I have a 1993 jeep grand cherokee with a 4.0. Here's the situation...It seems to start fine, but when it idles it will climb up to about 2000 RPM and then go back down to a normal idle. Sometimes when it goes back down to a normal idle it will almost die. When I give it a quick burst on the gas it has a split second hesitation. Also, when I drive it it has NO power at all in fact it will almost die the gas has to feathered to keep it going. Here is what I have done to it. First I replaced the fuel filter, plugs, wires, distributor cap and rotor. That didn't help. Next I replaced the fuel pressure regulator and the throttle position sensor. No help there either. Finally I dropped the gas tank cleaned it out and removed the fuel pump, cleaned the small internal filter on the pump (it was really dirty, I thought that was the problem but it wasn't). That didn't help. I bought a pressure gage to check the pressure in the fuel system, haven't done that yet, but my plan is to do it Saturday morning, in fact my goal is to get it running right Saturday. Some other things I considered was the fuel pump, crankshaft position sensor, camshaft position sensor, and testing the injectors, or adjusting the timing. If I adjust the timing, how should I go about doing it? I have been told to adjust it by rotating the distributor cap is that possible? Could I need new sprockets and a timing chain? Also maybe a vaccum line? Without a computer to check it I am left at trial and error. I have been replacing the less expensive things and working my way up. The jeep isn't making unusual noises when it runs. Just a inconsistent idle with no power. Any help would be greatly appreciated!!
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UPDATE: I just checked the fuel pressure at the fuel rail. I got a reading of 19 psi. I blew out the lines and checked again still 19 psi. I was told that it should be 31 psi at idle and 39 psi with the vacuum line removed at the pressure regulator (can you confirm these settings?) When I pulled the vacuum line there was no change in the psi, still 19. Bad fuel pump??
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