Code 32 on an '87 V10 305

[Boydness]

I just purchased an '87 V10 4x4 with the 305 TBI and on the first long trip the Check Engine light came on...

I was driving for about 15 minutes (maybe 13 miles) and the light came on. After turning off the engine, the light cleared and did not come back immediately when restarting the engine. It seems to only come on after 15 minutes or so of driving. There does not seem to be anything wrong with the running condition of the engine as there is no visible or audible performance issue when the light is on...

When I disconnected the battery to clear the code, it was 3 or more driving trips before the light and the code returned.


Any ideas?


There are two different issues possible according to: http://www.iroczone.com/specs/TroubleCodes.htm

Code 32

Baro sensor circuit
Short between sensor terminals B and C or faulty wiring therein.
Faulty or loose wiring and/or connections at the ECM (Terminals 1, 21 and 22).
Faulty Baro sensor


Code 32

EGR system
Faulty EGR valve.
Faulty or loose wiring and/or connections at the EGR solenoid.
Faulty, loose and/or leaking vacuum hoses to EGR valve.



I would appreciate any suggestions.


Steven

[72 CustomCamper]

My 90 Blazer does the same thing. Code 32. On my truck it's because the EGR valve has gone bad...


Chuck

[Boydness]

How long have you had the light on? I assume the light must have been on this truck for a good while and not something that just happened to appear now.
How would I know if it was the vacuum component or the actual EGR valve itself?

Doesn't a bad EGR valve cause the engine to run poorly (or not at all) and could leave you stranded on the side road?


Steven

[72 CustomCamper]

My light has been on for at least a year. Only comes on after driving over 50 for a few minutes. I found out it was my EGR valve by using a vacuum gauge on the EGR. I tried using an aftermarket EGR but they wouldn't pull a vacuum either. Talked to the local Chevy dealer parts dept and a new valve was over $100...


Chuck

[rfmaster]

Originally Posted by Boydness

I just purchased an '87 V10 4x4 with the 305 TBI and on the first long trip the Check Engine light came on...

I was driving for about 15 minutes (maybe 13 miles) and the light came on. After turning off the engine, the light cleared and did not come back immediately when restarting the engine. It seems to only come on after 15 minutes or so of driving. There does not seem to be anything wrong with the running condition of the engine as there is no visible or audible performance issue when the light is on...

When I disconnected the battery to clear the code, it was 3 or more driving trips before the light and the code returned.


Any ideas?



Code 32

EGR system
Faulty EGR valve.
Faulty or loose wiring and/or connections at the EGR solenoid.
Faulty, loose and/or leaking vacuum hoses to EGR valve.



I would appreciate any suggestions.


Steven

Steven you have a TBI system in your '87 and to troubleshoot that pesky Code 32 you may want to perform the following functional check:

Manually open the EGR by lifting the diaphragm by hand at idle and see if you can observe idle stumble. Be careful not to burn your figures or get them caught. If the passages are plugged there will be no difference in the idle when you manually push the EGR valve. Verify that EGR diaphragm is not blown with a MitiVAC hand pump - EGR should hold vacuum.

This code usually gets set because the EGR does not work or if EGR passages are obstructed with carbon. Code 32 also rears its presence when exhaust system is modified since exhaust back pressure determines amount of exhaust gases entering intake manifold. Depending on application there are several different kinds of EGR valves used. - Another subject all together.


The following is the test criteria that must be met for EGR DTC 32 test to take place. Information is for a 1993 C/K TBI 5.0, 5.7 and 4.3L (s/t), but 1987 used a similar ECM logic:
The actual test that sets the DTC code 32 is done when:
-Throttle position is between 10% and 25% angle
-Steady throttle with no more then 2% change in throttle
-Above 32 MPH closed loop operation
-Max short term fuel trim (integrator) is less then 6 counts for 3.2 seconds
-desired EGR command greater then 40%
-MAP above 47.5 kPa or less then 15 kPa.

Basically the ECM shuts off the EGR and expects to see a predetermined outcome.

The ECM monitors the EGR effectiveness by momentarily de-energizing the EGR solenoid which in turn shuts off the vacuum to the EGR valve. With the EGR closed, the fuel integrator counts must fall (mixture gets richer as exhaust gases are no longer diluting intake mixture) within calibrated window. The fuel mixture called for must change by an expected amount. After failing the test twice a code 32 will be set. This test is usually done during long, steady state cruising.

Your ECM should have service number 1227747 (unless replaced with later service unit) and probably has a four letter broadcast code (BCC) = ASDZ, ASDU or similar. If you can post you BCC code specifics of your calibration can be found (or not).

//RF

[Boydness]

Originally Posted by rfmaster

Code 32 also rears its presence when exhaust system is modified since exhaust back pressure determines amount of exhaust gases entering intake manifold.

Back pressure could definitely be the issue here!

What would be the long term effect of not having the proper back pressure?


Steven

[rfmaster]

Originally Posted by Boydness

Back pressure could definitely be the issue here!

What would be the long term effect of not having the proper back pressure?


Steven

Well, the DTC 32 is an indicator that ECM failed to verify EGR system function test sequence. Before jumping to any conclusions you'll have to verify component level operation - EGR solenoid, EGR valve, harness, etc. Not having EGR functional increases exhaust NoX levels and your gas mileage may drop. Otherwise, engine performance should be more less the same.

Depending on exhaust system and emission system requirements different EGR valves may be employed, for example Positive, Negative, Neutral or linear.
The positive back pressure EGR valve can be readily identified by the letter "P" stamped next to the part number and date code. A 'P' EGR 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 problems. Adding dual exhaust or headers on a truck designed for a single exhaust will reduce back pressure and set a Code 32. Positive back pressure EGR valves are used in simple vacuum controlled systems, as well as more complex pulse width modulated (PWM) applications - 1227747 ECM.

Code 32 problem has been around since CCC days and can be caused by a number of reasons. Every so often GM engineers altered ECM strategy for this code and depending on sophistication of the algorithm employed in the ECM causing enough grief and misinformation about Code 32. Unfortunately, Code 32 strategy has been inconsistently applied across different drivetrains over the years. The most common strategy entails the ECM monitoring fuel integrator counts to decrease momentarily when the EGR is commanded open. Since there is little or no oxygen in exhaust gases the integrator subtracts (causes a lean condition) fuel to compensate. This process relies on having a good working oxygen (O2) sensor. O2 sensor functional checks usually are not noted in the Code 32 troubleshooting flow chart, so be aware. Later BCC codes implementations look for a change in manifold absolute pressure (MAP) when EGR is flowing, which tends to be a more reliable method.
Negative back pressure may be best for modified exhaust systems. In this case as back pressure increases the valve will close. A positive back pressure valve needs back pressure to open. With headers and a decent exhaust there may not be enough back pressure to open it.

//RF

[Boydness]

Thanks for all the information.
I am pretty sure that it is attributed to back pressure with the exhaust. The exhaust is not a complete factory 2-1-2 system, so I presume that the back pressure could not possibly be correct for the original EGR valve.
I was intending to replace the system with a true dual system, so what would I need to do with the EGR then?
Leave the EGR as it is and make friends with the warning light?
Or is there some way that I replace the EGR to be correct for a dual system?

I was sweating the warning light being on, but now that I understand it fully, I am less concerned with it.


Steven

[Hart_Rod]

Originally Posted by Boydness

Thanks for all the information.
I am pretty sure that it is attributed to back pressure with the exhaust. The exhaust is not a complete factory 2-1-2 system, so I presume that the back pressure could not possibly be correct for the original EGR valve.
I was intending to replace the system with a true dual system, so what would I need to do with the EGR then?
Leave the EGR as it is and make friends with the warning light?
Or is there some way that I replace the EGR to be correct for a dual system?

I was sweating the warning light being on, but now that I understand it fully, I am less concerned with it.


Steven

Very old thread.....But was wondering if anyone found the answer to this? I have the same situation. No light. Installed true duals (with H-pipe) and now the light pops on. Pulled the EGR and it looked perfect (35K mile truck). Replaced the EGR any way and the light still comes on so I'm assuming its a back pressure issue. Is there any fix to this other than getting a new chip with this EGR check deleted? Thanks in advance.

Rob

[Greenlee]

Mine did this when I put headers on. Finally just bought a modified chip from Brian Harris at tbichips.com. I can’t remember exactly what he did but the check engine light doesn’t come on anymore.

[Hart_Rod]

Originally Posted by Greenlee

Mine did this when I put headers on. Finally just bought a modified chip from Brian Harris at tbichips.com. I can’t remember exactly what he did but the check engine light doesn’t come on anymore.

Thanks! Just ordered one, !

[Hart_Rod]

Originally Posted by Greenlee

Mine did this when I put headers on. Finally just bought a modified chip from Brian Harris at tbichips.com. I can’t remember exactly what he did but the check engine light doesn’t come on anymore.

Did you see much performance gain out of his stage 1 chip other than the SES light not coming on for the EGR?