Starts Up Then Stalls

[PVFCpug 6]

Probably got a bit ahead of myself here so obviously done something wrong. After fitting the omex 100 and getting it running with a base map I decided,(foolishly) to try out a rev counter adapter. Fitted it all up and first time of asking everything fired up and rev counter all OK, .

 

Reveresed it out of the garage to give it a run round make sure all was well, got it out the garage and then the engine cuts out. Turn key engine starts revs a few times then stops again. Now I am in the cycle that the engine starts runs at idle for a few seconds beofre giving up the ghost. Occasionally it will rev a few times but then stops again.

 

Am I correct in thinking that the tachy relay supplies power to the fuel pump whilst cranking and thereafter the power is from somewhere else. Sounds to me as if the fuel pump is not working once I stop turning the engine over by key. Therefore carb bowls fill up and allow it to run a few more seconds then gives up. Please tell me if that sounds correct.

 

I have been trimming some of the wires that used to be connected to the coil and i think this may have something to do with it but unsure. Any thoughts?

Edited December 3, 2009 by PVFCpug

[taylorspug 7]

To test your theory try hardwiring the pump with a switched 12v. In all honesty if you have an Omex 100 and carbs you have no real need for a tachy relay anyway, so it may be worth taking it out of the system as they are prone to failure.

[PVFCpug 6]

what so take the wire out of the back of the relay board and attach to a switched 12V?

[Tom Fenton 1,542]

Just lash a temporary supply in, straight to the pump if you like, or interrupt the wire to it near where the Tachy relay is or would have been. Doesn't have to be pretty, you just want to confirm or eliminate the fault for now.

[PVFCpug 6]

OK its not the pump. It has a supply to it whilst cranking but as soon as you release the key it drops to 0 Volt. Have to chase the wiring back. Sounds like the tachy relay is doing what it is meant to but thereafter the feed goes AWOL. Checked at fuse 15 and the same it has volts whilst cranking but nothing as soon as you release key!

Edited December 4, 2009 by PVFCpug

[Anthony 1,003]

OK its not the pump. It has a supply to it whilst cranking but as soon as you release the key it drops to 0 Volt. Have to chase the wiring back. Sounds like the tachy relay is doing what it is meant to but thereafter the feed goes AWOL. Checked at fuse 15 and the same it has volts whilst cranking but nothing as soon as you release key!

AFAIK the standard 8v tachy relay needs to see a pulse back from the coil (like the rev counter) to stay engaged once you disengage the starter motor, and one would assume that you've no longer got this feed since removing the 8v ignition setup?

 

Personally, I'd get rid of the tachy relay completely, and assuming that the Omex100 has a fuel pump output on it, use that to drive a standard green 4 pin relay for the fuel pump.

[PVFCpug 6]

The rev counter wire was connected to another wire on the same spade plug and connected to an O/P from the coil pack, so even though it was only reading half the revs this was probably enough to keep tachy relay closed.

 

Is the idea behind the tachy relay that it cuts the fuel pump in the event of engine stopping? Looking at the diagram it supplies power whilst engine is running to the SAD, the fuel pump and seems to come from a +'ve supply control unit whatever that is?

 

If I remove the tachy relay, there is no Fuel Pump out from the omex. Is there any other feed you can think of close to either the fuse area or tachy relay?

[PVFCpug 6]

Another daft question is once I re-establish a supply to the fuel pump will it take a while to re-fill the system?

[PVFCpug 6]

OK just taken it one step further.

 

Reconnected all the bits I thought I could do without. ie the rev counter wire back to ANother wire from the old coil.

 

Measuring at the fuse now we have about 8-9V whilst cranking and then 12V for about a second whilst the engine is still rotating. Which suggests to me the circuit now seems to be working fine to the fuel pump. The fuel pump does work, I have put a straight 12V to it and it does what pumps do ie. pumps. albeit out of the fuel tank. So I must have a bad earth going to the fuel pump. Surely this can be the only thing left. The earth I assume lookingat it does run back to the front of the vehicle, can I just attach the earth side to the bodywork close to the fuel pump to prove this?

[taylorspug 7]

So have you put a constant or switched 12v to the fuel pump and tried to start it? As in when you turn the ignition to the second stage, the fuel pump comes on and stays on? If you had a bad earth the pump wouldnt work full stop, it certainly wouldnt pack up a second after the engine fires. If you only have 12v for a second while the engine is started, that would suggest to me that the circuit ISNT fine, ie the tachy relay (which im assuming is still connected) is cutting off the feed.