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FPR Vacuum Line Needed?

LowKeyIdiots
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LowKeyIdiots Enthusiast

LowKeyIdiots

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I have a 2002 gmc sierra 1500 denali with the lq4, was running 45 psi fuel pressure idling i then changed the regulator and pump and now idles at 50 psi and is sluggish, if i remove the vacuum line on the regulator the pressure rises to 60 like oem spec says and it runs much better like this. My question is can i run the truck without the vacuum line connected? Will it go lean? Can i cap the line off? Definitely idles and pulls better with the line off.

riverbanks Senior Enthusiast

riverbanks

Posted
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With that port open to intake,you're leaning it out,or compensating for another issue,put it back original,try cleaning the maf,or throw it on a scanner,lazy c.t.s could run it rich

LowKeyIdiots Enthusiast

LowKeyIdiots

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3 hours ago, riverbanks said:

With that port open to intake,you're leaning it out,or compensating for another issue,put it back original,try cleaning the maf,or throw it on a scanner,lazy c.t.s could run it rich

Well with the vacuum line on my afr's are roughly 14.xx with that off they did go to 14.08 which seems lean to me but not much different from before. I really dont understand the truck its a 6.0 mated to a 4l65e with a 4.10 rear end so it should pull like a train but our escalade that is the same setup only with 3.73 rear end and supposed 10 more hp blows the doors off it like im not even moving lol

LowKeyIdiots Enthusiast

LowKeyIdiots

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2 minutes ago, riverbanks said:

That's at idle?what's the afr at 1500 and 2k rpms?

yeah it idles between 14.05 and 14.1 under load it stays around 14.5. i feel like its begging for more fuel, the ignition timing also goes up to about 55-60 degrees at 4k

CamGTP Senior Enthusiast

CamGTP

Posted
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Anything outside of power enrichment will run at or around stoich.

 

Stoich is going to be 14.68 in the tune and a wideband o2 sensor will report around 14-15 afr at idle and basically any rpm when not is power enrichment. You could zing the idle speed to 3,000rpm and it should still stay around 14-15 afr.

 

Once the engine is under the load the vacuum in the intake will cause the fuel pressure to rise. You should be able to watch that with the fuel pressure gauge as you drive.

 

I would be curious about other things like fuel trims for possible vacuum leaks or exhaust leaks.

LowKeyIdiots Enthusiast

LowKeyIdiots

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So i dont have like Hp Tuners all ive got is my obd scanner. At idle with the vacuum line connected Afr is 14.08 (which ended up being the same as the line off), Fuel flow was 0.37 gallons an hour (I will hook up my pressure gauge to the line when i get home) And coolant temp was 180. At 1500 rpm with line connected afr stayed at 14.08 fuel flow jumped to 1.29 gallons an hour. And at 2000 Rpm with line conected afr was still 14.08, fuel flow 1.65 gal/hr. For all of these data runs the coolant temp stayed at 180 and IAT's stayed at 37.4

Edited by LowKeyIdiots

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