Q: I have a problem starting my pug. It has started backfiring, but once it has been started (eventually) it will continue to start easily. I have just had the front exhaust changed and put some petrol in from a garage I don't normally go to. I have also noticed there is a lot of excessive water out of the exhaust. No obvious leaks and no water in the oil etc. Any ideas. Liz Hi, thanks so far for the replies. It backfires only on starting. I was wondering if it was the Lambda sensor as they put the old one back in the exhaust. It was the original one so it is old. They said they had trouble removing it from the old exhaust. What do you reckon? We checked the spark plugs and one was a little rich but all ok really. Liz
A: Hi, it is unclear if it is backfiring on the first start, or all the time. Is it using water? If it is, and the starter struggles to turn the engine evenly at first, then it could be that the head gasket is blown and leaking coolant into one of the cylinders. If this is the case, major engine damage is possible if one cylinder fires and tries to compress water in another cylinder, can throw a rod because water does not compress. If not water, does it smoke, partiuclarly on startup? It could be oil in the cylinders (possibly worn valve stem seals) . Or the plugs may be fouled or faulty, try a clean and check/adjust while they are out. If it is a fuel injected car, check for air leaks on the inlet manifold pipework. Re addition info: I doubt it is the lambda sensor that is causing the backfiring since I don't think they work until the engine has heated up. It sounds like it could do with replacing however as they do have a limited life. It may be worth checking the distributor cap. If there is some tracking there, it might be getting a spark to the wrong cylinder during startup. Perhaps you could try cranking it with one plug lead off (and insulated for safety). Try with each lead and see if there is a difference on any of them? Another thing to check would be the compression to see if there is an issue with any of the valves.