A couple of years ago I replaced my second Carter pump. I have a fuel pressure gauge installed. Early last summer, pressure would drop periodically, so I thought that pump was on the way out and ordered a FASS DDRP. When the pump arrived, I didn't have time to install it, and meanwhile the Carter was behaving again so I sort of just hung on to the DDRP as a back up.

Stupidly, I didn't send in the warranty info.

So, earlier this summer, the Carter started dropping pressure periodically again (sudden drop and then pop back to normal), so I figured might as well put the DDRP in. It gave me higher pressure and seemed solid....for about 5 weeks.

Suddenly, I had no pressure. When I turned the ignition on, all I could hear from the engine was a couple of clicks, no pump running. The engine was performing as usual, though.

Given the Carter was just doing the periodic thing, I put it back in, better than nothing while I tried to get the FASS straightened out. It seemed fine for awhile, but now it is back to the periodic drops, sometimes all the way to zero for a moment, sometimes lingering around five and then back up to 12 at idle the rest of the time.

I have heard the pump run when I started the ignition even though the gauge said 0. The power to the gauge is on, or at least the lamp is on.

My question is, might there be a problem with the gauge sending unit? Has anyone had their pump behave this way? I checked the high pressure side and there was no fuel leaking. The low pressure side seemed tight, but I had reused the crush washers from the Carter to install the DDRP since they don't provide new ones . I have ordered new ones just in case it is a priming issue.

Meanwhile, I even more stupidly didn't get around to trying to contact FASS until just outside the 1 year mark . I'm having a hard time finding a number to call them. I had purchased it through KLM Performance and emailed them but have got no response. I only got one month out of that thing - sooo much better than the Carter

Thoughts (aside from how stupid I am for being lazy about the warranty...)?

 

Sorry to hear about your bad luck. This is precisely why I installed this.

http://www.dodge-diesel.org/9fubomelipus.html

 

lots of help there.

If you are not noticing a difference in engine performance I would tend to believe that the sender on your pressure gauge might be suspect. As long as you are sure that all your electrical connections and grounds are good.

I would double check all my electrical connections for the gauge and the lift pumps first.

Did you install a draw straw kit or is it still factory? Is it possible your fuel lines are collapsing? have you checked the sender in the tank? Do the problems show up when the tank is at different levels or only when empty/full?

 

Find the receipt or have your vendor send you another then call FASS. I read 1 poster bitching about how bad FASS' warranty support was & what a crappy product they put out yada yada yada. The FASS people only wanted to know that they weren't being ripped off by someone who had trashed the pump then wanted after warranty replacement.

Sometimes things break before they should but call. Report back if good results. Don't hold them accountable for your error AND, the pump shouldn't crap out so quick.

 

After replacing several lift pumps, i got to thinking that surely that many pumps cant be going bad. I've been monitoring the voltage from the computer that feeds the lift pump and it fluctuates from 6.4v to 15.6v. A 12v lift pump motor isnt going to run with that low of voltage. Also, even adding the relay kit to the lift pump wont work because it takes 8v to pop the coil. I've replaced the computer and it worked for a year and a half, but now the same thing. My lift pump no longer runs through my computer at all. No problems since then.

 

The voltage fluctuation you measure from the ECM may be normal. The ECM does not put out a constant 12 volt signal to the lift pump when the starter is engaged. The 12 volts is chopped up into a square wave that switches between ground (zero volts) and 12 volts. Cummins thought this was a good idea to limit the fuel pressure to aid starting. After the engine starts, the voltage to the lift pump should be a constant 12 volts (or battery voltage).

The drawing below shows the voltage waveform the lift pump will see if everything is working. One problem in measuring the voltage is that most DVMs don't know what to do with a square wave when switched to measure DC voltage. I'm not surprised that the reading will be bouncing around. This does not mean that the ECM may not have been bad but be careful that you measure the voltage after the engine is running and the starter is not running.

 

The FASS is very quiet. You will have a hard time hearing it. I installed one this year and I too, thought it was not working.

 

bent valves is right. The voltage to the lift pump is supposed to be limited during cranking so that maximum fuel pressure doesn't reach the VP until the engine starts.

If you're uncertain about your sender, then before you do anything, find a mechanical fuel pressure tester that taps into the fuel line schrader valves in either the banjo fitting on the fuel filter housing fuel line or the VP inlet fuel line. You may be able to even get a diesel shop to do it for you for a few bucks or just buy your own. But the only way to read the gauge is to have the hose come out from under the hood and in the open drivers side window. Obviously not a permanent item.

Maybe your sender is bad but I'm leaning toward both fuel pumps being no good. The OEM lift pump (Carter) is notorious for failing in sporadic manners and the FASS DDRP also has a history of crapping out too. At least the earlier ones did. Not sure about the current version.

 

I have had more than one of the Carter pumps that would drop in pressure every now and then. I thought the gauge or sender was the problem but it was the pump. The pressure would be running about 10 or 12 lbs., then drop to about 5. It would stay there for a while and jump back to normal again. Changed the pump and the problem went away until the next pump failed. When the next one goes it will be replaced with something better, the Carter pump is a joke.

 

My issue isnt with the motor cranking it is all of the time. With the motor not running it was only at 6 volts. Not enough to even turn the lift pump. Before my fix of bypassing the computer, the voltage jumped all over the place sometimes allowing the lift pump to run, sometimes not. Mine doesnt run when the truck is trying to crank now with the relay setup the way i have it. I still feel that the extreme voltage fluctuations were what kept eating my lift pumps. It didnt matter what brand, the motors kept burning up in them. Low voltage isnt good on a motor.

 

How did you wire the lift-Pump without the computer?

Mike

 

good question. because i was thinking airdog for my 02.

 

All you would have to do is run keyed power to a relay and have your hot lead go directly to the battery. Easy peasy. Funny this is that this is how my Raptor wire loom came from Pureflow so I cant imagine your FASS not being the same way. The only difference is that my ECM still tells the relay when to allow voltage to the fuel pump.....not how much voltage. The way you want to set it up would eliminate the ECM having anything to say about when the fuel pump runs. When you simply turn the key on, the fuel pump would run. No prime, no bump start run, just run all the time.

 

If I can't make it work with the ECM I will try that with my truck.

Thanks, Mike

 

Could someone point me to detailed idiot proof instructions on how to by-*** the ECM? I swapped out the connector with a new deutsch connector, but the old OEM pump still didn't come up. So I put the DDRP back in and voila - got over 15 psi, so that pump wasn't the problem.

However, after driving a bit today, I experienced the same drops with the DDRP, hanging above 15 at idle, then dropping to 2 for awhile, then popping back up. Other times it would jump around before going back up to 15. Sometimes it would drop on acceleration, and then pop back up coasting, then drop on accel again. Other times it would stay up for acceleration. There's just no rhyme or reason to how it behaves! For the most part it stayed up, but I'm not happy about not being able to fix this!