So, the truck has a weird MAP sensor issue. It went bad a couple years ago, so I replaced it. That one started acting up maybe 6-8 months later, on the offchance that it was something weird I plugged the old one in and had no issues.
Fast forward another year or so, I'm rebuilding the engine and I figure "hell, I'll go all out and replace all the sensors with Ford parts."
Fast forward one more time and the MAP sensor is starting to act up again, I replace with the original one from the truck and all my issues have gone away. I'm at the point where I'm keeping all three MAP sensors, one plugged in and the other two in the glovebox of the truck.
Anyone have any idea what might be causing MAP sensor issues periodically?
'93 F150, 4.9L, E4OD
Given how those sensors work- electrical noise?
Those sensors are not like other MAP sensors, they use a frequency output as the return signal. No idea why it was chosen back in the day.... But noise would mess with that signal.
Yup. Did you upgrade plug wires to spiral core? Crusty alternator perhaps?
Also pretty sensitive to voltage/ground. Next time it happens, hook a jumper cable from the block to the negative on the battery and see if it changes.
So the MAP sensor is in the top left of this pic, it has a red question mark on it as I wasn't sure if it was a good sensor. The wires are on the right side of the pic and hidden by the block, head, and intake. The wiring doesn't go anywhere near the spark plug wires, from what I know of EMI you'd have to have a pretty strong signal to reach that far, especially with the lumps of metal in between. Am I wrong in that?
I've also been running the same wire type (Accel 8mm spiral) since my very first tune up over 10 years and 150k miles ago. Unless they changed the design of the wiring or there was a QC issue, but I believe I changed wire sets between the first episode and the more recent ones.
The alternator is fairly new, definitely non-crusty. I upgraded it from the stock alternator to Ford's 3G or 4G alternator (can't remember which without looking it up.)
As for the ground, maybe four or five years before I first had the first of these issues I rerouted the battery ground system. Originally it went from battery-frame-starter/block. I made my own cable, upgraded to 0 gauge wire and went battery-starter/block-frame.
In reply to alfadriver (Forum Supporter) :
I always assumed it was because a frequency would be relatively insensitive to shifting grounds.
On the other hand, Ford went with voltage for MAFs and GM went for voltage on MAPs and frequency on MAFs, so who the heck knows.
Mr_Asa said:
As for the ground, maybe four or five years before I first had the first of these issues I rerouted the battery ground system. Originally it went from battery-frame-starter/block. I made my own cable, upgraded to 0 gauge wire and went battery-starter/block-frame.
It's probably not the issue, but it's best to not get inventive when it comes to grounds routing. I acquired a cheap VW because it blew two computers in a row. The ground cable had been replaced, and I do not quite recall the OE routing vs. how it was run (battery-chassis-engine vs battery-engine-chassis?) and you'd think it should not make a difference, but this was a known issue and routing the grounds per OE did solve the issue.
Pete. (l33t FS) said:
In reply to alfadriver (Forum Supporter) :
I always assumed it was because a frequency would be relatively insensitive to shifting grounds.
On the other hand, Ford went with voltage for MAFs and GM went for voltage on MAPs and frequency on MAFs, so who the heck knows.
I really don't know- that was before my time- all of the vehicles I played with 1992 had MAF sensors. But they were just voltage sensors.
The frequency part is why I suspect some interference- just because a little shift in the frequency due to some noise will really mess it up. Just like a floating ground for a WB sensor... (chuckle...).
I'll double check on how the sensor works tomorrow- I actually have an EEV IV input/output book from 1993 that I just got from my office.
Is it mounted with the port facing downward? If not, it is possible for sensors to build up oil and cause them to misbehave.
As far as EMI, location has a lot to do with it, but we're talking 50,000 volts. I have seen circuit boards on sequential turn signals get messed up with CDI and solid core wires, and they were 15' away from the coils.
If you're holding a steel rod that gets hit by lightning, it doesn't matter if the rod is 2' long or 200' long, you'll get zapped.
Still, unlikely, just mentioning it as a possibility. I'm not really suggesting the second ground to suggest your current ground is poor. If you add a redundant ground loop that is a different length than the current (pun intended) ground, you can defeat an EMI frequency. Ever notice how if you touch both conductors of an RCA cable with your finger, a speaker will hum at 60 hz? The inherent oscillation of the AC current makes an EMI pattern at 60hz. When you touch both conductors, you are effectively shorting two equal-length conductors and amplifying the resonant ability. If you were to connect a 10" wire to one of them and then touch both, the effect would be less and you get less hum. Again, since it's a generated frequency, the length doesn't matter. It's the fact that they are equal length.
Old tricks from my CB days.
I'm also curious what the symptoms of "bad MAP" are. Is it reading incorrectly, or dropping out altogether?
It might be something as simple as a weak terminal in the connector, or a broken wire in the harness, and when you install a new sensor the connection is restored for a little while. Not sure about these older Fords but a lot of automotive terminals are only rated for four connections, so lots of unplugging and swapping around can cause problems in itself.
Pete. (l33t FS) said:
I'm also curious what the symptoms of "bad MAP" are. Is it reading incorrectly, or dropping out altogether?
I'm not quite sure myself as I don't have any monitoring stuff hooked up to the system, but I'm guessing that it is dropping out altogether. Off-idle throttle input while in gear from a stop causes the truck to stall out, shifts extremely hard (the transmission is controlled by the ECM,) stalls out while coming to a stop.
Pete. (l33t FS) said:
It might be something as simple as a weak terminal in the connector, or a broken wire in the harness, and when you install a new sensor the connection is restored for a little while. Not sure about these older Fords but a lot of automotive terminals are only rated for four connections, so lots of unplugging and swapping around can cause problems in itself.
The sporadicness of the problem is what is throwing me on this. Literally months and months, years even with no issues, then one day or night she decides to be obstinate
