1994 4.0 OHV Poor Power/ Fuel Mileage

[sholzy]

The MAF actually does produce a small voltage when air flows across the sensor. Look up a MAF at an auto parts website and compare the different years and engine sizes to see if it is the same part number.

I replaced mine back in the spring after checking bad. I don't remember how I tested it and my repair manual is 50 miles away in my dad's work shop so I don't have any references.

I'm thinking you may have damaged it by using carb cleaner on it.

There are quite a few threads in here on the 4.0 MAF. A search on it would probably bring up more info than what I'm able to give you. I'm surprised some of the other guys with (lots) more knowledge haven't chimed in.

 

[DasBaldDog]

I have been searching but the search on this website is far from the most useful search I have seen. I have found some stuff.

I don't think the carb cleaner hurt it as if it is the problem, it's been going on for months and the more I look at the Maf, the less I think the previous owner actually replaced it.

I am surprised as well that others have not commented but i thank you for your help, I will take any honest assistance I can get and appreciate it.

 

[multiranger]

i'd check the fuel pressure....

 

[sholzy]

i'd check the fuel pressure....

+1

It's probably getting a little hungry at the higher RPMs. If not pressure regulator, then maybe pickup screen.

 

[DasBaldDog]

I checked the Maf again and am still getting 0 volts.

When warmed up, the truck idles no differently with the Maf unplugged.... I didn't take it around th block just at idle.

Found a junkyard local that has one for $35, and a few on Craigslist but I need to find if different engines use the same part.

 

[DasBaldDog]

Gonna check the fuel pressure as soon as I figure outlaw and get the tool.

Interesting side note. On the way to work this morning, I stopped half way to work in a parking lot and unplugged the maf.... Then continued to work, no difference in engine performance. Cel came on though.

 

[DasBaldDog]

So... The manual didn't say anything about backprobing while the harness was connected... That answers a lot.

I got a reading from c and d at about .75 volts at a near warm idle (it was still warming up a bit) of about 750 rpms. It normally idles around 550-600.

According to Chilton, this means it's good. But I read on a different forum that the reading could be high or low, and the readings should increase in a steady manner as the throttle increases. So I will get the fiancé to help later when I get home.

Gonna stop by autozone on the way home to orrow their fuel pressure tester

 

[DasBaldDog]

Pulled the vacuum line from the fuel pressure regulator earlier.... No apparent fuel in the line itself though there was a white substance that looked like dried gas.... And the vacuum spout had a little fluid on it but I could not identify it as I had the smell of gas on my hands already.

Will check it again later.

 

[DasBaldDog]

Fuel pressure was 38 engine off and 30 at idle... Revving it didnot affect the pressure at all (I know it's not at load but I can't test it at load)

Intake was clear and Mac housing was spotless.

Maf itself gave a reading from .65 at idle and increase by about .2 every 500 rpms.

Coils are nice and shiny. I rechecked the spark plug wire routing.

The throttle body was caked in a thin but nasty layer of brown. One shot from the carb cleaner and it started to dissolve.

Going back outside in a few to check the Tps. It's frigging cold here.

 

[DasBaldDog]

Well the Tps is good as well.

A quick drive with freshly cleaned throttle body... Ehhh not sure if any improvement.


While I was under the hood, I pulled plug #5 as per the 4.0l tech library article and there was oil all over the plug threads. So I guess the intake bolts are loose.

Would that cause a problem?

 

[DasBaldDog]

From reading, I am guessing that a lose lower intake would give me a vacuum leak, resulting in lower power, poor mileage, and burning coolant/oil is probably responsible for that odd exhaust smell.


So... he's to hoping that it's a loose bolt or two and not a blown head gasket... *knocks on wood*.

Going to try to get to it this afternoon but with all this snow, not too likely. More likely this weekend.

 

[birdman]

Hey man, let us know what you find and if you can get pics.
i am having the same problem hoping to look at the truck this weekend

 

[DasBaldDog]

Well,

Tonight I am going to try and tighten the Intake Manifold down.... and depending on how well that performs, I may end up just putting in new gaskets (at this point it probably needs them, but I'm not rich at the moment).


I would start on the compression test but our area just got hit with 6 inches last night and my car doesn't handle snow... at all, so I need the truck to stay atleast partially working.


Trust me, I will be updating this.

 

[DasBaldDog]

Okay...

Well, pulled the upper intake manifold off.... DAMN its cold here. F this state, I'm moving back south.


Anyways, the inside of the upper and lower intake manifolds are covered in brown shittiness.... not clumps but a thin slime of brown that wipes away with a little carb cleaner.

One or two of the lower bolts were on there good but most of them took some snugging (I torqued then in the right order and with the right pressure using my torque wrench)... but I am worried that none of them too enough snugging where I think it will make much of a difference.

Worried about a blown headgasket or worse...

Got all the bolts torqued down and then cleaned up and came inside... too cold and snowing and with the early dark, working with a worklamp is just not something I want to do in this weather.

So.... tomorrow we will get it sewn back up and see if it did any good.

 

[mjw]

I'm going to chime in here with some info as I have the same year etc. My Ranger has the 4.0L with 5spd and 182,000 miles. According to the door sticker I have 3.08 gears in the rear end (code 92). It is happiest right around 2K rpm in all gears and I shift around 2500 rpm unless I am getting on the highway then I shift around 3500rpm. I have never been able to climb a steep hill in 4th unless it is around 3k rpm and even then its a dog. I get about 25mpg on the highway at 65 in 5th at 2K rpm, and 20 or so in the city if I don't jack rabbit my starts and at 182K I would prob break something. 5th really is OD and is not a passing gear.

My guess, based on your mpg is you are running really rich and is the MAF or O2 sensor.

Also for safety please check your fan at the hub for cracks and if you have them replace immediately there are a lot of stories about fans braking and killing people at the most and taking out your radiator and coming through the hood at the least. It is very common with the plastic fans. Mine was real bad. Get the special tool and fan from Advance, its easy to do once you realize the nut on the hub is reverse thead.