84 k30 6.2 fuel system (leak hunt)

[KamperBob]

I think I puzzled it out. Apparently there are two T junctions. The first is fed by the IP in the middle leg, odd bank on one side, then other side goes down on the passenger side. Tucked under the alternator it looks like the combo IP-odds enter the top leg, the evens enter the left, and the bottom leg goes down towards the lift pump and back to the tank. So I can resume with clear hose coming out the top of the IP as expected. Yes, no?

 

[Blue Ox]

Yes, resume with clear hose.

Picture an upside down Y. Driver's side injector returns connect to the end of the Y. Injection pump return connects to the "base" of the Y. The passenger side injector returns connect to a barb near the other tip of the Y and the tip of the Y attaches to the return hose on the frame, near the fuel pump.

 

[KamperBob]

Progress! Running. But. More to do. Turns out return to tank was obstructed. That's why the weakest connection in return circuit started leaking (injector 3). Fixing that revealed the next weakest connection. Whack a leak. I quit that game at round 2. Root issue has to do with fuel tank selection. RH obstructed. LH clear. Next, see whether it's the actuator itself, or downstream to the tank. Tomorrow. Today was eleventy six. In the shade. Truck wasn't. shrug

 

[rancher1913]

the drivers side return goes past the injector pump and picks it up then picks up the passenger side and down to the fuel pump area, it runs beside the fuel line back to tank. just order a kit and replace all the jumpers and lines, dont forget the plugs for the injectors closest to the firewall. have you done anything to the filter behind and under the air cleaner. also there is a rubber hose between the filter behind the air cleaner and the injecter pump, you will need to pull the intake off to replacce it. i installed an electric fuel pump about midway on my blazer and have a switch on dash that is powered by the ignition circut (turns off in case of wreck) that i use to prime the system when i need to work on it. i also put a marine hatch above the fuel sender to have easy acess to the lines there

 

[KamperBob]

Yes, resume with clear hose.

Picture an upside down Y. Driver's side injector returns connect to the end of the Y. Injection pump return connects to the "base" of the Y. The passenger side injector returns connect to a barb near the other tip of the Y and the tip of the Y attaches to the return hose on the frame, near the fuel pump.

On mine, there's no upside down V or Y. T, yes. Two actually. The pic I shared earlier today shows T #1 on top where the odd/driver injector returns join the IP return. That hard T line also bends down (sneaky bugger) behind/under my alternator. Hard enough to see. Forget about pix. On the way down it joins the even/passenger returns. That's T #2. That combo return goes down (by lift pump) and parallels the fuel supply coming up. Heading back towards the tanks, both supply/return lines split at the selector valve to RH and LH pairs. Aside from screw-type hose clamps (obvious replacements) at the tank selector valve, everything else looks stock. At least to my amateur eyes. History is murky. The truck was stolen and recovered long before my watch. A number of things were messed up. It ran when I got it. But with numerous issues. Many sorted out already. I'm still finding hidden puzzles. Chain of custody would be nice but that boat sailed long ago. I'm not stupid. I'm not an expert mechanic by any stretch. I've done my share over the years. I'm confident enough to bite off more. It's just extra challenging trying to learn with limited documentation. I still feel low on the learning curve. PDF libraries are great. Y'all rock too. I appreciate everyone's time and patience.

 

[KamperBob]

the drivers side return goes past the injector pump and picks it up then picks up the passenger side and down to the fuel pump area, it runs beside the fuel line back to tank. just order a kit and replace all the jumpers and lines, dont forget the plugs for the injectors closest to the firewall. have you done anything to the filter behind and under the air cleaner. also there is a rubber hose between the filter behind the air cleaner and the injecter pump, you will need to pull the intake off to replacce it. i installed an electric fuel pump about midway on my blazer and have a switch on dash that is powered by the ignition circut (turns off in case of wreck) that i use to prime the system when i need to work on it. i also put a marine hatch above the fuel sender to have easy acess to the lines there

I'm already replacing return lines with new Viton hose. My mechanical lift pump appears healthy so I'm not motivated to go electric at this point. The new filter is newer Duramax type with push primer. You may've noticed in the pix above. Along with fuel pressure gauge. That stays while the truck's on probation. Maybe indefinitely. I like gauges. Similarly, now that it's running, I'll leave the clear IP return line there for a bit to monitor signs of air in fuel. As probation officers go, I'm the trust but verify type. As for another fuel filter under the air cleaner on the back on the engine, I've yet to find any such critter on this truck. Access back there is real tough. I keep looking...

 

[rancher1913]

it should be bolted to the intake manifold on the back under the air filter. the one one the firewall is the main with water block and heater, the one on the intake is a finer one just before it feeds the injector. yours may be missing. adding an electric lift is easy and i only use it for priming after working on the fuel system, saves wear and tear cranking to get prime. i changed my stock intake for a j code military one to get rid of the egr crap and my little bit of smoking went away and the engine does seem to run better

 

[Blue Ox]

The metal tubular return connector on the front of the engine is the upside down Y I'm describing. Yes, there's an extra barb if you want to call that a T where the passenger side injector returns join it. But it follows the general configuration of the block across the front of the engine from the injector return on the driver's side to where it connects to the return pipe on the passenger side frame.

What you're describing sounds like the original return configuration.

The '82s had a different filter configuration with a spin-on on the firewall and a smaller spin-on on the back of the manifold with an inline fuel heater on the line coming from the lift pump. That all went away when they switched to the box filter.

 

[KamperBob]

Update. Yesterday the return was obstructed to RH tank but LH clear. Today I pulled the RH return off the valve. Of course disturbing things and may explain. Whatever the reason, poof, that obstruction vanished. None in the valve itself. Nor downstream to the tank. All clear now. Shrug. Anyway, the truck's back to starting quickly without any pedal with stable idling. Road testing probably resumes later today. I may exercise the tank valve a couple more times. Meanwhile, I'll probably go ahead and order this. If only for Murphy Insurance.

https://www.amazon.com/gp/product/B0013FY5KW/

BTW, having gotten familiar with the valve, I can't help but puzzle over an apparent 7th port (not connected). Pressure relief? Some kinda vent? If anyone solved that mystery, please share. Inquiring minds want to know.

it should be bolted to the intake manifold on the back under the air filter. the one one the firewall is the main with water block and heater, the one on the intake is a finer one just before it feeds the injector. yours may be missing. adding an electric lift is easy and i only use it for priming after working on the fuel system, saves wear and tear cranking to get prime. i changed my stock intake for a j code military one to get rid of the egr crap and my little bit of smoking went away and the engine does seem to run better

My 84 has J code. See also...

The metal tubular return connector on the front of the engine is the upside down Y I'm describing. Yes, there's an extra barb if you want to call that a T where the passenger side injector returns join it. But it follows the general configuration of the block across the front of the engine from the injector return on the driver's side to where it connects to the return pipe on the passenger side frame.

What you're describing sounds like the original return configuration.

The '82s had a different filter configuration with a spin-on on the firewall and a smaller spin-on on the back of the manifold with an inline fuel heater on the line coming from the lift pump. That all went away when they switched to the box filter.

It's good to be on the proper page. Those model year changes to filters are consistent with what I've seen under my hood and found in PDF manuals.

 

[KamperBob]

Update. After some answers the truck is happy. For Murphy Insurance, if the fuel return gets restricted again, ideally catch it early. This pressure switch is adjustable.

You must be registered for see images attach

It came preset to close contacts >4 psi. That seemed perfect for a warning light. (The yellow Tygon tube should be chemical resistant enough to diesel fuel to be a permanent sight glass for air bubbles.) After some design and 3D printing, this solution makes me happier.

You must be registered for see images attach

With the new fuel filter a mechanical gauge was included for under the hood diagnostics. That helped ensure the lift pump was healthy. I'd been wanting to monitor fuel pressure from behind the wheel to see what's what while driving. Since my truck doesn't currently have a radio that dash real estate was up for grabs. Since the 3D printer was out...

You must be registered for see images attach

That solution isn't permanent. I see more gauges in the truck's future. Tachometer and pyrometer projects are already in progress. My application will require more development. Choices don't make themselves. R&D takes time. Eventually, dash real estate can be jiggered. Meanwhile, road testing has begun.

 

[rancher1913]

why the pyrometer, just curious, cant see ever getting hot enough to melt pistons but it would look cool.

i got a "pull to eject" mechanism from a fighter jet that i have always wanted to install in a vehical and a few engine fire lights as well

 

[KamperBob]

Agreed. So far max boost is 5-6 psi. That's mostly with truck empty in town and short highway stretches with modest inclines. It may develop more boost with a heavier load and steeper grades. I've yet to prove it has no exhaust leaks limiting boost so that's possible room for improvement. Then EGT gauge may be more important. Meanwhile, I'd rather know how much headroom remains than fly blind. My build focus is reliability.

 

[Blue Ox]

Tygon, PVC tubing and diesel fuel don't get along. It will harden, shrink and become brittle. I don't personally believe that setup is necessary, but if you insist, I'd switch to polyurethane tubing. The kind with the reinforcing cords will handle the fuel and the pressure. Not so sure about heat in the ling run tho.

 

[KamperBob]

Tygon, PVC tubing and diesel fuel don't get along. It will harden, shrink and become brittle. I don't personally believe that setup is necessary, but if you insist, I'd switch to polyurethane tubing. The kind with the reinforcing cords will handle the fuel and the pressure. Not so sure about heat in the ling run tho.

Thanks. From research...

"Tygon F-4040-A is explicitly engineered to resist the swelling and hardening caused by hydrocarbon-based fluids, including diesel, and is commonly used for diesel-powered RC engines and small engines."

I could've been more specific.

Genuine Tygon F-4040-A Premium Cut Length Fuel Line (ID: 1/4" OD: 3/8") (3 Feet): Amazon.com: Industrial & Scientific

Genuine Tygon F-4040-A Premium Cut Length Fuel Line (ID: 1/4" OD: 3/8") (3 Feet): Amazon.com: Industrial & Scientific

www.amazon.com

I appreciate the caution about pressure. If my 4psi switch triggers the warning light, then it's obviously higher. But can return pressure get high enough to burst flexible hose? Based on bench testing, around 30 psi flexible tubing swelled enough to pop off the hose barbs I decided NOT to clamp all my returns to the injectors. As is, they act like mechanical fuses. If all clamped instead and return restricts again, unabated, then where would pressure relieve itself? Split a hose? I'd rather barbie pop hose and deal with leak.

Heat does give me pause. I really don't know how hot return fuel gets under the hood. Research suggests maybe not so much...

"The optimum diesel fuel temperature at the injection pump inlet is generally 45°C (113°F), with a recommended operational range of 30°C to 60°C (86°F to 140°F).

• Efficiency and Power: This temperature balances fuel density and viscosity; temperatures significantly higher than 45°C reduce fuel density, lowering power output and efficiency by up to 14%.
• Atomization: Slightly warmer fuel (up to 60°C) improves fluidity and spray atomization, which enhances combustion and reduces emissions.
• Limits: Temperatures exceeding 60°C to 80°C can cause performance losses, while extreme heat (above 135°F/57°C for mechanical pumps) may reduce lubricity and damage injection components."

Thanks, again, for sharing your experience. I'm not "insisting" stubbornly on being different. I know these forums don't help "read" others. If my logic is faulty, I wanna know! Cheers

 

[Blue Ox]

What you're using appears different than what we ran into with clear tubing. Either it was a different product, or just genericization of the name.

Inlet temps of 40° C are calibration specifications. I doubt that fuel in our trucks is that hot at the fuel inlet in regular operation. But I can't say I've ever measured it on the vehicle, so I guess it's possible.