4.0 weird issue

Tbarnes93 · Jul 25, 2014

So im back again with a strange issue with my 94 4.0 ranger. Everything is going great runs good warms up good no issues. Then I turn it off........ Wait about 10-20 min start it up sounds great no issues. Let out the clutch give it some gas, it stumbles. This only happens for a short period of time, maybe 50 ft. The thing that confuses me is that when it is stumbling or bogging if i press the clutch it acts normal revs up sounds good and if i let it out fast enough it will stumble for a split second and then everything goes back to normal. So i have done many things before posting on this forum lol. I changed my air filter thought it would be restricting flow but that was not it. I checked my plug wires and plug connections all good. plugs look brand new (less than 6 month old moto plats). If it is a fuel/air issue it would do this even with the clutch in right? I cleaned my intake with some carb cleaner. I also for giggles took my IAC off and checked if it was dirty, cleaned it off no change. I even threw some fuel injector cleaner in it and cleaned the maf with some expensive electrical cleaner. I'm clueless as to what the issue is. Any ideas guys? I will be grateful when i figure this out lol.

Tbarnes93 · Jul 25, 2014

it also passed koer koeo tests no issues there either

RonD · Jul 26, 2014

Check your fuel pressure, should be 40-45psi at idle and 2,000rpm.

Just thinking maybe the FPR(fuel pressure regulator) might be dropping the fuel pressure too much at idle, when you open the throttle, vacuum drops and FPR closes so pressure should come back up, but you could get stumbling until then.

You can't adjust the FPR.

Over all low pressure could just be the fuel pump just getting old.

Tbarnes93 · Jul 26, 2014

Okay thank you I will be going to my grandfathers shop in a few days to balance my tires and we will check it.

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Dazzlin' Dave · Jul 26, 2014

Tps?

I've been having some weird issues with my 94 4.0...
It was acting like it had vacuum leaks, which it did as well as a few leaks in the intake tube. I redid all the intake gaskets (make sure you ignore the instructions and use some Permatex! I didn't the first time and had to redo my intake gaskets!!) I also found some leaks in my throttle body shaft and replaced the o-rings. The thing was still acting funny, get to 1/2 throttle and it starts stumbling, unplug the MAF and it runs crappy, but I can get down the road. I broke out my analog voltmeter and checked the TPS again... I already checked it with a digital and didn't notice anything weird. Lo and behold! With the analog meter the needle rose as I opened the throttle and then started falling back!!
Diagnosis -Bad TPS!

Not to say that would be your gremlin, but I'd check it to eliminate the possibility.

Tbarnes93 · Jul 26, 2014

We can check that as well what is the voltage supposed to be?

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RonD · Jul 26, 2014

TPS gets 5volts from computer on one wire, other wire is a Ground, usually the center wire(3rd wire) is the voltage return wire, with key on engine off, this wire should read .6-.9volts with throttle closed.
As you manually open throttle plate voltage should steadily rise, no jumping around, at full throttle voltage should be at 4.5-4.7volts

Tbarnes93 · Jul 27, 2014

I went out and bought a multimeter and checked the tps 2 times. the closed was .89 and .9 and the open was 3.87 and 3.89 no jumps or drops and steady is it faulty?

Tbarnes93 · Jul 27, 2014

and the 5 volt wire was at like 4.97 or something close to that i think that is close enough to 5 lol

Tbarnes93 · Jul 28, 2014

I took the sensor off and drove it around the block didn't have any issues it just idled high when I initially took it off and the cel came on I think it is the sensor

Tbarnes93 · Jul 29, 2014

Well I messed the test up my dad got in and pressed the pedal and I guess I didn't press hard enough but it's .89 closed 4.62 open any other ideas? What about clogged cat?

Tbarnes93 · Aug 3, 2014

tested fuel pressure today at idle it was around 28 psi change it?

4.0 weird issue

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