1995 2.2 GMC Sonoma service engine soon light comes on whike driving between 45-60 mph. changed sparkplugs, O2 sensor, fuel filter, sparkplug wires, and have changed oil. (Tried to hook up to OB1 & OB2 scanner would not link!) What else could be causing this and how much to repair?

Cpuld be bad ignition wires, plugs. Dirty air filter. Plugged up fuel filter. Message me if intrested and I'll tell you how to check.the codes yourself using a paperclip.

Problem is did they tell you what # 301,303 or 305.this mean you have bad ;coil,wire,plug.

If you have a check engine light, that means there's a trouble code stored. Get the code read and that should give you an indication of where to start

I usually service Ford family Brands and will try to assist you. Back in 1995 there was a change to longer service life sparkplugs and the elimination of Distributors with Crankshaft sensor firing of the plugs. It really depends on the Manufacturers' idea of when to replace sparkplugs by mileage and the various filters on the engine.

You can install plugs and filters anytime you want; just a matter of prematurely spending money on something you do not need. Air filters 12,000 miles, Sparkplugs 50,000 to 100,000 miles, Serpetine Fan Belt 40,000 to 45,000 miles, Fuel filter 25,000 to 45,000 miles.

Check with Autozone, Advance, or Oreilys for information about Manufacturers specs. Stay on an oil change interval based on your driving habits. Sometimes oil breaks down without higher miles and you need to change by date rather than by use. Clean oil for Winter starts, clean oil for Summer driving. Twice a year is adequate for low mileage. Watch your Antifreeze, it chemically changes after 3 years and loses corrosion inhibitors.

I hope at least some of my suggestions are useful to you.

code 66 is the a/c pressure switch. which will not make car run rough and stall unless its back feeding power. run engine with ac off and unhook connector to high pressure switch. the most common reason for running rough could be a bad sparkplug or sparkplug wire, check the wires and plugs also check dist cap and rotor for arcing. and last is how old is the o2 sensor, a bad o2 sensor can also cause this problem.

Black would indicate a rich condition 2 4 6 are all on the same side, i would replace the oxygen sensors both before and after the cat on that side of the engine as they control the air fuel mixture (make sure you have no exhaust leaks)

First, you need to have it scanned for codes, then you will know what to look for. Dont replace anymore unneeded parts until you get a trouble code. you will need a OBD1 scanner. You will only know the cost and cause when you find the problem.

Check your fuel pressure.l Could be pressure regulator, dirty fuel filter, or weak fuel pump

could bea few things. Excessive moisure, low fuel pressure, Faulty coil pack, spark plugs gap or wires. Have you changed any of those at all? Let me know

1) Identify the foweling type http://www.gnttype.org/techarea/engine/plugs.html
2) "Worn piston rings or valve seals may allow too much oil to leak into the combustion chamber, leading to oil fouling." This could be your case http://www.ngksparkplugs.com/techinfo/spark_plugs/faq/faqfouled.asp?nav=31200&country=US
More reading http://www.autotap.com/sparkplugs/ppc_spark_plugs_replace.html
Good luck!