Not running lean, the PCM is still within its adjustment window to keep AFR where I want it.

 

I've got the the 255 pump/42lb injectors and running 425 rwhp NA. But I also installed the harness. Do you have the LT1 harness?

http://lonniesperformance.com/Racetronixpumps.htm

Edit: nevermind. Just read that you already have it.

 

I just purchased the Racetronics dual 340 pumps and all the requisite LT1 harness kits (bulkhead wiring etc) for my new turbo setup now I just have to get their -8an feed and -6an return braided hose and fitting kits. I'm going stainless braided PTFE hose from tank to rails and back and my fuel system will be complete.

 

Here's my latest attempt at a solution. I bought Racetronix's B-body bulkhead harness since they don't sell an F-body bulkhead harness and modified it to work with my car. The whole kit uses thicker wire plus an extra ground and an extra power wire on the in-tank harness. Racetronix claims this will improve pump performance by 10-20% and can handle up to 28 amps. On the old setup, 14 amps was the high end of what it would handle.

Here is the new in-tank harness hooked up with the old in front for comparison. That old harness is actually also by Racetronix. It's upgraded 14 gauge wire but has only 1 power wire.





The B-body in-tank harness was too short so I had to extend the wires. I used GXL wire with adhesive lined shrink tube.


This is both ends of the external bulkhead harness next to the old harness for comparison. You can see the power and ground wires are nice and girthy.


Here it is all buttoned up.


So far I have only idled the car up to operating temp. Sunday will be the real test, it's gonna be inching towards 80 around here.

 

I'm currently in the midst of a road trip and drove through the deserts of Washington where my thermometer was showing anywhere from 100-109* today. Even after everything I've done: the fuel cooler, the beefed up fuel pump wiring, the brand new fuel pump, I actually saw the lowest fuel pressure I've seen yet. It dropped all the way to 25 psi at times. Here's a breakdown of the cars behavior:

While cruising the pressure would slowly start to decrease after about 30 minutes of driving. Giving it gas would cost a couple more psi immediately but I would get them back when I let off. Once pressure got to around 50, it would fall even faster through the 40's. Usually bottoming out around 40 or high 30's while cruising. At one point I gave it some gas to see how the car performed to make sure the numbers were real and the car had no power.

The slower I went, the lower the fuel pressure would fall with idle being the absolute worst. That's where I would see the psi in the 20's and the engine would start surging. Once I got moving again, the pressure would rise back to the 30's or 40's. The pressure corresponded with vehicle speed, not rpm.

Usually the pressure would rise back into the low 50's again and stay there for a bit before falling back. Sometimes the pressure would drop off really quick, like 1 psi per second.

The time I shut the car off to get gas, the pressure was rock solid for another 30 minutes after hitting the road again before it started the sin wave pattern of losing pressure then getting it back then losing it again. Eventually it became evening and I was entering the mountain pass where temps fell to the mid 80's and pressure was rock solid at 60 psi for the next 2 hours no matter what kind of driving I was doing.

The only thing I can think of that I haven't touched that is related to the fuel pump is the alternator. I'm using the Racetronix hotwire kit and their bulkhead harness good for 18 amps. The pump is a brand spankin new 340 lph Racetronix pump. The fuel is nice and cool thanks to the fluid cooler. Maybe the Torqhead alternator I'm running can't handle the hot ambient temps? Is there some sort of diagnostic tool I can use that can display amps as I drive? The volt gauge on the dash is always just past midline even with A/C running, I just don't know what else could be affected by ambient temp so much that would drop my fuel pressure like this.

 

The 255 pump is not the problem. I have been running upgraded wiring, relay etc with a Walbro 255 for 4 years on E85 and the pump is 7 years old. Works fine with my 383 spinning to 7300 rpm. There are numerous people making over 500whp N/A with a 255 with LS. See below link as a example.

Walbro 255 408 LS

 

I agree the pump isn't the problem. I don't know what the problem is. I'm hoping people here have some ideas.

 

What is the size of the fuel pump outlet compared to the stock hardlines leaving the tank assembly? Is it possible that the fuel lines are sized too small for the flow and is overheating the pump over time? Just thinking about it, the return line has got to be sized to handle the excess flow of what the engine can't use....worst case would be idle as that's when it's sipping fuel. Also, the mainline needs to be sized right as well.

I've got a racetronix 255 system in my closet, but have not installed it yet. My old stocker is still going and the pressure is rock solid at 43psi WOT.....so I didn't see the need to dig into the fuel system just yet. Got it as a just in case. One thing I have not looked into yet is what size the fuel lines need to be for the 255 to work right. I haven't done any homework on fuel system line size yet.....so my question could be way off base. I'm not sure at what point the stock fuel line size could be an issue.

 

The pump outlet is 8mm, same as the feed line. It did cross my mind that larger fuel lines could help my issue. The problem is that this was happening with the Walbro 255 I had previously, now it's still happening with a Racetronix 340. Both pumps have a 8mm outlet and 19mm inlet. Adding a fuel cooler didn't change anything. Adding larger gauge bulkhead wiring seemed to help a little.

You said the symptoms being worse at idle could be a sign that the fuel lines are too small because the pump has to work harder. That got me thinking about what else happens when the car slows down. Below 45mph the fans kick on. I don't know how much rpm affects the alternator's charging but would I be getting less juice at idle rpm? Maybe when it's this hot out the extra load of the fans combined with the lower rpm combined with the extra work of the pump circulating more fuel back to the tank all contributes to lower pressure when the car's speed is slower and especially at idle.

Right now the pump is connected directly to the alternator. Could I try connecting it to the remote positive terminal instead? Would that give me more consistent current? And is there such a thing as running "too big" fuel lines?

 

I dont think your problem is electrical.
You seem to have that covered.
Have you considered your adjustable fuel pressure regulator being the offender?
What brand is it and where is it located?
I run a walbro 255 with a corvette style FPR (located in the back, close to the tank ) and have no fuel supply problems in my swap: 396 24X LT1

 

Its an Aeromotive adjustable fpr in the stock location. Would high ambient temp cause a fpr to behave all wonky like this?

 

While rabbit holes are fun to go down, Occam's razor is usually right with these sort of things.

There is something simple you are over looking. Stock fuel lines are not it IMO.

To rule out electrical, see if you can borrow a clamp on current meter and watch the fuel pump power leads at a hot idle. See if it surges etc, or just holds steady.

 

Could I test the current external to the bulkhead and get an answer that's just as reliable? I already changed the pump harness in the tank and the pump with no change so I figure I could start at the end of the hotwire kit and if it's showing a problem then I can check at the alternator to rule those out. I just don't even want to attempt hooking something up in the tank and then go drive.

 

Just in general, I think I've seen quite a few Aeromotive FPRs give plenty of headaches over the years. Their FPR's don't have a good rep in my book.

Per Shownomercy, amp clamping the wires at the pump is a good idea. See what the current draw is cold vs hot. This little UT-210e is a decent inexpensive amp clamp. If you are getting fast transients, it's display may not show it to you. There are amp clamps you can buy that will output voltage that can be graphed on a scope.

You can also use some t-pins to back probe the fuel pump connector and get a voltage reading to see if there is a drop from the battery to the pump. I tend to think that if the wire size was a problem that you'd have poor performance all the time, not just when it gets hot.

The video below is just to show off the 210e. It's not a Fluke, but it's got a much better price. My first amp clamp was close to $400(Fluke 337). So this little Uni-T for $50 is a pretty good deal in my book....does DC currents too.

 

I wouldn't do anything in tank. If there are two wires feeding the pump, Get readings off both and add them together.

 

Or if you want to be simple, just toss the clamp on the main wire off the alternator and then off the battery. Make sure you electric system is behaving as it should be the car is hot/cold.

You should see some small dips when fans kick on/off but voltage/current should be fairly stable. If things are wonky once the car gets warm, that may be a avenue to pursue.

 

Made it home without seeing the pressure drop like crazy again but the ambient temp also never got above 90. The best I could do for amp clamps was a Klein from Home Depot. I measured the current at the fuel pump wire right at the alternator and it was 14 amps with the engine warmed up. There was one time where I had to wait for road construction and as the car was idling and under hood temperatures rose past 100 I decided to check the amps real quick. I had lost 3 psi at this point and the amps were 12.5. Thing is, I don't know if the pump is drawing less or if the alternator is feeding less. Now that I'm home, I have a spare AC Delco alternator I'm going to install and run for a while to see if this keeps happening.

 

I went back into my upgrade history to look at when I bought my parts. I bought the fuel pressure gauge in 2016, the Aeromotive fpr later in 2016, and the Torqhead alternator in 2018. I don't have a specific memory of this issue until 2016/2017 and I was still running an AC Delco alternator at the time. I think it's safe to rule out the alternator at this point and not bother swapping in the AC Delco.

I don't remember this happening with the stock fpr, but I don't see how hot ambient temps could cause the Aeromotive fpr to drop my fuel pressure all the way to 25.

I went through my post history and noticed I was having a very similar issue in 2012 and 2015. Can't say for sure what the causes were because I didn't have my wideband or fuel pressure gauge yet. In 2012 I solved the issue by replacing the "big 3" (4 in my case: alt-battery, chassis-battery, block-battery, block-chassis with wires ranging from 4 to 0 gauge) and buying the Racetronix hotwire kit. In 2015 I was noticeably losing power half way down the drag strip over and over again. Never got an answer for that one.

I guess I'll try what shonomercy said and monitor amps on the alt and then the bat wires.

 

Just try and cross off easy things, so that you can narrow things down prior to rabbit hole falls lol

 

Get a fuel pressure reading on the fuel line before going into the FPR....that will give you direction on which end to chase.