So I just got this 94 f150 302 5.0 e4od, a couple months ago. Started to notice some things that I would have thought would pop on the check engine light. Hard shifting, gas smell in exhaust, lack of power (can’t really get it over 3000 rpms). Anyways I fixed the check engine light and ran the codes. I got 654 (not in park during KOEO) and 668 continuous code (transmission range circuit above maximum voltage). I’m thinking these are related. I, like a fool, thought I’d just change out the MLPS and it’d be good to go. Nope, codes still there (although I can start my truck in park and neutral now, before it was only park). I’m not the most handy using a multimeter but I’m getting better. So my first question will be, is it normal to get voltage to the power wire(w/p) with it unplugged from the sensor and the truck completely off, 12 volts. I can’t get into the harness to measure voltage while it’s plugged into the sensor, and I’m not too sure about pierce probing. Anyone know a sure fire answer to these codes?

 

You should put ALL the truck's details & history (as much as you know) into your signature so it shows with each post, as this page explains:

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Phone apps don't always show signatures, so you may need to switch to a real browser in desktop mode on your phone, or just use a desktop/laptop computer. Put your location (nearest city) in your profile & upload an avatar of the truck. The more pics you post of the truck, engine, wiring, labels, & undercarriage, the more likely we can help you. Not all its details are relevant to these issues, but you don't necessarily know which ones are relevant, so just put everything in now.

Codes do NOT mean to change parts. You should put the original/previous MLPS back on, and diagnose it properly. No, these trucks have very rudimentary EFI (maybe 8 sensors total) so they don't self-diagnose driveability issues; only severe electronic faults. Code 654 means you did the test wrong, so none of the other codes are valid. You have to do the test right, including preparing the truck before testing. Read this page carefully a few times:

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No sensor should be powered when the key is OFF.

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The old sensor is bad. I read 87 ohms between sigret and tr sig on 1st gear, every other position I’m reading 0 ohms. My truck starts in both park and neutral now and every other gear works. Is your post saying I’m possibly chasing a ghost code due to me using a cheap OBD1 scanner?

 

Yes. Scanners are notorious for displaying spurious codes for these old trucks. Always check with a jumper wire, as that page explains.

 

So I jumped them accordingly. Same codes through the CEL. 654 (Not in park during KOEO) and 668 continuous (transmission range sensor circuit above maximum voltage). I got the truck to operating temp and obviously was in park. I have a funny feeling my ecm is bad. How EXACTLY do I test the wires? Black pierce probing tr signal and red pierce probing signal return checking for voltage?

 

You can often insert the probe into the rear of a plug to reach the pin connector inside. You may need to work a rubber gasket out of the way first.

Before you replace the ECM open it up and check for leaking capacitors. If you can solder well enough you can replace them yourself. A search on here should find the info you need to get the right parts. Mine had two. I've heard some have three. I don't know what they do in-circuit, but when I fixed mine I went from no-start to starting and running better than before. Wish I had written down the part numbers though I don't expect to have to do that again.

 

Oh ok yea I didn’t think to remove the rubber to get to the connector. I read somewhere to disconnect the harness from ecm and measure ohms through pins 30 and 46 (can’t remember if those are right). I put one probe in the pin # and the other probe to…ground? Is that with the sensor unplugged and the ecm unplugged? Trying to eliminate a short or wire damage being the problem before I jump to the ecm.

 

Sounds like the pin 30-46 thing is testing the sensor through the wires so (assuming that is correct) I would you put one probe on each wire and cycle the shifter to see what reading you get in each gear? Key off, parking brake on.

 

Did you follow the link I posted above? Its definition list is better, and it contains links to printable versions.I'd diagnose that first - treat it as the root cause of the other code.Feelings are not diagnosis - ignore it.Like any other wires: unplug ALL the terminals of the wire to be tested, then measure resistance/continuity from one terminal to EACH OTHER terminal (or any pierce location) on that wire; it should be <5 Ohms/continuous everywhere, just like touching the meter probes to each other. This page links to the best pierce probes, but there are cheaper copies available:

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That tests the MLPS - not the wires. And it would show negative polarity since red is for the positive (TRsignal) side. To measure voltage, the MLPS/TR must be connected as normal with the key in RUN. IMO, it's quicker & easier to unplug the MLPS & test its resistance directly through its terminals using common probes.

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Yes I followed that page. Only thing different is it says operator error for 654. The truck is in park and all the gears work. I’m not sure what else I could be messing up. I’ll test tr signal and sig return for continuity tonight.