93 fuel pressure

[cbr600rx7]

So today I was checking the fuel pressure on the 93 2.3 and at first every thing was good. It showed 40 psi with key on/engine off. However with the engine on pressure drops almost out of tolerance down to 30 psi. This is where it gets interesting because when I unplug the vacuum source from the fuel pressure regulator pressure jumps to 40 psi and holds it even when reving the motor. To me 30 psi seems very low with a newer flue pump and new flue filter.

 

[RonD]

It is fine at 30psi.

Your engine has GOOD vacuum, which is............GOOD, and that pulls open Fuel Pressure Regulator more.
REV engine, as vacuum drops you should see pressure come up.
At idle, high vacuum, you do not need much fuel or pressure, when you accelerate the vacuum drops off and pressure goes up because you need more fuel, the more load on the engine the lower the vacuum and the higher the pressure, so it balances out

 

[tomw]

If it maxes out at 30, which is what I think I understood, the pump pressure seems lower than specification. It could be the fuel filter or the pickup screen is plugged.
Do you pump a measured amount that is enough? Do you have hesitation or misfire? Do you have low power, such as difficulty climbing a hill? The previous would indicate a possible fuel supply or pressure problem. A pump can have good pressure, yet not deliver fuel due to restrictions not measured without a volume or flow test.
tom

 

[cbr600rx7]

When the FPR is unhooked it will run a 40-42 psi. The fuel filter, fuel pump, and fuel screen are newer. The reason I am looking into it is my truck is having difficulty climbing hills some times even in 4th. Reg cab 2.3 with 26 inch tires and explorer 8.8 with 3.73s

 

[RonD]

That would be correct fuel pressure with no vacuum assist.

Test engine vacuum after warm up, should be 18" to 21"
Lower could mean your compression is getting lower, which means reduced power under load.
You can also use vacuum to test for exhaust blockage.

If fuel filter or pump was the issue it would "feel like running out of gas" as you climbed the hill and engine would also start to Ping/knock as fuel Leaned out.
And no mention of that

If 1993 had an EGR Valve then I would block its vacuum hose and go for a test drive, could be computer is opening the EGR valve too much, which can reduce power under load

 

[cbr600rx7]

Testing the vacuum off of the tree on the manifold is between 16-17hg at idle. Raising the RPMs to about a 1000rpms and holding it brings vacuum up to 18-19hg. Not sure if it matters but this was taken at about 600rpms and after running for about 90 seconds.

 

[cbr600rx7]

Also the I replaced most of the intake gaskets recently and did a full tune up to include a denso 02 sensor. The only thing I didn't replace that I wished I had was the PCV valve.

 

[RonD]

Don't see any major issue with compression at steady 16-17", a bit low but could be PCV

Good vacuum at 1,000, higher RPM compensates for small air leaks, so nothing much to worry about.

If you Blip the throttle, open it and close it quickly, you should see vacuum drop to 0-2" then pop back up to 16-17 quickly, slow return to 16-17 means possible exhaust blockages.

Raise RPMs to 2,500-3,000 and hold steady, vacuum should come up and stay steady, if it is slowly dropping then for sure exhaust blockage

 

[cbr600rx7]

Holding the RPMs at 2500 for a good 15 seconds showed a steady 18 HG of vacuum. If I close the throttle blade fast vacuum jumps to around 20-22 HG.