I finally threw a pressure gauge on my rail just to make sure I didn't have any issues before I tried to continue with what seemed like an impossible tune to nail.

It would run rich at idle seemingly no matter what I did to the tune, and then under any kind of load it would fall flat on it's face and either die instantly, or give me a nice big backfire out the intake.

The pressure gauge told the story. 75-85psi at idle, tons of needle fluctuation, and pressure drop to 35psi under an unloaded throttle blip. I popped it WOT real quick at idle and let it climb to 2500 rpm or so, and pressure dropped to 30psi and gave me a really nice backfire out the intake. Imagine what it's doing under load if I can get a 40psi drop by blipping the throttle...

Next on the agenda: New fuel rails, walboro 255gph in tank pump, mallory 100psi regulator, and all new line back to the tank. We suspect a combination of a weak pump and a failing regulator or clogged return line, but this is all stuff that needs to be replaced anyhow. Also ordered up everythign I need to redo my brakes. They are in horrible shape from all the sitting the car has been doing before and during my ownership. Rotors, pads, new rubber lines, new steel lines, new hardware, new calipers, parking brake cables already replaced, maybe master...

I'm glad I'm graduating in a week and a half, I will finally have time to make some progress on this piece. Oh, and money to work on it. That is usually an important thing too.

Anyways, make sure your base engine is good before you start chasing ghosts. I jumped to conclusions and wasted 2 months worth of tune time on this thing. It's not as bad as it sounds though, I only get a chance to tune a couple hours every couple weeks

Soon enough I can start steam rolling all these issues though. (I have a 100 item list of just 'basics' that I need to finish). Anyone want to paint my car? That will be coming soon too

Sorry if this post is all over the place, I'm about to go to bed here. I just wanted to get this reminder out there to anyone else who may be dealing with this.

 

Is there a return line on the regulator
Sound like the reg is never opening.
Good thing you already plan to replace it a run a new return line.

Good reminder advice though.

 

I don't understand why people like running small fuel pumps. The *extra* capacity of the larger pumps allows for a faster recovery, IF there is a downward spike in pressure during AE. IMO, it can't be understated how important a good fuel pump is. FWIW, I run 2, Walbro 340s for that reason. The second one comes on line at ~2 PSI of boost. There's lots of guys running faster then me, with less pump, but alot more guys replacing headgaskets then me.

Yep, that's why I yammer about base lining, and knowing what things are like, when things are **KNOWN**. Compression tests, leakdown tests, knowing one's fuel pressure, starting with new plugs, cap, rotors, etc, etc, are mandatory. Periodic replacing of ALL vacuum lines, is something else alot of people fail to do.

There's no such thing as paying too much attention to detail.

 

Few of the reasons I went with that one:

1. Cost. I got it brand new for $100.

2. It's just a 305 that I never plan on running over a low 13 with. 680 gallons per hour would be much to much overkill for me

3. If I do need the volume later on, I can always upgrade.

BTW, what do you run with that GN grumpy?

 

$100 will about get ya a 340.

It's not just about how much you use in an hour, it's also about how much AE you NEED, and you need an excess of capacity to have a quick refill rate.

Usually 93 Octane, but I can run 89 with only a 1-2d of Knock.

 

Grumpy, there are some guys having issues with the stock TBI fuel pressure and a walbro 255lph pump. At idle, it seems as if the pump is pushing a lot of volume and the 3/8 supply is fine with it, but the 5/16 return line isn't... or the passage in the regulator isn't large enough and is creating the restriction. In any case it's been claimed to have the pressure creap up. If it's true, that would be one reason why not to go with a huge pump. Now in a perfect world we'd all have the $$ and time to spend replacing the fuel lines with some 1/2" both ways and a large regulator... but it's not .
I for one haven't had any issue with the 255lph but that's with 28psi and a Holley TBI which has a larger regulator.

 

Forget I said anything....
When I saw 26 PPH injectors, and a 730 I thought it was single plane conversion, for TPI, not a TBI.

 

Just be more specific next time. MPFI, you can't have too much pump, with carb and TBI, you can.

 

It is a 7730/port injection setup

Would you recommend that I tape a pressure gauge to the windshield and watch for any transient drops in pressure during AE or PE? Or is the drop in pressure so quick that I won't be able to pick it up on an analog gauge?

I should have specified better, I was inquiring about track times

I remember talking to you a while back on a no runner manifold you were piecing together, but I never really followed up with you on it.