94 explorer. can't get past 1/4 throttle. seems to be "Loading up"

[systemhf]

I have a dilemma with my 94 4wd xlt.

Started running very poorly and bucking at about 1/4 throttle. I managed to get it home by idle. I could not event hit the throttle at all, I was like it had a bad fuel filter.

SO, I checked the codes looks like a bad tps, bad IAT, and a bad O2 (Always lean).

I have replaced all of them and the fuel filter, cleared the codes and NOW I have codes 114 and 116 and hard codes 172 and 176.

So, the IAT is reading hi/lo, the coolant temp is taking longer than expected, And I still have an Issue with the O2 sensor being always lean.
Do I have a bad MAF sensor? Or a bad ECM?

I have been farting around with this for over a week... It's making me crazy!

 

[arco777]

A bad MAF will throw all kinds of crazy unrelated codes. Try unplugging yours while the truck is running and see if it clears up a bit. Check also if your MAF is dirty. They do go bad and when they fail it makes lots of problems. They're not cheap but you will need one at some point anyways so it doesn't hurt to have a spare if it turns out that wasn't the issue.

 

[systemhf]

I will try that tonight. I just kinda dumbfounded that the MAF isn't throwing any codes. Really weird.

 

[arco777]

Sometimes the PCM will see a failing MAF and give codes for 'MAF reading too high/low' but not always. Sometimes the wonky MAF signal will simply throw off the PCM enough that it will command rich or lean mixtures - it believes the MAF's inputs because they are not quite too extreme. Though still they are wrong.

I hate to suggest throwing parts at a problem. So if you have a known good MAF from a donor vehicle (same configuration of Ford 4.0L V-6), try swapping that in, reset the PCM (unplug battery for 10-20 minutes) and see if that makes an improvement. I stress that you use a known good MAF because there are a lot of vehicles in junkyards (and still driving around) with MAFs that are not operating properly, but may be good enough for that particular vehicle that they will work in it but not in yours.

 

[systemhf]

I need to get "Ol' Rusty" back on the road this weekend!

I think that I'll just end up buying a re-manufactured from the local parts house. I looked on-line and I can get one for about $76.00. Not cheap, but after all the original one has been in operation since 1994.

Thanks so much for your help!

 

[systemhf]

could it be the fuel pressure?

so I unplug the maf while running, no change.. it still idles fine. tap the throttle with it unplugged... engine dies as expected.

The always lean codes to the ecm from the O2 have me wondering if I have a fuel pressure problem. going to try to find a gauge to rent or borrow to find out if I have a bad regulator or something.

 

[Corik]

You can test your regulator by unplugging the vacuum line from the back. The fuel pressure "should" increase. How long has it been since you replaced your fuel filter? and maybe you should try some seafoam or fuel injector cleaner and let it idle for a while.

If you want to check the O2 sensor, you will need a volt meter. crawl under the truck and use two needles to push into the back of the connector/wiring harness. Once everything warms up. You should see a steady swing of 0.3v-0.8v. The speed should be about 2 seconds per swing. low voltage is lean and high is rich.
If the voltage stays constant than you need to replace.
With a good manual and a volt meter you can check all the sensors.

 

[systemhf]

I have replace the fuel filter, O2, TPS and IAT sensors. I'm going out on a limb here and replacing the MAF.

Starts & Runs at idle great! once it's warmed up a little I can't get it to turn pas t 3000 rpm with out it running rough out completely stalling.

 

[Maniak]

Did you ever find a fuel pressure gauge so you verify that you are getting enough fuel to the FPR/ fuel rail?

~Mark

 

[systemhf]

I just borrowed one from a guy I work with. gonna check it tonight, If I don't freeze my fingers off!

 

[systemhf]

Ok, Hooked up the gauge. idle I get 30 psi. is that too low?

When I rev it the pressure drops to 25 psi but quickly comes right back to 30psi

So I think that it is probably the MAF going wonky right?

 

[Maniak]

It should be 32 or so at idle and when you blip the throttle (lose vacuum) it should go up, not down...

I'm leaning towards weak fuel pump at the moment..

~Mark

 

[systemhf]

The gauge set that I had was pieced together it had a t fitting with a large & small gauge hooked to it.

I did not try to remove the vacuum line from the regulator to see if the pressure went up. I was freezing!

 

[awood]

This thread is worthwhile reading....

http://www.explorerforum.com/forums/showthread.php?t=142801&highlight=1st+fuel+pressure

 

[systemhf]

Ok, tonight was very productive.

replaced the MAF, cleared the codes.. same thing. Idles great! step in the gas pedal, Almost dies. I know now that I have a fuel delivery problem.

hooked up the fuel pressure gauge.. 30 psi idle drops to 25 when you blip the throttle. Took off the vacuum line to the regulator, pressure does not come up.

So tomorrow I will be installing a new regulator.

I want to thank all of you who helped me in any way to get "Ol' Rusty" runnin' right. Your advice was a huge help!

Hopefully I will get her back on the tomorrow!

 

[Maniak]

My Guess is its more likely the fuel pump. Every regulator I've seen go has either let full pressure through or leaks fuel into the engine through the blown diaphragm. Fuel pumps however can and do get weak and won't put out the volume/pressure needed. This is what happened to our Fuel pump last year.

~Mark

 

[systemhf]

Maniak,

I HOPE that it's a regulator, I just hate the Idea of dropping the tank in 25 to 35 degree Michigan weather.

Funny thing, now that I think of it.. I didn't get any pressure reading when I turned the key on with the engine off. I suspect that the regulator might be stuck? Anyway, I have a new regulator going in it today.

Thanks again for your help!

 

[jakegator]

Hey i had a similar problem. This is just my 2 cents. Sine our gen explorer is pretty old its probably a few things that have been adding together over some time. I replaced my fuel pump which helped a little but still had issues. Turned out the fix was a vacuum leak (lower intake). If you replace the fuel pump and it still is acting up check your vacuum lines and then upper and lower intake gaskets.

-Good luck!

 

[Turdle]

Also

Sometimes the fuel pump relay contacts overheat and develop a bad connection. Tighten the lugs on the fuel pump relay socket, and, give the relay tabs a very slight twist. This will make them "dig in" to the contact lugs better.

It may not help, but it can't hurt, and it will not cost anything. Oh, while you have the relay out, try swapping it with another ( identical relay) in the relay box. This will eliminate the relay itself as the cause.

 

[arco777]

Maniak,

I HOPE that it's a regulator, I just hate the Idea of dropping the tank in 25 to 35 degree Michigan weather.

If it does turn out to be the fuel pump, you don't have to drop the tank. You can cut an access panel in the floor without too much trouble. I used an angle grinder with a cutoff wheel and it made the job pretty easy. Next time I have to mess with the pump I just pop off the panel. If you search the forum there are writeups on how to cut the hole required.