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Vincent, Ford Senior Master Technician
Category: Ford
Satisfied Customers: 1450
Experience:  28 years as Tech.
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A 31 Class C motor home on a E450 chassis with the V - 10..towing

Customer Question

I have a 31'' Class C motorhome on a E450 chassis with the V-10. The engine worked perfectly on a 2200 mile trip towing a minivan. I had just unhooked the minivan so the kids could go their own way and was nearing downtown Houston on the I610 overpass when the engine suddenly died, no chugging or anything. I coasted over the top and was able to safely stop without power brakes on a wide shoulder. I turned the ignition OFF and restarted it and it ran perfectly all the way home. I took it to Gulf Coast Ford today and they couldn''t find anything wrong, no error codes. They said it might have been a PCM reset. Has anyone ever heard of this problem? How can I trust this machine again if something isn''t fixed on it?
Submitted: 9 years ago.
Category: Ford
Expert:  Vincent replied 9 years ago.

When the vehicle (any) is driven over a altitude change, the engine control computer cannot recongize the change in the altitude without having the key cycled off an then back on again.

The other thing that you can do is make sure that you make a couple of wide open throttle pulls with the engine. Just having the throttle opened to 100% for a second or two will allow the engine control computer sample the air pressure.

But as for your original question. Yes that happens on a regular basis. As for how you can trust the vehicle? That is something that you have to decide. I think that you have found a mechanic that is honest and didn't just throw a part at your truck to make you think that something was fixed when nothing was.

Vincent and 3 other Ford Specialists are ready to help you
Customer: replied 9 years ago.
What confuses me about your answer is that I had been traveling for 12 days up and down the mountains of Arkansas and Missouri with no hint of a problem. I had stopped the engine about 50 miles out of Houston for dinner and the elevation wasn't 200' higher than Houston, which is 50' above sea level.

It seems to me that if the Engine Control Computer was getting the wrong information about the air pressure that it would run poorly and not just catastrophically quit.

Expert:  Vincent replied 9 years ago.

Let me give you a little geography note here: I live in Sacramento Ca, at about 50 feet above sea level. Just 90 miles up the road fro me, is Lake Tahoe at 5000 feet. I see this all the time.

When driving in the hills especially when going up, you are going to wide open throttle on a regular basis. This allows the engine computer to properly sample the air pressure and therefore make the correct calculations. When coming down the hill from Tahoe to here, the customer seldom goes to wide open throttle as they are coasting all the way down. When they get here and try to restart the vehicle, the engine just does not catch right away. And in fact it may take a couple of attempts to start the engine before the computer is able to make to correct calculations.

And this will not set a diagnosis trouble code or show up as a fault anywhere.

It can also cause a reading from one of the sensors to not be matching the air pressure that the engine is seeing. Remember we are dealing with a computer here, and the old rule of "garbage in, garbage out" still applies. In this case the "garbage in" was a sensor that had not updated to the correct vehicle air altitude. If the computer is making fuel calculations based on what IT thinks is 3000 feet, but the engine is at 500 feet, it is going to make a mistake. There is no way around that.


Other then the methods that I had already mentioned. Also I want you to understand that v10 engine is about the most reliable engine I have ever seen. We have vans that come in here with over 1,000,000 miles and are still running strong.

And a catastrophic failure, normally means that the engine is lying in the middle of the road in a pool of engine oil, bits and pieces.

Customer: replied 9 years ago.

I understand what you are saying about the altitude problem but I need to tell you about my geography. Friday in northern Kansas at 1900', Saturday & Sunday in Central Kansas at 1800', Moday in Tulsa at 1700', Tuesday driving to Huntsville at 200' with several engine stops and starts. Driving the last 100 miles at 100-200'. I never had a problem starting the engine. My question is: when the computer has a problem with altitude computation, will it just quit or will it start missing out? I'm at the dealer right now getting ready to pick up the motorhome.

Thanks for your help.

Expert:  Vincent replied 9 years ago.

It will rarely miss because a miss means that there is a problem on only one or two cylinders. When you have a issue such as this one, it will effect all the cylinders at the same time. That means that you might not feel the problem when it is starting to occur.

When the engine is running the engine computer is constantly compensating for the operating conditions of the vehicle. That includes altitude, temp, humidity, fuel quality, etc. There can become a point when the computers ability to compensate for the conditions is outside of its range. Say, the computer has been taking fuel out of the calculations to compensate for high alititude or lower air pressure.

Then all of a sudden (over a period of several hours even) the vehicle is driven from a hgh altitude or lower pressure zone (this can even happen during weather changes) to a low altitidue or high pressure zone and the computer cannot see that change while it is happening and therefore cannot make the compenstaion while it is happening.

That is why I first wrote how important it is to give the vehicle a full throttle pull on occasions. That is what allows the engine computer to see what the actual barometric pressure is. I have had cars that have been driven around all the time and never had them had a wide open throtte pull on them. After a while the engine will start to stall and hae a hard start. The fix is one of two things. Replace the Mass Air Flow sensor, or clear the engine calculation data and perform several wide open throttle pulls. Having watched the Baro reading while doing that, I have watched the reading go from 11 psi to 14.7 psi in a matter of 5 miles. When the vehicle is being driven around thinking that it is at 11 psi air pressure and it is at 14 psi (sea level) the amount of fuel being used is considerable different.

Customer: replied 9 years ago.
I think that Vincent is trying to help but his answers just don't seem to apply to my situation and I haven't seen fit to accept any. I should have asked Vincent if his scenario would cause the engine to falter or chug, not miss. My Ford dealer serviceman agrees with me that any of these fuel problems Vincent is talking about would affect engine performance not cause it to suddenly quit. The engine restarted easily. My Ford serviceman thinks it was electrical perhaps an erroneous PCM reset and may never happen again. I even gave him the opportunity to replace the Mass Air Flow Sensor and he said it wasn't indicated. I had shut off the engine several times since coming down from 1700' altitude and had numerous opportunities to goose it when getting back out on the freeway. I don't know whether I had given it a complete full-throttle pull but I know that I goosed it and got it up to 5000 RPM. I'm looking for an answer that tells me what to fix or someone to tell me that the engine suddenly quitting on an overpass isn't an unusual occurance and not to worry about it. If it happens again, I'll turn the ignition off and restart it. What more can I do? Vincent's answers just don't seem to apply. Regards, XXXXX XXXXX
Expert:  Vincent replied 9 years ago.


You can choose to accept my answers or not and I understand that. However, I can only give you my experience and try to relay that information to you. None of the information was fuel related, all of it was computer related as you must remember the computer is what controls the fuel flow. The computers job is to dispense and modulate the fuel flow to maximize economy, power and emissions. Three very different things.

What I do find interesting is just how reliable vehicles have become and the effect that it has upon us owners. 20 years ago, had a vehicle quit running, we as owners would have put the vehicle into neutral and attempted to restart the car or truck. If it had started, we would have put it into gear and carried on our merry way and not given it a second thought. Today it is a catastrophic failure.

All of the scenarios that I gave you apply to your situation as do the ones that the dealer gave you. I am sorry that neither I nor the dealer seems willing to tell you that there is a part that needs to be replaced on your truck. I think that is what you are looking for and that is what you pretty much stated.

Todays vehicles run for 100,000 miles with out so much as a tune up, start without touching the throttle pedal, idle perfectly 95% of the time, rarely hesitate or bog down, get decent fuel economy considering the load that they are required to haul, run hard when required, rarely overheat, and handle pretty much what ever we throw at them, whether that is in the city and stop and go traffic, or on the freeway, cruising at 70 mph with the A/C on.

And yet. It almost makes me long for the old days, where a vehicle had to be tuned up twice a year, it would take 5 minutes of high speed on the choke before you could put the engine into gear, the carb had to be adjusted when going from sea level to the mountains and when a truck would get 7 mpg, with no a/c, no cruise control, no load, and no comfort.

Goosing the throttle, is not the same as giving it a wide open throttle pull. I am talking about full throttle acceleration on a on-ramp type of pull, 10 seconds or more.

Customer: replied 9 years ago.
I will simplify my question. When the computer is getting the wrong information about the pressure and is selecting the wrong fuel/air mixture, will the engine start to chug and loose power, or will it suddenly and completely quit? Thanks, Marv
Expert:  Vincent replied 9 years ago.


It totally depends on just how far out of the computers parameters the information that it is operating on is. Keep in mind, this is something that I see Daily, due to my location. And yes it took me quite a while to understand why it was happening.

Let me try it this way. You have been operating in thin air (high altitude) that means that the oxygen molecules are few and far between. The computer adjusts the fuel flow and reduces it by an amount of up to -25%. The computer sees this air density becuase you have had to operate at a high throttle opening on several occasions because of a climb up a hill.

Now you have driven down hill, not really using the throttle as much, as you are letting gravity be your friend. The air is much denser and the oxygen molecules are much closer together. The computer is still operating the fuel at its old amount (the last time that it was able to update due to a wide open throttle pull) of -25%. But it really needs to go to +25%. That is a 50% change in the amount of fuel that the engine needs. The computer cannot see the reason that the Oxygen sensors are begging for the extra fuel. It is still looking at the old barametric reading and making its calculations based on that information.

But because you really are not loading up the engine, you do not feel the problem, or it is so subtle that you cannot notice it. You are after all driving a motorhome and pulling another vehicle. The amount of inertia that represents is very difficult for a small problem to over come.

The result, the computer throws in the towel and the engine shuts off. You pull over to the side of the road and turn the key off. The computer goes into a start up mode and looks at its old lookup tables for fuel curves. Because the engine has shut off, the computer is also able to now see the actual barometric readings at the air density that it is located at. It now understands why the O2 sensors were begging for the additional fuel and makes the adjustment. The truck starts and runs normally. Away you go.

Also one thing that you should try to understand. The sensors have limits that they can operate within. As long as they are within their limits, the computer will not detect a fault, because it expects to see that information. However, if the barometric sensor says that it is at 5000' and the vehicle is at 500' that is within its limits, but is not correct information. If the Baro sensors says that it is at 25,000' that would be out of range and would set a check engine light. The only way that the baro sensor will update is with a wide open throttle pull, or disconnecting the battery, or resetting the engine control computer. Of the three, only one is easy to do and expected on occassion.

Customer: replied 9 years ago.
Vincent, your first paragraph explains why you can't see my situation. Parts of Sacramento are at 33' and the Sierras are close by and at 5000' to 6000'. I would be hanging on your every word if I lived in Sacramento.

However, I live on the Gulf Coast and had supper in a Rest Stop north of Huntsville at an eleveation of 206', not 5000'. I don't want to talk about 5000'. When I started the engine at 206' after a fine supper that my wife had cooking for 8 hours in a crock pot, the computer was now able to read the correct actual barometric pressure according to your paragraph #5. I just can't see the situation that the computer needs a wide open throttle pull to read the barometric pressure correctly after I just started the engine at an elevation of 206'. I would be totally paranoid trying to find an uphill or a long overpass if that were true.

Your explanation also requires that I be very inobservant. I happen to be a 63 year old Sr. Electronic Design Engineer who has stretched the patience of my wife and son-in-law by frequently announcing that "it just down-shifted on this last overpass and is now at 3500 RPM." I pay very close attention to how the machine is operating.

I have driven the motorhome for 12,000 miles through the mountains of Kentucky, West Virginia, North Carolina, and Tennesee. I know what its normal operation is over a wide variety of circumstances. I didn't know what a Mass Air Flow Sensor was and didn't seem to need to know because the machine worked perfectly all that time.

Your explanation just doesn't make sense for the very benign situation of me starting the engine at 206', driving for 1 hour to 50' (probably less than a -.2% change in barometric pressure) while observing it downshifting normally for 15 or 20 regular overpasses indicating that the engine had good power, and then having the engine suddenly quit after getting halfway up a 100' overpass at the 610 loop.

My wife just told me to please hit the Accept button and get it over with and stop wasting my time but I can't do it. Your explanation simply doesn't address the wierd perfomance of this engine under these very benign circumstance after all of the driving situations I've been through in the last year.

This question is not worth more of your time. I'm going to save my $15 in my account for another question in the future. I'm sorry that you spent so much time on these answers.

Regards, Marv
Expert:  Vincent replied 9 years ago.


After our first dialog, I never expected you to accept my answer. And I have no problem of you saving your money for the next time. I was merely trying to explain the operation of your vehicle to you and try to explain what could have happened to cause your truck to stop running.

As a Electronic Engineer, you of all people should know that every now and then something occurs that unless you are monitoring everything when it happens, you cannot explain what just happened.

As for Barometric pressure, that also changes due to weather conditions. You do have a barometer at home, right? A weather pattern or a change in air pressure due to a cold/warm front can cause the same thing as a change in altitude.

The computer gets it information from the sensors that are on the vehicle, it has no other way of developing data, it does not have any sensors built into itself. Therefore it relies on what the sensors on the vehicle are telling it. The Mass Air Flow sensor gives the computer two pieces of information. One: the Mass of air being used by the engine. Two: The Barometric pressure of the atmosphere. The MAF will not give the engine control computer the correct barometric pressure, unless the vehicle is given a wide open throttle pull. In fact when I have to do tht correction at work, I normally have to do several WOT accelerations, just to get the Baro to update. And this doesn't matter if the vehicle was driven at 33' altitude for the last couple of years.

If you are uninterested in trying to understand how the system works, don't care or need to know what a MAF sensor is, then you are correct and I am also sorry that I spent this much tie trying to explain it to you.

However, what you can do with the information that I have given you is one of two things. One: you can use it so that when the vehicle runs out of warranty, you will have a better understanding of how the system works and processes information, and perhaps prevent you from........

Two: not use it and when the mechanic tells you that the MAF sensor is no longer working correctly, because the Baro is reading 12,000' and we need to replace the $200 part, you can spend the money.

Customer: replied 9 years ago.
Actually, I do appreciate your explaining the NORMAL operation of my vehical. I have learned a lot and thank you for that. As a very curious and experienced Electronic Engineer, I sincerely XXXXX XXXXX I had a log of the Baro readings from last Tuesday evening. If it had indicated 5000' as I went up the overpass at Loop 610 I would apologize and send you $150 but the situation as I observed it doesn't support that. I am quite convinced that something ABNORMAL happened when it quit. I'll live with it but I'll ask my Ford serviceman if he has the tools to read the Baro. I am very curious about that.

I will be on edge for awhile before I can totally trust this machine again.

Actually, I have changed my mind and will hit the accept button if you would explain quickly how the transmission computer works. I've driven this truck for 12,000 miles and have not been able to figure out the algorithm that controls how and when it downshifts. I usually have the cruise set at 63 MPH. When I get near the top of an overpass it starts to groan a little and the RPM jumps from 2200 to maybe 2300 or 2350. Then it actually downshifts and jumps to 3500 and then 5000 if its a really steep hill. If I anticipate the downshift and manually put it in 3rd it jumps to ~4500+. How many gears does this transmission actually have? I sense it going through 5 gears when I'm getting up to cruising speed. Should I always run it in Tow/Haul since this is quite a heavy machine?

Please don't spend a lot of time on it. Just a quick run-down. I haven't been able to find this info anywhere.

Expert:  Vincent replied 9 years ago.

Every Technican has the ability to read the Baro. However, I doubt that they are going to loan you a $1000 scanner so that you can monitor that information.

I would like you to reread the second paragraph in the fourth answer that I wrote to you. Being on edge waiting for your truck to mess up again is not a good way to spend your days. Just to put your vehicle in prespective. That truck has more computing power then the Apollo 11 moon shot. And all you are doing is driving around.

As for how the transmission shifts, there is no algorithm. The Ford computer is a adapative and learning computer. This has been the case for many many years. The systems are constantly trying to figure out how you drive and adapt to what you are telling it.

As for how many gears your transmission has: 6 plus a converter lockup. It can and will lock up the converter in the top four gears. That will make it feel like it has 8 speeds at times. Quite often the 1-2 shift will barely be felt, even by those of us (technicians) that are looking for it.

The 200 rpm change that you feel when getting to the top of an overpass is the converter coming out of lockup.

Torque converter lockup is used to remove two things. One is the slippage inside all converters during normal operation (without lockup). Locking up the converter makes the transmission act like it is a manual transmission, with a solid connection between the engine and the rear wheels. The second thing that is does is remove a heat source from the transmission fluid. When the converter is operating normally (again nonlocked up) that thing is beating the trans fluid hard and heating it up. When the converter is locked, there is little or no heat production. And the computer can and will shut down the vehicle if the trans fluid gets too hot. Just to protect itself.

Let the transmission computer do the shifting. The tow-haul button tells the computer to increase the shift pressures and delay the shift timing (shift later). It will also increase the engine braking available on deceleration. That is covered on page 154 of the owners manual.

As for the rpm that the engine runs at: Don't worry about that, the computer will not blow up the engine.

Customer: replied 9 years ago.
Vincent, thanks for your information on how my transmission (torque converter) works. You have confirmed some of my suspicions except that I have obviously missed the subtle 1-2 shift.

I bought the machine used and did not get an Owners Manual with it. I just went to and downloaded the Owners Guide and found your info on page 154. It's good to finally have a manual so I especially can understand the instrument cluster and the transmission.

I'm figuring that what the manual refers to as a 5-speed is actually the 6-speed that you described and they don't expect a layman to sense what the old people called a "kicker gear" in my Dad's '66 Olds.

I had suspected that Drive actually gave it control over 2 gears because of my surprise at manually downshifting on a hill and having it go to 4500+ RPM instead of my expected 3500. I was cured then and decided to let the computer make the decisions after that.

Thanks again for your help. I happily hit the "Accept" button now.
Expert:  Vincent replied 9 years ago.

Marv: That vehicle comes with two different transmissions, and the first printing of the owners manual did not make not of that. The 4R100 is a 4 speed transmission, with lockup. The Torque Shift is a 6 speed transmission with lockup. The owners manual does not have all the information that the shop manual has and yes I agree that sometimes I think that Ford thinks that the customer needs less information then they should be getting.

However, we joke about it all the time, the most Unread book in history......the vehicle owners manual.

And that 1-2 shift happens really quick and lightly, unless you are really on it.

Phew, I am glad that I was able to put a small smile on your face.

Cheers XXXXX XXXXX you.