Attention: TDR Forum Junkies 
So, you have guages, and begin to see shifting fuel pressure - or maybe like me, start your truck one morning getting ready to head out - then notice your fuel pressure is way down or gone completely - sound familiar?
In my case, we were just east of Mojave, pulling our 5er, and getting ready to hit the road for the final 350 miles on back home after 3 months traveling. The pusher pump took over, and provided about 10 PSI, so no worries, and we completed our travel on back home. We stopped several times that day - and each time I restarted the truck, PSI would come up to normal for about 45 seconds, then the stock LP would quit, leaving only the lower output of the pusher pump to keep fuel flowing.
Couple of days later, I decide to do more checking on the LP - and first hooked up my mechanical guage to verify the sender hasn't simply failed on my fuel pressure guage - nope, it was fine.
I next checked the voltage going down to the LP - and it also checked out fine - so it looked like it was time to do the notorious LP replacement...
WRONG!
It was only AFTER doing the swap - which totally restored my "lost" fuel pressure - and then disassembling the original LP that I discovered my own stupidity and failure to FULLY check ALL possible factors in lost fuel PSI thru the LP...
The original LP was perfect - NO mechanical problems to be detected - motor turned freely - rotor and vanes perfect - and pump screen was as new - and the spring and pressure valve was also perfect as nearly as could be detected. Reassembled the pump and applied 12 volts - it spun as it should, and was obviously putting out pressure, even though no fluid was present for a proper test.
I next jury-rigged a loop of tubing with the ends immersed in diesel fuel, and with my mechnical guage Teed into the output side of the pump, fired her up for a test - ran perfectly, and by clamping the tubing closed on the output to provide a restriction to flow, got rated PSI from the pump as long as was willing to allow it to run - the pump was NOT the problem!
What WAS the problem? Well, as nearly as I can figure - since it was the only thing I didn't check, was poor contact at the plug into the base of the LP. Adding to that assumption, is the fact that I had a number of similar experiences with the oil pressure connection on my old '91 truck, which also used a very similar contact setup - yeah, I shoulda known better!
SO, where did I get the spare LP I substituted? It came from another Dodge owner who had it installed for only a few hundred miles, but was seeing low PSI with it, so swapped in another one - and sent me his "old, defective" one to experiment with for another article I posted over in the DTR titled "Anatomy of a lift pump"... His "defective" pump installed on my truck is putting out as good a flow and PSI as my original did before this fiasco!
*I* coulda saved myself a lot of work by simply CHECKING that dern plug, cleaning the contacts, and making sure the power was actually getting all the way to the LP...
I wonder how many OTHER guys - including DC shop mechanics have also swapped out perfectly good LPs - and tossed them on the scrap heap, when there was absolutely NOTHING wrong with them - and then of course, the NEW one operates perfectly as the plug once again is making good contact on the new pump - and everyone walks away satisfied that they've "fixed" the problem - one that didn't REALLY exist, just as MINE didn't!
It's real easy to use a common mechanic's circuit test light to check the plug down at the LP - or a test meter if you have one - or at LEAST, try fully unplugging the power plug and reinsert it - if it shows some beneficial effect, clean the base plug on the pump and the plug end on the power lead with something like TV tuner cleaner and apply a little anti-oxidant paste to keep the contact as it should be - it worked on the oil pressure plug on my old '91 - and I've no reason to suspect it won't work equally as well on the LP contacts on my '02!
In my case, we were just east of Mojave, pulling our 5er, and getting ready to hit the road for the final 350 miles on back home after 3 months traveling. The pusher pump took over, and provided about 10 PSI, so no worries, and we completed our travel on back home. We stopped several times that day - and each time I restarted the truck, PSI would come up to normal for about 45 seconds, then the stock LP would quit, leaving only the lower output of the pusher pump to keep fuel flowing.
Couple of days later, I decide to do more checking on the LP - and first hooked up my mechanical guage to verify the sender hasn't simply failed on my fuel pressure guage - nope, it was fine.
I next checked the voltage going down to the LP - and it also checked out fine - so it looked like it was time to do the notorious LP replacement...
WRONG!
It was only AFTER doing the swap - which totally restored my "lost" fuel pressure - and then disassembling the original LP that I discovered my own stupidity and failure to FULLY check ALL possible factors in lost fuel PSI thru the LP...
The original LP was perfect - NO mechanical problems to be detected - motor turned freely - rotor and vanes perfect - and pump screen was as new - and the spring and pressure valve was also perfect as nearly as could be detected. Reassembled the pump and applied 12 volts - it spun as it should, and was obviously putting out pressure, even though no fluid was present for a proper test.
I next jury-rigged a loop of tubing with the ends immersed in diesel fuel, and with my mechnical guage Teed into the output side of the pump, fired her up for a test - ran perfectly, and by clamping the tubing closed on the output to provide a restriction to flow, got rated PSI from the pump as long as was willing to allow it to run - the pump was NOT the problem!
What WAS the problem? Well, as nearly as I can figure - since it was the only thing I didn't check, was poor contact at the plug into the base of the LP. Adding to that assumption, is the fact that I had a number of similar experiences with the oil pressure connection on my old '91 truck, which also used a very similar contact setup - yeah, I shoulda known better!
SO, where did I get the spare LP I substituted? It came from another Dodge owner who had it installed for only a few hundred miles, but was seeing low PSI with it, so swapped in another one - and sent me his "old, defective" one to experiment with for another article I posted over in the DTR titled "Anatomy of a lift pump"... His "defective" pump installed on my truck is putting out as good a flow and PSI as my original did before this fiasco!
*I* coulda saved myself a lot of work by simply CHECKING that dern plug, cleaning the contacts, and making sure the power was actually getting all the way to the LP...
I wonder how many OTHER guys - including DC shop mechanics have also swapped out perfectly good LPs - and tossed them on the scrap heap, when there was absolutely NOTHING wrong with them - and then of course, the NEW one operates perfectly as the plug once again is making good contact on the new pump - and everyone walks away satisfied that they've "fixed" the problem - one that didn't REALLY exist, just as MINE didn't!
It's real easy to use a common mechanic's circuit test light to check the plug down at the LP - or a test meter if you have one - or at LEAST, try fully unplugging the power plug and reinsert it - if it shows some beneficial effect, clean the base plug on the pump and the plug end on the power lead with something like TV tuner cleaner and apply a little anti-oxidant paste to keep the contact as it should be - it worked on the oil pressure plug on my old '91 - and I've no reason to suspect it won't work equally as well on the LP contacts on my '02!
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