94 Explorer hesitation

[Softballdad]

Hi all, I'm new to posting. Have been looking for some help. My 94 Explorer is having issues. It started bogging down on hills but was fine on the flats. Then that progressed into chugging from a stop until about 20mph at which point seemed to smooth out. I recently changed the fuel filter and it seemed to be a lot better in acceleration. Friday night it almost stalled out on me while I was at a stop light. I thought it might be getting overheated as my gauge was above where it normally is. Finally got through traffic and once I was moving again it seemed to smooth out. All the way home that night idle was fine. Yesterday I went to go somewhere and it started again. Turned around and came home. Now I'm not sure where to start. I'm going to go pull the plugs today. I have read many different posts that mimic my symptoms, and there are SO many different things it could be. Fuel pump? Lower intake bolts loose? I already checked the MAF sensor. I checked the battery cables for corrosion and they look fine. It had good response at highway speed, although I generally can't get it over 65mph.
Also, every once in a while it won't start. This could be related. I changed the fuel pump relay and it ran fine for a couple months. Then it happened again. This time I just had to wait it out before it would start. I don't know why, but I couldn't hear the pump turn on when I turned the key. Probably just a loose wire somewhere, but what are the odds that I switch out the relay and it starts just fine? Any help would be great ! Thanks!



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[arco777]

Welcome to the forum!

You might want to try posting in the 95-2001 Explorer section. This is the 91-94 section.

Your symptoms sound like a failing fuel pump. You need to check the fuel pressure at the rail with a pressure gauge. Best time to check would be when the engine is falling flat on its face. Some people may say it's not safe, but you can leave the gauge connected to the rail (tightly) and keep it from bouncing around - then when the car starts to sputter and die, pop the hood and check the gauge.

It will take some searching or someone else chiming in to say what fuel pressure you should expect. 91-94 models need 35-40psi, but at some point after 95 a change in the fuel system bumped that pressure up to 60psi if I recall correctly.

If your fuel pump relay is burning out, or is getting real hot during driving, it means your pump circuit is drawing a lot of power (or a faulty relay). Considering you have replaced your fuel filter, it is probably a failing pump. A pressure test should identify if this is true.

 

[Softballdad]

94 Explorer

Thank you Arco! Actually, it is a 94. We have a 97 Escort as well and I get the years mixed up all the time. So, I just got done with the plugs. Gap was WAY off. Factory is .54 and I had at least three of them into the .70's. That seemed to solve my hesitation at the pedal, but now I think I've just got water in the lines. It sat all winter with almost no fuel. It's almost on E now, so I think I'm sucking water. It starts fine, idles fine for a while, then starts sputtering and almost dies. Then it perks right back up to idle where it's supposed to. As for the fuel pump, why would it be fine for a week after I changed the filter, and then start acting up again? I would think if it's going out I wouldn't get that much more mileage out of it. I put some gas in it from my can, and I'm going to go get some gas dry and see if that solves it. Thanks!

 

[arco777]

If it's been sitting for a while, you might have actually sludged up the old filter and the new one. Either way a fuel pressure test would help.

If you get water in your gas, HEET works well to dry it out. I used to use it on snowmobiles all the time.

Are there any KOEO or KOER codes?

 

[Softballdad]

94 Explorer

It was blowing black smoke from the exhuast. I checked the Fuel Pressure regulator and the hose was off. Re-connected it, and it's still doing the same thing. Went to junkyard, got a new FPR. Going to try that next. No, I have not connected the code tester yet. I borrowed one, but then I couldn't find out where the connection was under the hood. I will get some HEET next time I hit the store.

 

[arco777]

The test connector you're looking for is in between the stock airbox and firewall, tucked in near the blower motor. There's a similar connector on the driver's side fender with a red cap you can test the ABS brakes at (codes are pulled the same way).

Black smoke seems to indicate too much fuel. Again this would be worth checking fuel pressure. But see what happens with the new FPR.

 

[Softballdad]

94 Explorer

FPR did nothing to improve the situation. I pulled off the air duct from the throttlebody to see if the butterfly was opening all the way. It doesn't seem to be. Is the electrical component on the outside that looks like it controls the butterfly the Throttle Positioning Sensor? I wonder if that part is bad....Still spewing black smoke and carbon all over the driveway. When it's idling it sounds like I've got a huge cam in it. Like a funny car. If I rev it to about 3000 it seems like its fine, but as soon as I left off it goes back to the same thing.

 

[arco777]

The Throttle Position Sensor is a black sensor located on the throttle body, as you mentioned. The TPS can be tested with a multimeter easily. It only has three wires; a ground, a reference, and a signal. The signal wire should read .98v at idle position (key on engine off) and smoothly rise to 4+ volts as you advance the throttle. Dead spots or an incorrect idle reading are signs of TPS issues. If you do a search on here you can find more info on testing your TPS and modifying it to allow calibration.

Have you checked for ignition arcing? Take a look under the hood at night with the engine running, and look for arcs jumping from damaged spark plug boots and such. Those will cause your engine to run like crap and act rich yet misfire, and will seem to clear up at high RPM.

 

[arco777]

I pulled off the air duct from the throttlebody to see if the butterfly was opening all the way. It doesn't seem to be. Is the electrical component on the outside that looks like it controls the butterfly the Throttle Positioning Sensor?

The Throttle Position Sensor only reads throttle position. The throttle body action is controlled by the throttle cable. The cable does stretch out over time and can be tightened up for free (search for the 50 Horsepower For 5 Cents Mod). A loose throttle cable will not cause engine problems, but fixing it will make your Explorer feel like it has a lot more power.

 

[Softballdad]

94 Explorer

Ok, maybe not TPS then. I pulled MAF sensor and it had a little fuzz on the wires. Dusted them off and re-installed. No difference. Still wondering why I have NEVER blown black smoke from the exhaust until today. What are the odds? I thought when I changed the plugs I had solved some issues.. Throttle response was back, but I guess that was it. Now I'm wondering if it could be the coolant temp sensor. From what I've read, that controls the rich/lean mixture. My temp gauge normally shows at about the 'N' in normal. It never goes above that. Saturday I was stuck on the freeway for an hour in stop and go traffic. It moved the needle to about the middle of the gauge. That's when I started having problems with the idle and almost stalling. Again, once I was able to actually start driving at normal speeds, the idle issue went away and I drove it home that night with no more issues. I am still not believing it could be the fuel pump at this point because of all the other variables that are present. I'm giving up for tonight, but I sure do appreciate your help ! Thank you so much!

 

[MrShorty]

Now I'm wondering if it could be the coolant temp sensor. From what I've read, that controls the rich/lean mixture.

Only partially correct. The PCM controls the A/F mixture based on the input of most/all of the engine sensors. Primary sensors used are the MAF and O2 sensor. Input from the ECT helps fine tune the mixture based on engine temperature. In order for the ECT to throw the mixture off enough to affect driveability like that, it would have to be way off (namely, intermittent full open in the ECT circuit or a short in the ECT circuit).

I would test it with a voltmeter. I've seen published tables of resistance vs. temperature for the ECT (Chiltons has it, I think, and it seems like it has been posted here before). From Ohm's law, you can convert those resistances to voltage drops across the ECT (computer supplies a constant 5 V reference voltage to the ECT). Then, set up your voltmeter to measure voltage drop across the ECT and see if it does something funny at the same time as the engine acts up.

 

[arco777]

Keep in mind that there are two temp sensors/senders. They're located very close to each other. One is for the gauge, one is for the PCM. Both have different outputs. The PCM uses the sensor, gauge uses the sender.

Check this page for ECT sensor testing info - http://oldfuelinjection.com/?p=28

 

[Softballdad]

94 Explorer

Just got home today from family camping vacation. I put a bottle of Heet in the tank and a few gallons of gas. Changed the air filter just for good measure. Still the same problem. What still bothers me is that I NEVER had black smoke coming from the exhaust before. It has never acted this way until now. I really thought changing the plugs was the answer as it seemed to perk right up to it's 'old' self. I also read about similar problems that were caused by bad O2 sensors? Are my Cats bad? What about the EGR valve? Would that cause it to run rich like that? Is my computer going out? Should I install another new fuel filter? I don't know anymore....Haven't gotten around to getting out the voltmeter. I think I will borrow an OBD reader. Tired of chasing this issue, I guess I will see what codes I come up with to narrow it down. Thanks again Arco777 and MrShorty for all the information thus far !

 

[Softballdad]

KOEO codes are 159 and 158. The book says Manifold Air Flow Sensor Fault. Voltage above or below normal. Could this really be all that's wrong with it? I pulled the connector off the MAF and it stays idling. A little rough though. As soon as I plug the MAF back in, it dies. Problem found?

 

[arco777]

That's usually a sign of a bad MAF.

 

[Softballdad]

94 Explorer

Ok, installed new MAF and at first it spit out a bunch more carbon from the railpipe. Seems to run smoother now without dying. There still seems to be a little bit of a 'miss' somewhere though. It just doesn't feel 100 percent.

 

[malohnes]

Did you check for loose Lower Intake Bolts? This sounds very familiar. Also, you might want to try disconnecting your battery and let the computer reset and relearn with new components.

 

[Softballdad]

I did read about the lower intake bolts maybe being a part of the problem, but honestly, I don't know exactly where they are or how hard they are to get to. I'm running out of time this week, and will probably have to wait until Saturday to get back into it. And I thought about disconnecting the battery also. I will do that. The other thing is that I wasn't able to get the #3 plug changed, so I'm wondering if that would make the slight 'miss' that I'm feeling. I took it out around town, and it had plenty of HP. No idle problems at stop lights, etc. It felt like a new Explorer, it's been a long time since my baby has run that well. Thanks again for all your expertise ! I have really learned a lot about things this last week.