94 B2300 wont start

[Earl43P]

You are certainly having a time of it!
I am sorry for your loss.

First of all, the PCM recieves power from that fuse (Yellow wire) AT ALL TIMES, not when the relay is energized, so skip that PCM being the problem of blowing the fuse.

Here are ALL the items powered by the red wire after the PCM power relay is energized:

Fuel Pump relay - remove it
WOT relay - remove it
MAF - disconnect it
Cannister Purge solenoid - disconnect it
Injectors - Connector C123 is beside the fusebox and feeds all the injectors, auto transmission, EGR solenoid, and IAC. It is one of 4 plugs ganged together (look for the RED wire).

Might be simpler to disconnect the IAC, EGR solenoid and transmission separately and just wiggle the injector harnesses.

If 1994 happens to have a Camshaft position sensor, add that to the list of items fed by that red wire.


So, set up the meter so you can see the short (key OFF), then start disconnecting things until the short goes away. Suggest you start with the IAC and MAF. Some meters have an audible tone for continuity. That may be easier than watching the meter (IF the short is direct enough to make the tone). Ron has a good point about wiggling the harnesses. Do that too with the meter hooked up; look for the ohms to vary, indicating you are close to the short.

Lastly, if your truck has AC, it should have the WOT relay. In the 93 book I am using, it shows the WOT relay next in line, at the end of the box. PCM relay, then Fuel Pump relay, last is WOT relay, all by itself, with an empty slot next to it.

If you send me a Private Message (click on my username) with your E-Mail address, I'll e-mail you these 1993 schematics to look at. 94 should be pretty close.

 

[martin]

When trying to find a short it's sometimes easier to use a bulb with a couple of wires on plugged in to where the fuse normally goes. while the short is still there the bulb will be brightly lit but when you remove the short the bulb will go dim or go out completely. It's not exactly rocket science but it's easier than trying to reader a meter, especially when you're standing on your head trying to disconnect or waggle stuff.

 

[daltond]

The output from the EEC relay leads to a diode, I dont know its function, and from there a red wire with green tracer leads to a wiring harness. Ohmeter on this wire shows 1.2 ohms on the 200 ohm scale. This seems low to me, and I believe is probably a good indicator of a short. Is there a reference that lists proper resistance values for each circuit on this truck. For example, If I disconnect the MAF sensor, what reistance should I see on each of the wires going to it if I am reading from each wire to a common ground?
Thank You all for your help to this point I really appreciate it. As to "If all else fails RTFM", that is only workable if You have or have access to the manual. My only internet access is my phone, and the screen is to small to read schematics and wiring diagrams. I will be checking out the various units you have mentioned, and hopefully will come up with something. Is the overdrive solenoid on the transmission tied to this fuse?
Thanks again for your assistance!
Daltond

 

[RonD]

A diode the a "one-way street" for power, they are used to prevent power from flowing backwards thru a circuit.

Yes, 1ohm from that wire to a ground would mean a short, have that hooked up and start moving wires around, and check the 1ohms each time.
Also disconnect things, like the MAF, and see if the 1ohm changes

No, there isn't any circuit measurements for the different systems, some devices might have OHM readings available for testing the specific device.

 

[Earl43P]

That diode routes power to the pcmrelay coil.
I don't see a red/green wire, but it sounds like you are testing the wrong wire.

Go to any component I listed, ring the red wire to ground. None of them should be getting a ground if the key isn't on. There should be 12v on each red wire if the pcmrelay were able to latch without blowing the fuse. 94 can't be much different than the 93 schematic. Sending it now.

 

[Earl43P]

Anyone have a 1994 EVTM?

This guy really needs pages 23-1 thru 23-4 to help track down his short.
He's working with the 1993 pages I sent him, but 94 could differ.

He also reports that it wouldn't go into overdrive, which in 93 was one of the two transmission loads on the red wire from the activated PCM relay contacts, the TCC and 3-4 shift solenoids.

I'm having him disconnect the transmission connectors to see if the short goes away, among other things.

I'm asking you'all to jump through some hoops to help this guy out. Ron, keep up with helpful suggestions! I'm off on a 5 day trip at 3pm, so my help is waning fast and he needs his truck.

Let's help !!!

 

[daltond]

I discoonnected all of the components on the load side of the EEC relay. The IAC, MAF sensor, and injector harness first and then went to the trans (a4ld) and tried to disconnect the connector for the TCC/OD solenoids. At first was unable to get this connector apart. Had to use a pry bar which finally got it. It turns out that the incoming wires in the male side of the connector were welde to their mates on the female side. When I pried them apart, the wires on the female side came up with the male connector. I pushed them back down in their seats, and filled the socket with silicine sealer in case of leaks. I then separated the wires on the male connector,nsulated them from each other and taped up the whole connector end. Then used a harness tie to get the dangling connector up away from the trans.
I reconnected all the other components, put a new EEC power fuse in, and the truck started immediately on the first try. Runs great! Took it out for a test drive, and other than having no 4th gear, everything works fine. This will do for the short term, til I can afford to fix it properly. I want ot offer my warmest thanks to Earl43p, and RonD, without whose help, I would still probably be going around in circles trying to figure out this problem. This is a truly great website, and the level of knowledge available in the various forums is incomparable.
Daltond

 

[daltond]

I discoonnected all of the components on the load side of the EEC relay. The IAC, MAF sensor, and injector harness first and then went to the trans (a4ld) and tried to disconnect the connector for the TCC/OD solenoids. At first was unable to get this connector apart. Had to use a pry bar which finally got it. It turns out that the incoming wires in the male side of the connector were welde to their mates on the female side. When I pried them apart, the wires on the female side came up with the male connector. I pushed them back down in their seats, and filled the socket with silicine sealer in case of leaks. I then separated the wires on the male connector,nsulated them from each other and taped up the whole connector end. Then used a harness tie to get the dangling connector up away from the trans.
I reconnected all the other components, put a new EEC power fuse in, and the truck started immediately on the first try. Runs great! Took it out for a test drive, and other than having no 4th gear, everything works fine. This will do for the short term, til I can afford to fix it properly. I want ot offer my warmest thanks to Earl43p, and RonD, without whose help, I would still probably be going around in circles trying to figure out this problem. This is a truly great website, and the level of knowledge available in the various forums is incomparable.
Daltond

 

[Andy D]

Good job by all.

 

[RonD]

Good Job

Transmission connector was way off my radar..........not any more, thanks

 

[work2do]

Do carefully inspect the wiring harness connection along the drivers side frame rail under the cab. After I replaced the fuel pump on my 99' and it still wouldn't start. Traced the wires back from the pump and discovered voltage was not getting through the large plastic harness connector due to corrosion. May be worth a look...