KevinEF7

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?

KevinEF7

I should probably mention that my pressure gauge is mounted on the rail, and those pressure numbers are with the vacuum line connected

skill178

pull the vac line and check it, should read 40-47 without the line.

KevinEF7

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??

KevinEF7

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

skill178

If its reading 40 you have sufficient pressure. Is the car tuned or stock base map?
Stock fuel system other then the pump?

KevinEF7

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)

4drEF

Sounds like your FPR is working properly.

Get a fuel pressure check on both the in and the out ports on the fuel filter.

skill178

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?

KevinEF7

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

skill178

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

KevinEF7

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

KevinEF7

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

4drEF

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?

KevinEF7

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

skill178

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

Former User

Clogged fuel injectors, valve clearance needs adjusting, failing wide band O2 sensor?

KevinEF7

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

skill178

valves tick at all?

KevinEF7

None audible over the open downpipe... if that counts... no valve tick

skill178

probably the pump or the regulator

KevinEF7

Any reason why? Or way to prove either now that I have the pressure up?

skill178

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

4drEF

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.

KevinEF7

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