wildfire0310

iTrader: (1)

TLDR:
Trying to track down why sometimes I am losing fuel pressure and it seems random. I have plenty of fuel to handle well above 200whp, but only pushing 140whp at best. Logs show pulling to 6k+ fine then later fuel pressure dropping doing a similar pull just 20 mins later after cruising.


Specs:
Car 1988 Mazda 323GTX
Engine: 1.6L
Turbo: Stock vj14(smaller then S13 T25)
Injector: KAInjection Gt500 injectors 630cc
Fuel Pump: New DW300
Adjustable Regulator, set to 45psi base pressure
DIYPNP with low dollar sensor
Fuel pump has a rewired, with a 30 amp relay, and a direct line with a 20 amp fuse.

So I have been trying to track down an issue with my "Miata". Start back in Oct after my first track day when once the car was hot, it would start misfiring on the track. After cooling down I was able to push it again before it started bucking again.
I then replaced the stock regulator with an SXracing Regulator(old stock from my old turbo Miata) to allow the use of a LowDollarMotorSports Fuel Pressure sensor. Where I was able to log the misfire and spotted my fuel pressure dropping. I have since replaced my old Walbro 255 with a new DW300 and replaced the fuel filter. The car drives great and pulls nice and strong, but once it starts losing pressure, it seems to be repeatable.

These current log files are with a fuel tank so no issues with low fuel levels.
low-pressure log has a pull around record ~1300 with no issues, and ~12000 is where the fuel pressure drops.
AfterCrusie is just me driving the car back afterward.
Small Sample Run is post-LowPressure where I did a few small pulls on the highway.


PLEASE HELP. Have another track day on May 15th.

patsmx5

iTrader: (16)

One thought would be to wire a volt meter to the two wires going to the pump. See if you're loosing voltage to the pump when this happens. Would help get you going in the right direction, if this is electrical or mechanical. Could be a relay on its way out.

wildfire0310

iTrader: (1)

Forgot to mention last night that the fuel pump has a direct line to the battery via a 30 amp relay, and 20 amp fuse. I wonder what the odds of the relay being bad are? Good call on getting voltage numbers from the pump during an issue. More data is always good.

olderguy

iTrader: (19)

Have you inspected the tank? Any **** floating around?

wildfire0310

iTrader: (1)

I did drain the tank recently and removed some rusty-sand like crap from the tank. Replace the fuel filter since the cleaning and the pump screen has been clean the last few times I have looked at it.

That logs are post cleaning. :(

fooger03

iTrader: (2)

Does this only ever happen after you've been driving around for 20+ minutes, or does it also happen soon after cold start?

wildfire0310

iTrader: (1)

Seems to be more likely after a 20+ minute drive or hot starts.

Will try and see if I can get some clear roads to do some hard pulls while "cold", to get more data.

Btw thank you, everyone.

wildfire0310

iTrader: (1)

Photo of the car for fun.

wildfire0310

iTrader: (1)

So did some testing last night, and while it looks like my Alternator needs to be replaced, the voltage at the fuel pump didn't change during hiccups.

Also, I was able to get the issue to happen about 5ish mins after a cold start. I did notice what may be some correlation, when the issue happens it seems to be at the highest boost level(aka overboosting) I need to look at the logs and see if my theory is right. Cause last night it seem to happen when it was hitting 15psi but the next pull at 10psi no loss in pressure. So I am wondering if my AFR is losing references or if the pump is somehow getting in way of the pump.

Supe

Any rubber hose that's submerged in tank - checked for cracks/gumminess? Checked FPR diaphragm for tears?

wildfire0310

iTrader: (1)

I am going to go over the submerged tank's hose again, it looked good when I swapped pumps but maybe under higher PSI it's failing.

As for FPR, this issue happens on the stock FPR and Adjustable aftermarket one.

I am thinking of running a test tonight of kicking the pump on with the car not running and then using my air compressor to run "boost" into the FPR and walk the fuel pressure up.

tblackey

So I've been having a similar issue that I believe I have solved. I had a DW200 pump and installed it with a new fuel sock. Pretty much every event after about a lap it would start starving on fuel after any prolonged boost. What I finally figured out it wasn't how much boost, but how long. I switched the FPR, rewired, wired direct to the battery, fuel filter, all the hard lines, cleaned the injectors, and swapped to a DW300 pump. Same frigging issue. Finally on a whim I swapped to the fuel sock (to a denso sock) that came with the dw300 pump. All of the sudden only on tight left hand corners it starved. Everywhere else it was good. So I replaced the sock with a new OEM sock and issue disappeared. What it appears is the sock did not flow enough and was very restrictive. At low boost it flowed enough that it would run, but under any prolonged boost it would empty the sock and start the pump cavitating. Just something simple to try.

wildfire0310

iTrader: (1)

Interesting.
I do think I may have resolved it. My current test drive didn't have that issue, but I made three changes and am not sure which one solved it but I think it was the first of my 3.
1) I raised the pump up in the tank, as the Miata-based filter was touching the bottom of the tank, in the gtx. Google said that too close to the floor could restrict flow(guessing suction to the tank floor, or dirt)
2) Swapped out to a Lotus filter which points it in a better direction in the tank and is flat.
3) I replaced the in-tank hose, the one on there seemed good but maybe(had a new one with my lotus install kit). I also replaced the clamps with higher-end ones that are used for air compressors and should hold at a high PSI. Granted 60 psi isn't that high but was under the hood.