P0171 code. Intemittent stall and vacuum leak.

[windman]

Hello again.
My first technical problems related post here.

It is 2004 Limited with v6 3.7 engine. I have duel fuel setup which utilizes LPG too.

I bought this car as used adn it is approximately 60K miles on its odometer.

I have a problem. I have a check engine light with p0171 code. I have computer to scan OBD codes and realtime data, also a scangauge car computer to do quick checks.

This problem is not related to LPG setup becasue, when i disable system and only operate engine on gasoline as it is used to operate on, engine stalls rarely.

Also its idle races slightly, sometimes it decreases and increases. when it decrease it i most likeliy to stall. It is acting like it has excess air after MAP sensor. why i know this is, once i owened a V6 Nissan, it has a LPG system hcih was installed wrong, and it could not receive enough LPG to idle at both V banks. It was trying to idle on only one bank. Also engine was idling fast due to cracked intake hose.

Now lets limti ourselves with gasoline only on liberty.
I start engine, it is cold outside, not problems, after warming up it is still ok. There is no significiant difference on idle. After heavy traffic and water temp is at highest possible level, higher than cruising temp of course, when i stop at red light, tachometer starts to go high and low slightly which is not normal. also it can stall without a hesitation like i turned it off.

after resetting ECU by removing battery leads and waiting, after 3 consecutive warm up periods, check engine light turns on, after 5 or 6 warm ups id dissappears. freeze frame data for DTC is P0171 each time i try this.

Bank 1 is lean.

I sprayed brake pad cleaner to PCV hoses, intake manifold, intake air control valfe gasket, pas sensor o ring. nothing happens. It stalls or idles as i have no effect on mixture ( as it should be). I do not hear hissing sound to indicate a vacuum leak.

I removed air control valve, cleaned every carbon or dust deposit, i cleaned idle controller, map sesnor pcv valve, responsze to throttle is better, no misfires, and idle is much smoother but problem is still there.

Any comments?

MAP sensor ( if it was, there should be both 171 and 174 codes simultaneously)

Fuel pressure? (it acts same way on LPG so this is not something we suspect)

O2 sensor on bank 1? ( i do not smell unburnt fuel at exhaust and no codes related to a specific sensor - also scanner reads similar values at both banks in terms on voltage)

Broken PCV hoses somewhere i cant see/find?

intake manifold gasket at bank 1 (which enlagers slightly when engine is warm)?

ECU problems?

any experience or insight on this issue?

 

[windman]

here is update.

I checked every pcv hose i can reach i, un plugged them i plugged them i coudl not find a crack or split hose. evaporation related can is hissing, i am not sure if it is normal but there is no hose related leaks i guess. do you have any idea about that canister with a electrical connector on it? it is attached to right side of radiator (not filter box side)

any comments?

what is idle speed for 3.7 engine when it is warm and neutral. it idles around 950 rpm which seems quite high to me. is there an adaptation process by dealer?

o2 sensors are both working at same voltage switching rate and they are operational.

 

[Luke]

no ideas .. but my idle speed is around 600

Good Luck

 

[windman]

i suspect that idle control valve is getting broken somehow. i also feel that p0171 is related to lpg setup.

 

[TwoBobsKJ]

Typically the P071 is as simple as a cracked or missing vacuum hose - and I agree with you that a P0174 would show up if the MAP sensor was clogged or bad since it would affect both banks.

Double check the vacuum hoses after the map sensor - especially the large hose running from the throttle body to the fitting at the back of the left hand cylinder head. There are also two plastic tubes that are prone to break and crack that run along the side of the left hand valve cover. I had a crack in one of those right at the firewall as the tube turned down toward the bottom of the body. I cut the tube and fit a rubber emission hose between the two halves of the tube and my P0171 code went away on its own.

Hope this helps.

Bob

 

[windman]

yes, only part i cant freely reach is the valve cover area at bank 1. i have LPG setup there and expansion tank. i will drive and check to see if code re appear when i operate engine only on gasoline not LPG.

erratic idling seems another issue, and developed newly.

 

[windman]

I ve been driving this car only on gasoline so, no DTC codes appear.
this can prove that my lean burn problem is only related to bifuel setup and its adjustment.

it seems erratic idling is something different and unrelated to p0171.

let me open a new thread for stalling and erratic idling issue.

 

[windman]

erratic idling and stalling was related to my broken TPS, throttle position sensor. I replaced that and also my p0171 code disappeared and did not re appear in two months.

TPS was the source of problems not bifuel setup.