So over the winter I installed LTs (with EGR and no AIR), 3” true dual pipes, 3” X-pipe and 3” Random Tech cats dumping into 2 ½” Corsas.

Now I have a code 32 (assuming low back pressure is causing this). The car threw no codes prior to this change and always passed emissions (did I mention I have to pass a sniff test every other year?).

I know I can get the chip programmed to delete the EGR diagnostics but I need to pass emissions thus the need for the EGR system to be functioning properly.

My question is has anybody found a solution to this short of reprogramming or adding more back pressure to the exhaust system (more restrictive mufflers in my case)?

The search function has revealed little other than the reprogramming solution.

Thanks in advance for the help.

Chris

 

I went through the same issue and unfortunately I can't help you with a new solution. I also got the dreaded code 32 after freeing up my exhaust system. After replacing all EGR components, hose, etc it was still throwing the damn code. As you alluded to, the only solution I found was to have a chip burned to delete the code.

 

Somewhere on the web I had seen where someone had used a couple of resistors to trick the computer. Can't remember where at the moment.

 

I have a similiar setup and no problems. Did the exhaust guy do O2 sensor(s) into the new Exhaust?
Take Care, -John

 

I should have stated that the O2 sensor(s) were up close to the manifolds/headers.
Take Care, -John

 

Mine has not thrown any codes over it. I do however think I may have gone a little overboard with the exhaust as it doesnt like to be below 1200 rpms going down the road. I suppose it could be an emissions thing but not enough to throw a code.

 

But are they heated O2 sensors?

I have (nearly) the same setup, and mine never once threw a code 32. You really need heated O2 sensors when you have a header. They are too far from the cylinder to work without it.

 

Yes, I have a single heated O2 sensor on the drivers side that was intstalled at the same time the headers were. Could it be a O2 sensor problem? My scanner says I'm in closed loop and the O2 sensor is fluctuating rapidly from lean to rich (say 100mv to 700 mv) at idle (haven't scanned it on the road yet) so I assume it's working. But then I am new to this scanning stuff.

Thanks everyone for the replys.

 

02 is fine.

From the FSM for '91:

CIRCUIT DESCRIPTION:

The Exhaust Gas Recirculation (EGR) valve vacuum is controlled by an Electronic Control Module (ECM) controlled solenoid. The ECM will turn the EGR "ON" and "OFF" (Duty Cycle) by grounding CKT 435. The duty cycle is calculated by the ECM based on information from the coolant temperature, air flow and engine rpm. There should be (NO EGR) when in park or neutral, Throttle Position Sensor (TPS) input below a specified value, or TPS indicating Wide Open Throttle (WOT), or the IAT sensor below 15~C (59~F). With the ignition "ON," engine stopped, the EGR solenoid is de-energized and by grounding the diagnostic terminal, the solenoid is energized.

The ECM will check EGR operation when:

* Vehicle speed is above 30 mph
* MAP is between 15 kPa and 70 kPa.
* TPS is between 8% and 30%
* No more than 0.4% change in TPS

NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for correct color code identification of circuit.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. By grounding the diagnostic test terminal, the EGR solenoid should close and hold vacuum. The vacuum may bleed off slowly, but this is not considered a fault.
2. This test will determine if the electrical control part of the system is at fault, or if the connector or solenoid are at fault.
3. By plugging the EGR valve side and ungrounding the diagnostic terminal, the solenoid valve should open and allow vacuum to bleed off through the vent
4. With the engine not running and vacuum applied to the valve, the valve should move to the fully open position.
5. Due to this engine using a negative back pressure valve, the valve should close when the engine is cranked over.

DIAGNOSTIC AIDS:

The ECM monitors integrator during a Code 32 test and must detect a change to pass the test. If a integrator is fixed to lean or fixed to rich when a Code 32 test is run, a Code 32 may set. Repair the problem which resulted in a fixed integrator. The EGR circuit can be inoperative if the P/N switch is mis-adjusted or faulty. The EGR is disabled when in park or neutral. To check the P/N switch refer to CHART C-1A.

Suction from the shop exhaust hoses can alter backpressure and may affect the the function of the EGR valve during in-stall testing.

Thoroughly check that the EGR vacuum harness is not plugged or restricted. If the vacuum harness is pushed on the solenoid to far, it may plug the end of the vacuum line and cause a Code 32. Make sure the vacuum lines are at the right locations of the EGR solenoid. The vacuum source goes to the orifice side of the EGR solenoid.


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With that said, I don't think backpressure is your problem. At idle the cam will overlap a hair and have vac in the EGR tube, but under any ammount of throttle is should pressureize the tube.


-- Joe

 

The problem is the lack of back pressure, not enough pressure differential to cause flow from the exhaust into the intake. The change in the integrator is what the computer wants to see, or you get code 32 on your '91.

The problem is not with the vacuum hoses. I switched back and forth between stock and true duals on my '91. No code with stock, code 32 with true duals.

The resistor trick is for the earlier L98 monitoring scheme which sences temperature in the EGR flow line.

 

Hrmm. Even without back pressure you'd think you would get enough flow into the EGR tube, especially when the manifold is under VAC.

-- Joe

 

The key to fixing this is to increase the valve opening.
Either increase the pulse width in the chip driving the
solenoid, or opening the orifice in the solenoid or the
valve operator. I don't know how to do chips. I "fixed"
this on a caprice by drilling the EGR valve restrictor with
torch tip drills. Moved up 1 size at a time til the check
engine light stopped coming on. Too big will cause a
stumble. Anethes 2nd pic shows it. benny

 

This is an excerpt I found on Positive Back Pressure EGR values:

The positive back pressure EGR valve can be identified by the letter "P" stamped next to the part number and date code. A back pressure valve is easy to spot because its pintle shaft is much thicker than the single diaphragm type. This is so because the shaft is hollow. The hollow design allows exhaust gases to flow into the shaft and push up on it. When positive back pressure in the exhaust system is sufficient, the shaft raises up and seals the built-in control valve. Once the control valve is closed, it allows applied vacuum to pull up on the diaphragm. Without back pressure to lift the hollow shaft and close the control valve opening, the EGR valve will not hold vacuum. It is bled off to the atmosphere. This design thus modulates EGR flow by modulating the applied vacuum. As engine load increases, so does engine back pressure, which causes the control valve inside the EGR to trap vacuum and open up. To test this valve, bring the engine up to 2,000 rpms to create back pressure, then apply vacuum. EGR should open and cause a 100 rpm drop or more. Exhaust leaks or a modified exhaust system can create havoc here. Adding dual exhaust or headers on a car designed for a single exhaust will reduce back pressure and set a Code 32 on GM cars. Positive back pressure EGR valves are used in simple vacuum controlled systems, as well as more complex pulse width modulated applications.

This is the link to the entire discussion:

http://www.asashop.org/autoinc/dec97/egr.htm

I was wondering if anyone had ever drilled the EGR pintle shaft larger and it looks like Benny has pulled it off with success. It seems like a rather inexpensive way to fix the problem.

Benny, can you desribe how you drilled the pintle shaft (by hand, drill press) and what size bits you started and finished with?

This has been a very helpful discussion. Thanks everyone.



Chris

 

The torch tip drills are from a local welding supply. The set looks like a
mechanical pencil and has a collet for holding the bit. The smallest bit
fit the hole in the orifice, so i worked up from there. It was trial and
error but it worked. Drilling it by hand helps cut the risk of damaging
the solenoid or valve. Sorry, i don't know the drill bit sizes, i should
have documented that better. Benny

 

Thanks for the help Benny.

I think I'll be shopping for some torch tip drills.

Give me a few weeks and I'll report back on how it all turned out.

Chris