Mercury Marquis



January, 12, 2007 AT 5:46 AM

'94 Merc Gr Marquis GS, 65,900 miles
All Maintenance done on time and oil chgs every 2000-3000 mi since new. Ran great till last 100 miles. Car jerks quite violently at acceration, starting at about 25 MPH until over 60 MPH and especially uphill, although never going downhill. Slight miss in engine heard too. Had complete 60,000 scheduled maint done already, except fuel injection cleaning. Had the vaccum hoses cleaned and new fuel filter installed though. HELP! Told by mechanic $1500 for trans overhaul needed plus whatever's causing engine miss!
He based this 'remedy' on a test drive?


Mis Fire -


21 Answers


Service Writer

January, 12, 2007 AT 7:03 AM

And you want an answer based on the internet : lol: Just kidding, we can help.

I have found that some techs, especially ones with good abities and experience get a little overconfident and jump to conclusions. I have also found that some customers don't want to pay for diagnosis. Further still, I have made the assumption a customer doesn't want to pay for diagnosis adn olnly give them a test drive opinion.
Vacuum hoses cleaned, can't say I've heard of that one. I think you are wise challenging the opinion.

While I like to give a shop the benefit of the doubt, I can't help but wonder If you are this type of customer: Generally says to go ahead with whatever the mechanic recommends. You are a loyal customer and trust where you take the car.

While they are Ideal traits of a customer, an unscrupulous individual can exploit this type of customer.

Let me see what I can find out and i'll get back : ) At this point I " think" that this is just a misfire problem.


Service Writer

January, 12, 2007 AT 7:24 AM

This is what I recommend: Ford are common to have a MAF-Mass air flow sensor problem. While I suspect it, I would first pull the codes from the computor. Autozone may do this at no charge, not that I like their parts. Post you findings and we can go from there.

If this isn't comfortable for you, I would try a different shop. The testdrive/ transmission diagnosis doesn't leave me with a warm and fuzzy feeling. But do your homework : wink: If no one responds here otherwise, my suggestion is to check with the local snap on tool dealer and have them refer you to a shop. They deal with the good, bad and the ugly and can point you in the right direction for hands on help.
Www. Snapon. Com
" Find a franchise"



January, 12, 2007 AT 3:22 PM

Good one! YES trust you guys online for accurate info to point me in good direction. You have nothing to GAIN in service work and I read a few hrs worth of your postings and advice here. Was very impressed with your knowledgeable answers to others!

Thanks much for the response. MORE INFO: MAF was replaced Jan '06 (dealer puter diagnostics) for hard start/rough running, which solved that problem. (Installed rebuild from Checker Auto Parts.) Replaced MAF again recently under warrenty cuz I suspected MAF again when this jerking acceleration problem started. So MAF isn't the remedy here.

Nobody in LV, NV can point me to a mechanic they trust. Answer I always get is 'they're all thiefs in this town". (Living here 16 yrs, I've found it's true.) The dealers serv depts are also not to be trusted here.

Mechanic with $1500 quote based only on a test drive was a shop I never used before. In business 30 yrs in LV, maybe indicates good mechanic? Always tons of cars at his shop, never lacks for repair jobs.

He charged $82 for diagnosis cuz no work done. (I never blindlly do high cost repairs without 2nd, even 3rd opinion.) He'll credit this chg to final bill IF car is repaired there. (At drop off told FREE diagnosis. I reminded him at retrieval but had to pay it. Didn't ask for FREE in writing cuz didn't want to insult him with lack of trust at first contact. Dumb me.) Asked then if he cked spark plugs/wires etc tho car had full tune up just 5.500 miles ago. NO troubleshooting like that done, just a long test drive needed with his 'yrs of experience as mechanic' he said.( Not good enough for me! I want to KNOW it's for SURE the problem before shelling out $1500+.)

Now car's at AAMCO transmission for a 2nd opinion. AAMCO only told symptoms, NOT what other shop recommends. Picking it up later today. Hopefully puter diagnosis, not just test drive? (FREE diagnosis in writing this time!)

We've also gladly paid the $120 fee to Merc dealer for puter diagnosis (as per MAF Jan '06) in the past, and maybe the best to do for this problem now?

NO warning lights have come on even once (like serv eng soon, etc). Since car went from driving like new to jerk-jerk-jerk. I know nothing about cars & being female that's a 'juicy combo' for rip-off mechanics! Even tho always more than 1 opinion whenever high-ticket repair looms on my cars, in the end I have to TRUST someone to remedy correctly.

Besides MAF any advice how best to get an accurate diagnosis to find the problem rather than repairing using a hit and miss approach?

BTW: original fuel pump, and no eng/trans repairs or parts replaced since car new except MAF, and ALL scheduled maintenance items. I love my car and treat it well always, like Bosch Plat Spark Plugs.

Thanks for any other input you can offer! (Sorry for my long post.)


Service Writer

January, 12, 2007 AT 4:04 PM

Find out what codes were stored in the computer.

It seems that a " missing" engine culprit is actually the computer's sensor inside the Mass Air Flow Sensor (MAF). It eventually just gets a little dirty or builds up its own patina in the filament wires. A dirty or slightly patinated filament will send the wrong air reading to the computer, saying it is getting more air than it really is and the computer will tell the EFI to send in the wrong mix of fuel, thus, the bogging.
If you have had bogging or missing or idle spots, about every 25K miles plan on this quick cleaning job: When your engine is cool, remove the wiring clip from the side of the black plastic sensor part of the MAF aluminum body. To remove the MAF interior sensor wire, you will need a Security Star (Size T15 or T20) screwdriver or screwdriver bit for a power screwdriver. Remove the two security star-head screws and carefully remove the sensor. You will see the two sensor filaments they look almost like the filaments on a light bulb. Carefully spray the filaments with an O2 safe carburetor cleaner, such as Gumout. Let it dry thoroughly. I help mine along with a careful blast or two of canned dry air. While it is drying carefully wipe the aluminum mount surface of the MAF body if there is any dust there, but be careful not to get dust in the mount hole. When the sensor is dry, replace the sensor back in the MAF body and secure with the security star-head screws. These don't need to be torqued down, just simply hand tight. Replace the wiring clip. Then start up your engine.

And Thanks for the compliment : wink:



January, 13, 2007 AT 12:37 AM

Ok, I think I can tackle the MAF cleaning. You make it sound easy enough for a novice like me. MAF was just replaced under warrenty (rebuild) less than 100 mi ago. Is cleaning needed now?

Will problem codes be stored in the motor (to maybe pinpoint 'miss' and/or jerking problems) even tho not even one warning problem dashboard light has come on since the problems surfaced? I called Auto Zone but they no longer pull codes for customers due to 'liability'. Suggested dealer puter diagnostic. Our dealer charges $120 for this, but if remedy besides tran overhaul can be found in codes, it's worth it.)

Do you suspect 'miss' is separate issue than violent jerking with acceleration (especially uphill, mostly between 25-60 mph) or do you think both problems most likely share the same cause and remedy? Could both problems be a 'dirty' MAF or a defective rebuild MAF part or some other simple common cause?

AAMCO Transmission today gave same diagnois as 1st opinion mechanic yesterday. He heard an engine miss too, but says the jerking remedy is a complete tran overhaul. (He said no codes were found in the car's puter to verify this, so basing remedy solely on test drive.) This quote is $2500, new parts to completely rebuild tran except torque converter is rebuild part. One yr warrenty parts/labor. (Car driven less than 6,000 mi/yr, doesn't seem like a good warrenty to me.) (Isn't 66,000 mi a bit soon to need a trans rebuilt with all maintenance done on time?)

Thanks so much! I do appreciate the advice!


Service Writer

January, 13, 2007 AT 6:12 AM

MAf replaced less than 100 miles ago? No cleaning then. Don't touch it. : Warranty on dealer parts are 12 months/12,000 miles. If your over that then it won't matter.
: idea: What I would do is pick up a code reader, for the little cost and you'll need it again in the future. Codes can be stored without the light coming on.

: idea: To increase odds of finding a shop,
My suggestion is to check with the local snap on tool dealer and have them refer you to a shop. They deal with the good, bad and the ugly and can point you in the right direction for hands on help.
Www. Snapon. Com find a franchise

If you see my signature below, spell out the cost of going to shop. This isn't theivery, It is very expensive to run a shop and draining to keep up with the technology. I have a great respect for anyone with guts to be in this industry as an owner and maintain honesty. Honesty is not inexpensive.

Think of it this way, the human body is essentially the same as it has been for many years, todays auto are not only individually complex and dynamic, There are over 100 different kinds every year. The constant training, frustration and folks that expect them to do " free" work such as diagnosing is relentless. Not to mention, the cost of insurance, finding and keeping good techs, maintaining equiptment and tool costs. Tool costs that easily reach $10,000 to diagnostic equipment and yearly $1000 software upgrades. Another $200-$500 for subscriptions to Alldata and or Mitchell1. (Somthing this site provides to me-so please consider a donation), and another $20,000 in hand tools that do wear out. Tool boxes can run several thousand dollars. I'm not chastisng you, just informing.
: wink: Okay, back to business : )
Has the transmission filter been relaced?

If so when and what kind of fluid?

What is the condition of the fluid? Pink, brown, burnt smell?

Would you consider this a vibration or shudder?

How old are the ignition wires, ignition cap and rotor?



January, 13, 2007 AT 1:27 PM

Has the transmission filter been replaced? YES

If so when and what kind of fluid?
--new fuel filter @ 59947 mi (car now 66,000 mi)
--Fluid Type: (was special type fluid Merc needed)

Condition of the fluid? Pink, brown, burnt smell?
--trans dipstick: fluid is PINK, no burnt smell.

Would you consider this a vibration or shudder?
--shudder (jerking back and forth)

How old are the ignition wires, ignition cap and rotor?
--these 3 parts are original, never replaced.


Service Writer

January, 13, 2007 AT 2:26 PM

Replace the cap, rotor and wires. There is enough age to get them out of the equation.

I found 2 tsb's. There is a technical service bulletin on a repair to the transmission I found that fits your description.



January, 14, 2007 AT 5:41 PM

At your recommendation, I'll request replacement of the cap, rotor, and wires while the car is at the shop Tues for a complete fuel injection service, (the last scheduled 60,000 maintenace item left to do on my '94 Merc Gr Marquis). They said they'll do a fuel pressure test too.

(BTW: cap/rotor/wires: are these transmission parts OR engine parts?)

Could you give me web links to the 2 tsb's you found about the same symptoms relating to TRANS repair? (My car at 65,900 mi may actually need a complete trans overhaul?)

Thanks! Your input is proving to be very helpful!


Service Writer

January, 14, 2007 AT 7:11 PM

The tsbs that I found were not on the web, but on an expensive program this site allows me to use. The shop you take it too I am sure can look them up. God help a shop without a program of this nature. They essentially entailed installed a transmission cooler, replacing the filter, flushing the lines and replacing the torque converter. Not necesarily all of them.

The ignition parts are on your engine.

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