I could use some help with fuel pump issue

[BulldogSS]

Checked my fuel pressure at the filter and got a steady 10psi. Once the key is turned off it drops back to 0 in less than 30 seconds. The reason I bothered to check is the new plugs look very white which indicates I’m running lean. From what I’ve read 10psi is on the edge of being unacceptable, with 12-14 being ideal. Also the quick bleeding down of pressure I would guess is some sort of check valve no operating correctly. A quick run down of the truck. 1994 c1500 5.7 auto. I’ve rebuilt tbi with pod spacer, Tossed the stove pipe and pulled flapper, v6 intake tube(fender to air cleaner), k&n filtered air cleaner top, new plugs, wires, cap and rotor. Exhaust is stock manifolds to flow master y pipe no cat, 3 wire o2. I’ve done some other maintenance but nothing that should pertain to engine performance. It’s probably worth mentioning when I installed the v6 air tube the truck surged at idle for about 1min and then smoothed out. Currently the truck starts a little slowly but not bad(uh,uh,vroom). I’m sure that’s from the pressure bleed down. It’s getting about 15mpg and is running quite well for what it is. So without getting to long winded should I be looking to replace the pump? I’ve read to use the 96 and up Vortec pump. Will replacing just the pump and not the whole unit correct the pressure bleed down? Any advice? Thanks Mark

 

[Schurkey]

Checked my fuel pressure at the filter and got a steady 10psi. Once the key is turned off it drops back to 0 in less than 30 seconds. The reason I bothered to check is the new plugs look very white which indicates I’m running lean.

White plugs does not indicate "lean". Hasn't for decades. Plugs quit coloring when the lead was removed from fuel. Takes thousands if not tens of thousands of miles to put color on the plugs now.

"Lean" is indicated by the O2 sensor. Connect a scan tool, look at the O2 voltage and cross-counts. How old is the sensor?

From what I’ve read 10psi is on the edge of being unacceptable, with 12-14 being ideal.

Spec is 9--13. Yeah, most of us would rather be on the higher end. This is a function of the pressure regulator in the TBI unit. (Unless the pump is so frail it can't generate more pressure than that.)

Also the quick bleeding down of pressure I would guess is some sort of check valve no operating correctly.

TBI does not retain pressure. Totally normal.

A quick run down of the truck. 1994 c1500 5.7 auto. I’ve rebuilt tbi with pod spacer,

Pod spacer is a waste of time, money, effort, and enthusiasm. The big-block trucks have one because they have larger throttle plates. Need to boost the injectors higher to get the cone of fuel spray to the edge of the bigger throttle plates.

Tossed the stove pipe and pulled flapper, v6 intake tube(fender to air cleaner), k&n filtered air cleaner top,

Stove pipe? And you removed the heated-air intake flapper? The K&N filtered lid has removed power on most dyno tests it's been used with. This is all a mistake.

currently the truck starts a little slowly but not bad(uh,uh,vroom)

Does the fuel pump prime for two seconds when the key is turned from "Off" to "Run"? If not, that's your extended cranking time. Engine has to crank long enough to build oil pressure, then the oil pressure switch bypasses the fuel pump relay to run the fuel pump.

How much voltage is in the battery when there's no load? What is battery voltage DURING CRANKING?

should I be looking to replace the pump? I’ve read to use the 96 and up Vortec pump. Will replacing just the pump and not the whole unit correct the pressure bleed down? Any advice?

You want more fuel pressure? Stiffen the spring in the pressure regulator. Some folks replace the spring, some folks try to make the regulator adjustable. Some folks just stretch the original spring and put it back together.

IF (big IF) the pump you have is in good condition, with PROPER POWER AND GROUND, putting in a different pump is a waste and won't change your fuel pressure.

 

[Hipster]

Stove pipe? The K&N filtered lid has removed power on most dyno tests it's been used with. This is all a mistake.

Yep!

 

[BulldogSS]

First of all thanks for taking the time for the very detailed answers. It’s very much appreciated. This is my first experience with tbi. I have some with carbs but mostly LS motors. I recently bought the truck and am in the process of getting everything back into good working order. I’ve gone through the brakes, a/c system and other basic maintenance. The “stove pipe” was actually missing when I got the truck and the “flapper” was in a bind about half open. So I pulled the pin and removed. I guess I could hit the local yards and hunt down replacements. As for the filtered lid, I could put the stock lid back on. I read on another site that it worked well. Same with the pod spacer. Bad info I guess, live and learn. Back to the fuel pump which was the main focus of the post. I checked the pressure and saw the 10psi and thought well thats with in range although the lower end, then noticed it didn’t hold pressure after the ignition was turned off. I thought this was NOT normal. Thought possibly the pump could be on its last leg. However, from your post this is all completely normal. The “slow” cranking really is not an issue It’s prob 2 sec between turning the key and motor firing over. As for getting o2 readings I’ve got a Matco obd2 scanner but no way to scan this truck. I can make a few calls and see if I can track one down. As far as fuel pressure, I was thinking I needed to be up more toward 12-13psi but is this just more bad info I’ve read on other sites? Really now that I know that my pump is not showing abnormal signs I would guess scanning the truck and letting the o2 sensor tell me if the truck needs more fuel would prob be best. As I’m sure most of you know there is so much info on the various forums trying to decipher through what’s good and bad info can be difficult. Again thank you for taking the time to educate me. Your response was was very detailed, I appreciate it.

 

[BulldogSS]

Also while I’ve got a chance to ask someone with the knowledge. What “mods” are worthwhile? I’ve read about the “salad bowl”, tbi spacer, doing away with the spacer ring between tb and air cleaner. I’m not looking to do anything major for now. The truck has 220,000 miles so as much as I’d love to do a cam and heads it’s prob best to leave it alone until it needs a rebuild. Are the pod spacer and v6 intake tube hurting performance?

 

[PlayingWithTBI]

Same with the pod spacer. Bad info I guess, live and learn.

Not necessarily, as @Schurkey said the pod spacer help to spread the fuel spray on bigger bore TBs but, it also helps with better air flow just like the "salad bowl" but, that all applies to modified engines. A stock 5.7L will breathe just fine with the OE intake. Until you start revving upwards of 4500K you'll want to look into a less restrictive system.
Here's a link to a bored out TB that will flow 650CFM and comes with the 1/4" pod spacer.
https://www.ebay.com/itm/46mm-PORTE...837306?hash=item3d963196ba:g:mpwAAOSw2xRYWVJj

I checked the pressure and saw the 10psi and thought well thats with in range although the lower end, then noticed it didn’t hold pressure after the ignition was turned off. I thought this was NOT normal. Thought possibly the pump could be on its last leg. However, from your post this is all completely normal.

Yes, pressure is on the low end and TBIs don't have a check valve at the regulator so, it'll drop almost immediately after shutting off the engine. An AC Delco EP381 fuel pump (about 100LPH more than the OE one) from a Vortec engine will supply anything you need once you pump up your engine. The whole thing about achieving Stoich AFR is developing enough fuel pressure for the injectors to produce enough flow to match your engine's requirements. Here's a link for an AFPR, scroll down a bit to see the adapter, gauge, and the AFPR.
http://www.rvmorsemachine.com/product.htm

 

[PlayingWithTBI]

BTW - here's a picture of mine set at 28PSI (with a 28PSI spring) so I can achieve 14.7AFR on my VE tables with a WBO2 sensor. HTH

You must be registered for see images attach

 

[Busted Knuckle]

Checked my fuel pressure at the filter and got a steady 10psi. Once the key is turned off it drops back to 0 in less than 30 seconds. The reason I bothered to check is the new plugs look very white which indicates I’m running lean. From what I’ve read 10psi is on the edge of being unacceptable, with 12-14 being ideal. Also the quick bleeding down of pressure I would guess is some sort of check valve no operating correctly. A quick run down of the truck. 1994 c1500 5.7 auto. I’ve rebuilt tbi with pod spacer, Tossed the stove pipe and pulled flapper, v6 intake tube(fender to air cleaner), k&n filtered air cleaner top, new plugs, wires, cap and rotor. Exhaust is stock manifolds to flow master y pipe no cat, 3 wire o2. I’ve done some other maintenance but nothing that should pertain to engine performance. It’s probably worth mentioning when I installed the v6 air tube the truck surged at idle for about 1min and then smoothed out. Currently the truck starts a little slowly but not bad(uh,uh,vroom). I’m sure that’s from the pressure bleed down. It’s getting about 15mpg and is running quite well for what it is. So without getting to long winded should I be looking to replace the pump? I’ve read to use the 96 and up Vortec pump. Will replacing just the pump and not the whole unit correct the pressure bleed down? Any advice? Thanks Mark

1996 Vortec fuel pump will flow 155 lph. Change the whole assembly. I ended up changing everything, tank and fuel lines due to corrosion. Use DELPHI HP10003. My '95 connector plugged right in. Check yours to see if a connector mod is needed. Also remove the old ground and create a new ground to the chassis by using an angle grinder to get fresh metal and use a stainless nut and washer to secure the new ground eye.

 

[BulldogSS]

Thank you to all that took the time to reply. I’m going to see if I can get my hands on a scanner to check o2 readings. At some point a previous owner had swapped from the 1 wire to 3 wire sensor. Which I’m reading is a good thing. I’m guessing there is no need to increase fuel pressure if the engine doesn’t need more fuel. Also with out being able to read the o2 info I’d be guessing at what pressure to increase to. Please correct me if I’m wrong.

 

[BulldogSS]

Also I’m going to check voltage as close to the pump as I can and take a look at the ground as well. Just to see if that is all good to go.