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Help needed diagnosing low voltage in boost/ fuel pressure drop

Help needed diagnosing low voltage in boost/ fuel pressure drop

 
Old 04-10-2019, 12:51 PM
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Default Help needed diagnosing low voltage in boost/ fuel pressure drop

I'm working on this car for a customer who lives 4 hours away in tri-cities area. So here's a basic quick run down on the car.

built turbo gsr
2000cc injectors, just flow tested
has aem 380lph pump in tank feeding an inline 400lph pump. I believe the feed line is a -8, return looks like a -6 to me. The car was previously tuned at another shop and made 480whp on 20lbs.

From what I've been told the only thing changed since it made 480 was the hondata coil on plug setup which is pinned into the alternator control (which his rywire harness doesn't have a wire for anyways)

Heres the issue. As soon as you start coming into boost it goes lean due to fuel pressure drop. Fuel pressure is at 60lbs and drops to about 20lbs around 5k or so. It's running out of fuel before 300whp. On data logs the car keeps dropping voltage when going into boost/ higher rpms. It will drive fine around 14v then in boost drop to about 12.0 and lean out. The fuel system should support a ton of power but something isn't right.

i have wired up a 30amp relay for the intank pump, 10ga wire. Soldered with new dual 12ga grounds. The pump sounds allot louder on priming but once running you only hear rattles from the car and the open down pipe really.

I found that the battery cable and alternator wire were backwards on the fuse box and have since switched them around

it has a new orileys alternator on it. Old one did the same thing.

i have repairs the ig wire for the alternator. It was barley hanging on.

i feel like I'm running out of ideas besides just testing actual voltage at the pump which I'm sure will come up low and that's what I think is causing the drop.


on a side note, the car will litteraly run for minutes with no fuel pump on and no fuel pressure. Sitting there it idles just fine. Never seen that before. I feel like I'm loosing my mind with this car lol.

Open to any suggestions, guesses or info that might help me figure this out



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Old 04-10-2019, 03:05 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

Something fishy with the fuel pumps.
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Old 04-10-2019, 03:14 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

It's either something with the pumps, a massive restriction in fuel flow or its due to the voltage drop. The voltage drop seems to go hand in hand with the leaning out. The boost collums where it leans out I've tried adding about 80% more fuel in and it makes no change what so ever. It's dropping pressure but only under load so it's a flow issue. I'm about tempted to just throw my lithium ion jump box on the pump wiring and see if it makes a difference. Unfortunately I only have like 4 more gallons of e85 for the car so I really won't be able to tune it if I keep trying one thing after another over and over again without any good results. This car is beyond frustrating. I always have a really hard time charging people for my time if I can't figure it out and fix it.
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Old 04-10-2019, 03:22 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

There's a 380 pump feeding a 400 pump. More demand is causing them to work harder and the flow rates dont add up.
Try removing the 400 and see what happens?
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Old 04-10-2019, 03:27 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

I don't think that's the cause but you never know. I however did just find that his wideband white wire (aem) is wired into ecu pin d10 which is the eld pin. I'm gonna wire it up right and see if that changes anything
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Old 04-10-2019, 03:37 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

Interesting. I'm using my ELD for WBO2. The settings were a bit different, but I never had any voltage drops. I wouldnt think that'd be a cause for the voltage draw **shrug** The voltage draw has fuel pump all over it, and the restriction-like results say that one of em is struggling.
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Old 04-10-2019, 04:06 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

Your probably right. I wouldn't be surprised if it was the aem 400 pump causing all the issues. All the reviews I've read on them say they are junk and I was never happy with mine. My fuel restriction ended up being the filter before the pumps. I didn't know that that's a big no no.
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Old 04-10-2019, 04:16 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

D'oh!!!

Now check that pump, yo!!
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Old 04-10-2019, 04:44 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

Good call on one of the pumps struggling. Pretty sure this little guy was the culprit. It's the hose from the intank pump to the hangar. New one fits snug like it should. This was loose and too long. Just did a couple pulls and the air fuels shoot straight to 10.0 the whole way through. Just needs tuned now. Thanks for your help man.



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Old 04-10-2019, 04:50 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

No prob! It helps sometimes to have that second set of eyes. Well.. Ummm.. We'll say differential diagnosis here since I cant see anything. lol! Good work, sir!
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Old 04-10-2019, 05:19 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

See how from the top view the hose is oval shaped? It's because it was too long and was on the S shaped portion of the fuel pump hangar. That in combination with it being too long caused it to not seal up. As soon as I put the new hose on the intake pump sounded different. Like before it sounded like a **** load of gas was coming out the retune into the tank and making allot of splashing noise. After it was quieter without the splash sound.

I had a 06 si I was trying to tune do something similar, the fuel pump sits in the hangar and is sealed to the feed by an o ring. The pump needs a spacer in between the pump and top half of the fuel pump housing. The guy didn't put the spacer in and the fuel pump essentially shot downwards causing no fuel pressure. We fixed it by the side of the road after putting gas in it thinking it was empty.
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Old 04-10-2019, 05:34 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

Ah, I see pics now! Must have been my interwebs.. Stupid satellite.. I can certainly see how that was an issue now. Squishy hose is never good. Seemed like a pump issue for sure based on symptoms. The voltage drop indicated that a pump was trying to compensate and working harder than it needed to, causing that draw on power.
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Old 04-10-2019, 06:19 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

having the wideband wired to D10 is the right way to go. D10 can read the full range of 0v-5v. Using D14 can only read 0v-3.7v.
When you use D10 for the wideband though, two things need to be done: make sure ELD is disabled in the MISC tab, and resistors R136 and R138 need to be removed from the ecu. R137 (middle of the group of 3) needs to remain installed.
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Old 04-10-2019, 06:28 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

Originally Posted by motoxxxman View Post
having the wideband wired to D10 is the right way to go. D10 can read the full range of 0v-5v. Using D14 can only read 0v-3.7v.
When you use D10 for the wideband though, two things need to be done: make sure ELD is disabled in the MISC tab, and resistors R136 and R138 need to be removed from the ecu. R137 (middle of the group of 3) needs to remain installed.
Also helps to ground the WBO2 with the ECU ground.

D14 is fine to use.. Honestly, you'll not need anywhere even close to 5v for wideband. If you're THAT lean, your car is gonna die before it's even a problem. Lol.
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Old 04-10-2019, 06:58 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

Good to know for future reference. I've never been big on using wideband data logging to tune afrs but it can definitely make a few things easier.
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Old 04-11-2019, 04:18 AM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

Originally Posted by K7-1Ktrevor View Post
My fuel restriction ended up being the filter before the pumps. I didn't know that that's a big no no.
So....you're saying don't run the sock that goes on the bottom of the pump?

Originally Posted by motoxxxman View Post
having the wideband wired to D10 is the right way to go. D10 can read the full range of 0v-5v. Using D14 can only read 0v-3.7v.
When you use D10 for the wideband though, two things need to be done: make sure ELD is disabled in the MISC tab, and resistors R136 and R138 need to be removed from the ecu. R137 (middle of the group of 3) needs to remain installed.
Curious what you guys think about using the analog inputs for wideband on S300v3 as opposed to D10 or alternate ECU inputs. I've currently got my wideband going into AN1 (running open loop).
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Old 04-11-2019, 06:43 AM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

No run the sock for intank pumps. Mine was on a sumped fuel cell, then feed line gravity fed to a filter then that fed to my pump. I didn't realize it but running an inline filter before the pump is a big no no depending on style of pump.
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Old 04-11-2019, 06:59 AM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

Originally Posted by DaX View Post
Curious what you guys think about using the analog inputs for wideband on S300v3 as opposed to D10 or alternate ECU inputs. I've currently got my wideband going into AN1 (running open loop).
I have a similar option with Neptune; there are multiple inputs available for just that purpose.. 5 I think. There was a reason i did not go that route and offhand, i honestly dont remember it precisely. I'm pretty sure it had to do with monitoring/datalogging concerns. It was just as easy to use D14 or D10 anyways. Lol! And as Moto pointed out, D14 only reads up to around 3.7v, and D10 requires some snipping of ecu components (simple to do really) BUT, as I mentioned, this is still REALLY lean.. In the realm of 17/18ish A/F ratio. My car was dying at that range from running so lean (at idle). So anything more isn't particularly necessary for **MOST** WBO2. Again, since all engines are indeed different, you may require the full 5v. **shrug**
Summary: It's up to you, amigo!!
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Old 04-11-2019, 01:39 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

Well, I thought the problem was gone but txdragon, I think you were right on the money. This car seems to have a large collections of problems that all add up to one thing, not enough fuel flow. Made 408whp on 16lbs but ran out of fuel pressure to make anymore. Saw some huge gains in the mid range from quick spool just didn't have enough fuel to make any real power out of it. I told the guy if it was my car I would replace both pumps just to be sure. Not sure how to test them unless anyone has any ideas.


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Old 04-11-2019, 01:50 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

Now that we're getting to the real meat of an issue, I would start with removing the inline pump and run just the 380; as a baseline. I wouldn't take previous tune into *much* consideration right at this moment. Start fresh, so to speak.
I honestly still think it's struggling because a higher volume pump is trying to pull from a lower volume pump. For some reason, that still pokes at me..
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Old 04-11-2019, 02:00 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

I was wrong he had a 380lph inline fed by a 450 intank.
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Old 04-11-2019, 02:23 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

Originally Posted by K7-1Ktrevor View Post
I was wrong he had a 380lph inline fed by a 450 intank.
Makes more sense that way at least but, remove that inline! She's chokin', give her a heimlich quick!!
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Old 04-11-2019, 05:51 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

I vote remove the inline, drop a new GENUINE walbro 450 in the tank, make sure the relay/wiring are good, and give it another go.
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Old 04-11-2019, 05:56 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

also, chase the feed line from the tank all the way to the rail and make sure it's not kinked or bent anywhere. You'd be surprised how many honda's with fueling issues I've resolved by finding a crushed metal line or kinked braided line.

Also a possibility is if the orifice in the regulator is not the right size. Often times people don't change it, and they usually come with the smallest one preinstalled. Which means at low fuel usage, the regulator is drastically being overpowered. So then people set base fuel pressure at idle (low fuel usage), and then when it gets into higher fuel usage the pressure drops a LOT. A 450 pump usually requires the middle sized orifice, or even sometimes the largest size orifice
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Old 04-11-2019, 06:15 PM
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Default Re: Help needed diagnosing low voltage in boost/ fuel pressure drop

Fuel line from the tank outlet to the rail is -8 I believe. Looked at the whole line and didn't find any kinks or anything out of the norm. I've tried messing with fuel pressure up to 75lbs and no change. Definitely seems like it's a failing pump issue like txdragon said. He's ordering two new pumps that I'm gonna throw in and re dyno it and see what's up.
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