My 1994 Ranger xlt 2x4 manual cranks over, but doesn't start. The relays have been replaced and I have 12v at the pcm relay with the key off. But, when I turn the key to the "On" position the voltage drops to about 1.5v-2v. I have replaced the ECU and the Ignition switch under the dash. There is a clicking noise coming from underneath the dash. I cannot figure out what module is causing that but if I unplug that it stops. It doesn't however allow the car to start. The wiring looks pretty good and there are no noticeable breaks or shorts. The previous owner threw a bunch of parts at this truck and gave up. I'm trying to save myself a similar fate. Thank you in advance for your help.

 

Welcome to the forum

Battery should have 12.3v to 12.8v
New battery 12.8v
3 year old battery 12.5v
5/6 year old battery 12.3v and time to shop for battery sales
Whats the exact voltage at the battery?

When you test the PCM relay slot again it should show EXACTLY Battery Volts, its a direct connection to battery positive thru fuse 4(30amp)
If its less then there is a bad connection
Check fuse 4, pull it out and test each of its terminals, one should be Battery Voltage, exactly

PCM relay powers several things not just the PCM, it also powers MAF sensor, the 4 injectors, the fuel pump relay, and EVAP system, a short in any of these should blow fuse 4 not cause a voltage drop
Point is, if the 12volts from fuse 4 thru PCM relay has issues then voltage drops alot because of all the amps needed by all the devices not just the PCM

Use RED wire at MAF sensor's 4 wire connector(unplug it) to test voltage with key on, PCM relay closed, just easiest place to check voltage out of the PCM relay

 

The battery is pretty new, but could use a full charge. I will charge it up and do some more tests. Thanks for your input this may be helpful in diagnosing the problem.

 

So I gave it a full charge last night I'm at 12.9ish at the battery and exactly the same at the fuse 4. But, when I test it at the MAF I only get 11.18v this is with multiple groundings ( coil, fender wire harness ground, and the battery itself) . What's the next link backward in the chain to check wiring, voltage etc ? Does the noise suppressor hooked up to the coil do anything ? It looks pretty shady.

 

EEC/PCM relay, pull it out, test slots, key off, should be one with exact battery voltage from fuse 4, if lower you will need to pull this fuse box up and check for corroded wires

Battery--------fuse 4---------------PCM relay----------------------------MAF sensor's red wire......(and many other devices including PCM)

 

Tested the eec relay slots with the key off. 30(+) has 12.9v (same as battery) and the same across 87 and 30. Reversed, slot 85 has ground (12.9v) and slot 86 only has like 1.4v is that closed by the ignition, or should it have constant ground ?

 

One slot, 85 or 86, is a full time ground on the EEC/PCM relay

Yes, the other one should have battery voltage with Key On
85 and 86 have no assigned polarity, as long as one is a ground and the other 12v the relay in this base with activate, and connect 30 and 87 together

30 and 87 are the same there is no "12v" assigned slot, one is 12v IN and the other 12v OUT when relay is closed, and these 2 slot are connected together
Usually 30 is the 12v IN, but as said really doesn't matter in most 4 pin relay wiring

 

So where would you recommend I start looking now. Should I back track from the MAF ? Or, is there something in the interior I should be looking at ? I replaced the ignition switch under the dash. The wiring all looks pretty intact and clean including the interior fuse panel which has no blown fuses either. Thank you again for your help. This is definitely a step in the right direction.

 

So 86 has no 12v with key on?
It should, if not it could be the PCM Diode, its in the engine fuse box, pull it out and check it
It has to go in the correct way, usually it will only go in one way as one terminal sideways, i..e "-- |"


EEC/PCM relay has to close to get 12.X volts at MAF red wire

 

I checked voltage at the diode slot and continuity. That seems fine as I have 12.9v at slot 30 with key off and that feeds from the diode slot. When I turn the key on all of the voltages drop to almost nothing in the pcm relay slots. My CEL isn't coming on. Which I assume means the (new) pcm isn't powering on. Does the wiring go into the cab before going to the pcm or is it fed directly from the fuse box ? I will try to check for voltage at the connector as soon as I can find the pin out (tomorrow). Or, do you think the fault is somewhere between the relay and the MAF ? Since I'm only getting 11.18v by the time it gets over there.

 

When you jumper PCM relay slots 30 to 87 do you get the same voltage drop?
i.e. at MAF sensor red wire

If so there there is a corroded/bad connection between battery positive and fuse box, or fuse box and fuse 4, or fuse 4 to slot 30

On the inner fender mounted starter relay(solenoid) there are two larger posts
One post has battery Positive cable, and several other wires connected with it, this is the 12volt distribution post for the whole vehicle, if it needs 12v its connected here

Disconnect battery Negative cable
Pull off all the wires on this larger post and clean them
You will see a Red wire, it runs to engine bay fuse box, it powers engine bay fuse box, all the fuses, and a few of them power Cab Fuse box and ignition switch

So all 12volt power for whole vehicle comes from that one Red wire connected to engine bay fuse box, with the exception of starter motor 12v which comes from the OTHER larger post on the starter relay, only cable on that post

Once you have clean connection between Battery Positive and that red wire hook up Negative battery cable, makes sure its clean and tight(same for battery positive cable)
Retest to see if you still have the voltage drop
If so you will need to pull engine bay fuse box and have a look at the other end of that Red wire where it connects to fuse box
Disconnect positive or negative battery cable before doing this

 

It's pretty soggy here in PA today so it's probably best not to attempt any electrical projects, as not to introduce moisture to newly cleaned connections, etc. But, once the rain lets up I'll be sure to address that whole area (of connections) very thoroughly. Thank you again for your help, it is very much appreciated. I'll post my results ASAP.

 

So I cleaned up all the contacts on the power distribution block. All of the wires had good voltage except the smaller one with red/lt blue. The red/lt green wire going to the pcm diode had good voltage. When I jumper the pcm relay the light on the dash comes on and stays on. But it loses ground at both 85 and 86 (4v) with key on. With key off, slot 86 has 12.9v ground (same as battery ) and 85 none. Should I be looking at the ground coming from the ignition switch ? Or, does that ground go somewhere else before it goes the relay? I forgot to check voltage at the MAF with the pcm relay jumpered. It started raining again . I downloaded (and printed) as many wiring diagrams as I could that were pertinent. But, I'm still having a bit of trouble deciphering them. Thanks again. I really feel like I'm making some headway, even though I'm not out of the woods yet.

 

Would that wire cause any of these issues ? I think it's just for the starter solenoid ( it turns over fine), and it could just be how I was testing it. But, I failed to get 12v from that wire and if it's plausible, I wouldn't reconsider taking a better look at the connection wherever that goes/comes from.

 

So, thanks to your help (and my own ingenuity) I stayed concentrated on that pcm relay and the ground that dropped when I hit the key. So, after checking and taking apart as much as I could, I traced that ground up by the radiator. It goes into some type of mass grouping and heads in front of the radiator over to the MAF. It looks a little shady in an area I can't see but by feel doesn't seem great. Either way, I decided to finally cut into the pcm ground and hook it directly to the battery. The truck was very intact and it was a decision I thought and rechecked several times before doing. But, I'm glad I did. Something must be turning the ground to positive a little further down the line ( two wires rubbed and crossed in front of the radiator ?) So, I hit the key with ground to the relay only and it didn't do anything. But when I connected the other side of the same wire I just cut to the negative terminal as well, the relays and everything came to life and I was pretty hopeful. Hit the key (ignition switch and a screwdriver at this point) and the thing fired right up? Ran a few seconds and stalled. I hit the key again and it ran like it's supposed to. Had to shut it down until I put everything back together, change fluids etc. and I'll pull the radiator and check that sketchy section to avoid future headaches. But for now she's running. Total cost approximately $100 in parts I mostly didn't need.
I'd like to thank RonD for giving me guidance as well as the Forum as a whole, and all it's members for the content helping to keep these old trucks alive. These resources are priceless.