Ok, my first post here....I have a 1990 k5 with 5.7/350 TBI (rebuilt so they said) with 700r4 tranny...I am the 5,422nd owner apparently. I bought the truck approx. two months ago and it keeps shorting out ECMB2 fuse while in reverse. Usually, you replace the 10amp fuse and problem is fixed. However, last weekend it went through seven fuses and would not start and I had to be towed from the desert by a Ford. Imagine the embarrasment please.

In 2005 P/O spent $500 at shop replacing fuel pump, fuel relay and oil pressure sending unit with wires (He gave me the reciepts). These three items are controlled by the ECMB2 fuse apparently. P/O took truck to the shop twice for the same problem I am having, except he was driving forwards when it died on him.

I recently fixed voltmeter gauge and temp. gauge in dash. Gauges were bad. The oil gauge does not work either and it pegs out when battery is plugged in, indicating to me that something is grounded out or sending unit is bad. Everything in dash is ok including fuses. Only thing not working now is oil pressure gauge.

Sooooooo....yesterday, I crawled into the engine compartment to find sending unit behind distributor. That was not fun! I removed dist. cap only, air box etc. to access that area. What I found was stock sending unit plug (3 prong) was unplugged. Somebody came in with 3 new wires and harnessed them into one wire that eventually leads to what feels like a bolt behind the block. These new wires are originating from the same large wire harness that the stock plug is tied into. So now I am confused and trying to figure out if somebody rigged the sending unit and wires, or did I just find a ground for something else????

#2 issue is I bought a new sending unit and if what I found earlier is in fact the location for the sending unit, it does not feel like it will fit in the area because the fuel lines are in the way!!!! The bolt that is in there now with the one wire attached is approx. 1/4 inch tall from the block. The new sending unit is like 2.5 inches tall past the threads!!!

The only way I can fathom even reaching that area with enough clearance is to completely remove the distributor, which I am not entirely comfortable doing and I do not know how to time it back into place. And even if I do get to it, is this rigged so much that fixing it right is not going to work???? I will try to get pictures, but it is unlikely since the area is so awkward and small...ANY HELP PLEASE!!!!!!!

 

Sorry about your situation.

I have seen the ECMB fuse blow as a result of shorted wiring where the harness to the pump transitions from the firewall to the frame. This is especially true if the body mounts have started to sag and closed up the clearances, pinching the wires.

It sounds as though someone has attempted to rewire those items which are on that fuse. This fuse also supplies power to two terminals at the ECM so there is wiring that passes through the firewall near the passenger side in to the ECM. Any one of those wires could be pinched and shorting out, causing the fuse to blow.

Attached is a copy of the wiring diagram for the ECM which includes the ECMB fuse.

 

Yeah I am just lost at this point....I would like to try one thing at a time and start with the sending unit since that was the problem before...potentially...The wires to the fuel tank/pump look intact and free from obstruction....but that is a possibility that I will need to look into further. Im just wondering if the wires I found yesterday are a ground for something else and my sending unit simply is not plugged in for whatever reason...I cannot see behind the block to see what all is back there and it is hard to get a hand in there to feel around......So I am not 110% sure I found the sending unit location....Am I going to have to take off the distributor completely to get to it???? This sucks I am thinking of plugging the new sending unit into that free plug and seeing if my oil gauge un-peggs itself and I would also like to see if that plug still has power to it.................Any mechanics who work for beer let me know hahahahahaha

 

Anybody have pictures of where the sending unit is???

 

Back rail on the engine block near the driver side cylinder head.

 

If thats the case I am a dumb*ss and the wires I described before are just a ground of some sort K, I will check that spot when I get a few minutes....Everybody keeps mentioning in all these other posts that there is a second oil sending unit above the oil filter???? One month ago I tore my oil cooler adapter plate apart for a leaky gasket set and I never saw any wires in that area other than the O2 sensor on the driver's side exhaust manifold????? Again, I have the three prong system which I believe is the only one on the truck right???? Sorry for all the long questions and problems, but this is my first truck to work on and I refuse to go pay the mechanic ridiculous amounts of money

 

Ok, I need serious help. I found the sending unit and it is present. The plug is not plugged in and has not been plugged in. The functioning gauge is pegged out, definitely indicating to me that it is not a bed sending unit (since its not plugged in) and that the wires are ground out somewhere. Keeping in mind what you said above, how do I even trace down where these wires go or even start to look into the wire probleM??? I put a voltmeter to the sending unit plug, with the engine on and I got no reading off of it at all....it flickered for a second, but nothing significant. I am beyond confused and just want to drive my damn truck!!!

 

I'm having the same problem. I just installed a new (used) motor in my 2001 blazer. The gauge pegs (actually over-pegs) as soon as I turn the key on - whether the sending unit is plugged in or not. When I turn the key to the off position, the gauge will ever-so-slowly decrease but only until about the 50 mark.

I've unplugged the battery to see if resetting the computer will help.

Any ideas out there?

 

Well, I am definitely no professional...but....it sounds like your sending unit wire is grounded out causing the gauge to peg.....also, how does your oil pump look? did ya change that with the motor? same specs as the old motor?

 

Thanks for your response. I did not change the oil pump with the motor. Motor was completely intact. I could turn the pump fine with a screw driver - which I need to do to line up the distributor.

Since the gage pegs as soon as I turn the ignition to the On position (with or without the op sending unit plugged in), I am currently assuming there is a short and am trying to trace the sending unit wire to the PCM. The wire color is kind of a brown/tan and I'm having troubles determining which wire on the PCM it is. Are there any PCM diagrams showing where the terminal connectors go?