Repairing an LPG ECU
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  1. #1
    1000+ Posts Beano's Avatar
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    Default Repairing an LPG ECU

    I have basic electronic skills. I have successfully soldered in ICs and once I repaired a 505's tachymetric relay after I examined it with a magnifying glass and found dry solder joints....there were tiny cracks I spotted.

    Recently I had a non-French car which I bought and sold to make money on the side, but it's come back and bit me on the bum....the LPG ECU has malfunctioned.

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    After I bought it I noticed in the paperwork that a repairer did some work on it after it had once failed to run on gas, and wrote that if the car failed to work on LPG once again, then the LPG ECU would need to be replaced. However they are quite expensive new ($600- $800), and my local LPG repairer said that secondhand ones are either unobtainable or heaps of junk.
    I did see a couple on Ebay but they are overseas.

    The type of LPG system is Landi Renzo. I wouldn't mind having a go at fixing the existing one....it is a lot easier and cheaper than getting another, either new or secondhand.

    I took out the ECU and had a close look with a magnifying glass at all the soldered connections but cannot see any dry connections.

    Does anyone know which components are the most likely to fail ? Perhaps capacitors / condensors ?
    I would have no problem buying a bunch of them and just soldering them in....

    The car was stalling about once a week, whilst simply going along on main roads....not when idling.
    It would re-start immediately, but it was unnerving, as you briefly lost the power steering.
    Then recently it refused run on LPG at all....only petrol.
    Last edited by Beano; 1st August 2019 at 06:31 PM.

  2. #2
    1000+ Posts FIVEDOOR's Avatar
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    Capacitors can fail, you can usually spot by looking at the round top. The ones I have had fail (bass amp) you could see slight bulging on the top, the round part. New one with same values was $3.70 at Jaycar. Ill see if I can find a photo of the failed one and add it here
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    Electrolytic capacitors are notorious for drying out, larger blue cylindrical things. Best of luck.

    Also look for burnt diodes or transistors, is this discrete components or surface mounted devices?
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    Real cars have hydraulics DoubleChevron's Avatar
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    I'd be looking at the converter.... or the filter to it. It sounds like it is injected gas. if they sense and error they will switch back to petrol by default. The converters get clogged up with a waxy substance apparently (injected ones should have a filter prior to the converter). Does it smell of LPG ever ?
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    1000+ Posts robmac's Avatar
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    I'd check out everything else before tackling an ECU repair to component level.

    Service companies have a habit of telling fibs when a repair threatens to be unprofitable or be difficult to repair.

    Start with a multi meter checking the Inputs and outputs. You should be able to find a wiring diagram on the net.

  6. #6
    1000+ Posts FIVEDOOR's Avatar
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    Quote Originally Posted by FIVEDOOR View Post
    Capacitors can fail, you can usually spot by looking at the round top. The ones I have had fail (bass amp) you could see slight bulging on the top, the round part. New one with same values was $3.70 at Jaycar. Ill see if I can find a photo of the failed one and add it here
    The one on the right is the damaged one. If you look at the top in comparison to the one on the left, you should be able to see the damage, it's not much. but it is visible. They were from a bass amp but I had the same issue with an old Seven Series BMW instrument cluster circuit board.

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    1000+ Posts Beano's Avatar
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    The components are mounted on a printed circuit board, but the capacitors (from memory) are not huge....just small ones.


    Quote Originally Posted by DoubleChevron View Post
    I'd be looking at the converter.... or the filter to it. It sounds like it is injected gas. if they sense and error they will switch back to petrol by default. The converters get clogged up with a waxy substance apparently (injected ones should have a filter prior to the converter). Does it smell of LPG ever ?
    It did smell of gas when I owned it. What does that indicate ?

    I took it in to a place to be checked but after looking at it for 30 minutes, they said they couldn't find anything wrong with it.
    He was a friendly guy though, and didn't charge me anything.

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    My personal belief is that sensors, and the wires to them, are the first things to look at. I know alot of mechanics use the old "needs a new computer" story, but I would think the actual computer board is the least likely element to have a problem.

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    1000+ Posts Beano's Avatar
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    I just found out that the new owners have gotten tired of mucking around and taken the car to a mechanic, and simply said "please fix it".

    It'll be interesting to see what the problem was, if I can find out.

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    1000+ Posts Peter C's Avatar
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    In regard to dry joints, I've found that not all dry joints can be identified by sight alone. At times, I've frustratingly got to the point where I've ended up going over joints with a soldering iron until I found the dodgy joint and it might be one that looked okay.

  11. #11
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by Beano View Post
    I just found out that the new owners have gotten tired of mucking around and taken the car to a mechanic, and simply said "please fix it".

    It'll be interesting to see what the problem was, if I can find out.
    Depending on "the mechanics" expertise and integrity, that is either the best or most expensive way to fix the car.

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