DropTrooperZim

Im about to replace my fuel pump and Im thinking about installing a simple in-line fuel filter in my 2000 XJ. Is there anything I need to consider before I install an in-line filter? Will it change my flow or pressure or have any drawbacks as opposed to no in-line filter?

investinwaffles

I would like to know this as well. I feel like a replaceable filter is just too easy vs. having a sump screen which leaves tons of dirt in your tank.

I think there are some rubber sections that you could easily spice into (its not all hard-lines), but I am unsure of the negative consequences.

I assume since the XJ is a returnless style system, that the pump will just increase its duty cycle to maintain ~49psi. So a non-clogged fuel filter should have no detrimental impact, other than causing the pump to increase its duty cycle slightly, if at all. Can anyone confirm that logic for me?

I would probably try and use one of these, since they come with brackets (I think)
http://www.oreillyauto.com/site/c/de...2515&ppt=C0025

odgreen

There are no rubber lines in the 97+ system. There are hard plastic lines. There is a fuel filter on the tank. It's the metal round part. Every fuel tank has a sock. Adding a fuel filter would gain you nothing except another maintenance item.

investinwaffles

I understand that it would "gain you nothing" in the sense that the original filter will still be dirty - but what level does the in-tank fuel strainer even filter to? From the pictures I have seen online (never held a 97+ fuel pump in my hand), it looks like it would probably only filter large particulate anyways.

Splicing in an external fuel filter, yes would be an additional maintenance item, but I can swap filters in less than 5 minutes on other vehicles so that is of no concern to me. What is of concern to me is that my fuel tank is probably filled with tons of crap from 18 years of accrued particulate, of which I am sure a discernable amount makes its way into the engine.

Necessary to filter that precisely on an XJ? Probably not.
Nice to have and doing things in line with the "do as best of a job as you can" mentality? I think so.

odgreen

You know holding the pump in your hand won't let you see the filter? That's just the pick up sock. The regulator on top (silver round part) has a micron screen.
Hacking your fuel system would just add a place for leaks too.
Install one if you're so gungho on it. Why as for advice if you don't want to hear advice?

salad

It's not a great idea. Since late 1996, the fuel pressure regulator was moved from a vacuum unit mounted on the rail itself to an integral component of the fuel pump module. The entire line from pump to rail must be uninhibited if you want correct fuel pressure.

investinwaffles

I wasn't really asking for advice - more asking for real world info which you unwittingly gave me
Mission accomplished, and thank you

I am not an engineer, so I am more or less going on logical thought here. Searched tons of threads and no one really mentions that there is an actual mesh screen on the regulator assembly itself (or maybe I missed it). I do know that most fuel pumps have better static pressure in a push configuration vs. pull which is logically why I would put the smaller micron filter downstream of the pump and assumed that the fuel strainer is the actual assembly filter. Most people seem to think this as well, based on random threads I have browsed.

Not trying to stir anything up except rational discussion

Nice - also good info that really isn't mentioned in any of the threads I have come accross (although that may be more in-depth as far as actual fuel system operation).

So I assume the PCM controls voltage to the regulator on the pump? How does it account for fuel density and varying pressure (I assume by increasing voltage to the pump)? Just curious at this point - On a V8 which needs more fuel with increased airflow we usually use a boost-a-pump to increase fuel pressure by increasing voltage, but my Mustang is a return style system so it varies the pump speed constantly vs the XJ which I thought was a "returnless" system (in the sense that the fuel pump is always at 100%, correct?)
Basically - how does a returnless style system vary fuel pressure at the pump/regulator itself?

salad

Negative

The OBD-I and Renix fuel systems work this way by using manifold vacuum. Pressure on earlier models varied a fair bit, 31 PSI at the low, 38-42 PSI at wide-open throttle (information from 1995 XJ FSM). But the OBD-II XJ system is different, it's actually very simple: The FPR - however it works (magic?) - is totally integral to the fuel pump module. The PCM has no idea what the fuel pressure is. The FPR is responsible for keeping the pressure up ALL the times. OBD-II 4.0Ls run 49 PSI regardless. The PCM adjusts fuel required by operating the injectors.

investinwaffles

Hmm, sounds like they must be "assuming" for pressure differential at the rail vs. pump/regulator and just ballparking it. Maybe its just not that hard to keep fuel pressure on something with smaller injectors. The constant 49psi was what had me wondering about how it keeps up with fuel demand, but I think the injectors must be sized against the pump to prevent that from happening regularly (pulling enough fuel to drop pressure significantly).

Thanks for the info tho - I wish we could have a Salad-wiki so I could just search your brain for the info I need. Way better than Google

salad

I'll give you better: http://cruiser54.com/?page_id=365

DropTrooperZim

Solid and helpful info.Thanks for the responses all! I'll mostly likely use the knowledge and advice given to not mess with the fuel line.

Thanks again!