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Vincent, Ford Senior Master Technician
Category: Ford
Satisfied Customers: 1450
Experience:  28 years as Tech.
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93 lincoln mark viii: getting code..scan tool..voltage..lean

Customer Question

i have a 93 lincoln mark viii. i'm getting code 181, 542, 587 in keep alive memory. data stream from scan tool shows the o2s with no voltage and short term fuel at 25% at idle indicating a lean condition. i raise the rpm's or wrap the thottle and the o2s will switch. the engine light does not stay on. it only comes for a minute and then go off at part thottle like the code says. i've tested fuel pump voltage at the enertia switch. according to alldata it should have 9v at idle and 13 at 3500 rpm. my test showed 12.1 at all times w/ no change.   i've change the vcrm car still does the same.   car runs pretty good other than a slight lope at idle when cold and still in open loop and a little bump under a heavy load. also the fuel gauge swings way above full during start up before leveling. i don't remember it doing that before. intake smoked with no vacuum leaks. think you can shed any light?
Submitted: 8 years ago.
Category: Ford
Expert:  Vincent replied 8 years ago.

Yep, Replace the Mass Air Flow sensor.


Also make sure that there is a proper paper air filter installed. The K and N style air filters are not compatible with the MAF on most Ford vehicles.

(the only exception is the Mustang, as the MAF is able to handle much more abuse)

Customer: replied 8 years ago.
maf sensor is only about 8 to 10 months old. and it is a ford sensor. scan tool will show voltage only not hz but voltage is in spec
Expert:  Vincent replied 8 years ago.

There is little that will cause that much of a lean condition;

Low fuel pressure.

Bad o2 sensors (they really only have a 60k mile life span)

And a bad MAF.


I don't know what your fuel pressure is:

I don't know what the history of the o2's are.

But I do know that all it takes is one water puddle hit and the MAF is junk.

Perhaps remove it from the air box and inspect the sensor wires on the maf.

If they are contaminated or damaged in any way what so ever, you are probably going to have to replace it.

I have had MAF's read in spec with their voltage, but be running at 7,000 feet altitude (120 hz or so). I am at sea level and that just makes the car run rather lean.


Customer: replied 8 years ago.

fuel pressure is well in spec at around 40 psi if i remember correctly. i even tried disconnecting the vacuum hose, pressure increased but still lean. also the lean only seem to be a idle and partial thottle triggering the light after that light goes as pedal is pushed down. also if fuel pressure was a problem it would seem to be revelant when you stomp on it. but this car runs better the more gas you feed it. has no problem reaching redline on highway and will hit the 130mph limiter before it goes into overdrive. it does not lack any power. the o2s will start switching and fuel trim will correct as soon as you increase the rpm's or wrap the thottle. also what would the maf have to do with a 542 code and a 587 code.

Customer: replied 8 years ago.
also shouldn't i get a lean condition on both banks if maf is bad
Expert:  Vincent replied 8 years ago.

Well the 542 is a high resistance or open in the fuel pump circuit. If that is occuring then the engine will not be running.

The 587 is a lack of communication between the PCM and the VCRM. This should have been corrected by the replacing the VCRM. But again that will NOT cause it to be lean.


So we get back to the engine inputs.


That engine is not known for vacuum leaks. However, there are a couple of spots at the throttle body when the PCV system connects to the throttle body.

It is possible that smoking the system (which puts pressure on the interior of the induction system, exactly the opposite of how the engine runs) will not show a vacuum leak, and that is about the only place that I would be looking for a vacuum leak. I would also look at the pcv valve itself. If it is old and stuck open, then it is possible that it is causing false air.


The 181 is XXXXX XXXXXmit reached, lean bank one. It is possible that you are lean on both bakns, but that the limit has not been reached on bank 2. The bank 2 code will not trip until the limit has hit that limit.

You mention that you are at +25% short fuel trim. Is that on both banks or only on one?

Any vacuum leak, will also effect both banks.


Again, what is the age and condition of the o2 sensors?

How well are they switching when they are working?



Expert:  Vincent replied 8 years ago.

Another thought that I have seen, just not on Mk8's. It is possible that the injectors are just too old and not flowing to spec. This will show up more on extended idle then anywhere else.

Just something to think about.


Customer: replied 8 years ago.

i'm pretty sure that there isn't any vacuum leaks. besides from smoking it i've also sprayed carb cleaner at every possible vacuum line fuel injector and up and down the air horn and the engine didn't make the slightest hic-up. the pcv may be a possibilty, i haven't the slightest as far as age. i'll check that in the morning. i know that 542 and 587 codes usually have nothing to do with a lean but all 3 codes are set at the same time. i don't have access to a schematic but is it possible that there is something that shares the same circuit or possible pcm failing?


short term fuel trim switches from 20 to 25 as the o2 switches on bank 2 at idle

bank one will not switch w/ fuel trim at 25. it will switch when rpm increase as will fuel trim.


i did replace 1 injector on bank side cyl 8 b/c of failing cyl balance test. problem was corrected. passes test everytime

Expert:  Vincent replied 8 years ago.

Again I keep going back to the O2's age and I would really look hard at the MAF.


Are you stating that bank 2 is running between +20 to +25%?


Customer: replied 8 years ago.
yes, the o2 on bank 2 switches and the fuel trim will change as it switches. but when the o2 goes rich the tup trim only peals back to 20 then back up to 25 as the o2 goes lean
Expert:  Vincent replied 8 years ago.

If that car is running at +20 to +25% short fuel trim on bank 2 as well as bank 1 then you are lean on both sides.

You should see, if the car was running correctly, at idle, +10% on both banks Long Term and Short term should be switching at between -5% to +5%.


The short term tracks the minor corrections that the O2 sensors are making as the engine is running. The long term is the major corrections that the short term requires.


You have a lean condition on both banks.


Unplug the MAF and see what happens during extended idle.


Customer: replied 8 years ago.
i've unplug the maf and the car ran differantly but no change as far as fuel trim and o2s. i stated before that bank 2 somewhat switches while bank 1 doesn't at idle. so i switched them to see if it is the o2s. no change. bank 2 still somewhat switched and bank one did not. so that rules out o2s. i removed the maf and cleaned the eliment which really wasn't dirty and noticed that it looked fairly new and it is a geniune ford. now that i think about it i believe i did replace not long ago. so i don't think it's the maf. i cleared codes and disconnected the battery for over 15 minutes to kill the keep alive and adaptive learning and then drove it. 181 and 587 came back, 542 did not. i don't understand 587 b/c of the new vcrm. i thinking the pcm could possibly be bad given the communication circuit is good. also, the vcrm has a low speed fuel pump relay and according to all data that there should be about 9 v at the enertia switch at idle. i have 12.3 v at all times. even if i take out the high speed fuel pump relay out of the fuse box i still have 12.3 v and the car runs no differently. is it possible that since the pcm and the vcrm don't know what the other is doing that the pcm is forcing a lean b/c there is too much fuel at idle. i believe the fuel pulse width should be around 4 to 4.3 ms at hot idle but the scan tool shows 3.3 ms which would cause the lean. also, i don't know what the fuel gauge, if anything, has to do with all this. the fuel gauge will sweep well pass the full only when cranking not with the key on or running just while starting and that only happens sometimes and only that gauge. i hope this info gives you a better idea of what's going on.
Expert:  Vincent replied 8 years ago.

Lets start with:

Please stop looking at the voltage going to the fuel pump. If your fuel pressure is correct (you said if you remember correctly it is at 40 psi, double check that with a pressure gauge. Do not assume that it is always at 40 psi) then the voltage to the pump is just fine.


The VCRM code, might be that you have the wrong VCRM or a pcm failure. Again not something that I am concerned with.

My concern is the lean running.


You need to stop thinking that 3.3 ms at idle is out of spec. Remember the injector pulse width is commanded by the pcm, because of what the pcm is seeng.

What I need from you is actual numbers from long term, short term and o2 switching.

I need + and - on fuel trims and the voltages coming out of the o2 sensors.

And not rough numbers. Keep in mind, if I was diagnosing this vehicle, what would I see? I would be looking at actual data, not what you remember them or believe them to be.


Also double check the charging system voltage and check the voltage drop across the grounds at the o2 sensors. In fact, check the voltage drop across the negative battery cable going to the engine.


Customer: replied 8 years ago.
okay, at idle and vehicle is in closed loop. bank 1 o2 changes from .01 v to .04 v at idle. short term is at +25% steady. bank 2 o2 changes for .04 v to .78 v at idle. short term changes from +20% to +25%. there is no pid for long term fuel trim. battery is 3 months old was changed b/c of age and a badly dragging starter finally did it in. check charging system at that time and all was good.
Expert:  Vincent replied 8 years ago.

"check charging system at that time and all was good."


What is the charging system doing now, what is the voltage drop across the battery cables (both positive and negative) now, what is the resistance on the ground circuit between the pcm and the battery, now.


I need actual data, not what you remember them or believe them to be.


What happens to the voltages at 1500 rpm? And actual numbers please as well as short term fuel numbers.

Customer: replied 8 years ago.
like i said earlier the short term fuel on bank 1 is stuck on +25% at hot idle and again short term fuel on bank 2 changes form +25% to +20% at hot idle. this is actual data! as far as the charging system goes, the car was doing the same thing now as it was doing then. i won't be able to get actual data till monday.
Expert:  Vincent replied 8 years ago.

And lilke I said, what are they doing at 1500 rpm. Now unless the car is idling at 1500 rpm, your hot idle data is not giving me what I need.


Back to the o2 voltage.

That low of a voltage on bank 1 shows the exhaust to be lean (below .4 volts is lean) that means that the computer should be addingfuel out trying to richen up that side of the car. Which your short term fuel trims are showing.

What happens with the O2's if you inject a little propane into the induction side?


One of the issues of the older Ford's is that the computer tends to burn in learned data to its memory. I have had timing data burn in and the onlly way I got it to clear is by disconnecting the computer overnight.

This is an issue with when you crossed the o2's (what I mean is, you swapped the o2s but did not see an imediate change in fuel trims. It is quite possible that the computer did not run for long enough to start the compensation)


I really am at the conclusion that you have a bad o2 on passenger side (bank 1) and a small vacuum leak in the pcv system.


Customer: replied 8 years ago.

i'll now have to wait till tuesday instead of monday to get the required data b/c the check engine light just came on in my wife's 07 escape. it's still under warranty so i have to drive it to work to drop it off at the dealer instead of the lincoln. should i disconnect the pcm now and let it sit overnight or would you rather me get the data you're asking for first before i try resetting the pcm? as for the pcv system all hoses and vacuum lines are good as i said earlier not only did i smoked it extensively pumping smoke through the brake booster vacuum hose i also soaked every inch of every vacuum line with carb spray w/o the slightest change in engine idle. the pcv valve itself would have to be the problem. as far as i know it's never been changed. with that said, i'll get the charging system, o2, and fuel trim info at 1500 rpm. i'll also see what happens with the propane but i can tell you that they both will switch with carb spray. i know you want the actual numbers when i did this but i can't tell you exactly just i know they both went at least .7 or higher. before you say it, i'll do it w/ propane and record the actual numbers.


with all that said, should i do all this before or after resetting the pcm?


Expert:  Vincent replied 8 years ago.

Why don't you try disconnecing the pcm over night now, just to see if the 587 comes back.

And I would really like it if you were to physically inspect the vacuum tee right at the throttle body. It is kind of buried behind the inlet hose and it is possible that you cannot get any carb cleaner to that area.


As for your wifes Escape. It probably just needs a PCM reprogram.

Customer: replied 8 years ago.

i'll go ahead a disconnect the pcm and give you an update on tuesday


your probably right about the escape b/c it runs fine, the light just came on for no apparent reason. thanks for your patients. and i'll talk to you tuesday.

Expert:  Vincent replied 8 years ago.
Let me know.
Customer: replied 8 years ago.

ok, i didn't get a chance to do the propane or check the voltage drop and resistances. i did check the charging system and i had 13.7v at 1500 rpm and no load. as far as the

o2s and fuel trims, they are still the same.


bank 1 @ 1500rpm: o2 .23v to .04v fuel trim +22 to +25%

bank 2 @ 1500rpm: o2 .81v to .12v fuel trim +15 to +20%


the o2s are still swapped. i haven't swapped them back to there original banks and bank 1 still seems to be the one more lean.


i do not have a vacuum tee on the thottle body. i have a main vacuum tree in center of intake that supplies the brake booster. just to the driver side and back a little from it there is the other main vacuum that supplies the pcv, egr, and imrc's. both come straight up out the intake.


i drove the car today and put about 50 to 60 miles on it and no check engine light so i guess that's a plus. also i'll be changing the pcv valve tomorrow. you can actually hear and feel it buzzing.

Expert:  Vincent replied 8 years ago.
Let me know what happens with the trims after you change the PCV.
Customer: replied 8 years ago.

okay, pcv valve has been replaced and it helped a little. here are the new numbers:


bank 1 o2: .08v to .78v @ 1500 rpm

bank 2 o2: .17v to .78v @ 1500 rpm


bank 1 fuel trim: +18% to +22% @ 1500 rpm

bank 2 fuel trim: +11% to +15% @ 1500 rpm


i'm thinking maybe i should change the grommet also it'll probably be friday before i can get one. the pcv valve is pretty easy to slide in and out of it. even though the pcv seems to have helped @ 1500 there is still no change at idle. if left idling long enough the pcm switches to open loop and engine starts to lope. it'll be friday before i can check anything else. i'll still check into the voltage drops and resistances. what else should i be looking for? also when i'm watching the o2s change they don't seem to be changing in stages as all data claims that they should. according to all data they should go lean, middle, rich, middle, lean. neither one switches exactly like that. should i be concerned about that?

Expert:  Vincent replied 8 years ago.

With the fuel trims at +18% at 1500 we can pretty much rule out a vacuum leak.

If the O2's are really lazy and slow to switch I would be changing them out. It is quite possible that they are biased lean and are what is driving the fuel trims. Not knowing the history of the car or the age of the o2s doesn't help.

I also have had the incorrect maf supplied and installed and caused this.


But like I wrote earlier, the o2's have a life span of only 60k miles. After that they are not suppling the correct information.


Remember how the system works. The computer looks at the MAF voltage to determine how much fuel to supply to the engine (injector pulse width), it then looks at the o2s to determine if that was too much (rich) of too little (lean) fuel. It then changes the pulse width and starts the whole process over again. On that car, it does that about 15,000,000 per sec. (the EEC IV processor is a 15Mhz proc).

If the computer is making the correct calculations based on Mass air flow, but the corrections (the o2's) are incorrect, then the fuel trims will be incorrect. Eventually the fuel trims will get to a point where the computer falls out of its ability to make corrections and it turns on the check engine light, et al.

Customer: replied 8 years ago.

but if i swapped o2s, don't you think the banks should have followed suit. as far as age goes, i don't know. all i can say is that one has been changed at one time. one of them is an aftermarket bosch o2 while the other looks factory. the bosch o2 was orignally on bank 2 and it's now on bank 1. also is it possible the o2s can burn out due to an extended period of running lean? b/c when i first got the car it was so lean it would lope so bad at idle it would sound like i had a solid lift cam in it or it would kill all together. especially when cold you could barely got it to take fuel. it would stall real bad if you tried to give it gas when you first started it. you had to wait a little to get it warm and then it ran ok after that. i replaced one injector and did 2 injector flushes and induction services. that got me to this point now.

Expert:  Vincent replied 8 years ago.

You are lean on both banks. You are swapping one side for the other, but both side are running lean. The +18 to +25% fuel trims mean that the computer is adding that much more fuel over what it would consider its normal calculations. That number is XXXXX on both sides. You are just getting a code for one side.


How long did the car sit?


What is the fuel like in the car?

If the fuel is old and varnished, then that is the problem.


The o2's will burn out, just by use.

Consider where they are located and what they do. They are in the exhaust gasses, that is normally over 1000 deg F. After a while, they are done.

Customer: replied 8 years ago.

the car has never sat for ant extended time. i've been using it quite regularly. i've got a lot of money tied into this car already. i'm just tired of throwing more parts at it with no results. can i try changing just one to see a change or does both need to be changed to see results?

Expert:  Vincent replied 8 years ago.
Go ahead.
Customer: replied 8 years ago.
you've spent a lot of time with me already and i really do appreicate it. i'm going to accept your answer so you can get paid. after that will i be able to talk to you if the o2s don't work.
Expert:  Vincent replied 8 years ago.



One of the problems is that my scanner would have given me a lot more information then yours is giving you. Long term fuel trim is what I really go by and rarely use short term.

Vincent and 3 other Ford Specialists are ready to help you
Customer: replied 8 years ago.
i know. i have two scanners. one is the OTC genisys which is the one i'm using. i also have a WDS but the thing only connect the 96 on up. oh how i wish that car was a little newer. i would have so much more info to look at. no of my ford bodies have a NGS. so i'm stuck with the OTC.
Expert:  Vincent replied 8 years ago.
Yeah. The only scanner that we ever had that was worth a damn on EECIV, at the dealership was the SBDS. But at close to $50k, slilghtly out of my budget. I have a MAC scanner that works with both OBD I and OBD II and use it on just aout everything, unless I need stuff that only the Ford systems can pull. And that only happens with the OBD II cars.