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Always Double Check And Don't Make Assumptions


megadodo

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Here is an opportunity to learn from my mistakes. First some background, over a year ago I converted my 6 pot BMW to run on lpg. It all went well except I didn't quite plumb in the lpg injectors into the inlet manifold "as per instructions" as my sceptical head said it wasn't required and that a conventional install would be fine. As it happened, the car ran fine apart from an occasional stall after lifting the accelerator quickly approaching a stop, being an auto it was a slight pain as you cant just turn the key to re-start! It was so intermittent though I could live with it!

Mistake number 1, follow the guidance of the professionals if recommended to do so.

When the car lost an exhaust valve over Christmas requiring a head removal I took the opportunity to plumb in the lpg injectors as I should have done. With this kit there are 2 banks of 4 injector wires that control the lpg injector rails. Being a six pot you use 3 from each rail. In the first installation I used A, B & C on cylinders 1, 2 & 3 and E, F & G on 4, 5 & 6 as the plumbing leant itself to a straight forward install. With me so far?

On re-plumbing with plumbing had to cross over itself and wouldn't sit nicely with 1, 2 & 3 all on the same injector rail. I had to plumb 3 to the rear rail and 4 to the front. No problem I thought swap the C & E control wires round, simple.

After the rebuild the car ran well on petrol but was slightly lumpy on idle on lpg, no issue I thought, its bound to need an lpg re-tune after re-plumbing. After a re-tune it was better but the idle still wasn't a smooth as it was before the rebuild. After a bout a week the idle became noticeably worse and I had to switch back to petrol but even that was lumpy, so much so that I thought the head had dropped another valve! Un-plugging the fuse for the lpg would give smooth running under petrol after a couple of seconds following a re-start. Plugging the the fuse back in would repeat the cycle of initial good running followed by deteriorating performance on lpg and then petrol.

I rechecked everything including specially looking at the lpg wiring as I knew I had altered it, A, B & E on the front rail. Noting that the rail wiring was indeed 2 swapped wires I carried on with my diagnosis. I didn't check the rear rail as clearly I would have wired that correctly! 2nd mistake.

Since then I have tried a different lpg ECU and a different petrol ECU all to no result. Further complicated by a failing prop-shaft leading to drive-train vibration that I assumed was engine problem related! 3rd mistake!

This weekend following the prop-shaft being repaired and re-fitted I had another go at diagnosis. I checked everything again This time I checked the rear injector rail as well expecting to find C, F & G only to find C, E & G??? WTF, checked the front rail to find A, B & F, WTF? No wonder the car was struggling under lpg, so much so that the petrol ECU would try and compensate by so much its went passed its limits to cause rough running under petrol as well! I don't know how I missed it (other than E & F are similar) but you always need to double check (if not triple check) everything after any work you do especially if a new fault appears after work to another problem!

I hang my head in shame.

BTW, the car is now running beautifully and I'm no longer thinking of removing the lpg install and selling her!

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and my fuel bill has been reduced by 30% and I haven't had a gas conversion

 

 

 

 

oh yes that's because those greedy OPEC producers have decided to give the world a break and produce enough oil :aggressive: :aggressive: :aggressive:

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