Car does not run as it should

Laredo GN

Jan 4, 2002
I have a 1985 GN and nobody seems to figure out how to make it run decent. I have a 3' Up & Down Pipe, 3' exhaust (Up & Down Pipe and exhaust) were made at a local muffler shop from a photograph taken from the internet from under the vehicle and the engine compartment. I also have Blue tops, heads have home ported, 390 gears, cold air ceramic coated pipe with a 12 inch K&N filter. The engine was completely overhauled with Postons High Performance kit, (3,000 miles on the new engine)

The Turbo has been modified and made much larger by Turbo omponents in Westland, Michigan. I had purchased the Ultimate Chip from Postons but as soon as I put it on the idle started surging up and down, I have a vacum/boost gage and I can not get more that 13 lbs of boost I made the actuator rod as short as it could get to see if I could get more boost (No Luck). I changed the chip and put the 93 from Poston and the car idles OK but I get 13 or 14 pounds of boost and it starts knocking and the cars boost gage goes all the way to the red lights, while the sftermarket gage rears about 14.

I am trying to get this beautiful car to perform as it should but here in Laredo, Texas my GN is the only one and no one knows how to fix it properly, I am wondering how fast could this GN be if it was tuned right. I' am going to order a Scan Master, but I do not know if my car has an 85 or an 86 ECM because it was changed at this garage because I could not start and they had it there for about 9 months trying to figure out the problem. I am in dire need of some help to get this car running the way it should with all the goodies I put in it. Any takers I need all the help I can get, I am trying to read as much as I can about this vehicle that I purchased about 5 years ago and it has never ran good. I also have a 1970 Plymouth GTX 440 Six Pack, 1969 Roadrunner 510 Cubic Inch 10:80 1/4 and a 1993 Z28 LT1 with several bolt ons, but I love my GN:cool:
I would start by finding out which computer you have for sure. If you have one of the later ones you need the later MAF sensor for it to run right. You must have the right chip for the right year also.

Make sure your fuel system is up to par. The stock pump is only good for a stock car. After a few basic mods it can't supply the volume needed.

Check for any exhaust leaks especially on the driver side header. Not only will you lose boost but it will throw your BLMs off because the 02 sensor will get false readings.

Good luck.
First of all I don't see that you have a fuel pump or hotwire kit. Do your self a favor and buy a Walbro 340 and hotwire - this will save your motor. Next if you are ordering a ScanMaster II you must have an 86-87 ecm. Ecm Swap

The ecm swap will require a chip - get a custom chip burnt for you.

This should get you going in the right direction.