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Blow Out My Lights

Here is a sad case of someone not paying attention. This happened in about 1990, when I was working part time for an LPG agent in Morgan Street,Gladstone,not far from where the shop was. I finished installing an LPG unit to a VN Commodore taxi several weeks earlier. Everything was fine with the installation but he took the vehicle to the dealers for a tune-up. A few days after the tune, he blew the left hand headlight clean out while attempting to accelerate up a hill. For those that don't know the air cleaner box is directly behind the left headlight. He went to the dealers who quickly blamed the LPG as the cause and told him to take the matter up with Doug the proprietor of the business I worked for. I was called in after work to check the vehicle out. The owner of the car wanted to show me how badly the vehicle back fired and so I jumped in the passenger seat and away we drove. Did I mention that the headlight assembly was replaced by this time. I bet you know what happened next. Yep, you guessed it, he blew out another headlight going up the same hill. Holly crap, what a bang, sounded like a bomb going off. Boy, did he start doing his block. Threatening to sue Doug for poor installation. We drove the car back to the workshop and I had a bit of a look under the bonnet. I was surprised that the headlight was the only thing that got damaged. I would have thought the airmass meter would be stuffed as well.

What was I looking for? A normal small back fire can be caused by several things, but the main ones are lean mixture and retarded timing. A big back fire can be caused by really, really lean mixtures, badly retarded timing or something simple like crossed HT leads. There are other factors of course but to keep it simple these were the ones I was interested in at the time.

I also learnt from Doug that the engine was tuned after I fitted the unit. Well that helped me get to the crux of it all pretty quick. Retarded timing, not impossible but highly unlikely, I ruled this out. Super lean mixture, no, afraid not. The LPG unit that I fitted was very reliable and there were no vacuum leaks and so I hunted for something else. Something else that had nothing to do with the installation but everything to do with the tune-up the engine just had. I checked the arrangement of the HT leads, starting at the No.1 plug and working through the firing order. OH OH what did I find? Two leads were fitted incorrectly. Now you would think that having two HT leads fitted wrongly would have affected the engine idle. Yes it does, but it can only be picked up with an exhaust analyser and/or using the engine cylinder kill test on an oscilloscope. Hang on I though this thing just had a tune up. I guess they didn't have this kind of equipment available. Oh well, bad luck I guess, the mechanic should have paid more attention. If only he had let me look around the engine bay before we went for a test drive, I may have found the problem and saved him another headlight.

Doug promptly told him what he thought of the situation trying to blame us when it was the tuner that was at fault. I wonder if they paid for two headlight sets.