2000 Ranger 3.0 flex-fuel, 4x4, automatic.
Swapped to a rebuilt engine about 30 months ago.
Before the swap I noticed that 4x4 was intermittent. I figured it was just a sticky / dirty solenoid.

The engine swap was in the fall, so six months later (about two years ago now) as it got hot outside I noticed that A/C wasn't working. Since I had to crack the like open to get the engine out, I initially figured it was pressure. Filed the lines and leak tested good. Still out, so I started checking electrical. Relay bypassed, the compressor worked fine, so I put in both new high and low cutout switches, but still no good.

That's when I first began to suspect ECU.

Now, the past couple months the starting gets finicky. Actually not the first time, but seemingly more frequent now. It turns and cranks, but no start (every 3rd-4th morning). Then a second attempt it might fire right up.
Just the other day as it did that, I thought I heard a click just as it decided to run. Semmed to come from back behind the glove box. Isn't that where the ECU lives?

Any ideas would be welcome!

Also, I've read here that changing the ECU might have complications with your ignition & key relationship, as they are coded to the ECU. Any guidance on how to properly deal with that issue, if I need to go with ECU?

I'm really not a mech, but I do deal extensively in electronics. Point me in the right direction, and I hope I'll be okay. I did tackle that engine alone, afterall! Haven't died yet...

 

Welcome to the forum

When you "open" any A/C system you must replace the Accumulator/Dryer, about $40
If not system can get clogged up.

Computer is not involved with 4x4 system in 2000, there is a separate 4x4 module, and the electric shift motor on transfer case, and 2 or 3 fuses, outside of the buttons on the dash thats all there is to the system.
1998 to 2000 Rangers did use PVH(pulse vacuum hubs), these never worked well, they wouldn't lock in place
Good read here on PVH: http://www.therangerstation.com/tech.../pvh_hubs.html
2000 Rangers could also have Live Axle, hubs always locked, all Rangers 2001 and up had these

Fuse or the shift motor are usual problems, fuse won't be intermittent, motor will be.

Good read here on that: How to: Rebuild 4X4 Shift Motor | Ford Explorer and Ford Ranger Forums - Serious Explorations


Could be time for a new fuel pump
Turn key on and count to 3, turn key off
Repeat this 2 or 3 more times
Then try to start engine

Your 2000 Ranger needs 60psi fuel pressure to run.
For safety reasons the fuel pump only gets 2 seconds of power when key is turned on.
2 seconds of power adds about 10-15psi of pressure.
Normally the fuel pressure in the system will hold above 50psi for a few MONTHS, not minutes, hours or days.....MONTHS

If you are losing pressure when engine is off then it will be hard to restart unless you build the pressure back up.
The fuel pump has a built in Check Valve the holds pressure in the system when pump is off, if it leaks then pressure is lost when truck sits.

If you smell gas then you have a fuel line leak

 

Ok, thanks! So chances are that these things are not related. I do still think that the A/C problem is in the ECU. If I bypass the computer and short the compressor relay, the clutch kicks in and pressure builds, and I get plenty of cold air. Trouble is, I can't get the cabin to call for cold.
I've tested the system for leaks, checked the pressure, and it holds a charge fine. Clearly, if I bypass the ecu too long, no input is received from the high pressure cutoff and the refrigerant pressure will reach critical levels. The high and low cutoff sensors go through the ecu, if I am not mistaken.

Great insight on the 4x4, thank you. I'll check into those. Early on I thought it might be a switch, or solenoid. That makes sense to me when you say the shift motor. It started where it would usually shift to 4by, but may not come back out, or at least not right away. The disengage would be very delayed, as in several to many minutes. Haven't used or needed it much, but now it seems to not respond at all.

Fuel pump? Yeah, maybe. I'll experiment with your idea for awhile. It really only seems to happen after an overnight stay, if at all. Which would seem to support your line pressure loss theory. I have nothing otherwise to suspect a leak. Might be very small.

Thanks SO much for your ideas and experience!
~E

 

Yes, PCM(ECU) enables A/C

The two pressure switches are the Ground for PCM A/C control

Ground--------------high pressure switch--------cycling switch---------PCM

So Ground is daisy chained thru both switches, if either switch opens then no Ground at PCM.

That Ground is used to activate the A/C Clutch Relay
The A/C Relay gets 12volts when key is on, but has no Ground so doesn't "close"
PCM Grounds that relay(using pressure switch ground) when PCM receives "Demand" signal(12volts) from cab selector.

This 12volt signal has its own fuse so check cab fuse box

Get your owners manual from here: https://www.ranger-forums.com/genera...1-models-3747/

It will have fuse panel lay outs

 

okay, so I've checked both high and low switches and the relay. All have battery voltage. The clutch kicks in when the relay is jumped, and after more than a year since charging, air temp still blasts cold. Checking the signal side of the relay I get battery on one side and zero on the other. Since I suspect the ecm I put the meter on ohms and tested for resistance to ground from the ecm control side of the relay. With engine off I get no continuity (open). With engine on I get about 10 - 14 ohms. Once the a/c is turned on, nothing changes. Well, the first time it started to drop to 7 ohms but returned and no change since then regardless the a/c setting. What do you think? ECM for sure at this point?

 

huh, now that you mention it, I do occasionally smell gas after parking or sometimes after a sharp turn. Is there a simple way to locate a leak? There doesn't seem to be a drip anywhere, and I'm all out of matches. Thanks for the tip!

 

They should be Grounds not battery volatge
At 10 ohms I would think the relay would close, but it should change when AC is OFF to N/C or very high ohms

One slot in the AC relay socket should have 12volts all the time, thats for compressor clutch power
One slot should have 12volts only when key is on, this is for closing the relay but ONLY when PCM(ECM) Grounds it using the Pressure switch Ground.

Relay Ground slot--------PCM------pressure switch 1-------pressure switch 2-------Chassis Ground

So PCM just connects the pressure switch 1 wire to the Relays ground slot.
PCM doesn't ground the relay internally.
This allows pressure switches to cut off AC(remove ground) if there is a problem



All Gas tanks are sealed units since 1985 or so, no vents
get a towel/rag and a short hose
remove gas cap
Put hose into gas tank and wrap towel around hose to seal the tank, towel can be damp to help seal it, there is already a little water in your tank, lol, but just damp not WET
Blow into the hose, gas tank should hold pressure
You can often hear air escaping if there is a leak, but may need someone else to help ID where it is coming from

DO NOT!!!!!! use an air compressor for this test, your lungs can generate about 2psi of pressure, which will be fine to find a leak, more pressure WILL BLOW OFF CONNECTORS on the gas tank

 

ok, so when I say that each switch has 14V, that now makes sense to me from what you say. I hadn't realized the flow through the switches and ecm to ground. As I mentioned, when removed the relay I get 14v on the acc leg of the relay input and nothing on the other leg. I thought that the nothing was a ground, but I am starting to think it is just a nothing. When I unplug a pressure switch and check I get 14 and nothing. However if I a small jumper across the switch and check again I get 0v. So the signal is getting pulled down to zero at the switch. My question is whether the ecm is doing it's job of connecting the relay leg to the switch as you suggest. Makes me think that I should do the same check that I did on the relay, but on a switch instead - with relay installed, compare switch low leg to chassis with engine off and on again. This might prove that the ecm is making the connection?

 

If AC relay is in place and key is on then its Coil should be getting voltage, and since it is just a coil of wire that voltage would run to PCM and if PCM had AC on, then that voltage would flow thru PCM to the first pressure switch, then the second, and then to Ground.
So if you unplugged either switch connector and put BOTH volt meter probes on the two wires, one should be ground and the other 14volts

 

Right, so I follow you so far. What I still need to determine is what is preventing the compressor relay from engaging? Somewhere along the chain chassis ground is dropped. I've replaced the switches, swapped relays, tested the compressor (by jumping the relay - switch side) and get full cool after doing so. Is the ecm killing the chassis ground? A pressure switch? Is it possible that, while I do have refrigerant, maybe it's low and a pressure switch is simply doing it's job? How do I narrow down the actual cause and rule everything else out?

 

Hook meter to battery Positive
Remove AC relay and hook meter to Relay Ground(from PCM)
Start engine and turn on AC

Should see constant Ground, 12-14volts, let it run as long as you think needed

Now jump compressor ON
If ground starts to drop then it is a pressure switch opening

 

yes, I've just performed this test as suggested. I get the full ACC with A/C on at the coil side of the removed relay. No change with the compressor jumped on the output side of the relay, still full ACC voltage. I feel like we're very close to finding the cause, but I still can't wrap my head around it. Thanks for the help.