99 l67 swap sputtering under wot and over 3800 rpms (Page 1/3)
jhobbins OCT 07, 06:31 PM
Hey guys, I'm having an issue where if I either ease into the throttle up to 3000 rpms, it breaks up when it gets there. I have 40psi of fuel pressure at idle and it maintains that pressure even when it's breaking up. If I go wot the engine also breaks up. According to my torque pro app, the commanded spark advance drops way down when it starts sputtering, so it seems like the computer is pulling the timing. Does this sound like an ignition issue, or a wiring issue? I've got fresh 93 octane fuel in it.
olejoedad OCT 07, 10:14 PM
Fuel pressure is low to start with....
jhobbins OCT 08, 12:23 PM
Oh really? I'm more familiar with SBC's so I thought that was a good pressure reading. I'll swap the fuel filter and see if that helps any
olejoedad OCT 08, 01:24 PM
You need 50+ lbs and rising higher under boost.

What fuel pump are you using?
OntarioKev OCT 08, 09:57 PM
Check fuel pressure at idle with the vacuum line to the regulator disconnected.

With the boost referenced fuel regulator under vacuum the pressure is lower and it increases with boost. Please let us know what the pressure is when running with the vacuum line disconnected.
jhobbins OCT 09, 09:52 AM
I'm not 100% what pump is in there, i bought the car with the swap already in progress. The PO said it was an SUV fuel pump that was recommended on the forums, but he couldn't remember which one. I'll test the fuel pressure again when I get home today thanks
jhobbins OCT 09, 05:01 PM
Key on, vacuum line unhooked, 41psi. Idleing 40psi.
BadNewsBrendan OCT 09, 05:20 PM
This link says GM service manual says 45-55: https://www.fastfieros.com/...uel_pressure_L67.htm

Also gives some procedures for testing fuel system.

"America is all about speed, hot nasty bad-ass speed" - Eleanor Roosevelt

1984 3800 II SC Build

jhobbins OCT 09, 05:50 PM
Scratch that, I'm an idiot. I unplugged the wrong hose. 40 key on engine off, 50 engine idling with the fpr vacuum line unhooked. Probably a bad fpr then?
Dennis LaGrua OCT 09, 05:54 PM
If your fuel pressure is up to spec and the exhaust unrestricted then you need to take the next step. I realize that many DIY mechanics don't like hearing this but a full diagnostic scan of the PCM will pinpoint the trouble. The symptoms you describe can be one of any number of things. Failing to do a scan is working in the blind. .

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