hey guys,

I have a 1980 f-150 with 302 2bbl carb, egr valve, smog pump.

I only use 89 octane gas from Exxon, Shell, etc

here are the symptoms-

only happens once engine is warm-

pinging and knocking on take-off and low-idle driving
run-on or dieseling when trying to turn off truck
hard to start when warm, must push gas pedal down
part-throttle stumbling/missing when taking off

The other day I adjusted timing, helped some but it's still doing it. Plugs, wires, etc all are good.
Thermoactor stuff on air-cleaner is all unhooked due to vacuum valves are no good and I must replace them.

From another member's suggestion it may be the EGR valve is bad?
Or could it be the vacuum advance on the distributor?
is there anyway to easily test either?
note it does not stall out when coming to a stop, etc.

any help appreciated
thanks

 

I would try some Seafoam in it first before I did anything. Kind of drip it in the carb while running. will clean up the carbon in the pistons. As for checking the vacuum advance, use a vacuum gauge/pump attached to it. Pull the dizzy cap and apply vacuum and see if it moves. Can do the same with the EGR also.

 

Sounds like you have way too much timing. What did you set the initial lead to? Where is the vacuum advance connected - ported or manifold vacuum?

The EGR valve can cause problems with pinging/knocking if it is not opening as it should, but if it is stuck open it should not cause problems like that. It can, however, cause problems with starting and part-throttle running.

To test the EGR valve, you can put a clean vacuum hose on it and try to pull a vacuum by sucking on it. If you can't pull a vacuum the diaphragm is leaking and it is bad. If you can pull a vacuum, then connect the hose to manifold vacuum. At idle the engine should either die or run very poorly, which means the valve is opening properly. If not, the valve is stuck closed, which could be the pinging/knocking problem.

Test the vacuum advance similarly. If you can't pull a vacuum on it the diaphragm is leaking and the unit must be replaced. If you can, and assuming you have the unit connected to ported vacuum normally, put the hose to manifold vacuum. The engine should speed up significantly. If not, there is something wrong and the unit is not advancing the timing.

 

Depending on the EGR Valve you cannot test it at Idle.

Most EGR Valves in this year range are Backpressure transducer types.

There has to be enough backpressure from the exaust for the EGR to open up. There is not enough backpressure at idle to open the valve. As RPM increases the more backpressure etc...

To test this type of valve raise the RPMs to about 2000 RPMs, disconnect the vacuum hose and plug it. The RPMs should increase about 50 RPMS.

 

Had never heard that, but good to know. Tnx

 

Yes, the best way to test the EGR is get the engine warmed up, and then rev it while feeling or looking for the EGR to move up and down. Sometimes you can barely get a pinky finger through the slots in the bottom of the EGR, and can feel it move. You also should be able to push up on it with your finger while the engine is idling, and make the engine stall if the passages are not clogged.

You hinted your vacuum lines are messed up, so that is a clue the EGR is probably not working.

Something I have done before to help the pinging with a EGR that is not functioning correctly, is to put a 180 degree thermostat in it. I would not use a 160, but a 180 seems to heat the engine up enough(and still have cab heat also) and eases the pinging a little bit.