is this normal for fuel pressure?

CJBEN · #1 08-03-2004, 04:45 PM

My 92 xj has beeen taking longer and longer cranking time to get the engine started in the last couple months. I am talking about at least 10-15 seconds.I have done all the tune up stuff,didn't make much difference. had a few minuites after work last night,and hooked up the fuel pressure gauge. I had 31 PSI with the engine running. but when I just turned the key on and didn't start it,the fuel pressure would jump to 30 real quick,then with in 2 seconds,drop to absolutely zero. shouldn't it hold pressure as long as the key is on? if this isn't normal,what would cause this?...thanks,Ben

CJBEN · #2 08-03-2004, 05:04 PM

forgot to mention it has the 4.0 and 5 speed tranny

ccjer · #3 08-03-2004, 05:53 PM

Mine does the same thing. It has come up many times before, but I do not think the problem cause and repair has ever been proven. Some will say cps (crank position sensor), but I am pretty sure it is the fuel pressure regulator and/or fuel pump. My regualtor is located on the top of the gas tank, on the outside of tank where the fuel pump goes inside the tank. Anybody changed one? How hard is it? What do you need to (tools and such) to change them out? I actually had the stealership test mine when I brought it in for a recall item (shifter would slip out of park). The said it was the regualtor, and another home town jeep mech. guessed without looking at it that it was prob. the regulator. The pump and reg. are not cheap. If you change it out, let us know... I have another friend with a '96 sport that is waiting for me to do mine to see how hard it is, and if it fix's the problem.

#4 08-03-2004, 06:34 PM

What happens if you turn the ign key to "run", allow the fuel pump to run and then shut off before cranking the engine? Does this reduce cranking time?

ccjer · #5 08-03-2004, 11:01 PM

Speaking for myself and a extremly similiar issue. No, leaving the key turned for even a minute does not seem to help. I can give it one very short crank, then hit it again and 9 times out of ten it will start right up. Once and a while a third hit is nessecary. My friends '96 sport 99,000 miles is the same way. His old '91 started doing it at 180,000, and my old '91 did the same thing somewhere over 120,000. I never changed the pump or regulator and drove it well over 200,000. Just lived with it. As I had it explained to me there is a little rubber diafram in the regulator that likes to leak and depressurize the system after shutting her down.

CJBEN · #6 08-04-2004, 12:01 AM

johnswann....no,not much change in crank time when I turn the key on and off again before I start it

NIX · #7 08-04-2004, 02:01 AM

I almost started with: when was the CPS last replaced? Didn't ccjer replace his a few months ago? That one might be counted out. Another problem with a dying CPS is (often) bad idling and the problems often happen erraticlly.

On an older XJ the pressure regulator is on the fuel rail. Very easy to replace. Dont forget to buy a new O-ring set. I think the O-ring for the connection regulator - rail is in the injector o-ring set (1 extra brown ring) the o-ring regulator - return line is in another set with connectors, plastic rings, also for the connection rail - fuel line. For this setup you need a philips driver and some pliers.

Maybe, if replacing the regulator and all the parts ready available a good idea to replace all o-rings at the rail and injectors. It might prevent a fire and you'll be surprised about the (bad) condition of the present o-rings. Besides, the sets are not that expensive...

Of course I have some articles about replacing o-rings and CPS .

#8 08-04-2004, 06:22 AM

I've had my pump/regulator/sender/screen/filter/pickup (it's a "capsule" unit) replaced at 120K. Engine would sputter and die during sharp left turns whenever fuel dropped below 1/4 tank and then resume after the turn. Common problem in the xj as evidenced by the number of similar complaints reported on the NHTSA website.
Odds are it is the unit causing the problems described here.
The dealer will say that the regulator is a non serviceable unit as it is a component of the fuel pump assy. This is not true. The regulator may be purchased separately and is attached to the capsule by a metal strap. Replacing the entire fuel pump assy is an expensive but easy DIY. Two straps secure the tank to the vehicle, remove the electrical connections to the fuel pump assy, then remove the f/p assy from the tank. If you have a tank skid, there will be few more bolts involved but that's no biggy either. So it's a judgement call as to whether or not you want to try the reg only first, in hopes that it solves your prob, or go with the entire assy and be done with it.

krabysniper · #9 08-04-2004, 12:22 PM

Strange that ya'll have such odd jeeps, every one I have ever worked on had the presure regulator on the front of the fuel rail on the engine. Hmmmmmmm, strange [img]images/graemlins/confused.gif[/img]

ccjer · #10 08-04-2004, 02:49 PM

<blockquote>In reply to:<hr />
Didn't ccjer replace his a few months ago

[/ QUOTE ]

I bought a CPS, but ended up returning it. I was going to install it when I put in new O2 sensors, but could not reach the CPS, so I said f-it. I then bought a new regualtor, it sat in the back seat for a month or so, so I returned it. Needed the money. It was over a $100 bucks if I remember right.

<blockquote>In reply to:<hr />
Strange that ya'll have such odd jeeps, everyone I have ever worked on had the presure regulator on the front of the fuel rail on the engin

[/ QUOTE ]

Yea, it is strange. There is no fuel filter in the rail either. I reseached the fuel pump, reg, and filter on the stealer ship micro-fiche, and it seems it is a all in one unit (filter and pump), and like john said the reg piggy backs on top. If I do pull the tank, I'll prob. do the pump, filter and reg. and be done with it. Knowing I have more new parts in the ZJ :-) The money situation is alot better these days as well.