LPG. Keeps switching back to petrol when revs drop.

LPG, Bio Diesel, Hydrogen, Fuel Cell Questions and Answers last answered over 2 years ago.
You may also want to visit the 80-90 Wiki(pedia) for a more structured index of T25 repair, maintenance, technical and ownership topics.

Moderators: User administrators, Moderators

Locked
KarlT
Registered user
Posts: 2958
Joined: 28 Nov 2005, 21:39
80-90 Mem No: 2266
Location: location, location.---Sunny South Devon
Contact:

LPG. Keeps switching back to petrol when revs drop.

Post by KarlT »

Hi all.
Have got an LPG system in my Doka. Was already fitted when I got it so know very little about it really.
Used to work fine. I had to remove engine but now its all back together the LPG has a cliche.
Keeps switching back to petrol when the revs drop. It stays on LPG while revs are up but when I change gear it switches back to petrol. If I rev it, it goes back to gas until revs drop again.
Tank is full.
Where should I start looking?

User avatar
steve8090
R.I.P.
Posts: 861
Joined: 07 Oct 2005, 16:21
80-90 Mem No: 2
Location: Member No.2 Club founder North Wales
Contact:

Re: LPG. Keeps switching back to petrol when revs drop.

Post by steve8090 »

Depending which system it is, it is more than likely the rpm sensor wire, some take it from the coil and some take it from the injectors, if you want to mail me a few photos I'm sure we can nail this.
Steve Shaw
Club80-90 Founder Member
Image
Full Service, LPG conversions, Security and Camper Accessories.
see http://www.gasure.co.uk for full details.
01244 659740

KarlT
Registered user
Posts: 2958
Joined: 28 Nov 2005, 21:39
80-90 Mem No: 2266
Location: location, location.---Sunny South Devon
Contact:

Re: LPG. Keeps switching back to petrol when revs drop.

Post by KarlT »

Okay. Had a good look around can't see any loose wires (even if some of the covers look loose)

I drove it a few times today & it was always the same.
Starts fine (on petrol) flicks to LPG & I drove it as normal for about 400metres. Then as soon as revs drop it switches back to petrol (gas light flashing) put my foot down & it flicks backs to gas. soon as I stop, back to petrol again. (gas lights flashing)

During resto, I did mess around with this valve. I turned the caps on the left, top & bottom. What are they?
Image

Image

Image

Red wire comes from LPG system & goes to coil.
Image

Image
.

User avatar
steve8090
R.I.P.
Posts: 861
Joined: 07 Oct 2005, 16:21
80-90 Mem No: 2
Location: Member No.2 Club founder North Wales
Contact:

Re: LPG. Keeps switching back to petrol when revs drop.

Post by steve8090 »

It doesn't look to bad, however the rpm sensor wire is the red one attached to the green wire which runs up to your gauges, connected to the yellow connection, trace this and see if there is a break in it or it is earthing out anywhere, it is this trigger that tells the lpg to switch over and it is obviously losing it at tickover, try moving the red wire to the other green and see if it makes a difference.

On a safety note, your tank is one of the older ones and those screws are valve cutoff's, screw them in to stop the flow of gas, the new tanks have an electrical solenoid on the output side, but what is concerning me most is the valve is in fresh air, this should be housed in a gas tight box and all of the gas pipes should be in tubes which are sealed to the box and interfaces through the bodywork, if the red valve should blow then you will have dangerous lpg vapour entering you vehicle that could be catastrophic to say the least, have you had the installation certified? if it did go up you do know that the insurance would not pay out don't you, purely because of this, it will be inspected carefully to COP 11 and seeing as you have no way of venting the lpg to the exterior of the vehicle then I'm sorry to say you may lose more than you van, take it to a specialist for a second opinion if you want but please do something about it.
Steve Shaw
Club80-90 Founder Member
Image
Full Service, LPG conversions, Security and Camper Accessories.
see http://www.gasure.co.uk for full details.
01244 659740

KarlT
Registered user
Posts: 2958
Joined: 28 Nov 2005, 21:39
80-90 Mem No: 2266
Location: location, location.---Sunny South Devon
Contact:

Re: LPG. Keeps switching back to petrol when revs drop.

Post by KarlT »

Hi Steve, been away from computer for a few days. Cheers for reply, will check out that red wire.
As for install, no paperwork, bus just came with system fitted. Tank is in locker (Doka) & has got vent holes fitted in floor. Also locker area, tank & fuel pipework is completely sealed off from cab area. Have told insurance company it has LPG conversion..."yeah, that's fine" the didn't ask any further or for any paperwork.
Thanks again.

Oh, where will that red-wire head to? Is the little black box the brains of the system? Is that where it goes to?

Locked