Hi All,

It is about 1998 Navigator, 5.4 engine 'L' series 4x4
A few days ago, I got the MIL and I felt that RPM at iddle are too high (about 1400-1500 on P and about 1100-1200 on D with foot on break paddle).
I connected interface (btw what are you using guys? I have only generic OBDII - without manufacturers specific codes interpretation and without tranny or airbag support) and I got:
P1506 - found it as air speed sensor
P0171 too lean
P0174 too lean
In addition, my MPG kills me now - I have about 8-8,5 while before I had about 14 (same conditions - 50/50 town/highway).
I cleared the codes but after few miles they are back.

Then I checked STFT and LTFT.
Not much difference between banks, but
LTFT are BADLY POSSITIVE - about 40-45 % (+)
STFT are NEGATIVE - about 35-40 % (-)

Now...Codes says too lean and bad economy confirms that. So this could be vaacum leak or something like that...

BUT

Trims shows (LTFT) that car is going RICH not lean...

So where is the truth?
I was trying to fine vaacum leaks but I couldnt. Looks ok. I dissconnected one hose from EGR and could feel a strong suction.
Infamous vaacum hose between PCV and the engine back is supposed to be ok as well.

I was trying to find that air speed something but I couldn't find it...
Today I will try to clean the MAS and will see...

Any ideas or sugestions how to diagnose it further ?

Thanks
Stan

 

P1506 Ford Idle Air Control Overspeed Error OBDII Engine Light Trouble Code | Engine-Codes.com

Did you check these? Seems to be pointing on PCV valve and IAC valve. The trims may be very confused if sensors and other stuff in the intake is giving bad or false signals. The MAF sensor may possibly contribute to the confused trims, so cleaning it won't hurt. But I doubt that the MAF is the main reason, check the IAC and the PCV valve itself, I think in the 1998 truck the PCV is a serviceable part, unlike the 3v '05+ engine where it's an integrated part of the valve cover. Others can correct me if I'm wrong on that.

 

I read that, thanks.
I found PCV on the passanger side of the engine, on top of the valve cover... Any help how to remove it from the car for cleaning?
But I can't find the IAC... Not sure how it looks like... Any help on this please?

Thank you very much

 

Correct me if I'm wrong, but a POSITIVE trim indicates the system attempting to ADD fuel to a LEAN system, while a NEGATIVE trim indicates that the system is REMOVING fuel from a RICH system.

The Long term fuel trim at a high positive rate is indicative of a lean system and thus the codes, the strong negative short term trims seems that it's trying to pull this back but for some reason is not able to, all in all, it seems the ECU is confused about what is going on, which can be explained with the IAC code.

 

That is my point. Negative STFT means that car is rich and computer is trying to push it towards lean (trying to reduce fuel)... So if it is rich, then why codes that says it is lean ?
Starting to beconfused a bit...

 

Check the IAC valve, this is from a '97 Expedition, but it should give an idea what to look for in the Navigator.

 

Ok, that was possibly the worst video I could've found on youtube... LOL.. But there are others more sensible ones, just search for IAC Ford Expedition or idle air control ford expedition.

 

Find and repair your massive vacuum leak, it's usually the PCV system. Reset the PCM by either disconnecting the negative battery cable or removing the KAM fuse for 10 minutes. You'll probably find everything is now back to normal operation once the PCM relearns its adaptive strategy.

Don't get lost out in the weeds with the fuel trim numbers or on Youtube videos or the IAC valve. This ain't rocket science...

 

yeah... but how to find it? Vacuum sem to be strong as it should be.

 

The P1506 sometimes will show up if the intake air ducting isn't sealed. The P0171 and P0174 tend to be the result of a large vacuum leak.

 

They're probably right on the vacuum leak. I haven't worked on a 1st gen yet, and my '05 doesn't have any IAC and the PCV is different on it.. At any rate, it doesn't hurt to clean the IAC valve while you're at it, as far as I've read it's not uncommon that these get dirty and sticky with time due to carbon buildup.

 

Yes, I will clean that ******* but I need to find that leak first.
I have no access to the smoking machine to run some smoke through the vacuum lines. Can't hear any air noice either.
So I need any good advice how to find that leak. I stripped apart and checked all air intake line from the filter to the throtle. No holes, no damages.

What I have found... Just right after I turn off the engine (having hood opened), I hear large air sound. But it is not 'ssssssssss' it is more like 'ssttrrrr ssttrrrr hhrrrr sss ttrrrr".
It comes from the small round part, located very close to the EGR, towards the front ot the car, drivers side. This part has a small hole on the top, electric connection and 2 air lines as well. One of them goes straight to the EGR, and the other one goes to PCV. The top of this part is labeled PP-GF30. The sound I'm describing lasts few seconds (maybe 7-8) and dissapears.
But:
I found the other air line that goes directly from PCV to some misterious part that hangs from the firewall, just over the break pump.
So I disconnected that line. I was trying to blow some air inside with my mouth... Something goes in but with very strong resistance.
Then I was trying sucking... And bingo...I was able to suck the air from the line very easly. In addition I hear that strange sound coming from the part PP-gf30 described above.
So the conclusion is when air is flowing inside the lines, and the vacuum exists, the air also comes in to the system through that part.
Question is what is that part, what it does, and most important if the reaction and symphtoms I'm describing are correct or not...
And again... How do I test it further?
Thanks a lot

 

Vin L engine, that's the 2v SOHC engine, same as in the Expedition, or is it the 4v DOHC?

If it's the SOHC, the PCV valve is on the valve cover on passenger side behind the oil filler cap. If it's stuck open, or the lines are leaking, this will be considered a major vacuum leak. On the forums, the PCV is a recurring issue causing vacuum leak. Also make sure the oil filler cap is properly sealed.

 

That small item is the EVR solenoid. It"s normal for it to bleed a small vacuum (that's already calibrated into the system).

 

Well... yes - it is 2v sohc. And yes - found PCV on the velve cover... But still have no idea how to test it... Can't belive the mechanics... I drove to the american car service... And based on codes, I got the quote to start with all 4 lambdas, 2 catalic converters, MAS, 8 injectors and 8 COP packs replacement...just to start with... to be sure.... Didn't even asked for a price estimation... So I'm alone here and have to pinpoint the problem myself...