Need some help... P0171 Code coming and going (1 Viewer)

[REZARF]

So I could use a bit of help here. I have one or two problems I am not sure if they are the same thing or two separate issue. Cruiser is a 1999 with original everything and 340k with good PM.

1. I have had a P0171 code that comes and goes. Manual says I have "Lean Bank 1"

2. I am also (though not certain they're connected) having some hesitation issues like a lack of steady power... it's like someone kinking the hose to the fuel line. I am unsure if they are one in the same problem but I would guess fuel pump and or filter on this one.

What has been completed already...

• Cleaned my MAF
• New OEM air filter
• Fuel injector cleaner (part of my regular PM)

What I know...

• My check engine light / P0171 code goes away when I fill up my tank until I hit about 1/2 tank then it returns.
• I haven't had another code in conjunction with the PO171
• My gas mileage is taking a hit (thinking upstream O2 sensor) I am down 2-3 mpg per tank.
• The hesitation usually happens early in the morning after my first start for about the first 1/2 mile and until I hit 2k RPM or so then everything seems to improve for the day.
• I have had a few sensations of the cruiser hesitating running down the road but I am not sure if I am psyching myself out or actually experiencing a hesitation. It would be slight if at all.

What I am planning on doing but would like advice...

1. Check my PCV hose and gasket.
2. Knock out the easy stuff and replace the PVC valve/gasket and pop in a new fuel filter, not sure when it was last done.
3. Order up a new upstream O2 sensor, which side is "bank 1" pass or drivers?
4. I might go ahead and replace the fuel filter with a new Denso unit as this is my daily and I travel solo quite a bit. I'd rather do it now in my driveway than anywhere else. I hear it's an easy swap with the seats out?

Anyone else have an idea of things to keep an eye out or thoughts about my symptoms? I want to see 500k on this motor and trans... help me make it!

Since everybody loves pics...

 

[Magikarp]

PCV grommet cracking? Trouble code and drive ability troubleshooting

 

[REZARF]

PCV grommet cracking? Trouble code and drive ability troubleshooting

Thanks, I missed that thread in my search somehow. I appreciate the link.

 

[2001LC]

Replacing fuel filter & fuel pump are two that should be strongly considered.

 

[KenH]

do you have access to the scanner that can read pids? check the fuel trims. You can try squire water around the intake/manifold and valve covers

." You can use brake cleaner or starting fluid and or carb cleaner but very careful may cause it on fire.. it if running better than you know where it's the problems."

From your statements it's the vacuum/air leaks.

purge valve for evap not closing

 

[Poncherelli]

I had similar issues...seems like it could be a few things from these comments but I’ll just let you know what I did:

Changed MAF, PCV, and O2 sensor and code went away but the “hesitation” remained.

Checked coils, replaced 2, hesitation remained.

Removed intake manifold and replaced gaskets (which didn’t look horrible but weren’t new condition either) and hesitation went away.

 

[REZARF]

I had similar issues...seems like it could be a few things from these comments but I’ll just let you know what I did:

Changed MAF, PCV, and O2 sensor and code went away but the “hesitation” remained.

Checked coils, replaced 2, hesitation remained.

Removed intake manifold and replaced gaskets (which didn’t look horrible but weren’t new condition either) and hesitation went away.

Huh, good to know. I’ve developed a small leak from the valve gasket on the pass side. It’s on my to do list, might be pushed to the top ASAP.

thanks for the help everyone

 

[Mauser]

I had similar issues...seems like it could be a few things from these comments but I’ll just let you know what I did:

Changed MAF, PCV, and O2 sensor and code went away but the “hesitation” remained.

Checked coils, replaced 2, hesitation remained.

Removed intake manifold and replaced gaskets (which didn’t look horrible but weren’t new condition either) and hesitation went away.

I replaced vacuum lines, oil cap, dipstick o-ring and about every other thing that had to do with vacuum before I decided to clean my throttle body and intake manifold. Since I had to pull the intake manifold apart to clean it I replaced the gaskets when I put it back together. Haven't had a problem since.

 

[Jrod]

@REZARF - Did you replace your fuel pump? My truck (300k LX470) never throws a code, but acts similar. My guess is the fuel pump is going out. I imagine the O2 sensors probably could stand to be replaced as well. I think we're getting the the mileage/age where it makes sense to just replace the fuel pump for piece of mind. No one wants to end up stranded...

 

[ClassyJalopy]

I have a very similar issue. Like you it goes and come back without much rhyme or reason. I don't feel much hesitation and the engine runs so smooth that it is sometimes hard to tell that it's running. Here's what I have done so far with no improvement:

1) Replaced fuel filter
2) Replaced gas filler
3) Replaced PCV grommet and both ventilation hoses for the valve cover
4) Replaced valve cover and spark plug tube gaskets
5) Replaced all 8 spark plugs and coils
6) Fuel pump was replaced with OEM unit about 50k Miles and 5 years ago
7) Replaced the MAF
8) Sprayed intake cleaner around the intake pipe and all lines to see if it would change the RPM (it didn't)

As someone suggested earlier in this thread, it may be the intake gaskets. Mine were replaced by a shop when they replaced the starter. Perhaps they didn't use OEM.
Another idea here is to replace the injector seals but I am not sure if they will be easy to replace and what are the chances of breaking something in the process.

 

[KFunk740]

[*]I might go ahead and replace the fuel filter with a new Denso unit as this is my daily and I travel solo quite a bit. I'd rather do it now in my driveway than anywhere else. I hear it's an easy swap with the seats out?

I think you might be misunderstanding a bit about the fuel filter. There's a fuel filter in the engine bay, next to the brake booster, which you should definitely change because its easy.
I think you're referring to the fuel strainer though (like a sock), which is attached to the bottom of the fuel pump. Yeah, it could have some crud on it. You can get to it by unbolting middle seats, and lots of tiny bolts under an access panel. I think I'd just go ahead and get a new Denso pump which comes with a new strainer if you're going that far, which I think was around $100 before.
But I would've done the easier fuel filter in the engine bay first, before going to that. Also be vigilant for rusty leaks from the main fuel line. It's the middle one of the set of three going from the tank to the fuel filer.

 

[Eicca]

Sounds to me like a vacuum leak in the evap system, especially since it doesn’t happen on a full tank. Check all the hoses leading to and from and around the charcoal canister.

 

[Mauser]

I ended up replacing my fuel pump a few weeks after I figured out my vaccum leak.

I was losing power uphill. I thought I screwed up the intake gaskets, but when I checked my fuel trims they were up somewhere around +30 on both banks. I replaced the fuel pump and fuel trims dropped back down to around 5.

A good way to to see if it is a bad vacuum leak. Start the engine, put in drive and while holding the brake give it some throttle. If it stumbles or even dies it is most likely a vacuum leak.

 

[REZARF]

No real update, I've got parts to go on tomorrow. Finally have a gap in my schedule and the parts on hand to crank....

• New valve cover gaskets
• Fuel Filter
• New PCV valve
• New vaccum lines, I found one that was cracked.
• Clean the MAF again
• New PCV gasket

I drove the cruiser last night and it stalled on me for the first time. It started loosing power and stumbling no matter how much gas I gave it. I pulled over, knocked it into N and started up fine and ran home the rest of the way. I'm gonna knock out the fuel pump now as PM.

 

[kruisinkid]

guy on here just had a somewhat similar issue. it was a nicked wire for the crank position sensor. just something else to check.
if fuel cap is original, certainly doesnt hurt to change that, OEM though.
and then yeah, it seems to be fuel pump season around here

 

[REZARF]

Update for posterity sake...

I replaced the following:

• PCV Valve (not needed mine was fine)
• PCV Valve grommet... my old one was crusty and dried out.
• New fuel pump
• New fuel filter
• New Valve cover gaskets
• New Spark plug gaskets
• Replaced two cracked vacuum lines.

I have no more hesitation nor stumbling (I'd bet on the fuel pump).

My P0171 code has not returned.

Thanks for the help folks, I appreciate the collective knowledge of this community!

 

[2001LC]

Update for posterity sake...

I replaced the following:

• PCV Valve (not needed mine was fine)
• PCV Valve grommet... my old one was crusty and dried out.
• New fuel pump
• New fuel filter
• New Valve cover gaskets
• New Spark plug gaskets
• Replaced two cracked vacuum lines.

I have no more hesitation nor stumbling (I'd bet on the fuel pump).

My P0170 code has not returned.

Thanks for the help folks, I appreciate the collective knowledge of this community!

Nice follow up

"P0170" That was a P0171 correct?

 

[REZARF]

Nice follow up

"P0170" That was a P0171 correct?

Yes, that was a typo. Good catch.

 

[2001LC]

What's interesting in your case. Is only the P0171. Even though I suspected fuel starvation. Typically I'd look for both bank 1 and 2 (P0171 & P0174) to indicate a fuel starvation issue, due to fuel delivery. I'm confident the fuel pump and filter did solve your issue, at least enough. But I suspect you've more to consider.

You said "Fuel injector cleaner (part of my regular PM)". Consider sending to someone like FIS. Also consider replacing fuel pressure regulator, considering mileage and your MPG drop.

When to Clean or Replace fuel injectors

Please post your experiences and thoughts on the subject. I’ve been considering cleaning or even replacing all 8 fuel injectors, is this wasting time and money. I understand keeping fuel injector clean by adding a can of additive to the gas tank, now & then, is a good practice. This keeps them...

forum.ih8mud.com

I did not see you mention spark plugs.

Ticking time bomb TICK TICK TICK: Spark plugs Alert Alert Alert!

TICK TICK TICK POP POP POP is a ticking time bomb, often mistaken as exhaust manifold crack or gasket leak leak. ALERT, ALERT, ALERT: Spark plugs are working themselves loose. "Walking Out" Then blowing out of head, taking their female threads of head with them! Very damaging! You think TICK...

forum.ih8mud.com

 

[REZARF]

What's interesting in your case. Is only the P0171. Even though I suspected fuel starvation. Typically I'd look for both bank 1 and 2 (P0171 & P0174) to indicate a fuel starvation issue, due to fuel delivery. I'm confident the fuel pump and filter did solve your issue, at least enough. But I suspect you've more to consider.

You said "Fuel injector cleaner (part of my regular PM)". Consider sending to someone like FIS. Also consider replacing fuel pressure regulator, considering mileage and your MPG drop.

When to Clean or Replace fuel injectors

Please post your experiences and thoughts on the subject. I’ve been considering cleaning or even replacing all 8 fuel injectors, is this wasting time and money. I understand keeping fuel injector clean by adding a can of additive to the gas tank, now & then, is a good practice. This keeps them...

forum.ih8mud.com

I did not see you mention spark plugs.

Ticking time bomb TICK TICK TICK: Spark plugs Alert Alert Alert!

TICK TICK TICK POP POP POP is a ticking time bomb, often mistaken as exhaust manifold crack or gasket leak leak. ALERT, ALERT, ALERT: Spark plugs are working themselves loose. "Walking Out" Then blowing out of head, taking their female threads of head with them! Very damaging! You think TICK...

forum.ih8mud.com

Yeah, I was hoping to get to 350k before sending the fuel injectors off for a rebuild. My plugs were all in good shape. I pulled them all while I was in there and looked for wear, color etc. Everything looked great. I hit them with a wire wheel and put them back in. Only one of mine was looser than i was expecting but was no where near just finger tight.