hello guys I am new to this site. well first thing is my mark has been running really bad for a while now ..the best way i can say it runs is like a carb car that someone has put a bath towel in the air cleaner with a huge cam . i have replaced the spark plugs with autolite 764 ,cop with accel all 8,fuel filter,iac valve and i have sea foamed the car before i did all that. i have hooked the car up to my modis and as far as i can see everything is reading fine .i have not checked the fuel pressures or removed the cats . also the car does not do this all the time most the time it will run great but then it will act up.
1997 markviii running really bad..
- Thread starter pro50347
- Start date
chris2523
93 Mark VIII
check and see if it has a chip in the computer. if it does, remove it.
KStromberg
Dedicated LVC Member
I would pursue your next thought and check the fuel pressure. Your fuel pressure regulator could be faulty/leaking and causing pressure loss across the rail.
KStromberg
Dedicated LVC Member
35-45 psi with KOEO and KOER.
chris2523
93 Mark VIII
my car acted exactly as described when my performance chip came loose.
40 or so engine off or vacuum unhooked.
30 or so vacuum hooked up and engine running at idle.
KStromberg
Dedicated LVC Member
I'm fairly certain the pressure reading should be higher than that. :shifty:
chris2523
93 Mark VIII
nope. not at idle. BTDT. seen the numbers on the gauge.
now, here is why.
the Ford EECIV system operates under a 40 psi assumption.
now, this 40 psi is across the fuel injector. the manifold is under vacuum. about 10 psi of vacuum. see where i'm going?
40-10=30 psi.
you stomp the pedal and open the throttle blades, you have no vacuum in the manifold. 40-0=40 psi.
so the system keeps the 40 psi constant across the injector. but it wont read as 40 because the manifold is under a vacuum.
thanks guys .i do think that there is a ground issue somewhere on the car cause, the headlights flicker at wot and when i turn the head lights off the head lights and dash lights go nuts blinking flickering all kinds of crazy stuff .
chris2523
93 Mark VIII
belt slip. new belt on my car fixed that.
dunno about that one.. my car has started blinking the message center and EATC lights for no apparent reason though. it quits flashing when i turn my headlights on.
ok just got the fuel pressure tested up and here is the results .
engine at idle vacume line on 29-30
engine at idle vacume line off 39-40
when reving the engine with the vacume lines on swings to 40.
so as far as i can tell they seem to be normal .but i was not able to get a reding with the engine running rough,seems to want to run right at this time . anyone got anything eles that i should check ..
engine at idle vacume line on 29-30
engine at idle vacume line off 39-40
when reving the engine with the vacume lines on swings to 40.
so as far as i can tell they seem to be normal .but i was not able to get a reding with the engine running rough,seems to want to run right at this time . anyone got anything eles that i should check ..
chargerxr
Dedicated LVC Member
Have you tried cleaning the mass air flow sensor?
yes i have cleaned it twice . just went out to the car and it has been running in the garage for a hour hook up the modis and looked at every piece of data the thing could display there was 2 things that stood out. the voltage at the computer with everything in the car on is 12.2, that seems really low to me . and there was 2 codes 1151 and 1153 but those codes would not make my car run like this right....
chargerxr
Dedicated LVC Member
Yes 12.2 volts is definitely too low. Low voltage can cause all kinds of strange problems. Try turning on headlights, blower fan on high, rear defroster etc, and see how far voltage drops and if your car starts running bad.
My Great 8
Dedicated LVC Member
Buy an alternator. Problem solved
chris2523
93 Mark VIII
the car is running when you check the voltages right?
chris2523
93 Mark VIII
yeah you need an alternator.
2nd gens have a history of running absolutely terribly when the alternators go out.
BTW Kirk, i nailed the fuel pressure numbers.
2nd gens have a history of running absolutely terribly when the alternators go out.
BTW Kirk, i nailed the fuel pressure numbers.
chargerxr
Dedicated LVC Member
I can't explain that either. Don't have much time on the modis. We use OTC scanners at work. Found out today that we're getting the latest greatest scanner out right now. Back to your car. I still think I would lean towards a bad mass air flow sensor intermittently causing problems. Possibly a pcm-ecm problem.
97MarkJA
Dedicated LVC Member
Been there done that. Depending on how many miles you have on the car you may want to replace the alt, I had the same problem you've described last year.
The car would run fine for a while and develope a slight stumble that got worse.
The voltage at the orbII port will always be lower, but with the car running for a while I could sit and watch the voltage drop and of course the stumble would get worse. I Haas replaced the alt power wire when I replaced the alt and battery and was getting to point to where I felt like I was chasing the ghost in the machine so to speak.
I happened to lean over the car to check the voltage at the alt and my hand touched the main ground cable going to the block.. it was warm.... Quite warm.
I replaced the big 3 as well as the ground on the passenger side of the block, I also put a main body ground under the battery tray and real wires going to the fuse main fuse box.
Problem solved.
When you replace the big 3 the stud on the motor mount is a bit of a pain to get to, just make sure you clean the surface good around that stud.
http://www.lincolnvscadillac.com/showthread.php?t=83685