Howell TBI Code 32

[thundley57]

Was on the trail yesterday and the check engine light came on with no effect to engine performance. Grounded the diagnostic terminal and got a code 32 which is "EGR System Failure". The diagnosis steps from the Howell manual include steps involving the "EGR Solenoid" which anybody that has the Howell TBI upgrade know that there is no EGR Solenoid but only the thermal vacuum switch.

My question is; does anybody understand how the ECM would detect if there was an EGR system failure? Would it be changes in the gases detected at the O2 sensor?

 

[PistolDave]

Cut and paste from a chevy truck forum:


What the EGR system does and when:

The EGR system allows exhaust gas to be introduced into the intake stream in order to cool combustion chamber temperatures under load. This reduces NOx emissions and helps prevent pinging (detonation.) The EGR valve is closed at idle. On throttle application, the EGR valve will be commanded open by the PCM as needed.

How the PCM tests the EGR system:

The PCM waits for many conditions to be met before running the EGR test. From 1994 factory manual: PCM must be in closed loop, above 32 MPH, throttle position 10% to 25%, steady throttle with no more than 2% change, MAP reading above 47.5 kPa or below 15 kPa, maximum short term fuel trim less than 6 counts for 3.2 seconds, desired EGR command greater than 93%.

In simple terms? This tends to happen when you're cruising on flat ground on the highway.

At this point the PCM will momentarily de-energize the EGR solenoid to close the valve. The PCM watches the fuel integrator counts to see if they increase compared to normal EGR operation. If it fails twice in a row, code 32 is set and check engine light is illuminated.

Possible symptoms of EGR trouble:

- Rough idle and rough part throttle operation (valve opening too easily or stuck open)
- May stall during transition from idle to part throttle (valve opening too easily or stuck open)
- Noticeable pinging (detonation) especially when engine is under load (valve inoperative)
- Trouble code 32 (valve inoperative)
- Hard or no start although fuel and spark are present (valve stuck wide open)

Possible Failure Modes:

- The vacuum supply from the TBI unit to the EGR solenoid can be disconnected, broken, clogged, or incorrectly connected
- The EGR solenoid can be faulty or the electrical connection to it can be missing or damaged
- The vacuum supply from the EGR solenoid can be disconnected, broken, clogged, or incorrectly connected
- The EGR valve can be faulty, clogged, or the incorrect part for the application
- The EGR passages in the intake can be clogged with carbon

 

[Lumpy Grits]

What were you doing on the trail, at the time the CEL came on?
Were you in water maybe??
LG

 

[thundley57]

Thanks for that info PistolDave, that makes sense. LG, no was actually on the way home at steady highway speeds which makes sense with what the info PD posted meaning that maybe the ECM decided the conditions were right to test the EGR and for some reason it failed. This morning went out and tested the ported vacuum to the valve downstream of the thermal vacuum switch which was about 10-12" at approx 2000 rpms. I then lifted the EGR diaphram manually with my fingers and it quickly stalled the engine meaning the passages are good. The only thing I really found was that the EGR mounting bolts were fairly loose so maybe I was leaking exhaust gases by the gasket.

At any rate I finished up and took it for a test drive on the highway and the light is now out. We'll see if it happens again.

Thanks again guys!

 

[Lumpy Grits]

What altitude do you live at?
What is your Hg readings at idle?
I would also be checking all the manifold bolts.......
LG

 

[thundley57]

What altitude do you live at?

What is your Hg readings at idle?

I would also be checking all the manifold bolts.......

LG

I live at about 450 ft. HG at idle is 20". I replaced the head gasket a year ago which means the intake & exhaust manifolds had to be removed and I was meticulous in evenly tightening them back up but if the light comes on again I will re-torgue them.


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