Installing Fuel Pump Cut Relay in CNG Installed cars


Thread Starter #1
Joined
Feb 21, 2012
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When we get our vehicle retrofitted with CNG retrofitter installs emulator (an electronic device to stop petrol going to engine from injectors) this thing works as when car is on CNG it stops current to injectors & when on petrol mode it again supplies yhe current making injectors work.
Now what they don't do is that they don't cut the current supply to the fuel pump resulting in running of fuel pump all the time even when the car is on CNG.
If the fuel level is low & the fuel pump continues to run all the time the this will definately melt /destroy the fuel pump.
Also if they cut hte supply they use the wiring from CNG switch to supply current to the fuel pump this also damages the pump as current going to fuel pump drops due to thin wires used in CNG switch.
If we can install a relay in this fuel pump wiring we can enhance the life of fuel pump because it will not run when the vehicle is on CNG & will start to run as soon as the car is switched to petrol.
I will post the pics but till then I will try to explain the wiring , wiring is very easy any DIY person will be able to do it.
Get a relay a normal small 4 pin relay will do (should be of some good quality)
there are four pins/legs of relay, they are numbered as 85,86,30,87
Locate yellow wire from CNG switch this wire will give 12v supply when the CNG switch is in petrol mode.
Locate wire to fuel pump usually this wire is pink in colour & is bit thick this wire is in wiring loom going to rear & is in right side running along with running board next to driving seat under the plastic upholstery.
connect yellow wire from CNG switch to leg no. 85 of the relay
connect leg no. 86 of the relay to some good earth point (body earth)
now cut wire going to fuel pump (usually pink wire)
connect one end of fuel pump wire to the leg no. 30 & other end of wire to leg no. 87
done now switch on the vehicle & as soon as the CNG switch is in petrol mode relay will make a small click sound this completes the circuit & relay installation. Now start the vehicle & check.
Now your fuel pump motor wll never run when the vehicle is on CNG
Goodluck
 
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Sorry for the interrupt, This kind of provision is given to avoid vapour lock formation in the fuel pipes. (i.e) when the fuel pump keep running it cycles the fuel from the tank thus maintaining the temp and when it is turned off, it blocks the cycle thus the stock fuel in pipes near to the engine, gets vapored due to high temp and forms vapor lock.... if am wrong kindly notify
 
Thread Starter #3
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Feb 21, 2012
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vopour lock if any, forms when fuel pump is mechanical ie vehicles with carburetor and mechanical fuel pump installed in the head. these are pressure fuel pump they throw fuel with pressure so as to help injectors spray fuel in correct pattern giving good engine performance.
 
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