Electric lift pump questions

[80Sierra]

I'm in the process of overhauling / turbocharging a 6.2L diesel for my truck to replace the gas 350 it has right now. My question is with regards to the fuel system. The engine uses a mechanical lift pump stock, but I'd prefer to use an electric pump if possible.

My truck has a TBI in-tank pump, which produces way more pressure than the 6 PSI that the mechanical pump produces. Is there any reason in specific why a guy couldn't feed the injection pump with a higher initial pressure using the TBI pump as a lift pump? I understand that GM uses an inline electric pump for the 6.5L pumps, so there must be some reason why they didn't just use an in-tank pump...

Thanks!

Russ

[DmaxMaverick]

Welcome aboard, Russ!

Your best option is to keep the electric pump where it is, and rig it with a momentary manual switch, for priming only. Install a quality mechanical lift pump for normal engine running. The best of both worlds, and more reliable and less expensive than just an electric.

The TBI pump is too much w/o a regulator to drop the pressure. More than 10 PSI will mess with the IP timing, making it very inconsistent. Electric pumps are OK for priming and such, but I suggest using a mechanical pump for normal engine running. Several reasons for it. You won't need to fab (or purchase a pre-made $$) a fail-safe. The fail-safe is necessary (and required, legally) to prevent fuel from being pumped while the engine is not running, like after a traffic collision. A mechanical pump will last longer and cost much less. It will also keep up with engine demands with consistent flow/pressure, as it is dependent on engine speed. Also, when a mechanical fails, it won't trash your fuel system (and IP), like the electric can.

[80Sierra]

Alright, sounds good! Never even considered the fail safe deal...

I'll just re-plumb the truck again to utilize the mechanical lift pump. It means I have to drop and rotate my fuel tank 180 degrees so the lines are on the right side of the truck, and put in an old style sending unit without a fuel pump, but that isn't such a big deal :)

Thanks for the warm welcome!

Russ

[Robyn]

A great big TDP Welcome to you :D


You really dont need to move the tank. You can reroute the lines up front to accomodate the location of the mechanical pump inlet.

I am 100% in agreement with Maverick on the safety issue.

It seems to me that if you use the original Oil pressure switch that came with the truck the TBI fuel pump will work fine. (also any wiring)
A simple little pressure regualtor up top right before the fuel filter will suffice to drop the pressure to the needed 4-6 PSI.

Tearing out the original setup seems like a waste to me as the system is basically all in a ready to go, unless the ECM is involved in running it

I never liked the tank mounted pumps, but they were a necessary evil with the gasser TBI systems to eliminate vapor lock issues.

They also aways seems to fail when the tank is topped off too :eek:

Several good ways to make this work. I always look to use things that are in place if they will do the job and not cost me any additional $$$.

What year is your truck???

Best

Robyn

[80Sierra]

My truck is a 1980 GMC 3/4 ton 4x4 pickup :) I'd originally swapped it to TPI, but was having some trouble getting it running, so I decided to give the carb another whirl by installing a single saddle tank temporarily. Winds up my engine has a wiped camshaft, so I decided that I'd finally go down the road I'd been tempted to follow for quite some time now, and retrofit a diesel in.

I've already got hydroboost brakes on the truck, and a ford vaccum pump to operate my AC controls. The transmission is current an SM465, but I have an NV4500 sitting on the shop floor ready to swap in with the diesel. My transfer case is an NP241 from an 89 Suburban. I've got a 4" lift on the truck (springs front, echobit flip rear) and 33s.

I've retrofitted in a 42 gallon Suburban fuel injection tank where my spare tire used to be, and ditched the tiny saddle tanks. I wanted a bit more range out of my truck so I didn't have to stop at every single gas station I saw... My fuel lines arn't exactly pretty (didn't have a tubing bender or know how to straighten coiled tubing at the time...) so I was planning on re-doing it all sometime soon anyways.

You can expect to hear more from me in the future, hopefully I don't run into too many problems though :)

[FEF]

Welcome aboard, Russ!

Your best option is to keep the electric pump where it is, and rig it with a momentary manual switch, for priming only. Install a quality mechanical lift pump for normal engine running. The best of both worlds, and more reliable and less expensive than just an electric.
You know....

I was thinking of putting in an electric pump that turned on (via relay) with the glow circuit, then regulating the pressure at about 5psi. The reason is, the glow light always comes on for the first crank of the day, and I don't really have any issues after it's been started once. I'm thinking it would not come on after it warmed up, adding a nice safety feature.

I can't think of any bad that would come of it. Am I missing something?

[DmaxMaverick]

You know....

I was thinking of putting in an electric pump that turned on (via relay) with the glow circuit, then regulating the pressure at about 5psi. The reason is, the glow light always comes on for the first crank of the day, and I don't really have any issues after it's been started once. I'm thinking it would not come on after it warmed up, adding a nice safety feature.

I can't think of any bad that would come of it. Am I missing something?

Not a bad idea, and would probably work fine. However, if you are having issues with fuel supply at a cold start, you need to look for other issues. The only negative feature I've ever found with a mechanical pump is priming after having the fuel system open, like a filter change. Other than that, there should be no need for any other fuel transfer help. Even on a cold start. Mechanical pumps are more difficult to replace than a frame mounted inline pump, but a whole lot easier than a tank mounted pump. If a person already has a tank pump, I would leave it there and use it, in place. If it fails, you are where you began. That is, if it will flow fuel through it w/o power. Many don't. The inline pump used on the 6.5's will allow fuel to pass through it when it is not powered (or working). Still, I'd be concerned with the type of pump. What happens when it fails? Will it dump a bunch of metal into your fuel system? You can't count on the filter to catch it all, as we've seen it before.

[80Sierra]

Well, I don't know about other pumps, but you can indeed draw fuel though the stock TBI fuel pumps, they even have a handy check valve in them to help keep the fuel system primed for the next use. Their vanes are made of plastic, so even if it does have a catastrophic failure for some reason, it stands a far lower chance of damaging the injection pump should the filters not catch everything.

Another good way to get the fuel system to shut down in the case of an accident would be to use the oil pressure switch off a stock TBI engine. They are normally open when no pressure is applied, and close once there is between 3 - 5 PSI of pressure applied to them. That way should you roll / flop or otherwise loose oil pressure, the fuel pump will be disabled.