'89 Jeep fuel pump

Reply

  #1  
Old 11-29-06, 12:28 PM
Member
Thread Starter
Join Date: Nov 2006
Location: USA
Posts: 1,342
'89 Jeep fuel pump

I've replaced the fuel pump in my Jeep and have a puzzling situation. With the key in the "run" position, the pump doesn't work, but it does while cranking the engine. As soon as I quit cranking and the switch goes back to the run position, the pump is no longer working. I relieved the pressure in the fuel rail thinking it just has enough pressure and isn't demanding more but the result is the same. Is there a sensor that knows when the thing is running and needs the pump but doesn't allow it to work without the engine running? I've also discovered I have no spark. Are the two related?
 
Sponsored Links
  #2  
Old 11-29-06, 01:12 PM
Member
Join Date: Apr 2006
Location: Floriduhhhhh Us of A
Posts: 611
A few questions..........The pump runs in the crank position if I read your post right........Does the truck start in the start position???
Two things I can think of off the top of my head.......#1 is the C101 connector.......a big gamg plug on the front of the firewall in front of the driver. Many problems with those.........something to do with the weatherproofing........The "fix was to solder and heat shrink each of the wires and eliminate the plug (as chrysler did on later models).......
#2 ............and you're not gonna like this ............If the pump works in start but NOT in run, we can surmise the pump works, and the relay works.......which would lead us to the ECU.......which was a weak spot in those years........It grounds the relay in start, but not in run
 
  #3  
Old 11-29-06, 02:37 PM
Member
Thread Starter
Join Date: Nov 2006
Location: USA
Posts: 1,342
You read correctly. I crawled under the Jeep and put my hand on the tank while my brother ran the ignition switch. With the key on, the pump didn't run. While cranking, it did. When he quit cranking, the pump ceased operating. I checked for spark when the thing wouldn't start after replacing the pump and there is now no spark. Perhaps knowing the history would help so here goes. About a week ago I noticed it took a couple more cranks than usual to get it started. Each start after that took more and more cranking to get it started until it eventually wouldn't start at all. I discovered the fuel rail had no fuel pressure in it and discovered the dysfunctional fuel pump during the investigation. Once I got the pump replaced, the rest of this was discovered while trying to start it. The Jeep is an '89 Cherokee Laredo with a 4.0.
 
  #4  
Old 11-29-06, 04:24 PM
Member
Join Date: Apr 2006
Location: Floriduhhhhh Us of A
Posts: 611
AAAAAHHHHHH.........The plot thickens...........No spark, no fuel????.........Can you check injector pulse??? (got a "noid" light?).........No pulse I'd be looking at the crank angle sensor, located high on the left side of the trans bell housing.......2 wires. White/red..........They should produce 1/2 volt AC current while cranking..............There was a bulletin/repair kit that would take those 2 wires and bypass C101.........If it hasn't been done already
 
  #5  
Old 11-29-06, 06:27 PM
Member
Thread Starter
Join Date: Nov 2006
Location: USA
Posts: 1,342
I don't know what a "noid" light is. Nerd, maybe. Noid, no clue. I'll check out your suggestion tomorrow on the crank angle sensor, check in again and get more marchin' orders. Thank you. At least this gives me a direction to work towards.
 
  #6  
Old 11-29-06, 07:56 PM
Member
Join Date: Apr 2006
Location: Floriduhhhhh Us of A
Posts: 611
Noid lights are little plug in bulbs that fit where the injector harness meets the injector..........When cranking the engine the light should flash indicating
A)that there is 12volts getting TO the injector and
B)the computer is grounding or "pulsing" the circuit to energize the injector....or flash the light..........
I'd be willing to wager you have no injector pulse as well as no spark.......
 
  #7  
Old 11-29-06, 08:16 PM
Member
Thread Starter
Join Date: Nov 2006
Location: USA
Posts: 1,342
OK, that makes sense. Do parts stores normally carry noid lights? If so, I'll get one tomorrow. I want to make sure I understand. I disconnect an injector wire and plug this light into it instead of the injector, crank the engine, and look for the light to blink when the harness tells that injector to inject. Your guess is, it won't blink due to no pulse to the injector. Ahhhhhhhhhhh......... marchin' orders!! THANK YOU!! I'll let you know what I find.
 
  #8  
Old 11-30-06, 07:23 PM
Member
Thread Starter
Join Date: Nov 2006
Location: USA
Posts: 1,342
The local parts store carries the light but were out of stock so I ordered one which will be in tomorrow. It rained all day and I was less than eager to work on the Jeep in the rain so there was no progress today. It's supposed to be better tomorrow and the light is supposed to be in so I should be able to do tests then. I'll let you know the outcome. (I know, "what a wimp".)
 
  #9  
Old 12-06-06, 05:20 PM
Member
Thread Starter
Join Date: Nov 2006
Location: USA
Posts: 1,342
Their idea of tomorrow, and mine, seem to be a bit different. The light came in today. I did the test and your suspicion was correct. There is no pulse to the injectors.
 
  #10  
Old 12-06-06, 06:51 PM
Member
Join Date: Apr 2006
Location: Floriduhhhhh Us of A
Posts: 611
...........Which leads me to believe the computer doesn't "see" the engine turning over, and thusly shuts the pump down after the initial 2 sec prime.......On the rt side rear of the engine, you'll find a weatherpack connector with a white wire and a red wire. That plug will take you to the Crank Position Sensor...It reads teeth on the flywheel........If the C101 connector is still in place (a large plug directly in front of the firewall/drivers side) and the wires from the sensor lead into it, ...........You'll need to cut and splice those wires so they DON'T go through the plug.......Solder and Heat shrink wrap..........The CPS only generates between 1/4-1/2 volt A/C current on crank......so it doesn't take much of an inperfect connection to keep the vehicle from starting...........and then you'll need a sensor.......
I'm 99 44/100% sure this will get you up and running........(kinda like Ivory soap?????)
 
  #11  
Old 12-06-06, 07:16 PM
Member
Thread Starter
Join Date: Nov 2006
Location: USA
Posts: 1,342
Is it pertinent to your diagnosis to know that the fuel pump operates as long as the engine is being cranked but stops as soon as the key is released and springs back to the run position?
 
  #12  
Old 12-06-06, 07:44 PM
Member
Thread Starter
Join Date: Nov 2006
Location: USA
Posts: 1,342
OK, I'll let you know how it goes. Thank you VERY much for your help.
 
  #13  
Old 12-06-06, 07:45 PM
Member
Join Date: Apr 2006
Location: Floriduhhhhh Us of A
Posts: 611
You only need few secs of fuel pump on to generate 35 PSI in the fuel rail......With now injector pulse, the only pressure release will be through the regulator and return line........No injector pulse.........no fuel into cyls.......no spark.......no fire.......More than likely central problem and the CPS sensor is a well known culprit
 
  #14  
Old 12-06-06, 07:50 PM
Member
Thread Starter
Join Date: Nov 2006
Location: USA
Posts: 1,342
huh..... I'm not sure how that happened. Responses 12 and 13 got reversed.
 
  #15  
Old 12-07-06, 11:48 AM
Member
Thread Starter
Join Date: Nov 2006
Location: USA
Posts: 1,342
OK, I've found the crank positioning sensor and the weatherpack connector with the two wires. It looks like changing the sensor requires small hands and certain contortionist skills.The wires come directly out of a large harness bundle through the connector and disapear down toward the sensor. I don't see any thing like you describe as the C101 connector. With the key on, I've got voltage to the weatherpack connector and with the key off, I don't. Is there any way to test the sensor before removal? I don't have small hands, am not much of a contortionist, and would like to make sure if possible. Sounds like you've got the problem dialed in though. The guys at the parts store agreed with your assesment and showed me a picture of the sensor so I'd know what to look for.
 
  #16  
Old 12-07-06, 02:58 PM
Member
Join Date: Dec 2001
Posts: 2,538
the best way to remove the sensor that ive found is by doing it from underneath the vehicle and using a ratchet and long extension like 2 - 2 1/2 ft long a swivel and socket.
 
  #17  
Old 12-07-06, 07:47 PM
Member
Join Date: Apr 2006
Location: Floriduhhhhh Us of A
Posts: 611
2 ways to test the sensor.......If you have access to a scanner that is capable of reading the Jeep.....(I believe 89 will still be in the "shadow" of Renault electronic's wise)........Hook up and read RPM while cranking. You should see 200 or so RPM..........Other way is to hook up to the sensor with a DVOM....Again, while cranking, you should see about 1/2 volt A/C current if the unit is good.......There was a time when I was able to "gumby" my way in from the top with a 7/16 or 11mm wrench...........but if you can get it in the air, an extension and flex socket is the way to go!!!!
 
  #18  
Old 12-07-06, 09:21 PM
Member
Thread Starter
Join Date: Nov 2006
Location: USA
Posts: 1,342
Unfortunately, I don't have access to any of this test equipment. I do, however, have extensions and swivels so I guess I'll replace the sensor and see what happens. I don't like throwing parts at a problem until it's fixed, but this one isn't all that expensive. I'll most likely have to order it so I'll let you know the out come as soon as it gets here and I get it changed.
 
  #19  
Old 12-15-06, 02:18 PM
Member
Thread Starter
Join Date: Nov 2006
Location: USA
Posts: 1,342
wrench47, you are a certifiable genius. The crank positioning sensor was the issue. It is in such a difficult spot to reach that changing it was quit a test of ingenuity to figure out how, without being able to actually get a hand on it, to even start the bolts when putting them back in. But it is done and, as soon as I turned the ignition switch to "on" and heard the fuel pump, I knew we'd made progress. It's warming up as I type in preparation for the big test drive. words cannot express my gratitude to you. I do floors for a living and if you ever need advice.......


bejay, the extension and swivel turned out not to be the best way. It was the ONLY way short of pulling the engine loose and raising it. Thank you.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes