EGR Valve on L98

Hmmm.... "badly stuck" can have two very different meanings:

The 1990 Vette has a basic negative backpressure EGR valve. It doesen't have
an electrical connection, so the ECU cannot directly determine if it is
functioning. The ECU calculates EGR functionality based on changes in sensor
output (knock and O2) when it "expects" the EGR to turn on/off. If it
doesen't see the change it expects, it will set a code 32 (EGR circuit). If
the EGR is stuck open, it will most likely set a code 45 (Rich exhaust). A
stuck-open EGR will reduce oxygen content in the combustion chamber at all
times though, resulting in poor performance (especially at idle).

basically...
Stuck open = runs bad, code 45 present, CAT damage possible
Stuck closed = runs well, no code 45, CAT damage doubtful

Fixitman

"gjt" > wrote in message
. ..
> Yep, that's what the guy at Firestone told me. If left alone and not
> corrected, the long term effect is loading up the CATs with carbon. He
said
> the CATS on an L98 are not cheap.
>
>
> "Butcher" > wrote in message
> ...
> >
> > "Eugene Blanchard" > wrote in message
> > news:QhLEi.26498$Pd4.10951@edtnps82...
> >> My answer is a little bit off topic but it concerns the egr valve.
Don't
> >> know where you live but if you don't have yearly smog tests to pass. I
> >> suggest you block off the egr valve.
> >>
> >> Now I don't have a 90s Vette but bear with me. On my 92 Ford Ranger,
the
> >> computer controls the EGR valve position using vacuum, then there's an
> >> EGR
> >> position sensor to verify that its working. So disconnecting anything
> >> brings up the Check Engine light and a trouble code.
> >>
> >> To get around the computer, I made a metal plate which matched the
> >> outline
> >> of the EGR valve gasket and installed it with the gasket. The EGR
> >> position
> >> sensor reports that the EGR is working and no error codes!
> >>
> >> Why block off the EGR? It recirculates the exhaust gas back into the
> >> intake
> >> manifold to reduce NOx emissions. Ideally, you want the coolest air in
> >> the
> >> intake, the EGR adds extremely HOT exhaust gas in. And it screws up
your
> >> fuel/air mixture - rather than clean outside air, you have hot CO gas
> >> coming back in. The result is less power and poorer gas mileage.
> >>
> >> Blocking off my EGR valve increased my overall hp (every little bit
> >> counts
> >> on a 2.3l ford) and increased my gas mileage by 20% around town.
> >>
> >> http://www.cadvision.com/blanchas/Ranger/egr.html
> >>
> >> Comments?
> >>
> >
> > Since my LT-4 doesn't have an EGR valve because of additional cam
overlap
> > I'm assuming the valve is supposed to close when rpm/throttle increases
> > (vacuum decreases, or should I say manifold pressure goes up), so it's
> > 'active' only with little or no throttle. And since the ECU controls
the
> > mixture thinking the EGR is working I'm wondering if the mixture will be
> > richer because of the blockoff (instead of just a cooler charge) --
> > enriching mixture is usually a good thing for power and throttle off/on
> > transition with these newer cars that run so lean, and more power means
> > less throttle at any given power setting so mileage would go up a little
> > maybe. But what about carbonizing the cat. over time because of the
richer
> > mixture? Maybe the fix will cause an expensive repair later on if the
> > cats. are left in place and block up?
> >
> > Just a thought...
> >
> > Butcher
> > '96 LT-4 CE
>
>

Butcher wrote:

>
> "Eugene Blanchard" > wrote in message
> news:QhLEi.26498$Pd4.10951@edtnps82...
>> My answer is a little bit off topic but it concerns the egr valve. Don't
>> know where you live but if you don't have yearly smog tests to pass. I
>> suggest you block off the egr valve.
>>
>> Now I don't have a 90s Vette but bear with me. On my 92 Ford Ranger, the
>> computer controls the EGR valve position using vacuum, then there's an
>> EGR position sensor to verify that its working. So disconnecting anything
>> brings up the Check Engine light and a trouble code.
>>
>> To get around the computer, I made a metal plate which matched the
>> outline of the EGR valve gasket and installed it with the gasket. The EGR
>> position sensor reports that the EGR is working and no error codes!
>>
>> Why block off the EGR? It recirculates the exhaust gas back into the
>> intake
>> manifold to reduce NOx emissions. Ideally, you want the coolest air in
>> the intake, the EGR adds extremely HOT exhaust gas in. And it screws up
>> your fuel/air mixture - rather than clean outside air, you have hot CO
>> gas coming back in. The result is less power and poorer gas mileage.
>>
>> Blocking off my EGR valve increased my overall hp (every little bit
>> counts on a 2.3l ford) and increased my gas mileage by 20% around town.
>>
>> http://www.cadvision.com/blanchas/Ranger/egr.html
>>
>> Comments?
>>
>
> Since my LT-4 doesn't have an EGR valve because of additional cam overlap
> I'm assuming the valve is supposed to close when rpm/throttle increases
> (vacuum decreases, or should I say manifold pressure goes up), so it's
> 'active' only with little or no throttle. And since the ECU controls the
> mixture thinking the EGR is working I'm wondering if the mixture will be
> richer because of the blockoff (instead of just a cooler charge) --
> enriching mixture is usually a good thing for power and throttle off/on
> transition with these newer cars that run so lean, and more power means
> less throttle at any given power setting so mileage would go up a little
> maybe. But what about carbonizing the cat. over time because of the richer
> mixture? Maybe the fix will cause an expensive repair later on if the
> cats. are left in place and block up?
>
> Just a thought...
>
> Butcher
> '96 LT-4 CE

You might of guessed it by now, but the cat is long gone...

--
Eugene Blanchard
http://www.cadvision.com/blanchas
Home of the DIY Hot Rod Kustom website

there is a concern that the cat would plug up with carbon if the egr is
disabled. You might of guessed that the cat is long gone too..

gjt wrote:

> Excellent info. Thank you!!!!!!!!!
>
>
> "Joe" > wrote in message ...
>> gjt wrote:
>>> Thanks guys......
>>>
>>>
>>> "Dad" > wrote in message
>>> ...
>>>> "Bob I" > wrote in message
>>>> ...
>>>>> Dunno about space issues on a '90, but I did the one on our '95 in
>>>>> about a half hour and that included waiting for the flat black paint
>>>>> to dry, because the replacement was cadmium plated and the original
>>>>> was flat black. I believe I gave about $65 for the valve at NAPA, so
>>>>> $70 is about right. Firestone will charge you dealer retail for the
>>>>> valve, so figure they will get what, maybe $140 for the valve, plus
>>>>> all the "nickle and dime" stuff like handy wipes and environmental
>>>>> disposal, and what ever other charges they can pad the bottom line
>>>>> with. Just make sure you get a clean gasket surface before you bolt it
>>>>> up.
>>>>>
>>>>> gjt wrote:
>>>>>> '90 L98 Vert. Service Engine Light would come on after about 15
>>>>>> minutes of driving. Any time I would turn off the engine, it would
>>>>>> reset. Comes right back on when it warms up. Took it to local
>>>>>> Firestone. They said my EGR valve was badly stuck. Said if I
>>>>>> continue
>>>>>> to drive as is, the Cats would eventually load up with Carbon. They
>>>>>> want $450!!! I think this is a bit excessive. Is there something
>>>>>> about an L98 that makes this a difficult job? From doing some
>>>>>> searches, looks like the going rate for the valve is around $70.
>>>>>>
>>>>>> Thanks for your input.
>>>>>> gjt
>>>> Bob's right on the money on this exercise ACDelco is the cheapest valve
>>>> at $60/$65 and they have 2 numbers 2145535 and 2141429 (plastic vacuum
>>>> fitting). Airtex is $70 and a metal fitting but shows no gasket with it
>>>> so check before you get back to work and there is none, FEL-PRO gasket
>>>> part # 70954, and ACDELCO part # 10077547. Wouldn't be a bad idea to
>>>> remove the valve to take it with you, but before you do that clean it
>>>> and the manifold up and see if the diaphragm will hold a vacuum and
>>>> work the plunger, if so put it back with the new gasket. The $450
>>>> repair just became a $2 job.
>>>>
>>>> --
>>>> Dad
>>>> 05 C6 Silver/Red 6spd Z51
>>>> 72 Shark Black/Black/4spd
>>>> 64 Red/red/white top/4spd
>>>>
>>>
>>>
>>
>> Take a close look. My '89, and I think all of '85 - '91 had the EGR
>> under the plenum --
>> not out in the open as in the LT1.
>>
>> If this is the case, you'll need a set of Torx bits and a flare wrench to
>> remove the plenun and the vacuum lines. It's tight but you can get the
>> EGR out without pulling the runners.
>>
>> As Bob says, get the little gasket for the EGR. Shop around and get a
>> partial intake gasket kit...one with just the gaskets between the runners
>> and the plenum. New throttle body gasket is also a good idea.
>>
>> If the '90 has a MAF, remove it but leave the throttle body hanging.
>> Disconnect the vacuum hoses to the plenum and check for an electrical
>> lead to a MAT sensor on the bottom of the plenum ...might not be one on
>> the '90. Gently tap the plenum to break it loose from the runners and
>> lift it out, vertically so as to not scratch the mating surfaces or drop
>> broken gasket material down the runners.
>>
>> Should be about two hours coming apart, 30 minutes to swap the EGR and
>> clean up the intake mating surfaces and a couple of hours putting stuff
>> together again. If the car has over 80K miles it might be good to clean
>> the inside of the plenum
>>
>> Looks like you're making about $ 85 an hour and have some "free" tools
>> for the next job.
>> Six-pack isn't included in this pricing. (8-O
>>
>> Suggestion: Not that I don't trust the highly qualified Corvette
>> specialists at Firestone... however, before you leap into this, dump the
>> codes and make sure you're dealing with an EGR issue.
>>
>> The Haynes C4 manual has some tests that can be run on the EGR. Making
>> sure there's vacuum to the EGR is a good idea-- a vacuum leak would
>> prevent the valve from working.
>>
>> HTH
>> --
>> pj
>> '89 auto / '02 6-spd

--
Eugene Blanchard
http://www.cadvision.com/blanchas
Home of the DIY Hot Rod Kustom website