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1995 C1500 with 4.3 has oxygen sensor issues

4930 Views 0 Replies 1 Participant Last post by  Sirwriter
Hi guys, it's me again. I'm only still fooling with this truck because I'm stubborn. And I've put more hours and money in this truck than ought to be legal. I need help/clarification. My truck has ONE oxygen sensor right in front of the catalytic converter. It is a 3 wire sensor, meaning of course that it is heated. I have two different manuals for this truck, plus I belong to an online service that has tons of drawings, pictures, and diagrams. I also use Autozone's online repair chapters, and they differ from ALLdiy./com. Each of them has a different point of view. Half say my truck is supposed to have two sensors, one upstream of the cat, and one downstream. The other half say one. Some say they are supposed to be a single wire, purple. As I understand it, the three wire OEM replacement have either a black and a white wire, or two white wires.

The white(s) and black just have to hook up to a positive and negative post, doesn't matter what order. This heats the sensor. When I look in Haynes at the wiring diagrams, I can only find one sensor, three wire, with a purple wire, a black, and a pink or pink/white leading to a sensor. Heated. I recently replaced the catalytic converter with the pipes, and took the original pipes off. There was only one sensor, located where mine is now.No other bungs on the pipes anywhere. The previous owner bought this new. (He is deceased). The cat was plugged so badly it was incredible. I took the muffler off, and it was about half plugged, so I replaced it too. The right manifold was cracked so I replaced it too. On this thread, I won't bother you with telling you all the emission and engine controls I've replaced. (Each of them had a code). I even replaced the ECM, making sure the wires were hooked in when everything was plugged back in. (Also,new distributor, plugs, and wires, all AC Delco).

Each time I replace something, the truck runs at least 75% better for about three or four days. Then invariably, I get a 44 code. In the newer manuals, that code says lean exhaust. But in my old 7 year old manual, it says lean exhaust and adds "Check wiring and terminals from the oxy sensor to the ECM. Check the ECM ground terminal. Check the fuel pressure. Replace the oxy sensor."

My fuel pressure is 9.8. This is the third oxy sensor I've tried in a month. I put a new wiring harness to the oxy sensor on.

When the engine is cold and I take off, this is the best running truck I've driven in years. It only has about 100k miles on it. When it warms up, it starts to hesitate and miss when giving it gas. If I feather it, barely pressing down on the throttle so it doesn't hesitate and buck and miss I slowly build up speed and cruise along at 65 with no problem. But when I stop, I have to go sooo slow until I build up a little speed, I have people honking behind me and holding up one finger.

Last fall I rebuilt the TBI with new injectors and checked the fuel pressure on both to make sure it was dead on, or close to it. A few weeks ago, due to a windfall online I scored a new, shrinkwrapped rebuilt TBI for almost nothing. Put it on and for a week it was great. Now, right back to where I was. New battery & alternator, new fuel pump and fuel filter. Timing is dead on.

Anyone have any ideas?

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