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**hatzie** · 09-30-2012, 01:23 PM

What's the build date? I remember reading somewhere that some of the really late 86 builds got the 1987 TBI setup. Don't know if it's true...

I'd check the switch first. GM used some really cheap polarity reversing rocker switches. I usually replace them with a DPDT ON-ON toggle switch.

Make sure the switching valve is in place and plumbed into the fuel lines.
Check for a frame mounted fuel pump... This would've been installed by someone converting to TBI "on the cheap". If it's between the engine and the valve it should not be affected by switching tanks. If they installed a TBI tank and sender they might've only installed one.

I attached links to my scans of the 1986, 1987, & 1989 GM schematics.

1986 GM CK Light Truck Wiring Manual
1987 GM RV Light Truck Wiring Manual
1989 GM RV Light Truck Wiring Manual

09-30-2012, 01:23 PM	#3
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 5,022	Re: Restoring the two has tanks What's the build date? I remember reading somewhere that some of the really late 86 builds got the 1987 TBI setup. Don't know if it's true... I'd check the switch first. GM used some really cheap polarity reversing rocker switches. I usually replace them with a DPDT ON-ON toggle switch. Make sure the switching valve is in place and plumbed into the fuel lines. Check for a frame mounted fuel pump... This would've been installed by someone converting to TBI "on the cheap". If it's between the engine and the valve it should not be affected by switching tanks. If they installed a TBI tank and sender they might've only installed one. I attached links to my scans of the 1986, 1987, & 1989 GM schematics. 1986 GM CK Light Truck Wiring Manual 1987 GM RV Light Truck Wiring Manual 1989 GM RV Light Truck Wiring Manual __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.