Electrical gremlins (fuel gauge going haywire)

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iandmccormick
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Electrical gremlins (fuel gauge going haywire)

#1 Post by iandmccormick » Sat Mar 23, 2019 6:05 pm

Hello - I am a relatively recent convert to lpg and I am hooked. I am quite handy with cars, but feel a bit out of my depth on the lpg side. I run a Nissan Tino with a Stag 300 system (fitted 2012). It ran perfectly for the 3 years I have had it until recently. It started with an annoying continuous quiet tone (quieter than a normal signal) from the fuel sensor. It was receiving a low voltage (~2v) which we traced back to the ECU - or at least, we sprayed some contacts cleaner on the main connector and it stopped! All good until I filled up the lpg tank and I got an engine warning light for a weak mixture (about a minute down the road). I thought it was the petrol side, but it went off after a few days, then re-occurred when I filled with lpg again. The fuel gauge also started playing up, the lights giving fairly random readings. I'm used to it misreading a bit when parked on a hill for example, but not 4 lights to one light on a couple of trips. While it is random it seems to always be under-reading. Right now it's on red, but the tank gauge in the boot shows just below half. I've given the contacts on the tank a good dousing down with contact cleaner, but not much effect!

The car seems to run fine in itself. Any ideas? Rather then the obvious - the sensor it bust - I'm wondering if the ECU is on the way out given the original short was there? Any help or advice gratefully received!
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Nissan Tino automatic, STAG 300 ISA2 system. Based in Penryn, west Cornwall
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Brian_H
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Re: Electrical gremlins (fuel gauge going haywire)

#2 Post by Brian_H » Sat Mar 23, 2019 9:22 pm

The sensors on the tanks aren't the best - If its exposed (outside the car - you've not said where your tank is) then they can suffer after a few years exposure to the climate. As you say if its parked on a hill with a fairly empty tank you can expect spurious readings and ignore them. They can also wear over time. Most people with problematic gauges just reset the trip counter and use that to indicate how much they have left.

If you can get to the sensor, remove it (tank doesn't need to be empty for that its only linked by a magnetic pickup) and check it with a multimeter - the most common ones give a resistance reading, you can move the pointer with a screwdriver on the back of the sensor or anything else magnetic to check through the range, if its all over the place then you probably want to replace it.

They do also have a configuration in the software to set what level the lights show that is adjustable, though if this has suddenly started happening its probably not configuration related.

I'd have a good look over the battery contacts (there is usually a negative and positive feed to the lpg ecu, negative might be on the body somewhere rather than the battery) and give them a clean up if you carry on having problems as well, as I've known that to cause odd problems, same applies to the inline fuse holder on the positive lead - pull the fuse out and make sure its not corroded on the blades or the socket itself, if it is then either replace it or clean it up as appropriate.

Its also possible that there is a short on the wiring somewhere causing the gauge to read incorrectly - melted bit of wire where its got onto the exhaust, or where its been rubbed through, or caught by a jack or other object under the vehicle (most of those should be avoided during installation, but that can depend on the original installer and whoever has been under there since - I'd take it from your post that the car was brought already converted?.

When its been showing lean running after filling up, is this when the tank has run completely empty (you drove to the filling station on petrol?) If so it would suggest your calibration on the LPG ecu wants some attention - not something you can do without the lead and a laptop to see whats going on, but worth considering getting one if you want to address it.

iandmccormick
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Re: Electrical gremlins (fuel gauge going haywire)

#3 Post by iandmccormick » Mon Mar 25, 2019 10:01 am

Great, thanks for the tips. I will have a go an report back!
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Nissan Tino automatic, STAG 300 ISA2 system. Based in Penryn, west Cornwall
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iandmccormick
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Re: Electrical gremlins (fuel gauge going haywire)

#4 Post by iandmccormick » Mon Mar 25, 2019 5:12 pm

The only connection which had some corrosion was on the fuse, so good call there. I had a good look along the cable to the sender and I could not see any obvious damage. It was a bit tight around the lip of the hole into the spare wheel well (tank is in that), but no obvious chaffing. I took the gauge off and it works through its range ok. I don't have a multi-meter, so could not test it, but that does seem the most likely culprit, so I have sent off for one. Put it all back and gauge looking good for about 10 mins then haywire again! I will see if I can get my hands on a multi-meter and test the two wires from sender to CPU.

On calibration, I do have a cable (had a remote service done a couple of years ago), but when I connect up I get the error 'No controller', so I think that means it is not actually connecting for some reason. I have reloaded the Stag software to no avail, so I am a bit stuck on that one. I'll post a separate question on that if I cant get to the bottom of it.
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Nissan Tino automatic, STAG 300 ISA2 system. Based in Penryn, west Cornwall
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Brian_H
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Re: Electrical gremlins (fuel gauge going haywire)

#5 Post by Brian_H » Mon Mar 25, 2019 5:30 pm

Can be a few things to cause that - One of which is the drivers on the laptop your using not working properly.

If its a usb cable, open device manager on your laptop and check the cable appears without any errors showing against it - if it does show errors, then sort those (maybe driver reinstallation will sort this, unfortunately sometimes windows updates manage to break the existing drivers by reinstalling drivers that don't work or aren't right). Shouldn't be any harm if its shown with an error in deleting the device shown, unplugging it and plugging it back in again to let it redetect the drivers. That sometimes can be enough to fix it if your lucky.

Bear in mind there are different types of sender, and if its a multivalve type there are slightly different sets of holes to allow you to rotate the gauge slightly when you install it as well. Given you can't access the software at present, you'd best keep the same type of sender (the usual one is a 0-90 ohm one matching the type of valve/level sensor you have). You can pickup a basic multimeter from Amazon which will do what you need easily or screwfix do them as well for less than a tenner if your in the uk if you still need to investigate further.

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Re: Electrical gremlins (fuel gauge going haywire)

#6 Post by LPGC » Mon Mar 25, 2019 9:06 pm

Does the software connect OK when it's running on petrol and fail when it's running on gas?
You've implied that there are other problems besides the gauge not working correctly. Some of the symptoms you've mentioned could point to a failing solenoid coil that's partly shorting thus drawing too much current and pulling voltages at the ECU, if a partly shorted solenoid coil was an issue it would only have such effect when running on gas.
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Re: Electrical gremlins (fuel gauge going haywire)

#7 Post by iandmccormick » Tue Mar 26, 2019 1:23 pm

Thanks again for your advice. I'm in Cornwall with a Screwfix round the corner so I will go and get one. The 'no controller' connection problem is all the time. I have used the cable in this laptop once before (to turn the service audio alarm off), but I have a feeling that may have been before I upgraded to Windows10. I will try the device manager test when I get back and run the multimeter over the gauge!
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Nissan Tino automatic, STAG 300 ISA2 system. Based in Penryn, west Cornwall
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Brian_H
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Re: Electrical gremlins (fuel gauge going haywire)

#8 Post by Brian_H » Tue Mar 26, 2019 1:43 pm

There is a good chance its device driver related given what you've said, it may be worth checking with the supplier of the cable if you know who's it is for the best drivers to use.

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Re: Electrical gremlins (fuel gauge going haywire)

#9 Post by iandmccormick » Wed Mar 27, 2019 11:48 am

Hi - yep, software now working! No errors, but when I ran the autocalibration it read 'Nozzles too large' and go for a run. The manual describes running on petrol and gas through a range of conditions then mapping one onto the other. I can't see how the nozzles can actually be too large unless they have been too large for 3+ years! I'll have a go at this later. Might explain the high mpg? A side note - when I was looking around, I did notice the inlet hose (between airbox and fuel injection unit had partly split around the jubilee clip on one end. I happened to have a spare so switched it. I haven't had the 'too lean' engine light since which kind of makes sense, but I realise I am changing several things at once, so hard to isolate one thing. I suppose at least I can confirm there are no physical leaks.

On the multimeter, got one, quick tutorial on youtube, and the gauge seems to be completely dead no matter what needle position. The LED gauge is now stuck on reserve but with gas flowing so I guess that could be right in that the meter has now totally gone. When the new one arrives I'll switch it and let you know. Thanks again for your advice - feels like progress!
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Nissan Tino automatic, STAG 300 ISA2 system. Based in Penryn, west Cornwall
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Brian_H
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Re: Electrical gremlins (fuel gauge going haywire)

#10 Post by Brian_H » Wed Mar 27, 2019 4:16 pm

You might be able to get rid of nozzles too large by adjusting pressure down a bit, it would probably help now you have access to the software to check what pressure its set to now, better still if you can identify what size nozzles are installed (and the injectors for that matter as I cant see anything that says which ones you've got).

Does sound like the gauge is faulty though, so at least you should be getting somewhere on that problem.

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Re: Electrical gremlins (fuel gauge going haywire)

#11 Post by LPGC » Thu Mar 28, 2019 10:00 am

Nozzles may or may not be too large but you should pay about much attention to this kind of message from software as you'd pay attention to a message on a car dash telling you to change up or down gear... better that a skilled installer / driver decides that kind of thing. I'd base that decision on the spec of injectors, shape of the map, multiplier at various points and minimum gas injector pulse duration better than any autocal system could. May or may not be a good idea to adjust pressure but don't have enough info to decide yet.
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Re: Electrical gremlins (fuel gauge going haywire)

#12 Post by iandmccormick » Sun Mar 31, 2019 4:01 pm

So, new gauge arrived, and the led display is stuck on 'full' rather than 1/4 it says on the mechanical display! Running through the options on the software, I have concluded the AC proprietary gauge is based on volts and the replacement one is a generic resistance type. Seems to all work stably when I select 0-90ohms option, but for some reason I don't get it only uses 3 leds in this mode rather than 5. Anyway, it seems to work, so 'dud' gauge not wiring on this problem.

Having gone through the software manual, the specific Stag 300 model I have (ISA2) comes apparently comes with an autoadaption feature for mapping. Auticalibrate then just do the petrol map, following audio cues for revs. Unfortunately (I think!), you have to go through specific rev ranges for specific periods of time for it to work. Given my car is a fairly puny 1.8 automatic, I was struggling to hold it over 3.5k rpm for any amount of time, so I only got a 'partial' map. I checked out the deflection chart anyway, and it is within the 10% tolerance, so I am assuming this checks out. The 'nozzles too big' message didn't come up this time, so perhaps just another temporary gremlin. When I filled up, I have got an average of 24mpg, but I have been doing a lot of town work, so maybe that is not completely ridiculous. I'm off up to Nottingham next week, so I'll see how it fairs on a decent run. Historically over a long period (months) it has averaged low 30s overall.

Thanks for all the advice. It has been interesting to get my hands dirty on this one, as I have been a bit reluctant to go into unfamiliar territory. I feel like I understand a lot more about autogas now generally.
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Nissan Tino automatic, STAG 300 ISA2 system. Based in Penryn, west Cornwall
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Brian_H
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Re: Electrical gremlins (fuel gauge going haywire)

#13 Post by Brian_H » Sun Mar 31, 2019 7:06 pm

If your are still having problems, it may be worth running it on petrol for a bit before you try calibration again - it would let the petrol ecu relearn the fuel trims, giving you a more stable base to start from.

On the level sender its a case of adjusting settings - Not sure about Stag, but most others you can choose a setting that lets you set the cutoff values for each light on the gauge. Best bet at that is work out your range with a full tank, then adjust the levels as you have a rough idea of whats left in the tank to suit. At least it sounds like the sender might be the problem so your moving in the right direction.

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