I think I broke it already

[moparedtn]

When WE were 20, they didn’t weigh near as much did they? Lol.

50 either !!!!

 

[moparedtn]

UPDATE:
Finally got the chance to take the GTX out today for a decent trial run.
The wife and I climbed aboard and headed directly to town to feed the thing - and don't you know the moment we got up around 50mph, I heard that same sickening, familiar sound that started this whole mess.
It's not as loud as before, but it's there again....

My wife starts listening around and fooling with things and announces that she doesn't think the noise is coming from the floor at all.
Instead, she says it sounds like it's coming from inside the dash somewhere.
By that time, we had reached the gas station, so I threw some gas in the car and reached under the hood to shut off the valve I have installed on the heater hose since it was a nice day and no heat was needed.
I climb back aboard and she's messing with the heater controls, asking why they all "stick".
I inform her the heater box is a mess and the blend doors are rotten, that the cables don't work very well, etc.
I then work each of the controls a bunch back and forth and shut off the fan.
We then set off again, as the plan was to take a drive up the highway to the next town (about 12 miles) to a store up there.

We get back up on the 4 lane and wouldn't you know - no noise.
The shifter needs some adjusting and the clutch pedal rattles going down the road (apparently Mr. Mechanic forgot a clip somewhere) but everything seems to be fine, so we enjoy the drive to the next town at about 60mph. It's in the low 70's and the car is running nice and cool.
We get to that store and park up front, which put the car in a nose-up incline position in the parking spot.
We're in the store about 20 minutes.

Back in the car, I go to start it up and the thing backfires through the carb!
(Keep in mind, the car has run beautifully since the engine swap and my fixing up the reman Edelbrock 750 on it.)
I crank it over again and it starts, but sounds like it's missing on a cylinder and the idle has decided to race up towards 1200rpm on its' own (it's usually 750-800rpm). This is totally different from how it ran on the way up there and totally different from how it has ever ru.
I jump out, take off the air cleaner expecting to see the choke slammed shut or something - nada.
Check all the spark plug wires, etc. - they all look fine. Distributor side, too.
Now I'm ticked.
We set off for home, me gingerly piloting the thing home and racking my brain on what possibly could have happened...
Car ran enough to get home, but it isn't nearly right.

The snakebit syndrome continues, apparently.

 

[khryslerkid]

Might have popped a vacuum line off with the backfire. That would raise the rpms after restarting.

So you think the heater/heater box was causing the noise?

 

[mopar 3 B]

Might have popped a vacuum line off with the backfire. That would raise the rpms after restarting.

So you think the heater/heater box was causing the noise?

Don't know why a heater fan would be road speed sensitive.

 

[Billccm]

I share your pain. These cars can be more of a frustration then pleasure.
I myself just did an oil pan gasket swap only to discover I still have the same leak, and somewhere I have developed another exhaust leak.
Thank you for the updates and keep us posted on what you discover.

 

[Fran Blacker]

Did your mechanic find anything wrong with trans?
Heat soak, boiled gas cause backfire or dripping carb?

 

[threewood]

Don't know why a heater fan would be road speed sensitive.

Could be ram air effect coming from the cowl and buffeting on the vent doors in the heater box?

 

[moparedtn]

Might have popped a vacuum line off with the backfire. That would raise the rpms after restarting.
So you think the heater/heater box was causing the noise?

I don't have any vacuum lines, short of the PCV valve - and this thing never backfires.

As far as the noise, when my wife said it didn't sound like it was coming from the transmission, I noticed that not only was it speed sensitive, but that it increased and decreased in frequency with the very stiff crosswinds we experienced today as they buffeted the car.
That was weird.

 

[69b3rt]

Maybe a dry speedometer cable.

 

[moparedtn]

Did your mechanic find anything wrong with trans?
Heat soak, boiled gas cause backfire or dripping carb?

The transmission guy replaced both main bearings and I felt the one afterwards; it was somewhat rough when spun.

Yeah, first thing I guessed was heat soak - except the darn thing continued to run like crap all the way home
and when we came to a stop at a traffic light, the idle was still nuts, too.

 

[moparedtn]

Could be ram air effect coming from the cowl and buffeting on the vent doors in the heater box?

That's sort of what the theory is right now, yes. Once I monkeyed around with the heater controls, perhaps I got a blend door to move enough to silence the noise, I dunno.

 

[moparedtn]

Maybe a dry speedometer cable.

The speedometer cable was eliminated as a possibility way back at the beginning of all this, as documented earlier in this thread.

 

[threewood]

On the backfire, I wonder if the mechanical advanced stuck open. It would raise the idle RPM as described and maybe cause a backfire.

 

[moparedtn]

On the backfire, I wonder if the mechanical advanced stuck open. It would raise the idle RPM as described and maybe cause a backfire.

Could be, I suppose. Wonder why it would do it at that moment? The distributor is one of three electronic jobbers I have, all new or almost new.

 

[oldbee]

3wood has some good thoughts. I know, blame it on the wife!!!

 

[threewood]

Could be, I suppose. Wonder why it would do it at that moment? The distributor is one of three electronic jobbers I have, all new or almost new.

Easy enough to check, pop the distributor cap off and turn the rotor and see if it returns by itself.

 

[moparedtn]

Easy enough to check, pop the distributor cap off and turn the rotor and see if it returns by itself.

Yup. Headed out there right now, been procrastinating today. Paranoid I'm going to find something catastrophic.

 

[moparedtn]

Well, the advance on the distributor is fine and loosey goosey. Plug wires all connected, no burn throughs.
I start looking around the carb and find this:

Look down on the intake to the right. That thar is a piece of linkage!
Looks like the fast idle cam can just flop around as it sees fit.
(I have the choke flapper thingy up top hard locked open on the other side of the carb BTW)

Ok, carb comes off the car...
We'll take care of that real quick:

There, that's better:

Let's see if that does any good. BRB....

 

[moparedtn]

Good news: The engine now idles at the normal speed again and holds that idle pretty easily.
Bad news: It's not quite hitting on one cylinder. One of those deals where it seems to hit on all 8 about 3000rpm, but not below that.
I ran the timing light around all eight plug wires and they're all lighting up, so...
I'm reckoning a plug got fouled in this process.
I hope.

 

[threewood]

Haha! Well, that would do it too.