Why is it happening?
* Worn camshaft lobe: The most likely culprit is wear on the camshaft lobe itself. Over time, the lobe can wear down, reducing its surface area and grip on the fuel pump pushrod. This is especially true if the original camshaft is still in place.
* Loose pushrod: The pushrod might be loose or improperly seated. This reduces the force transferring from the lobe to the fuel pump.
* Incorrect pushrod length: An incorrectly sized pushrod will prevent proper contact and can lead to the lobe backing out.
* Worn or damaged fuel pump rocker arm (if equipped): Some fuel pump setups utilize a rocker arm. If worn or damaged, this component can also contribute to the problem.
* Fuel pump itself: Although less likely, a faulty fuel pump can cause excessive pressure, putting extra stress on the camshaft. However, a failing pump would usually show other symptoms first.
What you should do:
1. Don't drive the car: This is crucial. Driving with a failing fuel pump can severely damage your engine.
2. Inspect the camshaft lobe: Remove the valve cover (if necessary depending on your fuel pump setup) and inspect the camshaft lobe for wear. Look for excessive pitting, scoring, or a noticeably reduced profile.
3. Check the pushrod: Inspect the pushrod for damage or bending. Make sure it's correctly seated and the right length for your application. A mechanic can measure this for you.
4. Inspect the rocker arm (if applicable): Check for excessive wear or damage on the rocker arm if your system uses one.
5. Check the fuel pump: While less likely, a faulty pump might be contributing indirectly to the issue.
Solutions:
* Repair: If the wear is minimal, the camshaft lobe might be refinished by a machine shop (although this is risky, as a poorly done job can worsen the problem). Replacing the pushrod is generally easier.
* Replacement: If the camshaft lobe is badly worn, or the cam is otherwise suspect, replacing the camshaft is the best option. This often requires a full engine rebuild or at least a camshaft installation.
Important Considerations:
* Professional help: This is not a beginner's repair. Unless you have significant engine rebuilding experience, you should take the car to a qualified mechanic specializing in classic cars or Pontiac GTOs. Incorrect repair can cause major engine damage.
* Parts Sourcing: Finding correct parts for a 1967 GTO might require specialized suppliers.
Ignoring this problem will almost certainly result in engine damage. Address it promptly to avoid a costly repair down the line.
