Have you actually checked the voltage at the pumps under load to see what it is doing? Perhaps your alternator is getting weak? Since you've replaced pretty much everything I would guess it has to be a voltage issue or a fuel pressure regulator issue.

Steve

 

I logged voltage from the alternator through the aem and I was seeing 12.6-12.8 under load.

You think that is too low?

 

Last time I checked voltage at my dual Walbros, I was seeing 12.8-13.1 volts. I have none of the issues you are describing, though. Just giving you an idea of what voltage readings I'm seeing at the pumps. Btw, my pumps are powered through relays by my Power FC. Good luck in getting this resolved soon!

 

Someone correct me if I am wrong:

What we do know for sure:

Base Fuel Pressure is set at 42psi, cold car, cold fuel, cold pumps.
The Denso fuel pumps should produce up too 80psi per pump no questions asked.
New filters, new pumps, new wiring.
When the car is warm the fuel pressure drops 10+psi.

IF... after your Fuel Pressure drops to 30psi after the car is warmed up, CAN you turn up the fuel pressure by turning the adjustment screw on the fuel pressure regulator??? If you can increase pressure by adjusting it, then your fuel pumps are producing adequate pressure to the fuel rail and fuel pressure regulator which would rule out your fuel pumps and really everything in the fuel tank and fuel lines up to the fuel rail.


Possible causes:

Fuel heating to close to boiling temp causing the FPR to have trouble regulating FP (This is what I feel is causing your this issue)?

Possible fuel leak where after the car warms up you are losing pressure?

Maybe a faulty injector?

Something to try:

Go warm up the car to the point where the fuel pressure is 30psi or what ever it falls too. Then turn the car off and go to the trunk of the car and jump the fuel pump relay so it turns on both pumps while the car is off. Check the fuel pressure and see if it goes up too beyond where it is when the car is turned off. You could also charge the battery so it has fuel juice when you test it this way. This will tell you if the alternator is the issue, which I am positive it is not the issue.

Also, you could remove the spark plugs and again jump the fuel pump relay and see if you have any fuel leaking into the engine. Be sure to do this after the car is warm and you have seen a drop in pressure.

Might also call areomotive and asked them "how does fuel temperature affect the FPR's ability to control pressure. They might have a response or have some good info on things to check up on!

Let us know what you find Chase!

 

Thanks for that post Cursed. I know you feel my pain.

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Well I just got off the line aeromotive tech department. Spoke with a guy named Brett. We discussed the regulator and its ability to control and hold appropriate fuel pressure when fuel temps are changing. He explained to me that the liquid filled gauges are not very good and will "lie" to you whenever there is a change in temperate either warmer or colder from the temperature when the static fuel pressure was set. Brett stated that for every 30 degree F change under hood the gauge will change 1 psi either upwards or downwards respectively. He said it is very possible that the gauge is reading incorrectly due to the heat. He also explained that the regulator is not affected by fuel temps and the only drop he has ever seen in relation to holding pressure and fuel temps was a 1psi drop, other than that he has never had an issue. He said that once the fuel reaches 140-145 degrees F it will begin to possible cavitate and introduce vapors into the lines which will also drop the pressure.

He said that I should drain the oil from the gauge and then set fuel pressure, drive the car and attempt to duplicate the problem, then check the current psi reading to see what the true change in fuel pressure is.

**************************************************************************

I can do this if necessary, but its pretty clear that something is changing as I watch my air fuels become leaner.

I am going to try some of the things mentioned earlier and will report back with findings.

 

Get yourself a quality fuel pressure gauge. One that you can monitor in the cabin. Is your liquid filled gauge mounted in the engine bay?

Steve

 

Yes it is.

 

Remove the liquid filled gauge and get a cheap autometer or PLX fuel pressure gauge and sensor, monitor it in cabin.

Also, I believe you should be setting your base fuel pressure when the car is WARM, particularly since you said you had a built engine, and forged materials will have a decent amount of vacuum change from cold to warm. Adam can comment more on this, but I believe he was seeing up to 3-4 psi difference in vacuum (and therefore FP) when the car was warm...

 

yeah I plan on getting a fuel pressure gauge for the cabin very soon, but until then im stuck with this one.

Interested to hear more about setting fuel pressure when the car is warm? Havent heard that before. ???

Personally, I would no less than 8 guage per pump or a single 4 gauge for both from the battery to the to the relays. I used to run 8ga per pump which experienced some fuel pressure drop once the car was at operating temp. Due to this, I upgraded the wire to 4ga from the battery to the relays which did help with the loss especially at WOT and idle condiitonsr

If your pressure is dropping, check the type of fuel injection hoses you are using on the fuel pumps to the bulkheads or connections on the fuel pump hanger. If you are using a non-submersible fuel injection hose while in the fuel tank, it will deteriorate and eventually fail resulting in fuel pressure to drop as load increases. I have ran into this twice on various cars due to fuel pressure dropping once under load.

DP

I cannot recall what comes with the BL kit, but I am thinking it is 10g, but maybe 8g. either way it sounds like I should be using 4g since I am using 1 relay to trigger both pumps.

I know that the hose in tank is ok, it is the gates fuel submersible line.

Speaking on power wires to fuel pumps, has anyone upgraded the power wires from the connector at the bulkhead down to the pumps???
It seems to be pretty thin gauge from what I recall.

not meant to thread jack but is related

recently i noticed on my fpr guage when car is moderatly warm or cold when i shut car off pressure would goto about 39psi with pumps off and very slowly bleed off then after driving hard and car is hot fuel hot as i turn pumps off pressure drops immed to about 20psi but heres the weird thing , drops to 20 then slowly climbs to 40 then bleeds off as normal

none of this has any affect on wot a/f at all , just thought i would throw this in there for apparently something is affecting pressure when heat is introduced

When I turn the car off the pressure immediately drops from 30, 40, whatever it is at the time to 0. It doesnt hold any amount of pressure in the rail, lines, regulator at all once the car is turned off. I have read that it supposed to hold pressure for a few minutes and slowly bleed off, also read that its not a big deal if it drops off immediately. what do you guys think?

 

Personally, I would no less than 8 guage per pump or a single 4 gauge for both from the battery to the to the relays. I used to run 8ga per pump which experienced some fuel pressure drop once the car was at operating temp. Due to this, I upgraded the wire to 4ga from the battery to the relays which did help with the loss especially at WOT and idle condiitonsr

If your pressure is dropping, check the type of fuel injection hoses you are using on the fuel pumps to the bulkheads or connections on the fuel pump hanger. If you are using a non-submersible fuel injection hose while in the fuel tank, it will deteriorate and eventually fail resulting in fuel pressure to drop as load increases. I have ran into this twice on various cars due to fuel pressure dropping once under load.

DP

 

not meant to thread jack but is related

recently i noticed on my fpr guage when car is moderatly warm or cold when i shut car off pressure would goto about 39psi with pumps off and very slowly bleed off then after driving hard and car is hot fuel hot as i turn pumps off pressure drops immed to about 20psi but heres the weird thing , drops to 20 then slowly climbs to 40 then bleeds off as normal

none of this has any affect on wot a/f at all , just thought i would throw this in there for apparently something is affecting pressure when heat is introduced

 

A few more notes:

We have factory Denso pumps which do not have check valves in them, so as soon as they lose power the pressure will bleed off very quickly from what ever pressure down to -0- in only 10 seconds or so.

Chase, I can guarantee your issues are NOT caused by your power wires or hoses in the tank and so on. I'd bet there are a thousand Supra's making 500hp/1khp or more with the factory wiring in tank with no problems.

You replaced the FP relay to a seriously over the top unit, the intake hoses were replaced with the only submersible fuel hose we could find, the pumps are brand new and you are using virtually new fuel filters.

I am starting to wonder if the FPR gauge is part of the culprit as we have both been using these to monitor our FP and logging using this gauge. Maybe the FP movement we have been talking about is primarily due to a faulty gauge??

Adam


EDIT:

Here's an idea. Start the car and check FP when the car and gauge is cold, then uninstall the gauge only and go to Home Depo or Lowes and get a plug from the plumbing area. Go drive the car for 30 min then turn the car off and reinstall the gauge and check the FP, the gauge will still be cold!! Let me know how that works!

 

I have a large list of things to check and will be doing most of them tomorrow when I get off work at 6 or so.

I understand why everyone is saying get a different gauge, the liquid filled gauge is bad, etc. I will be replacing that and monitoring in the car very soon.

Regardless of what the gauge reads the air fuels get leaner and leaner as the car warms up, so something is going seriously wrong. Hopefully tomorrow night when I report back with lots of info it will shed some light into this phenomenon.

 

Ok so this is the list of things that I am going to check. I will test/check on both a cold and warm engine to see what/how everything changes.

1. Fuel pressure at idle with vac line on and off.
2. Alternator output at idle
3. Alternator output under wot
4. Voltage going to the FP relay
5. Voltage going out of the FP relay to the FP's
6. Try another fpr gauge once engine is hot to see how the cold gauge reads


Anything else I should add to this list?

 

Update

Alright well I had a chance to drive the car and have some data to report in. Here we go.

The car had been sitting for a few days so it was very cold. Started it up and got to work with the multimeter.

Cold Engine - Fuel pressure when the pumps prime - 42psi,when I started the car the pressure only dropped a few psi, hovering around 40psi at idle when cold.

1. Voltage at the battery was 14.3v
2. Battery to FP relay was 13.6v
3. FP relay into the pumps was 13.6v

Took off for a small get car gathering at the local custard stand, decided I would take it easy, the wastegate only opened 1 time in the 10 mile cruise and highest rpm was 4700. I logged voltage the entire time there and this is what I saw...

Cruising around I was seeing 12.9-13.0v through the aem. When I would hit stop lights the voltage would start to drop. The first few stoplights it dropped to 12.5 while idling at the light.

The one time I got on it briefly I was getting 12.9v under load. The stoplight right after that it dropped to 12.30v. Leveled back out to 13.0v while cruising, dropped to 12.3 at the next light. Checked fuel pressure when I got there and it was 35-36 at idle on a warm engine and easy drive there.


drove back to my house to get the computer charger. The car is now at complete operating temperature.

At idle I was seeing 12.5-12.6v through the aem, The first 2nd gear pull I was seeing 12.8v under wot up to 7k. air fuels were 11.1-11.2 while WOT.

3rd gear pull I was seeing 12.7-12.8 under load and wot. air fuels were 11.4-11.6 this time around.

Small roll into 4th gear. 12.8v under load. Air fuels were 11.6-11.8.

Another small 4th gear rolling into it and was seeing 11.8afr and then let out by 4500rpm. Keep in mind this is a small turbo and I am seeing 17psi at 4k rpm.


Let the car cool down in the garage, but I immediately jumped out and took the multimeter to the alternator and was getting 13.5-13.6v at the battery. Measured at the fp relay and away from the fp relay going to the pumps was seeing 13.0V. Fuel pressure was at 35psi

When the car was cooling down idling in the garage the voltage was reading 12.9 and over the course of 2:30 min it had climbed to 13.3v.

Unfortunately I wasnt able to try another gauge right now. Maybe tomorrow I can do that.

What does everyone think???

 

seems like a battery/alternator issue....

 

I agree. I an going to get a new alternator and start from there.


Any other thoughts?!?

 

Def sounds like a battery or alternator issue. I would have the battery tested first. Your voltage is dropping too low under load.

Steve

 

I have been having the same issue as you. I replaced the pumps, fuel lines, filters and went bigger with everything...other than the gauge. I just drained the fluid out of my gauge, drove the car for 30 minutes and it didn't drop at all. I adjusted the pressure to what it should be, since I had it about 8 lbs. high, drove for another 20 minutes and it stayed exactly the same.

I would drain or replace that gauge and see how it goes from there. This obviously won't help your lean issue, but at least you'll know your gauge is working properly.

 

Ok so here is an update.

I installed a new alternator a few days ago. I took the car for a drive tonight and the same thing happened. Air fuels are leaning out after a few pulls. I logged voltage in the aem while I was driving and once again it was at 12.89 while cruising. same as before but with a new alternator.

Let the car sit for an hour or so and then headed home from an errand. Voltage was mysteriously at 13.25 this time through the aem and when i rolled into it in second I was seeing 10.1 afr's. So obviously the increased voltage was dropping my air fuels. The next pull was 10.9, and the next was 11.7.

I measure a few other things just to narrow it down some more once I got home.

1.I measured the battery when the car was off - seeing 12.67 or so (battery is 3 years old and nothing special, not an ultima or anything.) Just wanted to eliminate a bad cell.

2. Measured voltage at the battery at idle with new alternator after the long drive home and a few pulls. At idle and hot car I was seeing 13.6

3. Measured voltage at the FP relay on a warm car, going into the relay was 13.05

4. Voltage out of the relay into the pumps was 13.05ish as well


I am at a loss as to the next step for diagnosing this? Ideas?

 

Random thought... You don't by chance have multiple amps running subwoofers and such?

DP

 

Nope no subs or amps. Just a basic pioneer cd player. Still using the stock amplifier under the seat.


Another thought..... Is there a chance that the aem is not correctly monitoring battery volts???

The reason I ask is because I was looking at the log and when u was seeing 10.1 afr on the first pull I also was seeing 12.9 volts according to the aem.

 

Chase, I'm sorry your issues persist.

Whats going on with your fuel pressure now, have you changed gauges or anything?

I really think it is time to have your injectors looked at, or maybe even your fuel rail? I'm not sure it is a mechanical issue but you might look.

Adam

 

Adam can you or someone else measure the voltage you are seeing through the aem and also at the battery and fuel pumps to compare to my readings?

I want to be sure that something else is going on before I pull the rail and injectors. The 12.9 under load on a new alternator just isn't sitting right with me. Something is still very wrong here.

I looked at fuel pressure once I got home but the car had been sitting for a good half hour before I remembered to check it. It was solid and at 40psi when I started her back up.

I don't get a lot of change from the vac line being on or off. The vac line is a dedicated line off the intake manifold. This also bothers me.

 

Chase have you checked the grounding wires for any looseness? ... I also recommend to replace the FP gauge with electrical gauge like Autometer.

 

I will double check the grounds to make sure they have a solid connection.

I know there is a ground on the drivers side of the block, as well as on the intake manifold, then one by the iacv and the firewall, what other grounds should I check???

I will buy a fuel pressure gauge and monitor it in cabin.

 

This may be dumb, but when did this start happening? Did you do a recent mod?

Jeremy