1994 4.0 OHV Poor Power/ Fuel Mileage

[DasBaldDog]

Okay the facts,

145,000 miles
4.0 OHV 4x4
Manual Transmission
Not sure of tire size
Do not know what size rear end, probably standard.
No Check Engine Light
ABS and Brake light are out when the truck starts but after one decent braking, they both light up and stay on until the truck is turned off.


Purchased a few months ago and the truck seemed to run okay, but was a little down on power, seems like it has a miss somewhere (but I know nothing about poorly running vehicles so it could have a bad miss or no miss and I could be mistaken).

I knew that I was going to have to replace the exhaust and the cat as both seem to leak more than a little but less than alot. The comb of the cat rattles when you gas it.


When the truck starts up, it idles at 1500 rpm and eventually settles down to 600ish but the exhaust still smells a little gassy until its been run for a few miles.


I just kinda dealt with it but the slave is going out so I figured I would just give her the works and replace anything that was wrong.

Started with new plugs and wires and pouring in some fuel injector cleaner. Forget the wire maker but they're gray wires with red boots and the plugs are Autolite Plat AP105's gapped to .052. The old wires and plugs looked beat up so it seemed like a good move.

Afterward the truck seemed to run a little better not much but a little.

Last night we replaced the PCV Valve (Autozone sold me me with two spouts on it but the one on my motor only has one) and the fuel filter.... we then seafoamed the motor by pouring it into the vacuum line. Let her sit for 20 ish minutes and then drove her around the block a few times. Once again, the tiniest improvement but certainly nothing major.



To give a better description of what is going on, She accelerates fine in first and 90% fine in second, in third she is not nearly as strong and anything below 3000 rpm in 4th and she has no guts whatsoever especially on anything even remotely inclined.


The next things on my list in addition to the slave/clutch replacement is replace the leaking exhaust/cat, check the cylinder compression, check the spark plug ignition (I found on here that the more accurate way to check the ignition is to do the old "pull the plug, crank it and look for the spark" method).


Other things of possible import is that the previous owner I believe had the plug wires on Cyl's 4-6 on the wrong plugs but when I swapped them correctly, it did not seem to improve much if at all. I am not sure that they were wrong, but I pulled them all out and re-ran them and I think he had cylinder 4 as 6 and 6 as 4... but I can't remember. Just out of curiosity, if the motor is running, and I unplug a plug wire, what should happen?

Oh yes and the MAF sensor is new but I plan on checking the resistance of it anyways. I had planned on checking the O2 sensors as well but the Chilton manual I have says to do it between 60 and 70 degrees and its 20 degrees here and won't warm up until april.


So, sorry if this post is incoherent but I've been working on this in my spare time for two months now.

 

[DasBaldDog]

My personal theories about what could be going wrong,


-Clogged Cat/Leaking exhaust leading to poor emissions data
-Dirty or clogged Throttle Body/Injectors (really hoping the injectors are fine)
-Ignition Coil could be crapping out
-Could have fixed it already but the possible months or whatever of having the wrong wires on the wrong plugs have junked up those cylinders and it will take a while to clean out. May need to SeaFoam it again.


Or could be any combination of the above.



Oh and for the "What?" pile. When I was last under the truck and checking for the slave leaking, I noticed that the big wire that attaches to the bottom of the starter motor (the ground maybe, I dunno) was broken off..... but it starts. Either that is weird or I'm an idiot..... both are possible.... idiocy being more likely.

 

[sholzy]

Last night we replaced the PCV Valve (Autozone sold me me with two spouts on it but the one on my motor only has one) and the fuel filter.... we then seafoamed the motor by pouring it into the vacuum line. Let her sit for 20 ish minutes and then drove her around the block a few times. Once again, the tiniest improvement but certainly nothing major.

You can pull off the 2 spouts, it's just an adaptor.

Did you pull codes? Did you reset the computer after you replaced the MAF? No point spending a lot of money and time until you pull any codes that are stored. You might want to reset the computer and drive the truck a few miles first so it can re-learn what is normal sensor readings since you changed the MAF. Right now the EEC has old values from The old MAF stored in it.

 

[DasBaldDog]

You can pull off the 2 spouts, it's just an adaptor.

Did you pull codes? Did you reset the computer after you replaced the MAF? No point spending a lot of money and time until you pull any codes that are stored. You might want to reset the computer and drive the truck a few miles first so it can re-learn what is normal sensor readings since you changed the MAF. Right now the EEC has old values from The old MAF stored in it.

I did pull the codes, will post them below (Actually Autozone pulled them).

I did not reset the computer specifically. The MAF was replaced shortly I purchased the vehicle. I kinda think from this replacement that he may have known there was an issue. How do I reset the computer, just disconnect the battery for a few minutes?

I feel dumb about the PCV Valve. Oh well, have a spare one now.


The codes I got were

212 - Loss of IDM input to ECA
528 - clutch switch circuit fault
543 - fuel pump circuit open battery to ECA
556 - fuel pump relay primary circuit fault

 

[DasBaldDog]

I'm going to reset the Maf computer, reset the codes and the pull them again.

 

[sholzy]

Disconnect the negative battery cable for about 20 minutes.

 

[DasBaldDog]

Okay. Reset the codes and the maf. Drove it around for awhile.

Seemed to pull a little better.... Not a huge amount but maybe like 5%.

Came home and pulled the codes,
111
111


I wonder if the truck is running okay and I expect too much.... Though 10 mpg isn't what I expected to be sure. Hmmmm. Still going to do the compression and spark checks and what not...

 

[sholzy]

Disconnect the negative battery cable for about 20 minutes.

And also drive the truck about 15 miles to allow the EEC to collect the new data from the sensors.

 

[DasBaldDog]

Reset the computer, left the battery unplugged for almost an hour.

Drove it into Pittsburgh and back (was going anyways) and I take back what I said earlier, zero on the improvement meter.

I tried to check to see if the MAF itself is good and according to Chilton, I check the DCV between the connector A and B and should be above 10.5, I get 15.4, so check.

Then it says check the voltage between the Maf Sensor ports C and D and it should be between .34 and 1.96.... and the meter isn't reading anything. But that gets me thinking... how can a sensor with zero power going to it put off a voltage? So I check the connector ports C and D and I get ~5.0


Computer is still putting off codes 111 and 111, and then I get 157 and 158 which is MAF sensor above max and below min voltage....


Really hoping the MAF isn't bad. That's definately not money I had planned to spend.

 

[sholzy]

With the engine running, is there any difference when you unplug the MAF? I would get one from a junkyard and try it. Or, if you know someone with a ranger you can either try your MAF on theirs or try theirs on yours.

Did you get the MAF codes before or after you tested the MAF?

111 = System checks OK, which you will probably get every time, followed by the other codes.

 

[DasBaldDog]

With the engine running, is there any difference when you unplug the MAF? I would get one from a junkyard and try it. Or, if you know someone with a ranger you can either try your MAF on theirs or try theirs on yours.

Did you get the MAF codes before or after you tested the MAF?

111 = System checks OK, which you will probably get every time, followed by the other codes.

You know, as weird as it sounds, I cant remember. I did one and then the other and I can't remember which I did first.


As for what happens when I unplug the MAF at idle, the engine goes slightly rougher, starts to choke a little and then seems to even out a bit.

On checking the MAF, (since I am not a electrical genius by any stretch), I am putting the Voltmeter to 20 volts DCV and putting one prong to C and one prong to D and getting 0. So if that's the correct method, something is definately amiss.

I don't know anyone else with a Ranger, muchless of this year... and all the junkyards around here are far away from me. Do you happen to know other years and models that would fit this MAF? I can check some junkyards tomorrow.

 

[sholzy]

I'm not sure if '90 - '94 use the same MAF. Have you tried cleaning the MAF? Was the engine running when you tested the MAF?

http://www.therangerstation.com/tech_library/CleanMAF.html

 

[DasBaldDog]

Yes I have tried cleaning the MAF. I did it a few weeks ago with Carb cleaner, then again the other day with MAF Cleaner.


At first I checked the MAF with the engine off, but reread the Chilton and said at idle, so I turned the truck back on and did it again.

Like I said, it seems strange to me that the MAF would put off a voltage if no power was going to it (as it can't be if the sensor is unplugged).



ANyways, I had to run to the grocery store a few minutes ago, taking the wife's car but while her car warmed up, I tried an experiement on the truck. I had it idle, then unplugged the maf, waiting 10 seconds, plugged it back in, waited 10 second, unplugged it, etc...

I can discern that the motor REACTS to when I unplug it or plug it back in... but the overall performance, atleast in a parking spot at idle, doesn't seem to change very much. The Idle RPM is the same, the motor moves the same, it sounds the same, etc.

 

[DasBaldDog]

Sorry but this is really confusing me.


When I check A&B I believe that I am checking the cord that plugs into the MAF Sensor.


The manual seems vague on whether I am checking the cord, or the sensor when I measure C&D.... My problem is that when I check the cord, I get 5ish volts... and when I check the sensor, I get 0 volts... but how can a sensor put out power, if no power is going to it?

But the manual says to check C&D to make sure the sensor is working properly.... it just doesn't make any sense.

 

[DasBaldDog]

ALso, any idea if the 2.3L and 3.0L MAF's will work? The Chilton manual doesn't offer anything suggesting that it wouldn't.