No start. Then starts fine. Then just cranks

[CARTOYZ]

99 2500 Ram.   Pick up was parked all winter,went to start and just cranked over, shot it with either and started up and was good,thought just lost pressure. Then, at station getting fuel and same thing. I replaced full pump on block thinking that was it and get still does it. Dan a power wire to pump to toggle pump on but still does it with pump runnnning, Abby very annoying. I am thinking it is the control box on the side of block in front of pump. Anyone agree.  This is intermittent and can go weeks and be fine. It will always start with a shot of juice. 

Any ideas

[Mopar1973Man]

Tach working? Any P0336 error code? If there is any error code for tach signal (crank sensor) the ECM will not know to start the lift pump. 

 

Does the lift pump run when you bump the starter? Is there 12V from the lift pump lead? If not then you looking at sending the ECM for repair.

 

WARNING

I do not suggest putting a toggle switch on the lift pump or wiring the lift pump to the key switch. This is a huge safety hazard if you in an accident there is no way to shut down the fuel if you are unconscious. I highly suggest you have the ECM repair then replace the lift pump with an AirDog or FASS with a protection relay so the load of the pump is never on the ECM. 

Edited June 3, 2018 by Mopar1973Man

[dripley]

I definitely would check for any DTC's before assuming it is the ECM.

[Dieselfuture]

What is said above definitely worth looking into. But I always think this way, if it was fine before you parked at and now you have problems, then something has to happen in between. In my mind even if your lift pump was dead it should still start, VP has its own internal lift pump that will supply just enough to keep it idling without hurting anything. But it's definitely not enough to drive the truck. Whatever you do do not turn on lift pump prior to cranking and trying to start the truck, that will actually prevent it from starting as VP does not like pressure on startups. If I had to guess your problem is losing prime. Because when you use either it starts. You got a tiny hole somewhere whether it's in line or return line. Some people park on the hill nose down to keep fuel in lines so it does not siphon back out to tank. You can try that and see if it helps. Another thing you should definitely do is get a fuel gauge, you want minimum 14 PSI driving down the road. 

Either way let us know what the end result was, good luck. 

[CARTOYZ]

Yes the tach does work, However it has quit a couple times and comes back, Also, . when I left it 8 days ago it wouldn't start and havn't move the truck a inch and went out just now and fired right up. wth?.   Can I mount a fuel pressure gauge on top of fuel filter housing?  I am thinking I am not losing prime as it started, and it was parked on level ground.

Edited June 4, 2018 by CARTOYZ
wording

[CARTOYZ]

An update.  I put a scanner on the beast and came up with code P1690. when I looked it up it is telling me the crank position sensor does not agree with pump. I have only seen engine light on once and engine was running. Any thought?

[dripley]

Sounds like the CKP is on it's way out. Could just be failing intermittantly until it quits all together.

[Mopar1973Man]

8 hours ago, CARTOYZ said:

Yes the tach does work, However it has quit a couple times and comes back

 

4 hours ago, dripley said:

Sounds like the CKP is on it's way out. Could just be failing intermittantly until it quits all together.

 

I would investigate the crank sensor. Dropping of tach signal can prevent starting also prevent the lift pump from firing up.

 

8 hours ago, CARTOYZ said:

Can I mount a fuel pressure gauge on top of fuel filter housing?

 

Kind of hard to read the gauge if it's under the hood. You need to be able to see the gauge while cranking and driving for proper fuel pressure. 

5 hours ago, CARTOYZ said:

I put a scanner on the beast and came up with code P1690. when I looked it up it is telling me the crank position sensor does not agree with pump.

 

So you might be looking at that crank sensor first. Here is the article on the code and how to test.

 

Funny... AC noise possible too.

Quote

Measure AC noise to ECM by connecting DVOM between ground and terminals No. 48 and 50 (Red/White wires) at ECM harness connector. If AC voltage is 25 mV rms or less, go to next step. If AC voltage is greater than 25 mV rms, replace fuel transfer pump. See appropriate REMOVAL, OVERHAUL & INSTALLATION article.