1994 4.0 OHV Poor Power/ Fuel Mileage

[DasBaldDog]

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.

Don't think its the MAF as I get a reading, and it changes in a linear fashion with increased revs. The O2 sensor, I would expect a code for... but is defiantely on my list of things to check.

My truck hates 2000 rpm in anything but first and second. 2000 rpm in 4th and it lugs pretty bad. And I need to be at 3000 rpm in 4th to even accelerate on level ground.

Thank you for your input, tells me something is definately amiss.

Hoping I fixed the issue with the tightening of the intake manifold. Next step past that is a new intake manifold gasket, and I'd really like to avoid that.

 

[mjw]

Don't think its the MAF as I get a reading, and it changes in a linear fashion with increased revs. The O2 sensor, I would expect a code for... but is defiantely on my list of things to check.

My truck hates 2000 rpm in anything but first and second. 2000 rpm in 4th and it lugs pretty bad. And I need to be at 3000 rpm in 4th to even accelerate on level ground.

Thank you for your input, tells me something is definately amiss.

Hoping I fixed the issue with the tightening of the intake manifold. Next step past that is a new intake manifold gasket, and I'd really like to avoid that.

Good luck. Chasing this kind of stuff is time consuming but at least the '94's are still relatively simple.

 

[DasBaldDog]

Forgot to mention...

Did a vacuum test on it last night.... 14 inches and wobbling less than .25 +/-....

I am hoping this is a good indicator for not blown head gasket and just a vacuum leak.


Plans for reconnecting the engine and testing it out for tonight continue... and a compression test if I can get it in before it gets too dark/cold.

 

[DasBaldDog]

Got it running after a trip to Autozone to get upper intake nuts that I dropped in a snowbank.

No improvement. Did the chemical leak block test... And no apparent head gasket leaks.

The vacuum readings are the same as well.

I have no idea what my next step is. I think there is a vacuum leak due to the vacuum tester readings but a full can of Brakleen and I can't get a reaction out of the engine....

Back to square one. Could there not be a vacuum leak and something is just causing low vacuum? Like a cylinder not firing or something?

 

[DasBaldDog]

To recap, (as much for myself as anyone else).

Symptoms

Low Vacuum (14" Hg)
Low Power
Poor Gas mileage
Slightly rough idle
1/4 second hesitation on the throttle


Done So Far

Swapped Fuel Filter
Cleaned MAF
Replaced Spark Plugs
Replaced Spark Plug Wires
Cleaned Throttle Body
Checked operation of MAF
Checked operation of TPS
Retorqued Lower Intake Bolts
Retorqued Upper Intake Bolts
Checked for blown head gasket (Chemical test came back negative)
Tested Fuel Pressure (38 psi before start up and 30 psi at idle)



I think that's everything....

I am not convinced that the intake manifolds are leaking, especially not for a 25% reduction in vacuum... I could be wrong. I torqued down all the other intake connections and in theory the vacuum leak has to be between the throttle body and the intake valve....


Any ideas guys? I dunno what to check next for a vacuum problem.



Update: After reading several websites, I am going to check all the hoses, especially the PCV Valve hose which seemed a bit loose when I replaced the PCV Valve. Also, I am going to check the PCV valve itself because it may have been replaced with the wrong one, one that flows too much or isn't as snug as it should be. Also, I am going to check the EGR Valve and see if its leaking or sucking too much air. I know that this shouldn't affect the truck's open throttle application but the low throttle and open throttle problems in theory could be two different problems. Lastly I am considering a exhaust blockage, which is very possible considering that we know for a fact that the cat is breaking apart inside and rattles. Lastly tonight I think I am going to try a compression test.

 

[DasBaldDog]

Looks like I'm in for a Intake and Valve Cover gasket swap....

 

[DasBaldDog]

My truck apparently has no EGR..... damn. I was really pulling for that.


I had an ex Ford Mechanic (opened his own shop and does too well to be a retard) tell me that an exhaust problem will cause all the problems I am seeing and a few more.


I still think there might be the intake gasket leak due to the oily and fuzzy plug #5... but I am going to be doing the clutch and slave cylinder swap this weekend and am going to thoroughly examine the exhaust while I am at it. Cat should be arriving today (the one on the truck now is definately fubar'd as it sits).

 

[DasBaldDog]

Oh and one of the plugs was oil fouled..... Can't remember which one but I think it was on the passenger bank.

 

[Rangerboy]

I've got a 95 Ranger 4.0 OHV that had the same problems and I've got her working like a winner again.

1st off I would check the purge valve and the lines going to the throttle body. Probably have a dry rotted line right up underneath the bottom side of the throttle body. Purge valve is on the driver's side behind the headlight.

2nd would be to clean your EGR tube, EGR valve, EGR hoses, EGR solenoid, etc Clean or replace these.

I guarantee it will work!

 

[DasBaldDog]

It does not have an EGR... I checked, or a long time.

Got my fiance (who's about as eagle-eyed as I've ever met) and she couldn't find it either.


Its not on the VECI sticker, just the catalyst.


I will definately check the purge valve though. Thanks for the hint.

 

[DasBaldDog]

I found that the hose that goes from the Evap Canister to the fuel tank was rust rotted at a connection at the back bottom of the engine bay.....

Does anyone know if this, or if the purge solenoid were not opening would cause any of the issues I am seeing?

The hose between the throttle body and Purge solenoid, and between the solenoid and cannister appear to be in good shape.



Oh and the fuel pressure at idle is 39 psi.

 

[Rangerboy]

It might be the purge solenoid or purge valve acting up. I replaced the purge valve I think.