Engine Performance Help

Dads98mk8

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I got Dad's 98 Mark 8 out of the garage last week at 29,646 miles and have put about 800 miles on it. While I've had numerous fun moments burning the gunk out with some heavy feet and Lucas injector cleaner I have a couple of problems that aren't going away.

I have no previous maintenance experience with this type of car, so I don't know the regular problems that you guys run into. So, given these symptoms, where do you guys suggest looking first given the known issues of this model. (I have searched, but nothing has jumped out at me.)

1998 Mark 8 that has only had 3,000 miles put on it since 2003.

Runs up to 3,250 rpm like a scalded dog.

At anything less than 50 degrees outside it bucks like a drunken sailor between 3,250-3-750rpm. Even when above 50 degrees and at full operating temperature there is noticable hesitation in this rpm range.

Acceleration from 4,000rpm up is slower than keeping it below 3,200rpm. I haven't put a watch to it, but it's enough slower than you can tell by other cars and scenery.

I've run Lucas fuel injector cleaner with premium unleaded for 2.25 tanks and the following codes have come up when the CEL is illuminated.
Tank1
PO174: System to lean Bank 2.
Twice during the first 1/4 tank and once between 1/4 & 1/2 tank.
2 low speed backfires during this tank during acceleration.
Tank 2
No codes until less than a quarter of a tank, then a PO174: System to lean Bank 2.
1 low speed backfire occured during this tank during accleration in the first 1/4 tank.
Tank 3
About 45 miles of highway driving after fill-up and resetting the CEL from tank 2 then PO171 & PO174: System to lean Bank 1 & 2.

All CELs have occured at highway speeds, not under acceleration.

Average fuel economy a little over 18.5mpg in mixed city/highway driving 22.5mpg on highway only.


I'd guess I need to figure out where the fuel filter is, but I can't explain why it would run all the way to 6K with a partially blocked filter. The way it bucks and hesitates in the 3,000rpm range it seems more like a bad sensor (cheapish) or hopefully not an engine control module (ouch!).

What cha' think?
 
It sounds like your getting a lean condition on both sides so first check your PCV valve and lines for a clog, then make sure that your intake tube, air filter and MAF are all tight. Unmetered air might be getting into the system. Check for vacuum leaks from somewhere. your mixture of fuel and air is to much for the system to correct on its own. the fuel filter is in the passenger side front wheel well. you'll have to take off the wheel well cover (maybe the wheel also) and you'll see it there.
 
I got Dad's 98 Mark 8 out of the garage last week at 29,646 miles and have put about 800 miles on it. While I've had numerous fun moments burning the gunk out with some heavy feet and Lucas injector cleaner I have a couple of problems that aren't going away.

I have no previous maintenance experience with this type of car, so I don't know the regular problems that you guys run into. So, given these symptoms, where do you guys suggest looking first given the known issues of this model. (I have searched, but nothing has jumped out at me.)

1998 Mark 8 that has only had 3,000 miles put on it since 2003.

Runs up to 3,250 rpm like a scalded dog.

At anything less than 50 degrees outside it bucks like a drunken sailor between 3,250-3-750rpm. Even when above 50 degrees and at full operating temperature there is noticable hesitation in this rpm range.

Acceleration from 4,000rpm up is slower than keeping it below 3,200rpm. I haven't put a watch to it, but it's enough slower than you can tell by other cars and scenery.

I've run Lucas fuel injector cleaner with premium unleaded for 2.25 tanks and the following codes have come up when the CEL is illuminated.
Tank1
PO174: System to lean Bank 2.
Twice during the first 1/4 tank and once between 1/4 & 1/2 tank.
2 low speed backfires during this tank during acceleration.
Tank 2
No codes until less than a quarter of a tank, then a PO174: System to lean Bank 2.
1 low speed backfire occured during this tank during accleration in the first 1/4 tank.
Tank 3
About 45 miles of highway driving after fill-up and resetting the CEL from tank 2 then PO171 & PO174: System to lean Bank 1 & 2.

All CELs have occured at highway speeds, not under acceleration.

Average fuel economy a little over 18.5mpg in mixed city/highway driving 22.5mpg on highway only.


I'd guess I need to figure out where the fuel filter is, but I can't explain why it would run all the way to 6K with a partially blocked filter. The way it bucks and hesitates in the 3,000rpm range it seems more like a bad sensor (cheapish) or hopefully not an engine control module (ouch!).

What cha' think?

good below 3200 is classic IMRC's not opening, I'd guess-if it has been rarely driven for the past 7 years, a good tune up, oil change and fuel filter is a good idea (fuel filter is behind the inner fender liner, passenger side front, near the firewall). I'd also make certain the battery and alternator are up to snuff, and it wouldn't discount the stuck closed/malfunctioning IMRC causing the code. And if I was your father, I'd tell you not to beat on my Mark until it was gone through ESPECIALLY with only 29,000 miles on it...that thing (should be) treated like gold.!!!!!!:D Are you Ferris Bueller's friend Cameron, who destroyed his father's Ferarri???:confused::confused::confused:
 
Thanks!

Looks like I'll be doing the seafoam treatment this weekend if I have time.

It is a nice car, but you have to drive it enough to figure out why it is not running optimally.
 
The seafoam treatment works wonders. I did it twice and it's like somebody turned on the other half of the engine.

There is still some light surging at partial throttle in the 3,200-3,500 range, but foot to the floor it will go.

I'll have to do it a couple of more times next weekend.
 

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