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1970 GTX breaking up after 2500 rpm. Failing cam?

The first one I changed out was worse. Almost a full quarter inch of it was gone. This one is about an 8th inch gone. Comp Cams push rods suck *** and they are made of chinesium butter steel.
Agree totally nothing is made now a days like it should be.
 
If this is an electronic ignition system you can load test the entire ignition system up to the distributor cap with a soldering gun or electric engraver, without removing any components or changing any wiring.
 
Low float level ? Plugged jet ?
2200 is righ about where you start into main circuit.

I had a similar problem on a solid roller W2 motor .. it turned out to be a kink in the fuel line.
 
Low float level ? Plugged jet ?
2200 is righ about where you start into main circuit.

I had a similar problem on a solid roller W2 motor .. it turned out to be a kink in the fuel line.
I swapped carbs with a known good QFT 750cfm 4bbl no change. Also installed a electric fuel pump and wired it temporary to make sure it was getting fuel. No change.
 
If this is an electronic ignition system you can load test the entire ignition system up to the distributor cap with a soldering gun or electric engraver, without removing any components or changing any wiring.
Its an MSD Ready To Run distributor. And a MSD blaster coil. I replaced the coil with no change. Still breaking up.

Here is a list of what I checked.

  1. Changed Carb to rule out fuel issue
  2. Added an electric pump to rule out fuel issue
  3. Replaced coil
  4. Pulled cap checked for corrosion
  5. Checked timing
  6. Pulled most of the plugs out and checked them for lean or rich conditions.
  7. Checked all plug wires no damage. All are pretty new MSD 8.5mm wires these were installed at the same time as the RTR distributor.
  8. Pulled and replaced fuel pump rod old one was worn down about an 1/8th inch. Replaced with new one.
  9. Checked voltage at coil + 13.76 volts
 
As I understand the RTR is pretty much the same as HEI, with an external coil. To eliminate the distributor pickup, ignition module, wiring, and coil as a problem you can do this test. Remove distributor cap, put a spark plug in the coil to cap wire, ground the plug, ignition on, hold the soldering gun close to distributor. The soldering gun emulates the pickup coils' magnetic field building and collapsing and will fire the plug rapidly. I have used this method to find intermittent issues because it will stress the system as if it was running.
 
Swapping out the fuel pump is not what I would consider a good way to rule out fuel delivery. To rule out fuel delivery, install a fuel pressure gauge to read pressure at the inlet to the carb. Position the gauge so you can read it while driving, and monitor the pressure under WOT.
 
Swapping out the fuel pump is not what I would consider a good way to rule out fuel delivery. To rule out fuel delivery, install a fuel pressure gauge to read pressure at the inlet to the carb. Position the gauge so you can read it while driving, and monitor the pressure under WOT.
True, it wouldn't matter how good the pump is if the pickup screen on the sending unit or the fuel filter was plugged.
 
These are both good points I didn't have a fuel pressure gauge handy. But the QFT has an inline gauge. I didn't even think to look at that. Ill check it again. I did watch the sight window on the QFT and it never got empty. But it did not have a window on the rear bowl unless its on the passenger side. Humm things you overlook when trying to figure this crap out. Thanks will look into fuel pressure.
 
I tend to be glass half empty troubleshooting stuff too but there is no need to jump to "wiped cam". I had convinced myself my cam was finished when I had issues recently but took it step by step without throwing parts at it and it turned out to be something simple that I overlooked. The benefit of these cars is most of us have non-classic daily drivers so we have the benefit of time to think without the pressure of getting it running immediately. I would review with your friend what EXACT things he did during the air filter change like step by step. Run it without the filter, check for timing with vacuum advance off/on. Look inside the carb and the intake for stuff dropped in. Fuel delivery is what I would be taking a look at. Everytime I've had fuel filter clogs or low fuel pressure, the car noses over with part/wide open throttle off idle with load. Can always check lift at the valve if worried about cam, or pulling intake manifold.
 
As I understand the RTR is pretty much the same as HEI, with an external coil. To eliminate the distributor pickup, ignition module, wiring, and coil as a problem you can do this test. Remove distributor cap, put a spark plug in the coil to cap wire, ground the plug, ignition on, hold the soldering gun close to distributor. The soldering gun emulates the pickup coils' magnetic field building and collapsing and will fire the plug rapidly. I have used this method to find intermittent issues because it will stress the system as if it was running.
But will it stress it enough as under load , and at different or higher RPMS ?


If I had access to a points distributor , I might try popping that in next before ripping into the motor
 
Well I pulled the passenger side valve cover today and was checking his "noisy" rockers. Looked it over and saw nothing.. But did a second take and I was like thats not correct. He said whats not right. I said do you see those holes in the rocker shaft? He said yes,I said the holes are supposed to be pointing towards the head. The rockers from about 3/4 of the way up to the front had very little oil on them. I flipped it all back around the rocker noise went away. And I had him watch with me as the tube filled up and spit it out from the middle to the front rockers.

Here is what I found on the passenger side.
IMG_4916[1].JPG
 
But will it stress it enough as under load , and at different or higher RPMS ?


If I had access to a points distributor , I might try popping that in next before ripping into the motor
I have to pull the intake anyhow in a week or so so that I can swap the Performer RPM for a holley Street Dominator so the oval air cleaner will fit on the engine under the hood. Since I will be in there anyhow I'll take a look at the cam. This is how I found the worn lobe on the 383. But until then we will keep trying all the suggestions you guys have mentioned.
 
Well at least that's a decent reason to throw parts at it. I run the Holley SD on an N96 car for the same reason...hood clearance on an RB block. That intake makes good power.
 
He bought the car like it is. hes 77 and will do minor wrenching on it. I don't suspect he has ever torn an engine down. But he's a true GTX dude to the end. He bought this car at one of the classics resellers places. He is sending the picture to the builder of the engine. They are out of SC.
 
But will it stress it enough as under load , and at different or higher RPMS ?


If I had access to a points distributor , I might try popping that in next before ripping into the motor

Yes, you are simulating high RPM. Great way to check heat related issues also, as this will get the ignition system up to operating temp pretty quick.
 
Well I pulled the passenger side valve cover today and was checking his "noisy" rockers. Looked it over and saw nothing.. But did a second take and I was like thats not correct. He said whats not right. I said do you see those holes in the rocker shaft? He said yes,I said the holes are supposed to be pointing towards the head. The rockers from about 3/4 of the way up to the front had very little oil on them. I flipped it all back around the rocker noise went away. And I had him watch with me as the tube filled up and spit it out from the middle to the front rockers.

Here is what I found on the passenger side.
View attachment 1166070
Man....I've seen that soooo many freaking times that it's nuts. We've all learned from our mistakes over the years but some mistakes....are so needless. Books was all us old farts had but there's so much info on the net too these days. I'm just glad I had a good mentor when I first got into tearing down anything. He wasn't even a Mopar guy but preached paying attention to taking things apart. Problem is when someone else was in it before.....and that's when you need a good manual.
 
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