An engine won't run without a CPU to control it either. Does that say something about the engine design?

Point? What?

 

That this thread fell off the face of the earth with the whole "the E4OD doesn't really have a whole lot of electrical" & is now out somewhere around the orbit of Pluto.

 

Do you need to read the source code to diagnose a bad ECU (spilled cap, burnt board or otherwise)? Do you need to be an expert in casting technology to recognize when broken part broke because it was chock full of porosity? You don't need to be intimately familiar with every layer of a hardware/software stack to interact with it. When you start up your computer, log on and go to FTE and argue with strangers on the internet who are always wrong there's thousands of things happening behind the scenes. When something goes wrong you don't care about the whole stack you figure out how to fix it and do so. A few Google searches, an hour of reading and tinkering with settings and it's all working again.


Likewise, this forum is a testament to how little you actually need to know about the logic inside an ECU in order to maintain an EEC-IV system. There's as much or stuff on an engine, it's just not all hidden inside a case. A Haynes is sufficient for 90% of users. An FSM contains the required info for those hard to pin down gremlins in the next 9%. The theory of operation info in the FSM is fairly light on actual descriptions of how the code works. That's not by accident. It's unreasonable to expect the users or first few layers of service personnel to have a deep understanding of how the system work. The last 1% is where experts in the particular systems involved chime in. In the case of newer vehicles that's when the dealer picks up the phone and calls the service dept. If the first layer of service personnel need to understand more than the most basic overview of the software logic (e.g the stuff in the FSM) then its likely that some very questionable design decisions have been made.




I'm not going to (nor am I qualified to) teach you a class in software engineering but EEC-IV (end every other automotive system) was designed for a particular degree of serviceability. EEC-IV and the E4OD requires little knowledge to do lots of work. There's tradeoffs like a lack of certain features, it's data logging capability is dismal compared to EEC-V and its self troubleshooting would be blown out of the water by anything modern. IMO it's a pretty good fit for automotive enthusiasts.


TL;DR
You don't need to know how the entire system works to service it. Knowing more doesn't hurt but it's not strictly necessary.

 

Well that's a relief.

 

First thing you've said that I agree with.

 

Didn't mean to start a big fricassee with this thread. Jus needed advice on the TRS. Changed it and my problems solved. Thanks

 

Somehow, arguments are easily started on FTE. Don't feel bad about it!

 

Good to hear you got it.

 

Ya, next I want to level it.

 

I've been going through similar issues for the past six months with my newly acquired 1990 F150 5.8 with E4OD. I've replaced everything starting with the MLPS. I've changed the following... MLPS (4 times, last one being a Ford unit), MLPS harness with new style connector, solenoid pack (the correct one with diodes) with new harness, new TPS, transmission speed sensor, rear differential speed sensor, checked all the wiring and cleaned all the connectors that haven't been replaced, checked all the grounds and made sure they are good, fluid and filter change, etc. etc. etc. I've changed the MLPS four times because I keep getting a error code 67 and checking the resistance between the input voltage and signal return, my readings are all over the place. Voltage coming into the MLPS when it's unplugged is 5.07 V and it is consistent and does not vary. Plug the MLPS into it and it immediately drops to 3.99 V and will occasionally vary from mid 3's to mid 4's. The resistance values when in the different positions (P,R,N,D,2,1) are constantly changing all over the place from almost nothing to 4500+, as are the voltages from just slightly over 4 V to none at all in Park and similar inconsistencies in other positions. For example, in Drive the resistance will show nothing at all and then all the sudden I'll get a reading of triple what it's supposed to be, then half, then zero, then half, then zero, then triple, etc. Voltage readings are a little more consistent with values going from within a half volt of what it's supposed to be to zero (and shifting problems coincide) and then back to where it started. When driving the truck, it's pointless to watch the resistance values as there are no readings and when I do get readings they are continually changing in any position. Voltage values will hold within about half a volt for a while, then drop to zero or something way off and shifting problems occur, then voltage will go back to close to normal and shifting issues go away, sometimes for days. By shifting issues, I mean high gear starts (forcing a manual shift to first in order to take off), sudden neutral conditions slamming back into gear, gear hunting, etc. I'm at a loss. Surely four MLP sensors in a row have not all been bad? The first three were the same brand but from different stores, but the last one was a genuine Ford and the readings from it are worse than the others. I have triple what this truck is worth in it and it's still undriveable because of this crap. Can anyone offer any suggestions?

 

Sounds like you have broken or damaged wires between the PCM and the transmission MLPS harness itself.

 

I've used a direct ground to the battery instead of the sensor return to rule that possibility out for that wire and the 5V in only varies when it's plugged into the MLPS. Makes no sense to me.

 

The computer uses the same 5-volt feed for everything. Plug the MLPS in and check the 5v reference at another sensor - say the MAP sensor. If the MAP sensor's 5v is also varying with the MLPS's 5v, than the problem is likely with the computer.

If the MAP sensor's 5v is rock solid while the MLPS's is moving around, than the 5v wire going to the MLPS has a partial break in it, or a connector is corroded. It's probably connected well enough that without the sensor it reads 5v, MLPS is enough of a load that the high resistance pulls the voltage down.

 

So today more testing...
I tried what you suggested Lead Head, and found that all the other sensors that I checked did not vary but had consistent 5.08V, regardless of the MLPS status. Looking at the wiring diagram a little closer, it looks like the MLPS is on an individual 5.0V input from the PCM separate from the other sensors.
My readings KOEO are as follows...
P = 3.9-4.02V, no ohm value (range = 4.41V, 4.16k ohms)
R = 2.89V with no ohm value (range = 3.60V, 1.44k ohms)
N = 2.04V with a quick 1858 ohm then no further (range = 2.83V, 733 ohms)
D = 1.36V with a quick 1700-1900-no further (range = 2.09V, 401 ohms)
2 = 0.83V with 1291 ohms consistent (range = 1.37V, 211 ohms)
1 = 0.38V with 513 ohms consistent (range = 0.68V, 81 ohms)

The voltage spontaneously drops to 3.8V in Park with cascading effects with respect to other ML positions and no indication as to why, although resistance values remain relatively unchanged.

Also just to satisfy my curiosity, I connected only the 5.0V line in, to the MLPS while still physically attached to the transmission (out of the connector and connected by itself to its corresponding pin) and the readings immediately dropped from 5.07V to 4.88V. Is the MLPS grounded by the mounting bolts? If it is, I can't see how but it does seem to be by the resulting readings. Also, I checked resistance from the PCM to the MLPS and there is no notable resistance.
All indications point to the MLPS being bad, but I have tested the original one that came on the truck (old style) with the brand new one from Auto Zone, along with the new one from Ford. All readings are the same among the three. Are they all faulty in the same exact way? I have my doubts but what other explanations can there be? I don't want to lead anyone's thinking, but I'm still at a loss with a truck that I have triple what it's worth in and completely unusable!!

 

Can you detail as to how you're making your resistance and voltage measurements (for example, where are you making your measurements). Also just making sure, you're making your resistance measurements with the truck off, correct?