TBI No Fuel Condition

[BigWheelie]

Sorry this might be long and complicated and i might be missing some things but i noticed this is a common issue with these TBI models and mine seems to be different then all the common resolutions.

1987 Chevy R30 454 TBI 75k mi

I bought the truck not too long ago and after redoing the entire brake system and ran flawlessly. Clean steady idle, no vibrations, no misfires etc. Was an old mans truck with handicap plates and everything I've disassembled has been super clean. The truck came with one tank installed and the other in the bed. For some reason, one day my son accidentally flipped the tank selector switch to the driver side tank (not installed) and it was getting a CEL/SES light regardless if i cleared codes or switched to the correct tank. I ended up running a jumper cable to the tank selector connector to always run the passenger side tank (installed). From then the truck had worked for miles with no changes to any electrical components. One day we took it to the park and it died in the parking lot. One thing i immediately noticed was the jumper wires were hot and slightly smoking. I pulled the air cleaner and started cranking the motor and saw that i was getting no fuel. I looked for anything obvious initially but couldn't find anything until i checked the fuse box. I noticed i blew/melted the ECMB 10amp fuse. So i replaced it with spares i kept in the truck and the injectors still wouldn't fire.

When the truck was towed back to the house i started looking for frayed wires. I fixed plenty that seemed to be unrelated to the issue. I did find one wire that was hanging by a thread i thought for sure would fix the issue. It was the 2 wire connection that goes directly from the pump that was rubbing on the drivers side firewall. When i fixed that i still didn't get any fuel. I tested the injector pods with the 9 volt battery trick to see if they would engage and they did. I tested voltage to the ecmb fuse, injector harness and fuel relay which were good. I replaced the fuel relay anyways because the plastic slide on mount was broken and it was cheap. I cleaned every ground point and connector i could find as well as the power wires at the top of the firewall. I also got a new fuel tank selector switch. At this point i decided to drop the tank and check for signs of damage. BTW this whole time i could not hear the pump priming. With the tank half dropped, i disconnected the fuel lines and left the ground and electrical connections attached to see if the pump would push out anything at all. The pump did not push any fuel. So at this point i pulled the pump to bench test it. I supplied a 12v source to the pump outside the truck and it ran no problem.

Upon more research i noticed that the ICM seemed to be common with no fuel TBI issues. I installed one yesterday with the thermal paste and all. I reinstalled the tank and this time i cleaned the pump ground to frame to bare metal. I was still not getting any fuel however the injector pods would "drip" a little bit.

I am in the process of installing the other tank at the moment with a new pump. I have no clue what else to try and i don't trust professional help with older vehicles as I've never had a good experience with mechanics these days.

 

[Urbanburban22]

If you melted the ECMB fuese, you might check the ecm connectors to make sure all that is okay. along with checking the back of the fuse block. is 12v getting to the pump from truc wiring? Can you hook a test light to the injector connectors and see the light pulse when cranking?
Any other updatse for us?

 

[gmbellew]

If ECMB keeps blowing. The 440 circuit may be shorted to ground under the hood. It feeds power to fuel pump relay and to the ECM. Also check ECMI

 

[BigWheelie]

If you melted the ECMB fuese, you might check the ecm connectors to make sure all that is okay. along with checking the back of the fuse block. is 12v getting to the pump from truc wiring? Can you hook a test light to the injector connectors and see the light pulse when cranking?
Any other updatse for us?

Hi that test light idea is a good place to start. Only update I have is that it is getting spark since I had another hand to help check. Only 8-10v is making it from the truck wiring to the pump. I know these pumps do not like being undervoltaged but I havent been able to find anything that's giving this voltage drop. Where is the ecmb located and how easy is it to get to? Passenger side under the dash?

 

[BigWheelie]

If ECMB keeps blowing. The 440 circuit may be shorted to ground under the hood. It feeds power to fuel pump relay and to the ECM. Also check ECMI

Whats the best way to check the 440 circuit? I read it's the orange wire along the firewall harness? Just see if I get 12v off it ? I have not heard of the ECMI before either, is that at the fuse box? If so I believe I checked it since there were 2 "ecm" fuses

 

[gmbellew]

Whats the best way to check the 440 circuit? I read it's the orange wire along the firewall harness? Just see if I get 12v off it ? I have not heard of the ECMI before either, is that at the fuse box? If so I believe I checked it since there were 2 "ecm" fuses

check for 12v at the fuel pump relay on the passenger side firewall (orange wire) with key on. if you dont have 12v at the relay, the issue is upstream and yoi will need to trace the orange wire. if you have 12v at the relay, backprobe the relay on the wire running to the fuel pump w/n 2 sec of turning key on during the pump prime. if you have 12v there, the issue is farther downstream (fuel pump ground issue or harness issue). if you don't have 12v leaving the relay, the relay is bad.

ECM-I is the other ECM fuse besides ECM-B.

does ECM B blow when you install it immediately? does it blow after key on? it sure sounds like a short to ground somewhere in the fuel pump wiring or the 440 circuit.

 

[BigWheelie]

Hello quick update. I verified injectors pulse with a noid light as I forgot to do that. I have not been able to check the relay power since it's just me. Ecm b fuse does not blow immediately and don't know how to trigger it to blow if I wanted

 

[BigWheelie]

Update again: I got fuel although I'm scared because it just came back all of a sudden.... Still don't know what the issue was. I now have to do ignition timing and I think my timing light may have gone out. I'll keep updating this thread the more things I discover. I did notice a massive vacuum leak from the intake to TBI adapter gasket. After rebuilding the throttle body and replacing gaskets it couldn't hold idle very well. New IAC fixed that.