Fuel/Knocking problem

[Steve87GN]

Hey everyone. So, here's what I'm trying to tackle now, and I'm not sure if the two are related or not. First, I've had a knocking under high-throttle, high-boost for a while now that I can't get rid of. I just put in new injectors on Sat. and its still there. However, I noticed that when I went to do the new injectors, there was no fuel pressure in the rail whatsoever. The car had been sitting for about 12 hrs., give or take. Now, the car is a little harder to start (probably because I'm not using my factory-original injectors that were leaking).

So, on Tues., I hooked up a fuel pressure gauge to the rail. She was holding at 36 PSI. That's a little low, isn't it? I did the WOT test (pulled the vacuum line off), and the pressure dropped to 32 (at least, that's the WOT test on my 93 Z28). Again, isn't that low? So, I shut the car off with the gauge still attached and let it sit. 30 min. later, the pressure had jumped up to 43 PSI. However, it still took a little effort to kick over. So, I shut it off again and came back an hour later, only to find the pressure had dropped down to around 17 PSI-ish.

For the fuel system itself, here's what I'm running (to the best of my knowledge):

New Tomco 30 lb. injectors from Kirban
Bosch 237 fuel pressure regulator (TTA FPR?)
Supposedly, a Walbro fuel pump (not sure how much I believe that)

For ignition (in regards to the knock, if it is not fuel-related):
Stock coil
Taylor 8mm plug wires
NGK Iridium UR4IX plugs (part #7401)

Any ideas? As always, thanks for all your help everyone.

 

[TurboDave]

What do you mean by "knock under high boost"? What do you consider high boost??

And what is this WOT test you refer to??? PLEASE don't tell me you removed the vacuum hose from the fuel pressure regulator and went WOT

Don't worry too much about what the fuel pressure is doing when the car is off. It wont stay stable, with heat soak, etc. and will bleed down over time anyway.

 

[Steve87GN]

What do you mean by "knock under high boost"? What do you consider high boost??

Well, past about 2/3 throttle and the boost gauge pegged, I start getting a knocking sound plus a loss of power. The best way I can describe it is like a ball bearing in a tin can. Under normal driving or up to about half throttle, she's fine.

And what is this WOT test you refer to??? PLEASE don't tell me you removed the vacuum hose from the fuel pressure regulator and went WOT

The WOT test I'm referring to is to pull off the vacuum line and see what the pressure is at idle. No, I wasn't feeling stupid enough to pull the line and then go to WOT. To my understanding, this is supposed to simulate how the FPR acts under WOT conditions. At least, that's what to do with the LT1. I'm not sure if it is the same with the LC2 or not.

Don't worry too much about what the fuel pressure is doing when the car is off. It wont stay stable, with heat soak, etc. and will bleed down over time anyway.

So, the bleed off is normal then? Good to know.

 

[notacarlo]

Well, past about 2/3 throttle and the boost gauge pegged, I start getting a knocking sound plus a loss of power. The best way I can describe it is like a ball bearing in a tin can. Under normal driving or up to about half throttle, she's fine.are you using the little led boost gauge in the dash? Don't use that as a reference, get an analog gauge. Those things are eye candy after 20+ years and lose their calibration.



The WOT test I'm referring to is to pull off the vacuum line and see what the pressure is at idle. No, I wasn't feeling stupid enough to pull the line and then go to WOT. To my understanding, this is supposed to simulate how the FPR acts under WOT conditions. At least, that's what to do with the LT1. I'm not sure if it is the same with the LC2 or not.the LT1 wasn't boosted was it? Fuel pressure will rise 1 to 1 with boost. base FP set at 45, run 10 psi boost and the FP should be 55psi.



So, the bleed off is normal then? Good to know.

Totally normal

 

[Steve87GN]

Well, past about 2/3 throttle and the boost gauge pegged, I start getting a knocking sound plus a loss of power. The best way I can describe it is like a ball bearing in a tin can. Under normal driving or up to about half throttle, she's fine.

are you using the little led boost gauge in the dash? Don't use that as a reference, get an analog gauge. Those things are eye candy after 20+ years and lose their calibration.

Yes, I am referring to the stock LED boost gauge. I do plan on adding an analog boost gauge, but that isn't until I am ready to make the switch to a complete analog gauge cluster.

The WOT test I'm referring to is to pull off the vacuum line and see what the pressure is at idle. No, I wasn't feeling stupid enough to pull the line and then go to WOT. To my understanding, this is supposed to simulate how the FPR acts under WOT conditions. At least, that's what to do with the LT1. I'm not sure if it is the same with the LC2 or not.

the LT1 wasn't boosted was it? Fuel pressure will rise 1 to 1 with boost. base FP set at 45, run 10 psi boost and the FP should be 55psi.

No, my LT1 isn't boosted. But still, even with that 1:1 ratio, then my fuel pressure is way low. Like I said, with the vacuum line attached to the FPR, I'm only seeing 36 PSI. With it off, I'm only seeing 32 PSI. So, the problem is the FPR, right? Or, at least, that's a good place to start, right?

So, the bleed off is normal then? Good to know.

Totally normal

Thanks for the second. I do feel much better about the bleed-off now.

 

[mikestertwo]

No, my LT1 isn't boosted. But still, even with that 1:1 ratio, then my fuel pressure is way low. Like I said, with the vacuum line attached to the FPR, I'm only seeing 36 PSI. With it off, I'm only seeing 32 PSI. So, the problem is the FPR, right? Or, at least, that's a good place to start, right?

Something is not right. When you remove the vacuum line the pressure should go up not down. What regulator are you using? 233? 237? aftermarket adjustable? Get a boost gauge on that thing so you know where your at.

 

[Steve87GN]

Something is not right. When you remove the vacuum line the pressure should go up not down. What regulator are you using? 233? 237? aftermarket adjustable? Get a boost gauge on that thing so you know where your at.

Its a 237 unit, but I have no idea how old it is. I can smell gas in the vacuum line that connects to the FPR. That does mean at least the FPR is bad, right?

 

[Amelio]

you really need to get you a good fuel pressure gauge and set your static pressure...I have mine at about 38 psi line off .....I would then suggest to drive the car......as you accelerate you should see a fuel pressure increase .....about 1psi of fuel pressure with 1lb of boost.

If this is not the case then yes you may have a bad FPR or pump or line restriction....before you put a new one on make sure you have no restrictions in either your feed line or return line as this will cause a pressure issue.

Good luck!

 

[87granny]

Did your line come off the turbo housing by any chance after the Y if so the thing will boost to high hell did you check that by any chance if it did put it back on wire tie it and road test it and see how it acts also you may wanna get an aftermarket boost gauge the in dash LED's are horribly inacurate

 

[TurboDave]

87granny makes a good point. If all you have is the stock boost gauge, and it's pegged as you say, then you really have NO idea what boost you're actually running.

Until you actaully know how much boost you're making: 1. DO NOT get into boost until you know. 2. DO NOT rely on the stock gauge until verified.

 

[Steve87GN]

Did your line come off the turbo housing by any chance after the Y if so the thing will boost to high hell did you check that by any chance if it did put it back on wire tie it and road test it and see how it acts also you may wanna get an aftermarket boost gauge the in dash LED's are horribly inacurate

You know what? It actually did come off. Go figure. I put it back on and zip-tied it on and test drove it. Noticeable difference, but the knock is still there.

you really need to get you a good fuel pressure gauge and set your static pressure...I have mine at about 38 psi line off .....I would then suggest to drive the car......as you accelerate you should see a fuel pressure increase .....about 1psi of fuel pressure with 1lb of boost.

If this is not the case then yes you may have a bad FPR or pump or line restriction....before you put a new one on make sure you have no restrictions in either your feed line or return line as this will cause a pressure issue.

Good luck!

Well, from what you and most everyone else has said, the FPR is shot (which doesn't surprise me). I'll check for restrictions as well, but I would bet that FPR has been on there for a while and is probably due.

Well, what really sucks now is that the clutch master cylinder on my 93 Z now needs to be replaced, plus I gotta get it ready for the smog check coming up. So, the bad little Buick goes back into slumber for a bit. Thanks for all the help though guys, I really appreciate it.