I just swapped a 91 4.0 out of an Explorer into an 88 B2. Everything works fine except when I attempt to accelerate rapidly the motor misses heavily until it gets over 3500 rpm. If I take it very easty when accelerating the miss isn't so bad. I went on a 150 mile trip on Fri. and my mileage was only about 15 mpg. Any one know what's up?

 

Don't know specifically what's up, but I'd start by performing "quick test" (aka "pulling codes") to see if the computer knows anything. Also check the fuel pressure. The pressure may not be quite high enough for the fuel delivery to keep up to the demand of hard acceleration.

 

The codes I got were Intake Air Temperature signal high and Mass Air Flow signal low on the KOEO test. The KOER test said everything was A-OK. I cleaned the MAF but that didn't help.
Also I read somewhere in here that the spark plugs fire twice per revolution. If that's true, the left bank is firing properly but the right bank is only firing once per revolution.
What would be a good way to test the fuel pressure? And what should it be?

 

MAF low indicates a possible fault in the MAF or MAF circuit. Do a quick visual inspection of the MAF circuit and make sure it's intact (no breaks, shorts, etc.). If you don't find anything wrong, then get a voltmeter and check the input and output circuits to the MAF and make sure it is receiving the excitation voltage and the signal voltage is as it should be. A good manual will have the proper wiring diagrams and specifications so you can properly
test the circuit. For this sort of thing, I like to go to the library and look up the circuit "pinpoint" tests in Mitchell.
Don't often see codes for IAT, but the IAT does have a small effect on mixture and, if it's bad, it could cause some driveability symptoms. Give it a once over. A simple test procedure for the IAT is given in Haynes or Chilton (Free access to the equivalent of a Chilton's manual is available at www.autozone.com under vehicle repair guides.)
What's happening with the spark plugs is simple math. There are six cylinders, but only three coils in the EDIS. What they've done is paired the cylinders up so that there are always two firing at a time. On a given cylinder, the spark plug fires at TDC for the compression stroke and again at TDC for the exhaust stroke. I can't remember for sure, but I think the pairs are 1-5, 2-6, and 3-4.
Chiltons has a decent description of a fuel pressure test. Get a pressure testing kit that fits the Schrader valve (looks like a tire valve) on the fuel rail. Disconnect the vacuum line from the fuel pressure regulator and plug it. KOEO with the pump running (jumper FP test terminal is self-test connector) pressure should be around 40 psig. KOER pressure should be within a few pounds of KOEO value. KOER at accelerated engine RPM, pressure should still stay within a few psig. KOEO pump not running, pressure should hold steady and not drop off over a couple of minutes.

 

Ok thanks. Looks like I've got some equipment to pickup and a manual to find. I meant to get a manual for the Explorer before I started the swap but couldn't find anything locally and just went with what I know. Thanks for the tips, I'll let you know how it turns out.

 

hi,

I have a 92 4.0l with 295,000 km and I had a bad hesitation. I changed the plug wires and now it is alright. I might try checking the spark if I were you. Just a thought.

P.S. check out www.ford-trucks.com for some more help