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5.0 lean codes a mile or so after restarting... otherwise fine!

Discussion in 'Stock 1995 - 2001 Explorers' started by Ol' Mountaineer, June 26, 2019.

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  1. Ol' Mountaineer

    Ol' Mountaineer New Member

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    Hello fellows! Got a small conundrum here, and hope someone's willing to help out.

    My 2000 Mountaineer with 187k on the clock just got a new (stock style) exhaust from the headers back. All 4 O2 sensors are new. EGR valve & gasket, upper plenum gasket and elbow to plenum gasket, fuel pump and filter, all new.

    So, here's the issue: I can't seem to get the PCU to reset (need all but the last 2 reset here in NY, since it's a 2000) before pesky lean bank codes show up. The last few years I would just put about 50 miles on it after clearing any codes and pull in for an inspection... no problem. Then, often enough about a mile away I'd get an 0401! But at least I was inspected for another year.

    This year I'm having much more trouble... though the vehicle actually runs fine! Quite smooth in fact. (Except I'm getting as much as 5mpg less than should get.) The other day I put about 200 miles on her with no codes. The next morning I carefully start her up... perhaps superstitiously, first turn the key just to initiate the fuel pump a few seconds, then just allow a few turns of the starter and I back off, wait a second or two, then again a few more turns (trying to avoid a "lugging" start, which happens half the time anyway)... it seemed to start up fine (idles about 800-900) and I let her warm up a few minutes... but a mile out of the driveway "lean banks"! Damn, clear the codes and try again. Almost always "lean bank"codes about a mile or mile and a half after restarting a warm engine.

    Last week I had about 85 miles and one warm engine restart with no codes, pulled in for an inspection and the guy checked to see if the PCU had reset. Whoops, 5 items had not reset yet! So question 1: what's the deal with that? Exactly what does the car have to go through to reset the PCU... apparently 50 miles isn't enough anymore!

    Anyway, the guy told me the PCU needed the car cold again, and to start it and idle for a while as it warms up the O2 sensors. Next time around, I've laid down some mileage with no codes, shut her down... start up carefully in the morning, idle for about 20 minutes before putting it in gear. By the end of the driveway... lean banks! Reset and drove 65 miles without a code. But also without enough resetting of the PCU!

    Clues: 12 -14mpg when it should be 18-19. Lugging on startup, like not all cylinders firing... then catches up (tried a couple bottles of injector cleaner). Occasionally the brake pedal gets soft (thought it could be a leaky caliper, but maybe brake booster vacuum?)... I don't get a "brakes" warning light. If the freeze data helps, I have it.

    What's wrong with this thing... if the banks are lean it's not an air leak or I'd get the code constantly, not just after starting up. Any and all help will be greatly appreciated.

    Regards, Bob
     
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  3. 410Fortune

    410Fortune Firewood Season Staff Member Moderator

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    weak fuel pump
    That explains the long cranks also

    It sounds like the 02 sensors are doing their job and telling you of a actual lean condition
    The lean condition in BOTH banks points towards a fuel issue.
    In my experience with these trucks (alot) I would say your fuel pump is getting weak
    A fuel pressure test is in order

    it takes 12 drive cycles for the pcm to be in ready mode for emissions scanners
    Lean both banks means the computer has dete4cted a lean condition, attempted to add fuel to both banks and has failed to add enough fuel to correct the condition.
    On your truck about the only way this can happen is if the fuel pump is not able to keep up with demand anymore

    A properly running 5.0 with proper fuel pressure will startup with a bump of the key, any pro longed cranking is usually due to a poor state of tune OR a weak fuel pump

    fuel rail pressure test is needed, you should see the code GO AWAY and then go pass the inspection
    Lean condition is a BAD thing to be driving around with it can ruin alot of your new parts, and also can burn a valve or put a hole in a piston

    2000 mountaineer uses a returnless style fuel rail (single fuel line) you should have 60+ psi of fuel pressure at the rail
     
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  4. Ol' Mountaineer

    Ol' Mountaineer New Member

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    410, thanks for the response. The fuel pump is less than 2 yrs old... will try the fuel rail pressure test. In the meanwhile, I thought I'd submit some freeze data: st 17.95 and lt 29.67 both banks (st varies from 14.8 to 18.7, lt is always 29.6) ... I think those are the significant numbers. What is ideal and how do I get there? Meanwhile, guess I'll check again for leaks between the MAF and the throttle body...

    So you think I have a persistent lean condition, and not just on starting up? Once the PCU is cleared, I can drive 200 miles without getting any codes.
     
  5. CDW6212R

    CDW6212R Hauls the mail. Elite Explorer

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    Ditto, check the fuel pressure, it should be 60-65psi and never below 60. There are two rubber hoses in the tank for the pump and FPR. If the pressure is low, those can also be leaking and cause it.
     
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  6. fast_dave

    fast_dave Active Member

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    @Ol' Mountaineer

    Just Sayin' - So don't everybody in the peanut gallery get all riled up & pulling your suspenders;)

    Given what you have written in your 1st post, I'd like to suggest something simple, costs $0.00, and eliminates a variable that hasn't been discussed.

    Perhaps your problem is that your 19 year old fuel pump relay is starting to go bad - you know, the relay that directs power to the electric fuel pump???

    From memory - I believe that the Fuel Pump Relay is the same as the A/C Relay. There are many duplicate relays in the relay box.

    It wouldn't hurt to open the engine bay Relay Box, and swap out your Fuel Pump Relay with the A/C Relay and see what happens.

    If it doesn't work, well, you've eliminated that variable.

    If it does work, then buy a new one from any auto parts store for $10

    Your mileage may vary and good luck -
     
    Last edited: June 27, 2019
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  7. Ol' Mountaineer

    Ol' Mountaineer New Member

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    Was just under the hood... idling with my Mac Tools ET97 code reader watching the numbers. Idling at 730rpm... bank 1 st reading fluctuating but was averaging around 35 (seems high, shouldn't it be around 10?)... lt stays at 29.67. Bank 1 O2 sensor not getting a reading (?!)... where is it? Did I not plug it in when I had the plenum off? Throttle body to MAF rubber seems ok. Will swap relay...

    Thanks for hanging around the garage guys!
     
  8. fast_dave

    fast_dave Active Member

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    @Ol' Mountaineer

    I realize that you're in deep thought and chasing this problem down.

    With that said, please clarify what reading you're writing about (quoted ABOVE).

    Help us help you and pass me a cold one :thumbsup:
     
  9. Ol' Mountaineer

    Ol' Mountaineer New Member

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    My code reader allows me to look at the streaming data... I'm looking at the fuel trim numbers L.T. and S.T. for banks 1 and 2, though I really don't understand the numbers too well. Just now bank 1 was reading about L.T. 42 and S.T. 10 at idle. Hit the gas and it moved to 19 and 29.67. The freeze frame data when the lean bank codes show up is usually L.T. 19 (more or less) and S.T. 29.67.

    Swapped the relay with the power window relay, no noticeable difference.

    Also, if the fuel pump is the issue, why wouldn't it be a (worse) problem at highway speeds?

    Dave, I'd be handing out cold ones left and right for sure!
     
  10. fast_dave

    fast_dave Active Member

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    @Ol' Mountaineer

    OK - the Fuel Pump Relay has been eliminated = one less variable to worry about :thumbsup:

    Are you still getting Code 0401 = Exhaust EGR Flow Insufficient Codes like you said you were getting in past years? Please expand on this.

    You also mention your Mountaineer getting Lean Bank Codes (I assume recently). What codes are you getting. That will help the Forum help you.
     
  11. Ol' Mountaineer

    Ol' Mountaineer New Member

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    Codes 0701 & 0704. I never get just one bank. Both seem to show up a mile or two after a warm engine restart... even after idling for 15 minutes. Not getting the 0401 since the new EGR valve went in. Fuel pressure regulator? Hard to check that due to it being tucked under back near the firewall. Will try that next. May be able to check the fuel rail pressure tomorrow.
     
  12. fast_dave

    fast_dave Active Member

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    @Ol' Mountaineer

    FYI:

    * P0701 Transmission Control System Range/Performance

    * P0704 Clutch Switch Input Circuit Malfunction

    OBD 2 Codes LINK (Starting w/ Post 2): OBD-II Diagnostic Trouble Codes (DTCs)

    NOTE: Just for your sanity, you can even double check on Google - 0701 & 0704 are OBD 2 Transmission Related Codes!

    Hope this helps -
     
  13. Ol' Mountaineer

    Ol' Mountaineer New Member

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    Sorry! Got those numbers wrong. 0171 0174. It is lean banks.
     
  14. fast_dave

    fast_dave Active Member

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    @Ol'Mountaineer

    Look at what CDW6212R suggested in post #4 of this thread.
    410Fortune has similar thoughts in post #2.

    Fuel pump Regulator sounds easiest to start with.

    To expand on what CDW6212R wrote, I've read of instances where the rubber hoses on the in-tank fuel pump assembly can crack if re-used and not replaced when ONLY installing a new pump motor into the ORIGINAL fuel pump assembly.

    That is why when you buy JUST a fuel pump motor, they include new lengths of rubber hose and hose clamps.

    In your 1st post of this thread, you said you replaced the fuel pump - BUT we don't know if you replaced the ENTIRE assembly, or just the pump motor.

    If you replaced JUST the pump motor, did you replace the rubber hoses?
     
    Last edited: June 27, 2019
  15. Ol' Mountaineer

    Ol' Mountaineer New Member

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    Dave, Thanks again for sticking with me.

    I bought the whole fuel pump assembly and had a local shop install it. Probably has the fresh rubber hose.

    After doing some research on lean conditions, I'm suspecting a leak in the passenger side exhaust manifold is the issue. Definitely have the telltale ticking sound. I'm guessing air is getting in in front of the O2 sensor and tricking the PCU into thinking "lean condition" and so it keeps overfeeding the injectors. Thus the poor mileage. My fuel trim numbers are way too high. Funny that the 5.0 manifold leak is not a stranger to these forums, but I haven't seen the "lean" condition discussed as a result.
     
  16. fast_dave

    fast_dave Active Member

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    @OlMountaineer

    No problem, Bob!

    Just to close the loop w/ you on Fuel Pump Assemblies VS Fuel Pumps, I offer up the following.

    The whole fuel pump assembly comes with EVERYTHING already assembled - including 2 pieces of new rubber hose already hooked up to the fuel pump (see pic below). A complete assembly is more expensive than just buying the pump motor - which is the part that wears out.
    [​IMG]

    When you buy JUST the pump motor, you need to install it into your old pump assembly.
    Sometimes, due to time constraints, guys just install the pump, but without replacing the rubber hose & clamps.
    [​IMG]

    Your theory regarding the possible rich condition surrounding a blown exhaust gasket is sound.
    BUT - I'd imagine it would have to be a pretty big leak/tick to be causing such major problems & drop in fuel mileage that you write about in post 1.

    So, I'd start with what the other two guys suggested; Check the operation of your Fuel Pump Regulator.

    When the engine is running, and a Fuel Pressure Gauge is hooked up to the Fuel Rail, pull the FPR Vacuum Line, the fuel pressure should spike (simulates a Wide Open Throttle/No Vacuum Condition).

    Also, -when you pull the vacuum line that connects into the FPR, if any fuel is present, then the FPR is bad for sure.

    Report back - maybe even take some pics!

    Good luck!
     
    Last edited: June 28, 2019
  17. Dono

    Dono 347 V8 Limited turbo Elite Explorer

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    @fast_dave on the 2000 explorer/mounty the fuel system is returnless. This means the fuel pressure regulator is in the gas tank, and part of the pump basket assembly.

    That thingy on the fuel rail with a:vac line gong to it is a fuel pulse regulator. It does not control fuel pressure. you are completely correct that the bladder on it can rupture and the engine vacuum pulls more gas into the lower intake via the vacuum line.

    The op needs to check fuel pressure and checking hat vac line is a quick check as you stated.
    Lean both banks could easily be a large vacuum leak also.

    This might sound strange, but lean both banks could be unburnt fuel in the exhaust. It seems odd that this is on both banks though. that would mean a cylinder on the left, and right side are not firing. I'd hope the resolution will be simpler than that. OP, maybe pull each spark plug wire of the coils one at a time an confirm sparking, and listen for the engine to change idle at each cylinder you pull the plug wire.

    I'm just spit balling some things to try as you troubleshoot the issue.

    I just digested your idle/on the gas fuel trims. my money is on a big vacuum leak. At idle, vacuum is highest. Your pcm is adding all kinds of fuel.
    When you hit the gas, engine vacuum goes down, and your fuel trims show your pcm Is adding less fuel.
    I could be wrong, and have been before.
    Take the long term fuel trim and subtract the short term fuel trim. That's how much fuel is being added (or subtracted).

    Hope this helps.
     
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  18. Ol' Mountaineer

    Ol' Mountaineer New Member

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    @fast_dave

    Yeah, did the whole unit. I recently put a complete fuel pump assembly in the wife's Nissan Sentra.... a 5 minute job if you dawdle! There's an access hatch under the rear seat.

    @Dono

    It would be great if I didn't have to replace the exhaust manifold! Will report back after the rail pressure test.
     
  19. 410Fortune

    410Fortune Firewood Season Staff Member Moderator

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    many of the fuel pumps that are sold at the auto parts store, you are LUCKY if you get 2 years from one especially if you are the type to drive around with tank below 1/4 often

    First thing you do when you have lean on both banks is check for intake leaks after the mas air flow sensor and then do a fuel pressure and leak down test
    My $$$ is on the weak fuel pump or in tank issues, since this is a 5.0 and the intake leaks are not nearly as common as the v6's with their plastic upper plenum
    A small leak at one exhaust manifold will not cause both banks to run lean
     
  20. Ol' Mountaineer

    Ol' Mountaineer New Member

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    Alright, 410 you win!

    After checking the spark plugs (bank 1 plugs pictured below)... they look ok, I warmed her up at idle then headed out to the auto parts store. Before I got 2 miles got bogged down with flashing warning light 'cause cylinders were missing all over the place. Lean, you betcha! Hobbled home and waited for wife to return with her (extremely reliable) Nissan Sentra. Code reader showed fuel trims working overtime to correct things... and not doing it.

    So, today got the pressure gauge and sure enough 410 knows what he's talking about. 0 pressure when hooked up, rises to 28 with 5 key turns (held about 3 or 4 seconds each), and starts drifting down within a few minutes. (Why drifting down, since there's no return rail?)

    Moral of the story: Too much air can really mean not enough fuel. And don't buy cheapo fuel pumps (unless you enjoy installing them often.)

    Next... search the forum for "quick and easy tips for fuel pump installation"!

    Thanks all... you guys are great!

    bank1sparks.jpg

    highfueltrims.jpg

    pressuretest.jpg
     
  21. Ol' Mountaineer

    Ol' Mountaineer New Member

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    By the way, I made a stethoscope with some fuel line and a small funnel and hooked my shop vac up to the tailpipe. Couldn't actually see the exhaust leak, even with a small mirror, but easily located it at the back of the second header tube from the back (passenger side). That puts it a little aft of the sensor. Makes replacing the fuel pump look easy in comparison. I wonder how long I can go without burning a valve?
     

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