Topic: Code #P0171 System to Lean

[jeeplover]

My vehicle is a 98 TJ 2.5 with 67,000 mile.
Okay, I had this same problem about 1,000 miles ago. I ended up replacing the exhaust/intake manifold gasket. I had the exhaust and intake manifolds re-surfaced. I erased the code, and all was well, until yesterday. The check engine light is back on, and I am pulling up the same P0171 code. 
I checked my surface manual, so I understand the diagnosis. Just can't figure out what else could be the problem.

Any suggestions would be helpful.

Thanks

[Torch_Ind]

could be o2 sensor isn't reading properly could also be pluged fuel filter or injectors.  could also be air getting in anywhere could also be injector o-rings. also look for any vacuum leaks.

hope this is some help to you

[jcsanders79]

P0171 (M) 1/1 Fuel System Lean A lean air/fuel mixture has been indicated by an abnormally rich correction factor.
I agree it could be a sensor.
http://www.getahelmet.com/jeeps/tech/codes/

[Torch_Ind]

P0171 (M) 1/1 Fuel System Lean A lean air/fuel mixture has been indicated by an abnormally rich correction factor.
I agree it could be a sensor.
http://www.getahelmet.com/jeeps/tech/codes/

it could be all i mention above. I have delt with this problem on vehicles I have worked on. if you have plugged injectors the o2 sensor will pick up lean and make it abnormal rich. also if there is any vacuum leaks it will do the same due to un-metered air coming in that the computer can't compensate enough for.  and also a stuck none switching/ lazy 02 sensor can cause it also but usually will get a 02 sensor code also but not always.

being 98 obd2 it should pick up a 02 sensor. does the newer ones come with a "mass air flow" sensor??

[Torch_Ind]

I went through my repair manual and no sign of "mass air flow" sensors anywhere on the intake. best bet is to check for any vacuum leaks. maybe run some cleaner through your injectors see if it helps depending on miles might not be a bad idea anyway for maintenance and if that still didn't help you will need someone with a scan tool so you can see live data display and watch the o2 sensor to see if its fluctuating or not. but you will prob have to bring it in to a shop for that or just swap the 02 and cross your fingers.

if you know someone with a scan tool might be your best just to bring it to them first!!

[jeeplover]

I have sprayed starting fluid around the vacuum lines, had no rise in RPM's so I don't think it is a vac. leak. The O2 sensors are a year old ( may still have a bad one). Are the front and rear sensors switchable? As far as the scan tool goes, my friend has a very good one. That was how I pulled the P0171 code. I ran a diagnostic check, and all says okay.
My friend also has a live time scan tool that is plugged in while driving. Displays real MPG, etc. Is this the tool you are referring too?
As far as injector leaks, the O-rings are new. When I replaced the exhaust manifold gasket last time, I completely gutted the intake manifold and cleaned. So when I put things back together I figured I should replace the O-rings.

[Torch_Ind]

The scanner i'm talking about would be snap on/ mac/ matco/ or genesis/ there might be others but not it doesn't really give you mpgs though give you all your sensors inputs and outputs like garage would have. it's not just a code reader that you can pick up for 50$



but that's the most I can help ya other then working on it my self lol. your buddy's that ran it's own little test won't pick it up if you engine computer doesn't. the sensors should be interchangeable most of them are. but not always. you could swap them and try it and see what happens. your jeep should only have 2 right one in front of the car and one behind the cat?

[jeeplover]

The scanner i'm talking about would be snap on/ mac/ matco/ or genesis/ there might be others but not it doesn't really give you mpgs though give you all your sensors inputs and outputs like garage would have. it's not just a code reader that you can pick up for 50$



but that's the most I can help ya other then working on it my self lol. your buddy's that ran it's own little test won't pick it up if you engine computer doesn't. the sensors should be interchangeable most of them are. but not always. you could swap them and try it and see what happens. your jeep should only have 2 right one in front of the car and one behind the cat?

Thanks for all your help and insight.

[Torch_Ind]

does your jeep only have 2 sensors? one before and one after the cat?

[jeeplover]

Yes, 2 sensors. One just after the exhaust manifold, and one between the cat. and muffler.
Any chance you live in Michigan? I will have you work on my Jeep, LOL.

[jeeplover]

By the way I was on the Snap On web site. I guess you weren't kidding that your solus pro isn't a $50.00 scan tool. This thing must do everything at that price.

[Torch_Ind]

ya man there nice tools. I have worked with one before. there is also the old "brick" so it's slang name is lol. really old snap on one and i was looking in to buying a used one and there still about 1000$.

sorry dude I live in north bay Ontario canada. work for the chev dealer here. they have some nice junk lol. oh and were Cadillac dealer "enough said" lol. don't drive anything Gm. have my jeep thats my winter beater/toy & a 92 accord lowered with rims and exhaust and shit and made my g/f get a civic so i don't have to work on it that often lol.

[Torch_Ind]

hey man you never said if you checked your fuel system or not? did you check the fuel filter to see if it's plugged up or injectors. fuel pressure??? if your fuel pump is craping out with low pressure or low flow!!!

also still been reading my book and some have EGR valve witch brings in exhaust gas in to the intake. if that is stuck open it could cause that code. I don't have one on my 95 but maybe newer models have it for emissions..

[Torch_Ind]

fuel pressure should be 44-54 psi for 97+

95 & earlier with vacuum regulator hose connected 31psi disconnected 39psi.

[jeeplover]

I did not consider fuel delivery system. I will check the pressure. Since my last post, I have noticed a bit of a surge when accelerating, not a consistent acceleration. Then evens out when at a constant speed. Also noticed that when I shift fast, I get a small backfire between 2nd and 3rd gear.
I am losing my mind here. I just had it over at a mechanics shop, and his fancy $5,000.00 computer couldn't communicate with the Jeep. Yes it was plugged into the OBD port under the dash, LOL. I am also getting 12 MPG, which is down from 16-18 MPG. I have had this Jeep since it was new in 98'. I know every inch of this Jeep, but this one has me stumped.
This Jeep has no EGR valve. Just one fitting on the valve cover that connects to the intake plenum.

I sure appreciate your guys willingness to help me out.
And by the way, I will be leaving for North Bay Ontario, tomorrow morning, what is your address?? LOL