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Old 11-05-2010, 02:27 AM   #1
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Default Fuel pressure problems

This is on my 95 Regal, L67 swap. I'm having some very strange fuel pressure problems. I hooked up a fuel pressure tester, and here'* what I found.

When I'm at idle, hptuners reads ~27-30kpa. At that pressure, the fuel pressure regulator reads 47-48. If I disconnect the vacuum line from the fuel pressure regulator, the pressure goes up to ~52.

My injector mappings are (in increments of 10psi, from 0 to 100):

36.09549 36.51102 37.02563 37.75668 37.91079 37.98831 38.04389 38.09962 38.14432 38.27907 38.40343

I've replaced all of the vacuum hoses I can see in the engine bay, yet my idle still runs very lean. I can tell its running lean because my short and long term fuel trims point in that direction, the idle bounces around, and fails to stay at its assigned RPM. It will generally idle 200rpm higher than what its tuned to after running for a while.

Could I have a bad fuel pressure regulator? I thought that as vacuum increased, I would have higher fuel pressure, but this doesn't appear to be the case with this one. There'* a number 50 written on the side of the fuel pressure regulator.

Oh, and I just installed a high flow Walbro 255lph fuel pump thinking that was the reason why I wasn't getting enough pressure. Turns out that'* not the reason.
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Old 11-05-2010, 08:42 AM   #2
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Did you reflash the PCM with L67 MAF settings as well as MAP settings?
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Old 11-05-2010, 08:42 AM   #3
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How'* the pump not the reason?
When was the filter last changed?
Have you tested pre FPR to ensure you can build around 80psi
The poper way to test F is key clicking with engine off. I prefer a drive test. Idling really tells us very little about pressure except that the pump with no load can push something. I've found cars that passed the key click/idle pressures and the moment you drive them and use some fuel they starve because the pump won't keep up.

Walbro, was it made for your 95 or was the it standard ZZP/Intense one that is for GP'*? The standard one gave my Bonneville 28psi. TRE Performance hooked it up for a great price with a high flow pump that was a direct fit into my Bonneville. One quick call and I had things fixed up.
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Old 11-05-2010, 11:18 AM   #4
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Quote:
Originally Posted by BXX View Post
Did you reflash the PCM with L67 MAF settings as well as MAP settings?
I'm using a modified version of Cam'* L67 tune, with the L67 MAF table, modified for transmission purposes. I have not VE tuned yet. I don't have a reference stock L67 pcm file to look at.

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Originally Posted by BillBoost37 View Post
How'* the pump not the reason?
When was the filter last changed?
Have you tested pre FPR to ensure you can build around 80psi
The poper way to test F is key clicking with engine off. I prefer a drive test. Idling really tells us very little about pressure except that the pump with no load can push something. I've found cars that passed the key click/idle pressures and the moment you drive them and use some fuel they starve because the pump won't keep up.

Walbro, was it made for your 95 or was the it standard ZZP/Intense one that is for GP'*? The standard one gave my Bonneville 28psi. TRE Performance hooked it up for a great price with a high flow pump that was a direct fit into my Bonneville. One quick call and I had things fixed up.
Here'* the fuel pump I picked up, off of summit racing:
http://www.summitracing.com/parts/VPN-GSS342/
http://www.nolimitmotorsport.com/walbro/

I changed the filter when I dropped the tank. No reason not to.

Where do I test pre FPR?

I'm getting enough fuel and enough pressure from the pump. Wide open throttle pulls like a madman, its only idle that I'm concerned with, and I don't know if its normal to have a lower than 50 fuel pressure when you're sitting in idle. I thought that was supposed to increase with pressure, not decrease. I guess I'd have to connect the fuel pressure gauge back up to the rail and have it sticking next to my windshield as I'm driving to see what the pressure actually is.
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Old 11-05-2010, 11:22 AM   #5
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I believe I had 48psi at idle on my car. The pressure goes up when you unhook the vacuum line so that tells me it'* working right. Less pressure with higher vacuum, higher vacuum at idle. If it'* running poor at idle then you may want to look over the tune. What is your LTFT telling you at idle? Post up some numbers please.
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Old 11-05-2010, 11:24 AM   #6
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I believe I had 48psi at idle on my car. The pressure goes up when you unhook the vacuum line so that tells me it'* working right. Less pressure with higher vacuum, higher vacuum at idle. If it'* running poor at idle then you may want to look over the tune. What is your LTFT telling you at idle? Post up some numbers please.
LTFT at idle is +16.4. That'* how I know its running lean. Anything above idle the LTFT'* are within +/-8. They still need to be tuned a bit, but that'* where I'm at now.

It certainly could be the tune. I didn't know if that was normal. I don't know what numbers to post, so by all means let me know.
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Old 11-05-2010, 11:50 AM   #7
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get some carb cleaner and spray around anything that could leak vacuum, including the blower and lim. If the feul trims change a bit, then you found a vacuum leak.
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Old 11-05-2010, 11:57 AM   #8
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get some carb cleaner and spray around anything that could leak vacuum, including the blower and lim. If the feul trims change a bit, then you found a vacuum leak.
Well that'* going to be fun, if I find a vacuum leak outside of the typical hoses I've been replacing. I doubt its the LIM because that was changed with the revised design, but I'll give it a shot.
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Old 11-05-2010, 02:21 PM   #9
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I was just thinking about something earlier. These injectors are rated at 36psi. What pressure is that? I thought that was somewhere above 50psi. If the fuel pressure regulator, under vacuum, is reading 48psi, and I have the car tuned to think its at 36psi, isn't there a potential problem with that?

Also, I noticed that the car takes a while to crank in the morning. I'll have it cranking for a good 3-4 seconds before it fires up. Any thoughts? I've heard that'* a sign of a failing fuel pressure regulator.
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Old 11-05-2010, 02:29 PM   #10
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It is possible your injector tables are off a bit, but you also said your trims are fine when cruising and at WOT. At this point if I was doing the tuning, I would be looking at my idle MAF curve and start tweaking that. You will need to look at your scans and note where your LTFT is lean, that look at your MAF frequency and write that down. You should find a high and low reading. Then adjust your MAF curve within those readings. Seeing your off by 16% I would do a 5% adjustment and rescan.
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