The Dreaded p0174 Strikes Again!!

[deRangerous]

Riddle me this one, Rangers & Rangerettes:

'99 4.0, 5r55e 4x4 w/300k mi.
Engine was rebuilt several years ago, mostly successfully. A year ago the owner got nicked for several thousand dollars chasing this very code, eventually passing smog inspection after 2nd attempt at intake gaskets in Las Vegas shop. I promised my buddy that I (i.e. you guys) wouldn't let that happen to him again! Truck is due for inspection May 13. Tick, tock...the hour is late and the smog police draw near...Anybody? HELP!!

 

[Blmpkn]

Per Google..

 

[SenorNoob]

I'm having an intermittent lean off-idle (If it idles a few minutes I get a code.) that I'm convinced is an exhaust leak next to the O2 sensor. Something to consider maybe?

Is it constant?

 

[deRangerous]

That was great! Thanks. A bunch! Why, I remember back in the day, had to be '77 or mebbe '78 in shop class, I was under my car rotating my driveshaft and my girl crawled down there and Googled me right there on the floor! Boy, was I surprised!
I actually had hoped if I posted the freeze frame data, one of our esteemed members might recognize a pattern consistent with a previous experience and could narrow it down a little further. Those bank 2 numbers look pretty whack to me but I will see about a possible exhaust leak and appreciate that tip. I gotta say, finding a quality Google is not always easy these days! Regards~

 

[pentode]

You're at 60% load and 2300rpm... climbing a grade on the highway I'm guessing?

Looks like the computer is trying to throw fuel at the problem, so considering the likelihood of the various possibilities, I'd start looking for vacuum leaks first - try the old brake cleaner trick. Intake gaskets are a great place for a massive vacuum leak but that shouldn't be your problem if they were done properly. If you want a procedure for that, shout back.

Second guess - MAF. If there are definitely no vacuum leaks I'd try checking and cleaning the MAF if necessary. Just be extra careful, I don't know the 4.0 but in general MAFs are very easy to break. I guess there are specific sprays that may work but I've used a q-tip and isopropyl in the past with good results.

I doubt very much it's fuel pump as bank one seems to be not so far from normal. It's bank 2 that has the issue so could be O2 sensor on that side.

Haha, I just looked back at the AI suggestions and I realized AI is as smart as me. Guess I better quit my day job of doing nothing at all.

All I would change is to put checking fuel injectors last.

 

[deRangerous]

Hey, I appreciate you taking the time to reply! This is my friend's truck(same as my 4x2, which I caught with intake gaskets issues) and I don't know what fuel trims should look like on a 300k mi rebuild. My reader doesn't have live data complicating diagnosis. I swapped in MAF and going to try bank 2 sensor 1 O2 off my truck today. The smog police will be at the door 5/13 and when he went to local shop last year, it took them three times and k's of $'s before they took my advice and did the Intake gaskets. A year later, here we are with 174 AGAIN! I always make fun of shops that throw parts at problems, but unfortunately I don't have some of the tools that would make this so much easier. The truck runs great so no hints there. Funny that no issues hinders finding the issue! I know, sick sense of humor...

 

[deRangerous]

After trying the known good O2 and MAFsensors , I put a cooling system pressure tester on it and watched it climb to about 12lbs/psi and shut it off. It held this pressure for about 3 minutes, then slowly dropping as the engine cooled to about 9lbs before removing. It passed the IAC removal test so I hope that eliminates the intake gaskets. A) were the pressure test results acceptable? B) should I be moving along to the fuel side of the equation? Seeing it set the 174 at almost 2400rpm, , I was leaning toward a spray test w/brake cleaner at elevated idle or should I do the pressure test over and pump it up to 16lbs? My friend is worried we will CAUSE a leak doing this but I said it would be fine at 16lbs. How long should it hold at that reading once the engine is turned off?

 

[pentode]

I might be missing something here, but why are you testing the cooling system? You've got a lean condition, that shouldn't have anything to do with coolant. I'd try spraying some brake cleaner around the intake and every hose and line that goes to the intake, wherever they go in the engine bay. Do that at idle. It's way easier to hear the difference between 750 and 1000RPM than 2500 and 2750, and you've got more vacuum to pull in the brake fluid at idle anyway.

 

[Brain75]

I tend to go with engine-codes.com since they are usually more accurate in order of likelyhood (dunno, maybe they designed it towards fords more than other makes or something)..

P0174: Code Meaning, Causes, Symptoms, & Tech Notes

How to repair P0174 code Fuel Trim System Lean Bank 2

www.engine-codes.com

"
Dirty or Restricted Air Filter
Dirty or Faulty Mass Air Flow (MAF) Sensor
Intake Air Leaks
Exhaust Gas Leaks
Fuel Contamination
Faulty or Clogged Fuel Injectors
Faulty Front Heated Oxygen Sensor
Ignition Misfiring
Low Fuel Pressure
Positive Crankcase Ventilation (PCV) Hose Leaks
"

Those are the things I would look at, and in that order.

 

[pentode]

This wasn't mentioned before, but does the truck have any exhaust leaks before the last O2 sensor?

Edit: Hehe, I guess it _was_ mentioned before, as I was typing that.

 

[deRangerous]

Good point on the engine speed. I thought maybe the leak was intermittent since it was at 2395rpm when the code set. The cooling system check was for the same reason you can check head gaskets by doing a block test, which also involves sampling vapors released into your coolant. When my intake gaskets blew out/ sucked in, I found coolant in places it shouldn't have been. I think I'll try the spray test at idle but shouldn't that have shown up on the IAC(unplugged) test?

 

[pentode]

You really need more data points to be able to start drawing conclusions. You can't read much of anything into when the computer decides to turn on the MIL. All you know from that one snapshot is that your long term fuel trims are high on one bank and higher on the other.
So if you've tested the system with known good O2 sensors, did you take a look at the fuel trims then or did you just see if the light went out? You need to collect that data. Assuming the sensors are accurate, the next most likely cause is unmetered air getting into the system. An exhaust pinhole at just the right point upstream before the O2 sensors can cause a lean reading, but if the exhaust is totally intact, that's where you spray around the intake system looking (listening really) for leaks.
When you unplugged the IAC did the rpms drop at idle?

 

[deRangerous]

Yeah, almost to a stall.

 

[Randy]

My 97 Ranger 4.0 with code p0174 was to shops many times and no one could find the reason for the code or why it was dying at stop signs. It belonged to my sister in a different state and she gave it to me for those reasons. After I had it a year, I took it to a local Ford dealer. They said a leaking intake gasket and then replaced it (twice-mechanics mistake). It now runs like brand new. I think they used a smoke test to find the leak.

 

[deRangerous]

Took it to a "reputable " local shop, they said the CAT was toast which buried the rear O2.$550+ later...p0174, They did a smoke test and said intake was fine. We unplugged the IAC, it stumbled. I don't know what the hell to tell him. Well, Mr Ranger, Yogi and Boo Boo are up a tree with no pick-a-nick basket! Whatever shall we do?