Impact of fuel pressure swings of ~4 psi. FP Logged. *Lots of logs, data, and pics*

[halfspec]

*SOLVED* See post #29 for full details:

http://www.hptuners.com/forum/showpo...1&postcount=29




Hello

I've been a lurker here for a little while but haven't posted a lot. I've been trying to absorb as much as I can. However, I've been tinkering with this problem for a few months now and I thought I'd throw it at the pros to see what they think of it.

I'll ask my questions up front just so they don't get lost in the rest of the post.

To anyone with experience in logging fuel pressure and tuning Gen3 GM engines. Will a 4psi swing affect open loop tuning / locked fuel trims? I'm thinking it will because I haven't been able to nail down my MAF tune, but I'm afraid I may be chasing my tail here.

Can anyone who has logged fuel pressure post their logs here? I'm specifically looking for GM applications in the 58psi range. Stock or Aftermarket FPR is ok. I'm just looking to see what a normal pressure range looks like on a return style system


Ok, so here's the meat. This is what I've got:

Build thread with full details = http://www.norotors.com/index.php?topic=70.0

Chassis = 1993 Mazda RX7

Engine:
Ls1 aluminum block built for 10.4:1 compression with only 4k miles on it as built.
Complete assembly is balanced
Forged flat top 3.90" Mahle pistons
Forged Eagle rods
Forged Eagle stroker crank with 4" stroke designed to displace 383CI.
Patriot LQ9 heads with 72cc chambers 2.055"/1.60" valves with harland sharp 1.7 roller rockers.
Comp pushrods and lifters.
Gm performance oil Pump and chain
Arp rod and main bolts
Trick flow head gaskets
Patriot custom cam .585"/.585" lift, 226/226 duration and 112 lsa
0 miles on the Water pump, Ac Compressor and both tensioners
Stock coils
MSD wires
LS6 Intake + PCV conversion

My original fuel system layout was as follows

-8AN Pickup from aftermarket sump -> -8AN 100um Summit Racing Fuel Filter -> Bosch 044 In line filter -> -8AN 10um Summit Racing fuel filter -> Aeromotive 13101 FPR
Splits to -> -6AN to Stock LS1 Fuel rail -> SVO #42 Greentop injectors
-> -6AN return line to 2nd port on the aftermarket sump

Here’s what my original return layout looked like:



Yes, that’s me returning fuel directly to the sump…. I finally realized that my returned fuel was probably aerated and was probably being picked up hot and bubbly in the sump causing cavitation at the pump. To fix this problem I capped the 2nd sump OUTLET and re-routed the return hose to the stock fuel pump location after modifying the inlet / outlet to –AN spec.




Unfortunately it didn’t solve my pressure problems, but I’m thinking it was a good idea anyway.

Fuel system layout as it is now:



Green circle is the 100um pre-pump filter, the Blue circle is a Bosch 044, and the Red circle is the 10um post-pump filter.
And here’s an old picture of how I’ve got my regulator setup:



Fuel from the pump comes in from the -8AN inlet facing the rear of the car, fuel goes to the fuel rail out of the -6AN outlet facing the front of the car, and the return goes to the tank out of the -6AN outlet facing the bottom of the car. The only thing that’s changed is the post pump filter in the picture has been relocated.

Here’s how I am reading pressure from the fuel rail:




Here are some links to some of the bigger parts in my system:

FPR:
http://www.summitracing.com/parts/AEI-13101/

100um filter:
http://www.summitracing.com/parts/SUM-230118-B/

10um filter:
http://www.summitracing.com/parts/SUM-230116-B/

Mechanical fuel pressure gauge:
http://www.summitracing.com/parts/SUM-800199/

Fuel pressure gauge and sender:
http://www.speedhut.com/custom_gauge...number-474.htm


Here's what I'm dealing with:



Here's the CFG and HPL from the run that graph came from:
http://www.halfspec.com/downloads/RX...2Work2Home.hpl
http://www.halfspec.com/downloads/RX...MWB_121812.cfg

Please ignore the WB and LAMBDA_err traces as they weren't setup correctly for this run. Also, this tune is very rough as I'm still in the early stages of tuning.
During that run I also made sure my readings were correct by comparing the logged values to the in-bay mechanical gauge reading from the same pickup. I snapped the pics at the beginning, middle, and end of the trip:








Sorry for the blurry pics. The engine vibration made it impossible for my "auto focus" camera to work.


What I've tried so far:

1. Cleaned out 100um pre-pump fuel filter and 10um post-pump fuel filter (they weren’t really dirty).
2. Moved pump’s ground
3. Moved post-pump fuel filter closer to pump. Moved from engine bay to under the car. This was more about a hood clearance issue, but I figured it was worth mentioning.
4. Disassembled my FPR. I just took off the top to inspect the set screw and diaphragm. Everything looked fine
5. Rerouted fuel return to the top of the tank to the stock fuel pump hanger lid (converted to 90 degree -6AN).
6. Rebuilt -6AN fuel return hose for #5.
7. Installed mechanical gauge to verify digital sender’s output (it did verify).
8. Bypassed the Fuel Pump's relay and ran it straight from the battery
with 10AWG wire.
9. Logged the speedhut FP sensor's 5v reference (it is fine and solid at 5v)
10. Logged the voltage across the fuel pump
11. Logged the current through the fuel pump using a shunt resistor.
12. Swapped out the Bosch 044 fuel pump for another Bosch 044 fuel pump.
13. Replaced the flared (Doh!) FPR fittings for ORB fittings
14. Swapped out the AEI-13101 FPR for another AEI-13101 FPR.
15. Disconnected the speedhut FP gauge from its sensor and powered + grounded the sensor independently with a regulated 5v circuit.

I am happy to post any data from the 15 things I've already tried if requested.

Any help is GREATLY appreciated as I've been scratching my head over this issue for months now.

Lane

[WS6FirebirdTA00]

I didn't read it all, but yes I would expect that to cause some issues.

[robbyredneck]

i would expect to see the reduction given your fpr is before your injectors. also if you have a vac reference you should see a pressure reduction.

[halfspec]

Thanks for the replies guys!

WS6FirebirdTA00 - Yeah, I know it's a beast of a read. Sorry about that. I actually copied the bulk of the message above out of a 4 page thread I have on the topic on another forum. I posted here because I was hoping to get a definitive answer on if this type of variation is normal and if not if it's something that would affect tuning with locked fuel trims. Thanks for the input.

robbyredneck - Both of your points are very interesting to me. You are correct in saying that the FPR is before the rail in my setup. I am using a stock LS1 fuel rail, so that's the only way to set it up that I know of. I've considered going to aftermarket fuel rails and running my -8AN supply line straight to the rail and then exiting the rails to the regulator. I haven't done it yet because I didn't know of any advantage for my power goals. If you think having the fuel rails in-between the fuel pump and the regulator offers a more controllable system, that's a huge advantage for me. Is that what you're saying?
I do have a vacuum reference, but it isn't being used and it's just exposed to atmospheric pressure. I was under the assumption that the corvette FPR isn't vacuum referenced, so I didn't reference my aftermarket regulator. Is this incorrect?

Thank you both for the help!
Lane

[robbyredneck]

that is what i am saying. put the regulator after the rails. you can vac reference or not but it should be reflected in your flow rate vs kpa data in your tune

[WS6FirebirdTA00]

Yeah I may have misunderstood the post, but you really have to look at your delta across the injector. As long as that is constant, you use a referenced regulator and your IFR is setup correctly then fuel pressure changes are common but the differential should be relatively stable.

[halfspec]

that is what i am saying. put the regulator after the rails. you can vac reference or not but it should be reflected in your flow rate vs kpa data in your tune

Got it. I'll look into it. I'm using Greg's tables for my 42lb SVO injectors which I believe aren't vacuum referenced so I'm going to just keep them that way and not make any changes to the FPR's reference.

Yeah I may have misunderstood the post, but you really have to look at your delta across the injector. As long as that is constant, you use a referenced regulator and your IFR is setup correctly then fuel pressure changes are common but the differential should be relatively stable.

I'm not really sure what you mean when you say the delta across the injector? Can you expand on that?

Thanks again guys
Lane

[WS6FirebirdTA00]

fuel pressure + intake vacuum

or

fuel pressure - intake pressure

basically you are looking at the absolute pressure differential across the injector.

[halfspec]

fuel pressure + intake vacuum

or

fuel pressure - intake pressure

basically you are looking at the absolute pressure differential across the injector.

Alright, I think I'm getting what your saying. However, my FPR is only referenced to atmosphere and I'm planning on keeping it that way since my fuel injector data is setup for that and I don't know of any reason to change it on a NA application. Is there an advantage to running my FPR referenced to intake vacuum on a NA application that I don't know about?

Thank you
Lane

[WS6FirebirdTA00]

OK, I guess I should have read better

Correct, you can just keep a constant pressure. So back to what I was saying earlier, with it not being referenced that pressure drop is going to cause some fueling errors.

[halfspec]

Alright, do I'm considering switching to closed loop which will re-enable my fuel trims and do some VE tuning. Am I correct in assuming that this mode of tuning won't be sensitive to these fuel pressure variations?

Thanks for reading

Lane

[WS6FirebirdTA00]

No, it will still be sensitive to it.

[halfspec]

Thank you WS6FirebirdTA00

Lane

[halfspec]

I guess now I should repurpose my thread into a "can you find what's wrong with my fuel system" thread

Anyone care to take a shot?

The more I think about it, the more I'm not convinced that placing the fpr after the rails will fix the issue. A lot of OEM's have the FPR/Return before the rails so I'm of the mind that it should be good enough for me, but I haven't completely thrown the idea out.
I think I've eliminated almost everything simple and I'm down to a rail/injector problem or a sump outlet problem.

Any help/comments is appreciated
Lane

[WS6FirebirdTA00]

If pressure is fluctuating it is either a regulator that is not regulating properly, may be bad, or it could also be the fuel pump not providing enough flow at the conditions it drops off.

If I read correctly, it seems your log was over time in various conditions where it was not holding steady, seems like the regulator is just not keeping tight enough control.

[robbyredneck]

what you may want to consider, given your investment in your fuel system. pump>rails>fpr>return and run it referenced. that way in your tune your ifr vs. kpa stays a static number. also if you boost it there is no more work. having your regulator after your rails is quite stable as it can control your pressure with more direct of an effect. when you tune your ve with wideband error you should have no fuel trims on(open loop) and make sure you clear them with the scanner.

[halfspec]

If pressure is fluctuating it is either a regulator that is not regulating properly, may be bad, or it could also be the fuel pump not providing enough flow at the conditions it drops off.

If I read correctly, it seems your log was over time in various conditions where it was not holding steady, seems like the regulator is just not keeping tight enough control.

While I agree with your diagnosis the FPR and Fuel Pump have been two things that I've ruled out by replacing both. It's #12 and #14 of the things I've tried so far.

12. Swapped out the Bosch 044 fuel pump for another Bosch 044 fuel pump.
14. Swapped out the AEI-13101 FPR for another AEI-13101 FPR.

I also ruled out the wiring of the pump by temporarily hard wiring the pump directly to battery (well, I fused it for safely, but it was directly to the battery) and moving the ground around, while logging the voltage across the pump (consistent and the logs are available if anyone wants to see them) so it's not a relay or wiring problem.

what you may want to consider, given your investment in your fuel system. pump>rails>fpr>return and run it referenced. that way in your tune your ifr vs. kpa stays a static number. also if you boost it there is no more work. having your regulator after your rails is quite stable as it can control your pressure with more direct of an effect. when you tune your ve with wideband error you should have no fuel trims on(open loop) and make sure you clear them with the scanner.

While I see what you're saying, I'm just finding it hard to believe changing over to a pump->rail->FPR->return setup is going to make that big of a difference with my particular problem. I mean, I know that there will be super quick tiny drops in pressure inside the rail around the injector feeds that may be better compensated for with a pump->rail->FPR->return setup, but a slow drop in pressure shouldn't be something that happens to either setup. The fuel inlet and outlet are connected within the FPR's main chamber so the pressure 'should' be the same on both lines entering the FPR if it is operating properly. The only thing a rail-first setup would accel in is quicker compensation, but that's not my biggest problem.
As for referencing the FPR. I'm open to it, but I don't have plans to turbo my engine as I've already got space concerns NA'd. Also, I'd hate to lose track of being able to tell if my FP is behaving correctly. I guess what I'm saying is that with FP that is fluctuating, how am I supposed to know if the FP is at the level it's supposed to be at any given minute?

That's just the way I see it, but I'd welcome further discussion. I definitely don't know everything and I'm here to learn.

Thank you for the help gents.

Lane

[robbyredneck]

you are measuring your fuel pressure post control. your expecting to see static pressure after consumption and regulation delay. i don't think given your perspective you will find your solution. i am not saying that you can't get your rig dialed in with your current configuration as your ve table will suck up a ton of b.s. but your chasing a "problem" that may not even be there.

[halfspec]

I agree about the "problem", and I certainly don't want my perspective or my weak grasp of this problem to be a hangup in solving it. If you think my thinking or methods are flawed, please feel free to tell me like you just did. I'm not some newb that's going to get pissed off when you tell them something they don't want to hear. I just like to learn 'why' I'm wrong when it happens so I can chalk it up for future knowledge

So you're saying measuring fuel pressure at the rail is a bad idea. I can wrap my head around that. Truth be told, the only reason I'm sampling from the rail is because my FPR is mounted very close to my clutch master cylinder + reservoir, which has caused a clearance issue that won't let me mount a gauge/sensor directly to the FPR's NPT port. I'd have to come up with some plumbing to remotely sample the pressure at the FPR. That's definitely possible, and if you're of the opinion that that's where I 'should' be measuring, then I'll start planning it out.

Thank you for your time

Lane

[flame]

I found when I used an electric sender off the rail port that temperature underhood really affected the readings. I was only looking for pressure drop at wot so accuracy didn't matter.

Two things about your fpr when did you set it? Hot,cold,running? Also I would cap the ref port if you aren't using it.