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TPI Fuel Pump Plumbing

B

BCCHowdy

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Location
Tucson, AZ
Hello!

I'm a new member and recently acquired an '85 K5 Blazer. I have a freshly rebuilt 350 to go in it along with a TPI fuel injection system and I'm having trouble finding a good location for the inline fuel pump I purchased. I'm also concerned about the size of the return line being 1/4".

The fuel tank has 3 lines. Supply line is 3/8". Vent line to charcoal canister is 3/8" (5/16??). And the return line from the original mechanical fuel pump is 1/4". If I remember right the vent line has an orifice on the tank side which would greatly restrict flow and inhibit use as a return line. I put about 20 psi of air to the vent line and there's quite a bit of back pressure. The 1/4" return line seems to be ok as far as back pressure in comparison to the vent line, but I'm concerned it's not big enough. I purchased the walbro 255lph high pressure pump and I'm concerned the 1/4 return line will be too small driving pressures higher than what the pressure regulator on the fuel rail will manage.

Does anybody know if the 1/4 line will work as a suitable return line? My alternative is to plumb the pump in a loop with pressure gauge and see what it does with nothing else hooked up.

I'm having a heck of a time finding a location for the inline pump. If anyone else has done this type of conversion, where did you put the pump?

I've done a carb to TPI conversion in the past on an '84 GMC halfton dual tank system. I had a high volume low pressure pump mounted on the passenger side wheel well in the engine bay pull from the tanks and push to the low volume high pressure fuel injection pump. Sounds kinda silly, but it worked flawlessly. I'd like to do a cleaner install this time around with the fuel pump back by the tank. I'd like to avoid installing a new tank and in-tank pump and new fuel lines (proper return size) if I can get away with it.

I intended to put this post in the 1973-1991 K5 Blazer | Truck | Suburban forum but I don't have privileges to do so. I appreciate any feedback or pics of similar installs.

Thank you!

-BCCHowdy
 
I have tpi on mine with a frame rail mounted pump.
But your best bet is to get a ‘87 up tank and sending unit with internal pump. But in both cases, I ran a new -8an/-6an feed line and used the original 3/8” feed as the return.
 
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Borrow the fuel tester checker from autozone (if you have them) and run the pump. The only time I can see it being an issue is when the injector duty cycle is zero or very low (coasting, idle) so if you don't see an issue with the engine not running, I don't see why you'd have an issue at any other time.

Another potential option I suppose, if it were an issue, would be to use an adjustable fuel pressure regulator, and reprogram the ECM for the higher pressure.

Really wouldn't be good for the fuel temps however, if you do see a pressure rise due to restricted return flow to the tank.
 
Sorry for the delay in getting back to this posting. Been doing engine R&I and then the front output shaft on the transfer started dripping overnight so did an R&I and seal change on it too.

I got the pump plumbed to the original 3/8" supply line with pre-filter. I added an inline fuel pressure gauge and looped right back in to the 1/4" return. I get about 12-15 PSI of back pressure. Not great, but not bad and I figure it'll work. However, I'm pretty sure the pump is cavitating. And I have a surprising amount of debris in the pre-filter. Not sure if it's from the tank or from the lines. Tank is approximately 2/3 full.

Here is the pre-filter after the pump being run for about a minute then shut off.
Pre-Filter.jpg

This is what the pre-filter looks like while the pump is running. Looking at the pictures more closely this looks more like air ingestion rather than cavitation.
Pre-Filter Cavitation.jpg

I wonder if this could just be dry rot of the original fuel lines from the top of the tank to the steel lines and I'm sucking air somewhere. Either way, I'm going to have to drop the tank to find out. Bleh...
 
Do you have an access panel cut out for better access to the sending unit,
I have to agree with you looks more like air ingestion.
on a safety note do not run the specter glass filters, especially underneath the frame like the one rock or piece of debris an you will have fuel spilling out the back ruining a good day. look at the wix plastic filters
 
Ah yeah, good point on the glass. I was trying to go for a mesh type filter (lowest restriction possible) that I could inspect without having to disassemble. The Wix plastic filters look great, but only seem to come in 1/4" and 5/16". I couldn't find this type in 3/8". Is this what you intended, or did you have something else in mind?

33972.JPG
 
If you have to drop the tank, then I'd suggest just installing the pump in the tank. In tank pumps will run cooler quieter and longer. Get a '87+ sending unit and modify it to install your Walbro pump onto it.
 
Wix 33003 filter is a plastic 3/8" inline universal one...but its a paper element type..
They may make a mesh style one too..
 
This is what I run on my small block although mine is on top right before the carb.
Chevy305 also has a good point in regards to the I tank fuel pump

Screenshot_20200101-173554_Chrome.jpg
 
I've paid less than $5 for those at local parts stores!..or 3 for $5 at the flea market..
 
For my TPI I used a stock TBI Blazer fuel tank and sending unit. A TPI pump drops right in.
 
Thanks everyone for the feedback! I appreciate how active and helpful this community is. I should have time to drop the tank sometime this weekend and will report back my findings.
 
I dont see reference to ethanol. Under low pressure it MIGHT not be an issue, but really a very bad idea to be using any hose that isnt ethanol rated, for any fuel line.
 
Also those Wix plastic fuel filters are most likely intended only for low pressure carbed fuel systems,not EFI...I'd be leery of using one on a system with more that 12 psi ..might be OK on the "suction side" of the system though..
 
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