Will not start, cranks, fuel pumps not shutting off....

[2quik6]

This is on a 2005 SRT10. I have had this happen 4 times now, 1st time about a month ago, and now its happened a few times since and I just now noticed the fuel pumps are not shutting off once I energize the key...
It will crank all day long, but not even try to fire up...after letting it sit from a minute or 2, it would fire up, and the pumps shut off after energizing the key and before pushing the START button.
I have 2 external puller pumps as well as the in the tank pump, all are on the same relay..they were added with the super charger install.
So that leads me to believe that maybe the intake pump is sometimes getting stuck, and is in a position so that the puller external pumps can't pull any fuel through the supply line to pressurize the system????

I guess next time this happens I need to quickly pull the supply line apart before the twin external pumps and see if fuel sprays out.

Any other ideas?

 

[Slitherbeast]

Does it happen when the gas tank is less than 1/4?

 

[VENOMOUS1 RACING]

I'd start with your relay but you may have fubared the pcm if it's triggering all 3 pumps. Check/swap fuel pump relay and ASD relay if you can. :rock:

 

[Slitherbeast]

How full is the tank? I had my pump inlet screen come out of it's perch and it would fall on it's face starting off. The pumps won't stop if they see air..... Once they stop and have pressure to the injectors it does start?

 

[2quik6]

Tank is currently full. It did it again this eve, it has been sitting all day. So almost daily it will do this. Try a few times, let it sit a minute, then it works fine.
Today I put a fuel pressure gauge on the rail, of course after that it did not do it....
Yes, if the system pressurizes successfully (At least I think that is what is happening when they do shut off, will know when it does it again with the gauge on) Then it starts fine.
So I will leave it on and see if it will do it again tomorrow and see if I'm getting any pressure or fuel at all up to the rail.

The pumps have been wired that way for 7+ years. This should be how they are wired otherwise the external pumps would never shut off after priming when the key is on, but engine off.

 

[2quik6]

Ok, it finally did it again, the fuel system IS pressurizing, gauge indicates 58 psi, so no pump issues it appears, but for some reason it must think the system is not pressurized so the pumps keep running.

So, what sensor would be detecting if the system has pressure or not, and would it keep the ignition from firing if it thinks it is not pressurized??? I've read most of the fuel system part of the service manual and am not finding anything.

Thanks

 

[2quik6]

Update, a friend of mine is a mechanic for a car lot, although he has never worked on a Viper or SRT10, his best guess is that the PCM is either seeing or reporting rpms when the key is turned on. Maybe a PCM issue, or whoever is feeding the rpm reading or used for calculating it is sending some voltage/pulses incorrectly.
There is no pressure switch that tells the pump to stop priming.
I confirmed this in the Service Manual, it indicates the pump just runs 1-3 seconds upon turning the ignition on, and they shut off unless the "Starter" is pushed, or the engine is running.

Recommends getting a scan tool hooked up to see what is being reported by the PCM....so off to find one...

 

[2quik6]

I disconnected the 2 puller pumps that were part of the Paxton setup. Problem finally occurred again, the in-tank pump does run for 3 secs and then shuts off as it is supposed to when key is turned on, but not pushing the START button, pressure in the rail goes to 58 psi.

Remember before the puller ext pumps would continue to run...so I assume then they are not tied to the fp relay, so the Paxton piggyback FMU unit must control them independently.
So I hooked up a volt meter to the leads for the ext puller pumps, I can't get it to register any voltage with key on to prime, or with the engine actually running..so I am not sure what controls them or how....seems like voltage would be commanded to them while engine is running even if the lead is disconnected as they ran before.. Guess I will hook them back up.

Maybe the Paxton FMU thinks the engine is already running also, and they are not commanded on when key is on and engine is off.....still need a scan tool.

 

[rbabody]

When you say it did it again are talking about crank and no start or fuel pump running all the time? Yes find a scan tool or check for injector pulse and spark. Is your check engine light on?

 

[2quik6]

When you say it did it again are talking about crank and no start or fuel pump running all the time? Yes find a scan tool or check for injector pulse and spark. Is your check engine light on?

Crank and will not start. So the fuel pump in the tank is just running for the 3 sec when the key is turned on and it shuts off then before the START button is hit...so it is acting normal. It's only the ext puller pumps that seem to continue to run ONLY when it will not start...I have them disconnected currently so I could hear the in-tank pump.

 

[2quik6]

I think I have the problem solved! I have replaced the crank sensor, and so far so good, has started flawlessly for about 30 times now... Would not start twice yesterday before I replaced it.
Suspect it was reporting rpms when the motor was not running...hence not starting. I also contacted Paxton to determine what signals the Paxton FMU needed to command the external fuel pumps on..it needs a boost signal which is 0 psi, atmosphere, and rpms...so it had 0 psi since motor was not running, and rpms most likely from faulty crank sensor.
Will post back if anything changes...but solved for now.

 

[2quik6]

NOPE..spoke too soon, did it again today after starting fine 30+ times....took me about 10 minutes and 20+ tries today to get it to start....so on to changing the cam sensor hopefully this weekend....

 

[2quik6]

Changed cam sensor, still has same issue...has also started dying driving down the road...has done that twice now. Currently removing the intake and inspecting all the wires and swapping out the coils and spark plug wires while its off....then on to removing the paxton FMU next.

 

[rbabody]

Do you have access to a scan tool?

 

[2quik6]

Do you have access to a scan tool?

Not at the moment, a friend of mine has the Snap On but he is 2 hrs away. Will get it the next time we see each other, which may be in Bowling Green next week.

 

[2quik6]

I found the problem...after redoing all of the wiring connections for the Paxton SC FMU as they were all crimped, I took them apart and soldered them all...still had the problem... So I removed the Paxton FMU altogether and re-soldered the original wiring for the cam and crank sensors back together to the factory ECM..problem resolved. Have driven over 1000 miles over the past 2 months without a single issue.
Just had to be careful not to get into boost, now I will be buying a new fuel pump, bigger injectors, and reprogramming the factory PCM, and remove the 2 extra external pumps from the Paxton kit.

 

[VENOMOUS1 RACING]

I found the problem...after redoing all of the wiring connections for the Paxton SC FMU as they were all crimped, I took them apart and soldered them all...still had the problem... So I removed the Paxton FMU altogether and re-soldered the original wiring for the cam and crank sensors back together to the factory ECM..problem resolved. Have driven over 1000 miles over the past 2 months without a single issue.
Just had to be careful not to get into boost, now I will be buying a new fuel pump, bigger injectors, and reprogramming the factory PCM, and remove the 2 extra external pumps from the Paxton kit.

Paxton fmu is a POS for sure! Glad you figured it out :rock: