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MG ZR ZS ZT Technical - Supermarket Petrol

Not one of the MGs but the Toyota failed to start yesterday morning. Weather was the unique British combination of just short of freezing and everything soaked in dampness. Cranked over normally, fired once, then cranked with a really strange noise but wouldn't fire again. Spark OK, fuel OK, cambelt OK, compression way down on one cylinder which was odd as it had been running fine. Battery cranking voltage was 8 point something which is lower than it should be but jumping it from the V8 (which started as normal) made no difference. As I had been cranking it a bit I put it on charge while I pondered things. Then tried again about half an hour later and it cranked faster and was obviously trying to fire. After about 30 secs of that it eventually staggered into life, obviously firing on 3 cylinders and sounding like one of the exhaust valves was sticking open. After a few moments of that it started running normally, presumably as the sticking valve unstuck. Between us my son and I have had this car over 10 years with nothing like it before, the only other difference being I had changed from using Shell ordinary unleaded to Tesco petrol just two tankfuls ago. I've heard other comments about supermarket petrol in the past, has anyone experienced anything like this?
Paul Hunt 2

There are two possible reasons for this Paul, the first is the most likely and the Ford Zetec used to suffer with the same concern when using Supermarket fuels.- It is sticking valves in the guides caused by a build up of carbon caused by poorly refined fuel. Change back to a branded fuel and this seems to eventually clear any problematic carbon thats built up. The other reason is hydraulic followers that have jacked open to far caused by incorrect grade of degrading oil used,- again the Zetec suffers with this and Ford had to produce their own grade of oil to cure the problem back in the early 90's. I regularly work on a V6 Honda engine in a Rover 800 that uses the correct grade of oil but after about 5000 miles the oil must get a bit too thick and causes it to run on 5 cylinders on cold starting. Hope this helps.
By the way, the oil concern is amplified if you start the car with no problem, let it run or drive out of the garage for 30 seconds or so then switch off. - The next time you come to start it is when the misfire happens.
Steve Tyler

Thanks Steve - poor refining/lack of additives was my thoughts, also this garage caused mayhem a few weeks back by putting unleaded in the diesel tank (or the other way round)! A friend suggested dosing it up with Redex. It's a possibility, but I don't see the point of spending money on Redex just so as my wife gets a few more points on her Tesco card :o) It's been OK two mornings since, although the precise set of circumstances hasn't been repeated yet and may not be for a while.
Paul Hunt 2

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Paul

This thread was discussed between 09/01/2006 and 12/01/2006

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