Fuel pressure problem 1990 4.0L

My 1990 Cherokee 4.0L takes a long time to start. I need to crank it about 30 seconds before it fires. It is just as hard to start next time, hot or cold.

I noticed that the fuel rail pressure bleeds down to nothing after about 2 minutes. From reading all the cautions in the FSM, this rail is supposed to hold the pressure, right? I clamped off the return line from the regulator and still have the problem.

Surely there is a check valve somewhere in the system to hold this pressure. Can anyone tell me where it is? I am open to any other suggestions you may have.

TIA!

If I´m understanding correctly? The line coming out of the side of the regulator isn´t the return line, it´s the vacume line (actuator) for the regulator. The return line is at the rear of the fuel rail.
I have had many XJ´s that lost some pressure. But it never did get bad enough, to have to seriously deal with. I´ve been keeping an eye on mine.
Have heard the check valve in the fuel pump, can cause loss of pressure. The fuel rail, should hold about twenty PSI after half an hour. I`ve most times, barley/almost had that much pressure.
Using a couple extra pieces of rubber (as protection), I clamped the rear fuel return line shut with a pair of vice grips. Pressure still fell off, so I´d guess my pressure loss, is in the front of the fuel rail (pump check valve) or possibly a leaky injector (smell any fuel?).
I´ve looked at a couple of in line check valves (after market) but they all seemed to choke down the fuel line diameter considerably.

8Mud - Take another look under your hood. There are 2 hoses on the pressure regulator. The small one on the passanger side is the vacuum line and the larger line on the driver's side is the fuel return line. If you clamped the line at the rear of the rail, you clamped the supply line. It the rail did not hold pressure, you regulator is probably bad.

I bought an assortment of aftermarket plastic checkvalves from a plastics distributor, with hose nipples from 1/8 to 3/8 inch. I am told by the manufacturer that they will hold up to gas, but they are not designed for it. I hesitate and do not want to cut a hose under the hood and risk a fire. If I can't find the root cause, I am about due for a fuel filter replacement and may open a hose back there and add a valve. If I go that route I will let you know the results.

I forgot to mention in the last post, I have new injectors and O rings. They were replaced because 3 of them were leaking at the seams in the body. The loss of pressure symptom remains the same.

Failure of the check valve in the fuel pump is a common problem with age. Do a search and you'll find info. I think someone found a BMW check valve that was less than $5.

Figures I was bassed acwords, probably confusing my XJ with my Chev. Happens when you get old.
I did a regulator test in the middle of summer. Pressures were close enough. But have noticed the hard starting problem, getting worse lately. Probably going to be dealing with the same thing you are, soon.
Thanxs for setting me straight. Wouldn´t it be a bummer to install the check valves backwords? :eye:

I thought when the key is turned to the on position (not start) the fuel pump turns on to bring the pressure in the fuel rail up. What if you kept the key in the on position until the fuel pump stopped and by reason then the fuel rail should be at the proper pressure. Of course I maybe wrong or just thinking in the wrong direction.

I just tell my wife when it takes that long to start I am just getting the oil moving before the Jeep starts so the engine will last longer. :doh:

I usually let it sit for 10 seconds or so, with the key in the on position. Typically takes five seconds (5 or 6 revolutions of the starter) for it to crank over. If it doesn´t crank, I stop for a few seconds and try again, usually cranks on the first or second revolution. I always guessed (figured) that the fuel leaked down and there was a bit of air in the system, that required some circulation and/or injector action, to purge.
Figured out my confusion about which was the supply line and which was the return. My Haynes manaul, shows the return as being the rear line to the fuel rail, in the MPI pressure test, section. And the front (which makes more sense) as being the return, in the fuel rail assembly and dis-assembly section. No wonder I was confused. Next time I´ll use the shop manual.

Lunatic728: That is the behavior I have had in other cars with an electric fuel pump. However, the Jeep appears to turn on the pump for a few seconds, then turn it off. This might be some protection against fire for a fuel leak, I can only speculate. It does help some if I turn the key on, then off, then back on a few times, like I was reading the codes, if this were a newer 4.0. Not much help, though because the pressure bleeds down so fast.

I had done a search of the archives here and came up empty until PaulJ recommended I add "BMW" to my search string. I found the check valve part number to be 16 14 9 068 988. This is actually a kit that BMW issued so they would not have to replace so many fuel pumps under warrenty for hard starting. I did a google search and found the part listed online at BMA:
http://www.bmaautoparts.com/

I read in a previous post here and one on a BMW forum that the kit cost is between 3 and 5 bucks. I don't know how much they will want for shipping, but the total will surely be less than a pump and much easier to install. I will call them in the morning and order it.
MoFo

I just called BMA at 888-262-3911 and ordered 2 of these check valve kits.

BMW part number 16 14 8 068 988

The cost was $2.40 each with $4.00 to ship via priority mail. They said it would take 2 days for them to get the parts and 2 more days for them to get to me. I will have the check valves by Friday.

Thanks again guys!
MoFo