Weird fuel pressure problem

[1158]

This is for a boosted 98 GSR I have listed the pertinent setup details in the text below

I'm having something strange happen with with idle/low load fuel pressure once the engine has come up to temp. My pressure will start off at 38 psi (which is what base is set as) but drop about 10 psi as the engine warms. The drop doesn't occur all at once, but it isn't a steady decrease either. It seems like pressure starts dropping once the car gets into closed loop. Only very light load and idle is affected which is causing a lean condition at idle and light cruise. I went out for a drive this afternoon and the data log showed fuel pressure of 62 psi when manifold pressure was 24 psi. So that is spot on. Even part throttle at higher tps values but while still in vac show fuel pressure right around 38 psi.

I went through and checked all the wiring for the fuel pump and even tried another 30 amp relay. The wires are all 8 gauge and all have good continuity. The pump is a walbro 400 lph, regulator is an A1000, using OEM filter which is relatively new, ID 1000 injectors with mostly stock lines, -6 AN from filter to fuel rail then -6 AN from rail to regulator then back to stock return line. As far as I can tell I have no fuel leaks (no fuel smell anywhere) and car is not acting like there is a vacuum leak. Battery is less than a year old (optima yellow top). I use a float charger if the car isn't going to be driven for more than a week (rarely happens). I have both a fuel rail gauge and a pressure sender running off the FPR with both showing the fuel pressure drop.

I have some partial data logs but not a complete one showing the transition from full pressure at idle to low pressure at warm idle. I will get one tomorrow showing the whole event if that will help.

Currently the alternator control is not disabled and I wonder if this could be the issue. I looked at battery voltage and it's right around 14 the whole time. I'm wondering if although the battery volts appear good the amperage is dropping when the alternator output is cut which is then causing the pump to put out less fuel. That makes sense to me but that doesn't always mean anything. I don't think the issue is ignition related but I am using the Hondata CPR setup so I would guess 4 coils need more juice than 1 so want to throw that out there.

I guess my first question would it be plausible for the alternator control to cause this issue. If not does anyone have any other ideas? I didn't think to disable the alternator control until after I had finished with the car for today so I haven't had a chance to test that hypothesis yet.

TIA

[1158]

Well disabling alternator control didn't help. I have a datalog of the issue but it's 24 minutes in length since the problem is so gradual. It's too long to post up the whole thing. How would you guys like me to handle that?

[Spunkster]

Without seeing datalogs of it, it is really hard to give much advice on this.

[1158]

Without seeing datalogs of it, it is really hard to give much advice on this.

Well do you want the entire 24 minute datalog or just part of it? I just know I can't attach the entire thing. I guess I could break it into 4 or 5 sections if you want. Do you just want to see the section when fuel pressure starts dropping? I guess I can post that up right now.

[1158]

Here is a section of the datalog. Note the large voltage drop at 4:32 is the fan coming on. This is normal and has been like that forever. You will notice the voltage does climb steadily back to where it needs to be. I checked the battery voltage as well as did some testing on the alternator. Both seem to be good. Battery voltage with car off is 12.8-13. With car running battery voltage is around 14.10 and reving the engine does not change the voltage by than a few tenths of a volt (always goes up).

I did not check what voltage at battery with everything turned on. Maybe I should check that too.

[1158]

So no ideas I take it. This is driving me nuts. AFR is fine for first 20-30 min I drive the car then it acts up and idles at high 17s to around 18 AFR. Short term trim is pegged at 10. I mean I can raise S trim to 20 or 25, about where it needs to be, but that doesn't really address the problem.

Someone suggested maybe the pump is going but would that really cause this issue? Under full load/boost it's fine which makes me think it can't be the pump.

Just want to add I don't really think this a S300 problem. Just wondering if anyone here has any insight.

[Spunkster]

The graph appears to be a linear drop in pressure and appears to be related to temp(heat soak). It could just be your fuel pressure regulator.

[1158]

The graph appears to be a linear drop in pressure and appears to be related to temp(heat soak). It could just be your fuel pressure regulator.

I had that thought. It isn't that old (less than 3 years) and is gonna piss me off if it is that. I guess I can get another one to test.

Thanks for the feedback.

[1158]

So figured I would add an update.

I was looking around under the hood after driving the car today and noticed a very light sheen around the injector #1 seal. Touched it with my finger and found it was wet. Barely smelled of fuel but I'm guessing because it was just so little fuel. However it didn't appear that the leak was coming from where the injector goes into the fuel rail. That area was dry.

I took the injector plug off so I could get a better look at where the leak might be and I noticed the inside of the plug was wet, also with faint fuel smell. It appears the injector is leaking fuel up through the plug. Anyone ever have this happen to ID1000s?