Got a tough one for you all...
Truck - 1998 Ford Ranger XLT with the 4.0 V6, automatic and 4x4.
Problem - Problem started out as a hesitation at a constant speed... I would be going along at around 45 and the truck would start to buck and miss, if you put it to the floor it would continue to buck and sputter and hesitate then it would drop down a gear and take off and when I stopped it would idle really rough but after a while it would go away. It didn't do it all the time though... Now the truck constantly lacks power down low until around 3,000 RPM then it starts to pick of power but it surges a little never any codes however. Originally, since I didn't have a scanner to hook up, I thought it was the TP sensor since the tranny wouldn't downshift so I replaced it and... Nothing. Then I read a service bullitin that said the mass air meter could cause it and Ford recommended cleaning it and dis-connecting the battery... Seemed to fix it for a while but started doing it again. This time I connected a scanner and noticed the LT fuel trims were way high like the engine was running lean... Disconnected the EGR vacuum line, and unless the valve is leaking by, there is no problem. Because of the fuel trims I replaced the Mass air meter (Not with the Ford part because it was like $300 and I just don't have that much money) Fuel trims are still over + 15%. The other problem... The transmission has a really soft shift into 2nd (Which disappears when you disconnect the Mass air meter)
New parts - The spark plugs are bosch +4 that were installed about 30,000 miles ago and the wires are Ford units replaced at the same time... The IAC went bad last year so thats new... The DPFE and lines are new becuse it had a code for low flow and I found the lines were split and the DPFE nipple was busted. Mass air sensor is new (as stated above) as is the IAT sensor and TP sensor.
My thoughts - Haven't been able to look at the o2 sensor voltages (Hard to do with a laptop on the dash while driving) maybe the sensors are bad, or possible a bad ECT sensor or possible the plugs are worn and causing a misfire and becuase of the miss fire a false lean condition.
Sorry this is so long just want to make sure all the info is there... Any help is greatly appreciated.
- Phil

 

Running lean gets me thinking that you have a vacuum or some sort of manifold leak around the engine.

Too little fuel in the mix (to much air, really) until the revs pick up would get me to think that and since the fuel is in supply at higher revs, I doubt the fuel pump and filter are in bad shape--that should have set a code anyway.


"lean O2 sensor readings" without the quotes in a google search should help. I will let you read thruough what you wish.

Good luck, btw...hope it doesn't get too painful from here.

 

Agree with Alfred.

 

Vacuum leak is the first guess. The 4.0l's have a habit of leaking around the intake manifold, check to see if the bolts are tight, you may have to replace the gasket to be sure. A vacuum guage reading sure would be helpfull.
Dave

 

I agree with a vacuum or air leak being something to seriously consider. I'm sure you know the drill about checking hoses and connections, etc. You might even try the propane torch trick to help you try and locate a leak.

Have you been able to check the FP? It should be @ 64 +/- 8 psi for both KOEO and KOER (idle). How about the fuel filter, has it been changed recently?

Personally I would dump the Bosch plugs, they can cause problems in Ford DIS/EDIS systems. Stick with Motorcraft. Speaking of which, have you pulled any of them and looked them over? Maybe there's a story to be told there.

Another thing you might consider too is the wiring harness underneath the cab near where the fuel filter assembly is. It can chafe against the undercarriage and cause problems:

https://www.ford-trucks.com/forums/s...d.php?t=315257

Good luck, keep us posted.

 

Shure sounds like you might have a unmetered intake side air/vacuum leak.

So, as has been suggested, you need to eliminate bad vacuum lines, PCV hoses or valve, lower intake manafold loose bolts/suckd in gasket possibilities & keep us posted on your progress.

Most auto parts stores will scan the computer at no cost, so maybe a opinion scan by them could be helpful, if they uncover a more specific trouble code.

Post ALL the codes you find. pawpaw

 

Pretty much all the same symptoms I'm seeing on my '99 ranger. Same engine - tranny combo

Looks like I'll be checking a lot of the same places...

>>> Rockledge, Is the propane torch trick the same as looking for vacuum leaks with gumout on carburetors....???

Will keep you posted.

Greg

 

Yes, same principle.

BTW, welcome to FTE.

 

Is it overhead cam (SOHC) or overhead valve(OHV)?

If it's SOHC i would replace the intake gaskets (actually a bunch of rubber-band looking o-ring type things)

If seen them leaking so bad the truck wouldn't even hardly run cold, and no codes were set.

Good luck!

 

My 99 b-4000, Auto, 4x4, had the same problem between 45-50 mph with a little load on engine. She would buck and miss but it didn't all the time. Listen to Rockledge dump the bosch plugs, this happen to mine on two seperate occasions the set of plugs autolite reg. and second were Bosch Plats. For some reason the plugs wore prematurely they had less than 20k but looked like 100k was on them. Put on the Autolite double plat. they are still runnin smoove today.

 

I have a '98 Ranger XLT SuperCab and I'm experiencing many of the same problems you've listed. It's a 3.0 liter V-6, 2 wheel drive.

It began hesitating and jumping a couple of weeks ago when I would start up any hills. It wasn't bad but it was noticeable. It has progressively gotten worse until now it occurs all the time. Driving into work this morning, the check engine light came on and remained lit.

It's to the point that it is nearly undrivable. I am a greenhorn when it comes to vehicle repairs so I am unfamiliar with many of the suggestions listed to date. I have looked at the vacuum lines but they all seem okay.

I can make general repairs but I do not have the equipment nor expertise to get very technical. Is there anything you can recommend that a novice may be able to understand and repair?

Thanks in advance.

 

Welcome to FTE!

What you need to do first is go to your local Autozone or similar parts store and have them pull the code(s) from the computer on your truck. Most of these places will do it for free, or charge a very small fee. The fact that the CEL is on means that there is at least one trouble code stored in memory. Make sure you write the code number(s) down so you don't forget them. And don't purchase anything at the parts store until you post the code(s) here and get some feedback.

 

Thanks Rock. Will do.

 

Some things I've tried so far since my last post... all to no avail...

1. Changed back to autolite 2x platinum plugs
2. Replaced fuel filter
3. Cleaned throttle body (it needed it, and only made the idle much smooooother....)
4. Checked the underside for the chaffed harness (looked good)
5. Tried checking for vacuum leaks w/ propane but the fan moves so much air it's hard to know if the propane got where it was suppose to go...
6. On a dark moon-less night tried spritzing the ignition module with water looking for any breakdown... nothing...

Still plugging away...