what are the symptoms of actually running out of fuel pump or injector?

[thor'svr4]

Theres been a lot of discussion and posts on how much HP a particular injector will support and a few posts on how much hp a 255lph fuel pump will support. However I couldn't find any info on how to tell if you actually need bigger injectors or a stronger fuel pump.

last week i finally started messing around with increasing my boost level after installing water meth. i went from 16psi before water meth to 24psi with the water meth. after a few tweaks to the SAFC NEO i was doing consistent 24psi pulls with no knock showing on the data logger. However i noticed that once i got to 22psi the car would begin to lean out from 6,000rpm-7,000rpm. I tried adding a LOT of fuel using the SAFC to the 6,000rpm-7,000rpm range but no matter what i did the tune would still lean out dramatically. below 20psi my AFR's are normal but once i get above 20psi they begin to lean out at high rpms.

Since i wasn't seeing any knock on the data logger and the car wasn't breaking up i decided to add some more boost just to see what happens and the problem got worse as more boost was added. at 24psi my AFR's would lean out to 18+:1 from 6-7k, but the data logger still showed no knock, no timing retardation, and the car wasn't breaking up. I did notice that the IDC's were ~110% from 6-7k.

I know my knock sensor and data logger are working properly. so i'm starting to think that perhaps i'm running out of fuel injector or fuel pressure at high rpms. I'm currently running RC 550cc injectors and a hot-wired Walbro 255lph. I figured that would have been enough fuel for 13T's.

so back to my initial question, how far can you push a set of injectors? at what IDC% should you begin to think about upgrading your injectors? IIRC lawdog was running something like 140% IDC's on his 13G/360cc car a few years back. also is there any way to tell when you've run out of fuel pump without having an in-cabin fuel pressure gauge?

Thanks for any help guys

Edit: since i know someones going to ask if i pressure tested i'll answer that in advance. No, i haven't pressure tested recently. I will be doing that Thursday night. I'm not even sure if a boost leak would cause this issue, but i will check for any boost leaks Thursday night. I might even do the hairspray mod

[mb3000]

18:1? Holy shit!

Sounds like you're running out of pump to me. Of course if your IDC's are through the roof as well it might be a combination of both.

[Chris@Rvengeperformance]

you stayed in it with an indicated 18:1 afr at 24 PSI? you are insane.

There are a lot of variables here. Assuming your tune is ok you should hit fuel cut before it would go that lean if your injectors are too small.

13Ts have made 500 wheel, so it is possible your fuel pump is about out of breath. You can either put on a fuel pressure gauge or get a bigger pump, but the first thing I would do is actually measure the voltage you are getting at the pump. Barring that I'd confirm the pump isn't leaking inside the tank.

[thor'svr4]

I didnt see any knock or timing retard on the data-logger so at the time i was doubting my wide band... in hindsight that prob wasn't smart. The ECU cuts fuel based off the narrow band readings right? If so what would be a lean reading for a narrow band O2 voltage? Maybe my narrow bands weren't reading lean. it might be worth comparing the wideband reading to the factory narrow band readings on the data-logger.

i could easily swap in a walbro 400lph or 450lph fuel pump, but would that over run the stock FPR? im guessing that once i install a larger pump i will need an AFPR.

[Chris@Rvengeperformance]

the ecu does not do any such fuel cut based on narrowbands. It is strictly based on engine load.

[RealMcCoy]

I can't believe it was really that lean without kicking the rods into your lap.... I'm guessing you're getting some spark blow out and the unburned mixture is skewing the wideband.

In case you missed it from earlier posts... DONT DO THAT!!! If you see it heading north of 12:1 get out of the throttle...

[mb3000]

Just lean out the idle cells. Once you get going the engine consumes the extra fuel that the FPR can't handle and goes back to normal. You just lean out that area and then you're good to go.

[thor'svr4]

the ecu does not do any such fuel cut based on narrowbands. It is strictly based on engine load.

so would that mean my ecu thinks the engine load is acceptable?

I can't believe it was really that lean without kicking the rods into your lap.... I'm guessing you're getting some spark blow out and the unburned mixture is skewing the wideband.

In case you missed it from earlier posts... DONT DO THAT!!! If you see it heading north of 12:1 get out of the throttle...

i cant believe it was really running that lean without something going boom either which is why i'm not sure it's actually running that lean. so at this point ive got to either figure out what was causing the car to actually run lean (fuel pump / injectors) or what was causing the wide-band to perceive the exhaust mixture as being lean (maybe a boost leak?)

and don't worry i haven't continued to do any pulls since then. my car sits in the back yard while i'm at school.

Just lean out the idle cells. Once you get going the engine consumes the extra fuel that the FPR can't handle and goes back to normal. You just lean out that area and then you're good to go.

good to know.

[Chris@Rvengeperformance]

if you run ACTUAL 100% IDC the ecu recognizes this based on the airflow it sees and if it is happening for a long enough period (a sec) then it will hit fuel cut and it feels like you ran into a wall.

[mb3000]

so would that mean my ecu thinks the engine load is acceptable?



i cant believe it was really running that lean without something going boom either which is why i'm not sure it's actually running that lean. so at this point ive got to either figure out what was causing the car to actually run lean (fuel pump / injectors) or what was causing the wide-band to perceive the exhaust mixture as being lean (maybe a boost leak?)

and don't worry i haven't continued to do any pulls since then. my car sits in the back yard while i'm at school.



good to know.

Exhaust leak would cause the wideband to read lean, as long as the leak is before the sensor.