What could be a possible cause of a long crank when the motor is hot?

Starts great when cold

Fuel pressure constant 17 psi

Cranks great

Thanks in advance I won't have internet access till first of the week

 

PSG on top of vp my first guess. Other than that could be a number of things. Try dumping water on vp next time and see if it helps. This was an issue with early vps.

 

That was my thought also just hoping it was something else. I have replaced it twice already. Thanks for the response

Any codes at all

No codes at all

I guess try water and then maybe hot wire test to eliminate the ecm

Lets put it this way PSG overheating is extremely rare. I would say the fuel pressure being to high during cranking being more of a cause. No more than 12 PSI while cranking. If above 12 PSI hard starts happen.

Wired a relay in that cuts power to the LP in start position.  Went to to the store this evening seems to be starting good now,  will know for sure Monday after towing the RV this weekend.  Thanks moparman1973 for the tip, sure better than another VP.

Is your Fass not connected thru a relay triggered by the oe harness?

1 hour ago, mountaindan said:

Wired a relay in that cuts power to the LP in start position.  Went to to the store this evening seems to be starting good now,  will know for sure Monday after towing the RV this weekend.  Thanks moparman1973 for the tip, sure better than another VP.

I did that with the last IP I had because of hard hot starts. Worked for a while. I used 2 relays in line to power the LP. 1 triggered off the ECM and 1 triggered off the power window fuse. That way the ECM is still in control, but power is cut 100% when cranking. Remember if the pump is wired to a key on hot and you're in a wreck the pump will keep running pumping fuel on the fire if there is one. Just something to think about.

1 hour ago, mountaindan said:

Wired a relay in that cuts power to the LP in start position.

 

Let me know if this ends up being a good long term solution. I was thinking about doing this.

In my case it kept a dying VP going for a while longer. Each case might be different though.

This is so you don't have to wire anything in, just replace the relay with this one. As long as you have an aftermarket harness that comes with Fass or airdog, otherwise you'll have to wire in a relay base a factory setup. 

https://m.delcity.net/store/Time-Delay-Relays/p_804415.h_804416.r_IF3003?mkwid=8TgfXoca&crid=11472933143&msclkid=244a8de769fc10e0a1ddd14a10340b58&utm_source=bing&utm_medium=cpc&utm_campaign=Shopping - PLA's(BSC)&utm_term=1100315444392&utm_content=Ad group %231

 

Edit 

I'm just reading the instructions on this relay and it's working opposite from what we need, it keeps things powered on after the ignition is off not the other way around. 

Maybe there is another one that does the opposite  @IBMobile

Edited April 26, 20196 yr by Dieselfuture

That's a neat idea. Need an on-delay relay instead of an off-delay relay. Except then your key-on prime will get shortened, or cancelled.

47 minutes ago, kzimmer said:

That's a neat idea. Need an on-delay relay instead of an off-delay relay. Except then your key-on prime will get shortened, or cancelled.

Yeah but I don't think it will be a huge deal, mechanical pumps don't prime ether. The only other thing is if it's cold and you have to wait for wts to go out. And the initial key on sends juice to relay and if it's when it triggers it then not sure if it will work ether. Beyond my thinking. 

Why not just measure the fuel pressure and adjust it to so in not exceeding 12 PSI at cranking. Pretty simple eh? 

 

My AirDog is set for 17 to 18 PSI at idle and cranks right at 10 to 12 PSI no issues. Most people have them turned up way too high and wonder why the hard starting. 

12 hours ago, dave110 said:

I did that with the last IP I had because of hard hot starts. Worked for a while. I used 2 relays in line to power the LP. 1 triggered off the ECM and 1 triggered off the power window fuse. That way the ECM is still in control, but power is cut 100% when cranking. Remember if the pump is wired to a key on hot and you're in a wreck the pump will keep running pumping fuel on the fire if there is one. Just something to think about.

What do you mean "worked for awhile"?

56 minutes ago, Mopar1973Man said:

Why not just measure the fuel pressure and adjust it to so in not exceeding 12 PSI at cranking. Pretty simple eh?

Keep it simple.  Doing an adjustment is a lot easier than doing a lot of rewiring.

If that doesn't work you might try this.

 

 

Just returned from our first camping trip this year truck performed great, thanks to everyone for the suggestions and especially Moparman1973 high pressure seemed to be the problem.

Thanks @IBMobile, I've been looking for a wire that's switched with engine running. I'm going to use it to disable the grid heaters through a 200 amp solenoid I got off of Amazon while the engine is running. I think it's the simplest way to protect the alternator from the grids. Sorry to get the thread off topic.

 

@kzimmer, I will be installing a different type of grid heater control on @JAG1 truck next weekend and doing a write up on that if you can wait and see what it is.