Do I need a new Fuel Pump?

[Victory]

I've been having problems with knock recently and I checked my fuel pump pressure (line- off) to ensure I'm at 42-43 and found a problem.

Upon start up (whether cold start up or starting again after I've taken it out for a spin) if I check my fuel pressure it reads 42-43 line off. As I let it idle (again hot or cold), the pressure would slowly drop to under 40 and driving around I would get knock.

At this point (after the slow drop) if I readjust the the line-off pressure to 42-43 and take it out again I will have little knock and some small retard (<2), but when I cut the car off then start it up again my line-off pressure idling will be at 45.

Is this the kind of behavior that occurs when your FP is dying? Could I have a leak somewhere?

Thanks for the help,

 

[bmackinnon]

Is this the kind of behavior that occurs when your FP is dying?

Sounds like it... :frown: You REALLY need to verify that the FP is rising 1 lb per lb of boost under operating conditions... this will likely confirm your suspicions. I WOULD NOT run the car hard until I performed said check.... you are risking a catastrophe otherwise, and the odds are not in your favor....

 

[Steve V]

If you haven't already,turn off the alky and turn down the boost. Do you have a way to watch the pressure when you go into boost? Start with this let us know.

 

[Victory]

I don't have a fuel pressure gauge that I could see while getting into boost. I have a rail mounted liquid one.

I do have TurboLink v4 and a Scanmaster could either of those help? Is there another way I could do this?

 

[Adam Connell]

Sounds like it... I have been having tuning issues but the e85 kills any knock I might have... I only get about a 10lbs worth of fuel when I get on it. Im 99% sure my walbro is the culprit because everything else checks out.

 

[Steve V]

You need a guage that will make it to the windsheild so you can see what the pressure does at WOT. Or you can just replace the pump and hope that's it.

 

[Just a Six??]

Get the guage you can tape to the hood or an electrical you can mount in the car but do that before buying new parts for a possible cure. The guage will get used many many times over the years so its well worth it!! Caspers has one for about $50 that will reach the windshield.

 

[Victory]

This is the one I should pick up?

Casper's Electronics, Inc.: Fuel Pressure Extension Gage

 

[Steve V]

That's a good one to have!

IMO..your fuel is dropping a few pounds after it warms up probably not gonna cause knock esp since you have alky. Did you turn up the alky and see if the knock went away? Our cars need more fuel when it's cold outside. Cold air is more dense=the need for more fuel.

 

[TurboV]

im with steve, adjustments are sometimes necessary with a change in weather. Make sure your tune doesnt need to be verified. STAY OUT OF IT until you get that gauge.

 

[Victory]

It's actually been doing this since late in the season (before old man winter kicked in). I brought a new fuel pressure to double check problem, but I brought a rail mounted one.

I'll pick up the Casper's gauge and revive the thread when I receive and test the car. How should I run the test...just find a spot to run WOT? What, exactly, should I see on the gauge?

To answer Steve's question...in the fall I tried turning up the alky (from 6 to 8) and I still had more knock than I thought I should have. I have a hotwire kit, but I'm not sure what pump is in the car now (I brought it in spring '06). I'm thinking it just might be time to change it out, but like you guys are writing I want to troubleshoot it right and learn something. I don't want to just throw money at it and hope it fixes itself.

Plus the only money I have left is change throwing that would scratch the finish.

 

[Steve V]

How many lbs of boost?How much knock,when does it start?

Fuel pressure should rise 1lb of fuel per 1 lb of boost.

Base presure 43 +20 psi=63,is enough fuel for 20 lbs of boost. Add or subtract accordingly.

As said before turn the boost way down,12 lbs or so. Turn off the alky. Do you still have knock?

 

[bmackinnon]

IMO..your fuel is dropping a few pounds after it warms up probably not gonna cause knock esp since you have alky. Did you turn up the alky and see if the knock went away? Our cars need more fuel when it's cold outside. Cold air is more dense=the need for more fuel.

Well, your opinion is wrong... and your advice to turn up the alky is just plain terrible... It is absolutely imperitive for the fp to rise EXACTLY 1 lb per lb of boost... dropping fp as the car warms is absolutely indicative of a problem. ALL cars need more fuel when the weather gets colder, BUT NOT via turning up the fuel pressure... that's why the ecu runs in closed loop and corrects for the increased fuel requirement itself via increased INT's and BLM's based on oxygen sensor readings.... sorry for the rant, but misinformation in this context can have catastrophic results.... verify the fuel pressure, OP... and if it's dropping, 'sumtin wong'..... and don't run it hard until you've assured yourself this problem is fixed....

 

[bmackinnon]

Or you can just replace the pump and hope that's it.

Sheesh.... No further comment required.....

 

[bmackinnon]

How many lbs of boost?How much knock,when does it start?

Fuel pressure should rise 1lb of fuel per 1 lb of boost.

Base presure 43 +20 psi=63,is enough fuel for 20 lbs of boost. Add or subtract accordingly.

As said before turn the boost way down,12 lbs or so. Turn off the alky. Do you still have knock?

Now that's more like it!! :smile: I freaked out without reading further.... I guess I'm prone to do that now and then.... again sorry for the previous rant, but I just don't want to see anybody grenade their motor based on unsound advice.... I'm calm now.... :smile:

 

[86GN-862+2]

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