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  #1  
Old June 16th, 2010, 21:59
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Heat soak no start

What's really going on when this happens? I'm sure XJ's didn't do this when they were new? I replaced the CPS and did a complete plug,cap rotor wires thing but still get starting issues sometime. I know lots of guys install hood vents to help eliminate this and I probably will too, but I want to know the real root cause of the problem. I hate bandaids if I can fix something instead.
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Old June 16th, 2010, 23:07
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Re: Heat soak no start

im pretty sure heat soak is the same thing as vapor lock and if so it is caused by heat boiling the fuel in the fuel rail and causing it to vaporize and therefore of no use to the injectors (hard to vaporize a vapor)
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Old June 17th, 2010, 04:36
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Re: Heat soak no start

Do a hood lift befor nwfest!! Works gr8 to keep the heat out. It's fast and s
cost less then 5 bucks
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Old June 17th, 2010, 05:38
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Re: Heat soak no start

What year is your xj?
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Old June 17th, 2010, 06:18
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Re: Heat soak no start

Sorry mine is a '93, 4dr, 4.0, AW4(of course). But I thought this issue is common to most XJ's?
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Old June 17th, 2010, 06:48
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Re: Heat soak no start

It was most common to the 2000-2001 XJ's due to the addition of two pre-cats in the exhaust manifold. Jeep's fix was heat shields for the fuel injectors that didn't really fix the problem. My 2001 suffered from the heat soak issue and I added Genright hood vents and it hasn't happened since. The heat soak would never cause it not to start though, it would just run like crap for about a minute until it used up the vaporized fuel. If yours just refuses to start, it might be something else, like a bad starter. Also, I didn't get any heat soak issues until I added the factory rubber splash shield and I assume that prevented some air flow around the engine.
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Old June 17th, 2010, 06:59
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Re: Heat soak no start

Quote:
Originally Posted by Ian Christiansen View Post
It was most common to the 2000-2001 XJ's due to the addition of two pre-cats in the exhaust manifold. Jeep's fix was heat shields for the fuel injectors that didn't really fix the problem. My 2001 suffered from the heat soak issue and I added Genright hood vents and it hasn't happened since. The heat soak would never cause it not to start though, it would just run like crap for about a minute until it used up the vaporized fuel. If yours just refuses to start, it might be something else, like a bad starter. Also, I didn't get any heat soak issues until I added the factory rubber splash shield and I assume that prevented some air flow around the engine.

I might have to remove mine. I was just thinking about that last nite, when I was considering removing some plastic under the front bumper.
I have an 01.

Last edited by 420BlackXJ; June 17th, 2010 at 07:07.
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Old June 17th, 2010, 09:21
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Re: Heat soak no start

On a 93? Wow, that's funky. Should not be an issue (at least, as much) on anything below a 96, since that's when they switched to the returnless fuel delivery system. From what I've seen, it is a non-issue on 95 and earlier, then becomes a very rare issue on 96 and later, then becomes far more common on 00 and 01 due to the pre-cats as noted by Ian.

Try keeping your electric fan running for a few minutes after shutting the jeep off.
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Old June 17th, 2010, 09:50
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Re: Heat soak no start

As Kastein said, this shouldn't happen on a '93. Look for cracks in your exhaust near the top that heat up the intake manifold. You can coat the underside of the intake manifold with some kind of heat reflective paint and that might help alot.
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Old June 19th, 2010, 21:15
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Re: Heat soak no start

Quote:
Originally Posted by R.DesJardin View Post
Sorry mine is a '93, 4dr, 4.0, AW4(of course). But I thought this issue is common to most XJ's?
The TSB and Heat Soak issue is a 99-04 Jeep 4.0 issue. Elimination of the fuel return (96) followed by the manifold changes (99) and the mini-CATs on the 50-state emissions equipped vehicles certainly didn't help, however, the TSB covers the 49-state emissions vehicles too.

A 93 should not be suffering the TSB covered heat soak issue. However, there are other components under the hood susceptible to thermal failure--the crank sensor CPS/CKP, the coil, relays, even the PCM, and just about any other electrical/electronic item under the hood.

You seem focused on ignition, so I will A**ume that you have confirmed the issue is spark and not an injector pulse/fuel issue?

If no spark, is there 12 volts to the primary side of the coil? If not, check the ASD relay. If yes, check the harness/PCM and CKP/harness for issues.
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Old June 20th, 2010, 14:52
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Re: Heat soak no start

I didn't mean to imply electrical, I'm up for any input. Would a weak fuel pump cause this, or a leaking check valve, or? Sorry EFI is new to me, I'm old and grew up with carbs.
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Old June 20th, 2010, 19:41
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Re: Heat soak no start

Quote:
Originally Posted by R.DesJardin View Post
What's really going on when this happens? I'm sure XJ's didn't do this when they were new? I replaced the CPS and did a complete plug,cap rotor wires thing but still get starting issues sometime. I know lots of guys install hood vents to help eliminate this and I probably will too, but I want to know the real root cause of the problem. I hate bandaids if I can fix something instead.
I have this once in a while. It'll be running fine, then I'll shut it off, and it won't start again. Or it will start but run like crap and buck and surge, unless I keep it over 2k or so then it purrs.

I'm strongly suspecting an intermittently leaking fuel injector. That could certainly cause vapor lock in a hot engine, and rough idling in a cold engine.

One clue; when it does it, the exhaust smells super rich. It does seem to happen more often, but not exclusively, when the engine is hot on a hot day.

Mine is a Renix BTW.

Last edited by n1ywb; June 20th, 2010 at 19:45.
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