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Author Topic: Starting issues on the ZJ  (Read 1203 times)

Offline jwebb1998

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Starting issues on the ZJ
« on: March 12, 2015, 10:37:32 AM »
Does the engine typically fire up when you turn the key or does it take some cranking? Was there a recent time when it wouldn't start and you had to crank extensively? Are all cylinders firing?
Not trying to hijack but my 4.0zj has these symptoms.  Fires rigjt up after i turn it off, but if it sits for an hour or more it does it again.  Its actually really bad if i let it sit for 10 minutes then try to start it.  Any idea whats causing it?
But you are. Please start a new thread in tech, I'd be happy to help if I can as I'm sure other will as well.
I copied this post from another thread because my symptoms were mentioned.

John previously mentioned it could be bad fuel injector o rings leaking fuel while its sitting.  I have purchased new o-rings, just havent been able to install them yet.  Plus when i was reading the chiltons it said something about also doscarding the centering rings while doing the orings, but i havent been able to locate replacments. 

Thanks gents.
« Last Edit: March 12, 2015, 10:39:55 AM by jwebb1998 »

Offline Posimoto

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Re: Starting issues on the ZJ
« Reply #1 on: March 12, 2015, 11:53:48 AM »
What is the history of the engine?
When was the last time it had a complete tuneup, including fuel filter?
What is the fuel pressure?
"That's the trouble with research on the internet, there's no way of verifying its truth" --Abraham Lincoln

71 CJ5 V6/T14/D18/Warn OD (from CO)
79 CJ5 304/T-150 Silver Anniversary
79 CJ5.5 360/T-18/4.1 D-300
77 CJ5 360/T-18/3.15 D-20
77 CJ7 258 Fuel Injected T-18/D-20 (from CO)

Offline jwebb1998

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Re: Starting issues on the ZJ
« Reply #2 on: March 12, 2015, 12:36:11 PM »
Jeep has sat for the last 8 years, before that there weren't any issues.  It has 82k on it. But while getting it back on the road, I have changed the fuel pump, which includes the filter, i also scrubbed the tank clean while I was in there.  I've replaced the spark plugs and did an oil change, new air filter. It doesnt misfire and isn't throwing any codes, so i believe its firing on all cylinders, it also runs fine, only acts up when starting.  I plan to but haven't yet, replace the fuel injector o-rings, after i look into the centering ring more.  Today or tomorrow I'm going to do another oil change since I've gotten some miles on it and ran it.  I was also going to replace the coolant, not a full flush, but just drain it and refill it a couple times.  I'm edgy about doing a full flush because of how old the engine is.  Ive also had to replace the fuseable link on the engine fuse box, but the only replacement i can find is a universal one which doesnt fit the terminals well and I feel might be a weak spot.
« Last Edit: March 12, 2015, 12:46:37 PM by jwebb1998 »

Offline Posimoto

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Re: Starting issues on the ZJ
« Reply #3 on: March 12, 2015, 12:53:48 PM »
I would do a voltage drop test to make sure your getting a full 12v while cranking.
It would be helpful to know fuel pressure as well.

Edit: Make sure your getting full 12v at the coil.
« Last Edit: March 12, 2015, 12:59:42 PM by Posimoto »
"That's the trouble with research on the internet, there's no way of verifying its truth" --Abraham Lincoln

71 CJ5 V6/T14/D18/Warn OD (from CO)
79 CJ5 304/T-150 Silver Anniversary
79 CJ5.5 360/T-18/4.1 D-300
77 CJ5 360/T-18/3.15 D-20
77 CJ7 258 Fuel Injected T-18/D-20 (from CO)

Offline jwebb1998

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Re: Starting issues on the ZJ
« Reply #4 on: March 12, 2015, 06:41:14 PM »
I will try to check fuel pressure, im assuming i just need to pick up a fuel pressure gauge at the parts store and check it at the schrader valve on the rail? 

But doing a voltage test at the coil is not something im familiar with, ill look into it.  Hopefully i will have that info in the next day or2.

Thanks

Offline Twisty

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Re: Starting issues on the ZJ
« Reply #5 on: March 12, 2015, 07:40:25 PM »
Not sure if a Jeep would do it, but I ran into an issue on a 1998 GM that would not start when warm after shut off.  Turns out the coolant temp sensor was bad and it was messing with the timing (or so I think).

Any check engine codes? 

Next time you start it, turn the key on and listen for the fuel pump to buzz.  Then turn the key off and on again.  Do this a few times and see if it starts easier.  If it does, then you are loosing some fuel pressure.
88 MJ buggy, 4.0/AW4, 203/205, 3 link front/4 link rear on airshocks, 42" Iroks, full hydro

"Only wealthy men can afford to buy cheap things."

Offline Posimoto

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Re: Starting issues on the ZJ
« Reply #6 on: March 12, 2015, 08:43:01 PM »
I will try to check fuel pressure, im assuming i just need to pick up a fuel pressure gauge at the parts store and check it at the schrader valve on the rail? 

But doing a voltage test at the coil is not something im familiar with, ill look into it.  Hopefully i will have that info in the next day or2.

Thanks
The fuel pressure gauge isn't too expensive and a good tool to own. Yes, on the schrader valve.
For a quick test remove a plug wire, hold it about 1/4" from ground (engine block) and have someone crank the engine. Use insulted pliers to hold it. Post up the color of the spark, is the spark snap crispy or dull, wide or thin. 
"That's the trouble with research on the internet, there's no way of verifying its truth" --Abraham Lincoln

71 CJ5 V6/T14/D18/Warn OD (from CO)
79 CJ5 304/T-150 Silver Anniversary
79 CJ5.5 360/T-18/4.1 D-300
77 CJ5 360/T-18/3.15 D-20
77 CJ7 258 Fuel Injected T-18/D-20 (from CO)

Offline Krome

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Re: Starting issues on the ZJ
« Reply #7 on: March 13, 2015, 10:48:43 AM »
You can also rent one

Offline Twisty

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Re: Starting issues on the ZJ
« Reply #8 on: March 13, 2015, 04:17:29 PM »
I use my fuel pressure gauge all the time.  I find its quite a useful tool.
88 MJ buggy, 4.0/AW4, 203/205, 3 link front/4 link rear on airshocks, 42" Iroks, full hydro

"Only wealthy men can afford to buy cheap things."

Offline SPYDER

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Re: Starting issues on the ZJ
« Reply #9 on: March 14, 2015, 12:56:38 PM »
im joining this late, and taking from the info you posted in Twisty's tread...but it sounds like it starts fine when cold but not once warmed up.  there is a tsb about something similar on early tj's that is very similar.  I just did a quick search and couldn't find it.  but if I remember correctly it was something to do with heat soak into the injectors.  the solution was to put reflective sleeves over the injectors to help keep them cooler.  if I can find the tsb ill add it...


edit...found the tsb...google search "Chrysler tsb 18-031-03"  similar to what it sounds like you are having problems with but also a little different. 
« Last Edit: March 14, 2015, 01:05:04 PM by SPYDER »
05 Tj d44's, 4.88s, ARB's, 37's and some bling
99 TJuggy d60,5.13s, ARB/Spool, 40's, backhalfed
06.5 GMC 2500
05 WK 2" w/32's


 



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