SS NSTAG8R

I know there was a recent thread close to the same as this but our setups are a little different and I didn't want to steal his threat. Anyway, here goes.

I have a 95 formula with an lt4 setup, made close to 400whp n/a. Has rebuilt factory bottom end so im only running 7psi for now until someday I have money to finish my forged 383. I am running a p600b and a custom front mount intercooler. For fuel I have 2 walbro 255 in tank pumps, and an 8an feed line to parallel fed rails, with 80lb injectors. each rail has its own return that comes together and goes to a boost reference fp regulator then returns to the tank through a 6an line. Running like 44 psi at idle as increases with boost up to mid 50's. I've tried bumping up the fuel pressure and it wouldn't do enough. I have to shut down around 4500 because by then the at gauge is hitting 12:1. So you know all the info, its been being tuned using tunercatz, the battery has been moved to the back, and I cut/lengthened the wiring harness to get it off my wheel well. Kinda regretting doing that until I had bugs worked out. The harness is back together with butt connectors for now and im gonna redo them with solder and heat shrink in case that's causing an issue... still has the obd1 computer, could this be causing issues? Are the guys with higher boost lt1's switching computers or what the deal there? This is the 2nd time I wrote this due to the computer screwing up so hopefully I didn't forget anything. If you wanna any more info id be more than happy to answer, im just trying to figure out what's going on... thanks in advance for all your help!

mrmint69

You should add a "signature" to your profile with all your mods. Really need to know what all thats been done to the vehicle. The LT4 alone, will not make the HP your stating before the boost. This does sound exactly like the other recent thread. These can be hard to track down, since we are talking about so much HP and so many variables.

SS NSTAG8R

Before this whole build, single w255 fuel pump with otherwise factory system. Pacesetter headers with true duals, head and intake ported/polished by jordan mouser, had heads gone through and flow tested before the blower, flowed 280. Cc306 cam, 58mm tb, moser 12 bolt rear end with 3:73 gears. That's what else is done before and currently. Highest number we saw with the blower was 560whp and 510 I think tq. Had tuned it down to about 520-530 for a little more safety. Timing is turned way down right now at wot just trying to get the fuel right then add timing in later... oh ya, MSD 6al-2 ignition also.

Kevin Blown 95 TA

It sounds like you built it correctly for good power. Maybe you could start by seeing if you have a voltage drop or bad ground back at the pumps. Maybe run an 8 or 10 gage wire back there from the alternator and another one for ground. Make sure it isn't getting lost in the tank connections, either in case you went through that little yellow connector.

Another thing to check is that both pumps are turning on. You can do some basic troubleshooting to see if they are both running or the second pump is turning on, however you have them configured - switch them around or run them one at a time...

SS NSTAG8R

Ive taken voltage readings at the pumps before and they were good. I was gonna take some reading today at the battery, alternator, and injectors but its cold out and flooded trying to start it. Ill pull the pumps out and check them again while im at it, but when I turn the ignition on and they pressurize the line I can tell the difference in sound if one or both are running. But I can pull them and check connections and everything. I didn't use the factory little yellow connector, I custom fabbed a new plate for the lines to come out of.

MikeGyver

butt connectors?
I'd fix that **** just because it's so wrong. I doubt it's your fueling problem though.

Then your problem has to do with the mechanical setup. Two walbros will support over 1000hp for forced induction.

SS NSTAG8R

Well I will for sure solder the connections instead. While on the topic, what did you do for connections in tank? I didn't see my fuel system being too small. I figured 80'sid would have been enough for e85, let alone 93 octane. So you thinking electrical? Guess I can fix that and go from there...

mrmint69

For years I was searching for a power loss at higher rpm's and I replaced the injectors first and it helped some, but didn't completely fix my problem. I then had the battery and alternator tested and both came back bad. I started checking my positive and negative cables and found they were in bad shape. I replaced the positive side and cleaned all the negative connections really well and now I have zero issues. My guess is my voltage would drop and it caused just enough loss in voltage to make the injectors go static or not work correctly. Just something to think about or check if you have not done so already. Does anyone know if moving the battery to the rear can cause issues?

Kevin Blown 95 TA

The battery's main job is to start the engine - it doesn't have much other function once the engine is running other than to help the regulator stabilize the alternator output voltage. But grounds are very important, regardless, and you need good bonding from alternator to engine, chassis, and battery. When in doubt or having problems, run an extra ground wire. Old cars and pickups would always lose the ground in the back and tail lights would act all funny and fuel gauges would quit working. Reestablishing the ground would fix a lot of weird problems like that.

But to answer your question, yes it can cause issues with cranking the engine if the cables used are insufficient gage or the batt isn't grounded well or there is high resistance in the ground path (if you are using the chassis).

MysticBowtie

I moved mine to the back, but went to Home Depot and got 20' of 4 guage wire to make sure there was no power loss. It's works great.

SS NSTAG8R

I haven't got the soldering done yet, been too busy with work. Bit I also ran a #4 wire back to the front as a ground because ive heard nightmare grounding stories. So I wouldnt think that could be an issue. Used a 1/0 wire for my positive running up...

SS NSTAG8R

Ok, well its all back together, solder and all, and same result, still going lean, as I expected... but at least the wiring is done right now... any other ideas? Anyone messed with tunercatz and maybe the guy tuning it just isn't doing something right? Or im open to ideas...

Kevin Blown 95 TA

Well for one thing, 12.1 isn't lean, it is rich. But I understand your concern if the thing is going from very rich to only sort of rich and you think it is going to keep on taking away fuel. That doesn't mean its going to happen, but it could. And can you come up with some sort of datalog to show what is happening? Also what do you have for an exhaust? Where is your wideband sensor located?

SS NSTAG8R

It continues to go more and more lean, I just mean I consider 12:1 pretty rich for wide open throttle on my stock bottom end. I've already blown one set of head gaskets prob from overheating. It has lean popped on me before so I know it keeps losing fuel. I have true 2.5" duals with dynomax flo flo mufflers dumped before the axle. The wideband is right after the passenger side header flange.

Kevin Blown 95 TA

Do you mean up near the head? or down near the collector? Either way, are you sure there are no leaks at all in the header flange? If it is sucking in any air at all, that could be your problem.