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Discussion Starter #1 (Edited)
Hey guys. Was trying out forscan and stumbled on something confusing.

I have had no CEL, and no driveability issues. 1997 F-250 7.3, E40D.

While checking codes I came up with a P0236. (Map out of range). So off to the PID's I go. Here is what I found.

KOEO-

MAP 81.5 kPa
MAP 102Hz
BARO 29.21 kPa
EBP 84.4kPa

Quick conversions tell me the map and exhaust pressure readings are real close to correct for my altitude, but the baro seems really low.

Am I on the right track? Seems like I'm in the market for a new baro sensor.

Seemed strange to me because I've had no problems, runs good, pulls good, no smoke, MPG's dropped a bit but I attribute that to winter warm ups. I cleared the code and it hasn't come back, but I haven't worked the truck, just cruising back and forth from the house.

Any ideas?

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Also, upon finding the initial code, I checked the map sensor line, connection, and checked for manifold pressure leaks to be safe.
 

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The barometric pressure will fluctuate depending on if you are in a high or low pressure zone or if the pressures are raising or going down. If I remember right you said that you were around 6000' which would put the baro pressure at 81.22 kPa but if there is a low pressure area such as a storm where you are at it will be lower. That 81.22 kPa is just where they start measuring it for your altitude.

A good way to watch the pressure is to just watch the TV news and weather for your area. I am not sure if they still do it but they used to show the barometric pressure as a gauge for a weather change.

Now that I have you totally confused I wouldn't worry about it as long as the glow plug system is working alright. The baro sensor and the EOT is what tells them to come on and for how long.



I just looked at what the pressure was in my town on The Weather Channel and it shows 30.12 inches which is 103.1 kPa and if you look at the chart I should be 500' below sea level while I am sitting at +6500'
 

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Discussion Starter #3
Thanks! I like the stuff that doesn't need worried about.

I have a barometric pressure app, so that's what I was comparing it to. It also has an altimeter, your memory is great!


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I doubt that the baro has anything to do with the map sensor, two independent sensors.
 

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Discussion Starter #7
Ok, I didn't know if it relied on a baro reading to get a 'range' for the map sensor. I'm still learning how smart the computers in these things actually are.

I know pressure change has a noticable effect on a mechanical engine, but that's as far as my experience goes thus far.

So if the map code comes back any idea? I read a pile of other threads on the matter, but they seemed to have significant mpg loss and check engine lights.

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If nothing else you could always just replace the map sensor.
 

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Discussion Starter #9
Ok thanks. Not really excited about spending money on a maybe, so I'll see if it comes back first. And be sure to check codes again next time it drags a load. I also read about "over boost" codes, but couldn't discern if it could throw the p0236, or if was only the p0238.

That came to mind because it hadn't really been opened up until recently, not abused just worked a little harder than normal.

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As I recall the MAP sensor will get “confused” if the MAP sees boost over 22psi and will show an out of range code. When this happens the PCM defaults to stored linear fuel tables (not dynamic, based on MAP, because it’s out of range). Now pending mods you have on your rig this may reduce HP/torque output. A work around is to install a boost fooler (regulator in MAP line) such that MAP never sees over 20 psi. Other option if running tunes is have programer to account for MAP overboost. Incidentally on the SD version of engine over boost results in a de-fueling which guys assume happens with the OBS, which my understanding is not the case.

If you feel a loss in power or noticeably more smoke, unhook the Wiring harness from MAP so PCM reverts to linear tables and if it drives more normal might be MAP sensor is booogered. If running tunes check with vendor to see if program files have accounted for above 22 psi boost.
Cheers,
j
 

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Discussion Starter #11
That is exactly what I was doing. I assumed it would do all kinds of alarming things, thanks for explaining that to me, and anyone else who reads this! I had not previously seen that unplug and run test, really glad to learn that. (Truck is stock, save a tymar type air cleaner)

Thanks for the help gentlemen.

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I thought that it was interesting that you had a app that had the barometric pressure on. I downloaded the app or a app for it.

I found out that for me the temperature and barometric pressure comes from the local weather station at the local Airport. I was actually watching my elevation change as the satellite got further away or closer. Since it goes by the GPS in my phone. I'll have to get my actual GPS out and see how accurate it is.

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Discussion Starter #13
Cool! Hope you have fun with it!!

Mine came on the phone, supposedly the phone itself measures the pressure, then it guesses the altitude. Altitude has to be corrected manually, so it's off a bit if the weather changes, or when traveling. The barometric pressure side is really good, but the altimeter can't be trusted, although it's usually within a couple hundred feet of my Garmin. On top of Lizard Head Pass it's off by 300 usually.

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You might want to download the free app and then compare the two.

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Discussion Starter #15
Indeed, would be interesting to see how they compare, I've compared it with the National Weather Service page a couple times, just enough to deem it "close enough".

Did you use a specific app?

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I just searched for barometric app and picked a free one. There are some small adds that pop up on the bottom of it but not where you would really notice them.


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Discussion Starter #17
Ok, so more correlating info, kinda.

Short version of a long story, a buddy decided we needed to get an OBS in Denver this weekend. Truck was a junk pile." No Major Rust" loosely translated to ratchet straps holding the bed together. So after a polite "thanks for wasting 870 miles of my time" to the seller, we headed back home. Then through a Craigslist miracle, a better truck was found in route home, and subsequently purchased. So silver lining I guess.

Truck is a twin to mine, 1997, super cab long bed, 4x4, E40D.
*Except-387k miles, 6pos chip of some sort, and rebuilt trans.

Here's where it gets interesting.
Used forescan before purchase:
Found P0107- MAP/BARO circuit voltage?
P0344- CPS signal inactive?
P0236- High MAP at Idle

Checked PID's and found similar results to mine, from the earlier discussion in this thread. EBP/Map numbers were really close, but the baro was pretty low, around 20kpa. ( We were around 6700', between storms.) But still low by my reasoning.

On mine I tried another baro sensor at one point, and it reads the same, and fluctuates with weather and elevation, so I don't see a problem. Just thought I'd post it up, since it's a documented case of two doing it.



The P0107 and P0344, along with botched cable ends and new batteries makes me think these could be the result of long cranks and jump starts, so not terrified just yet.

Only hiccup in route home, is it died when shifted to reverse at a rest area, acted like the TC locked, but not sure since I wasn't driving it. Doubt it's related to the matter, but E4OD's are odd. Only did it once.

Cleared the codes, we'll see what happens, if any of y'all have a suggestion, idea, moment of clarity and enlightenment, or an epiphany, the feedback is always appreciated. Figured I'd share the puzzle.

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