If you happen to have a GM product made in the 70's I have a tip for you if it starts slowing down, getting less fuel mileage, or just refuses to start.
At the independent shop I worked at we had a 1972 Chevy pickup rolled in … It would not start, it cranked ok, but the engine would not start up and run.
Naturally, we tuned it: points, plugs, condenser, wires, rotor, and distributor cap.
No change … it just cranked … did not even act like it wanted to start … I figured it must just be tired.
The man I worked for had been in this business for the past 35 years.
He overhauled the carburetor and replaced the fuel filter.
No change.
The customer came up, and told us that it had been using a lot more gas and oil of late, so suggested we just rebuild the engine.
We did.
No change … now this was getting embarrassing.
This was a 350 small block engine … it had a cross-over exhaust pipe …
as each pipe came from the exhaust manifold, they came together just under the cab, and only one pipe went out under the truck … with the muffler and tail pipe.
My boss told me to disconnect the exhaust from each manifold.
I did, and guess what?
The engine started, it made a heck-of-a-lot of noise, but it was running.
Mr. J. told me to take the hack-saw and cut the exhaust pipe into, just down from the flange that connects to the manifold.
You will not believe what I found.
The exhaust pipe had a liner in it … In other words, the exhaust pipe was two pipes in one.
The inner pipe had separated and had closed off the flow of exhaust … choking the engine.
When the exhaust can not escape, the engine will not start and run … like putting a potato inside the tail pipe … I saw that in a movie one time.
We replaced the exhaust manifold cross over pipe, from the manifold to the muffler, and the vehicle ran just great.
This was a fairly expensive procedure, and not a normal job, but no one, not even the techs at the dealership, knew that GM had to put the double-pipe on their vehicles at this time.
Note: A catalytic converter will stop up and cause the same problem on newer vehicles.