Chevrolet Repair: Chevy Blazer stalling out, fuel filter replacement, chevy blazer

Question
Hi and thanks in advance for your help. I have a 96 Chevy Blazer, 4x4, four door, with a 4.3 vortec and automatic trans. I purchased it around last September, and about a week later is when the trouble started. While cruising down the interstate at normal speeds for maybe ten miles, I hit the offramp and started to accelerate and it just lost power. It was like I completely removed my foot from the gas pedal. After a few seconds, and after turning the a/c off to maybe help the situation, it seemed ok. But if I immediately pressed the gas a bit harder, it would do it again After maybe less than a mile, it seemed to be back to normal.. So the first thing I did after a couple of these same instances was to replace the fuel filter. At that point, it began to get cooler outside, and didn’t have the problem again, so I figured the fuel filter replacement fixed the issue. So all winter and until about a few months ago, it was fine. Then it started again. Checked the fuel filter, blew right through it like a straw. Soon after, the check engine light came on, so I took it to autozone, and it showed a bad o2 sensor on bank 2. Had my brother replace it, but forgot to tell him it was bank 2. He obviously replaced the wrong one, but the engine light didn’t come back on for a while, so I dismissed it. So it’s coming back on again, and after talking to a friend about a rattle underneath at startup, we determined it was the catalytic converter. It was bad. Thought that was it, but guess what. So then I noticed a pattern. It would only act up when the fuel level was half tank or less. It would never do it at half or above. I’ve tested it over and over again. So the engine light comes on again, this time it’s the map sensor. Changed it and it’s still doing it. The funny thing is it seems to do it after I’ve been sitting at a red light for a few moments, and then accelerate. Always when I accelerate. With the a/c going too. When I shut down the a/c, it seems to help a bit. It did it today, but after it did it, it was fine, and wouldn’t do it again even after I pushed it. Twice it shut off a while back and it wouldn’t immediately crank back up. It sounded like it was dieseling or jumped timing at that point. The rpm’s would go high and low. Then it would crank and be fine. Thought about changing the fuel pump, but wanted to check this out before I spent anymore money on this. A mechanic friend of mine seems to think it’s the pump or some trash in the gas tank. But I get a different story from other people. So, it seems it’s doing it only when it’s hot outside, and at half tank or less.
I understand you may not nail the problem on the head (or you may), but any suggestions would be appreciated.

Thanks again, Chris


Answer
Hello Chris,
I'd do a couple cheap things first.
One is clean the idle air control valve.
Usually it can be done without removing it from the throttle body, but removing it is no problem. Just use some spray carb/PCV valve cleaner.
The other thing I would do is remove and clean the EGR valve. If it happens to close on some carbon, it will act like a vacuum leak, but the carbon can be blown out the next time it opens, so can be hard to find.

The half tank thing is strange, but a borderline pump could be affected by the additional lift, but that is a stretch.

Van