Running lean

X

XJRunner

NAXJA Forum User
Location
San Diego
I have an 87 XJ with an 89 engine thats .060 over with a comp cam, precision injectors and a borla header. I pulled my plugs the other day and they were as white as paper. Every sensor on the engine is new basically, I was thinking about getting an adjustable fuel pressure regulator but their $150. What should I check or where should I start?
 
.060 over. i thought 40 was supposed to be the magic number. do you have any over heating problems? with being bored .060 over and running lean i would like to guess that your rig runs on the warm side.
 
damn i wish mine would run that way. mine fan is hard wired to a switch as well but it still gets warm and im only .030 over and my rig isnt running lean. what kind of radiator are you running?
 
im runnig a 3 row as well. do you have anything special done to your cooling system that makes it perform so well?
 
nope lol brand new radiator, new hoses, new pump, new thermostat and I made sure the passages were super clean when I put the engine in
 
damn well congrats on that. everything under my hood is NEW and my rig still runs warm. i didnt do the newer cooling system swap though. just replaced everything that was there.
 
I ran into the same lean issue with my 4.6L. With the gauge on the rail you could see about a 15-20lb drop in pressure when you opened the throttle body. We ended up putting in a in line fuel pump to support the in tank pump as well as a external regulator. Been running like a champ ever since.





 
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well the fuel pump is old, like atleast 5 years old, I just put a new MAP sensor in since my dad has crap like that laying around his shop. We're gonna go for a drive with the gauge on it later
 
redneck said:
I ran into the same lean issue with my 4.6L. With the gauge on the rail you could see about a 15-20lb drop in pressure when you opened the throttle body. We ended up putting in a in line fuel pump to support the in tank pump as well as a external regulator. Been running like a champ ever since.





Click to expand...

impressive...
 
XJRunner said:
I have an 87 XJ with an 89 engine thats .060 over with a comp cam, precision injectors and a borla header. I pulled my plugs the other day and they were as white as paper. Every sensor on the engine is new basically, I was thinking about getting an adjustable fuel pressure regulator but their $150. What should I check or where should I start?
Click to expand...
basic things plugged fuel filter, vacuum leaks, carbon...... like you said regulator?!?
 
rckstarTV said:
huh?!? that wouldnt be an accurate reading. it needs to be tested @idle and under a load for an accurate reading
Click to expand...

huh?!? the pressure at the rail should remain relatively constant at idle and under load-- that's why the pressure regulator is there.

I agree that a failing pump can produce sufficient volume and pressure at idle but not at speed, but his question was specific to "pressure at the rail" which shouldn't change for more than the time it takes for the regulator to "catch up" to engine demand.
 
Shorty said:
huh?!? the pressure at the rail should remain relatively constant at idle and under load-- that's why the pressure regulator is there..
Click to expand...
The regulator actually is designed to keep the fuel pressure constant compared to the pressure inside the intake. That makes the injector action constant over different manifold vacuums.
 
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