I know this has been beaten to death, but I still keep getting 171, 174 codes. 1998 4.0 4x4 auto Ranger. I have replaced fuel filter took out K&n and put in new paper air filter, new Ford pcv, Tried new mass air,[took it back after codes came back] replaced upper plenum and fuel rail gaskets. cleaned mass air, looked for leaks with starter fluid thought it inreased idle when spraying around press. diff. hoses, repaced press diff hoses......The cel comes back on every time between 8 and 126 miles, drivin me nuts. I am almost ready to put a picture over the cel for peace of mind. The truck runs great , but maybe idles a little rough in drive.I havent replaced plugs or wires or oxy sensors yet, but that may be next. What scan tool are you guys using that gives you more in depth info on whats going on? the Autozone one just runs codes. I just remembered I also checked fuel pressure, I thought it ewas high but the tool book said ok, it was68 lbs. The thing is , that it didnt change when I dicod the vacuum line to the regulater, that sounds to me like a bad regulater? I also initially suspected the fuel pump because my fuel gauge is off by 1/4 tank, and I understand the sender is on the pump. Help! Tim

 

68 PSI is fine for your '98 which has a "returnless" fuel system. And that wasn't the regulator that you pulled the hose off of. Check out: https://www.ford-trucks.com/forums/8...-wont-run.html

Regarding those lean codes, I'm kind of at a loss. It sounds like you've done everything conceivable to find the source of the problem. I suppose it's possible that a lower intake gasket leak could be allowing unmetered air in, but usually lower intake failures on the 4.0L OHV involve coolant leaks into the cylinders and misfires.

Clogged fuel injectors might also cause lean codes, but what are the chances of at least two injectors being clogged, one on each bank? I'd say slim. And you've probably already run a fuel system cleaner through.

Another thing you can try is another "sniff test", this time using an unlit propane torch to poke around all the gasket areas and hoses (the entire lengths, not just where they connect up).

 

Yeah, i.ve run a couple lucas treatments thru it, and will keep doing that. The injectors were very dirty when I looked at them, I cleaned them a bit with a paper towel. I too wondered if it was lower intake but didnt want to go to that extreme if I could help it. The sniffer I kind of tried but just used a cheap welding kit with propane and the welding tip. I didnt find anything but some vacuum hoses kind of dissappear too. Like in the pass. firewall area{ for heat, a/c?] and very front pass. side down low, and a large one to the gas tank for venting? Thanks for the thoughts, how bout a scanner that gives more info?

 

Yours is a '98 4x4 which means it has the Pulse Vacuum Hublock (PVH) engagement system. These are prone to vacuum leaks. Do you any problems with the 4WD engaging or disengaging?

Some automobile diagnostics shops would have the more sophisticated OBD-II scanners that you are talking about, able to read "real time" sensor data and stuff like that. Or you can pick one up yourself. For example: http://www.amazon.com/Actron-CP9185-.../dp/B000T8UG52

 

I assumed I didnt have any problems with the hubs. It SEEMS to go in and out fine, but it workswell in wet grass and pulling my trailers up thru it. I know what you are talking about tho, I had a 1999 and 2000 superduty 4x4, they would easily get stuck in wet grass on a slight hill unless in 4wd. They had auto hubs that did not work well, so you had to manually engage the hubs. My ranger doesnt have the ability to engage manually tho.But each time i've tried 4wd in the ranger it seems to have worked well. Maybe I'll try to propane test that vacuum line if I can find it.

 

Pull off the passenger front wheel and remove the splash guard, you will see the vacuum reservoir tank in plain view. It'll be easier to follow the vacuum lines from the tank that connect up with the vacuum source and PVH solenoid.

 

Good trouble shooting & ideas so far.

Maybe include a check of the PCV valve & it's hoses & rubber fittings.

If the PCV valve sticks open, it'll cause an uncalculated for air leak that can mess with fuel trim & cause a rough idle.

Another thought for your suspect list.

Let us know what you find.

 

The purge canister and the related lines and solenoid belongs on your suspect list. If the solenoid leaks, you will have no detectable external leaks. It has a vacuum line that is not always part of the vacuum tree. The hose can split and leak, and depending on the source of the leak, it can sometimes be intermittent. Had this issue on my dad's '96 2.3L The purge solenoid was not closed completely. He had an intermittent code for the solenoid, but a constant lean code. I guess it was grey area for detecting the solenoid fault, but it was leaking all the time.

 

Is that the solenoid on the drivers side inner fender? It has a hose going to the throttle body and a Y and a hose to??? the gas tank? I did also wonder about that because if you suck on the hose [to the tank?] it pulls air , it is not stopped, Thanx guys, Tim

 

Update: ok I pulled the pass front wheel off to look. Found a couple things. I have had an oil leak, I thought I fixed most of it with new valve cover gaskets and oil press sending unit. I have a pretty oily mess Plus a few drips of anti freeze at the timing cover. Did not see an idle increase when spraying starter fluid around vac hoses for r side hub. By the way I found more noticeable idle change with starter fluid vs. propane. Then I started spraying starter fluid around top of motor again. this time I noticed An increase and even a stumble when alot of spray near the egr inlet to the upper plenum. I moved the press diff sensor aside and sprayed it, no change. Sprayed up the egr tube and it changed. Looked at the plastic seal, and it is partially hanging out. I can even hear the vac leak when my fingers move around it> Sounds like great news but... I've had the plenum off a couple times now and I surely destroyed the seal FIGHTING!!!!! the intake over the tube. I can only hope it leaked before too, because the 171 174 codes were why I pulled the intake to begin with. Well I'm off to get a new seal and pray that seals the deal[pun intended, Tim

 

The stupid starter fluid or propane method is an invalid test and here is why. If you encounter the leak, the added mixture would cause an increase in idle except that the idle air controller will respond faster than you can possibly detect the change. The result is that to your ear there will be no perceptible change. You need to have a pretty severe and obvious leak before the propane method will have a measurable result.

Now maybe this test could have some merit if performed with the IAC disabled during the test.

 

checked for vaccuum leaks and found nothing. it runs fine on high idle but once it warms up begins to miss and even dies at lights or stop signs. haven't clean the maf yet or checked the plugs. any advice on what to check first?

 

checked all the vaccuum lines i could trace and everything seems good. cleaned the MAF and changed the PCV and air filter. have over 135k miles and don't know if the oxygen sensors have ever been changed because i bought it used. i guess the next step is to pull the passenger side tire off and check under the splash guard. everything seems to be working fine...just run rough once it gets to warm up and high idle kicks out and it dies sometimes when idling. i also need to pull the plugs and check them. thanks for the tips on where to start.

 

Highly improbable that it's the O2 sensors.

I would have first suggested a hole in the PCV "elbow" which is fairly common on the 4.0L SOHC, but you said the PCV valve was changed and so I assume any hole in the elbow would have been noticed and the problem rectified.

After that, I would consider bad intake gaskets.

 

went to see if my friendly corner mechanic could show me any short cuts and pull for any more codes. he did a whole system fuel cleaning and changed the filter while i was there. the gas in the filter was black and dirty...may need to clean out the tank!! he reset the codes and it did fine on the highway but was still rough idling on the streets. went back and he pulled codes again...o2 sensors...found two of them with burnt and exposed wires. my next step is to change spark plugs and o2 sensors! after 135k miles those poor guys are toasted! i just hope that fixes it!