I had the MIL light come on the other day along with the restricted performance alert for a few minutes, and it was P0171. Cleared it, now yesterday another MIL light with restricted performance for a minute.. This time it was P0174... Checked ST and LT fuel trims, hot (201*F, 93.8*C coolant temp) and at idle (approx.725 rpm) and at 2,500 rpm, parked after a 35 mile ride. Below are the readings, and nothing seems too out of range. Any thoughts? (2003, 3.0, 106k miles).

@ Idle:
Bank1 STFT -1.6
Bank2 STFT -.08
Bank1 LTFT -3.9
Bank2 LTFT -5.5
O2 Bank1 Sensor2: .825v
O2 Bank2 Sensor 2: .795v

@ 2500 rpm:
Bank1 STFT 1.6
Bank2 STFT .8
Bank1 LTFT .8
Bank2 LTFT -1.6
O2 Bank1 Sensor2: .640v
O2 Bank2 Sensor2: .575v

 

have you cleaned your MAF.
maybe also monitor fuel pressure under load.

 

Plugs/coils? Lean codes hopping from bank-to-bank don't really support a vacuum leak; I'd think it would be one, or the other....or BOTH but not alternating. Misfires have been known to trip lean codes but not misfire codes on occasion.

Also, at 106k, keep an eye on your radiator - it's past time for your right side tank-seal to start leaking..bout 2/3- 3/4 down, back side....leak will blow onto the DCCV and make you think it leaks.

 

Fuel pressure was 55 psi

MAF was cleaned a couple of months ago

Plugs/coils were changed out at 80,000 miles, however I kept my oem Denso's after my aftermarket Lucas coils started failing after 17,000 miles, and re installed the Denso's.

BTW radiator and cooling system good thus far, no leaks!

 

Doesn't look like an air leak - unless it's an odd one like a hose with a small break that flexes. Unlikely, but not impossible.

Next time you get a code don't clear it till you've read the freeze frame data - it will show other values (like speed) that might be a clue.

I would not be overly concerned at this point.

But... might your battery by getting tired? Weird code flagging happens then. Also RP.

 

I read the data before I cleared the MIL.... but when you're saying freeze frame data, you mean data that is stored at the point the MILwas turned on? Didn't know that was accesible.

Checked battery voltage after 8 hours of rest: 12.3 vdc

 

I would add a can of BG44K to your fuel first. The codes you are getting is for poor fuel and air mixture and because it is intermittent I am thinking bad fuel or injectors may be restricted.

Gus
www.jagrepair.com

 

+1 On the MAF... Even swap it out for a new one. Ebay has chimese copy ones very cheap. If that fixes it, buy a good one!!!!

 

Your battery needs charging. Voltage should be 12.5 or higher. Low battery will often trigger false positive codes.

 

Is BG44K similar to Techron? Never heard of it.

Second battery, even fully charged with a new Battery Tender, never gets higher than 12.3, testing with more than one meter.

I drive 350 miles a week, so car is not laying around, and I never have any associated quirks that normally comes with a low battery ( gearbox fault, etc etc), so not too worried about battery.

No issues since I posted this thread, I'll see what happens...

 

12.3 is wrong. Bad battery or something.

May or may not be causing false codes. You get to guess / fix the voltage.

Freeze frame might help.

Or you can try other things that might or might not fix things. With so little data I'd try to get more or do cheap things.

 

BG44K is better than Techron and available at most good repair shops.

Gus
www.jagrepair.com

 

Check your intake plastic tubing carefully. Several people have found worn spots and this does flex as the engine is running and the car is driven down the road.

Long shot but no cost to look.
.
.
.

 

OK now this is strange..... As I was driving home this afternoon from work, the MIL came on with restricted performance..... I was low on fuel, so just a moment ago, I just filled up the tank. I started the car , and the MIL is OFF! What the......?!?

 

Is there a capacity diferance between the two tanks ?
I wonder if that might confuse the cars fuel leval calculations .

 

Just read the codes. They're kept stored. Also, the freeze frame data.

 

Well, the MIL is lit once again, and the codes are P0171 & P0174 yet again...

I checked with my OBDCOM scantool and obtained the freeze frame data and it is as follows: ( it only showed data for P0174 because it was the last code in?)

Fuel System Status: S1: Closed Loop, S2: Closed Loop

Engine Coolant: 199.4*F

LTFT Bank 1 : 11.7%
LTFT Bank 2 : 11.7%

STFT Bank 1 : 10.9%
STFT Bank 2 : 13.3%

Intake Manifold Pressure : 23.33"Hg

Vehicle Speed : 71.5 MPH ( 115 Km/h)

MAF Rate : 33.32 gm/sec

Calculated Load : 47.8%

Fuel Pressure : 55.70 PSIG

RPM : 2124

Intake Air Temp : 39.2*F

TPS : 20.8%

 

Good (well, bad, but hey)... do you still have very small trims at idle & when revving as you did before?

ECT looks plausible. I don't know what the weather is actually like but if it's fairly cold then IAT is also plausible.

Trims for both sides are bad but similar. Not only are the LTFTs too high but it's weird the STFTs have not migrated into the LTFTs.

Anyway, really means you're looking at a cause that affects both banks, so it's not something like an exhaust leak on one side. (Or both sides, I mean they'd never both occur at once and be so similar.)

Are all the supported OBD monitors set OK, so that you have P1111 (so not P1000)?

What happened to the issue of the poor battery voltage?

 

Did you add the fuel additive?

 

Gus, how would it help - in theory even? He's got a fault affecting both banks so you can't say it's injectors!