Intermittent Fuel Delivery Leaks - How?

[AnotherOldJeepGuy]

I figure a leak is a leak, so I have some work to do.  But I'd still like to understand an intermittent leak in the fuel injection delivery.  About a week ago I smelled gas, looked, saw one leaky injector.  It appeared to be leaking at the seal into the hole it goes into.  I have had these leaks before, I have replaced 3 of my 6 injectors, and the last time I had it apart I replaced all the o-rings and had no leaks.  But that's not the question, the question is still why intermittent.  I have looked a couple more times over the last few days and the leak has never showed up again.  I looked at both engine hot and cold.  So scratch head.

 

This morning I installed a new battery and started up to make sure the new battery was happy.  I smelled gas again, looked, the aforementioned injector was dry.  But I see dripping fuel from the bottom of the fuel pressure regulator and a small fuel pool under in in the area of the blue outline.  So Alexa, add a new regulator and fuel line quick connect to my shopping list.  But 10 minutes later I decided to look more closely and capture the leak in a pic, it's no longer leaking and the fuel in the pool has dried up.  There is some dampness still visible on the regulator but no active leaking.  Again the intermittent question.  Truck has not been driven or even run long enough to warm up a lot, but still, scratch head more.

 

Anyone care to kill my cat (quench my curiosity for those that don't decode that metaphor)?

[llhat]

i would still plan on replacing the regulator,  be sure to also source the 'kit' for the hard line "o" rings..... 

 

this 'could' be pressure related, as the pressure drops from engine off, the leak threshold is lowered.

"Could" be temperature related..  

waaay out in left field, porosity on the regulator housing...  
good luck!

[AnotherOldJeepGuy]

Rock Auto lists a PR21T (Adjustable, $48.79) and a PR21 (Not Adj, $57.79).  They look the same in the pics, and there isn't anything in the details that explains what adjustable means (although I assume it's pressure) or how you adjust it. Both list the same OEM numbers.  I'd prefer not to mess with adjusting, but, what does it take to adjust it and should I consider this?   And of course I'd rather spent 49 that 58, but if the adjustable is something I'm going to have to screw with often, the extra 9 would be worth it.

 

[llhat]

on the 'stock' regulator,  it self adjusts by the connection of the vacuum line.  

IIRC,  at low vacuum ( experienced during acceleration) the pressure to the injectors is increased for additional fuel flow.  High vacuum the pressure is lowered.

 

I'd have no idea on the differences between the two listings on RO

 

those two listings...  the specification table seems a bit confusing to me... with a lot of contradictions, especially on the PR21T 

part finish... chrome, then regulator finish, silver.. ??

material.. stainless steel ?  

boost vacuum reference port  (no), then below stating 'reference port included  (yes)

connector type (pin)... there is no real connector on these.

inlet quantity (1)...  where PR21 shows (2)...   hmmm  

 

 

 

think i procured mine off of evilbay and 'so far so good'... 

 

[AnotherOldJeepGuy]

Good points on the inconsistencies.  So it sounds like "adjustable" doesn't mean "user adjustable", but somewhat of an on-demand kind of thing, and the one that isn't adjustable is in someway going to attempt to maintain a preset pressure, which seems to still be kinda on-demand adjusting thing so hmmm again!

[llhat]

i believe the Renix system relies on a variation in fuel pressure to perform,  the standard regulator does just that... 

 

mine IIRC  when just running is about 32psi,  if the vacuum line is removed from the regulator, it increases to 39psi 

i think that is by design.

 

confirmed with this entry from a manual i downloaded...  

 

 

renix regulator.pdf

[pizzaman09]

On 9/24/2026 at 5:39 PM, llhat said:

i would still plan on replacing the regulator,  be sure to also source the 'kit' for the hard line "o" rings..... 

 

this 'could' be pressure related, as the pressure drops from engine off, the leak threshold is lowered.

"Could" be temperature related..  

waaay out in left field, porosity on the regulator housing...  
good luck!

I think you have hit 50% of the answer with the reduced pressure comment.  Seals use pressure to help push them to the edge of the cavity they are attempting to seal.  The other part of the problem is that all rubber seals experience a phenomenon called compression set.  This is effectively when the rubber takes the shape of its compressed state and doesn't spring back to its original as molded design.  Temperature can also play a roll and the answer very well could be a combination of all three.

 

I find it unlikely that housing porosity could be a source but it's possible, similarly corrosion or rust can do the same thing.