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hgs_notes · 10-14-2022, 07:54 PM

The truck continued to run poorly and stalling randomly while cruising along. The only codes I got were cam position sensor, misfire, MAF high and low and oxygen sensor. Nothing consistently except maybe the cam position sensor. Even though I changed it to another used one and then a new one. It got worse the more I drove it. Eventually I checked the fuel pressure and found the problem, sort of. Only 8 psi, how did it even run? The pump was running, the regulator is good, changed the fuel filter. The whole fuel system was new and probably only a few thousand miles on it. A walbro pump that maybe is pushing fuel out of a bypass so it can't build pressure. I don't know for sure because I didn't pull the tank to check.

Instead I got the passenger side tank out of the shed, pulled the sending unit out and inspected it. Inside looked like new but the old sending unit doesn't really work for adding an in tank pump. Got a new 87 sending unit for EFI locally and used the brand new mustang fuel pump I just got but wasn't using. I figure a 98 mustang GT is probably similar power level as the LM7 so it should be adequate capacity. I was surprised that the plug for the 87 Chevy fit the one on the mustang pump.

Working in the parking lot at Schwanke engines for a couple hours I had the new/old tank installed and power and hoses hooked up. A few cycles of the pump and it started right up. It's really a shame that there isn't a fuel pressure sensor. Would have saved me a bunch of trouble trying to diagnose it.

I had the ECU flashed with a higher performance tune. He also shut off some little things like the gas cap trouble code. Another issue I've had is inconsistent shifting which could be associated with the painless harness only having a single VSS plug to the transmission. Which works for a 4L60 but the 4L80 has two. I bought the plug harness for the second VSS and showed me how to connect it into the ECU plug. Hopefully that helps.

Next I want to get the dual tank setup working again. I'll have to check out the other fuel pump of course.

10-14-2022, 07:54 PM	#164
hgs_notes GEARHEAD Join Date: Aug 2003 Location: MN Posts: 6,107	Re: HG's Bigass Farm Truck The truck continued to run poorly and stalling randomly while cruising along. The only codes I got were cam position sensor, misfire, MAF high and low and oxygen sensor. Nothing consistently except maybe the cam position sensor. Even though I changed it to another used one and then a new one. It got worse the more I drove it. Eventually I checked the fuel pressure and found the problem, sort of. Only 8 psi, how did it even run? The pump was running, the regulator is good, changed the fuel filter. The whole fuel system was new and probably only a few thousand miles on it. A walbro pump that maybe is pushing fuel out of a bypass so it can't build pressure. I don't know for sure because I didn't pull the tank to check. Instead I got the passenger side tank out of the shed, pulled the sending unit out and inspected it. Inside looked like new but the old sending unit doesn't really work for adding an in tank pump. Got a new 87 sending unit for EFI locally and used the brand new mustang fuel pump I just got but wasn't using. I figure a 98 mustang GT is probably similar power level as the LM7 so it should be adequate capacity. I was surprised that the plug for the 87 Chevy fit the one on the mustang pump. Working in the parking lot at Schwanke engines for a couple hours I had the new/old tank installed and power and hoses hooked up. A few cycles of the pump and it started right up. It's really a shame that there isn't a fuel pressure sensor. Would have saved me a bunch of trouble trying to diagnose it. I had the ECU flashed with a higher performance tune. He also shut off some little things like the gas cap trouble code. Another issue I've had is inconsistent shifting which could be associated with the painless harness only having a single VSS plug to the transmission. Which works for a 4L60 but the 4L80 has two. I bought the plug harness for the second VSS and showed me how to connect it into the ECU plug. Hopefully that helps. Next I want to get the dual tank setup working again. I'll have to check out the other fuel pump of course. Attached Images __________________ If no one knows what you're doing, they can't tell you you're doing it wrong HG's Dream Car Build - Shelby Cobra Kit Build your own adjustable track bar 71 Long Fleet C/10 72 Jimmy 4x4 (Junkyard Jimmy) HG's Plow Truck '78 K35 Dually Bigass Farm Truck HG's thread of miscellaneous stuff