Low Fuel Pressure, running lean
#1
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Thread Starter
Low Fuel Pressure, running lean
Hey guys, this is on my 89 Crx si with fresh built d16a6-turbo.
So as of late (3 days or so) I noticed my car running lean on the wideband while cruising and idling. But its not constant, sometimes its fine sometimes its 16.5:1 or even leaner to where the car doesnt want to accelerate.
So I pop my hood at the gas station at notice my fuel pressure gauge shows like 28-30psi... low.. when i put the engine in I had about 35psi, which even then I thought was low. Just now I swapped in another FPR from my old dohc zc, but the pressure stays the same.
The car has a walbro 255 pump, but it was not brand new when installed, it was in my last setup and then sat in the garage for about 4 years.
Im not quite sure where to go on diagnosing this. I do also have a buddy with a spare B&M FPR, but Im not sure if throwing that on and possibly adjusting the pressure up is just a bandaid for a bigger problem. My fuel filter is only about 10k miles old aswell if that matters.
What to do?
So as of late (3 days or so) I noticed my car running lean on the wideband while cruising and idling. But its not constant, sometimes its fine sometimes its 16.5:1 or even leaner to where the car doesnt want to accelerate.
So I pop my hood at the gas station at notice my fuel pressure gauge shows like 28-30psi... low.. when i put the engine in I had about 35psi, which even then I thought was low. Just now I swapped in another FPR from my old dohc zc, but the pressure stays the same.
The car has a walbro 255 pump, but it was not brand new when installed, it was in my last setup and then sat in the garage for about 4 years.
Im not quite sure where to go on diagnosing this. I do also have a buddy with a spare B&M FPR, but Im not sure if throwing that on and possibly adjusting the pressure up is just a bandaid for a bigger problem. My fuel filter is only about 10k miles old aswell if that matters.
What to do?
#2
Honda-Tech Member
Thread Starter
Re: Low Fuel Pressure, running lean
I should probably mention that my pressure gauge is mounted on the rail, and those pressure numbers are with the vacuum line connected
#4
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Thread Starter
Re: Low Fuel Pressure, running lean
I disconnected the vac line with the car running, instant 40psi
I connected the line and squeeze the rubber return line with a pair of pliers, the pressure did increase
Does this indicate a good ump or could it still be fuel filter at all here??
I connected the line and squeeze the rubber return line with a pair of pliers, the pressure did increase
Does this indicate a good ump or could it still be fuel filter at all here??
Last edited by KevinEF7; 02-20-2013 at 11:21 AM.
#5
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Thread Starter
Re: Low Fuel Pressure, running lean
edited my post above, first time I squeezed the feed line doh lol
Im going to try and install the B&M fpr, just to see what it does, and probably try and get the idling pressure to atleast 35psi, and see where that goes
I noticed when i tried to boost today, that my entire tune seemed to have leaned out, when it was normall 11.5:1 in boost it was near 13 today (only went to 2-3psi and let off) and the crusing AFR is about 16.5:1 now
So I know I can probably just adjust my tune to compensate, but what changed ....... the weather is still cold (I originally tuned it in the cold)
What would cause this
Im going to try and install the B&M fpr, just to see what it does, and probably try and get the idling pressure to atleast 35psi, and see where that goes
I noticed when i tried to boost today, that my entire tune seemed to have leaned out, when it was normall 11.5:1 in boost it was near 13 today (only went to 2-3psi and let off) and the crusing AFR is about 16.5:1 now
So I know I can probably just adjust my tune to compensate, but what changed ....... the weather is still cold (I originally tuned it in the cold)
What would cause this
#7
Honda-Tech Member
Thread Starter
Re: Low Fuel Pressure, running lean
Its street tuned. Has 680cc low imp precision injectors, stock resistor box
I just dont get what would cause the AFR difference across the entire rpm range, yet sometimes will run just fine (very seldom the last few days)
I just dont get what would cause the AFR difference across the entire rpm range, yet sometimes will run just fine (very seldom the last few days)
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#9
Honda-Tech Member
Re: Low Fuel Pressure, running lean
Na or boost? If have had the afr vary like this on my brothers boosted rsx due to the boost varying
Just saw edit, does your boost still rise normal or is it over-boosting?
Just saw edit, does your boost still rise normal or is it over-boosting?
#10
Honda-Tech Member
Thread Starter
Re: Low Fuel Pressure, running lean
I dont really have a way to check pressure at the fuel filter. Should I just change it even though its only got 10,000km on it?
Its boosted, but the afrs arent just higher in boost, just cruising it is signifigantly leaner than it was in the same spot a week ago
Its boosted, but the afrs arent just higher in boost, just cruising it is signifigantly leaner than it was in the same spot a week ago
#11
Honda-Tech Member
Re: Low Fuel Pressure, running lean
Can you datalog and check or anything? If your getting 40 at the rail you have enough But if its dropped any that will cause you to run lean, I don't see the filter doing it, never once changed them even on 20yr old Hondas. Might be the pump going bad or a bad fpr
#12
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Thread Starter
Re: Low Fuel Pressure, running lean
Well yes my datalogs show me running lean, but they do not/cannot log the fuel pressure while driving.
I tried a second FPR last night, another known working one from my last Zc engine, and got the same results on the way to work and back today. I do have a B&M adjustable that Im going to install right now but I doubt that will change anything
Fuel pump is a possibility, but the fuel pressure rose significantly when I squeezed the return line while running which to me says its capable of producing whatever pressure my car is asking for...? Could be wrong
I tried a second FPR last night, another known working one from my last Zc engine, and got the same results on the way to work and back today. I do have a B&M adjustable that Im going to install right now but I doubt that will change anything
Fuel pump is a possibility, but the fuel pressure rose significantly when I squeezed the return line while running which to me says its capable of producing whatever pressure my car is asking for...? Could be wrong
#13
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Thread Starter
Re: Low Fuel Pressure, running lean
The car ran MINT up until this week with the setup, no changes were made to the tune or any parts, always 94 octane, and the tank is 4/5ths full right now
I just dont get what part would fail like this to cause the lean condition almost overnight
I just dont get what part would fail like this to cause the lean condition almost overnight
#14
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Re: Low Fuel Pressure, running lean
35~41 per factory service manual.
I think you are on the right track so far.
I don't think they 30psi is right for idle.
It's supposed to be about 5psi less than when you have the vacuum line disconnected.
Do another pressure test.
Prime the system and then remove the key.
Does the system hold pressure for a few minutes?
I think you are on the right track so far.
I don't think they 30psi is right for idle.
It's supposed to be about 5psi less than when you have the vacuum line disconnected.
Do another pressure test.
Prime the system and then remove the key.
Does the system hold pressure for a few minutes?
#15
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Thread Starter
Re: Low Fuel Pressure, running lean
I primed the pump and it held 30psi for the entire 10 minutes I was cooking my burger, didnt drop at all before I took the FPR off
So I just went and installed the adjustable FPR, dialed it in to 40psi with the line on and 48 with it off. And sure as poop the car runs pretty nice, touch leaner at idle than I remember but the whole rpm range and the little boosting I did was right on
I highly doubt I had 2 failed stock FPR's (they were both bang on 30psi with the line on)
Do you guys think I still have a problem somewhere? Id love to just run this B&M and call it good, but I fear an underlying problem.
I also only drove it about 2 miles on the test drive cause its snowing like crazy here, maybe Im jumping the gun on the good analysis
So I just went and installed the adjustable FPR, dialed it in to 40psi with the line on and 48 with it off. And sure as poop the car runs pretty nice, touch leaner at idle than I remember but the whole rpm range and the little boosting I did was right on
I highly doubt I had 2 failed stock FPR's (they were both bang on 30psi with the line on)
Do you guys think I still have a problem somewhere? Id love to just run this B&M and call it good, but I fear an underlying problem.
I also only drove it about 2 miles on the test drive cause its snowing like crazy here, maybe Im jumping the gun on the good analysis
#16
Honda-Tech Member
Re: Low Fuel Pressure, running lean
if it starts to drop again it might be your pump going out or somehow getting low voltage to the pump.... just go with it for now and see if it comes back, then youll know
#18
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Thread Starter
Re: Low Fuel Pressure, running lean
Injectors are brand new less than 750miles on them
Valve clearance is definetely a possibility, but I triple checked when I set the lash
WB02 sensor is 750 miles old aswell, its still good
Valve clearance is definetely a possibility, but I triple checked when I set the lash
WB02 sensor is 750 miles old aswell, its still good
#23
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Re: Low Fuel Pressure, running lean
if two regualtors both stock had the psi at the same numbers then it has to be either a loss somewhere (leak) or not enough supply, did you check the lines for a leak? also check the pump and make sure it sealed off under the security box
#24
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Re: Low Fuel Pressure, running lean
You are now running rich if you had it tuned with 35 (vacuum connected).
He did the pressure drop test with the key off. No drop = no leak.
He did the pressure drop test with the key off. No drop = no leak.
#25
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Re: Low Fuel Pressure, running lean
I dont believe there to be a leak.
What do you mean check the pump is is sealed off under the security box
I guess in theory it should be running a bit richer with the bump in fuel pressure 4DREF, but it didnt seem to be, kinda what makes me think the problem is still there i just didnt drive the car long enough before the snow storm to recreate the lean condition.
So Im hoping to check other things and get more ideas
What do you mean check the pump is is sealed off under the security box
I guess in theory it should be running a bit richer with the bump in fuel pressure 4DREF, but it didnt seem to be, kinda what makes me think the problem is still there i just didnt drive the car long enough before the snow storm to recreate the lean condition.
So Im hoping to check other things and get more ideas