I'm battling a rich issue on my 85 and have gone through 2 Holley Regulators (diaphragms gave way on both of them at low PSI, really odd) and am now back to stock diaphragm with an AFPR. With both the stock FPR and AFPR I can't get any lower than 48 PSI uncapped, but with the Holley unit I can easily get 34 PSI.

The question I have is do I need to do anything to brand new Delphi diaphragms to "break" them in before using them? I have 2 and both won't allow for very low pressure at all. I have performed all of the tests in the FSM and even made my own test return line that I know was clear and free of kinks. No matter what I can't get my FP down low enough. Any suggestions? I'm debating giving the Holley one more chance hoping for a bad run of diaphragms. This is probably the most frustrating thing I've dealt with on this Vette.

 

That does seem strange. With a cheap (relatively speaking anyhow) replacement aftermarket (NAPA) diaphram/spring and an adjustable cover on mine I can get the pressure wound down to a bit more than 30 psi. without vacuum attached. Motor running (it'll show a bit higher pressure than that if the motor is Not running and the fuel pump is just jumpered on).

The same brand "stock" diaphram/spring on my Truck ('85 vintage TPI setup on it - long story) without an adjustable cover, just the stock tin can, reads at about 40 psi. no vacuum, running.

Both vehicles have "stock" replacement aftermarket fuel pumps in them - I don't even know what brands.

I don't know what you would do to "break in", or whatever, a new diaphram. I also don't know why Holley diaphrams would be failing. It's not like there is That much possible pressure in these systems.

To get lower fuel pressures it would need Less spring pressure. Take a hammer and flatten out (from the inside) the top indent of a stock steel cover and see what happens. That would compress the regulator spring less. If you went too far you could bend it back In some, or shim the spring back up (the NAPA regulator comes with a stainless washer in the box for apparently that purpose, If you wanted to use it..)

I suppose you Could have a high pressure if the Pump flowed so much that the return line couldn't keep up with what the regulator was "dumping" back to the tank - which leads me to wonder if you have a restriction someplace in the return line. Does the FSM test have you just dumping the return into a can or something right off the fuel rails to ensure no back pressure? I could look in My manual and answer that for myself..

Or maybe a restriction in the Porting at the regulator base? I had a Rust problem in the regulator on Mine not long after I bought it - the stamped ring on the diaphram assy had rusted (appeared to be just plain steel), I assume from water in the fuel collecting in the depression right there in the regulator base, and that rust had built up to the point where it was preventing the seat from sealing properly. Result - really fast pressure bleed off, etc. I suppose if a chunk of rust or whatever had gotten stuck in the return line or port that it could restrict it...

There are non -"stock" aftermarket pumps available that have much higher flow rates and possible pressures, do you know that you have a "stock" one in the car? Also - is the pump connected to the carrier assembly tube with the "check valve", or "pulsator", thing in place, or is it just connected with a piece of hose? That little valve functions as a pulsator to "shake" the regulator and make it work more reliably. Perhaps without it the pressures would be higher - I'm guessing

 

I actually did some thinking and I figured 2 things...

1) I did some more looking over my Holley today. I don't think it ruptured, I think it just slipped (cover) a little during the install. I'm going to look over the machining of it. I know of a few people that had this issue. I know for a fact that I can get that thing down to 30 psi and as high as 65. I'm gonna give this regulator another shot.

2) If I remember correctly, I think the diaphragm for the 85 was different than the 86-90 or so. I'm pretty positive mine is just a Delphi replacement for "85-90". So after some thought, I'm going to see if I can put a little heat on my extra diaphragm to do pretty much just what you were suggesting too. It's a good experiment that might resolve my issue.

As for the test, I did go by the FSM and even fabbed up my own return line to dump into a gas can. That's how I learned that my return line (Saginaw fitting back to fuel tank) is OK cause the pressure was the same both times. I'm really thinking I just have to adjust that spring some the more I sit here and waste my time thinking about that and not thinking about my job. :-)

 

I do know for a fact that this has a stock fuel pump just replaced last Christmastime actually. As for the rest, I'd have to pull it and check. Unfortunately I did not install the fuel pump, but you have me curious now. Gives me something to mess with on my vacation time next week.

 

 

You know, I doubt that I can get mine up to 65 psi no matter how far I twist that adjustment screw in the cover - I don't think the pump will get that high even dead headed. 50-55 is about it, I'll guess. It does hold the 40 (or so) psi even under full throttle, for as long as I keep it there under load though - no issues with Volume capacity.

A lot depends on the individual pump. I've had new replacement pumps that wouldn't pull the 40 psi per spec and taken them right back to the parts store for refund. I won't be buying a pump (or anything Else electrical) from That place again (a chain which will go unnamed, but starts with Autozon..).

I don't expect you would have gotten a "stock replacement" pump with a really high flow rate or pressure bypass, but I guess anything is possible.

 

You know, I just looked at that wording... I really meant I've had it, for a fact, as low as 30, but is advertised up to 65... though I've never attempted to get it much higher than 45 PSI. That probably makes more sense.

 

All it took was a little MAPP gas. I am now able to achieve the fuel pressure I'm looking for with no problems at all. This actually fixed my tune issue up quite a bit too.

 

FWIW, the Holley diaphragm actually manged to pull itself off from where it's pressed into (where the spring rests). That's why fuel was blowing past the diaphragm on me there.