[Gmecm] 93 CHEVY g20 VAN

Mon Jan 2 03:49:52 UTC 2006

Good find Tyler
Funny they would only worry about the pump noise at idle on the XLR. My old 
L-van sounds like a 747 when it gets down to 1/8 of a tank -especially from 
outside!!
WOT

----- Original Message ----- 
From: "Tyler Townsley" <ttownsley at sprynet.com>
To: <gmecm at diy-efi.org>
Sent: Sunday, January 01, 2006 8:35 PM
Subject: Re: [Gmecm] 93 CHEVY g20 VAN

> Here is the current setup for the Corvette and XLR, the only ecm control 
> mentioned is on the XLR to reduce pressure at idle.
>
> http://service.gm.com/gmtechlink/images/issues/mar04/TLMar04e.html#f1
>
> Tyler
>
> 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..............
>>>
>>>
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