car gets poor mileage and falls on face at 75mph

[garretberg]

I have a 87 gn just bought 51000 miles on car rebuilt turbo new exhaust car has sat for a couple years till recently car gets good mileage and power till you nail it once car gets beyond 70 it starts missing and mileage sucks i am thinking plugs wires and coil packs even new fuel filter any other suggestions would help

 

[BlackMetal]

I'd look for weak ignition components if it only happens after a certain speed or RPM.

 

[garretberg]

is there anything that provides power to coil packs that could be faulty or did the plugs wires and coils packs pretty much cover it.and also is there a way to test coil packs any good plugs and wires recomended for this car
thanks

 

[BlackMetal]

Coil packs, plugs, wires, also check ignition module. Easiest thing to do would be to find a shop that has a full-fledged ignition scope around. You could view the ignition patterns on it and spot a weak cylinder, etc. I'm not sure if they're common at most shops.

Spark plugs stick with AC Delco R43TS, for plug wires I'm personally very happy with the MSD 8.5mm plug wire set specifically for our cars.

If you're able to find your problem, I've seen guys in the "For Sale" forum selling ingition modules and coil packs, etc.

 

[turbo39151]

also, check your maf and cat

 

[1970gsx]

To check the coil pack, place the probes of an ohm meter across the terminals of each pack. The readings should be between 11k and 13k ohms.

 

[SloGN]

did it ever occur to you that your fuel pump could be getting weaker and not able to maintan correct pressure for the injector to spray correctly. a poor fuel spray will cause that. The car is 18 yrs old. If the fuel pump has not been changed i would do that first along with a hot-wire kit.

 

[TurboBuckeye]

did it ever occur to you that your fuel pump could be getting weaker and not able to maintan correct pressure for the injector to spray correctly. a poor fuel spray will cause that. The car is 18 yrs old. If the fuel pump has not been changed i would do that first along with a hot-wire kit.

Good advice. A poor connection or weak alternator will act like that under load sometimes. I personally would do a spring cleaning including wires (MSD), hot wire the fp, have the alternator checked and go from there. Even if that doesn't fix your problem you certainly won't have wasted your time and money

Garretberg, am I correct to assume you don't have a Scanmaster?

 

[garretberg]

I will check pump what pressure should there be and I will get a hotwirekit I seen a couple on ebay alternator is good and I checked all connections to it and coil packs all seem good I am buying one coil pack to see to try and check others and have new plugs and did get msd wires will be doing saturday as far as a scanmaster I have heard of them but what does it do
thanks
my DAD has an 86 t-type has a t61 turbo bigger intercooler 42 injectors roller cam and lifters headers aluminum driveshaft strange axles worked trans with 2800 stall alcohol injection and some other stuff not all sure car has run 11;80 at 123mph he bought car this way so we are both learning together had lots of hot rods but this is a new thing for me