Full Blown Dual Pump System - Things You Should Know
Oct 17, 2010, 12:00 AM
#64
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Location: New Mexico
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I know this thread has been going on for a while now but i have a question. I am running into what i think is the same problem only im running two pumps in series. After full throttle it takes a long time to get the engine to come back down to idle. could this be caused by this siphon tube backing it up?
Jan 28, 2011, 05:50 AM
#65
Sharing my recent experience with twin pumps and high fuel pressure... I am only running one pump at a time however I did in fact have a base pressure problem similar to what was seen here.
I have a Buschur twin pump setup, Iraggi HO alternator, 1/0 gauge power and ground wiring in the engine bay for the alternator to the battery, and 8 gauge wiring upgrade running my fuel pumps via relays. The primary pump is triggered by the factory wiring and the secondary pump is triggered by AEM. I was getting a base pressure of 59psi and could not lower it. After testing everything and isolating the problem specifically to the siphon tube it was drilled out as described in this thread and my pressure dropped around 10-12psi base pressure.
Idle instantly was more stable and while driving I am not getting extreme lean conditions like I was before. Now I need to retune the fueling on the car to get it right since I was fighting the extreme base pressures. So far I only have around 50 miles on a full tank of gas and the siphoning system appears to be working without issue as the needle has barely moved but I am going to keep a close eye on it. It would be impossible for me to run both pumps full time but at least I have more control now.
I have a Buschur twin pump setup, Iraggi HO alternator, 1/0 gauge power and ground wiring in the engine bay for the alternator to the battery, and 8 gauge wiring upgrade running my fuel pumps via relays. The primary pump is triggered by the factory wiring and the secondary pump is triggered by AEM. I was getting a base pressure of 59psi and could not lower it. After testing everything and isolating the problem specifically to the siphon tube it was drilled out as described in this thread and my pressure dropped around 10-12psi base pressure.
Idle instantly was more stable and while driving I am not getting extreme lean conditions like I was before. Now I need to retune the fueling on the car to get it right since I was fighting the extreme base pressures. So far I only have around 50 miles on a full tank of gas and the siphoning system appears to be working without issue as the needle has barely moved but I am going to keep a close eye on it. It would be impossible for me to run both pumps full time but at least I have more control now.
Jan 28, 2011, 07:06 AM
#67
I have the Buschur and it works great, as David said drilling out the siphon isn't needed. The set-up as is can get you deep into the 9's and probably beyond so rewiring everything isn't "needed".
Just keep an eye out for the regular issues when drilling/running like this itz. When you get down to around 1/4 of a tank either carry some gas or park on a flat surface and pull the passenger side float out. With it out turn the car to "ON" but don't start it up. Look at your gas gauge with your passenger float bottomed out to see it it drops all the way to the E or very close to it. If it does, your siphon system isn't working properly.
Just keep an eye out for the regular issues when drilling/running like this itz. When you get down to around 1/4 of a tank either carry some gas or park on a flat surface and pull the passenger side float out. With it out turn the car to "ON" but don't start it up. Look at your gas gauge with your passenger float bottomed out to see it it drops all the way to the E or very close to it. If it does, your siphon system isn't working properly.
Jan 28, 2011, 07:48 AM
#68
I have the Buschur and it works great, as David said drilling out the siphon isn't needed. The set-up as is can get you deep into the 9's and probably beyond so rewiring everything isn't "needed".
Just keep an eye out for the regular issues when drilling/running like this itz. When you get down to around 1/4 of a tank either carry some gas or park on a flat surface and pull the passenger side float out. With it out turn the car to "ON" but don't start it up. Look at your gas gauge with your passenger float bottomed out to see it it drops all the way to the E or very close to it. If it does, your siphon system isn't working properly.
Just keep an eye out for the regular issues when drilling/running like this itz. When you get down to around 1/4 of a tank either carry some gas or park on a flat surface and pull the passenger side float out. With it out turn the car to "ON" but don't start it up. Look at your gas gauge with your passenger float bottomed out to see it it drops all the way to the E or very close to it. If it does, your siphon system isn't working properly.
I have a completey stock hanger setup so if this doesn't work I will make changes and swap to the other siphon system again and downgrade the power supply back to stock. I do still have higher than average pressure using the factory wiring which I am guessing is probably due to the HO alternator. I am also running AEM Series 2 so it may not have been running the hi/low switch for the pump system either so time will tell.
Jan 28, 2011, 09:16 AM
#70
I am still baffled myself but I isolated it to ONLY the siphon and even tried my spare siphon assembly along with checking everything in the plastic assembly there is no other obstruction. I even bought 15' of fuel line and bypassed the factory lines straight to the full pump assembly. Pull it and direct it into a bucket and pressure is perfect at 43.5psi.
There is a 3~5psi difference in the output of my primary pump over my secondary also which I find a bit strange but it works perfectly fine otherwise.
I guess we'll see what happens over the next few days.
Have you confirmed your fuel availability is still exactly as factory and you are not getting shorted out a gallon or 2 form the saddle side?
Jan 28, 2011, 09:28 AM
#71
I don't drive the car much, and I usually refuel when I get to the 1/4 mark because I don't want to take a chance on running lean. One thing I did notice recently in a long freeway drive is I didn't see the gauge needle move below 1/4 or a reserve light. I assumed it was an issue with the main float travel, but I'll just have to run it low and have a look.
Jan 28, 2011, 11:42 AM
#72
I don't drive the car much, and I usually refuel when I get to the 1/4 mark because I don't want to take a chance on running lean. One thing I did notice recently in a long freeway drive is I didn't see the gauge needle move below 1/4 or a reserve light. I assumed it was an issue with the main float travel, but I'll just have to run it low and have a look.
Jan 28, 2011, 12:01 PM
#73
You'll probably make it to the bottom of a tank before I do, so report back. Obviously, I can't rule out anything from where I sit, but it would be surprising if this were the case. After all, the design objective with the siphon is to make it just large enough to maximize velocity without creating a pressure backlog. The factory size works for one pump, but not two. The degree by which it is enlarged is minor enough such that it shouldn't diminish its operation. I didn't catch wind of anyone else with my issue, and I assumed it to be a function of the Fullblown assembly and float in my particular case. I've already had to remove it and make adjustments more than once.
Jan 28, 2011, 12:29 PM
#74
You'll probably make it to the bottom of a tank before I do, so report back. Obviously, I can't rule out anything from where I sit, but it would be surprising if this were the case. After all, the design objective with the siphon is to make it just large enough to maximize velocity without creating a pressure backlog. The factory size works for one pump, but not two. The degree by which it is enlarged is minor enough such that it shouldn't diminish its operation. I didn't catch wind of anyone else with my issue, and I assumed it to be a function of the Fullblown assembly and float in my particular case. I've already had to remove it and make adjustments more than once.
Sucks on the FB unit, I've read so many "quirks" about it... I almost bought one a long time ago but decided to go with Buschur's instead.
Jan 28, 2011, 12:49 PM
#75
It's important that we find out if this is just an annoyance of the FB unit, which is why your feedback is valuable.
Both the Main and Sub float assemblies are just variable resistors wired in series, and the resulting voltage is what is indicated by the fuel gauge. If there is a residual fuel issue in the Sub tank that prevents that float from reaching bottom when the Main is low, that would cause the issue. However, if the body of the FB unit obstructs the Main float such that it cannot reach its bottom position, that would also cause the issue. I suspect the latter is what's happening in my case, but I'd like to know with reasonable confidence before I consider post a notice to all FB users.
Both the Main and Sub float assemblies are just variable resistors wired in series, and the resulting voltage is what is indicated by the fuel gauge. If there is a residual fuel issue in the Sub tank that prevents that float from reaching bottom when the Main is low, that would cause the issue. However, if the body of the FB unit obstructs the Main float such that it cannot reach its bottom position, that would also cause the issue. I suspect the latter is what's happening in my case, but I'd like to know with reasonable confidence before I consider post a notice to all FB users.