P0171/174 and P0442

[Ilikemice]

Hi all, long time no see!

My US spec 1999 Explorer XLT with the 4.0 SOHC engine started showing a P0171 code. I changed the upper+lower intake gaskets but then it started showing both P0171 and P0174 codes!

After clearing the codes it seems it will come back if I drive reasonably hard (For example overtaking up to 70mph, or going up a hill), but I can drive for a few hours without seeing this.

I've cleaned the MAF, replaced the gaskets, and gave the various vacuum lines a check to see if there's anything obviously torn but it all seems okay.

The next area I was planning on investigating was fuel delivery, and today I got a P0442 at the same time as the other two lean codes. I'd replaced my fuel filler neck as it was corroded enough to have a hole in which is where I've seen the P0442 code before, but haven't seen it since until today.

Could this all be linked to fuelling issues? What can I look at next?

Also is it safe to drive it as it is? I've not noticed any loss of power or anything besides a light ticking noise every few secs, with the A/C off.

Thanks!

 

[Ilikemice]

After a bit more research, could it be my EVAP purge valve lines? It might explain the vapour and vacuum leak codes. I'll have a look when I get home

 

[Ilikemice]

So I hooked up a crude smoke machine to it and put smoke through it at 2 bar. There was a tiny tiny leak from the line going from the valve cover, and (I think) a tiny leak from the main gaskets, but I reckon 2 bar is way too high of a test (is it?), and I ran out of smoke pellets

The next port of call is going to be testing the fuel pressure. I'm certain the gaskets are in place correctly and no smoke leaked from anywhere else.

 

[ERUSH97XLT]

An EVAP code and lean codes to me suggests a vacuum leak in the EVAP system to me. When the EVAP system purges, it's drawing fresh air in addition to fuel vapor. The only way I know of to solve it is to do a smoke test - which it sounds like you've done. Have you replaced any parts you've observed to be leaking? When you did your smoke test, how did you command the system to purge itself? I understand a capable OBDII device is needed to manually command the system to purge in order for the smoke test to be valuable.

My suggestion is to resolve the EVAP issue then we can systematically diagnose your lean codes as those can be a pain.

 

[bigred4x4]

My evap purge solenoid replacement fixed my intermittent lean code issues . Do you get burping noises coming from the gas cap?

 

[ERUSH97XLT]

Yes. Sometimes when I fill up and my gas tank is under vacuum I observe an "air relief" or burping noise from the filler neck. I think this is normal.

 

[bigred4x4]

I mean when your idling or even driving down the road and you can hear the burping noise randomly coming from the fill cap area. If that's the case your evap purge solenoid is stuck open drawing constant vacuum on the gas tank and the cap will burp air in to equalize the pressure thus the burping noise. Which for me caused random evap and bank lean codes.

 

[bigred4x4]

But some air release when you take the cap off to fill up is normal

 

[Ilikemice]

Hi, thanks for the replies! I wasn't able to purge it manually but I know the thing under the battery (Think that's the evap purge stuff) can get corroded but mine looks okay and didn't seem to leak from there.

I've not seen the evap code since so it may be a red herring, and I certainly have no odd pressure from the gas cap. I had to replace my hole-ridden filler neck a while back because it was throwing P0442 code and the hoses I left on weren't in the best shape, but were still intact. It could be those coming back to haunt me.

As for the lean codes - I'm not as alarmed about it as I was before though... having to replace the heater core put things into perspective regarding actual vehicle failure versus a silly light occasionally

I will get round to checking the fuel pump and re-checking the evap stuff though

 

[bigred4x4]

Lean conditions are not good actually it's very bad for the engine you should address them if they come back under lean conditions combustion temps rise (more oxygen ..... It's like blowing on a fire) sometimes to a level to damage pistons, rings, valves,cat,etc.... If your exhaust smells like eggs you're burning lean, rich condition isn't as bad it mostly will just Rob your gas mileage and clog your cat. Plus your power will suffer with both . That's why although I'm not a fan of it when it goes bad because it cause all kinds of issues is the egr some people delete it but I'd rather have it if it's working probably I really could care less about emissions but the inert air it recycles lowers combustion temp and is good for your engine. There is a reason why today's cars last so long and older cars odometers reset once it hits 100k. But it's also much more complex and harder to work on and diagnose.

 

[Ilikemice]

Fair enough. I’ll keep looking into it! I’ve had a couple of moments where I thought I’d fixed it only for the light to come on after a few hundred miles which is slightly frustrating

 

[bigred4x4]

That's what happened to me it was intermittent ended up being the purge valve under the battery tray. Not saying I know this is your problem but it could be.