5.7 Tbi Dual Fuel tanks

[biggsteve97]

I have an 87 Silverado 4x4 with a mildly built 350 Tbi v8 and I am having two issues though they might be related. One is when I switch to the left tank, the engine just dies. The gauge doesnt move and the left pump doesnt turn on. I have replaced the fuel pump relay twice, the dash switch 3 times, and the switch valve atleast 4 times. They are now all OEM AC delco parts and still no change. I checked the wiring from the switch all the way to the tanks and found no physicall damage of any kind and all connections were good. Have replaced the sending unit and fuel pumps twice with no change. Sometimes I have power at the connector on the left tank but most of the time I do not, however I never lose power to the right tank. Have been trying to figure out the fuel tank issue for two years. Second is I Was driving home about 2 weeks ago, truck running as good as ever but when I got off the highway as soon as I pushed in the clutch, the engine died. No warning of any kind. After that, the engine would only start and immediately die. I checked fuel pressure and still have 18 psi that its been at for 10 years. Pulled air cleaner and tried to start it and the injectors are still spraying nicely. I had to let the truck sit overnight before i could do anymore testing. When I tried to start it, it started right up and ran as if nothing had happened. After 4 minutes the engine died. Still had fuel pressure and the injectors were still spraying while cranking so I checked for spark and I had none. No spark what so ever. So I pulled the MSD distributor and put in a distributor from a running engine and I still had no spark. I then swapped ignition coils, still no spark. I checked for codes in the computer and had a map sensor code so I swapped map sensors but no change. I eventually figured out there was no signal to the coil on the primary side of the coil and since I had changed the distributor I decided to swap computers, still no spark. The whole time the injectors where still spraying while cranking and strong fuel pressure. I even swapped the ESC module on the bracket next to the throttle body for good measure no change. All this being said, if I let the truck sit for 24 hours it will start right up and run great but only for 4 mins then it dies and will have no spark or primary signal to the coil for approximately 24 hours. It may be less but I usually get frustrated after 2-3 hours and walk away. I am utterly lost. I have inspected the wiring harness from the throttle body to the computer and have found nothing wrong. I am unsure of where to go from here. Is there something in the column or behind the cluster that could cause this? I can live with only one fuel tank working but the spark issue is of major concern. I checked the grounds on the engine and the radiator core support and those grounds are good and clean. I have not been into the dash further than swapping computers so i have not been able to check the grounds in the dash yet but dont see them causing this since there are no interior electronics issues.

[kdh454]

Sorry, but I got lost in that. Do you have power going to the coil with ignition on? If not, start there.

As for the fuel pump wiring. Computer switches power to the switch, where it splits out and runs to the tanks. If one tank works, and not the other, your problem is between the switch and fuel pump.

A test light/meter is going to be your friend here. Make sure you have 12V, or something close to it while the load is still applied (don't disconnect the wire to test). A broken wire may still show 12V, but drop when load is applied. Just shooting in the dark here.

[biggsteve97]

Yes there is power to the coil with the key on. Its just after it dies the test light stops pulsing and just stays constant on on the wire that should lead back to the computer. Atleast I believe thats where it leads.
When ive tested the voltage at the fuel pump connector with it still connected it shows 11.6 volts with key on engine off during the 5 second prime cycle. The pump has only run once since i replaced it again last month but the fuel guage reading never changed to read the left tank. Battery voltage was 11.9 volts that day. I cant help but wonder if a ground somewhere i cant find has failed or a ground wire is open now by they way it acts when i flip the switch to the left tank. If it is a ground, i wonder if it too could be effecting the prinary side of the coil.

[RUN GMC]

I wonder if your power distribution connector to through the firewall to fuse block has melted or corroded from water leak or the bolt backed out......any problems with your key ignition switch in the steering column its like you have power then you just loose it after it warms up a bit.............

[biggsteve97]

No power problems whatsoever. Now I will say that about a month ago I realized I had headlight problems and it was due to a ground issue. about 2 weeks ago I determined that the problem was either at the firewall or under the dash so I ran a short jumper wire from the drivers head lamp connector directly to the core support with the ground from the headlamp harness disconnected from the drivers headlamp connector and everything worked as it should but I am unable to trace the headlamp ground through the firewall. I don't know if the this is related or not. I am hoping to pull the dash apart soon to start testing inside the dash. At this point Im hoping that maybe ive just lost a main ground inside the dash and not an actual wiring problem. I am starting to suspect the computer signal wire for the dual tank issue though but I haven't been able to discern which wire it is coming from the computer.

[biggsteve97]

Originally Posted by RUN GMC

I wonder if your power distribution connector to through the firewall to fuse block has melted or corroded from water leak or the bolt backed out......any problems with your key ignition switch in the steering column its like you have power then you just loose it after it warms up a bit.............

I will also pull the bulkhead connector from the fuse panel and inspect it for melting and connection issues. Hadnt thought about that.