter
 
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Thanks Jim! Yeah, I know its like asking why I have a fever. I had the car on a scope and they said it was pretty good, but number 2 cylinder was a not as happy as the rest at idle. It has MSD ignition, but you are right, I have no idea as to the health of the wires or plugs. I know I have exhaust leaks, so I will start down the road of triage.

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post #5 of 10 (permalink) Old 04-14-2017, 10:15 AM Thread Starter
 
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Thanks "Shake". H being August makes no logical sense, but that's how things are.

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post #6 of 10 (permalink) Old 04-14-2017, 10:16 AM
 
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Thanks Jim! Yeah, I know its like asking why I have a fever. I had the car on a scope and they said it was pretty good, but number 2 cylinder was a not as happy as the rest at idle. It has MSD ignition, but you are right, I have no idea as to the health of the wires or plugs. I know I have exhaust leaks, so I will start down the road of triage.


Sounds like a plan. Just have to go a step at a time and sometimes know what the problem isn't in order to learn what it is.
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post #7 of 10 (permalink) Old 04-19-2017, 09:45 AM
 
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im pretty sure "H" is the 8th letter = August.
BTW my 400, TH400 auto car shipped 10/5/68 and my #62 heads are dated H298 (August 29, 1968), and I118 (Sep 11, 1968), within 2 weeks of each other I have heard could have been normal, so I believe they are the originals, I do wish they were marked same day though.
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post #8 of 10 (permalink) Old 04-20-2017, 06:03 PM Thread Starter
 
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Thanks Cleveland, apparently I was drunk in my earlier comments, or forgot how to count to 8. Ugh, Yes H is August. Ha ha, not my finest hour!

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post #9 of 10 (permalink) Old 04-22-2017, 05:44 PM
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What is the compression on #2 cylinder compared to the others? In my experience with these cars, lower compression and popping out the exhaust has always been burnt exhaust valve(s). Not saying it is, but a compression test and a leakdown test of that cylinder will confirm it or rule it out. If you are running a cylinder leakdown test and hear air escaping from the exhaust pipe, it's an exhaust valve.
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post #10 of 10 (permalink) Old 04-23-2017, 10:31 AM Thread Starter
 
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What is the compression on #2 cylinder compared to the others? In my experience with these cars, lower compression and popping out the exhaust has always been burnt exhaust valve(s). Not saying it is, but a compression test and a leakdown test of that cylinder will confirm it or rule it out. If you are running a cylinder leakdown test and hear air escaping from the exhaust pipe, it's an exhaust valve.
Thanks! It will bum me out if I have to pull a head. Then again, I want to put a hotter cam in it. I will do a compression test when I am able and triage the issue. Hopefully driving it is not hurting it.

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