Fuel sending unit

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  #1  
Old 11-01-02, 06:53 AM
RobSchaef
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Fuel sending unit

I have a 96 Jeep Cherokee 4.0L that wouldn't start. I replaced the relay with a new one and check the fuse. No noise coming from the pump. So I replaced the fuel filter and pump. It worked great for about 4 blocks. Then no power to the fuel pump. I pulled the relay and fuse out a couple of times and put them back in and got it to start again and it ran for about 2 min and then died. Still no power to the pump. My assumption is that it is the fuel sending unit, or a short in the wiring. I don't know much about wiring but thought if it had a short it would never get power, and along that thinking think the sending unit it bad. Do you think I am on target? Is a sending unit something you can get at an autoparts store or a dealer only item. If it's a dealer only type item, is this a part you would feel comfertable getting from a salvage yard. Any help would be greatly appricated.
Thanks,
Rob
 
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  #2  
Old 11-01-02, 10:36 AM
RobSchaef
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Turns out the eletrical plug that goes into the pump wasn't all the way clipped and came loose. I would be done putting it back in but the rubber boot that goes on the end of the assembly has come off and floating in the tank. Trying to fish it out for the past two hours but no luck. I am going to try to drop the tank but the bolts are very tight. I put penetrating oil on them a few hours ago but no luck. Any tips on dropping the tank?
 
  #3  
Old 11-01-02, 04:28 PM
Joe_F
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Soak the bolts good with WD40 or PB Blaster and they should come loose.

No, do not order any part like that except OEM/dealer new.
 
  #4  
Old 11-01-02, 07:39 PM
RobSchaef
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Thanks Joe. I got the tank off and got the boot out. What a pain. Now its bank together and works except the fuel pressure is at 50 PSI and should be 14-15 psi. Chiltons says on my model it is part of the sender mechanism. Does that sound right? I thought all the fuel sender did was comunicate with the fuel gauge. Please let me know if you think the sender could control fuel pressure. Perhaps I damaged it somehow in all of the tank removal and install shinanigans that went on today.
Thanks,
Rob
 
  #5  
Old 11-01-02, 07:40 PM
RobSchaef
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Also, how bad would it be to drive about 5 min away to have a shop see if they can get the pressure right. I am worried about trying that becuase it seems to me that pressure 3 times what it should be at idle might bust some seals.
 
  #6  
Old 11-01-02, 08:00 PM
Joe_F
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The Chrysler dealer's parts book should break it all down and say what comes only with what.

As I recall, the pressure regulator is built into the tank unit/module/fuel pump. Perhaps you reversed a line there?

If the fuel pressure regulator is bad, your pressure will be haywire.

I assume you are checking the rail pressure with a fuel pressure gauge?
 
  #7  
Old 11-01-02, 08:05 PM
RobSchaef
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Yes, I am. It is frustrating also because the nice fuel pressure guage I bought from Autozone is just a little big. Hard to use it and keep it one, but after about five min you can get it to stay on and read the pressure. Hooked it up the same what I had it hooked up yesterday and it read 16 PSI but exhanged the pump today to make sure the other one didn't go bad after running with the wire plug partially unhooked. I would like to drive it to the shop and let them fix the module and pressure but worried about driving it anywhere with the high pressure. Maybe I will see how much a sending unit is and change that for kits to see if it is really all the same part.
 
  #8  
Old 11-01-02, 08:13 PM
Joe_F
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Something doesn't sound right here. 16 PSI is too low for MFI Chrysler like that.

Make sure it is a fuel pressure gauge and not one used for fuel injector cleaning purposes. K-D, Craftsman, Lisle, and others make fuel PRESSURE gauges. Double check that with AZ.

Compare your readings/test procedures/findings with the specs shown in autolibrary (linked in my signature file below).

Tell us what you find.
 
  #9  
Old 11-01-02, 08:36 PM
RobSchaef
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I wish.
From that web site:
Start the engine and let it idle.
The pressure gauge should read 14-15 psi (97-103 kPa).
Totally bumming. I don't see how I could have missed something. It was pretty idiot proof. Somehow I must have either pulled a wire off the regulator-sender unit by accitdent or damaged it.

Maybe a fresh start in the morning will help!
Thanks for the info.
 
  #10  
Old 11-02-02, 04:57 PM
RobSchaef
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You were right about the pressure. I don't know if it was the gasoline bath I took yesterday effecting my brain or it just being so late. The site and my book say that the 96 4.0L is a multi port injection system. It say's that the pressure should be 31PSI but I have 41PSI here is my quandry:
The books and the site refer to models that have fuel return systems. On the others it says if you take the vacum hose of the fuel regulator it will go up to 39PSI. Well mine is the only model that have the fuel regulator in the tank and no vacum hose to remove. Then the books and site say that if the pressure is above 45PSI look for pinching in the vacume and gas lines. Mine have no pinces.
My thinking is that since mine is the only one with the regulator in the tank 39PSI is my normal, and under 45PSI is Ok.
Here is what I have done:
Replaced the relay.
Checked the fuse.
Replaced the fuel filter.
Replaced the fuel pump.
Replaced the fuel pressure regulator.
Checked lines for leaks and kinks.
My thinking is the it is fine at 41PSI and plan to call Chreysler on Monday.
I sure would like to hear some opinions.
 
  #11  
Old 11-02-02, 08:21 PM
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Location: Colorado
Posts: 431
Fuel Pump Pressure (psi) 47 - 51
With the vacuum line disconnected from the fuel pressure regulator (if equipped). Fuel pressure is measured at the test port pressure fitting on fuel rail.

1996 Models
The fuel pressure regulator on 1996 models cannot be serviced separately. If it is found to be defective the entire fuel pump module must be replaced.

I believe that this one has to be tested with a special fuel gauge/adaptor and may need to be hooked up to a special scanner. Your best bet is to talk to the Chrysler Service Manager.
 
  #12  
Old 11-02-02, 10:06 PM
RobSchaef
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Thanks. I replaced the fuel pressure regulator. It does say special tool or equivalent. I used a fuel pressure gauge at the valve fitting on the fuel rail. I would think it is safe to drive for testing. That was my main concern but hoping someone would have a spec listing that tells the fuel pressure for my vehicle. I have looked on the internet for hours. Lots of specs but non stating the pressure for a 96 Cherokee 4.0L. There is no vacum hose equipped and 41 is inbetween 31 and 51 so I am thinking its Ok.
 
  #13  
Old 11-03-02, 07:15 AM
Joe_F
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You might just call a Chrysler dealer and ask or, go to a Jeep forum and see if someone has a Jeep shop manual they can peek in for you.

Alternatively, if you are getting into these types of repairs, owning your OWN copy of the Jeep shop manual is a good idea .
 
  #14  
Old 11-03-02, 07:47 AM
RobSchaef
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Thanks! I really appricate all of the help!! I do plan to pick up the shop manual now that the car has 70k and I think the repairs are going to come more often and I finally have a garge and some tools to do the work!
I have a dealer CD for my 99 Cougar. I wonder if there is such an animal for the 96 Cherokee. That CD is great. Exploded views and specs on everything.
 
  #15  
Old 11-03-02, 11:24 AM
Joe_F
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You could check with Dymet, who does the OEM manuals for Chrysler.

The link with the contact information is in my signature file below.
 
  #16  
Old 11-03-02, 11:50 AM
RobSchaef
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Thanks. I found some on Ebay including a CD.
Took a more extinsive search on the Autolibrary.org link in your sig and found the 50PSI plus or minus 5PSI is good. Also, mine does require a special tool to check the pressure, go figure.
Thanks for all the help and I hope this post will help others with 96 Cherokee 4.0L's!!
 
  #17  
Old 11-03-02, 01:43 PM
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Join Date: Sep 2002
Location: Colorado
Posts: 431
Fuel Pressure Gauge Adapter - Usage
Available from Miller Special Tools


NO: 14-03-98

GROUP: Fuel

DATE: May 1, 1998

SUBJECT:
Fuel Pressure Gauge
Adapter Usage

MODELS:
1996 - 1998 (AB) Ram Van
1996 - 1998 (AN) Dakota
1996 - 1998 (BR/BE) Ram Truck
1998 (DN) Durango
1996 - 1998 (XJ) Cherokee
1996 - 1998 (ZJ) Grand Cherokee
1996 - 1998 (ZG) Grand Cherokee (International Markets)


Currently, four different fuel pressure adapters are required, depending on application, to attach a fuel gauge for pressure testing. The matrix lists the adapter part numbers and their application.
 
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