'98 ZJ 4.0 Cranks but will not start - Lots of parts replaced - Please Help! - JeepForum.com
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post #1 of 27 Old 12-21-2016, 02:44 PM Thread Starter
TheGrimJeeper
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'98 ZJ 4.0 Cranks but will not start - Lots of parts replaced - Please Help!

***HUGE UPDATE***
It started today and STAYED running! I am posting an update reply explaining the details.

Let me start off by saying, any help will be appreciated...
Okay...a few weeks ago my 1998 Laredo Special - 4.0 Straight 6 started to drive pretty rough. From a stop I would have to put the pedal to the floor to get the truck up to speed and even then it would take a while just to get to 35mph. After about a week of that, the temperature dropped to below 20 degrees f and one morning it wouldn't go above 1200 RPM (roughly) and I could only get up to 15mph. I had it towed home...started it a few times over the next day or so. Then it stopped completely.
It would crank, and sound like it wanted to start but just wouldn't. I had a friend plug in his computer and I recieved a "P0123" code (TPS malfunction) and a "P0505" (Idle Air Control malfunction) So, here is a list of parts that I have replaced since:

-Throttle Position Sensor
-Camshaft Position Sensor (Pickup Coil)
-Crankshaft position sensor
-Fuel Pump
-And I have cleaned the Idle Air Control valve (IAC) thoroughly.

My check engine light isn't on, either.

**UPDATE: I tested the fuel pressure and it''s at 0. Does this mean my fuel pump isn't pumping? Or could this be something else? I just replaced the fuel pump and can hear it operate...but i guess it's possible that the new one isn't functioning.

I have checked for missing/broken wires, blown fuses, relays, etc...My battery charges as well. I am at my witt's end and any help is appreciated. The motor still cranks but does not start. Sounds like it's getting gas as well.

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post #2 of 27 Old 12-21-2016, 07:25 PM
LiftedXJ666
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Fuel pressure is at 0 after cycling the key?
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post #3 of 27 Old 12-21-2016, 07:56 PM Thread Starter
TheGrimJeeper
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Quote:
Originally Posted by LiftedXJ666 View Post
Fuel pressure is at 0 after cycling the key?
Yes, unfortunately.
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post #4 of 27 Old 12-21-2016, 08:22 PM
LiftedXJ666
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Could be that the new fuel pump is no good but since you just replaced it, everything is hooked up good to the fuel pump? What brand is the pump? I replaced the fuel pump in a previous zj i owned with an airtex and about a week later it crapped out
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post #5 of 27 Old 12-21-2016, 09:11 PM
MrRoundel
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If you've got zero fuel pressure at the rail, either your pump isn't working or there's a massive fuel leak between the tank and the fuel-rail. As was mentioned, using an aftermarket pump is asking for trouble. To avoid pulling your hair out over wondering if it could be a bad part, put in the good part. The good part for a fuel pump in a ZJ are either Bosch or Mopar-branded Bosch. I know that it's not fun dropping that tank. That's another reason for going OEM. Good luck.

1998 Laredo 4.0L 4x4, 242 TC. 197.5K miles in 10/17. Original owner.
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post #6 of 27 Old 12-21-2016, 09:58 PM
LiftedXJ666
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Quote:
Originally Posted by MrRoundel View Post
If you've got zero fuel pressure at the rail, either your pump isn't working or there's a massive fuel leak between the tank and the fuel-rail. As was mentioned, using an aftermarket pump is asking for trouble. To avoid pulling your hair out over wondering if it could be a bad part, put in the good part. The good part for a fuel pump in a ZJ are either Bosch or Mopar-branded Bosch. I know that it's not fun dropping that tank. That's another reason for going OEM. Good luck.
Exactly, i would work back to where you started from, drop the tank check out the pump, check all the connections, ensure there isnt any leaks or restrictions robbing pressure from the rail. Although i would think if there was a leak you would smell fuel or see it leaking . . also dumb question but ill ask anyway you did refill the tank after you put in new fuel pump?
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post #7 of 27 Old 12-23-2016, 12:35 AM
MKCoconuts
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Disconnect line as close as you can to pump, put line in some type of catch container and cycle pump. See what, if anything comes out. The pressure regulator which is part of the pump assembly could be bad and not allowing the pump to build pressure
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post #8 of 27 Old 12-24-2016, 01:17 PM Thread Starter
TheGrimJeeper
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Quote:
Originally Posted by MrRoundel View Post
If you've got zero fuel pressure at the rail, either your pump isn't working or there's a massive fuel leak between the tank and the fuel-rail. As was mentioned, using an aftermarket pump is asking for trouble. To avoid pulling your hair out over wondering if it could be a bad part, put in the good part. The good part for a fuel pump in a ZJ are either Bosch or Mopar-branded Bosch. I know that it's not fun dropping that tank. That's another reason for going OEM. Good luck.
Yeah, It's a "Precision" brand fuel pump. I will take your advice and go with something better like Bosch or Mopar. Luckily I think I can still receive a refund from O'reilly Auto. The one I purchased was still almost $200. I found it odd that you can HEAR the pump start, but it's crazy quiet and you have to have your ear to the fuel tank to hear it.

Quote:
Originally Posted by LiftedXJ666 View Post
Exactly, i would work back to where you started from, drop the tank check out the pump, check all the connections, ensure there isnt any leaks or restrictions robbing pressure from the rail. Although i would think if there was a leak you would smell fuel or see it leaking . . also dumb question but ill ask anyway you did refill the tank after you put in new fuel pump?
Yes, I even put in 5 gallons more than I had in because I thought maybe there wasn't enough to purge in the pump. I have retraced all lines and everything, there is no leaking going on and all my hoses are getting gas. I personally think the fuel pump is bad, like MrRoundel said. It's insane how bad it wants to start. It actually turns over then dies after the first second or so.

-Thanks everybody, gonna replace this after Christmas. I'll update with the results!
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post #9 of 27 Old 12-26-2016, 10:11 AM
ihbinder
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I had a similar situation. After I installed the Mopar fuel pump I had on the shelf, it started, ran a bit and quit. I swapped the fuel pump and ASD Relays with the horn and wiper delay relays. It ran for several minutes and quit again. New CPS, still no go. Swapped relays around again, except I used "new" ones from a couple of the other circuits. Problem solved, so far.

However, I'm using Bosch 02 sensors, and the word on the street is that they cause issues with the PCM's ASD circuit? (New NGK's are in the mail).

Also, work your way through the "12 steps" program...

Update: I installed the new NTK 02 sensors. The "older" relays worked for the short time that I ran the engine where they did not work at all when the Bosch 02 sensors were in place.
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post #10 of 27 Old 01-04-2017, 05:38 PM Thread Starter
TheGrimJeeper
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So, I replaced the fuel pump and now get fuel to the rail, although I noticed there was fuel coming out of one of my injectors and the motor still doesn't turn completely over. Is this probably a bad o-ring? Would the motor still start with a bad injector ring? Also, it is 6 degrees F and -10 F with the windchill....I know sometimes the cold can cause some issues with this vehicle.
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post #11 of 27 Old 01-05-2017, 10:22 AM
MKCoconuts
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Does it come out with only the pump primed? If so, it's a leaky injector which would cause loss of pressure to the rail after shutting the truck off.

Unless the battery is weak or you have water that froze up somewhere in the fuel rail, the cold shouldn't have any effect on starting. Any chance of a video of what exactly it's doing?
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post #12 of 27 Old 01-05-2017, 10:33 AM
YeepinBlue
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I've heard of fuel injectors cracking and leaking/sucking air in, might want to take off the fuel rail and inspect all the injectors.

I had a crank, no start issue about a year ago, replaced the iac but still didn't start... long story short ended up being corrosion on the battery terminals. Took off the terminals cleaned the surface between the post and terminal and started right up.

Mine always runs rough when it's cold out.

Keep Yeepin!
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post #13 of 27 Old 01-06-2017, 06:41 PM
ZeeJay1997
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Swap the fuel pump relay for the horn or wiper relay. Sounds like there's not enough power for the pump to operate.

Injector oring will not keep it from starting.


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post #14 of 27 Old 01-07-2017, 11:58 AM Thread Starter
TheGrimJeeper
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I hear the fuel pump purge, so I am pretty sure that is functioning how it should be. I haven't checked the pressure to the rail yet because before I replaced this new pump I wasn't getting any visible pressure even when just releasing fuel with a screwdriver. Now it sprays while the pump is on.

I replaced the battery terminal and ground cable.

I started it up this morning because the sun has been out all day and it's not as cold out and it started for just a split second and died. It just didn't want to stay running....The battery was at 100% but now it's low from trying to start it a few times.
I will record a video when the battery is charged to 100% since it is sunny today and for once I am home before dark. Can I just drag and drop my video? Or will I have to upload to Youtube?
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post #15 of 27 Old 01-07-2017, 12:40 PM
ZeeJay1997
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it takes two minutes to swap a relay.


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cps , fuel pump , iac , tps

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