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

[LSxpwrdZ]

I would pull the pressure sensor from the rail and place it in the regulator to take out that surge of fuel on each injector pulse to see if that stabilizes your readings any. You also have to take into consideration fuel temp, engine bay temp, vibration etc.

LS1's don't normally come with pressure sensors so logging fuel pressure for me has been limited to those particular setups that someone actaully has installed one. My personal car doesn't fluctuate much that I've noticed... but that is reading a physical gauge and not logging it with a sensor such as yours.

[robbyredneck]

i have never personally logged fp at all. most guys are looking for issues at wot like flame. i am strictly speaking out of my ass. but as far as i know measuring on the outlet/waste side of any regulator is not accurate as before the plunger. sorry if i came off as a dick but i am in for the answer just so i know if that minor of a pressure swing can affect your overall tune even if you compensate in your ve or maf table. if the dip is constantly repeatable than i would think you could easily predict whats going to need to change in your tune.

[LSxpwrdZ]

Technically the way he has it setup up it is still on the pressure side of the plunger however its not between the flow of the feed and the plunger which is a minor detail that usually gets you.

The factory system is setup like this as well only the regulator is all the way back in the tank on the return line (if Fbody) and the feed is T-d after the filter and run to the rail where it is dead headed.

[68Camaro]

I have a lot of experience building fuel systems for very fast cars and noticed something I would change if it were my car. The fuel pump is located in front of the fuel tank (towards the engine) if I am interpreting your pictures correctly. Electric fuel pumps are very effective fuel pushers but very poor fuel pullers - the pump needs to be located behind the sump or as close to even with it as possible. I have seen this cause lots of problems many times. Cars will make good #'s on the dyno but perform poorly at the track (because the pump does not have to contend with g-force on the dyno). I would move the pump and then check your pressure.

[LSxpwrdZ]

^^^ Thats a good call as well. Didn't pay much attension to the pictures but gravity feed is def a must for that pump to work right accelerating.

One question I have... What were the conditions when you measured these different fuel pressures? Sitting idleing, accelerating down the road, cruising at steady state down the road? RPM, Load, Throttle Transient?

[halfspec]

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.

Temperature is actually a concern I've had myself. I'm definitely going to look into relocating the sensor to reference the FPR and when I do I'll look into making a heatshield for it

I've set the FPR every way known to man. Hot, Cold, Pump jumped without engine running, Idling, etc etc etc.

Thanks for the tip about capping the reference port. I'll do that too!

I would pull the pressure sensor from the rail and place it in the regulator to take out that surge of fuel on each injector pulse to see if that stabilizes your readings any. You also have to take into consideration fuel temp, engine bay temp, vibration etc.

Thanks for the suggestion. This is definitely something I'm going to start planning out and will execute ASAP

i have never personally logged fp at all. most guys are looking for issues at wot like flame. i am strictly speaking out of my ass. but as far as i know measuring on the outlet/waste side of any regulator is not accurate as before the plunger. sorry if i came off as a dick but i am in for the answer just so i know if that minor of a pressure swing can affect your overall tune even if you compensate in your ve or maf table. if the dip is constantly repeatable than i would think you could easily predict whats going to need to change in your tune.

It's all good man! I definitely don't mind being chewed out for something stupid on my end if I'm doing something stupid I'd rather get a thrashing and some answers then no answers at all. Yes, I agree, FP logs or people that have logged FP are few and far between. Its another reason I think I'm overthinking this whole thing and I'm probably chasing something that isn't a problem at all. I'd just like to 'know' it's not a problem if you know what I mean.

I have a lot of experience building fuel systems for very fast cars and noticed something I would change if it were my car. The fuel pump is located in front of the fuel tank (towards the engine) if I am interpreting your pictures correctly. Electric fuel pumps are very effective fuel pushers but very poor fuel pullers - the pump needs to be located behind the sump or as close to even with it as possible. I have seen this cause lots of problems many times. Cars will make good #'s on the dyno but perform poorly at the track (because the pump does not have to contend with g-force on the dyno). I would move the pump and then check your pressure.

^^^ Thats a good call as well. Didn't pay much attension to the pictures but gravity feed is def a must for that pump to work right accelerating.

One question I have... What were the conditions when you measured these different fuel pressures? Sitting idleing, accelerating down the road, cruising at steady state down the road? RPM, Load, Throttle Transient?

Very sound advice guys. I'll definitely start building/planning out a mount to get my pump level and closer to the sump's outlet!




For the conditions I've been testing using my route to and back from my place of work. It's 1/2 60mph crusing, and half 35mph stop and go traffic. All in all it's about 15 minutes each way; 30 minutes total. Here is some recent data from a run I did:

Here is the HPTuner’s cfg file for anyone that wants to read the logs I’ve posted below:
Please don't pay attention to the WB or LAMBDA Err traces because on this run they weren't configured correctly (recently switched from an innovate LC1 to a AEM UEGO)

http://www.halfspec.com/downloads/RX...MWB_121812.cfg

Here is a graph of my drive across town after adjusting my FPR to 58psi:


Here’s the HPTuner’s Log:
http://www.halfspec.com/downloads/RX...Drive2Work.hpl

Here’s a graph from the same run only I drove home in this one AFTER readjusting my FPR to 58psi (adjusted at idle without shutting down my car in my work parking lot):

Here’s the HPTuner’s Log:
http://www.halfspec.com/downloads/RX...Drive2Home.hpl


After the runs above, I let the car sit overnight WITHOUT adjusting my FPR and took it out for the same drive the next morning. For this drive I did not stop and adjust the regulator to 58 in the middle of the run like the data above:


Here’s the HPTuner’s Log:
http://www.halfspec.com/downloads/RX...2Work2Home.hpl

This is pretty consistent with what I’ve seen with my own FPR. A drop and rise in pressure over the course of the drive. It's also consistent that a setting of 58psi the previous day will start up at 60+ psi the next day.


Thank you everyone for the insight and help.

Lane

[LSxpwrdZ]

That almost looks like something thermal causing the regulator to fluctuate. Being winter time and all the temperature that the regulator sees will reflect how much spring pressure is applied to the plunger. Between heating of the fuel and engine bay heat it appears that the on two of the occations initially cold the pressure is higher and as it heats up the pressure slowly drops off a few PSI. The only part that throws me for a loop is when you stopped in the middle of the first run and readjusted the pressure back up to 58psi and the pressure then increased for the rest of that drive.

Like I said earlier it may be sensor placement with engine heat and it may be a simple problem with that type regulator and thermally changing the spring rate causing actual pressure to change. Very odd to say the least.

What does your fuel trims and wideband say with these pressure swings? Is it a large swing in afr or fuel trims? I'm not on my tuning PC or I'd look at the datalogs to check them out.

[halfspec]

That almost looks like something thermal causing the regulator to fluctuate. Being winter time and all the temperature that the regulator sees will reflect how much spring pressure is applied to the plunger. Between heating of the fuel and engine bay heat it appears that the on two of the occations initially cold the pressure is higher and as it heats up the pressure slowly drops off a few PSI. The only part that throws me for a loop is when you stopped in the middle of the first run and readjusted the pressure back up to 58psi and the pressure then increased for the rest of that drive.

Like I said earlier it may be sensor placement with engine heat and it may be a simple problem with that type regulator and thermally changing the spring rate causing actual pressure to change. Very odd to say the least.

What does your fuel trims and wideband say with these pressure swings? Is it a large swing in afr or fuel trims? I'm not on my tuning PC or I'd look at the datalogs to check them out.

That's the same line of thinking I had when I swapped out the FPR for a FPR loaner from a friend. I was thinking the spring rate of the FPR's spring may have been changing with temperature. However, the swap didn't agree. Also, my FPR is mounted beside my brake booster and clutch master cylinder all the way back in the driver's back corner of the engine bay. I wouldn't think it would see extreme temperatures back there and my fuel lines are shielded with DEI fire sleeve whenever they get within a foot of the exhaust / manifolds.

I think the sensor placement is key now. I've been laid off from a company collapse for the last 2 months, so money is scarce, but I'm hoping to get an offer on a new job this week, so I may be able to buy the parts to make the move soon

For the logs above, my wideband wasn't setup correctly due to a WB system change (Innovate LC1 to a AEM UEGO). I have looked STFT's vs map, maf, and rpm and they don't seem that much different from the start of the run vs the end (~2.5%). That could indicate I don't really have a problem. However, my tuning knowledge is definitely amateur so my conclusions aren't solid.

Lane

[halfspec]

Resurrection!!!!

I believe I've got this bitch licked!
Unfortunately I don't have a single fix I can point at to say that's what did it because I got anxious at the end and put in two fixes instead of testing them separately. The two fixes were:

1. Replaced my fuel pressure gauge and sender. I knew the gauge was faulty but the sender was within spec according to Speedhut (based on pressure to voltage curve verified through analog gauge). However, when I went to return the gauge to Speedhut, they asked me to include the sender as well. Got the package back and BAM! They had replaced both of them
2. Relocated the fuel pressure sender from the fuel rail to the fuel pressure regulator.

I believe #2 is what did the damage here.



This took me forever do do because on top of having to physically move and re-mount my FPR so the FP sensor would clear the MC reservoir, I had to remove my fender to get to the nuts on the other side because I didn't nutsert the FPR mounts the first time...

My first log was of 3 separate runs I made a couple of days ago:



The first trip I logged it coming back from the gas station after a MUCH needed fill-up. I was basically running on fumes so i attribute the slightly low start then ramp to ~58 to working out some bubbles. The first trip ends at the 55psi drop.
The second trip picks up immediately afterwards although it actually starts the next day. It's a drive from work to my house It also ends with a 55psi drop
The third trip is a trip from my house to work WITH the AC ON. It apparently makes my fuel pressure rise ~1/2 psi which seems pretty reasonable to me. The first little stumble at the end is a quick cycle of my AC compressor (I was figuring out what was going on with the slight rise in pressure). The last little drop is when I turned the AC OFF 1 mile before I arrived at work. You can see the fuel pressure return to a little over 58psi which is what I'm aiming for.

The second log was from 2 runs I made today:



Like the first log, the 2nd run comes after the 55psi drop.
1st run is from the gym to my house which is a 25 minute drive of stop and go + highway. AC OFF
2nd run is from home to work. AC OFF

So there you have it. I didn't really 'fix' anything, but I've ruled out fuel pressure as a problem and can continue tuning the car. Its been a while but my big hangup on this was that I was having a REALLY hard time tuning my MAF. After 12 tuning runs I decided something was wrong and started logging my fuel pressure. Now that I've eliminated that as an issue. I've started looking elsewhere aaaaaannnd I think I found it today actually. I'll be updating my build thread shortly.

The moral of this story is to KISS (Keep It Simple Stupid) and don't go chasing complicated possibilities when it's probably something much simpler, or you'll end up like me, depressed and unmotivated for months. Moral #2 - Don't mount a fuel pressure sensor on a LS1 fuel rail if you want feedback that isn't influenced by the injectors.

I appreciate all the help I received in and outside of this thread. There were a couple of you that guessed that the problem was sampling from the LS1 fuel rail. I expect you were right.

Thanks again!
Lane

[WS6FirebirdTA00]

Thanks for posting back up, too many times resolutions don't get posted and make the search nearly useless.

[DrLoch]

Thanks for posting back up, too many times resolutions don't get posted and make the search nearly useless.

What he said.. Thanks for your time.

[halfspec]

Thank you gents.
I try to wrap up all my threads on all the forums I'm a member of. I, like you, also get frustrated by unresolved posts.

Lane

[marksrig]

This is obviously way late to the game, but this thread still helped me.
Moving my sensor from the fuel rail to the regulator fixed my issue. Fuel pressure is solid now.
Thanks from the future.