Push-starting is bad for your cat (according to the Ford owner's manual)

[basjoos]

I was looking in my 97 Ford F150 owner's manual and it said that push-starting can damage the catalytic converter. How would this possibly occur? The reason I am curious about this is push-starting is the same as bump-starting as far as the engine is concerned and I've been bump-starting and push-starting my cars for decades without any catalytic converter problems.

[Fat Charlie]

How does the cat know exactly where the starting force comes from?

[Frank Lee]

All I can figure is they somehow are equating push starting with the higher possibility of flooding the engine. I suppose if there is a fault that could happen, but for our EOC bumps, there is no fault that will cause flooding.

[digital rules]

Can't imagine why it would make any difference??? Would be nice to know the reasoning.

[elhigh]

Push is pretty much the same as bump, and as far as I can tell the concern is negligible.

However you start the engine, everything is cold upon starting. Some uncombusted fuel is going to make it through. I can't see how push starting the engine puts it into a significantly different operating paradigm than conventional starting.

Bump starting is just like push starting, except everything - including the cat - is pretty close to operating temperature. I think Ford is just hedging against possible damage claims.

[cowmeat]

Been bump starting the Black Widow for months now, with no negative effects whatsoever as far as I can tell. The motor mounts need to be changed, so I get a bit of movement from the engine, but I already knew I needed to replace them long before I began bump starting

I could gut the cat and my car probably wouldn't even notice the difference

[oldtamiyaphile]

Every owners manual I've ever read (apparently only two people on this thread do that!) warns about CATs and push starting. I've never understood why, but in a modern car, the ECU does 'know' if the engine's bump started or if the key's been used. Theoretically, it could run different mixtures if key started vs bumped. Essentially, a the ECU knows a key start is coming, while a bump start is a surprise.

That said, it's still warned against in cars with carbs and cats.

[RedDevil]

Only thing I can think of is that you can keep turning the engine over for a long time when push starting it (like rolling down a hill).
If the engine does not ignite the fuel inevitably will build up in the cat.

The same happens if you try to start it with the key, but the battery will run out at some point and protect you from killing the cat.
Hook the non-firing engine's battery up to a running car's battery, keep key starting and you'd kill the cat just like that.

So, nothing to worry about as long as the engine does fire up, carbs or not.
As bump starting won't cause the voltage to drop like key starting does, chances are that it will even fire up easier and cleaner than by key.

[oldtamiyaphile]

60Ah battery is 720Wh

1hp starter motor is 746W.

Assuming a 1/3 useful battery capacity, theoretically, a full battery will turn over an engine for about 20mins if you keep at it. It would take a significant hill or a lot of stamina to keep push starting a car for that long.

[RedDevil]

The manual will have something to say about how long you can run the starter motor maximally