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Under boost, my fuel pressure ramps up as expected, then suddenly drops to around 18psi and leans out (see below image).
Another thing I noticed. Voltage at the battery or alternator is 14.5 or so as expected, but voltage on the supply or feeder side of the fuel pump relay is only like 11.5.
I'm tempted to swap the supply to direct battery (through a breaker), a new relay, and a new 10awg feeder to the pump, but I'm curious if this is a wiring issue or pump failing.
I find it odd that the pump is perfectly fine until a certain point, it seems like a volume issue when my injector DC goes up. But I guess voltage drop could cause that too.
Unfortunately, I don't have a easy way to monitor fuel pump voltage while driving.
If the pump is undersized then fuel pressure should glide down, not just drop off suddenly.
Voltage across the pump definitely has an impact on the flow rate. The pump manufacturer probably has performance curves at different voltages to give you an idea what it can do.
If the pump is undersized then fuel pressure should glide down, not just drop off suddenly.
Voltage across the pump definitely has an impact on the flow rate. The pump manufacturer probably has performance curves at different voltages to give you an idea what it can do.
It's a 400lph walbro. Definitely should be big enough.
I'm wondering if it's failing or wiring. Maybe ground issue?
I hope you upgraded the wiring.... My walbro 450 pulls something like 18amps at 70psi or something like that. You should be running at minimum 14 gauge to the pump through the tank from a relay close by, but 10 gauge to a relay by the tank. I just ran 14 gauge from my rear mounted battery as its less than 6ft worth of wire.
I hope you upgraded the wiring.... My walbro 450 pulls something like 18amps at 70psi or something like that. You should be running at minimum 14 gauge to the pump through the tank from a relay close by, but 10 gauge to a relay by the tank. I just ran 14 gauge from my rear mounted battery as its less than 6ft worth of wire.
Negative...
What gauge is the factory wiring? I assumed 12.
I have some rolls of 10 AWG wire. I was gonna run a 30 amp relay, breaker, etc and just re-run the ground and power to the fuel pump connector.
Run the relay near the pump? I was gonna mount the new one in the engine bay and discard the factory wiring.
I have some rolls of 10 AWG wire. I was gonna run a 30 amp relay, breaker, etc and just re-run the ground and power to the fuel pump connector.
Run the relay near the pump? I was gonna mount the new one in the engine bay and discard the factory wiring.
-- Joe
Not even close. Factory wiring is lucky to be 16 gauge from the engine bay and then at the tank its prob closer to 16-18 gauge. The stock wiring is barely adequate for a 255lph and they still benfit from a wire upgrade. You should for sure run 10 gauge to a relay by the tank, then run 14-12 gauge to the pump. I drilled a hole in my sender tank top and ran 14 gauge to the pump. Otherwise you spend $$ on a wiring kit that upgrades the bulkhead on the sender bc its sealed. I just used JB weld inside and out to seal mine and its been fine for years. The wiring on a aeromotive 340 or walbro 450 is 14 gauge at the pump pigtail so you need to run a minumim that but since our cars run power from the engine bay you need to upgrade everything.
You can run the pump relay in the engine bay but your still going to have to run a large gauge to the back to the tank which will neck down at the tank. Its sorta easier to run a large gauge to the tank with a relay then ground at the body there and then a simple trigger wire which is why the aftermarket harnesses run it that way. Either way will work tho. But you need a minimum of 10 gauge to the back... or maybe 12 gauge at the minimum.
yes, i believe that pump would call for 10ga wire from the battery/relay. i looked but couldnt find the recommendations on it. however, i worked on a c5 with i believe the same pump, and he had an instruction sheet showing the required 10ga wiring. i would bet if you watched the voltage at the pump as it begins dropping psi, your voltage would show extremely low.
So it looks like the factory wiring is 14 or 16 gauge. Which is interesting considering the fuse for that circuit is 20 AMP.
I removed the factory relay yesterday and installed a new 30 amp breaker and relay direct to battery. I'm going to run some 10awg from the relay to the back of the car.
I did a voltage drop calc, and if I leave the small bit of wire from the sending unit connector to the pump itself voltage drop will be a about .068 volt, which is acceptable.
Guess I'll give this a try and if it still has issues I'll swap the pump again. Pump was installed in 2014.
The stock wire on my '89 was 14 AWG if I remember right. Just abandon the stock wiring.
I reused it for a different circuit where I needed to have a firewall pass-thru to the engine bay. I think it's wired to a momentary switch in the console waiting for some future use.
At the back end of the car I repurposed the pump ground wire to become the fuel tank sender ground after I installed a plastic 4th gen tank.
The stock wire on my '89 was 14 AWG if I remember right. Just abandon the stock wiring.
I reused it for a different circuit where I needed to have a firewall pass-thru to the engine bay. I think it's wired to a momentary switch in the console waiting for some future use.
At the back end of the car I repurposed the pump ground wire to become the fuel tank sender ground after I installed a plastic 4th gen tank.
I'm trying to decide how I want to do the connector at the rear. I think I want to run a 10AWG ground right at the body in the back. Not sure if I should use a factory style connector or swap to something else.
I'm trying to decide how I want to do the connector at the rear. I think I want to run a 10AWG ground right at the body in the back. Not sure if I should use a factory style connector or swap to something else.
I originally had the intention of stuffing the 10 AWG wire through the stock connector (behind the rear seat), but it just can't be done. So I cut out a cover plate with a set of tin snips and ran the wires through a motor vent tube. Don't laugh... it works! And there are no wires routed under the car.
There is no shortage of bulkhead connectors available to create a proper wire pass-thru. Problem is the connectors stand really tall and can't be fit under the carpet or behind the seat. I did what I did just for the sake of keeping everything under the carpet like stock. It's a bit "hack", I'll admit that. But then again it's not a proper 3rd gen unless there is some extra velcro, gasket maker, and zip ties holding things together.
I originally had the intention of stuffing the 10 AWG wire through the stock connector (behind the rear seat), but it just can't be done. So I cut out a cover plate with a set of tin snips and ran the wires through a motor vent tube. Don't laugh... it works! And there are no wires routed under the car.
Looks good! That's basically what I was planning. I've got 10AWG running to the rear. I ordered some 3 pin connectors though, I'm gonna run a pigtail through the hole and replace the OE connector.
Traveling this week and next so I won't be able to get to it until the following week.
The hot wire kits racetronix sells basically use stock wiring on body as the 12 volt trigger for the separate relay/relays and run big gauge wire from battery or alternator. Always worked great for me
The hot wire kits racetronix sells basically use stock wiring on body as the 12 volt trigger for the separate relay/relays and run big gauge wire from battery or alternator. Always worked great for me
i got my twin 255’s running constantly now
you could do something similar
There is nothing wrong with that approach, but it took literally 15 minutes swap to a common bosch style relay in the engine bay and run 10AWG to the rear of the car.
The only thing I'm waiting on is some 3 pin weatherpack connectors I bought to use for the sending unit plug.
The only downside, if you even consider it one, is that my fuel pump circuit no longer goes through the oil pressure switch, so in the event of a relay failure the car wouldn't run. But that's fine, the relay could be jumped in a pinch if needed to get back to the shop.
So you opted for twin 255s over a 400 or 450 ? How's that working out ?
I'm still not sure if my fuel pressure drop was due to voltage drop on bad wiring, or if the pump is failing. I think I'm gonna do a volume test when I get back before road testing it again.
same system as my old setup basically except i had 3 255’s with 2 staged on boost switches
worked great
now i left tank alone but wired 2 of the 255’s to feed my front surge tank for the belt drive. Works good so far but still havent really pushed it.
Did you combine them into a single -10 or something?
I'm running an OE sender. I've seen people run dual pumps on the OE sender with some interesting mods to the plumbing. I'm not at the power levels to need that stuff.
4th gen tank bucket was modded for twins but when i added the third pump i cut the bucket off. But two pumps go out a new fitting i installed in the top. -6 3/8” line. One pump used to come out the stock outlet which is 3/8”. Then both Outlets Y into a -8 single feed. Its running e85 now so the volume is needed
4th gen tank bucket was modded for twins but when i added the third pump i cut the bucket off. But two pumps go out a new fitting i installed in the top. -6 3/8” line. One pump used to come out the stock outlet which is 3/8”. Then both Outlets Y into a -8 single feed. Its running e85 now so the volume is needed
I didn't realize a 4th gen fuel bucket fit the tank..
Interesting.
They have the quick connect fittings up top too, if I recall. I modified a 2nd gen tank once to use a 4th gen bucket.
Yeah basically bolts in. Take out the reg. -6 an adapters to the disconnect style fitting. Stock body harness wiring used to trigger relays. External hotwire harness with two relays one for each pump
i think its a 96-97 grand prix or something like that sender unit which bolts in like fbody style but correct thirdgen ohms
Yeah basically bolts in. Take out the reg. -6 an adapters to the disconnect style fitting. Stock body harness wiring used to trigger relays. External hotwire harness with two relays one for each pump
i think its a 96-97 grand prix or something like that sender unit which bolts in like fbody style but correct thirdgen ohms
thirdgen tank a 400-450 lph would make sense
That's what I will do. Did you cut a little access hole for the sender ? I'm thinking while the tank is out, maybe weld an OE style ring to the floor with a plate + gasket to make a access panel like on a nissan.
Would be nice to be able to swap pumps without having to drop the rear end, exhaust, etc every time.
With 4th gen tanks you dont have to do anything, the tank slides out easily and you can change pumps in minutes really. If you have exhaust in stock location you might have to disconnect it
With 4th gen tanks you dont have to do anything, the tank slides out easily and you can change pumps in minutes really. If you have exhaust in stock location you might have to disconnect it
Why is it so much easier than the thirdgen tank? Because the filler neck is two-piece ?
So I was at 72% duty cycle on some 72.4lb/hr injectors. I'm using a Walbro 400.
I know my fuel pump voltage was 11.5 because I was getting voltage drop.
My fuel pressure right before the pressure drop was 54psi.
Looking at this chart:
I'm going to assume my volume was just under 300lph.
Now, if you calculate the injector flow at that duty cycle and pressure, I'm coming up with 468 lbs hour of fuel delivered, which is 294 liters per hour.
So there is a good chance there is nothing wrong with the pump at all, just can't keep up at that voltage.
Based on the wideband data at wide open, it appears the injectors are required to keep the AFR up but the pump might not be enough to satisfy the injectors at this fuel pressure. My regulator goes roughly 1:1 with boost.
So I was at 72% duty cycle on some 72.4lb/hr injectors. I'm using a Walbro 400.
I know my fuel pump voltage was 11.5 because I was getting voltage drop.
My fuel pressure right before the pressure drop was 54psi.
Looking at this chart:
I'm going to assume my volume was just under 300lph.
Now, if you calculate the injector flow at that duty cycle and pressure, I'm coming up with 468 lbs hour of fuel delivered, which is 294 liters per hour.
So there is a good chance there is nothing wrong with the pump at all, just can't keep up at that voltage.
Based on the wideband data at wide open, it appears the injectors are required to keep the AFR up but the pump might not be enough to satisfy the injectors at this fuel pressure. My regulator goes roughly 1:1 with boost.
Hrmmm..
-- Joe
Thats the chart for a Walbro 450 not the 400... look at the flow at 13.5v thats how you know. your putting a solid 50lph less at any given pressure. With that being said it also pulls 15-16amps at your base pressure of 54psi. Once you add 10psi or more the pressure shoots up to 64psi + which flow continues to drop but your amps shoot up as well. If your on the stock wiring then its for sure your problem. However the walbro 450 comes in 2 flavors, the regular 294 I believe and the 274 which is the high pressure version (might have gotten them mixed up). But the regular in the graph has a 90psi check valve hence the cliff drop off, the high pressure version I believe has a 110psi check valve and its perfect for LS base plus boost. I have both but have the low pressure installed as I don't really feel like dropping the tank ever again lol.
FWIW the walbro 450 should have no issues supporting 800-1100hp on pump gas, but your high base pressure plus boost is pushing it into its uncomfortable zone of flow drop due to pressure. I would rather you drop base pressure and gain the flow back. But if you wanted to upgrade a simple high pressure 450 should be more than enough for those 72lb injectors at 100%.
So I ordered the f90000285 pump (helcat 470lph. @ 13.5 volts and 43.5psi).
I'm doing the LS1 plastic tank and bucket. Have all that in the shop now.
So I tested my fuel pump voltage at the pump, and I'm getting 11.8 volts so it's dropping about a volt.. this is the stock wiring before the 10awg. I wanted to test before and after.
With the f90000262 pump I get about 254lph at 0 psi, and 226lph at 50 psi.
I did multiple tests for 30 seconds each.
So I don't know if the 11.8 vs 13.5 makes that much of a difference in flow but that is quite excessive.
Anyhow, I'll get the new 285 pump wired up and in by the weekend.
So I ordered the f90000285 pump (helcat 470lph. @ 13.5 volts and 43.5psi).
I'm doing the LS1 plastic tank and bucket. Have all that in the shop now.
So I tested my fuel pump voltage at the pump, and I'm getting 11.8 volts so it's dropping about a volt.. this is the stock wiring before the 10awg. I wanted to test before and after.
With the f90000262 pump I get about 254lph at 0 psi, and 226lph at 50 psi.
I did multiple tests for 30 seconds each.
So I don't know if the 11.8 vs 13.5 makes that much of a difference in flow but that is quite excessive.
Anyhow, I'll get the new 285 pump wired up and in by the weekend.
-- Joe
I had similar results when I tested my 264 which is the low pressure 450lph walbro. I calculated about the same lph as you. Are you running stock lines all the way to the engine bay?
I think on the voltage charge you loose 50lph across the board going from 13.5v to 12.5v. So 1 volt make s a noticeable difference... if your getting less than 12.5v at the pump now thats a big deal.
I had similar results when I tested my 264 which is the low pressure 450lph walbro. I calculated about the same lph as you. Are you running stock lines all the way to the engine bay?
No, I'm running new hard line to about the front of the door, and then PTFE braided from there on. -6 feed and return.
I did this test at the pump though. Literally out of the sending unit into a 4qt measuring cup. I did the 0psi flow test to rule out any plumbing. The pump just loses a ton of volume when the voltage is low.
Originally Posted by customblackbird
I think on the voltage charge you loose 50lph across the board going from 13.5v to 12.5v. So 1 volt make s a noticeable difference... if your getting less than 12.5v at the pump now thats a big deal.
Crazy huh.. So I have all 10awg now running to the back of the car. So hopefully the voltage will stay around 13.5. My alternator connects direct to the battery, and the battery has a 3 foot 4 gauge wire that goes to the solenoid on the firewall. That's where the fuel pump relay gets it's feed now. So there really shouldn't be any voltage drop now.
(My starter is wired for a remote Ford style solenoid on the firewall).
I need to modify the LSx sending unit to output the correct resistance for the fuel gauge. I measured my spectre sending unit and I got 18 ohms empty. That sound right?
I thought it was 0-90 ohm ?
Believe most buy the 97 grand prix sending unit as its ls1 style and bolts in. 0-90 ohm i believe
Thats what I gathered from reading older posts. I ordered one for a 97 grand prix, naturally aspirated. Was $25 free shipping.
I figure I'll either use it as is or replace the fuel sender/resistor from it into the LSx one.
I dunno if I should run a new 10awg ground to the battery, or just attach it at the body. I believe the only body ground strap is the one on the firewall up front so maybe I should add another one from the back of the block to the frame like on the C4.
Thats what I gathered from reading older posts. I ordered one for a 97 grand prix, naturally aspirated. Was $25 free shipping.
I figure I'll either use it as is or replace the fuel sender/resistor from it into the LSx one.
I dunno if I should run a new 10awg ground to the battery, or just attach it at the body. I believe the only body ground strap is the one on the firewall up front so maybe I should add another one from the back of the block to the frame like on the C4.
-- Joe
The second revision fuel pump will not accept the Grand Prix sender, just an FYI. Not sure which version bucket you have
That should work, looks like the first revision
Not a big fan of buying unknown quality parts off ebay, especially something as critical as the fuel pump
That should work, looks like the first revision
Not a big fan of buying unknown quality parts off ebay, especially something as critical as the fuel pump
I bought it just for the plastic bucket. The fuel pump is going in the trash lol. I suspect it's made by Apex like the Fbody one I bought for $28.
The walbro I bought from Summit. I wasn't going to take a chance on a chinese knockoff.
Is the 'second design' the venturi style? Trying to understand what you mean.
Interestingly enough, the "2001 camaro V8" fuel pump bucket/module I bought does _NOT_ have the venturi system like previous LS1 assemblies I had. (I had one in my second gen camaro: http://nastyz28.com/threads/ls1-fuel...n-tank.228464/) wow that was ten years ago.
I'm guessing it's a V6 fuel pump module Apex sent me.
Good to know on tossing the actual pump, lol. I had put a Racetronix in my original tank setup, but I killed the pump two years ago.
The second design is still a venturi, it just has physical differences, the level sender is different and the connector for the bulkhead is different and came with a new connector with pigtail. Supposedly GM had some problems with the top of the hat on the assembly melting the plastic since the pump would pull a little more current than designed? Might have to do with stuff not being new and some design flaws not anticipated? That is what I remember reading. After I killed the Racetronix pump I din't want to mess with the venturi tube in the bucket again, it was difficult to put on the R pump when it wasn't almost 20 years old and the other pump assembly I had that tube was brittle. After pricing the necessary parts from Racetronix to replace those plastic tubes I decided to just put a new Delphi pump assembly in there since I was going to be using someones lift and I needed to get in and out ASAP. That's when I realized the GP board wouldn't fit in the housing for the float arm lever. So I have been driving with no fuel level for almost 2 years.
Here is a stock photo off Rock Auto, you can see how the board is on different
Good to know on tossing the actual pump, lol. I had put a Racetronix in my original tank setup, but I killed the pump two years ago.
The second design is still a venturi, it just has physical differences, the level sender is different and the connector for the bulkhead is different and came with a new connector with pigtail. Supposedly GM had some problems with the top of the hat on the assembly melting the plastic since the pump would pull a little more current than designed? Might have to do with stuff not being new and some design flaws not anticipated? That is what I remember reading. After I killed the Racetronix pump I din't want to mess with the venturi tube in the bucket again, it was difficult to put on the R pump when it wasn't almost 20 years old and the other pump assembly I had that tube was brittle. After pricing the necessary parts from Racetronix to replace those plastic tubes I decided to just put a new Delphi pump assembly in there since I was going to be using someones lift and I needed to get in and out ASAP. That's when I realized the GP board wouldn't fit in the housing for the float arm lever. So I have been driving with no fuel level for almost 2 years.
Here is a stock photo off Rock Auto, you can see how the board is on different
Interesting. Well I guess we shall see what I get and hopefully between the parts make something work.
Or I'll just change the resistors in the fuel gauge.
I thought about skipping the connector for the pump power and just drilling a hole and running some thicker wire to the pump, then just epoxy the hole.
I thought that other thread said that changing the resistors in the gauge didn't really work correctly?
I found a few threads on it. It does/can work if you use the right resistors. I'd rather do the pump properly so when my cluster dies like they all do I can buy another cluster lol.
THWN wire is rated for gasoline resistance. Do you think it is ok submerged in fuel ? I wonder what the prefered wire jacket grade is for submerged wire in gasoline.
No, I'm running new hard line to about the front of the door, and then PTFE braided from there on. -6 feed and return.
I did this test at the pump though. Literally out of the sending unit into a 4qt measuring cup. I did the 0psi flow test to rule out any plumbing. The pump just loses a ton of volume when the voltage is low.
Crazy huh.. So I have all 10awg now running to the back of the car. So hopefully the voltage will stay around 13.5. My alternator connects direct to the battery, and the battery has a 3 foot 4 gauge wire that goes to the solenoid on the firewall. That's where the fuel pump relay gets it's feed now. So there really shouldn't be any voltage drop now.
(My starter is wired for a remote Ford style solenoid on the firewall).
I need to modify the LSx sending unit to output the correct resistance for the fuel gauge. I measured my spectre sending unit and I got 18 ohms empty. That sound right?
I thought it was 0-90 ohm ?
-- Joe
I don’t remember the sender ohm but I want to say 130ohm or something. My speed hit gauge accepts like 6 different readings so I just use the one that read correctly. Check the ohm at full as well might be like 120 or something which puts the tang 120-18.
I found a few threads on it. It does/can work if you use the right resistors. I'd rather do the pump properly so when my cluster dies like they all do I can buy another cluster lol.
THWN wire is rated for gasoline resistance. Do you think it is ok submerged in fuel ? I wonder what the prefered wire jacket grade is for submerged wire in gasoline.
-- Joe
I guess you weren't the guy that did the resistors thread proof, lol. I am pretty sure it was proved that the resistor changes does NOT work properly with the resistance on this setup, but maybe I read it wrong.
I don't know the insulation that well, but I think teflon insulation is OK for fuel submersion.
Interesting. Well I guess we shall see what I get and hopefully between the parts make something work.
Or I'll just change the resistors in the fuel gauge.
I thought about skipping the connector for the pump power and just drilling a hole and running some thicker wire to the pump, then just epoxy the hole.
-- Joe
Thats what u did. Drilled a hole and ran the supplied gas submerged rated wire that came with the pump. After I was done I used JB weld on both sides. Been like that for almost 2 years no issues. The wire used in the tank needs to be rated for fuel, as does the hose to connect the pump to the outlet pressure line. Otherwise both the wire and hose swells and you got problems. No way I was going to pay $200+ for a relay setup and some wire.
08-04-2019, 07:19 PM
