98 Ranger 3.0L Loss of Throttle Issue

[bradberry]

Here is one for the "I am stumped" book. I have a 98 Ranger 4WD XLT with 3.0L and about 178k miles. Has always run great. I normally use it for dump runs and personal errands. Both of my sons have driven it more than I and while their rigs are under any type of repair. This truck has always been dependable.

My son was heading over to our house and called me and told me that the truck just lost throttle and he was on the side of the road. Funny thing is , if he shut the truck off and restarted it, it would run just fine for a while, then POW, loss of throttle.

Checked for codes and it had one on there for a MASS Air Issue. (I did not read it my son did). So we figured we had a vacuum leak. We found the Vapor Canister Vent Solenoid was pulled or fell out. I went online to Rock Auto and bought, the Vapor Canister Vent Solenoid, EGR Pressure Feedback (DPFE) Sensor, EGR Pressure Feedback (DPFE) Hoses, Idle Air Control (IAC) Valve and the Throttle Position Sensor (TPS).

Yesterday I replaced all items except for the Throttle Position Sensor (TPS). Boy that one is a SOB to get at to remove. Ran out of time, so I left the Throttle Position Sensor (TPS) for a Wednesday replacement.

After I replaced all but the Throttle Position Sensor (TPS), I took it out for a spin. Wholly CRAP batman, the truck runs like a raped ape. No holding this thing back (for a 3.0L anyway). On the way back to my sons, I was running at about 60 mph when I had to slow down into a 40 mph zone. As soon as I exited the slower zone I started to throttled up to full speed and POW no throttle, idle was fine but no throttle. So I, while cruising at 45 mph, put the truck into neutral (while coasting), shut the engine off and restarted the truck and got full throttle all the way home.

Once I got home I tried to pull codes and nothing showed up. I have read, read and read several different blogs and I am leaning towards replacing the TPS, MAF, and the Crank Position Sensor. Any other thoughts or suggestions? I am at a LOSS! As of now this is the only vehicle my son has to drive. Someone slammed into his 95 Toyota and totaled it for him. He is currently looking for a new rig, so he has borrowed mine. Our local FORD shop is like most dealer shops, they love to stick it to you and most of the time THEY ARE WRONG!

 

[RonD]

Welcome to TRS

None of what you replaced fits the symptoms, except for the EGR valve leaking causing issues but that would effect lower RPMs more.

Wouldn't be TPS either.
CKP(crank position) sensor either works or doesn't and if it doesn't engine won't start or run.

Computer only controls air/fuel mix, out side of the "rev limiter" it can not prevent engine from reving up, it could be limiting fuel but that would causing lean pinging or "running out of gas" feeling at higher RPM, not mentioned, rev limiter is about 3,000rpms and only kicks in when in park/neutral and speedo is at 0MPH, rev limiter cuts fuel, and you know it because it sounds like it is running out of gas, not mentioned in symptoms.
A gas engine's RPM is limited by the air it can pull in, that is how the throttle plate works, it limits air flow into the engine, if opened all the way RPMs will increase rapidly, engine may start misfiring and pinging if fuel supply is low, but computer can't stop RPM increase, TPS just monitors throttle position it can't control it.
MAF is also just a monitor, computer knows it is in a 3.0l engine, so already knows approx. how much fuel to add at specific RPMs, a bad MAF could cause stumbling, or bogging, same with bad TPS, but limited RPMs wouldn't be a symptom.

"No throttle" is a bit subjective.
If engine doesn't want to rev up to higher RPMs then there are two reasons that come to mind.
Air can't get in, OR air can't get out.

Assuming the air intake system has been checked for blockage, no critters, plastic bags or nests blocking air flow, then air out would be next place to check, the exhaust system, remember the old potato up the tail pipe trick, well "potatoes" grow inside Cats and mufflers, lol.

An exhaust system blockage does fit symptoms, pieces have broken off inside and are opening and closing off exhaust pathways, once opened engine runs great but when exhaust slows a piece moves and RPMs are limited because air can't get out so new air can't get in.
Shutting off engine, no exhaust flow, allows piece to move and you get open pathway again.
I would bang on Cats and Mufflers and listen for rattling, you can check for exhaust back pressure with vacuum gauge on intake.
Or have your hand over tail pipe while someone revs the engine, you can often tell that exhaust out pressure gets to a certain point and then doesn't change even as RPMs increase.

Since a vehicle computer is just using an IF>THEN logic the exact code numbers it uses are very important, if a sensor is mentioned in a definition it usually means that sensor is working or the problem wouldn't have been detected, so grain of salt is needed when looking up codes and what they mean, the computers used are very basic.
When you look at a code number look at all the code numbers near that number, because the code numbers the computer did NOT use can tell you alot about the number it did use.

There is a list of Ford OBDII codes here: http://www.therangerstation.com/tech_library/OBD-II_codes.shtml

Most have never looked at the codes in this manor, as a list, they tend to just google the one code number; when seen in list form you can see how many codes refer to one sensor in the description, so the code chosen by the computer from that list is important, but so are the codes it didn't chose.

 

[bradberry]

Thank you and I will try to have my son look at this tonight. I/We were going on the assumption of vacuum leak, fuel starvation issue. I have a new fuel filter and will try to replace that also.
My son stated that when the truck pulled this throttle loss on him, he would pull it over to the side of the road, then give it throttle and the motor wanted to chug.stall or die. Which is not what it did to me after replacing the parts I had previously listed.

 

[bradberry]

Update...tonight i took the truck out for a test drive and for about 25 mins it ran great. As soon as i turned the corner to head back to my sons...bamm. idle dropped to 1k and everytime tried to throttle up, the truck chugged and acted like it was going to flood out and die. Shut off the truck and boom....ran just fine until i got to my sons driveway. Then it acted like it did not want to shift into the next gear, then boom, it repeated the same idle then bogging down issue. It feels like if i were to floor it, it would choke and die. It was kind of like my sons f350 6.7d and we found it was a fuel sensor.

Parked it in the shop. Could not get the cat or the muffler to rattle like something was loose inside. Placed a towel over the exhaust pipe while the truck was running and it seemed like it wanted to blow the towel off. Check for codes and all i got was a p1000. Apparently i did not run the truck long enough.

 

[RonD]

P1000 can be ignored, and it can take several drive cycles to clear.

Pressing throttle pedal down on a fuel injected engine doesn't give the engine gas like it did with a carb.
It gives engine more air so the vacuum in the intake, that keeps RPMs low, drops and engine can rev up.
Computer does add gas as RPMs increase or air flow going passed the MAF increases.
And the computer also compares RPMs, MAF sensor data and TPS data, to confirm all 3 match each other.
Computer "knows" how much air should be flowing in on a 3 LITER engine at specific RPMs, a 3 liter engine will suck in 3 liters of air every 2 RPM if throttle is wide open, less as throttle is closed and vacuum builds up.
So computer uses the MAF and TPS data to fine tune air/fuel mix, but it already know approx. mix that will be needed based on RPM alone.
All this is Air Flow data, not fuel, and since there are no codes saying RPMs, MAF data or TPS data do not "match", it could be fuel pressure is dropping but I would expect Lean codes to popup, at that time.

You said engine "idle" dropped down to 1,000rpms, after a 25min drive that is way to high.
And also said it acted like it was flooding out, why did you pick flooding out vs "starving out"(lack of fuel), could you smell gas fumes?

 

[bradberry]

Flooding may not have been the correct term. Every time I would press the throttle it would cough and jug. No gas smell at all. I believe I now understand that really we are not giving it fuel when we apply the pedal, we are actually giving it more air. After the 25 min drive and when this happened the truck seemed to only allow the truck to idle. Idle but not allow me to throttle up. Shut down the truck and after a restart all would be fine for a short time then the action would repeat itself. So, I repeat the action and so on. I am really leaning towards the MAF. Tonight I will replace the fuel filter, needs it anyway I am sure, and also the MAF. I have the TPS but have yet to replace it due to the fact that I will have to unbolt the throttle body so my big hands can have their way with the TPS. What else can I be missing? Like I stated earlier, it runs GREAT until it seems to warm up, then BAM! I checked all the items like you stated earlier and did not find a rattle or any sign that the CAT was an issue.

 

[TxGasRacer]

http://easyautodiagnostics.com/ford/4.9L-5.0L-5.8L/maf-sensor-tests-1 http://easyautodiagnostics.com/ford/3.0L-3.8L/how-to-test-the-tps-1 http://troubleshootmyvehicle.com/ford/3.0L-3.8L/how-to-test-the-crank-sensor-1

 

[RonD]

MAF sensor doesn't fit since the computer would default to TPS or RPM, and would set a code saying MAF sensor didn't match TPS and/or RPM.
Or it was a TPS issue then same thing, a code that says TPS and MAF don't match.

TPS is easy to test with volt meter.

Lack of codes is just as important as having codes, you could even be looking at a computer issue, not there yet but can't be discounted.

If fuel pump was shutting off then engine would completely stall out within a few seconds, but failing pump could lower pressure or if fuel pump relay was toggling power to pump, it could do the same.
Shut off the key and turning it back on reboots computer and fuel pump relay.


Going around a corner and having an issue could mean the fuel pickup tube in the tank has a crack or leak, and air was sucked in.
Have you noticed that fuel level in the tank is related at all?

 

[jeremysdad]

Stopping this.

OP, change the parts you already bought, then report back.

It's probably the "lays down around a corner' phenomenon, RonD....but...

RonD nailed it. Leaking fuel intake tube. Replace fuel pump/sending unit (AS A COMBO, NOT JUST FUEL PUMP), problem solved.

Makes sense. Good call.

 

[bradberry]

Update...yet again...

OK i made some progress or maybe not. Tonight I replaced the fuel filter and for the heck of it, the MAF.

I found out my OTC Code checker does quite a bit more than I thought. It is a model 3111 and is quite the little unit. I have uploaded the data I captured in a PDF format. Maybe this will help since I have no clue as to what it is telling me. Sorry for the lack of knowledge this is not my area of expertise. I am mechanically inclined but this trouble shooting $hit kills me. There lots of tests to run and I took screen shots with my phone on the tests. The truck has a high idle but you will see that in the report.

The fuel pump makes since but the issue rears its ugly head even when I do not turn a corner. No time to drive the rig tonite....just barely time to work on it.

 

[jeremysdad]

How much gas is in it? Watery gas? Eating out your inlet through electrolysis?

Literally out of ideas.

Maybe ASDM or some other OBDII knowledgeable human will step in and fix it.

Subscribed, and best of luck!

 

[bradberry]

Fuel

it is full. Just filled it up while it was performing its wonders on my nerves.

 

[RonD]

Data shows MAF is most likely OK, .80lb/min = 6 grams per second, and at 1,000rpms that would be about right, and "about" is what MAF sensor does, that's why O2 sensors are needed.

Change your scanner from lb/min to gm/sec(grams per second) for MAF data
At 650-700rpm MAF should read approx. engine displacement
5.0l would be 5-6gm/sec
4.0l 4-5gm/sec
3.0l 3-4gm/sec

Engine temp was at 185degF which is fully warmed up, was that correct, was engine fully warmed up?

If so then there is a problem with the idle that needs to be address first.
When engine is warmed unplug IAC Valve, it will close and idle should drop down to 500, or engine may even stall, either means no vacuum leak and the high idle is either being caused by the IAC Valve or the computer.

If idle stays high it could also be that someone has adjusted the "anti-dieseling screw" on the throttle linkage, this "looks like" an idle screw, it isn't.
Whole point of having computer controlled idle is so it can set idle within a range from 500 to 2,000 using the IAC valve, if someone has manually opened throttle plate more(the screw) then IAC valve can't set a lower idle.
The anti-dieseling screw server 2 purposes, one is to prevent "run on" or "dieseling" after engine is shut off, fuel injection pretty much eliminated this because air flow can't suck in fuel from an injector like it did from a carb, so no fuel to keep hot engine "running on" after spark is cut, but it is possible with a leaky injector.
2nd purpose is to adjust TPS throttle close voltage, .69-.99volts

If you think someone has adjusted this screw then you need to reset it, warm engine, IAC unplugged, idle is above 500rpm spec.
Turn screw until idle is down to approx. 500 rpm, below 600.
Shut off engine
Plug IAC valve back in, restart engine.
See if warm engine idle is now down in the 700 range, for automatic in Park, 600-650rpm for manual trans.
Idle may wander for a bit as computer relearns settings, that is a good sign

 

[bradberry]

I will try that. I would have to say that someone has adjusted the it. I bought it in 2005 and it has always Idle High. I just replaced the IAC, so that part should be good. The engine was warmed up. It had been idling for about 20 mins. Is this idle screw on the throttle body itself? Also what should the fuel pressure be on this rig? I am going to check this before, during and after it has one of its episodes. I really do thank you for this assistance.

 

[RonD]

It is on the throttle linkage, where throttle cable and cruise cable connect.
Also with engine off open throttle and disconnect both throttle and cruise cables.
Then start engine and see if idle drops down, bad cable can hold throttle open, but it tends to be intermittent.

1998 was the first year of Returnless Fuel system, so fuel pressure should be 65psi, 60-70psi.
No lower than 50psi with engine off, and it should hold above that for a few months, not minutes, hours or days, months