Ok. Long post coming up. 88 300EFI/M50D,1356. Upon start up, the truck runs great. No hard start or anything weird. After it warms up it will start skipping and missing under load kind of like the vacuum advance isn't working(I know this truck doesn't have vacuum advance) I pulled the mile-long list of codes today and my KOEO codes are 21,24,32,67,19. ECT, ACT, EVP, NSS and EEC all failed. CM codes are 29,32,41,63. VSS,EVP, TPS all failed and I'm running lean. Not sure where to start here guys. Electrical and computer related issues aren't exactly my strong point(yet) I'm used to working on carb'd vehicles. A tree fell on my girlfriend's car last Wednesday night and all we have to get around is a Bronco that only runs good untill it warms up. I recently replaced the exhaust system from the manifolds back and put in a new 02 sensor. Also recently replaced the coil, plugs and wires. The cap and rotor appeared to be recent and in good condition. Any help is greatly appreciated. Hope everyone stays safe and has an awesome New Years.

 

Ok, given the sheer number of Codes that refer to an "out-of-range" or "low-voltage" condition, I would recommend starting with a check of the reference voltage coming from the ECM (EEC-IV computer). Pin 26 of the computer is the ORANGE/WHITE wire coming from the main computer harness. It sends reference voltage (VREF) to every sensor in the truck (except the KS "knock sensor" and HEGO "O2" sensor). Reference voltage is approximately +5VDC. Anything lower than about +4.9VDC will trigger all sorts of fault Codes because the computer is programmed to read voltage responses from the sensors based upon this +5VDC reference signal.

To test Reference Voltage (VREF) probe the wire from pin 26 of the ECM and take a voltage reading between it and negative (any good bare metal surface on the body/frame of the truck). If VREF is below +4.9VDC, the reference voltage is too low to begin with and consequently the entire system will be compromised.

The reason you won't see the issues caused by this until the engine has warmed up is because until the engine reaches full operating temperature a good portion of the control systems are off-line or more accurately, waiting to engage.

Now, it is possible that you have a problem with each sensor however, given the sheer number of Codes pulled, I would tend to believe the issue is more likely to be common to all of the sensors rather than individual issues with each one.

 

So after some digging I found that my coolant temp sensor has been out quite a while which is why my temp gauge doesn't work. My A/C doens't work either so that rules out the ACT. I don't know much about the EGR position sensor but I do know the PO removed the cat and blocked the tube that leads to the smog pump so I'm sure thats messing things up. I'm starting to wonder if total engine replacement or a new vehicle are my only options. My girlfriend is finishing her degree at App State and I work full time and I doubt the money is in our budget for a new vehicle.

 

The ECT sensor has ZERO correlation to the temperature gauge. The gauge uses a completely different sensor than the EEC-IV computer.

 

Thanks Greystreak I'm on it.

 

Ok had to go buy a new multimeter but any suggestions how to test for this? I can't get to the harness outside the truck just under the dash on the drivers side and I'm pretty sure I found the orange/white wire;.

 

Check the source voltage at the air charge temp sensor and the coolant temp sensor . If the are at 5 volts you should be good to go as far as the ECM is concerned .
Next you'll want to ohm the sensors out .
I'm betting the coolant sensor is the issue .

 

Thanks for the info twisted.

 

And it turns out the 30$ multimeter i bought doesn't come with a battery WTF!!!!!

 

I'm reading 3.76 at the green wire on the ECT. I'm guessing thats bad.

 

Check the other sensors to see if you're getting similar results .

 

TPS showed 5 on the orange wire.

 

And I can't seem to locate the ACT. I'm noticing alot of my connections at these sensors are quite corroded. I'll clean them up tomorrow before work but I doubt this is where all my problems are coming from.

 

It's on the number one cylinder intake runner , on the lower intake .
I was going to ask about the condition of the connectors .
Try to clean them up a bit , clear the codes and drive it .

 

Thanks buddy. I'll get on that.