Prins solonoid problem

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Beetlebum
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Prins solonoid problem

#1 Post by Beetlebum » Thu Feb 18, 2021 5:09 pm

No voltage to tank solonoid on 2004 beetle with prins lpg. When lights come on green and orange light goes out car immediately stalls. Checked small control unit and fitted spare one, still same. Been through all wiring under bonnet appears fine. Tank sender and temp sensor must be fine as lights come on green when up to temp and show correct level. By placing test non magnetic circular magnet on tank solonoid car will run fine, so evap solonoid fine, but lack voltage to tank solonoid. The wiring looks decent under the car. What brings on the tank solonoid? I awaiting a new cable, can I wire it into ignition or in tandem to front solonoid if all else fails? Would it be dangerous to have the solonoid wired to come on with ignition, relying in the evap solonoid to come on with the button? I'm pretty good with cars but this has got me beat so far. Is there a safety cutout somewhere? The 10amp and 4 amp fuses are fine. Ordered a new cable to test solonoid wired to the feed for the other. Will that be okay as permanent solution?

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Re: Prins solonoid problem

#2 Post by Beetlebum » Thu Feb 18, 2021 5:09 pm

Meant non electric magnet to test

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Re: Prins solonoid problem

#3 Post by Beetlebum » Thu Feb 18, 2021 7:04 pm

Okay, will get my coat. 🙄

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Re: Prins solonoid problem

#4 Post by Gilbertd » Thu Feb 18, 2021 7:08 pm

Some systems have the solenoids in parallel, others have separate feeds to each, so picking up a supply from the reducer solenoid shouldn't cause a problem.
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Beetlebum
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Re: Prins solonoid problem

#5 Post by Beetlebum » Thu Feb 18, 2021 8:32 pm

Good. Will do that then cheers. Ordered ebay front to back cable with connector to save bodging home made wires. Just link into evap solonoid. Save pissing around like I have for last two afternoons

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Re: Prins solonoid problem

#6 Post by LPGC » Thu Feb 18, 2021 9:20 pm

Seems like you've had a bad couple of days trying to fix your LPG system.
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Re: Prins solonoid problem

#7 Post by Beetlebum » Fri Feb 19, 2021 6:13 am

Yes. But discovered so much and quite knowledgeable now on how it works so can work on it myself. I'm an air conditioning engineer and a lot of it is similar in principle. Just annoying that a voltage drop in one place can't be traced. Difficult without taking whole harness out which I'm not going to do.......

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Re: Prins solonoid problem

#8 Post by LPGC » Fri Feb 19, 2021 1:47 pm

There's the cooling effect of gas evaporating in the pressure reducer but that's just about all I can think of that's similar between an AC system and an LPG system?

A voltage drop is due to a higher series resistance in the feed or higher load (lower parallel resistance) both easy to find without taking the whole loom out when you know what / where to check.

The Prins system solenoid coils are controlled by a single channel output from the ECU and are connected in parallel, usually switched through a relay.

Tank coils are generally more likely to fail than reducer solenoids / coils because tank coils are more likely to be in a harsher environment (in case of external tanks). But Prins reducer solenoids are a bit prone to getting gummed and coils to fail than average. You've found the problem seems likely (though not fully conclusively yet) to be the tank solenoid coil or it's power feed because when you use a magnet on the tank solenoid post the system works. It does seem likely the problem is the tank solenoid but it isn't uncommon for a reducer solenoid coil to fail / partly short circuit which pulls down the voltage to the parallel wired tank solenoid, in which case the reducer solenoid might open while the tank solenoid doesn't. Have you confirmed the problem is the tank solenoid coil by e.g. checking resistance across the tank solenoid coil? Or checked voltage on the wires at the tank end (momentary voltage when the system tries to switch to gas because as soon as the engine stalls there will be no power)? There is nothing special about wires under the car to the tank, Prins installers often use 3 core (or to a lesser extent 4 core) wire to provide an earth, solenoid +ve and level sensor signal wire (lesser extent also an earth for the level sensor). Nothing special about plugs on the end, you could put plugs on the end of a wire in much the same way as any factory put plugs on the end of a wire.
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Re: Prins solonoid problem

#9 Post by Beetlebum » Fri Feb 19, 2021 2:00 pm

Cable only 5 quid with correct plug otherwise would grab any cable. Checked the resistance, fine. No voltage with lpg running with magnet on to keep unit running. Should be voltage 12v get 3v. Similar in a way to some chiller systems i work on with water and gas circuit and solonoid valves, I still call it a/c though. Awkward to get to lots of the connections as its all cable tied where awkward to get hand in to reattach, the small controller box I can remove but no room to get in with tester while attached hence I would have to pull the loom out to test. Will just connect to evap solonoid feed and see what happens, unless the 3 core appears damaged under the car but initial checks are fine

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Re: Prins solonoid problem

#10 Post by LPGC » Fri Feb 19, 2021 2:40 pm

What coil resistance did you read? Bearing in mind the 2 solenoid coils will be wired in parallel it would be best to disconnect the coils from wiring to measure resistances separately, they should be around 12Ohms each or 6 Ohms if still connected in parallel.
Without any load at the tank end (with the tank solenoid coil disconnected) the voltage should read 12v if there is any connection on the live feed to the rear coil at all provided the front to rear wire isn't shorted somewhere along it's length. It seems unlikely there's a short along the length of the wire because if there were we'd expect a blown fuse or for the voltage to be dropped to the reducer solenoid coil preventing the reducer solenoid from opening.
Might expect to read 3v on the signal wire connected to the level sensor.
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Re: Prins solonoid problem

#11 Post by Beetlebum » Fri Feb 19, 2021 4:06 pm

Yes the sensor reads hardly any voltage. The resistance was within range both coils. Work when connected to a battery with a bolt in middle to test. I did find a wire just now, orange, from the switch that had chafed against a self tapper which I have repaired, didn't expect a difference and still no volts. As prev said, tried 2 different of the small box switch is connected to. So can only assume a wire fault front to back. Didn't look the best install anyway, I would have done a better job. Tidied it up a bit since. The large ecu looks fine. No damp inside and connections look good. Anyway it's all fun. Don't learn until you teach yourself. Somewhere I read about a feed from an ignition coil or injector needed for valve to actuate (to do with rpm) but read that much now going back to basics. Prob a dodgy solder

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Re: Prins solonoid problem

#12 Post by Beetlebum » Fri Feb 19, 2021 4:08 pm

Will test evap coil again in case dragging down voltage. My meter is pretty vague at times will use another I use for work

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Re: Prins solonoid problem

#13 Post by Beetlebum » Fri Feb 19, 2021 4:09 pm

Is there any fuse on prins apart from the 10amp and 2 amp....

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Re: Prins solonoid problem

#14 Post by LPGC » Fri Feb 19, 2021 4:46 pm

The Prins ECU can only handle 30v on it's RPM sensing wire so to protect the ECU from voltage spikes when it's rpm detection wire is connected to a cam sensor or ignition coil an 'RPM module' (which cleans up the rpm signal and sends a lower voltage pulse to the ECU) may be fitted and these can go wrong, I replaced one the other day. But in that case it probably wouldn't even attempt to switch to LPG and yours is attempting to switch because it stalls when it switches.

Number of fuses may depend on how the installer fitted it, the system will usually have a fuse for the ECU (probably 10amp) and a fuse from the ignition on wire to the ECU (the 2amp). In addition it may have a fuse for the solenoid coils if they are switched through a relay (or the installer may have taken the feed for the relay from the same place and fuse that the ECU uses).

Why don't you check for continuity over the length of the front to rear cable on all of the cable's wires, also check for shorts between the wires? You'd just need another length of cable to connect to one end of the existing cable to reach back to your meter... but a voltage test should prove the same things anyway.
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Re: Prins solonoid problem

#15 Post by Beetlebum » Mon Feb 22, 2021 5:01 pm

Solved. 18 inch wheels on the beetle and bit wider. On full lock we're slightly scuffing the cable to rear solonoid and damaged live feed. Replaced cable and linked rear solonoid into evap solonoid as easiest way. Now working sweet. Scuffed gas line too but have cut braided hose and fitted over to prevent scuffing wire or gas line again

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