Swap pros, need advice
 

hate to clog up the boards with another thread, but I'd figure I would get more traffic here than my build thread.

let me start from the beginning. truck has fired up great since I first tried it a few months ago. haven't left my driveway for a run, but started and idled fine. I did my exhaust setup by myself, welding in 2 flowmaster fx mufflers in and dumped the pipes after the TA Xmember. I left the 02 sensors in while welding. I installed everything and connected the battery. truck wouldn't crank first try, but did second time. it would stumble and hesitate over and over. I bought new 02 sensors thinking I fried the others.. same issue with the new ones. finally after a bunch of start ups it finally idles nice and doesn't cut off.

but now it's throwing p0102 code, which is low voltage to MAF. I checked the power and ground wires with key on for the MAF plug and they both are reading 12 volt.. ish. when I try to take it for a spin, it bogs down and nearly shuts off and backfires a little when u give it a little pedal in gear. so, I swap in a new MAF, same problem.

I then rent a fuel pressure gauge, I'm getting 15 psi at the rail! running or just key on, it's 15. so I check the stock fuel regulator by pulling the vac line and there's no fuel, which is good. however, when I pull the vac line while the truck is running, the fuel pressure doesnt move at all, stays 15 psi. I know the gauge works, I tested it on my 2002 avalanche with a 5.3 and it shot up to 55-60

I did pull of the fuel line at the rail and turned the key on a few times to cycle fuel to maybe push out any clog, but I didn't see any.

so, maybe my entire issue is the damn fuel pressure. it has a new stock style fuel filter (I did order a K&N that I will try for the hell of it), new acdelco ep381 fuel pump (listed for a 1997 Tahoe). all new AN hoses. I will pull the sending unit today and see if maybe the pump hose is damaged? or maybe the screen fell off?

wether it's related to the MAF code or not, I need to solve this fuel pressure issue.

Re: Swap pros, need advice
 

well son of a gun, pulled the pump and found the small pickup hose barely on! straightened up and now with key on it jumps to 55, then settles at 50. truck running it sits at 45 it seems according to the gauge. the truck did fire right up first crank and I punched it a few times back and forth in the driveway and no bog like before! pressure does seem low though, wonder if it's because the pump is for a 97 Tahoe? I went with this pump because I read somewhere it was recommended for LS swaps

Re: Swap pros, need advice
 

Oh wow..
I'm not sure on the min pressure ,but both mine are sitting right at 58psi on the rail, with no real drop while running

Re: Swap pros, need advice
 

Its been a long time since I installed that pump, but shouldn't it have fuel injection type clamps on it?

Re: Swap pros, need advice
 

That pump should be good, the 97 Tahoe spec is 56-62. Are you using SUBMERSIBLE fuel hose, or just fuel line from the parts store? There is a difference and it cost me a $500 tow home from a show in my camaro when the hose popped off in the tank and I couldn't repair it on the side of the road at 1:30am.

Verify you have the correct fuel hose and clamps on, and then check your connections again and re check fuel pressure. I ended up fighting a similar issue again in my Camaro where the correct fuel hose split and would give dead nuts fuel pressure at idle and light cruise, but give it any gas and it lost it. Took a while to find that one.

https://www.amazon.com/Gates-27097-S.../dp/B001R5XX56

Re: Swap pros, need advice
 

the hose and clamps came with the acdelco pump. I actually want to swap it with one that's about an inch longer. this one fits but another inch of bite won't hurt

*edit*

after looking at the ebay ad, it's showing different clamps. maybe I used the ones from the fuel tank kit. hmm think I'll run to O'Reilly's and get a new hose and fuel injection clamps and try another test

Re: Swap pros, need advice
 

Let us know!!

Re: Swap pros, need advice
 

bought the clamps but they didn't have the hose, so I found the 5/16 one on Amazon. little bastard was 30 bucks a foot though.

Re: Swap pros, need advice
 

Yeaaa, that hose ain't cheap, it hurt when I figured that one out too. But really wish I found out before I was on the side of road for 2 hours waiting on a tow truck in the middle of the night.

At the time my NAPA was really good so they were able to get it for me, but it was like 27 bucks for a foot.

Re: Swap pros, need advice
 

ya we have a napa about 15 min down the road, but I was cutting it close on the Amazon deadline so I didn't have time to even try napa lol. oh well at least it's peace of mind knowing that tube should never be an issue!

I'll post back when I get it back in. but out of curiosity, if it stays at 45-50.... could it be considered normal... or would the next culprit be the stock pressure regulator?

Re: Swap pros, need advice
 

45-50 is still on the low side. The computer can probably compensate under normal conditions, but it's not right. What is the rest of your fuel system like? Any sharp bends or pinched lines pre test port/regulator?

Re: Swap pros, need advice
 

nope not at all. I used evil energy AN hose for the entire system, not one hard line. stock filter located maybe a few feet from the tank along the frame. the regulator is the stock style mounted on the engine, original to the motor.

I looked at a how to to test it. when engine is running, if the diaphragm is busted fuel will shoot out the vacuum port. it did not. but the second test, if you unplug the vaccume port while running, the psi shoot up like 5 psi, but it did nothing. when I get the hose in tomorrow I should have the pump back in by Thursday and I will try another pressure test, and also test that regulator again

this is the stock pressure regulator below..

Re: Swap pros, need advice
 

those pressure regulators usually cause hard starts, smell of fuel, etc. I don't smell fuel and when I got the pump back in yesterday it fired right up first crank. I'm just not sure how they actually regulate the pressure?

Re: Swap pros, need advice
 

Check where you installed the AN fittings into the braided hose. I had some cheaper hose and fittings gouge the inner rubber of the braided hose and it would act as a check valve and block fuel and gave all kinds of starvation issues. I've gone through a lot of issues with the fuel system in my Camaro and wish I had just done the Aeromotive drop in unit and PTFE line from the get go. PTFE is a lot easier to work with.

I learned a lot because of my issues though, plenty of people use the evil energy stuff with out issues but there's the chance with any fitting or line combo to have issues. I'd pull every connection you can get to while you're in there and use a flash light to make sure you don't have a piece of trash or rubber inner hose giving you fits. Don't remove the fittings from the hose, just unscrew them from their connection at the pump, filter and engine, etc. If you have compressed air it cant hurt to make sure you don't have a blockage anywhere.

The factory regulator has a calibrated needle and seat and spring that allows a certain amount of fuel to bypass to the return lines to maintain correct pressure. The vacuum line allows the pressure to rise with load on the engine. Also if you had a restriction in your return circuit you'd be fighting higher fuel pressure at the rail. My first pump was oversized when I was still running a carb and needed to regulate down to 7PSI, I had the regulator pretty much wide open with -6 return, upped to -8 and I could actually use the regulator. Now that set up is fuel injected and return is technically over kill, but it won't hurt anything.

Re: Swap pros, need advice
 

That is a flex fuel regulator in your pic, so I'm going to assume it's a flex fuel engine in which case 45-50psi is normal.

Re: Swap pros, need advice
 

well damn, your right! I saved a picture of the vin and there sure is a "V" in the vin. well at least I won't have to mess with that regulator

Re: Swap pros, need advice
 

The z in the vin is what ID's it as flex fuel. Good catch LS1Nova71! Has any sort of tune been done to the ECU? If the tuner messed with the base fuel maps thinking they were going to have xx amount of fuel and really have lower this it could cause some issues. But your main issue of the insanely low pressure at first and wrong in-tank hose should get you all fixed up!

From ALLDATA-
"Measure with the Key On Engine Off with the fuel pump commanded ON.

Vin (V,T,U)
Fuel Pressure (gasoline) .................... 55-62 psi

Vin (Z)
Fuel Pressure (ethanol) .................... 48-54 psi"

Re: Swap pros, need advice
 

no tune, just sent it to Brendan at lt1swap. he asks for certain info and that's what I sent him, although he never asks for the vin or if it's a flex fuel...

https://lt1swap.com/programming.htm

if u follow that link and scroll down to the 99-07 section, you can see what info requires. he does ask if you will be using an aftermarket regulator or stock vaccume style regulator.

this truck engine will stay stock so I'm hoping what Brendan did is enough to get it on the road and keep it there.... unless a tune to a stock engine is still normally required?

Re: Swap pros, need advice
 

Even in stock form a tune helps these trucks motors, but is not necessary. If you gave him the injector part number and they were the correct ones for the truck all parameters should be good. I'm betting it runs leaps and bounds better with proper fuel pressure though.

Re: Swap pros, need advice
 

ya, he did ask for the injector numbers. i havent even been able to make it out of my driveway for the maiden voyage yet beause of the stumbling lol. my truck has no glass at all, and no rear lights. i just want to run it down some of these side streets for the first time since ive owned it in 14 years. cant afford for it just to just shut off on me down the street!

Re: Swap pros, need advice
 

I wanted to throw this link up I found on youtube regarding what "normal pressure" is. swear I learn something every day around here. it explains the 3 different type of fuel systems for the 99-07 systems

https://youtu.be/wA6mmc8fvQo

Re: Swap pros, need advice
 

new hose came in today. i cut it to size and clamped it on but damn it was so tight. could only slide it up on the tube about an inch or so and clamped it. other side slid on no issue. so i couldnt double clamp it but it should be good to go..i dont know how in the world it could even slide off without cutting it off lol.

anyways, bought myself a cheap harbor freight pressure gauge just because, and im getting the same 42-44 psi at idle. pulled the regulator vac line and it shoots to 50-52?...which seems normal. FYI, dont be a dumbass like me and unhook the pressure gauge while the truck is running :( anyways, truck starts right up, idles fine, even pulled out the driveway and back in with no issues. believe the problem is solved i hope!


i have enough hose leftover to do at least 1 or 2 more pumps if anyone is interested. sucks paying $30 per foot and only need like 4 inches.

Re: Swap pros, need advice
 

Sounds like you've gotten your problem fixed up, you verified your pressure regulator is working, and your pump/system is capable of over 50PSI. Truck should run great now.

Re: Swap pros, need advice
 

I fought this issue on a couple of builds. I went with the expensive submersible hose and injection style clamps BUT ALSO used zip ties around the pump body and pickup tubing to prevent it from flexing. It really made a difference.

Re: Swap pros, need advice
 

that is a good idea. i remember when i installed the pump the first time and i know i did not install the hose like that...but i figured maybe the worm clamp wasnt enough to hold it. flexing along with the cheap clamp probably was the reason it did slide off. i know now though that upper part of the tube is on SNUG. now you have me worried about the bottom part where the hose slides on the pump :(

it was really tough though getting that hose on this time. i had to pull the sock to free the pump out of the little housing. then i slid the upper part of the hose on as far as i could on to the sending unit, then slid the pump into the bottom part of the hose. THEN i had pry the pump into the bottom housing, and slide the sock on from there. it was not easy. if it still manages to slide off, im throwing it across the field