Question: Does failing EGR system affect fuel mixture?

Case 1. EGR valve stuck open

Case 2. EGR flow blocked (valve stuck closed or blocked by carbon buildup)


The first case might lead to difficult running or starting I would have thought as you are introducing lots of soot and oily muck into the combustion chamber. If the car has adaptive trim then eventually that’d max out. Intuitively, I’d have thought the lower the rpm, the more problematic it’d be.

The second case ought not cause a worry. All cars pre-1974 didn’t even have EGR.

That’s just gut feel.

kind regards

Would it cause the fuel trim to run rich?

No. With no EGR, if it’s running more efficiently, it’d just make a bit more power but emit slightly higher NOx levels. EGR is only there for emissions purposes so it has no upside, engine wise. There is always a downside though if it reintroduces soot and muck into the combustion chamber, i.e. if you already have a problem, it’ll recirculate some of it rather than just flush it down the exhaust.

kind regards

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