lmt0705

iTrader: (7)

Did more pulls today, I'm on e85 running twin 465s -10 feed,-8 return. I was at 90% DC at 1140. Added some fuel and kicked up the eboost2 a little. Hit 1200 rwhp but DC went up to 100%. I changed the base pressure to 58 and repeated. No better. Saw pressure starting to drop off at 20 psi of boost. Am I out of fuel pump? Can I just add a 3rd pump.

BOOSTAT4500

iTrader: (17)

What size injector?

lmt0705

iTrader: (7)

Wow! How did I forget that! Lol! High impedance 160lbs

stevieturbo

When you say fuel pressure is dropping off...I assume it is boost referenced ?

Any graphs of what fuel pressure is doing vs rpm ?

Exactly when are you hitting 100% IDC ?

It may well be out of pump....it could be wiring/power issues, it could be other flow issues...filter, etc

And if you need more flow, yes adding another pump will resolve that. If of course the electrical system/wiring is good for all those pumps.

Those bigger Walbros can easily pull near 20A each, so all wiring and connectors needs to be good and proper

You could try recording pump voltage as near to the pumps as you can, and also checking current draw before changing anything.

A few volts loss can have a big effect on flow.

lmt0705

iTrader: (7)

It is boost ref. I am using 44 base and was seeing low to mid 60s on the gates, the last 2 pulls it would climb to 67 or so then drop into the 50s at the end of the run, I kicked the base pressure up and same thing happened. Duty cycle was almost identical. I was hitting 100% at around 6300 till the end of the run. Don't have fp logged. It sounds like I just need another pump.

stevieturbo

17psi drop is a fairly large drop, something needs rectified.

svslow

Increasing the base pressure would further decrease the output of the pumps, but increase the injector flow rate. I would say you are out of pump.

lmt0705

iTrader: (7)

I see plenty of people running triple pumps on e85. Honestly didn't think I was going to make that much power to need 3. Guess it's not a bad problem to have!

stevieturbo

If that is the problem.

Again, check wiring, voltages etc

It probably is the pump, but a couple of easy checks first will do no harm. Of course the other aspect is these pumps claim huge numbers...open flow. They nearly all take a huge dive once at normal operating pressures.

lmt0705

iTrader: (7)

I'm running a pretty beefy racetronix wiring kit right now so with 2 pumps I'm not concerned. I'm not thrilled with my voltage as it's only low 13s. I'll be looking into why it's not higher when I get the car home this weekend. Will I be OK piggy backing wiring for 2 pumps off my Hobbs switch or is there a better way to do it?

JoeNova

13 volts is way low. Getting your voltage up to 14.5-14.7 where it needs to be will help.

lmt0705

iTrader: (7)

It's a custom alternator setup with the battery in the back, I'm wondering if the length of wire is too long or not big enough gauge wiring coming up. I have 2 gauge from the battery to starter then 4 to the alternator and fuse panel. Don't mean to get off topic but not sure if that's the issue
Think I could use another ground or 2 as well

JoeNova

Sounds like its an alternator problem. I take it you haven't changed the wiring of the alternator from the factory?

You can measure volts at the alternator itself to see if it is indeed an issue with resistance and voltage drop.

stevieturbo

What alternator ? What size wires ?

I assume you mean one hotwire kit per pump ?

13v isnt great, what voltage are you seeing both at the pump, and at the alternator itself ?

lmt0705

iTrader: (7)

It's a custom 1 wire 150 amp alternator, it's a wiring kit built for there pumps, very nice setup. Individual relays and fuses for each pump. Wiring to the pumps is 10 gauge out of the relays

stevieturbo

And what voltage do you see at the alternator when running, and what at the pumps ?

Really if wiring etc is all good, there should be minimal volt drop between the two.

What do they use to pass through into the tank itself ?

LilJayV10

iTrader: (39)

Do a voltage drop test on the power and ground when you make a pull. That will give you a better indication if it's a wiring issue or not.

lmt0705

iTrader: (7)

How do I do that?

LilJayV10

iTrader: (39)

Use a multi meter. To do a voltage drop you check positive to positive or negative or negative. You can only do a voltage drop test when a circuit is loaded(has current moving through it)

All a meter measures is difference in potential( buy the difference between the leads) It doesn't know or care if it's positive to negative, positive to positive, etc.

Lets say you want to test the positive from the alternator to the pump. Put one lead on the B+ on the alt and the other at the connector for the fuel pump and make a pull.

For example, when you were doing your pull the meter showed 2 volts, that means you are loosing 2 volts from the back of the alt to the pump. This can be from a bad wire internally, connection or bad ground. Also a fuel pump that is drawing excessive amperage can show a voltage drop.

Do the same thing on the ground side. Typically .50 volt or less is acceptable. There should be very little to no voltage on the ground side. Grounds get over looked a lot. You can have all the battery voltage in the world but if the ground side can't carry it back it's just as bad as having too little power.

A voltage drop will show problems in wiring/circuits that you can't find any other way. Most people us Ohm's to test a circuit. IMO the Ohm test is freakin' worthless and rarely ever use it.

LilJayV10

iTrader: (39)

If you drop test from the alt to the pump and it's around .50 volt or under it's not a wiring issue. The fuel pump is getting the same amount of voltage as the alt is putting out.

The same with the ground to the the neg post on the battery.