dulery

Hello everyone, I am new here. Just wanted to say thank you in advance for this forum... I have came here in the past and found some very valuable information. Now onto my problem...

I have a 1996 Jeep Cherokee Classic, 4.0L, automatic transmission, 160,000 miles, and I have been experiencing a very odd fuel problem that I think I have narrowed down to the fuel pressure regulator that is in the tank, with the fuel pump on this particular year/model. Here have been my symptoms:

For the past, I would say 3 months or so, very rarely, the Jeep was hard to start. Sometimes it would blast right off, while others I might have to crank on it for 15 seconds, depress the gas pedal a bit, and it would finally start, but it might not do this again for a week. Well, it did it again, and before I had to go on a 1000 mile round trip, I changed the fuel filter, because I thought this might be causing the problem. This didn't help, as it did it again. This was step 1.

Another symptom that I had been experiencing right before it died for good was, the engine would idle up slightly higher, to around 1000 rpm's or so. I thought this was odd because it had never done it before, but didn't think a whole lot of it because it was running good otherwise. Well, last weekend I took it for a small trip, came back, shut the vehicle off, and the next day it would not start. I am fairly mechanically minded, and had always noticed the fuel pump coming on for a couple seconds, and shutting off... well, it was not doing this any more, so I assumed it was either the fuel pump/fuel pump relay.

Next thing that I did was buy the fuel pump/new fuel pump relay. I installed the new relay, and it did nothing, so I proceeded to remove the fuel pump and change it, thinking that this had to be what the problem was... well, it wasn't, and it is doing a couple of strange things:

1) I can turn the key on, and of course the fuel pump will not engage... I can try to start it, and it will still not engage.

2) Sometimes, but not always, I can turn it over... I then go up, pull the fuel pump relay out, and plug it back in... sometimes I hear a clicking sound in the tank, and sometimes the fuel pump will start, and run indefinitely until I a) turn the key off and turn it back on, or b) try to start it.

I did check that there was fuel pressure at the rack, and there was some... I don't have a fuel pressure gauge, but it doesn't seem like it is 50 psi, and this is only after the fuel pump is manually engaged by removing/re-installing the relay as I have stated. If you bleed the fuel pressure off after this, it does not regain pressure until the pump is manually engaged as I have stated. As a side note, I called the local Dodge dealership, and the parts man said that there isn't a fuel pressure regulator on this vehicle. I know this is not true, because in my repair manual it specifically states that there is one, but on the 1996 it is in the tank above the fuel pump, on the assembly that fits in the tank.

I apologize for the long post, but I wanted to provide as much information as possible, as I have already spent $150 for the new pump/strainer/relay, and don't want to just start throwing parts at it. Any and all information would be greatly appreciated.

Thanks again,


David

superj

is your ignition switch good? how about your tps and nuetral safety switch?

start by checking your tps with a meter and make sure its reading hte proper resistance at closed and open. then i guess you can clean the nss and make sure its adjusted right? not sure if those really affect anything that has to do with your pump even though they do affect your starting ability.

the ignition switch sounds like a pain to check is why i listed it as the last thing ot check but maybe someone else cna give you a better idea.

also, all fuses are seated well with no corrosion on the pins or blades? and the socket is clean also?

dulery

I appreciate your response. I had thought of the ignition switch, but had not checked it because all of my other systems seem to be functioning properly with the key on. The TPS has not been checked. I will check this, as this might have something to do with it. I don't know if the TPS has direct control over the fuel pump, but it is a definite possibility. I have not checked the fuses, however, I am assuming the fuse that controls the fuel pump is fine, because I can manually make the fuel pump come on. As far as the NSS, I cleaned it about 6 months ago because my backup lights were not working, and it was not starting in park, so I am going to probably rule that one out.

Do you know if the TPS has control over the fuel pump? I am open to all suggestions, b/c I am about to pull my hair out with this. Thanks again!

dulery

Bump

Are there any others with any suggestions? Does anyone know if the TPS controls the fuel pump? I am in serious need of some advice from someone who may have had this specific problem, or one similar. Thanks again!

DM_MKV

This may sound crazy but have you check the crankshaft position sensor? I had the same problem..
Read the last post:

http://www.naxja.org/forum/showthrea...t=start&page=2

Also changed my coolant temp sensor and that helped too.

dulery

Hey, thanks for the reply! That is exactly where I am headed next. I pulled the fuel pump/pressure regulator assembly, and discovered that I was mistaken about it being electrically controlled, so it most likely isn't that. I will likely go ahead and change it though before I reassemble, even though it is about $70. I don't want to ever have to be back in the tank again... or that is the plan. I am going to go buy a good multimeter today and test the Crank Position Sensor, and hope to have a "eureka" moment. Really about to pull my hair out with this... I am hoping that it is. I will re-post my findings, just in case someone else might be having this problem.

dulery

Well, I would like to thank this forum again for the valuable information, it was the Crank Position Sensor. I would like to let everyone know how it is that I came to the conclusion that this was the problem.

Frustrated by this problem, I went and purchased a new fuel pressure regulator as stated above, but I also purchased a diagnostics code reader ($129, but hey... been needing one for a while). After I plugged it into my Jeep, following the instructions, the reader continued to say "Unable to link to vehicle". Thinking that this was strange, I checked the reader on my other two vehicles, and, it worked. So, at this point, I was thinking "man, I bet this is the computer"... so I did a little more research.

Apparently, when the Crank Position Sensor fails, it causes some sort of "short" in the computer, which does not allow the computer to connect to a code reader. Long story short, if your Jeep dies, and you can't hear the fuel pump, no fuel pressure at the rail, and it will not connect to a code scanner... run, don't walk to your nearest auto parts store and pick up a new Crank Position Sensor, because this is likely the problem. I changed this, and it started right up.

Now, on another point of note for those of you with a high mileage Cherokee... while I was under my Jeep, looking up at my CPS, I noticed that my valve cover gasket was leaking at the back, so I picked up one of those as well. When I was moving the hoses and such away from the valve cover, one of the outlets on my Heater Control Valve simply snapped off. I was kind of shocked that it had done this, because I hadn't put enough force to the part for this to happen. Well, it turns out that the plastic on this part had deteriorated to the point that I could simply chip it away with my fingernails. Turns out, this is an $18 part, but it could put you in a world of hurt on a long trip. My advice: if your Jeep has over 150,000 miles, CHANGE THIS PART!

Thanks again to everyone who has tried to help me.

David

carfleet mntc

The C.P.S. controls the auto shut down relay. No C.P.S. no voltage to the fuel pump or the ignition.

kbad

right on, David!....any little tip always helps us along with our problems....cheers and enjoy your ride!

NewXJaddict

I have been having a similar problem with mine too. Changed the pump, filter, swapped the relay with a known good one and still nothing. At first I had fuel at the rail but no pressure and the next day I had no fuel at the rail at all. The new pump never kicked on (that I could hear) so I thought I got a bad pump. Before digging into the tank again I am going to clean up the CPS and hope that solves my problem. I am to the point of ripping my hair out trying to figure this thing out. lol.

Thanks for being sure to post the results. Makes it much easier for someone like me who is not all that mechanically skillful to narrow down problems.