Specific engine issue 4.0 OHV 1994

[Tater Tot]

It ran just as crappy with the new ones as it did with the old ones lol

 

[rusty ol ranger]

Your 29 PSI fuel pressure seems low.

Have you changed the filter and pump?

Im not sure how you would diagnose an ECM issue in this situation.

@RonD

 

[Tater Tot]

Your 29 PSI fuel pressure seems low.

Have you changed the filter and pump?

Im not sure how you would diagnose an ECM issue in this situation.

@RonD

I’ve changed the fuel filter like 3 years ago, no to the pump. Fuel pressure seems a little low but barely, not seemingly enough to cause this issue. I mean when I rev it it’ll go up past 30 psi on the rail and stay there. So I don’t understand how that would be the problem. Haynes says 30 psi min. I’ve seen 30-40 psi on several threads for my engine, seen others with like 28 psi than ran fine. Fuel injectors can be opened for longer to account for the minimal pressure differential by the pcm.

 

[Tater Tot]

If it was the fuel pump, then I don’t see how it would work better at high rpms.

 

[Angie]

#9 " Done vacuum tests, vacuum (if idle stays up) is like 19 Mercury. It stays there, goes to 20 or so when revved. Drops down low when it idles low, but when it’s idling high, the vacuum seems alright. Like when I rev the engine, the vacuum is fine. "

When you rev a engine the vacuum pressure on the intake should drop. not stay the same or increase. check the brake booster for air leak, vacuum leak, if you are sure all other lines are fine.

 

[Jointslit]

I have a 94 ranger 4.0 2wd. Long time issue. Replaced many sensors. Timing issue? Vacuum leak? Ugh please help.

~112k miles

Symptoms, all in order:

Engine cold start: RPM’s always low at idle when cold. Always starts. Engine starts up fine, revs high for a few seconds and immediately drops idle very low, no tach but engine and truck visibly shakes, seems like it could die at any moment but never does. Exhaust sounds like a putter patter, Engine doesn’t rev up when cold at idle, even worse when a/c is on. Air idle valve is new. TPS, ECT, thermostat, spark plugs and wires, PCV, fuel injectors, upper intake gasket, o2 sensors, crankshaft position sensor, all <2 years old. MAF is 3 years old. Fuel rail pressure is 29 psi. Engine computer battles to regulate rpm, letting idle for a while, sometimes the engine rpm will shoot up randomly, but it tends to just idle super low mostly.

Taking off driving: I have decently loud exhaust, engine misfires while accelerating (muffled misfiring, not bangs or pops), when hot or cold (used to be intermittent misfire, now constant problem whether hot or cold). I live in FL so temp is never that cold.

Still driving: Seems like the engine won’t climb rpms, misfiring (not loud, chokes misfiring). Transmission short shifts, can’t climb rpms.

In 3rd gear, the gear seems long enough, once I reach a certain rpm, the engine springs to life like nothing is wrong. It’s misfires, has no power and won’t go anywhere even when floored and when it hits a certain rpm and everything seems normal and dandy. Sometimes I can’t hit a high enough rpm before it shifts, it seems like, and I can’t accelerate out of the problem. Trans maybe 30-35k miles on it. Transmission seems to work fine.

It’s done this most of the time I’ve had it, 3.5 years. Gotten way worse with my first full summer in hot hot FL.

Cleared all codes today, when misfiring after clearing codes while driving, the only code was 177 (rich left side).

Did check test with Innova for obd-1 immediately after driving. Only codes then were 136 and 172, lean right and lean left.

What the heck is going on?

Vacuum leak- if it is a vacuum leak, it’s not from vacuum hoses. I disconnected and plugged all vacuum lines, unless it’s the fuel pressure regulator leaking (new vacuum line to it). Seems doubtful, the regulator seems fine. Lower intake leak? Upper intake gasket is new. No audible hissing or other vacuum noises. Doesn’t seem to be oil or coolant in gas. Exhaust is clean, no smoke or vapor or anything. No clogged cats.

Why does my engine come to life at a certain rpm like nothing is wrong? Like you would think the engine could die at any moment, never does, then I hit a certain rpm and everything is just as good as it could be.

I’ve noticed as well when I get to 35-45 mph, before it was struggling all the time, the engine has a power jump that starts at higher rpms. Timing issue? PCM - CamshaftPS - motorcraft EDIS 6 (module behind front driver headlight basically).

Why would my truck not be able to accelerate and misfire, even when floored, then seemingly hit a certain RPM, and run amazingly?

I’ve been going through the same levels of hell. At 53 years old I buy my 1st Ford ever, 94 Ranger 4.0 XLT a4ld A/T 76K original miles very neglected . My 49th vehicle. New tires, hubs-bearings-rotors, shocks , pads, calipers, New heads water pump, oill/coolant temp sensors and still wasnt running right. Then I replaced everything in the fuel pump all the way to the engine fuel pressure regulator on rail. Finally the truck was running and driving the best It has in two years. The only thing left was fuel injectors. So as I’m getting ready to move and my rear main decides it wants to start spewing oil. Friend and I dropped my trans installed rear main seal . I look in haynes and chiltons books and asked AI AFTER REINSTALLING TRANS, WHICH SIDE MY O2 SENSORS ARE SUPPOSED TO BE HOOKED UP TO IT ON HARNESS AND THEY ALL SAID RED TO DRIVER SIDE BLACK TO PASSENGER SIDE THEN AFTER THREE WEEKS OF GOING THROUGH CHECKING ALL VACUUM LEAKS, CHECKING FUEL RAIL I STARTED GETTING ERROR CODE 159 AND 171 SO THEN I GO AND CHANGE MY MAP SENSOR ((sorry all caps.. talk to text did that ) and change my O2 sensors then I start getting 163 and 172 one side of my engine running super rich and the other side running super lean. I just filled my tank up and within a hour of running at idle to diagnose in about five or six sessions, the truck went through a 3/8ths tank of gas . So then I did my first test drives engine was not shifting 1st to 2nd properly going up to 35 or 40 miles an hour and then have to let off the gas for it to shift to second then all other gears shifted normally and reverse shifted normally. upon further in investigation, I find out that my transmission modulator went bad sucking in transmission fluid so I change that then it starts shifting better through fourth but reverse starts kicking harder. Then all of my codes changed and I started getting 164 173 still running super lean on one driver side and Rich on passenger side so after three weeks I go on a revisit the O2 sensors and switch sides red to passenger side to black to drivers side and then the truck starts running way better. Now, new problem I go to pull out my new transmission modulator thinking maybe it was defective and I find engine oil coming down the tube to the modulator when I had the first modulator problem ,FYI, I took off the vacuum line at both ends sprayed it down with brake cleaner, blew it out multiple times with the airline let it dry for a couple hours before putting it back together. Back to today , I pull off trans modulator and it has what I believe Is engine oil coming all the way down to new modulator gunking up vacuum port. Truck is running pretty good. Still has a weird hiccup when you hit the gas sometimes it stumbles . in 36 miles of test driving And an hour and 10 minutes of idle and checking things I’ve went through a 1/2 tank of gas. Sorry to be long-winded, but this has been the most expensive vehicle I’ve ever owned other than buying a brand new vehicle. Anybody have any ideas of what I can check ? I have to have an open circuit somewhere or something else entirely. Fuel rail good pressure. No vacuum leaks found after 1 can of brake clean and 3 1-2 minute smoke machine tests over last 3 weeks . All of my codes have went away and I haven’t gotten any new codes and it’s still just driving like trash not sure if this may or may not be my last Ford ever . HELP!!! These last caps intentional