[Gmecm] 93 CHEVY g20 VAN

[WopOnTour]

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..............
>
>
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