Vacuum question.

FormulaXtreme · Mar 29, 2007

Where the vacuum line plugs into the big black box before the throttle body I have no vacuum.
At first I thought it was odd because typically at wide open throttle the lower vacuum should let the regulator close and add about an extra 5-10 PSI of fuel pressure to the tips of the injectors.
However you don't have vacuum before the throttle body so why is it set up this way? I was trying to figure out why I have a shudder at idle that gets annoying and went with a slight lean miss idea and went after a vacuum leak.
I smoked the whole intake and found nothing and started it and unplugged the line to the fuel pressure regulator and was expecting to hear a hiss and the RPMs to jump a hair.
Nothing, Found this rather odd.
So if someone wants to pull off their line to the fuel pressure regulator and see if they have vacuum. It seems it should but because it is before the throttle body it shouldn't and it just doesn't make any sense.
Thanks in advance guys!

FormulaXtreme · Apr 2, 2007

Anybody?

Canyon08Z71 · Apr 2, 2007

You have vacuum on the other side of the throttle body... Pull the brake booster line to believe me.

The fuel pressure regulator has a vent line that keeps fuel vapors from being released into the atmosphere. They go back into the intake to be re burnt. That is all that does. Fuel pressure is at a constant 58 psi (I think), regulated by the spring presssure in the Fuel Pressure Regulator.

Check/clean the throttle body itself. Take it off to do it, that might be your idling issue, dirty TB.

FormulaXtreme · Apr 3, 2007

I know I have vacuum on the engine side of the throttle body. Engine wouldn't run if it didn't. I was just wondering why you would put a vacuum line to the fuel pressure regulator that doesn't get vacuum.
I have cleaned the TB many times and have replaced the fuel filter at 15K along with pulling the spark plugs and making sure they look fine which they did.
I am running premium gas in it now and am about to put the AC Delco Iridium plugs in it. They are the replacement to the stock platinum plugs that are in it now.
Who knows, all I know is the shudder is freaking annoying!

xtremecrew · Apr 4, 2007

my shudder was the trans.

DBNissan · Apr 4, 2007

FormulaXtreme said:
I know I have vacuum on the engine side of the throttle body. Engine wouldn't run if it didn't. I was just wondering why you would put a vacuum line to the fuel pressure regulator that doesn't get vacuum.
I have cleaned the TB many times and have replaced the fuel filter at 15K along with pulling the spark plugs and making sure they look fine which they did.
I am running premium gas in it now and am about to put the AC Delco Iridium plugs in it. They are the replacement to the stock platinum plugs that are in it now.
Who knows, all I know is the shudder is freaking annoying!

The MAF sensor may be fouled, you may have a bad o2 sensor, fuel filter could be dirty, plugs look clean but are really fouled, it could be a combo of any of that.

I too had the shuddering and replaced the plugs with Denso Ir plugs at 15,000 miles and it went away. Then I got a lean code DTC and found out that I had a bad o2 sensor which was caused by a faulty wire in the MAF sensor harness at 17,000 miles. Once the truck warmed up it would shudder at idle. Got that all fixed under warranty and then got the PCM tuned and it has been running smooth for the past 30.000+ miles. I just turned over 45,000 miles and did oil/filter change and AEM filter/MAF sensor & Throttle Body cleaning and it feels like a new truck again!

Shipwright · Aug 12, 2007

The search works, I think I can get an answer here! Is there a hose I can T into so that I can mount a vacuum gauge (I've had them in my vehicles for years and they are great diagnostic tools) but this is my first non carburetor vehicle (the closest was my S10 with a Webber) and my first one with a computer. Any help would be appreciated. Thanks

DBNissan · Aug 12, 2007

The only direct port for manifold vacuum is the brake booster hose.

Shipwright · Aug 12, 2007

Thanks, one more year on the warrantee, so I think I'll wait before I start cutting and splicing (just in case)!

DBNissan · Aug 12, 2007

Shipwright said:
Thanks, one more year on the warrantee, so I think I'll wait before I start cutting and splicing (just in case)!

Eh, it's just a rubber hose that can be easily replaced. I cut mine the first month after I got my truck lol

Shipwright · Aug 13, 2007

Well, I go for my inspection sticker next month! I think I'll do it right after! Desided to sell my condo and the stress and time with realtors is leaving not much time for anything else (light bar, backup alarm, TufOil and vacuum gauge on the to-do list).

Vacuum question.

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