Need help with FASS not triggering

S

skav

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Oct 16, 2008
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Hoping to get some ideas from the experts on why my FASS is not being triggered when starting. This is an intermittent issue, but seems to be happening more and more often.

I've been having this issue for about a month or two now. When I turn the key to the start position, my fuel pressure gauge reads 0, and the motor won't light. If I turn the key off, then back to start, it can hear the relay, the fuel pressure will spike, the motor lights, and then the FASS builds pressure.

What would cause this? At first I thought it was the relay, but it still does this even after I installed a new relay. I'm tempted to wire the relay to trigger when the key is in the run position, but would rather figure out why this is happening instead of using a fix.

It acts like the pump is loosing prime, and I replaced the fuel pressure line at the pump inlet because it was actually dripping a bit of fuel. This didn't make a difference. Also, it seems to happen after I fill up too.

Again, i defer to the experts, as I'm not sure what would cause this.

Any advice is appreciated.

Thanks,

Sean

Sean
 
I assume your running it wired to the ecm still?
 
You are aware that it is not supposed to run all the time after the key is just turned on correct?
 
BRE said:
You are aware that it is not supposed to run all the time after the key is just turned on correct?
Click to expand...

I understand that. Before, if you cranked, and it didn't fire, the pump would run for about 30 sec, then shut off. That's why I didn't want to wire it to come on when the key is in the run position if I can avoid it.
 
skav said:
I understand that. Before, if you cranked, and it didn't fire, the pump would run for about 30 sec, then shut off. That's why I didn't want to wire it to come on when the key is in the run position if I can avoid it.
Click to expand...

Ok just double checking is all.
When the key is turned on without cranking its supposed to run like 2 seconds if memory serves me right the. After crank and no start it runs for like 45 or something close. Have you checked all your connections both hot and ground? And tried a different relay? Just because a relay is new doesn't mean it's good.
 
Drain the water separator and bump the key. See if it runs till it refills the w/s. It wont always spike if the pressure is there upon startup. I had this problem a while back. Also, do what Rick says. ^^ Check your relay. I had to rewire mine because of corrosion on the relay and wires, it caused intermittent issues such as yours.

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The driver in the ECM has been known to fail, use a meter and check the activation signal from the ECM while you are cleaning the contacts. My truck did the same thing but lost the signal from the ECM, pretty sure a bad pump (had a Holley Blue run by the ECM at the time) killed the circuit.

On Edit, some more info about this since I was asked. Before the Airdog and FASS systems came along one of the popular upgrades was to install a Holley Blue pump by the fuel tank, this will work, and work well, until the pump dies. They are not made to push diesel nor to be a constant duty pump, but it was what you could get if you were on a budget. The stock lift pump is rated to draw around 2.5-3 amps as best I remember, the Holley will pull about 5(ish) so many folks were just tying into the stock wiring for the lift pump to run the Holley units. This is what I did, and I know better, but got pressed for time, then never fixed it right, crap happens. What will happen over time, if the pump shorts internally, a gremlin gets in the system, just pick your cause, is that the circuit gets overloaded and burns out. Now you have no signal from the ECM to run a relay or anything else.
 
Last edited:
Billysgoat said:
The driver in the ECM has been known to fail, use a meter and check the activation signal from the ECM while you are cleaning the contacts. My truck did the same thing but lost the signal from the ECM, pretty sure a bad pump (had a Holley Blue run by the ECM at the time) killed the circuit.

On Edit, some more info about this since I was asked. Before the Airdog and FASS systems came along one of the popular upgrades was to install a Holley Blue pump by the fuel tank, this will work, and work well, until the pump dies. They are not made to push diesel nor to be a constant duty pump, but it was what you could get if you were on a budget. The stock lift pump is rated to draw around 2.5-3 amps as best I remember, the Holley will pull about 5(ish) so many folks were just tying into the stock wiring for the lift pump to run the Holley units. This is what I did, and I know better, but got pressed for time, then never fixed it right, crap happens. What will happen over time, if the pump shorts internally, a gremlin gets in the system, just pick your cause, is that the circuit gets overloaded and burns out. Now you have no signal from the ECM to run a relay or anything else.
Click to expand...

Same thing happened to mine. I was looking for a new ecm for a while, but not its just wired to a switch I put on the knee bolster. One day I would like to wire it into the oil pressure switch. That way when the truck builds oil pressure the pump comes on.
 
You can route around the ECM by taking the red wire that connects to the truck harness and attach it to a key on fuse like power window or windshield wipers. When checking prime on the system leave the water separator (little filter) tight and crack open the fuel filter (big filter) and key on the pump you should hear the tone change on the pump. I have attached the video to help with priming.

[ame="http://www.youtube.com/watch?v=ACbjqxjIhes&feature=plcp&list=PLD71B479EE763BAA5"]How to Prime a FASS System - YouTube[/ame]
 
I would avoid wiring around the ECM in my opinion. I've heard many tales about hard starts if the VP gets too much pressure while cranking (that is why the ECM bumps it for a second, then shuts it off until the engine fires). Find the problem, don't bandaid it. $.02
 
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