Speedfreak999

L98 EGR System
Theory of Operation
The function of the Exhaust Gas Recirculation (EGR) system is to introduce exhaust gasses into the intake under light throttle conditions. This lowers combustion temperatures which reduces NOx emissions and also reduces the tendency to ping.

The L98 EGR System consists of one static component and three control components, in addition to the ECM:
1) The EGR Tube connects between the right exhaust manifold and the EGR Valve; it conducts exhaust gasses to the EGR Valve.
2) The EGR Valve, located under the center of the plenum, controls the flow of exhaust gasses into the intake manifold. This valve opens when manifold vacuum is applied to it.
3) The EGR Solenoid, located (usually) under the front of the plenum on a bracket attached to a bolt on the thermostat housing, when activated by the ECM pulling it's Gry wire to ground, applies manifold vacuum to the EGR Valve. When the EGR Solenoid Valve is deactivated air flows through the filter in the solenoid to the EGR Valve, allowing the valve to close.
4) The EGR Temperature Switch, located atop the EGR Tube, is normally open when cold and exhaust gas is not flowing though the EGR Tube. This switch closes when heated by exhaust gas flowing through the EGR Tube. This pulls the EGR Diagnostic Dk Grn wire to ground.

At startup the ECM examines the status of the EGR Diagnostic Dk Grn wire. If this signal is at ground, indicating that the EGR Valve is open, the ECM throws the EGR code 32. After the ECM has activated the EGR solenoid it again checks the status of the EGR Diagnostic Dk Grn wire. If this signal is not at ground, indicating that the EGR Valve has not opened on command, the ECM throws the EGR code 32.
Test the EGR Valve
Once a code 32 has been detected, open the connector in the Or wire near the battery for a minute of so to clear the code(s).

Then carefully examine the manifold vacuum tubes between the plenum and the EGR Solenoid and those between the EGR Solenoid and the EGR Valve. Also assure that the air inlet into the EGR Solenoid is not clogged, as that would cause the valve to remain closed.

To test operation of the EGR Valve, apply vacuum to the EGR Valve and use a small mirror if necessary to see if it opens. If the EGR Valve fails to open, replace the EGR Valve. If you don't have a vacuum pump handy, simply connect a tube between the Fuel Pump Regulator's vacuum fitting on the right side of the plenum to the EGR Valve vacuum fitting and start the engine.

To test operation of the EGR Solenoid, reconnect the vacuum line from the EGR Solenoid to the fitting on the EGR Valve, start the engine, pierce the Gry wire and jumper it to ground while observing that the EGR Valve opens. If the EGR Valve fails to open, replace the EGR Solenoid.

To test operation of the EGR Temperature Switch connect the leads of a Digital Multi-Meter (DMM) between the EGR Temperature Switch lead and ground (with the DMM set to read DC Volts), start the engine, open the EGR Valve and observe that the voltage goes from 5Vdc to 0Vdc after a few minutes. If not, raise the engine idle to say 2,000RPM for several minutes to provide more exhaust gas flow. If the voltage reading remains at 5Vdc, replace the EGR Temperature Switch.

NOTE: 1) Before replacing a componet, verify related electrical wiring is in tact.
NOTE: 2) The connector in the Dk Grn wire from the EGR Temperatrue Switch is located behind the intake base to the left of the distributor. If you cannot open that connector, cut the Dk Grn wire, install a new EGR Temperature Switch, cut the connector from the new switch lead and splice it into the Dk Grn wire. use heat shrink tubing over the splice to provide weather and corrosion protection.

Fake the EGR System
This technique can be used when there is insufficient exhaust gas flow through the EGR Tube to heat the EGR Temperature Switch resulting in a code 32. This can arise when the EGR System has been eliminated and sometimes after long tube headers have been installed.

The idea is to use the ground command signal from the ECM to the Gry wire at the EGR Solenoid to provide the 0Vdc feed back signal to the ECM on the Dk Drn wire from the EGR Temperatrue Switch. However there is a problem of differing voltage levels between these two circuits.

When the ECM is not pulling the Gry wire to ground there is 12Vdc on that wire to the ECM. But when the EGR Temperature Switch is open there is only 5Vdc on the Dk Grn wire to the ECM.

So, we want to allow the ground command signal on the Gry wire to pull the Dk Grn wire to ground. Meanwhile we need to block the 12Vdc from being applied back to the ECM on the Dk Grn wire. This can be done by connecting a silicone diode (available at Radio Shack) between the Gry wire and the Dk Grn wire as follows.

EGR Temp. Sw Dk Grn wire diode EGR Solenoid Gry wire
-----------------------------------O-------------------|>|-------------O------------------------------------

Here the diode symbol ">" points toward the Red or Blk bar on one end of the actual diode.

NOTE: Before connecting the diode between the two wires, remove the negative battery terminal. After the diode is wired in (use heat shrink tubing over the diode and all splices), use your DMM to assure that resistance measured from the Dk Grn wire to the Gry wire is low AND that resistance in the reverse direction is very high. If not reverse the direction of the diode in the circuit. When finished, reconnect the negative battery lead and test the circuit.

To test the circuit, turn the key on, ground the Gry wire and verify that the signal on the EGR Temperature Switch has gone from 5Vdc to nearly 0Vdc. Actually it will likely be about .6Vdc.

Read and Learn,specially you CFI-EFI.

Redeasysport

Seen it before.Only needed for long tube header cars(mabey) if not LTs then fix it.

REDC4CORVETTE

And did you check your information in reference to an 86 with cast iron heads?

CFI-EFI

HUH???
Where did THAT come from? Did I post erroneous information on a code 32?

RACE ON!!!

Redeasysport

CFI your memory is slipping.This is the guy who had the post about faking the EGR code and you and I said to fix it because he said it was caused by lack of back pressure.Someone came in with a link at the end to the above info.I think he needs a few thousand more posts and to help 100's of people before he starts trying to school anybody IMHO.

CFI-EFI

I plead guilty to the memory slip. I think it jumps a tooth every day. Back pressure, my A$$! I can't imagine giving false info on a code 32, because my car doesn't even HAVE a code 32, and I readily admit, I don't know what it takes to trigger one. As with most codes, I'll bet as often as not, the cause isn't the EGR valve, itself. I CAN imagine recommending that someone fix the EGR, because when I have had mine disabled the fuel mileage dropped. Also, the car is more prone to knocking.

Thanks for the memory jog. If he knew all that, I wonder, why did he post such a question? Maybe we inspired him to do some of his own work and actually learn something. He presents that as fact for all L98s. Ya think?

RACE ON!!!

Speedfreak999

Is 35 years of successfull car building and drag racing enough or do I have to have experience in drag racing and modifing my keyboard too.

RETCH ON

CFI-EFI

Are you asking if your drag racing experience qualifies you?Or are you asking if you should go get the experience? What a MAROON!!!

Redeasysport,
Thanks again for the memory jog. That, and this most recent post, reminded me that this is the genius that suffered a loss of intake manifold vacuum because his exhaust system was too free flowing. In this thread he argued with everyone that attempted to help him and then he called us all. "whitetrash". Mr Moto had to close the thread. He has 35 years of something. I just haven't figured out what, yet.

RACE ON!!!

Redeasysport

Yep CFI a waste of typing.Like you and I did not read the link in his previous thread.So what he asked for a resistor to do it.He needed a diode.So he was wrong then and his attitude is showing again.We are not trying to save the world just trying to help those that need it and with 35yrs of experience he appearently does not need the help of this forum.

Speedfreak999

If you could only for a second drop the self important attitude
and get off your pedestal and stop your immature insults (I checked your comments to others questions) you might not get the negative resoponse.I do believe this a forum for Corvette enthusiasts not for building up your lacking self esteeme.Have a nice day

RETCH ON

eschoendorff

I guess he sure told you, eh CFI??? Sad thing is he's probably been working on that for a while. Form what I have read, the EGR system is part of the "big picture" for fuel injection rates and spark advance during part-throttle conditions (80% of the time for most of us). Why anyone would want to fake the system (on a stock, ie: no long tube headers) is beyond me. Long tube headers are another issue. But I certainly wouldn't consider faking the EGR system to eliminate a code 32 a good idea... maybe a last resort.

Mr Mojo

It's 40 years of age