low fuel pressure - 2004.5 3/4 ton

[cpyle]

The sending unit on the fuel pressure feature of my Quadzilla commander failed and I had inaccurate readings for almost a year (waiting for Quadzilla to obtain a dependable replacement sending unit. ) I did have a flow test at the time of the failure which showed the pressure was above specs. The truck was running fine at that time and continues to run well. The gauge was sent to Quadzilla and returned with replacement sending unit, new harness and having been "flashed". After installation, the gauge read only 5-6 psi at idle and 2-4 under load (empty and not pulling the travel trailer). Changed the f uel filter but pressure reading remained the same. Removed the new sending unit and checked with test gauge and got the same low reading at idle. Then replaced the lift pump (which I had on hand from Genos). No change in pressure at idle or under load. What should I do now? Also, if these pressures ar accurrate, am I at risk for damage to cp3 & injectors or is the positive pressure adequate to prevent harm. Lastly, if the pressures are accurrate shouldnt the truck be running poorly ( which its not ) ? Thanks for any advice. cpyle

 

[p-Bar]

I think those are fine for stock lift pump. I assume you are using the filter mounted LP? Just as long as you are not pulling it down to zero on a full load. These CP3's are pretty bulletproof

 

[cerberusiam]

Chekc it with a manual gauge to verify. The electronic ones just don't seems to be accurate. As long as you can hold 3-4 psi under a load that should be good if there are no other symptoms.

 

[cpyle]

P-Bar/Cerberusiam- Thanks for the response, I feel better in local driving for now. But I am concerned about having lower pressures when I hook up to 10k trailer and pull some hills which Ill do right after xmas. So Id like to see some better numbers before I go on the road. So- is it true the these low readings have to be the result of the lift pump alone or are there other possible causes? Related to this, have there been any reports of Genos replacement transfer pumps ( the FP 943 ) having any problems? Before I send the Genos pump back, Id like make sure theres not another solution. Finally, since the Quadzilla Commander faulty fuel pressure sending unit was replaced (which revealed the low pressures ) could this play any part in low readings and have you heard any talk about problems with the reworked Commander?. Thanks again Cpyle

 

[cerberusiam]

In my experience, do not trust the electronic readings. At the very least, add a temporary mechanical gauge that allows you to do the comparisons between the two to verify.

 

[p-Bar]

Curious what stopped you from replacing the LP with the intank unit. Mine went out at 75k and was taken in for warranty and replaced with intank version

 

[cpyle]

e P-Bar I guess I wasnt clear. The problem started with my Commander guage giving me low and erratic readings but when I had Dodge do a flow test they said the pump was ok since the test showed above specs. When Quadzillsa returned the gauge after the upgraded sending unit and after the install, the gauge gave the low reading I described in original thread. I thought at that point it could be the LP and since I had one as back up (Genos) and had 67k miles on the original pump, went ahead and changed it. Result- same low pressures. Given that I pull a 9K travel trailer up steep grades, am I likely to have TOO low pressures even with down shifting ? What would you do in my situation, I havent yet double checked with a mechanical gauge. Ill let you know how this comes out. cpyle

 

[p-Bar]

I like that Raptor mechanical pump that piggybacks with the stock pump or since you have the older pump setup you don't need to install a "draw straw" in the tank so an airdog or Fass may be the hot set up too plus you get the extra filtration which is really needed. When the stock 04. 5 pumps fail they just stop fueling they don't seem to slowly go. Good luck keep us posted may want to try a mechanical guage as mentioned by "cerb"

 

[RKerner]

cpyle, my Commander with the fuel pressure kit reads 16psi with the key on, 13-14psi at idle and 10-11psi at WOT. I have not verified with a mechanical gauge but I could use a calibrated pressure source from work if need be. I also had trouble with getting the system to work but it had more to do with the firmware and board issues than with the sender.