4.3l express backfires & no acceleration when hot

First verify fuel pressure just to be sure.Could be a few different things. Is or has the check engine light been on? Try loosening the exhaust flanges and driving it, noisy but will eliminate the possibility of plugged exhaust. Have the PCM scanned to see if any trouble codes have been stored.

The check engine light is not on, but I will check it with a code reader.

I also noticed that there is a high pitched whine that could be coming from the fuel tank. I don't like the thought of dropping the tank again to replace the $250 fuel pump, but I will pick up pressure gauge and check it. Any idea what the pressure should be?

Thanks...Dan

Should be between 41 and 47 psi.

Well, I got further today. Based on a list of things to try I unplugged the MAF and Air temperature sensor, and all of a sudden it ran fine. When I plug either one back in it sputters and backfires on acceleration again. Is it possible that both of these sensors went at once(doesn't seem likely)? Or does this point to a different problem. I also cleaned both sensors with MAF cleaning spray.

I am planning on replacing both sensors, but I'm wondering if this could be a sign of engine control module failure or something else.

I've replaced the MAF sensor and air temperature sensor and it still backfires when accelerating. It idles fine and there are no check engine codes. I'm not sure what the next step may be.

If I disconnect the maf and air temp. sensor it runs much better, but not perfect. Any ideas?

I finally picked up a fuel pressure gauge and checked the pressure. With the key on, but not started the pressure is exactly 50lbs. Once I start the van it fluctuates when I rev the engine between 47 and 52.
You said it should be between 41-47, I was expecting to see lower numbers if there was a problem, but is it a problem if the numbers are higher?

It turned out to be the fuel pump. It took me a while, checking everything but the fuel pump, because I thought I was ok with the comment about 41-47 psi.

But I found another site where someone told me that it should be 58-65. My pump was putting out about 50psi, and I didn't think the slight difference would matter... but it did. It's running great now.