Question about 2006 Mercury Grand Marquis

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06 MGM hesitation when accellerating between 1200 and 2000 RPM's

About 6 months ago in a blizzard, I noticed that my car would hesitate almost every time I attempted to give it gas. It happened a lot during the snow storm since I was in traffic running around 15-30 mph for 2 hours. It did it so much that I was trying to pay attention to the RPM range when it happened.

It still has this issue and it is no longer cold outside. It does it when the car is cold or warmed up (although, I rarely accellerate much until it's warmed up). It's most noticable when on an on-ramp since you accelerate hard to get up to free way speeds. My commute is 60 miles one way with 70% being free way, so I run into this issue pretty often.

I run 89 octane, oil change every 2500, car has 55K on it now, K/N air filter. I bought some MAF cleaner and cleaned the MAF, but that didn't appear to help much.

Now, last night on my way home, the hesitation was as it has been, but running at about 1800 RPM's at 75mph, it felt like I was running into wind. There wasn't any wind. It wasn't all the time, but about 2 times I felt the car shudder a bit. Then this morning, my CEL came on about 10 minutes from my home.

I'm borrowing a buddies code reader tomorrow so I will see what code has been thrown.

Anyone have any thoughts?

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  • 4 more comments 
  • Bryan L
    Bryan L May 14, 2009

    Got the codes from Autozone tonight. Didn't want to make my buddy go out of his way to drop off the reader.

    The codes thrown were P0171 and P0174. Autozone printed receipts with descriptions.

    P0171 -
    OEM Brand: Domestic

    Definition:
    Fuel trim bank one condition

    Explanation:
    The pow fnition fault (no that isn't a typo)

    P0174 -
    OEM Brand: Domestic

    Definition
    Fuel trim bank two condition

    Explanation:
    The ECM has detected a rich or lean Air/Fuel ration condition on engine bank two

    Probable cause:
    1 - If bank one and two are set together suspect a fuel preasure condition or MAF sensor fault
    2 - Failed HO2S21 (not sure if that's an O or 0 - letter or number)
    3 - Ignition misfire condition
    4 - fuel injector problem
    5 - egine mechanical condition


    Any thoughts?


  • Bryan L
    Bryan L May 14, 2009

    Thanks, but most of that is more than I'm willing to safely futz with. I generally try to stay out from under the hood. Thinks like battery replacment, air filter upgrade, brakes/rotors, o2 sensors, I'll mess with.

    The K/N has been in it for a year. Replaced it the week after I bought the car. Sorry I wasn't more clear on that. I've been using them in all my cars for about 10 years. Adds 2-3 mpg usually. I run about 35K a year. So it adds up pretty quick.

    I have no idea what to look at for the vacuum hoses or pressure regulator.

    The fuel filter I've seen and replaced on my old 98 MGM, but I can have that changed easy enough at an oil change place. However, I'm pretty sure I changed it about 10K ago. I fill up my tank from 1/2 every other day (literally), so it doesn't really sit with low fuel in the tank ever.

    More than likely, it will end up at a mechanic and eat a few of my vacation days to do so. Was just hoping it was a sensor or something I could easily diagnose/change and be done with it.

    I can get my friends ODBII reader to clear the CEL, so I don't have to reset the computer by disconnecting the battery. Unless disconnecting the battery actually does something else.


  • Bryan L
    Bryan L May 15, 2009

    That's what I was thinking.

    I used to go to a small private shop, but got boned there pretty bad. Cost me a new engine...

    The shop I go to now is a place I've been to a few times with my last merc. It's a Ford dealer, but they seem pretty honest and willing to work on a Mercury. I'll probably end up taking it there as I don't want to do the same thing. Sure, I can replace a fuel filter or a MAF, but then I'm out $100 and have a high liklihood of still having a problem.

    The rig has had a rough idle pretty much ever since I bought it. It ran fine otherwise, but IMHO, idled far too rough for an "old folks" car. My 98 idles better than this thing did with 165K on it vs the newer on having 18K when I bought it. It's probably had a problem with something somewhere and is finally failing bad enough to throw errors.

    Thanks for the help.

    When I do take it in, I'll post up my results just to help anyone else out.


  • Bryan L
    Bryan L May 16, 2009

    Got a new code today:
    P0191 - Fuel Rail Pressure Sensor Circuit Performance

    My buddy dropped off his reader anyway, so I changed the fuel filter, cleaned the MAF, took apart and cleaned the throttle body (nasty oil/carbon buildup inside it, looks like new now), then fired it up. Idles much better than it ever has, so I let it run a bit, then shut it down and plugged in the reader.

    Now I have 3 codes:

    P0171 - Fuel trim bank one condition
    P0174 - Fuel trim bank two condition

    New one:
    P0191 - Fuel Rail Pressure Sensor Circuit Performance

    I plan on taking it in next Friday as that is really the only "good" day I have to take off.


  • Bryan L
    Bryan L May 31, 2009

    It ended up being my fuel pump. $649 to diagnose, order/ship next day and install. The pump was $393.13 of that according to the bill.I found a few OEM spec pumps online for half that, but shipping next day brought it to about 80% of that.

    So, if I did it myself and had a week to wait, I could have gotten it for $175 or so, then dropped the fuel tank (in a garage I don't have), installed it alone laying on my back... praying to god that I didn't dump fuel all over myself or brake something else in the process...

    After doing the throttle body cleaning and MAF cleaning I did, then getting the pump replaced, this thing didn't run this good the day I bought it over a year ago with 18K miles on it.

    Just thought I'd post up the resolution in case anyone else has an issue similar.

  • Teddi B May 11, 2010

    The easiest way is to scan for codes like you mentioned and find out what you car is trying to tell you. Let me know what the code is and what ever else you find.

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  • 232 Answers

Air and fuel mixture incorrect, restart the computer. Disconnect the negative or ground from the battery, turn the lights on to drain the computer faster, wait five minutes then reconnect. The computer is set to work with an old clogged filter, now you have more air coming in due to the K&N. The p0174 is the O2 sensor picking up on this, too much oxigen. Too much oxygen or not enough fuel. If restarting the computer does not work, replace the fuel filter and pressure regulator then restart the computer. You'll have to drive around for the computer to set, during this time do not mess with anything you'll throw off the computer. There should be some information in your vehicles manual about the relearn period. Before anything ceck for vacuum leaks, if there is air entering the engine after the MAF sensor the computer can not mesure it. Check for loose, disconnected or cracked vacuum hoses and replace if necessary. Start from there and let me know.

Posted on May 14, 2009

  • Teddi B May 14, 2009

    I think you should restart the computer, it might reset to compensate for whatever is causing the problem. Maybe it'll drive better, it'll also turn off the check engine light. If it happens to come back on then you can turn it off with your friend's tool. Be careful with mechanics they like to guess and replace things at random. Little by little you'll end up with a rebuilt engine with the same problem. Take it to a shop with a good OBDII diagnostic tool. They look like a regular OBDII code readers. But the difference is they can run tests in real time with the car running. Then they check the information they get from the sensors and compare it with OEM specs. This is the only way to find the problem for sure without guessing.

  • Teddi B May 16, 2009

    Too much oxigen too leattle fuel or combination of both. 1You have a vacuum leak meaning there is air entering the engine after the MAF sensor, unmeasured air. 2You have a weak fuel pump a clogged fuel pump screen or filter. Faulty fuel pressure regulator or leaking injectors or injector(s) O-rings. Perform a fuel pressure test or just replace the fuel pressure regulator make sure to install new O-ring(s), then you must restart the computer. The fuel problem P0191 is the causing the P0171, P0174, catalytic converter O2 sensors peaking up on the screwed-up fuel and air mixture. The number one cause is a faulty fuel pump relay(s) swap it around with a headlight or fog-light relay(s) to find out. Then go to a junk-yard and bring a pocket full of relays. Problem solved, your welcome.

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