My son's '95 Explorer, with auto trans,has a major miss under load. Not really a miss, more like the engine wants to stop running. At idle, no load, one can feel a minor miss or hesitation. However, under load, such with the A/C on, or at a light in gear. the miss is very noticable. Nor is it consistant. It can go for 1 minute, and nothing, then a big hesitation that feels like the engine is going to stall.
OBD1 code reader shows not codes. Though it did show a fault code for the EGR Valve Pressure/Positon sensor. That was replaced, ending the code. No new codes are showing ,but the miss problem is stillpresent.
I have already installed new plugs, and wires,a new air filter, and cleaned the MAP.

 

Didn't mention the fuel system. Was the fuel filter replaced? This will cause those symptoms. Also check for proper fuel pressure. Not enough pressure and it can fire up but not keep up with the fuel demand.

 

I agree id be checking into that fuel system., in addition to the above mentioned things to check into i would get a noid tester and see that each of the fuel injectors is in fact getting power as they should. if they all get power and they all pulse then the injectors can probably be ruled out as far as electrical anyhow, they could still be dirty or have bad seals. but id imagine by the time you check your fuel pressure and replace filter the problem will hopefully be figured out. hope you get it figured out.

 

Well, I just tested the fuel pump. Pressure, key on, engine off is 39 - 40 lbs. Book says it is supposed to be 35 - 45 lbs. I guess I will replace the filter and go from there.

 

does your book say if you can test fuel pressure while the engine is running? ive done it before but i cant say its right to or not but id be checking what the fuel pressure is doing while its running if you really want to find out if it stay consistant or if it is irratic. also look into the noid light/tester this will give you an idea of exactly what each injector is doing.. my explorer wouldnt start this past winter for like 2 months, right after i had rebuilt the 4.0 engine. i drove myself nuts trying to figure it out i tested everything testable on the engine...guess what it was..there was just enough moisture in thegas in the injectors when i tore the engine down for the rebuild that when i got it back together in the middle of january they were frooze solid for 2 or 3 months till we got the first nice warm up. then it started right no problem. point is sometimes its just little stuff we over look sometimes that can seem like a really big thing youll get it figured out keep us posted here im sure its not going to be a bid thang in the end.

 

I have now tested the fuel pressure, and am pretty sure it may not be the pump. But, the pressures are:
Key on, engine off......................40#
Engine running, vacuum line on....30#
Engine running, vacuum line off....40#

All pressures are normal, within specs, except the engine running/vacuum line on test is on the low end. Book calls for 30 - 35 psi.

 

yep it sounds like the fuel pump should be good from what them test concluded. Id check vacuum lines being that the fuel pressure test you did had low end engine on/vacuum on results. Also have you used a noid light yet to check each injector? you should be able to rent one at auto zone or something its called a noid light but if they act confused just call it a fuel injector test light ,them parts store guys are bone heads sometimes. somthing else to look into is possible ground issues maybe you have a weak or intermitant ground causeing the problems. Also did you get the fuel filter replaced yet or no that may be the problem in itself. Well i hope you find somthing out im really interested to see what exactly is going on with that thing. good luck

 

The other thing to check for with the fuel pressure is the LEAK DOWN. Basically you turn the key on, check the pressure gauge. Notate the pressure, turn the key off and watch to see if the pressure drops. It should hold the pressure if you have no drooling/leaking injectors. However, I can't remember how long you watch it for. I believe it's for 10-15 minutes.Don't see anything in regards to you changing the fuel filter.You can have a dirty fule filter and still get proper fuel pressure readings but not supply enought fuel when the engine is running. Being a 1995 model, if it hasn't been changed in the past year, itshould bedone anyways.

 

Okay, I just replaced the filter. I then started the engine and ran it to normal operating temperature. It seems to do it less, when the engine is cold. The engine ran smooth while cold, but the problem seemd to start as it warmed up. I am not sure if it has anything to do with temp, or just that as the engine warms the RPMs come down.
I also disconnected the Throttle Position Sensor while the engine was running, and the problem seemed worse with the TPS off. The engine totally shutting down. When I reinstalled the TPS, the miss was still there, though not as bad and the engine didn't shut down.

 

Sound more like an intake leak opening up as the engine warms up. Could be upper or lower intake gasket(s). When it starts to act up, spray some carb cleaner on the intake mating surfaces to see if it goes away. If it does, then the spot you hit when the problem clears is where the leak is.