QuestionI have recently had my 4.3 Liter v6 1995 chevy motor rebuilt for my 1500 4x4. It doesn't get gas mileage as it did before and seems to be running very rich as opposed to prior to rebuild. I installed the motor my self, all vaccuum lines are placed according to schematic drawing, new plugs, rotor button, distributor cap, plug wires and such. The truck used to get about 21-22 mpg now it is like 13-14 mpg. There are no apparent leaks that are obvious or the smell of any underneath truck or hood. The catalytic converter just went bad on me because of the rich run. I have replaced it, and am going to replace injectors and fuel pressure regulator. Any help or knowledge would be greatly appreciated. I have ran a diagnostic computer check, nothing showing.
AnswerThe only problem I ever came across on your vehicle that would cause bad gas mileage is a defective central port fuel injection unit. It needs to be replaced as an entire assembly. I've replaced over a hundred of them.
There is a bulletin out on replacement of the CPFI unit. The part has been updated and improved.
Also the bulletin recommends running top engine cleaner through the engine to clean out the combustion chamber and improve driveability.
Be very cautious using TOP Engine Cleaner...it can cause damage. I'll tell you a funny story...not so funny to the owner of the vehicle. I was working on a fairly new 95 blazer for running rough, hesitation, and poor performance. I diagnosed the CPFI unit as the cause of the problem. I removed the upper intake manifold and replaced the CMFI unit. At that time my service manager approached me with a hand written procedure from Chevy zone meeting he just attended. It stated to removed the brake booster vacuum hose, run the engine at 2000 rpm, stick the hose into a can of GM TOP ENGINE CLEANER. Well it sucked that cleaner in so fast it hydrolocked the engine. Engine now would not even crank. I could barely get the #5 spark plug out. When it did come out the pressure sprayed top engine cleaner all over the place. The engine now started and ran but had a rod knock. It bent the #5 rod, all while the owner was waiting and looking through the service dept glass. We put him in a rental and he ended up getting a new engine.
Moral of the story is: TOP ENGINE CLEANER does help the engine run much better. Suck it into the intake slowly using the small vacuum hose at the front of the engine not the brake booster hose. Suck a quarter of the can in, let the engine stabilize, keep the idle up manually, suck another quarter can, stabilize, keep repeating until can is empty. Road test the vehicle...be heavy on the throttle to blow out all the carbon. Change the oil and filter...some TEC does get into the oil thru the rings.
Use only GM TOP ENGINE CLEANER.
Put a bottle of Chevron Techron Plus into a full tank of gas every 3000 miles or so to prevent new CPFI unit from failing. Chevron Techron Plus is the only injector cleaner GM recommends in their vehicles.
Use only TOP TIER GASOLINE.- see www.toptiergas.com
Hope this helps
Bob
