87 R10 is Blowing Fuses

[DnStClr]

I've recently started having trouble with ecm fuses blowing, causing a no-start. Previous owner had put a 20 amp fuse in place of the 10 amp fuse that's supposed to protect . The 20 amp fuse blew too! I'm putting 10 amp ones back in now. I've been having trouble with a high idle too. Since it's tbi, I'm leaning toward a bad injector. I've noticed that both injectors have the plastic semi-melted at the top of the injector next to the wiring connections. I've replaced the throttle position sensor and cleaned the IAC. If I can make it home tonite after work I'll check for frayed wiring at the tbi unit. Any more thoughts are sure welcome.
 Don

[Leevon]

Same problem here and I haven't been able to figure it out until today when I was showing the truck to a buyer.  I leaned on the air cleaner and it moved the alternator connector which had been busted.  Truck died, and I found the blown 10A "ECM1" fuse.  Going to fix the connector and should be good.  You may want to check yours. 

[VileZambonie]

sometimes the injector harness chafes through at the tbi unit.

[DnStClr]

I'll continue to look at the harness. I checked it over pretty good, but ya never know. The fuses (there are two for the ecm) have each blown . Actually bad health has kept me from troubleshooting more thoroughly. I'll definitely check the alternator! It sure acts like a wiring short, goin away and coming back .
Leevon- you're selling that great looking gold truck?!

[VileZambonie]

Don't die on us Don!

Check the wires that run down behind near the firewall and toward the starter. If they check out ok start doing some component disconnecting. Does it consistently blow both ECM a and b?

[Lt.Del]

Don't die on us Don!

   I hope it's not that bad.

If it is, I get first dibs on your truck--i have lots of fuses 

[DnStClr]

I have deteriorating spinal arthritis or something like that. Dr said it might likely put me in a wheelchair.but it won't kill me.So keepyour fuses. My lower spine .It impinges on the nerve bundle and puts me out of action with sciatica. I get to have shots in my back that make me cry. Pretty lucky huh? I have to be pretty careful not to overdo anything..
Anyway, the blown fuses are not consistent. Both ecm1 and ecmB have blown seperately.
 

[bigkountry]

I have a degenerative spine (vertebrae are loosing their cushion), so in a weird way...I feel your pain.

Hope you get to feeling better.

[VileZambonie]

Don, #1 is your health! #2 is your truck. So don't kill yourself over this. I'll look up the schematics and draw the most sensible conclusion tomorrow. If you have anything to add to the symptoms let me know!

[DnStClr]

I have the factory service manual and factory electrical schematics book- just need to make the time to get after it properly.

[VileZambonie]

ECM B fuse protects the fuel pump circuit and should be a 10A

The ECM fused circuit check the Injectors and EGR circuit.

[Leevon]

I'll continue to look at the harness. I checked it over pretty good, but ya never know. The fuses (there are two for the ecm) have each blown . Actually bad health has kept me from troubleshooting more thoroughly. I'll definitely check the alternator! It sure acts like a wiring short, goin away and coming back .
Leevon- you're selling that great looking gold truck?!

Hope you get this figured out, I would check the injector wires like Vile said (listen to him first please!).  Mine was kind of pinched, maybe this was the real issue and not the alternator.  It was the 10A fuse that blew on mine, I called it ECM 1, but I think it's actually "ECM A"

I'm selling my truck but only half-heartedly for my wife.  If I don't get what I'm asking, it stays in the driveway.  I do have a nice '71 swb that keeps a smile on my face though if it does sell. 

Good luck keep us posted.

[DnStClr]

Well my code 42 (EST) returned and has now gone away again. No codes today and no fuses blown for a couple of days. I checked voltage signal with a test light at the fuel pump relay and got a light. Now I'm supposed to check for a voltage between the relay and circuit 450, which is the neutral safety switch on the steering column, and I'm wondering if it could be out of adjustment.Circuit 450 goes to engine ground, so I checked from the fuel pump relay to engine ground and got a light too.
Also, the emissions service book says the pump should be energized for 2 seconds when the ignition is turned on,and then shut off if the engine isn't started.. But my pumps continue to run. no shut-off. 
I'm thinking that the ecm controls that shut-off signal, and maybe the ecm is bad?