Engine/Transmission (1998.5 - 2002) Changed fuel filter, now fuel pressure readings are lower

[24V-DSL]

Normal change of fuel filter today at regular 10K interval. Old filter was fine, and the canister was absolutely clean. After truck re-started my fuel pressure guage (electric Auto-meter) is reading 2-3 psi lower throughout any rpm range. Took a 25 mile trip at different speeds and had two shut-offs and re-starts. No improvement.



New lift pump 5K ago... at 50K, and the fuel filter had only 5K on it so I didn't change. Changed lift pump to the new 3990105 because my psi readings had been steadily declining. New lift pump gave me very strong readings of 15-16 (pegged) at idle, 14 at steady 60 mph, and 9-10 at WOT.



I really believe that these lower numbers are related to the filter change, but I can't think of why????



truck is 01. 5



EDIT: Fuel pressure is measured after the filter.

 

[Gary - K7GLD]

WELL, my crystal ball is all cloudy, and my mind-reading ability gettin' sorta poor, so I'll hafta resort to the old fashioned way:



Wherinhell do you read the dern pressure, BEFORE, or AFTER the fuel filter... ?



It sorta makes a difference...



IF you read presurre BEFORE the filter, then it's pretty likely the old one was either dirtier than you think, or other characteristics changed the readings...

 

[Chipstien]

A little off subject.....

24v-dsl, how's that sender holding up. I went through 4 senders in three month then gave up. Returned the quage and went to mechanical and got back 150 bucks.

 

[24V-DSL]

Sorry....

Gary... . My pressure is read AFTER the filter. Sorry I left that out. Anything else in your crystal ball?



Chipstien... . Still running the original sender... . ~30K miles

 

[illflem]

My experience is much like Chipstien's, surprised your sender has lasted as long as it has. More often than not low fuel pressure readings are the sender's fault. Check with a mechanical gauge and see what's up. If your sender is out it will be cheaper to replace the entire setup with a mechanical gauge than to buy just a sender.

 

[24V-DSL]

thanks, illflem....

Well, this is wierd. Pressures are now back to prior readings. Gradually worked back today after full warm-up and ~50 miles. If they don't stay this way, I'll be looking for a sender replacement.

 

[Gary - K7GLD]

AH! My guess would be an air bubble in the line to the sender due to the filter change that finally worked its way out - theoretically might not supposed to make a difference - but bet that's what caused yours!



That's why it's important to know where the sender/line is installed...



This is all good stuff to hear about - because MY fuel pressure line is also after the filter - right at the VP-44...

 

[JCyrbok]

Air bubble

Air bubble is my thoughts too. Mine does roughly the same thing after a Fuel Filter change for a day or two. Mine consists more of slower readings and when the key is first turned on when the pump " primes" the VP for acouple of seconds my gauage doesnt pick that up. Acouple of start-drive-restart cycles cures it.



Probably air in the line like Gary said.



Happy Holidays

J-

 

[Jvann]

Same thing here

I get the same thing after fuel filter change for a couple of days. The reading seems to be a couple PSI below the old filter reading but gradually goes back up. Pressure is read at the pump. It must be air bubbles because it does go back to normal shortly.