The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - 1991 GMC runs poorly after engine is warm

ChevyTech · 12-26-2006, 11:04 PM

4.3 liter engines had trouble keeping the O2 sensor warm enough to function properly under some conditions. Some of the first heated (3 wire) O2 sensors were used on 4.3 engines. Under SOME conditions the AIR pump does help warm the O2 sensor. Air pumped into a rich exhaust stream causes combustion in the exhaust system making it hotter.

All that being said if it were my truck, and someone had removed the O2 sensor, I would put an O2 sensor in it without putting an AIR pump on it, and see if I could get by with it. Before I spent money on an AIR pump, I would be adding a relay so I could use a heated O2 sensor, if 1991 4.3 liter engines don’t use a 3 wire sensor.

12-26-2006, 11:04 PM	#14
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: 1991 GMC runs poorly after engine is warm 4.3 liter engines had trouble keeping the O2 sensor warm enough to function properly under some conditions. Some of the first heated (3 wire) O2 sensors were used on 4.3 engines. Under SOME conditions the AIR pump does help warm the O2 sensor. Air pumped into a rich exhaust stream causes combustion in the exhaust system making it hotter. All that being said if it were my truck, and someone had removed the O2 sensor, I would put an O2 sensor in it without putting an AIR pump on it, and see if I could get by with it. Before I spent money on an AIR pump, I would be adding a relay so I could use a heated O2 sensor, if 1991 4.3 liter engines don’t use a 3 wire sensor.