jetlude

iTrader: (9)

As the topic says. My static fuel pressure at idle seems to fall as the fuel or engine bay warms. Has anyone seen this happen? The pressure is checked with the regulator vac reference hose disconnected. What is the most likely cause? Could it be my fuel pumps or regulator failing? I have tested my pumps individually and both produce over 100psi maximum pressure. My tune is done at 38psi where the pressure is about the lowest. My injector duty remains consistent.

Here's my setup.
2 x Bosch 044 pumps
Aeromotive Fuel Pressure Regulator
1000pri 1600sec injectors
BW s366- 25psi boost

Any input appreciated.

Slides

If it's a mechanical gauge the reading can change as it heats up if the guage vent port isn't open to atmosphere.

Diaphragm in the regulator may soften a touch with heat, fuel may be slightly less viscous and lower density with will reduce pump capacity slightly.

jetlude

iTrader: (9)

Makes sense. It could be a combination of these two factors. Plus, its been a damn hot summer so I'm pretty sure the under-hood temps have been even higher than usual.

iceman4357

iTrader: (2)

Could be an off the wall suggestion, but can you pull a log of your voltage? I was dealing with goofy issues and it came down to the diodes going out in my alternator. Voltage was all over the place when cold, warm, idle and higher RPM. Alternator was sending out irregular voltages all over the place. Might be an easy way of eliminating another thing off of the list.

Have you ran a direct wiring kit to the fuel pumps?

jetlude

iTrader: (9)

Interesting point, Yes i should have logs of the voltage cold vs warm. I will investigate, thanks for the suggestion.

IRPerformance

iTrader: (41)

I've seen fuel pressure drop on cars when the fuel got overly hot. Are you monitoring fuel temperature? Fluctuations in voltage could do it too.

F1blueRx7

iTrader: (5)

I do log this, but I've often looked at the temperature range and not been able to pinpoint a correlation in pressure drop over time (but I also don't log below 2000rpm). What fuel temp is too hot for an rx7?

jetlude

iTrader: (9)

Hey guys, thanks for the responses. Based on your suggestions it could be a few things combined that's causing this indicated low fuel pressure when the engine bay is fully warmed.
I am using a manual fuel gauge which is oil filled and believe its sealed and not vented. My fuel tank has only been 1/3 to 1/4 filled lately, and combined with high ambient temps at the time I believe that my fuel temps have been pretty high.

gxl90rx7

iTrader: (1)

I am have the same or similar problem that seems to be temperature related. My symptom is AFRs drop about a point after it warms up. Like if I cold start the car, AFRs will be a point too rich,even after warming up. I park it, let it sit, go for another drive, and AFRs will now be back to normal. Same issue driving it on track, first session, first few laps the AFRs are off the scale too rich. Second session, AFRs back to normal.

my setup:
hydramat pickup
AEM 400 fuel pump
oem resistor relay
factory 5/16in lines
fuel cooler
radium pulsation damper
fuellab regulator
ID2000 injectors

I added a fuel pressure sensor to try to see what was going on, inially I thought it was a pressure issue, but I discovered my chinesium sensor reads a few psi lower when it gets hot. Still could be a pressure problem though, the sensor shows 5psi drop when it gets hot.

I was originally running a walbro400 pump, I dont recall seeing the issue with it, problems started when I swapped it out for an bosch 044, then I swapped the 044 out for an AEM 400. I have not tried going back to the walbro.
I tried different regulator aeromotive A1000, had no affect
I have also tried replacing the hydramat, thinking it was clogged, had no affect
I added the radium inline FPD, had no affect
I then added a fuel cooler in front of the intercooler, which actually made the problem more noticable, which confirmed to me its a fuel temperature problem. Without the cooler, the fuel temp would just get hot and stay hot. The cooler makes it fluctuate more, depending on air flow.

I still use the oem pump resistor relay, it keeps temps down by circulating less fuel through hot engine bay during low load. Although I modified it with 0.5ohm 100W resistor, because it was getting hella hot on the aftermarket pumps.

I also read somewhere that certain ID style injectors have an internal part that swells with heat, restricting injector flow, but they say should not be a problem with ID2000's

I still want to try swapping back to the walbro, but Ive been lazy. I am thinking maybe the 044-stype pumps cavitate more with heat than the walbros??

XanderCage

iTrader: (1)

I had the same issue and am also running the Fuelab regulator. I tried a bunch of stuff to minimize pressure drop at higher temps and didn't really know the root cause. I redid the wiring to my pump, bypassed the factory resistor and relay, I redid the in-tank hose to ensure a proper seal, a friend suggested upgrading fuel pumps so I ditched my Aeromotive Stealth 340 for a Walbro 450, but I was still getting pressure drop when the engine bay got hot.

Finally, I ended up buying a turbo blanket and heatwrap for the downpipe. This reduced the issue greatly! I really think that the Fuelab regulator doesn't like getting hot one bit. Mine sits towards the rear of the engine semi-close to the hot side of the turbo, and it would get hot. Like really hot. I was losing 3 to 5 PSI, and up to 10 when it was on the dyno but that was an extreme case. I was going to replace it to see if that fixed the issue, but now that it doesn't get blasted with heat there's really no noticeable loss. So that's my solution just for info, not saying that's the definitive answer, but it worked well for me.

Testrun

Well, I thought my issue was resolved after adding some more cable to my charging system, but I was at the Miami speedway oval track and after x amount of laps my afr started to climb again. So frustrating. I did not of course add my fuel pressure guage because everything seemed ok. I logged a 60 knock event and probably my non aggressive timing and water injection saved me. I just changed oil and plugs so I did a quick compression test and it still hits over 120 on all sides front and rear.

I was down to a half a tank so I attributed it to the 1/2 tank syndrome and stopped. I went to fill up and got right back on. The same. I don't believe it is a fuel temp problem for me. It is obviously heat related.

Now my primary turbo is only boosting 8psi (wastegate) on the 3KAI. I believe it to be the only damn solenoid I didn't replace with new,, so the uim is coming off and it will be a good time for me to check out everything.

I am running the factory primary with 2200 in the RP fuel rail. I have heard of these 2000 "2200" swelling before. There was a GTR having issues on the dyno. I will eventually swap them out for ID1600s. I am running a supra pump wired directly no 2 step relay.

I am getting ready to dive into how the whole fpr works with the vacuum/boost line. If there is a relay involved maybe that's what it heating up?

There are no turbo blankets for me. I will be trying to do some more "thermal management " while uim is off, and probably getting a vented hood in December. I may "throw a part" at it and replace the fuel pump with something else.

Sorry this post is a bit sporadic my caffeine hasn't kicked in yet this morning.

Oh BTW I will be swapping my boost guage out for a safeguard boost/afr which will open the spot on my pod for the fuel pressure guage finally.

Very frustrating problem that keeps coming back to haunted me.

jetlude

iTrader: (9)

This issue is more common than I thought. However, the logged AFR's under boost, or even when cruising, don't change much even with the underhood temps really high. This kinda leads me to believe that the actual fuel pressure is not changing(dropping), but it might be just the gauge reading low. If the say the regulator or pumps were dropping pressure as they warm, I think it would be reflected in the AFR's

Testrun

If your afr and knock are gooarI would say guage. I hope that's your issue!!! It is definitely not my issue.