03 Envoy XL -- Bank 1 & 2 System Too Lean

[dciolek]

Model XL SLT 4WD, Engine "P" with 103,000 miles

I have been getting a Service Engine Soon light P0171 and P0174 setting repeatedly (have reset twice just to make sure it wasn't a one time thing). It doesn't come on right away, or every time it is driven -- and the only noticeable symptom is rough idling (but that is only noticable sometimes).

Recent maintenance items were air filter change 3 mos ago, tune up (new plugs and wires) 1.5 months ago and the light started about 3-4 weeks ago. I changed the fuel filter a week ago and added fuel injector cleaner. I just added fuel intake/fuel system cleaner on my next fill up (today). Also sprayed the Mass Air Flow sensor with MAF cleaner today. I tried to get it to run through a drive cycle with a code reader attached and it wouldn't "complete" after I followed the cycle directions. Will try that again tomorrow (idle 4 min, drive 18 min 45-55 mph, idle 2 min).

I am waiting to see if all the above makes the issue disappear this week -- but am not convinced I am working in the right spot and don't want to be missing a better place to start troubleshooting. I realize that the most "recent" fix was the tune up -- but I am not getting any spark plug codes or misfires.

The code information also mentions fuel pump, O2 sensors and vacuum leaks as possible causes -- but I am getting no other codes hitting that point in those directions, and no stalling or hesitations when accelerator is pressed.

Any other ideas would be appreciated so I don't keep chasing rabbit trails...

Thanks.

[maxwedge]

Welcome to AF. I assume this is the 5.3 8? Anyway, low fuel pressure, vacuums leaks, dirty injectors are the most common areas for these codes. See what happens after your recent work.

[danielsatur]

Because of Age + Mileage, suspect bad rubber, plastic, gaskets, or seals.
Call around for a Smoke test, and focus on the EGR, PCV, and Inake system.

[dciolek]

Yes, sorry -- it is the 5.3 V-8 engine if the engine code I gave was the wrong "letter/number" to designate that.

I got no SES lamp this morning on a 20 mile drive to work, but it didn't complete the drive cycle again and was definitely running rough at idle when I started up this morning (cold morning though). I'm going to try to get it to dump values to a Code Reader triggered by the SES lamp coming on.

Can you be more specific on calling around for a smoke test? I assume that is something a shop can complete to locate vacuum leaks? Anything I can do in the home garage to try that (or is that over a rookie's head)?

[dciolek]

Whoops, spoke too soon. Just started the car (cold after sitting for most of the day at work) and the SES light came on immediately at cold start (P0171 and P0174 pending). The SES light/MIL was OFF when I parked it at work this morning (I know because I had the code reader attached trying to get a drive cycle to complete).

After driving it for a short errand, I stopped at a stop sign, turned off the key and gave the reset code. Started back up, no SES, but this was a warm start instead of a cold start. Another short drive and the code did not set again.

I suppose it could be associated with a cold start, but not certain. Will test out this condition over the next couple of days to see if there is a link between cold start, rough idle and the code setting. I think I remember seeing the light come on during a longer drive not too long ago -- but not certain.

[danielsatur]

I found a video, see http://www.youtube.com/watch?v=FfiQ7qWiG-M

It's probably $80-$120 for test, but are the technicians going to tell the truth?
The smoke machine cost around $1200.

For $20 including S&h, I can send you a smoke test, see daniel_satur@hotmail.com

[dciolek]

I have been looking for some reference to an EGR for this vehicle on RepairPath.com and cannot find it. Also stopped by AutoZone and asked for an EGR valve for the car and they don't pull anything up.

Is it possible that this part/system was renamed on this vehicle -- or does this engine not have an EGR system?

[danielsatur]

It might not have one, I got a 2000 Jag 4.0, that doesn't have a EGR.

See http://www.alldata.com

[maxwedge]

No egr on this engine.

[dciolek]

Rented a fuel pressure gauge from Autozone. After a bit of searching, I found the test port on the passenger side located on the crossover pipe that connects the fuel rails.

On the initial ON cycle (engine off) -- it developed 51 PSI. A few cycles OFF/ON (engine off) it developed a maximum of 54 PSI. At idle, it settled to 47 PSI.

In the fuel gauge tester booklet -- it lists the 5.3 V8 "P" engine type as rated pressure of 55 - 62 PSI. Not sure if that means with engine off or running at idle.

Not sure if that is close enough or part of the problem. Do this sound like a fuel pump going bad (weak pressure)?

I didn't think about this before, but should i pressurize the system, and then turn off the fuel pump (no engine running) to see how quickly the pressure bleeds off? Would this indicate a tank leak?

[dciolek]

Did another fuel system pressure test:

First accessory on: 51 PSI
Accessory on/off 3 times: 54 PSI
Five minutes after key off: 50 PSI
Ten minutes after key off: 44 PSI

[maxwedge]

Start it up see what you have, you seem to be on the low side, 62 is at full throttle, you need 55 running at no load.

[dciolek]

I get 47 running at no load/idle speed (no accessories turned on, but engine running).

Since you say I need 55 at this situation and 62 at full throttle, sounds like I am down 15% or so on pressure. I just put a new fuel filter in -- so does that take me down the troubleshooting path to:

1) A new fuel tank filter (ugg - gotta drop the tank)
2) A new fuel pump (ugg - gotta drop the tank)
3) Looking for a hole in the tank/fuel line somewhere? (ugg -- gotta get a smoke test)
4) Bad gas cap? (wouldn't that be nice)

Does losing pressure at about 1 PSI per minute after energizing the pump (no engine running) lead me to a leak in the tank/fuel line/gas cap or is that normal?

Thanks for all of your help so far!

[danielsatur]

Test's are so much cheaper!
Fuel pressure Test
Compression Test
Smoke Test
Catalytic converter back pressure test.
Ignition Test.

Backyard Smoke Test -

1) Remove Air filter.
2) Wrap Air filter with glad wrap, or plastic bag.
The idea is to block all are going into the Intake.
3) Put Air filter back in box.
4) Remove the Brake booster vacuum hose.
5) Light a Black & Mild cigar.
6) Blow puffs of cigar smoke through the brake booster vacuum hose going into the Intake, and cover vacuum hose with thumb inbetween puffs.
7) Focus on EGR, PCV, and Air Intake system.
If you see any smoke, you found the problem.

Good luck - danielsatur

[dciolek]

Backyard smoke test performed. Have one lead I can follow up on with that, although its probably low odds -- but here's the story...

After I finally figured out how to keep the smoke in the intake hose (I actually had to take the air filter off the intake to the filter compartment and wrap the hose with a ziplock bag with about 6 doubled up rubber bands to keep it on when I blew smoke. That was all trial and error after wrapping the filter failed to keep the smoke back and just a single rubber band wasn't enough to keep the bag on the intake hose when I blew in the brake booster. (And yes, I did use the Black & Mild brand -- quite a treat).

The only thing that leaked (and it was just a little bit of smoke, but it was there) was just past the MAF sensor housing. That housing didn't seem to be "quite" seated with the intake hose just past it. Upon further inspection, both clamps (before and after) the MAF were a little loose and it seems that the last person to change the air filter "forgot" to screw down 2 of the 4 bolts securely (that would be the oil change place my wife took the car to). My guess is that being loose for a few months, the filter box got to moving a bit and might have worked the intake hose slightly out of 100% connection.

Anyhow -- its all put back, 4 bolts screwed down, the hoses all making positive connections and the clamps screwed down extra tight. I ran the car hard and didn't pull any codes, but we'll see. It doesn't seem to me like that little (very small) potential leak could screw things up that bad...

Another week of driving should prove it out. I'm going to rent the fuel pressure tester again to see if anything is different (and check the pressure at higher RPM, which I didn't do before).