considering engine rebuild

[monkeydude3]

Hey to all~
I have a 1994 Ford Explorer with a 4.0L OHV V6 engine. It has a 5 speed manual transmission. Only modification is a glasspack thrush muffler, one of the straight through mufflers. My problems I'm having are poor gas milage, backfiring, and occasionally when I start it hot it has a very rough idle. I've replaced the PCV valve, plugs and wires, DPFE sensor, egr valve and tube, 02 sensors, fuel filter, and air filter. Could I have bad compression? Could I have a few bad injectors? Are there any indications to bad compression without testing it, as I haven't haven't compression tested it YET. Are there any indications to bad injectors without testing them, since they are all buried. Should I return to a stock muffler, or get a baffle style turbo muffler (would this help my conditions). I know I asked a lot of questions but it's all stuff I'm just looking for some opinions on. Take care all, if you can reply to me here or monkeydude3@cs.com

George

 

[MrShorty]

CYLINDER BALANCE TEST

NOTE: This test is only available on Sequential Fuel Injection (SFI) Engines.

Start an engine running test and press the accelerator lightly within 2 minutes after the last code is output. The PCM will cancel each cylinder in turn and measure the RPM drop. If any weak cylinders are noted their number will be output as a multiple of 10 (e.g. 30, 40). The output is the actual cylinder number, not the number in the firing order. NOTE: Will not always pinpoint bad injectors.

From what I can gather, your '94 should have SEFI, so this should work.
A cylinder balance test can be a good first screening test for noncontributing cylinders. Because the computer test cancels the injectors, it can, as noted, have trouble isolating bad injectors. If the computer comes back with any bad cylinders, then you can proceed to diagnose those cylinders to figure out why they aren't contributing (low compression, no spark, etc.). If it comes back ok and you want to verify that the injectors are all contributing, do a manual cylinder balance test by pulling the spark plug wires one by one with the engine running. Each time you pull a wire, the idle should stumble. Any cylinders that don't affect the idle need further diagnosis.