BlazinOR

Noticed the EGR duty cycle never moved off 0% during a 30 minute drive........is this normal?

Sorry for my ignorance, but I am not clear as to when the EGR is supposed to work (ie cold engine, etc.).

Thanks.

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'79K5 Blazer with 406TPI

Vader

Blaze,

The EGR is commanded to open under only a very narrow band of engine operating conditions. This is a typical conditional set for a MAF/TPI engine. Some of the specific operation points may vary slightly with other years and fuel systems, but the idea is the same:

The engine coolant must be at least 56°C (133°F) for the EGR to operate. Maximum duty-cycle of the EGR solenoid can occur only above 80°C (176°F);

The TPS siggnal must be between 20% and 60% of maximum (relatively light throttle);

The engine speed must be above 1,400 RPM;

Intake air mass must be below 120 g/S (or MAP must be below 0.54 BAR).

In essence, the engine must be warm, cruising at part throttle, under relatively light loads, and the trans must be in either 3rd or OD on an automatic. Load is extrapolated from the data sent by the VSS, TPS, EST, and MAF/MAP sensor.

It isn't uncommon to have an EGR never open on trips around town, with stop/go driving. After about ten minutes of highway cruise at 50+ MPH and light throttle, the EGR should be open.

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Later,
Vader
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If you want to beat the World, it might reach up and pull you down...
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