I wonder if there is a restriction in the exhaust system. Perhaps a check of the engine with a vacuum gauge is in order.
I think Rod Knox may be on to something. If you live in a state where you don’t have to deal with emissions checks, it might be worth junking the whole system and putting a standard HEI distributor and a standard Q-jet or other 4BBl carb on it.
For what it’s worth, I had a caprice wagon with the 307. It was a crap motor, no power barley had enough grunt to get up to speed. The chevy motors were much better. Even the 305, it just ran better/stronger. Don’t expect much for power, but again it should get better mpg.
My nephew had an ‘80s cutlass with a 4 bbl. 307 that wouldn’t get out of it’ s own way. A mechanic found that the timing was a few cogs off. Fixing that made a huge improvement.
Do you potentially have a fuel leak while in motion.
It would be far easier to fix than the carb/emissions nightmare on this vehicle. Anything of the 80’s/carb is a nightmare.
Sounds like they may have disabled the CEL after toying with the carb.
Somethings is very wrong if the car won’t go easily past 60mph. Gas mileage might not be great, but these babies had no problem with 60 mph and shouldn’t really be breathing hard up to 100 mph. I think the carb set up is totally messed up.
Fuel economy this bad can be achieved by misaligned front end. If people change tie rod ends without an alignment there could be massive loss of fuel economy. If the idler arm is worn out you could get the same results. A siezed brake caliper could also cause trouble but there should be some smoke involved too. An open thermostat… Then there are the fuel system problems as well as the engine related stuff.
The front end is aligned properly, the previous owner took very good care of the car. I’ll be taking i to another mechanic tomorrow, hopefully that will end the MPG riddle.
I’m going to assume you calculated the mileage correctly.
Do you know if the “replaced engine” was a boneyard motor, a shortblock, a longblock, or a “turnkey” crate engine? Was it the same size as the original engine?
Find a good speed shop to go over the vehicle. They’re much more experienced in carburated systems than many of today’s shops. the possibilities in a vehicle this age with a replaced engine are countless. A lot more information needs to be known before one could even start to guess.
If the engine replacement was a different engine, the gearing may not be appropriate.
If it was a shortblock, that means the heads were swapped, That means the valve timing and other associated items become suspect.
If it was a longblock, that would send me first to the carburator setup.
If the replacement was boneyard, its condition would need to be evaluated.
There are just too many roads to choose from witout a lot more information. That’s why I think a speed shop is your best bet.
You might want to take off the air cleaner and, with the engine off, have someone push the accelerator to the floor. Open the choke butterfly and look down and the throttle plates. With the accelerator on the floor, these should be at 90 degrees to the base of the carburetor. If the throttle isn’t opening all the way, this could explain why you can’t exceed 60 mph.
after doing what everybody else tells you, go buy a new carb and have someone install it.
ECM fuse was blown. Runs great now, not sure what the new MPG is going to be, just filled it up, going to fill it back up after about 50 miles and see what kinda fuel usage it’s at.
The olds engine was crate, holy cow the a/c even works now. Who wants a ride? Just drive on down to misouri and look for me.
You are kidding!?!?!? A blown fuse?? Wow never saw that coming, so glad it was a ten cent part!!
I’m humbled. Like Gsragtop, I never would have thought. I too am glad is was something simple…and will try to take a lesson away with me; always check the fuses!
wowzers, up to 15 mpg by my first estimate. What a relief!
Do you know what the fuse was for?
the ECM was the computer for the car they told me. It was shorted or burned out, this ECM was the main thing that communicated to the different bits of the car.