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3.0 Intermittent Stumble then Quit


97Ranger3.0

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Hey guys,

About a month ago, out of nowhere when I started my truck (97 3.0 Ranger) it started stumbling/misfiring and then stalled out on me about 30 seconds after running. When I tried to start it back up, it would start after longer than normal cranking and run for a very short period of time, misfiring and stumbling until it would stall out. After a few tries then it would not start at all. I scanned to see if it set any check engine lights, and there were no new ones. (I've had a P1443 (evap) and a P0175 (running rich) for a while that I haven't been able to fix yet but I haven't had any issues for as long as I've had those codes until now). I tried several times spraying starting fluid into the intake to determine if it was a fuel issue, but it made zero difference. Also, I replaced the fuel pump about 30k miles ago so it shouldn't be failing. After letting the truck sit for a few hours, I tried one more time and after a rough start, it quickly smoothed out and acted like nothing had happened. I drove it for another month with no problems, but then again this happened to me.

However, this time it acted a little different. It did stumble and die out, but it took way longer for it to happen and I was able to keep it running for probably 30 seconds misfiring and stumbling before it just finally would quit. I could keep getting it to start up and run normal for a short period of time, then it would repeat the stumbling and dying process. Again though, there were no new check engine lights. I really thought that having it misfiring and running so bad for an extended period of time should have at least thrown a misfire code, but to my surprise, still no new codes.

It's hard to diagnose this issue because it is intermittent, but I have a few suspicions. I'm guessing it's possibly the camshaft or crankshaft position sensor failing, or possibly the coil pack starting to fail. But, the fact that it's not throwing a misfire code after running like that for a long period of time is making me concerned that the ECU could be on its way out. What I'm wondering is, does anyone have information on how I can test the cam & crank sensors, the coil pack and the ECU? I haven't been able to find any voltage and/or resistance values for testing those sensors and circuits in my searches. Or, does anyone have any insight into what else could be causing the issue?

I know I should fix the other two codes that I have as well, but I don't believe either of those are causing this issue. I did try to fix the P1443 code, but didn't have any luck after basically going through the entire EVAP system. I also did have a P0172 code a long time ago that I was able to fix by replacing the intake manifold gaskets, so I'm surprised I now have a P0175 code for running rich on the other bank, but haven't been able to diagnose the issue yet.
 


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97Ranger3.0

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I also should give some background on the truck and what I've done to it so far. When I first got the truck, it had trouble starting. It would crank for a long time, but eventually start then run fine. I determined this was a fuel pressure issue, and it turned out to be a leaky injector. After replacing the injectors as well as the pump & fuel filter just to ensure there were no problems in the fuel system, it was all fixed and would start and run fine. I then did a lot of basic tune up stuff like the spark plugs, wires, and coil pack. I also replaced the camshaft synchronizer/sensor assembly since I know they are an issue with these motors. I've only put probably 30k-35k miles on the truck since doing all of this work.
 

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Doesnt the 97 3.0 still use a distributor?

If not i would definatly think it was the crank sensor, problem is with it cutting out randomly i dont know if a test would really be reliable.
 

97Ranger3.0

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Doesnt the 97 3.0 still use a distributor?

If not i would definatly think it was the crank sensor, problem is with it cutting out randomly i dont know if a test would really be reliable.
Nope, I think 94 was the last year of distributors for the 3.0. I've got a coil pack instead. Yeah that's true, but what I was thinking was if I had the testing info on hand I could test the sensor (or sensors) the next time this issue happens to me. I have a multimeter in my tool box at all times, so the next time this issue arises I can test it right then no matter where I am.
 

97Ranger3.0

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Well, I believe I solved the P0175 code. I swapped my fuel filter & air filter out per the maintenance schedule guide that came with my truck. And that code went away, and my long term fuel trims are now much lower. They were about 20-25% before (hence the code) and now they're at about 5%. If I remember correctly, I used a K&N fuel filter when I first replaced it a few years back. My theory is that because it's a high flow filter it was getting too much fuel at the rail, but I would think the fuel pressure regulator should be able to take care of that? But either way, I'm glad that resolved itself. I am still left with my P1443 evap emissions code which I am going to try and diagnose soon, but don't think it's related to this intermittent sumble/quit that I'm experiencing.

I've also gotten to thinking, could this possibly be a failing MAF sensor? I thought the ECU pretty much only used the MAF during open loop before the o2 sensors are hot, so I ruled it out before. But if it does rely on the MAF sensor more than that, I could see it as a possibility. The truck has done this to me both on a hot start and a cold start. But, what I've realized is that this stumble/quit scenario has only happened to me on starts within probably a minute of running which made me now suspect the MAF. Any thoughts/input would be appreciated. I still would like some info on testing these suspect sensors (CKP, CMP, MAF).
 

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CKP(crank sensor) is the big Kahuna of sensors, only sensor that can cause a no start, it either works or doesn't, so not your problem in a 1997

MAF sensor is actually used to WEIGH the incoming air, so it is used all the time, open or closed loop
The computer already "knows" its running a 3 LITER engine, so it "knows" exactly how much air is coming in at any RPM, its just math, what it doesn't know is how much that air weighs

Gasoline's air fuel ratio is 14.7 to 1, this is a WEIGHT ratio
14.7 pounds of air to 1 pound of gasoline, or 14.7 grams of air to 1 gram of gasoline
So the weight of the air is extremely important
Gasoline's weight doesn't change that much

Air's weight does, "hot air rises"......because its lighter than colder air, so air temp is important, there is also an air temp sensor, IAT or ACT sensor
Air at 3,000ft elevation weighs less than air at sea level
So MAF sensor is import for computers baseline calculation of how much gasoline to add to the engine to get a good burn.
Base calculation is STFT 0
-10 to +10 STFT will be seen in normal driving
LTFT is a memory fuel trim, so computer doesn't have to relearn engine system changes every time it starts up
i.e. lower fuel pressure, lower compression, smaller air leaks, normal wear and tear over the years

Yes, a dirty MAF sensor can cause bogging or stumbling, but easy to clean these
 

97Ranger3.0

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Thank you RonD for the info. You were right about the MAF being bad. Unfortunately though, that's not the complete issue it seems. Here's an update on what's been going on.

Okay, so this issue almost seemed to disappear completely for a few months. After the last time I had posted in April, I went all the way until I think November before the truck started doing this again. One day I was sitting in a parking lot idling when it started stumbling again and slowly quit. It would start back up sometimes and run for a bit, then stall again. I ended up having to get a tow home because I was far away and it was getting late. But of course, once we got back, the truck started up and ran like nothing happened. The truck continued to act up, sometimes stalling out occasionally but after that first reoccurrence, thankfully it would at least start back up and run fine again.

At this point, I was living in Houston, TX about to graduate school in December, and had to drive back home to MA for a couple weeks for the holidays in between the programs I'm in, and then move again to SC. I was going to school full time and working full time, so I really didn't have time to try and properly diagnose this or deal with it at all really. So, I fired the parts cannon at it unfortunately. I know, I know. Not ideal but I was stressing at the time having only a month to go before I had to drive thousands of miles across the country with all my stuff. I started with parts I felt were the most likely culprit and then kept replacing parts until it seemed to stop. I ended up replacing the crank sensor, MAF, TPS, coil pack, fuel pump and maybe a few other small things I'm forgetting now.

What I ended up finding out were a few things. Number one, my running rich code came back at some point. I started driving around with my scan tool hooked up while I drove to monitor stuff when things got funky. One thing I noticed was that my MAF readings were very high, and sometimes the number wouldn't increase as I was driving. Which is why I ended up replacing the MAF after some of the other things I replaced. This fixed the rich code, and did improve some of the stalling issues I have, but didn't fix it completely. The other thing I noticed was sometimes at higher RPM, the truck would start to feel like it wasn't getting enough fuel and would start bucking hard would either stall out or just die while I was in gear and moving. I would flick the key off and back on again and the truck would continue to run fine. I watched the fuel trims go crazy when this would happen, and it looked to me like the fuel pump was dying because when this would happen the fuel trims would act like it was running way lean and would spike to like +30% and then once I got it running normally again, they would settle back down. So I replaced the fuel pump. This seemed to solve all my issues... for a while. I'm confident that the MAF and fuel pump were going bad because of what I saw with my scan tool and how much it improved after replacing those two parts. The rest of the parts probably didn't need to be replaced but I replaced them all with Motorcraft or NAPA parts so I at least can feel more confident in them, as some of those I had replaced previously with cheaper aftermarket parts. That's how I'm justifying firing the parts cannon at it :icon_rofl:

Anyway, back to the issue. The truck doesn't stall out on me anymore, but it's not 100% right. The issue I have now is that sometimes when I start the truck up, (cold or hot start doesn't matter), it'll run fine and idle normal and everything but if I try to give it gas, the RPM won't increase and the truck will sound like it's misfiring and want to die out the more gas I give it. If I let off, it idles fine again. But here's the weirdest part to me. When this happens, I flick the key off and back on again quickly, and the problem goes away. I guess I'll have to start driving with my scanner hooked up and see if I still see anything funky going on.
 

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You have to think in terms of fuel injection
There is no "gas pedal", its an "air pedal", carbs actually squirted gasoline into engine when you press pedal down, that doesn't happen with EFI

When you press the pedal down with fuel injection more air comes in, that's all, and THEN after that the computer should add more fuel after it calculates the air flow

Engine WILL ping/knock if it starts to get Lean fuel mix

If the "new" fuel pump was a 3rd party brand, not Motorcraft, then it is very common for those to fail, but within the first 12 months so you can get a new one under warranty, just a pain to swap it out
So yes check fuel trims again

Sensors don't "reboot", they have no software
Modules do "reboot" they do have software
1997 only has 1 engine control module, the PCM(computer), it runs spark and fuel
Key off and on reboots PCMs factory software, so as a "fix" that points to PCM issue
But your PCM seems to communicate with OBD2 reader OK, which is a good sign its working OK, but not definitive
There is no "test" for PCMs

Electric motors, like a fuel pump, can also "reset" with key off and on, its not a software thing is an electric motor thing, lol
i.e. starter motors do this

Check the ECT sensor voltage, temp, with OBD2 reader, see if its "sane", warms up and then stays warm, thats a test of the PCMs 5volt internal power supply for the ECT and other sensors
 

97Ranger3.0

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You have to think in terms of fuel injection
There is no "gas pedal", its an "air pedal", carbs actually squirted gasoline into engine when you press pedal down, that doesn't happen with EFI

When you press the pedal down with fuel injection more air comes in, that's all, and THEN after that the computer should add more fuel after it calculates the air flow

Engine WILL ping/knock if it starts to get Lean fuel mix

If the "new" fuel pump was a 3rd party brand, not Motorcraft, then it is very common for those to fail, but within the first 12 months so you can get a new one under warranty, just a pain to swap it out
So yes check fuel trims again

Sensors don't "reboot", they have no software
Modules do "reboot" they do have software
1997 only has 1 engine control module, the PCM(computer), it runs spark and fuel
Key off and on reboots PCMs factory software, so as a "fix" that points to PCM issue
But your PCM seems to communicate with OBD2 reader OK, which is a good sign its working OK, but not definitive
There is no "test" for PCMs

Electric motors, like a fuel pump, can also "reset" with key off and on, its not a software thing is an electric motor thing, lol
i.e. starter motors do this

Check the ECT sensor voltage, temp, with OBD2 reader, see if its "sane", warms up and then stays warm, thats a test of the PCMs 5volt internal power supply for the ECT and other sensors
Right, I get that. So to me, that symptom sounds like a MAF issue to me. When I open the throttle and the truck stumbles out, that to me sounds like the MAF isn't adjusting to the increase in airflow, so the PCM doesn't adjust fueling. That's just a guess, which is why I'm going to start driving with my scanner hooked up again to monitor that. However, it doesn't ping and knock like it's running lean when this happens. It sounds more like a misfire that gets worse the more I open the throttle. But, as you said sensors don't really reboot like a computer does. So that doesn't exactly line up, but it's somewhere to start looking when this happens again. Which thankfully isn't super frequent.

Anyway, I forgot to mention in my last post I also bought a spare used PCM for this truck. If I remember correctly, after swapping the MAF & fuel pump and no longer having the stalling issue, I had this weird issue I described in my last post start to happen sometimes instead. So, running out of ideas and also the fact that it would seem to fix itself after "rebooting" I suspected the PCM, although I know it's rare that they fail. Anyway, I did put in a used PCM in the truck and it still does this. To verify this though, I just swapped the original PCM back in the truck earlier today, and I will have to see if this issue comes up at some point again. If it does, I highly doubt I have two bad PCM's, both of which communicate with a scan tool and both with the same problem lol. That's why I find this whole thing so strange.

Whenever this happens again I will have to try and get a video of it and post it here, that might help to see/hear what I'm talking about.
 

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Actually the MAF sensor is for air WEIGHT not strictly air flow
The computer knows(is programmed) for a 3 LITER engine in this case, so at any RPM is already knows exactly how much air is coming in, its just math
Gasoline engines use an air/fuel mix of 14.7/1, this is a WEIGHT ratio
14.7 Pounds of air to 1 Pound of gasoline
OR
14.7 grams of air to 1 gram of gasoline
This is why Fuel injectors are rated in lbs(pounds) of gasoline per hour

So the air temp sensor and MAF sensor are both there so computer knows approx. WEIGHT of the incoming air
Cold air is heavier, thats why "hot air rises"
Cold air intakes can increase power because heavier air means more gasoline can be added so more power released on each stroke of engine
And at 5,000ft elevation air is lighter even if temp is the same
MAF sensors main job is to report air weight, but it only samples about 10% of the air so small errors cause bigger problems

The TPS(throttle sensor) is there to give the computer a "heads up" sooner than MAF sensor could, that's it's main purpose, that and WOT(wide open throttle) at WOT computer will ignore O2 sensors and pump in rich fuel mix for best power
So a hesitation on throttle position change could be TPS issue
But can also be spark advance issue, or fuel pressure
If you are able to see TPS data then you should see 17-19% with throttle closed, and 91-95% at WOT
TPS is a 5volt sensor, should be just below 1volt throttle closed which is just under 20% of 5volts
And 4.5volts when Wide open, so above 90%
 
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97Ranger3.0

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I believe the problem is with the MAF or it's circuit. When I was driving today, the truck did the same thing twice to me where it's idling, and I open the throttle and it starts bogging down and missing until I let off. I was just sitting in a parking lot both times it happened luckily, so I hooked up my scan tool and tried to see what was going on. The only abnormal thing I caught both times was that when this is happening, the MAF reading will be stuck on some random reading (not even what it should be at idle) and not fluctuating at all when I open the throttle. Both times, I flicked the key off and back on quick and the problem disappears. The MAF starts showing normal readings and adjusting with the engine speed. I wish I thought to take a video of it while it was happening and also to show the MAF readings. Next time this happens I will make sure to do that.

I have my doubts that its the sensor itself, but you never know I guess. I just doubt it because the problem I'm having now is still similar to my original problem, just that now I can get it to fix itself and keep running easily instead of it completely dying on me. Also, after I had swapped out my original MAF for the new one, the one I got was doing something similar. Sometimes when I was driving, the truck would bog down and struggle to rev, similar to my issue now. And when I drove around while monitoring my scan tool, I noticed that sometimes the MAF reading would just get stuck at some random number and not change with engine speed. A lot like what I'm having happen now, although currently it really only seems to happen on startup, not while I'm driving. But anyway, because of this, I warrantied out that MAF and didn't have this problem for a while with this one. Anyway, my point is, I find it unlikely I've had 3 MAF's with basically the same exact problem. But they were aftermarket Delphi brand, not Motorcraft.

Anyways, RonD, I have looked at the TPS data on my scan tool and it's pretty much spot on what you said. It's around 17% at idle and fluctuates with the throttle position changes quickly. I haven't checked what it's at when at WOT but it seems to be consistent so I don't suspect it being problematic. I can also back probe the sensor to verify the voltage you mentioned, but at this point I really think there's a problem with the MAF.

So, I'm wondering what you would suggest I do next? How can I verify it's the MAF itself, or the wiring from the MAF to the ECU?
 

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How can I verify it's the MAF itself, or the wiring from the MAF to the ECU?
Until RonD returns, and probably with better advice than I can offer :), I'll jump in with a suggestion to read the "Testing" part of an article from this very site: Mass Air Flow Sensor Removal, Cleaning & Installation

Also, in case it helps, here's a year-old thread about MAF diagnosis (from another site) that you might find interesting, from a person (with unknown vehicle) whose problem sounds a lot like yours. Spoiler Alert: This person tapped on the flat-lining sensor and it started working, helping to confirm a bad sensor as opposed to bad wiring. But check out the interesting graph in that thread.

Good luck!
 

97Ranger3.0

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Caught it this morning on my way to class. It was raining hard so it's a little hard to hear. But you can still see and hear the truck stumbling out when I open the throttle. I do that a couple times before showing my scan tool. I know the fuel trims look a little whack, but I've noticed that when this happens they do that (which makes sense to me) and then once I get it working right again, they normalize again after a short drive.


Hopefully this helps show what I've been saying. You can see that the MAF reading was stuck on .052 lb/min even when I was giving it throttle. Then when I shut it off and restarted it, the MAF reading would fluctuate with engine speed again, and the problem is gone. I'm hoping that the next time this happens it'll happen when I can actually take the time to try and diagnose it using the guide that Orca shared.
 

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MAF data freezing would be more likely to be a computer issue than MAF issue, IMO
 

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MAF data freezing would be more likely to be a computer issue than MAF issue, IMO
Yeah, this situation is pretty strange. In my mind, I would agree with you, especially seeing how the issue goes away after being "reset". Just seems like a strange PCM issue. But, I have my original PCM and a spare used PCM that both function properly but both have this exact same issue. So, the chances are slim that I somehow have 2 bad PCM's with the same condition. When I get a chance to test the truck while it's acting up, we'll hopefully find out for sure what the problem is.
 


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