31-32 at idle, jumps to 37ish momentarily when I rev it, and drops back down whether I keep it revved or not.

I'm just wondering if the pressure rise and drop when revved is an indicator of anything in particular, or is that normal? I haven't tried it yet with the vac line unhooked.

I think my pressure gauge is working ok, after hooking it up and bleeding it, I get a prime of 45, and it holds steady around 40-41 for awhile.

I replaced the fuel filter a few months ago, and it started easier and seemed to run better for awhile, but now I'm back to where I was. (my cold-start injector is unhooked. Needs a new connector) I was able to pump it lightly a few times and it would start, now I'm back to pumping it, letting up, turn off and back on, re-prime, and then it starts.

Chilton's is vague on pressure, Haynes says should be at least 34 at idle.

 

Burn that Haynes. And get a GM service manual, which says that the fuel pressure KOEO should be 37-47 PSI. The pressure rises when the throttle opens because you're changing the air pressure behind the regulator diaphragm momentarily until the engine vacuum normalizes.

Pumping the pedal does NOTHING on a fuel injected vehicle. Unless you hit the pedal to more than about 70% WOT, which shuts off the fuel pump while cranking. You have a pressure loss somewhere, which is why you need the second prime.

 

That clears up a few things, thanks. I thought about the pressure rising when I revved it, and realized I had it backwards over what was going on with the vac in that line to the regulator now that I read that.

It'll probably start normally once I get my CS injector hooked back up again. It's only the first start up of the day that is a PITA.

I'll start doing some figuring on what would cause pressure loss while running then. I figured it was the filter a few months ago, replaced it, and it was starting fairly easy for awhile and seemed to run better, but now I'm back to where I was.

Not sure how the filter might have gone bad over a few months, but I suppose it's possible. It's all I can think of at the moment, as I said, primes right up to 45 and holds at 40-41 for awhile, until I start it.

 

CSI is necessary for the cold starts... I found that out the hard way when I was forever getting stuck putting starting fluid down the brake booster hose to start the engine in the middle of winter... It also provides some extra fuel until the engine coolant reaches 100*F.

 

It actually just shuts off the injectors, pump stays running. Below is the table. It's pretty much the same for all OBD1 masks.








pull the vacuum line off to the FPR, if it holds 40-45 PSI PSI with the car running then the FPR is fine, it should drop down once the vac line is connected.


Now.. what happens to the pressure if you prime it then shut the car off?

Does it stay for a while or bleed off quick?

 

Ok, got sidetracked with other stuff and my truck (another weird fuel pressure problem), and had to remember where I put my vac line plugs, so on and so on.

Here's what I have.

42 running with vac line unhooked from regulator
45 prime
40-41 after prime with no start (holds pressure just fine for quite a while.)
31-32 running with vac line hooked up.

That all normal?

That 32 just seems low to me.

 

Umm, mine runs at about 36psi which the reference line on at idle. Id say your ok? But would wait for others to chime in.

 

Operating range for GM OBDI multi-port injection systems is 37-47 PSI. However, the FSM indicates that the system pressure may drop as much as 10 PSI with the engine running at idle.

 

Revving it up to around 1500rpm creates that momentary spike to 37ish, and then settles back at 32.

 

Thats normal, when burping the throttle with the ref. line hooked up it will see a decresed vaccum and raise the FP.

 

That cold start injector helps a LOT. I even went as far as buying a replacement 2.8 fuel rail so I could use mine as I was sick of having to put starting fluid down the brake booster hose on a 15-20* morning or having the battery die on me from cranking (with NO fuel pressure loss at 43 PSI). Yes, I know it's not that cold there now, but the point is the same.
You said you needed a connector for the CSI... Which one, the one on the switch in the manifold (with the BLUE connector) or the one on the injector itself? I have both (if I haven't thrown out the 2.8 harness I'm no longer using).

 

Side-tracked again for awhile there. The connector I need is the one that plugs into the injector itself. There's no shortage of them at Pick a Part. I can just grab one there next time I happen by.

Does anybody know of any bad side-affects of running the car with the pressure regulator vac line unhooked and plugged?

I'm curious if my power and mileage will improve at all if I raise the pressure a bit for about 120 miles. ( long enough for me to notice any improvement)

 

You're only looking at, on average, about a 4 PSI increase in fuel pressure with the line unplugged for the regulator... If that's what you're going to do, make sure to plug the end as it's a manifold vacuum line and you'll have a constant vac leak if you don't.

 

So we can block off the fuel pressure regulator and run without it?

 

You can....but NO dont do that. Leave the FPR ref line hooked up. This is my opinion on it.

 

I'll give it a try tomorrow. Will only take me about 80 miles actually to know if it helps.

Timing is at 10, sprayed water on most of the places it could have a vac leak and didn't notice anything, air filter is clean, maf clean, o2 is a few months old, cat is new, plugs, cap, rotor good.

I'm going to have the alignment checked, and might try a new t-stat. Temp has been a bit higher than usual.

Maybe I should say hell with it and stick the brake booster line in some seafoam.

My power and mileage are slowly getting worse, and there's no noticeable problems to work with directly.

There's a clicking sound sometimes somewhere behind the gauges that is rpm and load related, but i'll need to get the dash ready to yank out next time I drive it so I can maybe locate it while idling.

Holding the rpm steady is impossible, because it goes up and down about 100 rmp when holding it at around 1500.

Eventually I'll yank this 3.4 and put my old 2.8 back in, then start putting a 3500 top-end on the 3.4. Unfortunately, I never did get the 165 ecm swap to work, so I don't know for sure if a 3x00 distributorless ecm setup will work either.