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I've tried a search on this subject with no result. I seem to think that I have read that you should not bump start a car that is fitted with a catalytic converter, but I don't understand why not. My "knowledgable" work colleagues insist it is to do with sending an enriched mixture down the exhaust. I can accept this is if the engine is not firing, but it would do this anyway if being turned over by the starter. My query is for when the battery has been flattened overnight and you need to bump the car off. Cheers.
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>>but it would do this anyway if being turned over by the starter.
No as long as the plugs are firing the gas is getting burnt
I think what you mean is if engine turning over but with no spark.The car manual doe`s specify if engine wont fire up in a few turns there must be a problem.you may have fuel injection
working ok but as it is not getting burnt the compression off each cylinder pushes the unburnt fuel straight into the exhaust ie into Cat.Is it worth the risk?
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I've had a quick google, but only came up with this:-
"If you attempt to bump start a car (with a run down battery) this has the same effect as a misfire. Unburnt fuel travels into the CAT and can destroy the catalyst."
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Not quite the same but some 40 odd years ago dropped the girlfriend (still the wife) off outside her house. She lived on a steep hill. My first car a MM series11. Released the handbrake gathered speed and let the clutch out.
Everything fine until I turned the corner at the bottom of the hill and realised I had not turned the ignition on and did so.
The explosion late at night sounded like a bomb going off and the exhaust was blown apart.
If a cat had been in there it would have stood little chance...
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I take paul's point that if for example an engine were slow to fire, turning it over even on the starter would still be putting unburnt fuel down the exhaust pipe.
That would suggest that prolonged cranking by whatever means is undesirable, if the non-start is caused by say lack of spark rather than non-injection of fuel. The cause of the starting reluctance should be determined rather than just using prolonged cranking and hoping.
The warning against bump-starting possibly is especially relevant because of the circumstances in which it is generally tried - ie dud battery, or battery already flattened by trying to start a reluctant engine. This would cause a very poor spark, so allowing a lot of unburnt fuel to pass before the engine fired.
Another reason could be that often activating the starter motor sends a signal into the system. Absense of this signal (as in bump starting) may cause problems. Certainly in a system where the coil has a ballast resistor then the spark will be weaker if the starter is not used.
All in all bump starting seems a risky business best saved for emergencies only.
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If the engine is cranking well but not starting there is something wrong mechanically, ignition-related, or fuel-related, and bump-starting is not likely to improve matters. If the non-start is due to a slighty weak battery it may go, but if battery is totally flat/failed, it is still not likely to go due to lack of votage for fuel and ignition systems.
If the ECU is receiving a siganl from the engine speed sensor but there is a fault on the igniton then there may well be fuel injected but unburnt, and bumping is going to do just as much harm as cranking.
Personally, I am of the opinion that Cats are are great deal more tollerant than manufacturers would have us believe. I have seen numerous instances of cars run with total misfires for more than just a few miles, cranked for ages with ignition faults or poor compressions, or run with serious managemnet faults, yet when the fault is corrected / engine started (given perhaps a decent fast run) the Cat has recovered to give normal emissions.
The biggest Cat killer is the short journey / gentle use pattern to which many cars, especially small cars, are subjected.
Regards, Adam
Whatever is rightly done, however humble, is noble.
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If the cat is cold, it wouldn't bother it anyway, and as long as you don't flood the engine, by repeated tries, there should be no problem.
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If the reason for bump starting is a flat battery, then I can't see how fuel can be injected without the spark occuring, as the injectors need a voltage to work too. Once the engine has started to turn over (from pushing or gravity) and wake the alternator up, your engine isn't going to start until the ECU gets enough voltage to work. Without that voltage you aren't going to get fuel injected or sparks firing. So I can't see why bump starting is a problem in that respect.
On the subject of cats being destroyed, I had a faulty HT coil on my Megane which killed the spark on two cylinders. Over time it got worse and worse, but probably did no more than 2 miles total running on two cylinders. But that was enough to destroy the cat, which of course made a mess of the following baffle boxes with all the honeycomb being jammed into them. When the other HT coil 'coughed' a few months later, I made sure I replaced that right away, as I wasn't going to risk losing another cat again!
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As in the thread "406 Cambelt Done - Worth Repairing?" I mentioned I have had the cat on my 406 "emptied" or rodded out and now it's just an empty box. Also replaced middle box. Power is up, torque and smoothness are incredible. Went through the MOT the very next day. Cost £5 rather than £200+ for a replacement, Due to cat rattling quite badly (ceramic matrix had broken up)
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What year? Not post 93 surely?
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Diesel, I think..
--
groups.msn.com/honestjohn - Pictures say a thousand words.....
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Another issue with bump starting cars is the possibility of making the cam belt jump. This used to be a probem with race cars when I was mechanicing and Cam belts had just started to be used. Most manufacturers warn about continuously turning the engine over on the starter if t car doesn;t start. This also fills cylinders with fuel so bump starting would do the same thing.
Jim
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bump starting a car with a cat
Sounds cruel! How big is your moggie? :-)
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