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Unread 04-03-2014, 08:42 PM   #16
lfhoward
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2008 KK Liberty 
 
Join Date: Nov 2012
Location: Philadelphia, PA
Posts: 447
To the OP: I had exactly this issue on my XJ. It turned out that the ambient heat from the engine was turning the fuel in the fuel rail and/or injectors from a liquid state to a gas, which prevented startup while the engine was still hot. This was never a problem if the engine was already running, as the cooling system kept the temperature down and the gas kept flowing, but when the engine is stopped the temperature increases temporarily as the coolant is not flowing. This problem is called 'heat soak' and you can find it in the XJ section here as well as over at cherokeeforum.com. I wrapped my fuel rail and injectors in fireproof insulation and this helped a lot, reducing the problem by 90% or so. The rest of the time, I just popped the hood and the cool-down time went from 30 minutes to 5. Some guys on the forum installed hood vents to let the heat out, which worked great for them. Try popping the hood next time this happens. If you can start it after 5 minutes instead of 30, you have identified your problem.

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Unread 04-03-2014, 08:59 PM   #17
Gageraid
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I've had just about every issue with my last carbureted car. I'm surprised you haven't replaced the plugs yet. At least check them.
If the fuel filter is easy to get to and cheap that Troy mentioned, that sounds like it might be the problem, too.
What would happen if you start it up when cold, let it idle for say no more than 3 or 4 minutes, then shut it off and try again? I'm suspecting fuel delivery.
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Unread 04-03-2014, 11:05 PM   #18
JeepOwner33
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Sounding very promising.

If its cool and just sits for a few minutes, it doesn't really give me the issue. I think this is the main reason why the shops couldn't find the problem, as I bet that they wouldn't get it properly warmed up first.

As for the wires and plugs, will be a good idea to get those replaced anyway so I will go ahead and do that.

I have heard the suggestion of the insulation being the issue before. I am going to try this and see what happens. I think this one is probably the culprit.

These seem like relatively cheap and easy fixes so I will try them first, if it does not help I will go to something more drastic.
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Unread 04-03-2014, 11:28 PM   #19
JeepOwner33
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Check this out guys this is my exact issue I just found on another site.

http://www.cargurus.com/Cars/Discussion-t7060_ds552905

I think I am on to something here with the insulation suggestion. Finally a year of frustration might be coming to an end.
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Unread 04-04-2014, 12:08 AM   #20
crusher8101
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Quote:
Originally Posted by JeepOwner33
I have been having an issue with my 2003 Jeep Liberty Renegade for about a year now. This issue has stumped 2 different repair shops and a jeep dealership. Maybe you guys have heard of this before and give me a little advice. So the issue is this. The Jeep runs fine. Starts easily at the turn of the key. Perfect. Until the engine gets warm. If you drive about 4 or so miles and the engine gets warmed up, the next time you turn the engine completely off it will refuse to start for about half an hour. It turns over just fine and cranks... and cranks... it just will not kick on. I am guessing it's either a heat or fuel line issue. If I leave the jeep sit for about 6 hours after driving it seems to be fine, but if I want to go somewhere immediately after its warms up, I have to wait half an hour. It's almost as if the jeep specifically waits half an hour after I first turn the key and it fails to start. It's amazingly frustrating. I have replaced the fuel pump, the crankshaft sensor that was bad, and the fuel pump sensor and still have the issue. Next I was going to try the spark plugs and wires and maybe even the coil packs to see if it does any good. I have had the jeep at a couple of different good repair shops and even a jeep dealership shop and no one seemed to be able to chase down the issue. I am sick to death of having to sit around and wait half an hour before I can go somewhere. I have been stranded like this about 10 times minimum. I am even considering a trade in, but I love my jeep. Please help!
Just went thru this very issue w my 99 GC. had both a bad cam position sensor & a bad crankshaft position sensor. Replaced both and problem solved. I can trust it to get me back and forth to work again.
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Unread 04-04-2014, 03:29 PM   #21
Bilge
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It sounds just like vapor lock (or as lfhoward put it; heat soak). This used to be very common on carburated vehicles because the fuel pump was usually located on the engine, and they were designed to pump liquid, not vapor. But this is a horse of a different color because the pump is in the tank. Still, vaporization can be a problem.

Here's what I'm thinking;
engine compartment gets hot,
engine is turned off,
fuel starts to heat and vaporize,
vaporization causes the pressure in the fuel rail to skyrocket (ever left a gas can in the sun too long? and that's not nearly the heat we're dealing with.. LOL),
this causes back pressure against the check valve (if this is great enough it will not allow new fuel to pass),
this can also keep the fuel injector pintles (valves) from opening if the vapor pressure + spring pressure is too great for the injector coil to overcome.

So, you have a situation where the system (because it's a non-return type) cannot allow the pressure to escape. Thus a no start situation, until sufficient time has passed for the vapor pressure to subside naturally.

If you know someone with a fuel pressure tester, I'd check the pressure at the fuel rail while it is cold (been sitting for a few hours), hot (heated to the point you have the problem), and 15 mins after you shut it down and then at 30 mins. These last three you will probably have to do on separate occasions, as each test will likely affect the result of the next test. Although a quick way to see is by using the tester to release the pressure once you have a no start condition then see if it will start.

There are a lot of good suggestions here and without being there in person to diagnose the problem, it could be any one of these. I just thought I'd through my $.02 in there and hope it helps.
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Unread 04-04-2014, 04:28 PM   #22
grnd93
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Quote:
Originally Posted by Bilge
It sounds just like vapor lock (or as lfhoward put it; heat soak). This used to be very common on carburated vehicles because the fuel pump was usually located on the engine, and they were designed to pump liquid, not vapor. But this is a horse of a different color because the pump is in the tank. Still, vaporization can be a problem. Here's what I'm thinking; engine compartment gets hot, engine is turned off, fuel starts to heat and vaporize, vaporization causes the pressure in the fuel rail to skyrocket (ever left a gas can in the sun too long? and that's not nearly the heat we're dealing with.. LOL), this causes back pressure against the check valve (if this is great enough it will not allow new fuel to pass), this can also keep the fuel injector pintles (valves) from opening if the vapor pressure + spring pressure is too great for the injector coil to overcome. So, you have a situation where the system (because it's a non-return type) cannot allow the pressure to escape. Thus a no start situation, until sufficient time has passed for the vapor pressure to subside naturally. If you know someone with a fuel pressure tester, I'd check the pressure at the fuel rail while it is cold (been sitting for a few hours), hot (heated to the point you have the problem), and 15 mins after you shut it down and then at 30 mins. These last three you will probably have to do on separate occasions, as each test will likely affect the result of the next test. Although a quick way to see is by using the tester to release the pressure once you have a no start condition then see if it will start. There are a lot of good suggestions here and without being there in person to diagnose the problem, it could be any one of these. I just thought I'd through my $.02 in there and hope it helps.
You could also take the cap off the schrader valve on the fuel rail and release the pressure there
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Unread 04-04-2014, 07:17 PM   #23
Bilge
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Quote:
Originally Posted by grnd93 View Post
You could also take the cap off the schrader valve on the fuel rail and release the pressure there
Yeah, I personally would try that if I could control certain variables. But I have a tendency to take risks.

I wouldn't suggest that to anyone else because vaporized gasoline only needs a 495 F heat source to ignite. Considering that exhaust manifolds can get to anywhere from 600 to 1000+, then I'd have to go with, "Don't try this at home kids." The testers usually have a tube to "vent" the fuel away to a safer location, and that's why I made that suggestion. Especially since this "test" will be done while the engine is still hot.
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Unread 04-04-2014, 11:25 PM   #24
Bilge
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This illustration may help to clarify what I mean. We're both saying bleed off the pressure via the schrader valve. I was just suggesting the use of the tester to do it in a more controlled fashion. I apologize for not being clear on that.
pressuretester.jpg

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Unread 04-06-2014, 03:11 PM   #25
JeepOwner33
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Thanks for the suggestion on the bleed, but I think I will not attempt that one.. When the issue happens, the jeep is already hot so... might not be a good idea. I am not much of a car guy. I ordered some of that insulation and I am going to give this a go. Anything beyond that and I will take it to one of the repair shops with EXPLICIT WRITTEN INSTRUCTIONS FROM THIS FORUM as you guys seem to know what you are talking about, and they don't. I appreciate all the help you guys are giving me. You have no idea how inconvenient this issue has been every day for a YEAR now.
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Unread 04-06-2014, 03:24 PM   #26
streetglideok
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2005 KJ Liberty 
 
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Seems like a pretty straight forward problem. As long as it's easily replicated, shouldn't take an Einstein to figure out. A gas engine has to go suck bang blow. No reference to hot dates either. When the engine won't start, you're missing something. Either you're missing fuel, or spark, or both. I don't see a mechanical issue being the culprit here. When it acts up, do you have spark? Hook up a node light to a fuel injector connector and verify it flashes when cranking. If you have both, and it won't start then I would use a fuel pressure tester with a bleed off hose as described. See if you are getting solid liquid fuel or a vapor. If you don't have spark and/or injector pulse, then check for power to the injectors and coils while cranking.
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Unread 04-06-2014, 03:34 PM   #27
JeepOwner33
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heh like I said... not much of a car guy, not only do I not own most of the described tools, but I understood at least 5 of those words!

Doesn't stop me from printing all this off and taking it to the shop though. I just don't see how 2 shops and a dealership were not able to diagnose this problem. I gave them as many details as I gave you here, and even let them keep the jeep in the shop for a few days.

Shop 1 said they could not replicate issue, which its EXTREMELY easy to replicate if you drive it around for 5 minutes.

Shop 2 said bad crankshaft sensor, fair enough. Had them replace. Issue still happened, and they couldn't figure out why.

Dealership said bad fuel pump... Shop told me fuel pump was fine but... I stupidly went ahead and let them do it. $400 later and problem persisted. I called and told them their $400 dollar suggestion did nothing, and they said "huh, that should have done it".

I am from a small town, and this was pretty much every shop in town.
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Unread 04-06-2014, 04:00 PM   #28
streetglideok
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Shop 2, they replaced the crank sensor(CKP sensor). What did they use? Guessing bautozone or equal quality part? With tricky drivability issues, it is important to use good quality parts, and OE is the only way to go. Don't be shocked if the problem goes back to the crank sensor if they used a cheap inferior part, but again it may not. A lot of shops -are strictly a pull-a-code to diagnose problems, as are a lot of dealer techs.
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Unread 04-07-2014, 09:28 AM   #29
Bilge
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My best friend used the live not far from you. But since he passed, I don't get down that way any more. Ft. Wayne is the closest I get to Greensburg or I'd be happy to look at it.

Let us know when you get things figured out, or at least update us on any progress, good or bad. I'm very curious as to how this plays out. I'm always eager to learn more. Every bit of knowledge is a tool. Unfortunately, I keep misplacing my tools! LOL
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Unread 04-07-2014, 06:24 PM   #30
JeepOwner33
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I will keep you updated. Installing the insulation when it arrives tomorrow.
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