This is a hard one to explain. I have a 1995 Ranger with a 4.0. It had sat for a while when I bought it a year ago. I cleaned and cleared the fuel system, replaced the fuel pressure regulator and managed to clear some of the issues I had when I first got it. Recently, it has begun a new bad behavior. The truck has gas in the tank and as I said, the fuel pump and filter are new. Basically, the truck starts fine. It also idles nice and smooth. It accelerates good and generally runs strong, until it looses fuel. I say fuel, because it seems like that is what happens. It doesn't loose power, as it doesn't matter how hard you depress the accelerator, there is nothing there. That being said, it seems the engine does respond when you are on the accelerator very lightly. Otherwise, when the truck has one of these fits, there is nothing to do but pull over. There is no rhyme nor reason to this. Hot day, cold day, half empty tank, full tank, up hill, down hill, driving fast, pulling a load, cold engine, warm engine, nothing makes a difference. I've driven it for days without a problem, and then I've had times where I barely make it to the end of my road before it acts up. It is literally like the truck just looses fuel. There are no engine lights on and the gauges are not registering anything unusual. When it runs, it is awesome. When it acts up I pull over and it idles like nothing is wrong. There is no smoke of any color before, during, or after this happening. I shut it down and wait 5 minutes and it will usually straighten itself out well enough to get a few miles down the road, but this is also a hit or miss thing. The only consistent thing is it starts and idles fine regardless. Otherwise, it anyone's guess how many times I will have to pull over and shut it off on my way to work. If anyone could throw me a suggestion I would greatly appreciate it.
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Check the MAF sensor, and the TPS. If I'm reading this correctly, you're saying it does fine until you load it. Also check the air filter if you haven't, a dirty filter will let air through until you require lots of air under WOT. I've checked the MAF by unplugging it and driving it. It takes off very poorly, but I regained the power i needed to accelerate in 5th gear, which points to the MAF sensor. It's a guess.
