EGR system

[secondchance]

I believe EGR system was added after 93 model year LT5.
I always thought EGR came into play after cold start and its purpose was to aid in faster warm up in order to control emissions.

A few minutes I was talking to a local mechanic regarding light detonation at light throttle and he was saying that it may be due to clogged EGR valve.

Does EGR come into play after motor has been fully warmed up?

Your thoughts?

[Jeffvette]

I believe EGR system was added after 93 model year LT5.
I always thought EGR came into play after cold start and its purpose was to aid in faster warm up in order to control emissions.

A few minutes I was talking to a local mechanic regarding light detonation at light throttle and he was saying that it may be due to clogged EGR valve.

Does EGR come into play after motor has been fully warmed up?

Your thoughts?

EGR was added in 93. It was planned for the earlier models but was not included, hence the boss on the side of the plenum.

What you are thinking of is the air injection system which helps push air in to the exhaust system to help the cats get up to temp quicker.

EGR only functions while at a cruise.

[Jagdpanzer]

Hey Jeff,
Do you know under what specific conditions the EGR valve opens and closes?
Does it operate either fully open or fully closed or is it proportional?

[secondchance]

Hey Jeff,
Do you know under what specific conditions the EGR valve opens and closes?
Does it operate either fully open or fully closed or is it proportional?

That was my next question.

[Aurora40]

I suspect he is referring to a malfunctioning EGR valve. In which case the operating parameters for it are not that relevant. If the valve won't close properly, you can have driveability issues. I don't know that detonation is one of those issues, though.

I don't know how prone the LT5 system is to that, nor how easy it is to check or clean the valve, etc, since my car does not have EGR.

Do you get detonation at light throttle?

FYI, as Jeff mentioned, the AIR pump warms the cats up faster. EGR I believe is to prevent excessive NOx emissions by cooling down the combustion chamber

[secondchance]

I am getting mild ping when fully warmed up, 2000 to 3000 rpm, moderate acceleration.
One suggestion was to drive the hell out of the car (to 7000).

I was thinking of running BG K44. Should besafe, right?

[carter200]

Quit running that cheap 87 and step up to some 93 :p

[secondchance]

Quit running that cheap 87 and step up to some 93 :p

Ha, ha. Very funny!
I use to run Sunoco 94 'till they droped it about 5 years ago. Since then, either Exxon or BP (Amoco) 93 - Mostly Exxon.

[Kevin]

are you talking about tip in knock or does this happen with no throttle changes?

[secondchance]

At tip-in. Starts right around 2000 to 2200, sometimes continuing to around 2600 to 2800.
This only occurs with slight acceleration and goes away if I push the throttle more aggressively.

[Kevin]

sounds like tip in knock to me, nothing we can do about it. But i'll defer to the experts ehre

[carter200]

At tip-in. Goes away if I push the throttle more aggressively.

Sounds to me you need to mash that pedal on the right more and let that big dog eat :wink: Just funnin with ya :wave:

[secondchance]

sounds like tip in knock to me, nothing we can do about it. But i'll defer to the experts ehre

Are you saying this is typical? If so, I don't recall this occurring w/ my 91.

[secondchance]

Sounds to me you need to mash that pedal on the right more and let that big dog eat :wink: Just funnin with ya :wave:

I hear you. I just have that "gotta run perfect" OCD.:hello:

[Kevin]

tip in knock is normal and there is no way to get rid of it.

[Aurora40]

By tip-in, you mean the knock that occurs when the secondaries open, correct? There's apparently some small amount of time between when the butterfly opens and when the extra fuel injector starts firing that causes a temporary lean condition and triggers knock retard.

If that is what you mean, then it may depend on your definition of "moderate" throttle. I.e. is it enough to open the secondaries.

That also shouldn't continue to happen while maintaining the same amount of throttle.

At least, this is my understanding. Not based on my expertise or experience (of which I have little).

[secondchance]

O.K. Back to metal (in our case, plastic) to the metal (fiberglass) option.

Seriously, I am thinking BG K44. Anyone had any good or bad experience with this?

Another option is GM top end cleaner spray into the horn (I know, interference motor, do not let the motor die...).

[Aurora40]

Have you scanned the car? Is it pulling timing and registering knock events?

[secondchance]

I talked to Jim from Westminster yesturday. He has a scanner but the connector will not fit 94.

He said he will bring Tech 1 just in case to Frederick for Cumberland run. I hope he remembers.

Will you be there?

[QB93Z]

I have the Tech 1 (an OBD I scan tool), but I do not have an adapter to plug the Tech 1 into a 1994 or 1995 ZR-1.

Note: "OBD I" means Onboard Diagnostics, first generation.

It turns out that in 1994 GM shifted the Corvettes to the newer OBD II style connector (under the steering column) but kept the OBD I computer interface. SO, I need an adapter (part # 3000053)

I also have a ADL Cable and interface to use the TTS DataMaster software to record operating engine data. The cable I have works on my 1993 and my 1990, but I need a special ADL cable to scan the later year ZR-1's.

I have ordered the ADL cable, but I won't have it by Saturday's outing.

I am looking for the Tech 1 adapter. Does anyone know where I can get one?

Jim

[Aurora40]

I've the '94-95 OBD-II style cable and can use it with Datamaster or the EZ-Scan 6000. You've got a PM.

[secondchance]

Last Friday I made an excuse to drive out towards Leesburg (not quite all the way but about half) since Route 7 is relatively quiet after Baron-Camaron. I opened her all the way up in 2nd and 3rd about half a dozen time.
On Satureday I drove out to Frederick, MD along I-270. After Gaithersburg traffic was relatively light allowing me to open up all the in 4th a few times.
This "petal to the metal" approach seems to have cleaned out most of, if not all, 4-5 years worth of DC daily commute carbon build up.
When hot I get split second of what sounds like a light pining around 2300-2500 rpm. Is this what you call a "tip-in knock", Kevin?

[QB93Z]

......On Satureday I drove out to Frederick, MD along I-270. After Gaithersburg traffic was relatively light allowing me to open up all the in 4th a few times.
This "petal to the metal" approach seems to have cleaned out most of, if not all, 4-5 years worth of DC daily commute carbon build up.......

Cleans it out and IT IS A LOT OF FUN!!!! :dancing:dancing

The knock that I was experiencing two years ago was not an "audible" thing. (At least not by me.) The knock sensor on the block is very sensitive. There were only a few (less than 10) detected knock counts showing up on the scan, but that is enough for the ECM to put in spark retard (lower the spark advance) and lower the power.

Jim

[secondchance]

Cleans it out and IT IS A LOT OF FUN!!!! :dancing:dancing

The knock that I was experiencing two years ago was not an "audible" thing. (At least not by me.) The knock sensor on the block is very sensitive. There were only a few (less than 10) detected knock counts showing up on the scan, but that is enough for the ECM to put in spark retard (lower the spark advance) and lower the power.

Jim

Hey, Jim,

I will be replacing the chip w/ Haibeck version tomorrow (seems Phil has all the parts I need!). If there are any spark retard due to false knock, knock filter embedded in Haibeck chip should take care of it.

Last Friday I drove west on Route 7, passed Baron-Cameron, drove for a few miles revving up to 7000 in 2nd and 3rd a few times. Then I pulled a u turn and got on Baron-Cameron to go to Homedepot in Reston.
Along the way at the stop light 350Z provokes me. Well, I was out there to clean out carbon, right?

Well, I spanked him pretty good twice. He will be staying away from C4s for a while.

[Kevin]

I will be replacing the chip w/ Haibeck version tomorrow (seems Phil has all the parts I need!). If there are any spark retard due to false knock, knock filter embedded in Haibeck chip should take care of it.
.

marks chip will not get rid of the retard it will just reduce the amount of timing pulled and allow it to recover faster. :cheers:

[Aurora40]

Hey, Jim,

I will be replacing the chip w/ Haibeck version tomorrow (seems Phil has all the parts I need!). If there are any spark retard due to false knock, knock filter embedded in Haibeck chip should take care of it.

Last Friday I drove west on Route 7, passed Baron-Cameron, drove for a few miles revving up to 7000 in 2nd and 3rd a few times. Then I pulled a u turn and got on Baron-Cameron to go to Homedepot in Reston.
Along the way at the stop light 350Z provokes me. Well, I was out there to clean out carbon, right?

Well, I spanked him pretty good twice. He will be staying away from C4s for a while.
Knock due to carbon buildup and such is not false knock. I'm surprised you can hear it though.

7 grand in 3rd gear! :mrgreen:

[secondchance]

Knock due to carbon buildup and such is not false knock. I'm surprised you can hear it though.

7 grand in 3rd gear! :mrgreen:

First, demon I had been chasing was a real detonation, not loud but certainly I could hear it. At the time I replaced and checked all 2ndary vacuum lines under the plenum. It helped but could not totally get rid of pinging. At the time, the mechanic who worked on the car scanned and told me passenger side 02 readout was fluctuating (or comment similar to this) but could not offer any course of action.

Then about a month ago it got real bad (I could hear rattling noise). Simultaneously she would idle at 1000 then sputter down to 750 when the compressor kicked on, back to 1000 when compressor disengaged.

Finally, I concluded one of my primary injector went bad and on Sunday before last summoned all courage and dug in.

Pulling the plenum I discovered broken check valve stem, replaced both check valves, confirmed sealed vacuum and confirmed secondary flap actuation w/ vacuum pump.

I also replaced all 16 injectors.

Once buttoned up car ran infinately better and also high idle/idle fluctuation was fixed. However, when hot (207+ temp), I could still hear very muted pinging at 2300 to 2800 rpm under light throttle. A few excursions into 7000 seems to have pretty much cured this (probably blew out carbon deposits). However, I can still hear one brief ping when secondary seems to start coming on (2300 or so rpm). This may be what Kevin was referring to as "tip-in knock.

As for false knock(nothing to do w/ hearing it), I am aware that over active knock sensor falsely believe there is a knock when shifting at full throttle and retards timeing unnecessarilly. Haibeck chip has a filter to avoid this situation, from what I understand, maintain timing advance avoiding hp loss.