Chevy van 1987 vs 1988 fuel mileage


After driving a 88 chevy van and getting almost 20 mpg on the highway I went and purchased an 87. I am now hardly braking the 14 mpg mark on the highway. Reading reviews, an 87 is rated 11 in the city and 14 on the highway. An 88 is rated at 14 in the city and 19 on the highway. Both have 350ci fuel injected with an 700r4 trans,and the same gear ratio rear. So whats the difference ? What can I do to get to that 19 mark with out just buying an 88 or newer? Would it be better to un plug the the toqure converter so the engine isnt lugging or constintly locking and unlocking during highway travel?




It doesn’t look too good for cheap modifications. You won’t get more mileage out of the 87, nor can you count on a different 88 to get the gas mileage that the other 88 did. The E-150 cargo van with 16" tires will get 19 MPG on a long highway trip. It was an 05 with 4.6 engine, auto,and air with electric this and that. Back at the 87 level, just trade it or sell yours and buy one.


I agree. No cheap mods can get you there. Even tho the engine and transmission are the same, the difference is the engine management system. You’ll need to swap over the entire induction system, sensor system, and ECM to get the same performance.


Also, unplugging the lock-up torque converter will not save you any mileage. This feature was designed to save gas at highway speeds. I tried that on an old '88 Buick once, and got truly awful gas mileage without the lock-up feature on. Try 16 mpg without, and 21 mpg with. Big difference on that 500 mile trip.


I believe both of these models use the same ignition system, distributor wise.
You might check the ignition timing. Due to the age, it’s entirely possible that someone in the past may have checked and adjusted the timing without using the grounding plug. Failure to use this plug will throw the timing way off and that is very critical to performance and mileage.


I should have added another possibility. A partially clogged catalytic converter can cause a drop in fuel mileage also. This could be checked with a vacuum gauge.




So the difference is in the fuel injection system? My understanding was they were both throttle body injection systems. Could i swap out the injectors for a newer model setup or are they different.


where is the grounding plug ??


On this van, I don’t know where the plug is. They’re usually located on the firewall on the right side. I’m thinking the wire color is brown or brown/black.
I can’t remember so I’ll take a look at one of my books and be back later.




Most likely different. Remember, this '87 model is running as rated, and the '88 model has a better rating. Somewhere in the management system they found a better way. Finding the difference will be hard if the mechanicals look the same.

So, the difference is most likely in the ECM programming. But, if the ECM is programmed that differently then the sensors are probably calibrated differently. I had this problem before with an engine swap once. Replacing the sensors from the blown engine to the swapped engine fixed the problem.


The wire colors should be tan/black and the test plug should be located near the rear of the right side valve cover.

If the timing is ok and there is not a problem with converter clogging, my next step would be to run a compression check.
Lowered compression numbers can also kill power and mileage.