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Posted by: lmcchesney Jan 20 2004, 08:45 AM

Thinking about designing the dual pump fuel rales.I was thinking of keeping both pumps up front trunk, and run a second 3/8" fuel line through the center tunnel so each large fuel line feeds each fuel rale on each side of the engine. The return like would be a solitary one from the fuel pressure regulator. However, on arrival to the front trunk, can you connect the return to each pump in series as in the diagram or will it require parallel?
Also, trying to get everything done before the return of the engine, is there anything I should change in the MPS at this time? ie. inserting a space for shims in the spring?
I do not think I have the resources for the replacement of the leaf springs, but is polishing helpful?

For image see http://www.shoptalkforums.com/viewtopic.php?t=62928&start=15

Thanks
L. McChesney[/url]

Posted by: ArtechnikA Jan 20 2004, 08:59 AM

two fuel pumps ?

what on earth problem are you trying to solve ?

Posted by: redshift Jan 20 2004, 09:33 AM

He's opening up a second front in the war of fuel delivery.

The paranoia is based on pseudo-petrodynamics.


M

Posted by: DNHunt Jan 20 2004, 09:50 AM

I can't imagine you need to provide that much fuel. You mention the MPS so you must be running D-jet. It might look cool but, I don't think I would want the potential for more problems. Maybe I missed something but, this seems too complicated.

Dave

Posted by: Bleyseng Jan 20 2004, 10:09 AM

Why not use a larger flow pump? I know the fuel pressure can vary by 1 to3 lbs when you punch it.

Posted by: lmcchesney Jan 20 2004, 12:31 PM

Probably not explaining it well enough.
Most of this data is from Ray Green's experience with the adjustment of D-jet.
The rapid increase to WOT, stock rales sees variation in fuel pressure (a decrease from a working 35psi to 20psi or lower). Since the injectors are effected by a reduction in working fuel pressure in the rales results in lean spots in the throttle range. In addition to Ray's theory, I plan to increase the holding volume of the rales, thus decreasing the change in pressure in the rales as a result of injector removing fuel from the rales. The reason is to eliminate the lean spots in the throttle range with an increased displacement engine combined with a D-jet FI system.
I agree, the use of a high flow pump could be used. The stock pumps are capable of 45-55L/hr. Additionally, because I am changing from a 1.7 system to a 2.0 system, I have two stock fuel pumps readily available.
L. McChesney

Posted by: ArtechnikA Jan 20 2004, 12:41 PM

okayfine, it's your car, do what you want...

IMO you're chasing a non-problem. have you verified that there actually -is- a lean spot commensurate with the reduced fuel pressure ? (due to the effect of the TPS throttle enrichment "acellerator pump" more fuel is injected during transients...) what is the duration of leanness, if it does occur ? if it's less than a revolution, i don't think it's hurting you.

maybe you're planning a HUGE displacement increase (doubling to 4,0-l or more...) maybe this is a sand drag engine and instantaneous transition to WOT is a major factor. that kind of operating environment would make a difference...

i think i'd just use a CIS fuel accumulator to tide the fuel RAIL over its potential low-pressure transient and be done with it...

Posted by: Mueller Jan 20 2004, 01:04 PM

A fuel accumilator* would be a much easier and effective solution**

*used on some CIS systems

**to problem which might not exist

I don't think there is a problem with the stock FI fuel system delievery.....a few of us have used/are using most all of the stock parts with an aftermarket ECU

If there was a problem, these aftermarket setups would run lean as well due to the fuel rail problem

Posted by: Bleyseng Jan 20 2004, 01:40 PM

I have never seen this problem on mine dyno runs, fuel charts but mine is a 76 with the larger pump up front.

Geoff

Posted by: DNHunt Jan 20 2004, 03:26 PM

I run my car with a wide band O2 sensor and have watched exhaust O2 levels in all sorts of driving. I have datalogged this and looked at it on the computer. I run a stock fuel pump with stock lines and fuel rails. My car flucuates constantly in terms of how lean, rich it is. The only time it ever crosses Stoich to a lean condition is when it under compression or very light load.

There is plenty of fuel available for acceleration enrichment, in fact, it was a challenge not to over enrichen it.

If I was worried about adequate fuel pressure I might consider a new larger pump but I wouldn't put in more plumbing and another electrical circuit. I'd keep it as simple as possible

Dave

Posted by: seanery Jan 20 2004, 03:37 PM

remember the KISS principle:

Keep It Simple Stupid

Posted by: kwales Jan 20 2004, 05:02 PM

If ya want a cheap accumulator, buy a fuel filter for a VW vanagon. They are quart sized and are installed after the fuel pump to feed a 2.1 Digifant system (modified L-Jet).

While chasing a fuel tank full of dirty gas problem, I accidently knocked off one of the wires to the fuel pump and the engine didn't even notice.

I was able to realize what I did, find the end of the wire, and reconnect it onto the pump without any change in RPM.

That ought to stop your fluctuations!

Think I want one of them on my teener after watching the engine run off the accumulator.

Ummmm....mebbe not. I hate watching 914's burn.

About $10.00 at Bus Depot.

Ken

Posted by: ejm Jan 20 2004, 06:20 PM

Fuel can be pressurized but it is not compressible. A filter will not take the place of an accumulator which has a spring loaded diaphragm to maintain pressure. Anyone who's had CIS and a bad accumulator will agree.

I agree with Seanery: KISS= reliable

Posted by: lmcchesney Jan 20 2004, 06:40 PM

Thanks Guys,
All very helpful information. That's why I ask these things on the forums. One persons experience may not be truly representative. The plumbing and wiring is very simple. With the engine out, I think I'll place the additional fuel line in the tunnel and wait to see what direct measurments will show. If the pressure is stable on one line, the additional line can always be backed up and use as a conduit for trans-tunnel wires.

Thanks again,
L. McChesney