4.0 OHV drivability problems

boosted2.3 · Jul 21, 2014

Hello all, It's been quite a while since I last posted. I have a '94 4.0 ohv ranger with a 5spd. It has 114,xxx miles. I has always ran fine, but the other day I was just on a narrow road and in third gear and the "check eng light came on and it started bucking real bad, I went to 2nd and got the rpm's up to 2k and it smoothed out, after a few minutes the check engine light went out but the problem persisted. It idles fine at about 800 or so, and when over 2k it runs great. I got it home and the next day on cold start the idle was searching between 800 and 1100 or so. I tried to get it to an advance A/P to get the codes read, but it started getting worse, and the check engine light started blinking on and off. It still runs good above 2k, but if I let off the throttle is falls on its face till it gets to idle. I have some serious traffic between me and the scanner, so I'm kind of stuck. I ran the voltage check on the TPS thinking it was it, and the reading seems right and smooth, but I noticed that the throttle body lever the cable connects to has some slop in it, but no vacc leak. The tps still reads true, but the lever moves about 3/4 of an inch before the the reading starts. I would appreciate any help or experiences I can get. There are no backfires or anything. It seems to run great till I reach the speed I want and then bucks real bad, If I stab the throttle it runs great. Thanks in advance. :icon_confused:

cp2295 · Jul 21, 2014

My dads f250 did the whole bucking thing, and he threw a new fuel pump and filter in it and it went away. Just my 2 cents on that. But I would do the basics first, new plugs wires filters that sort of thing. Then move on to the more expensive complicated stuff (fuel pump, injectors, etc)

As for the idle issue, sounds like a vac leak, could be the iac valve. I would double check all vac lines and Ports and spray some carb cleaner around the intake gaskets just to be sure you have no vac leak.

boosted2.3 · Jul 22, 2014

Thanks for the come back, but the truck runs great from 2k rpm on up. The FP is but a year old. I also tested the throttle pos sensor and it seem to be working fine too. It idles fine, except when cold start when it seems to search for just a couple minutes, then it settles at about 900 rpm. After taking off it bucksban between 1500, and 2000 rpm, any acceleration is good but after backing off the throttle at speed it bucks, if you go down a gear and keep it above 2ooo it runs great. I'm starting to think it might be an ignition problem. A friend is coming over tomorrow with a scanner and do a code search. The check eng lite blinks when it it bucking. Thanks again. :icon_confused:

boosted2.3 · Jul 23, 2014

I finally got the codes checked on this thing. 122,, 125. both are low voltage return on the TPS. I tested the tps and it was smooth all the way from idle on up. I'm seriously stumped on this one. I going to get a fuel pressure test today to look into that. I can't figure how the tps codes could set if it is actually good. any input would be appreciated.

JimRummy · Jul 24, 2014

Try checking the coil pack. A bad coil will cause a bucking from a cylinder misfire. A multimeter, a screwdriver, and 20 minutes is all you need.

boosted2.3 · Jul 24, 2014

I finally found a code reader for EEC-IV, and they were tps low voltage return. the tps tested good. A friend suggested I unplug the tps and drive it and see what happened. It ran good, but had a high idle. I plugged it back in and it still ran fine. It might have been a connection problem, but the connection looked clean. time will tell. thanks again for the help.

Dazzlin' Dave · Jul 26, 2014

Analog Meter?

Did you use a digital or analog meter to check the TPS?
I tested mine with a digital the first time, was getting to 1/3 - 1/2 throttle and fell on its face, found some vacuum leaks and fixed them, but didn't cure the prob. When I broke out my old analog meter I watched the needle come up to 1/2 throttle then started falling back after that!

boosted2.3 · Aug 1, 2014

I really appreciate all of your replies. I cleared the codes again and it came up low voltage return from the tps. I unpluged the tps and it ran ok, I plugged it back in and it ran good for a day, then went right back to the same thing. Today I put a new tps on it and it ran like crap in the driveway. I started to read the codes and when I turned on the switch the relays in the relay center started ticking like pop corn popping, and the scanner light, and the check eng light blinked right along with the clicking. I shut it off and disconnected the scanner and started it and it fired up and then died and hasn't run since. I'm thinking it has been a wiring problem the whole time and has steadily gotten worse. I'm wondering if anyone on here has had a similar problem. Again THX for the help. :icon_confused:

SteadyMobbin13 · Aug 7, 2014

it sounds like bad wiring, bad ground, corroted wires if its popping like that. Check the fuses and the idle control valve if there is one. also at anytime that you tryed to read the codes did it come up with any?

4.0 OHV drivability problems

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