[Gmecm] 93 CHEVY g20 VAN

[Jay Vessels]

Hi there!

First, a note:  While every GM TBI I've seen is referenced to the 
atmosphere, if memory serves some of the 2" bore 454 TBI regulators had 
a vacuum reference.  Maybe I'm just remembering a DIY hack?

<* CSH on *>

I understand the "traditional" fuel line/regulator/return line system 
(i.e. TBI, TPI, etc.) where fuel constantly flows through the fuel line, 
through the regulator, and back through the return line.

On something like the LS1 that has a single fuel line and no return, how 
is the pressure controlled?  I would have expected a PWM-driven pump and 
a fuel pressure sensor, where the PCM controls fuel pressure in some 
form of closed-loop control.  From WopOnTour's description, this is not 
the case.

So, now for two questions:

1)  How does the single fuel line system work -- how does it maintain a 
constant relative pressure across the fuel injector?  If the pump has 
constant power on it, does it just "deadhead" against the injectors?  If 
there is a regulator, how does this regulator work?

2)  Could such a system be adapted to older EFI systems like a TBI or 
TPI swap?  Could a single fuel line system be made to work on a TBI or 
TPI install?  I assume this would mean either some code patches to the 
ECM (i.e. a BPW adjustment based on MAP to compensate for the change in 
pressure) or a standalone controller that would read fuel pressure and 
adjust pump power accordingly.

Jay Vessels
1982 Chevrolet S-10 Sport, 2.8V6 TBI
1984 Chevrolet S-10 Blazer Sport, 2.8V6 (TBI pending)

WopOnTour wrote:
> Sorry Phil but it's not the LS1
> I've just looked at the FP wiring schematics for the LS1/LS2 from 
> 1997-2006 and NONE of them have the ECM/PCM controlling the fuel pump 
> voltage in any way. (Other than turning on the relay of course). Go back 
> and look at your GM training manuals or eSI Description and Operation 
> again, it very clearly states what the vacuum compensation on a pressure 
> regulator is actually for. Quite simply it's for LOWERING fuel pressure 
> when vacuum is high, not RAISING it when vacuum is low (at least on a 
> naturally aspirated engine).
> An injector's delivery specification (lb/hr. g/s, cc/min etc) can only 
> be maintained when a consistent pressure differential exists between the 
> internal injector pressure and the point to which it's being 
> delivered.Since the software calibration in the ECM/PCM assumes this 
> injector delivery, it must rely on the regulator to apply the 
> appropriate compensation. Newer systems (like the 2.2 Ecotec in the 
> J-body for instance) don't even have a vacuum source connected to 
> regulator (even though they have a vacuum line) and instead the 
> compensation is handled by reducing injector base pulse width when MAP 
> pressures are low.(Maybe THATs what you meant??)
> 
> On the GM dual-point TBI (as this van would have) the regulator gets 
> it's atmospheric reference via a large vent that the regulator diaphragm 
> chamber seals against (a large foam o-ring) when the regulator/injector 
> housing is installed onto the TB. Since this places it OUTSIDE of the 
> airfilter it does not require a "vent" line such as the Tracker or other 
> import TBIs.If this regulators diaphragm ruptures, you would know it in 
> hurry as fuel would be running directly out the back of the TB onto the 
> intake.
> 
> So my point being it would be almost impossible for the regulator system 
> in this particular fuel system to result in a rich mixture without a 
> significant and obvious fuel leak. Of course if the return line was 
> somehow restricted... But until Michael.b get back to let us know what 
> his fuel pressure is, it will be of course extremely difficult to come 
> up with ALL of the possibilities that would result in a RICH condition. 
> Considering the fact that I don't recall any failure particularly 
> "chronic" in the TBI system of that era.
> HTH
> WopOnTour
> ----- Original Message ----- From: "Phillip Kuhn" <pmkls1 at yahoo.com>
> To: <gmecm at diy-efi.org>
> Sent: Saturday, December 31, 2005 5:16 PM
> Subject: Re: [Gmecm] 93 CHEVY g20 VAN
> 
> 
>> Wop on tour,
>> the GM returnless systems that use the pcm to control
>> fuel pressure are the newer systems used on the ls1
>> engine and all of it's derivatives and basically any
>> new engine they use that has a returnless system which
>> the list is pretty long nowadays but it first appeared
>> on the ls1. I do not remember ,however, what type of
>> signal they use but I think it is a pwm type signal.
>> As far as what I wrote about the vaccum reference for
>> a fuel pressure regulator that is exactly what GM
>> trainers tought me  the purpose was. Reguardless of
>> what the purpose of the vaccum signal is it DOES
>> significantly affect fuel pressure and fuel pressure
>> significantly affects fuel mixture. What I am
>> interested in more than anything else at this point
>> though is what is wrong with this guy's van. And back
>> to my original suggestion, fuel pressure regulators
>> are notorious for having the diaphragm rupture and
>> leak raw fuel which on most engines gets sucked
>> directly into the engine causing it to smoke black and
>> die (exactly the symptoms described about this van).
>> Also, somebody else mentioned the IAT sensor going bad
>> which on GM cars when they do they usually read
>> something like 40 degrees below zero and will also
>> cause a significantly rich condition and smoking and
>> wont always set a DTC. So at this point I would like
>> to hear back from the guy that has the van to see if
>> he has found anything yet..............