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Blowing ECM "B" fuse

Re: Blowing ECM \"B\" fuse

That circuit looks similar to my TPI stuff.

Before I installed my setup I scrutinized the wiring harness, and noticed that some of the wires leading up to the fuel pump relay had the insulation "shrink" back from the connector...there was enough copper showing on wires next to each other, that conceivably(sp?) if the wires were moved the right way, they would touch and short.

Oh, and the '165 ECM is a P4, just like the MAP ones.
ECM info
Just didn't feel like resurrecting another post. So you don't have to feel sorry for us MAF guys. /forums/images/graemlins/smile.gif
 
Re: Blowing ECM \"B\" fuse

Do this logically by eliminating the most common, easy to check things. Remove the relay and check. Unplug the oil pressure switch (down by the filter?) and see what happens. Don't just start throwing parts at it.

Shorted wire or bad relay, start there...

Andy
 
Re: Blowing ECM \"B\" fuse

[ QUOTE ]
Oh, and the '165 ECM is a P4, just like the MAP ones.
ECM info
Just didn't feel like resurrecting another post. So you don't have to feel sorry for us MAF guys. /forums/images/graemlins/smile.gif

[/ QUOTE ]

Crap, you're right it is a P4! You just took away the one excuse you had for not switching to MAP when you swapped /forums/images/graemlins/screwy.gif /forums/images/graemlins/tongue.gif

I actually scanned in my 730 drawings before i dug up that 747 drawing. They are wired up alike.

Andy
 
Re: Blowing ECM \"B\" fuse

now i think i remember where the oil psi's are. I think the gauge one is near the oil filter and the other is up near the distributor, or maybe that is exactly backwards.
 
Re: Blowing ECM \"B\" fuse

Thanks Ill write back tommorrow
 
Re: Blowing ECM \"B\" fuse

On my 89 the oil pressure gauge sender is behind hte intake manifold and I believe the other switch is somewhere on the bottom end of the block. If I wasn't so loopy from the drugs the doctor gave me I would go out and look around. But I do agree with everyone else check the wiring, especially if the fuel pump is new. There are spots where the condiut detiorates and rubs on the back of the intake manifold and block and could cause you to blow a fuse. Also pull the various connectors off and check for burnt contacts. Do you remember when you had the sending unit out when you replaced the fuel pump if the contacts were burnt bad?
 
Re: Blowing ECM \"B\" fuse

No contacts were burnt and no wires seem broke or stripped on any of my sensors.

Here is what happened yesterday. I went home and started going down these checks. First I removed the fuel pump from the circuit by disconnecting the connectors in the drivers side frame right above the axle. Then I turned on the key and it blew the fuse. So fuel pump is not the problem. Reconnected fuel pump. Then I pulled the oil pressure sending unit connectors (under distributor) and did the same thing. It blew the fuse. OPS not the problem. Reconnected the OPS. Then I pulled the fuel pump relay and wulah no blown fuse. I then plug it back up and pull the ECM itself. Turn the key and wulah no blown fuse. So I go to auto zone and buy a new Fuel pump relay. Doesnt make a difference. SO I call a friend and we go through the whole troubleshooting thing again and he is convinced it is the relay (even though I had just changed it we do it again just to be sure). Nothing so now he is telling me it has to be my wiring or the connector for the relay. Here is the questions I have

CAn the ECM fail so that it only blows a fuse in relation to the relay. Because I would think that if my ECM failed (which I cant understand how) that it would have blown the fuse with the fuel pump or the OPS unit disconnected also right?

WHat is the fuel module and could it becausing it?

I also ont understand why when I replaed my fuel pump the problem went away temporarily and came back but doing all this troubleshooting removes the fuel pump from the list of possible problems?

So please tell me what I am doing wrong and where to go from here. I am almost going to take it to a shop but if they troubleshoot it for as long as I have been then I will go broke. Please help and thanks for all that you have so far.

-Shaun- /forums/images/graemlins/1zhelp.gif
 
Re: Blowing ECM \"B\" fuse

Let's think about this. Removing the relay disconnects the wire that runs to the fuel pump from any possible +12. I think the +12 supply wire that runs from the fuel pump relay to the fuel pump itself is shorting out somewhere.

EDIT: correction, it could be a fragged ECM but I very seriously doubt that. Check the wire that runs to the fuel pump before you do anything else.

Removing the ECM prevents that relay from applying power to the fuel pump, and thus won't blow the fuse.

Remove the fuel pump and that relay and do what I said about 50 posts ago... Get an ohm meter and see if there is resistance between the +12 pump wire (pin "E" on the relay) and ground (the frame of the truck). That's how you figure out if there is a short on that section of wire. Try it again with the ECM also unplugged and see what the result is.

Andy
 
Re: Blowing ECM \"B\" fuse

OK I will give that one a shot. What should I read there and what does it mean if I do or dont. I should know this but aftewr 5 days of trying to fix this thing I am completely brain dead. Thanks Andy.

-Shaun-
 
Re: Blowing ECM \"B\" fuse

We have been looking at this all wrong /forums/images/graemlins/doah.gif

Look very closely at the ECM B circuit. It goes from the fuse into the ECM. From there the ECM sends a signal to turn on the fuel pump relay and goes to ground.

5427747ecm4.jpg


I've color coded the ECM B circuit in Yellow as power into the ECM. Red is the power output off of the ECM B circuit. Blue is a seperate circuit that is run off a 20 amp fuse and powers the oil pressure switch as well as the fuel pump relay and fuel pump. If your problem was with the Oil Pressure switch or its wiring, the fuel pump or its wiring you would actually blow that 20 amp fuse.

So:
Check the ground at the Fuel pump relay (BLK/WHT wire)
Check the wiring between the fuel pump relay and the ECM (DK GRN/WHT wire)
Last thing will be to replace the ECM at this point since unplugging the ECM with no blown fuses tells me the power wire between the fuse and ECM is good.
 
Re: Blowing ECM \"B\" fuse

Ok, I remembered what went bad in the ECM of the truck we had that was blowing the ECM B fuse. It was the CalPac. Apparently its what controls the fuel on the older style ECM's, we were able to remove it and not have a fuse blow, then reinstall it and have the fuse blow. Also try jumpering the relay, there should be a diagram on the relay. By doing that you check the circuit to make sure its capable of handling the voltage.
 
Re: Blowing ECM \"B\" fuse

I tried jumping the relay. I ran a wire from pin a to pin e but even with the key off it still was passing current (wire got warm and sparked when i first made contact) and when I turned the key on it didnt turn on the pump (dont remember if it blew the fuse)

So should I replace the ECM. (after doing those checks suggested by Andy and Kenny)
 
Re: Blowing ECM \"B\" fuse

[ QUOTE ]
I tried jumping the relay. I ran a wire from pin a to pin e but even with the key off it still was passing current (wire got warm and sparked when i first made contact) and when I turned the key on it didnt turn on the pump (dont remember if it blew the fuse)

So should I replace the ECM. (after doing those checks suggested by Andy and Kenny)

[/ QUOTE ]

If you want to eliminate the ECM from the equation just unplug it and jump A and E again. If the pump runs and it doesn't blow the fuse the ECM is fragged.

If you really got sparks with the ignition off then you've got some kind of wiring issue. That relay isn't supposed to have any power unless the ignition is on....

Andy
 
Re: Blowing ECM \"B\" fuse

I thought we were blowing the fuel pump fuse? Hmmmm... I need to read back to the beginning I guess. If fuse B is the main power to the ECM as this picture shows then this is a whole new game!

But taking the relay out prevents fuse B from popping... Hmmm.... Sparks between A and E on the relay... If there is any power on E with the key off then either there is a short to +12 on that circuit or the ECM is toast.

Andy
 
Re: Blowing ECM \"B\" fuse

So I should chase the ground on the relay and then if it is good, replace the ECM?
 
Re: Blowing ECM \"B\" fuse

[ QUOTE ]
So I should chase the ground on the relay and then if it is good, replace the ECM?

[/ QUOTE ]

Clean that ground and trace the wires that I mentioned first. Other than that I'm thinking the ECM may be your problem.

Also, try this. Unplug the ECM and jumper A1 to B1 then turn on the key to see if the fuse blows. If it does it is probably in the wiring, if not it is probably in the ECM /forums/images/graemlins/thumb.gif
 
Re: Blowing ECM \"B\" fuse

I will try that first
 
Re: Blowing ECM \"B\" fuse

scrap your jimmy and buy a malibu /forums/images/graemlins/hack.gif /forums/images/graemlins/weld.gif
 
Re: Blowing ECM \"B\" fuse

Here is my theory. (i didn't read the last few posts very carefully, so I could be wrong). When you were jumping your truck w/ the loose bat and it hit the rad support, it shorted the positive terminal to ground (the rad support). When this happens It heats the $hit out of all the wires because they are extremely overloaded and melts the wires together or melts the insulation off. I would check the main ECM harness from the ECM to ECM fuse B. If you peel apart the big bundle of wires I bet you wil find one or both of the 12v wires to the ECM from fuse B melted to some ground wire.

I am a tech also but not for the dealer(anymore) and I specialized in electrical and driveability diag for about 5 years. Whatever thats worth /forums/images/graemlins/smile.gif
 
Re: Blowing ECM \"B\" fuse

Easier to check than that. Run a continuity test from the fuse feed for the ECM to ground.

Constant short to ground should blow any fuse you put in there instantly, and that doesn't appear to be the case.
 
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