87 k10 350 tbi tuning?

[bd]

Is the pressure regulator monitored by the ECM? Could it be stuck open?

Fuel pressure IS NOT monitored by the ECM.  Yes, the pressure regulator could be stuck partially open and returning too much fuel to the tank.  You can check that by temporarily pinching off the flexible return line that runs back to the tank.  Static fuel pressure output from the in-tank pump with no fuel return should be in the neighborhood of 40-60 PSI, IIRC.

I could just connect the gauge to the fuel line post filter and read the pump only.

Correct.


JP, in order to gain a proper diagnosis and ascertain fuel system health, you absolutely must accurately determine the fuel pressure.  Because the fuel pressure of the first-generation TBI is so low (11-12 PSI), deviation from the factory specification of just a few PSI can cause notable drivability problems.

[JohnnyPopper]

bd, as usual you are the MAN!

Will do, and will report back ASAP.

[Shifty]

Tape the gauge to your windshield, and go for a drive!

[JohnnyPopper]

Wish I could Shiftmeister, she won't run on her own without me feathering the gas pedal.

The test rig has all the right fittings and gauge setup, just the wrong type of gauge.

Going to a industrial liquidator now to source one in a lower range.

[bd]

15 PSI

30 PSI

Etc.

Just add the appropriate fitting to match the hose end of your existing gauge.

[Captkaos]

If you can verify your pressure and it is accurate, and you can verify that clamping off the return side helps..  This is the first thing I would check

This is my TBI that was having similar issues where it would not run without giving it gas the regulator spring was broken in mutiple places. (I rebuilt it here: http://forum.73-87chevytrucks.com/smforum/index.php?topic=24770.0)
The whole troubleshooting thread is here: http://forum.73-87chevytrucks.com/smforum/index.php?topic=3984
I also use this for scanning most TBI's  http://www.winaldl.joby.se/


Again Verify Fuel pressure first and report.

[JohnnyPopper]

Thanks for all the support guys!

Well, looks like I'm running 5 PSI after the (new) fuel filter. Started to uncover the tank switching valve assembly. Notices there is one pink wire showing voltage.

I was under the impression that the tank switch on the dash was a simple SPDT unit. Au Contraire mon frere!

I do notice that when I'm keeping it running and I select the right hand tank, the engine dies as though I cut power to the left hand tank pump.

So, prior to dropping the LH tank, I want to get the tank switch to operate, mainly to see if the RH pump works.

BTW, Where are the pumps fused? All my fuses are good, there are none listed as 'fuel system', only ECM 1 & 2.

[VileZambonie]

ECM B protects the fuel pump circuit. IGN Protects the fuel gauge circuit. Don't go down a rabbit hole. Validate fuel pressure with BOTH tanks and make sure there is gas in both tanks.

[JohnnyPopper]

Thanks VZ, good advice.

Need to verify tank switching valve actually works.

Are there secondary fuses at the ECM B location?

Finally, do the pumps have constant B+? If not I would suppose they are switched at ECM B? Would that be a signal from the tank selector switch?

There is no B+ at the tank switch inside the cab.

[JohnnyPopper]

Okay, did some digging into some of VZ's old rants and came up with this:

Fuel Pump Relay (FPR) gets signal from ECM B fuse.

ECM gets signal from oil pressure switch, then signals FPR to energize coil, sending voltage to the Tank Selector Switch TSS

TSS sends voltage to each respective Fuel Pump AND signals motor/relay within Fuel Tank Selector Valve FTSV to move to correct tank.

The B+ I measured on the pink wire at the FTSV is from the ING fuse and signals the Sending Units from the Fuel Module, ergo the weak voltage.

Starting to think the problems are ground related.

Thanks for the roadmap VZ!

[VileZambonie]

The oil pressure switch is a backup to the fuel pump relay. A better description is here http://forum.73-87chevytrucks.com/smforum/index.php?topic=29825.30

[JohnnyPopper]

So Close...Thanks man!

This is the diagram I studied this morning, but the link you sent has much more relevant info.

I'll conduct the test(s) and see where the path takes me.

So, with the truck off, I should be able to apply B+ to the 490 RED wire going into pin C of the relay, and going through the tank selector switch, it should energize each pump respectively. Yes?

Where is the location of the test terminal? I'll look but it didn't jump out at me.

Also if I energize the D pin on the FPR I should hear/feel the relay close.

Thank again buddy!

[VileZambonie]

The pigtail is hanging off of the relay. Yes

[JohnnyPopper]

So I learned a few things today.

The ECM gives a two second signal to the relay, but after that there is no power going to the pumps or tank switch.

I wired the pump test connector directly to B+ and heard good things, like the left pump, and the tank switching valve.

Right pump no so much, I hear a faint noise, gurgling out of the fill pipe, NO pressure.

Left pump much more vigorous out of the fill pipe, sounding like the gas was circulating inside. Still 5 psi.

So electrically she is good, the ECM, tank selector switch, and tank selector valve are working.

Q: has anyone seen things come loose in the tank, where something breaks and it circulates thus dropping pressure? It really sounds strong.

Or maybe the internal filter is clogged. Good chance of that, during muh covid some tweakers cut the elbow hose that drops into the neck on top of the tank and siphoned it out. Probably tweaker dust is clogging it.

In any event, looks like I have to drop it...or both at some point in time.

Thanks again for all your help. I'll keep you posted 

[Captkaos]

If you have been running E10 (ethanol gas) in it it will disolve the hose between the pump and the pickup tube.  This is especially true if it has been sitting.  I highly recommend replacing that hose with a submersible EFI E85 safe hose when replacing it IF that is your issue.