94 Explorer Stumble on acceleration and loss of power

[Alan_V]

OK, checked all vacuum lines. Couldn't see a problem there. Checked MAP, it's clean and putting out all the proper voltages. Double checked connectors to fuel evaporator, and pcv. Nothing seemed to be wrong. And of course for good measure I changed the air filter.

Engine vacuum??

 

[lonestar]

I have a very similiar issue. Seemed to start out as a slight stumble between shifts, and now all of a sudden on my way home it misses and bucks like the drivetrain going to fall out, almost if I turn key off/on and it push starts. Seems to does OK if I accel very slow, and it runs up to 4K fine, any accel around 2K seems to trigger it and I have to let off gas. Idles fine.

And it seems to start while warm, or atlest registering on temp gauge. Maybe a close loop issue? Oxygen Sensor?

 

[Alan_V]

I have a very similiar issue. Seemed to start out as a slight stumble between shifts, and now all of a sudden on my way home it misses and bucks like the drivetrain going to fall out, almost if I turn key off/on and it push starts. Seems to does OK if I accel very slow, and it runs up to 4K fine, any accel around 2K seems to trigger it and I have to let off gas. Idles fine.

And it seems to start while warm, or atlest registering on temp gauge. Maybe a close loop issue? Oxygen Sensor?

Disconnect it. Car will run without it. Yes you'll set a code, but if the problem is still there, ride a different horse.

An O2 sensor won't make a car run bad unless it's shorted. Open should have no effect.

 

[MDewell]

Disconnect it. Car will run without it. Yes you'll set a code, but if the problem is still there, ride a different horse.

An O2 sensor won't make a car run bad unless it's shorted. Open should have no effect.

That's not a bad idea there...I think I'm gonna try that too with the problems I'm havin..at least that will eliminate the O2 sensor.

 

[lonestar]

Did some more testing. Started cold and drove paying attention to temp. Ran great until it reach normal temp (N on NORMAL), than it started stumbling, unless I accelerated realllyy slow.. Stopped in Autozone and picked up fuel filter and did a free code scan...

Stored Codes
67 - neutral safety switch open (didn't think manual had one, just a clutch switch)

Continuous Code
95 - air/fuel mixture out of range or fuel pump open circuit (PCM to motor)

Then it seemed to run better even though already up to temp, but it started after about 5 minutes. Maybe it just takes that long before it goes into closed loop.

Changed fuel filter just to be sure, still no improvement.

I guess I will start test driving with sensors unplugged one at time until maybe I find something. what would cause fuel pump circuit to be open, fault inertia swith?

 

[lonestar]

Next Test

Short trip until it started stumbling, unplugged MAF, truck died, restarted with MAF unplugged and it ran great, plugged MAF back in and it ran fine, stopped and restarted and it ran like crap, stopped, unplugged MAF, restarted and it ran great...

So I'll leave MAF unplugged a day or 2 and make sure it's not a fluke.

 

[opelgtman]

mine does the same thing. I have swapped out the maf with 3 others and as soon as I plug the MAF in and drive around, I get horrible performance from my explorer.

 

[lonestar]

So your saying unpluged it runs good, but plugged into even a new MAF and it runs horrible. hmmm, interesting. Maybe unplugging sensor prevents it from ever entering a close-loop, thus bypassing all sensors?

How terrible? Mine stumbles so bad that if in 1st or 2nd gear the tires chirp.

 

[Alan_V]

I don't know if this works for Fords, but for many mfgs, unplugging the MAF puts it in "limp home" mode. It ignores all of the sensor inputs and runs on pre-set outputs. If it runs better and continues to run better, it's a sensor, and not necessarily the MAF.

 

[lonestar]

UPDATE.....

It ran better, for while.... It started doing it again on my way to work this morning, althugh not near as bad or as long, only about a mile. With the MAF connected, it did it constantly...

That makes sense withe the 'limp' mode, thats what I was afraid of...

SO, what can it be now? Could it be a sensor at all? After some searching around on the net, here are the posibilities I have found...

Airflow Sensor (MAF)
Crankshaft Sensor (CPS)
Throttle Sensor (TPS)
Oxygen Sensor (O2)
Coil Packs
Ignition Module
PCM Capacitors (someone here replaced bad caps inside the PCM)

Know of any tests to try? I thought I may be able to unplug sensors one at a time to help track it down, maybe not.

Just to recap, Changed plugs, fuel filter, and inspected wires in the dark.

 

[JohnJ]

UPDATE.....

It ran better, for while.... It started doing it again on my way to work this morning, althugh not near as bad or as long, only about a mile. With the MAF connected, it did it constantly...

That makes sense withe the 'limp' mode, thats what I was afraid of...

SO, what can it be now? Could it be a sensor at all? After some searching around on the net, here are the posibilities I have found...

Airflow Sensor (MAF)
Crankshaft Sensor (CPS)
Throttle Sensor (TPS)
Oxygen Sensor (O2)
Coil Packs
Ignition Module
PCM Capacitors (someone here replaced bad caps inside the PCM)

Know of any tests to try? I thought I may be able to unplug sensors one at a time to help track it down, maybe not.

Just to recap, Changed plugs, fuel filter, and inspected wires in the dark.

If disconnecting the MAF helped a lot I'd say you're probably looking at one of the following:
-dirty or bad MAF
-corrosion at the connector to the MAF
-vacuum leak including leak between MAF and throttle body
-incorrect ECT signal (bad sensor or corrosion at the connector or low coolant)
-low fuel pressure
-bad O2 sensor

You should specifically NOT be looking for:
-Exhaust restriction or clogged cat
-TPS problem
-Ignition problem (plugs, wires, crank sensor, coil pack)

 

[lonestar]

Given my ride home, I wouldn't say a lot....

Ran great as usual until it warmed up, although it did seem it took longer to start 'bucking'. Just as it started I noticed that if I 'nursed' it slowly accelerating it kept the jerking to a minimum and slowly accelerated, but if tried to accelerate faster than grampa, it would fall in its face, buck and chirp tires. Then I came to hill, slowly chugged up the hill, and it took off and ran great again once at the top. Then about 4-5 miles later it started again for about 0.5 mile and seemed to repeat every 4-5 miles. It did seem to occur mostly in the 2K-2500 range. When it does run good, it seems like it may run better with MAF unplugged.

Don't know what to think... Kinda hard to explain, but it's not like it's just sputtering out of fuel (I did run out of gas about a month ago). Depending on throttle position, varies from similiar to running out of gas, no power and missing pulsation to something like it dies and jumps back to life, picture repeated ignition on/off with manual tranny.

Something that keeps popping up int he back if my mind is
Continuous Code
95 - air/fuel mixture out of range or fuel pump open circuit (PCM to motor)

Could it be bad ground somewhere causing these issues? Ground to PCM? Battery Cable?

thanks for tips, I'll definitely check those out too.

 

[fixxxer]

Mine had the same symptoms the first week I had it, intermittant at first then progressively worse. Turned out I had a clogged fuel filter, you did say you ran it out of gas recently, right?
ok, I just re-read your post above where you replaced that already, duh!

 

[lonestar]

I'm am thinking that if unplugging MAF would puts EEC in 'limp' mode, ignoring all sensors, and it still runs bad, then it would suggest it is not sensor related.

 

[lonestar]

Seems to occur only under load. Started bucking again, hit clutch and it revved just fine up to 4K+, soon as I let clutch out it spit and sputtered, reved it again, and it started running fine...

Recap...
Bucks and jerks while driving
Changed plugs and fuel filter
nothing changed..
unplugged MAF and seemd to run good
drove with MAF unplugged just to be sure
started bucking and jerking again under load

So since problem still occurs with MAF unplugged, creating a 'limp' mode, I assume this leads me away from a sensor related issue?

That leaves:
ignition module
coil pack
ground issue
faulty relay
PCM

Problem is I don't know where to start. Maybe I'll start with misting wires and coil with water to check for any shorting, look into grounding issues (TPS ground or battery cable), and swap fuel pump relay.

 

[boggs1227]

this may help or not but just my 2 cents here....back years ago one of my friends had a f-150 and had a simlilar problem but it was his plug wires that were at fault.at night time being dark as it can be in the area that your looking under the hood ,while they would rev the engine i looked under the hood and saw what looked like a lighting storm ( blue arcs of electricity went every where in the engine compartment ....really cool to look at tho )... bought new wires and cured the problem .

 

[MDewell]

I'm kinda watchin this thread and since the TPS might be my problem..is it possible that it could be yours?

 

[lonestar]

Don't know, maybe. With it having issues while in 'limp' mode with MAF disconnected leads me to beleive it is not sensor related.

I did find this...TPS GROUND ISSUE

I inspected wires in dark, nothing, but it was running fine at the time, only runs bad under load when hot. Thought I may try the misting technique to encourage any shorting that may be present.

 

[lonestar]

Did some testing tonight...

MAF supply voltage = battery voltage
Can't remember which way, but there was approx a 0.4V difference between MAF ground to batt POS and MAF + to batt NEG.

TPS supply voltage = 4.83
TPS supply to batt NEG = 5.03V
TPS supply @ connector by alternator = 4.83V
TPS supply voltage @ PCM = 4.83V

Inspected wires again in dark, sprayed them down with water to check for short.

Removed PCM and inspected, didn't find anything visually bad, like a oozing capacitor or burn marks.

I may have found something though. The first time I turned key ON I don't remember hear fuel pump. Started and it died. Started again and it ran rough, acted like it was not getting fuel, gave it gas and and stumbled for awhile and cleared up. Turned key off/on several times listening for fuel pump, heard it a few times, not others, and couple of times something sounded kinda odd, not sure if it was pump or not, but it seemed to start and idle fine several times.

Plan to check fuel pressure next, hopefully I can find a way to monitor while driving. I'll try swapping relay first before dropping tank if pressure looks bad. Maybe thats my code 95.....

 

[KingpinVinny]

My did the same, ended up being a cracked vacuum line. Would have never found it if I didnt do this: Easiest way to see if you have a vacuum leak it to get a can or starting fluid with the lil straw. Spray in increments around your entire engine, mostly around your intake and vacuum lines, throttle body, MAF. If your idle rises when you spray a certain area, there is a vacuum leak in that area. Thats were you should start your search. I spent weeks looking and found nothing, my neighbor came over with a can of starting fluid and found the leak in 2 minutes.