JUICEDZ4 build thread


According to MS im totally out of injector. 100% duty.

Im using:

Walbro 255l/hr hp pump
stock, 3/8" lines
Aeromotive A1000 regulator, obv boost referenced
Siemens/Dekka 80lb/hr injectors
50psi base fuel pressure
~6500rpm limit

Now, I have been having some alternator issues now and then where it fn shuts off over like 4k rpms. This obviously isnt helping. I have yet to test the voltage at the pump itself, but the wire I ran should be adequate (with proper voltage).

Im going to setup MS to log fuel pressure tonight. Im curious to see if its really keeping up or if its tapering off. I thought I could compare fuel pressure to boost pressure. If the two always track, then its ok, if they diverge at all its bad.



80lbs should be able to support around 400ish pretty easy I would think? Also I would log and look at the msec reading on the injector and not pay as much attention to the % when logging.


Ya, I should easily be able to make 4-500 on 80lb injectors, especially since Im not turning 9k or anything crazy.

Well, it took WAY to fn long doing a/d math, modifying the .ini file and getting the scaling just right, but Im now logging fuel pressure on the MS. MS and the dash gague are within 1psi from 20-90psi.

Im hoping I see fuel pressure not keeping up. Then itll just be an easter egg hunt to figure out why. I know the voltage isnt helping. The fuel pump flow really falls off fast, I think a 1.5V drop is ilke a 15% flow reduction.



I run the same injectors! <3

Yeah each of my pumps has its own power right from the battery shared with nothing else. 10ga wire to each


So ya, def have a fueling issue, Im hoping its just b/c of the voltage drop from the gd pos alternator.

I checked the belt tension. I cant turn the motor over by the alternator pulley nut like I was told you should be able to. I mean I can until compression, then it slips. So Im not sure if thats good or bad.



:fu: alternator


yep. I need to fig out a way to determine if its slipping.

So far the , “it should turn the motor over via the alt pulley nut” doesnt work. It cant get though compression.

The other idea is to mark the belt / pulley and watch wtih a timing light as its rev’d. But im not sure that will work at 5k rpms.



So I said F it and ordered a Powermaster 8072 CS121 one-wire race alternator from Summit… $250 to the door.

I spoke with the Powermaster tech and he said its capable of 20k+ rpms and that my 2.5:1 pulley ratio was perfect, putting it at 17,500 peak alt rpm.

Im hoping that fedex delievers it sat am. If not, I guess Ill get back to this next week.



every build has to have a needle in the hay stack… i guess this was yours


heh, my build feels more like a pin cusion at this point.


well it is good it isnt a boat…


Hopefully that solves the fuel problems. Then… more tuning :slight_smile:

It’s inevitable when 99% of the parts on the car are custom made though.


lol, truth.


Got the new alternator in today, it works awesome. However, I still have a fuel pressure issue. It just wont make stable pressure over 60 psi. booo



I hear that, loud and clear.

What is your fuel system setup? How about your pressure transducer setup? Check with mechanical gauge?

Edit: I see the fuel system now. I have a very similar system, except I have an AEM reg and 72lb Deka injectors(waaaaay overkill, lol)

Edit again: where in the system is the pressure transducer located? How quickly can it respond?


shit pump?


Ok, I made a new graph. “Test” is the fuel pressure - 50psi so it can be directly compared with the boost pressure. The fuel pressure tracks fine to 60psi (10psi boost pressure) and then it goes wonky. The pressure transducer is installed in the FPR. Its the sender for my Autometer fuel pressure gauge. The gauge shows the pressure limited to 60, which Im guessing is the average of the wonky part of the graph.

Im going to test the FPR later today or tomorrow.

The pump could be bad, but it could also be the pumps internal pressure relief. Ive heard they are set to around 75psi, but since its just a spring, Im sure there could be a varying relief pressure.



I tested the FPR this afternoon. It works perfect. Fuel pressure tracks the reference port plus base pressure perfectly. No funny stuff.

So Im down to pump wiring (unlikely) or an issue with the pump itself or something internal to the tank.

Im assuming my 3/8" lines arent an issue.



-Shorted the output of the FPR and the Walbro is able to make ~90psi with just the priming signal. It bleeds VERY slowly. A couple mins to get down to 78 ish. After that it looks like it might take forever to drop to 0. So the pump isnt bypassing at 60psi or anything.

-Checked the fuel filter, its mint. I was hoping it was all gummed up from running E85. Nope.

-Checked pump voltage. There is a 0.7V drop at 80psi and 11.8V batt voltage. So thats not awesome, but its not horrible either. With my new alt Id still have over 13.5V at the pump when running.

It could be that the pump cant keep up with the volume and pressure Im asking of it. I dont really have a way to bench test that, easily anyway.

My other thought is the tank vent is too small.

Or perhaps the map signal to the FPR sucks. But it has its own idependent line from the intake mani direct to the FPR. Its maybe 1" from the MAP sensors port, which looks fine, so idk.

Running out of ideas…



Dual pumps ftw. My hacked in inline Walbro did the trick.

So the intank must be on the way out. Or I have a voltage issue at the pump (which I dont think is the case).

Now, what to do as a permanent solution…