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Chasing the root cause of heat soak (2001 XJ)

While these are good questions, somebody has to do the testing to find the figures. The actual numbers or times really don't matter, the check valve either works, or it does not. The starting behavior is all the test you need.

If you have starting problems, you most likely need a new Check valve.

My 2000 needs a check valve and starts on the second try. My 99 has a new fuel pump assembly and always starts instantly even after sitting for several weeks.
 
Thanks for the input Tim. In my case, only hot restarts are an issue. Cold starts, even after sitting for a week, are never an issue (first try every time). Does this indicate my check valve is likely okay?
 
There is no doubt that the presence of the pre-catalytic converters is ultimately what triggers this issue

Yes, there is doubt. In fact, that's flat out wrong. I've had heat soak issues without the additional cats. IIRC the TSB applies to ALL 00 & 01's regardless of their emissions package. I'm sure the extra cats don't help, but they're not the cause of the issue. The cause is a fuel rail on an iron block and iron head engine with the aluminum intake manifold, that also holds each injector, sitting directly above the exhaust manifold.

Are you referring to that foil mat sitting on top of the intake manifold? If so, I still have that in place.

Yep, that's what I was referring to. It worked well for me.
 
Finding the reason for the heat soak is a very good idea. It is the first step to solving an old problem.
Funny thing but my 1996 XJ have that problem and have had that problem for as long as I have it. At this time of the year in South Florida it happens on 1 out of 4 starts if the XJ is sitting less than an hour.
I will continue to monitor this thread for an update.
 
2001, It was just off of a lease from a New York owner and dealer. I have pre-cats.

Why can I not remove them, and who would know and how?

I have MAJOR heat soak. I plan to replace the plug rail then new injectors and maybe some aluminum foil, hood vents...fan timer...
 
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Insulate the intake manifold, leave plenty of airflow around the fuel rail, and put a reflector on the bottom of the intake manifold as well. I'm gunna do this soon and I'll let ya know if it helps.
 
2001, It was just off of a lease from a New York owner and dealer. I have pre-cats.

Why can I not remove them, and who would know and how?

I have MAJOR heat soak. I plan to replace the plug rail then new injectors and maybe some aluminum foil, hood vents...fan timer...
I've already had a thread on this topic - simply swap the exhaust manifold and engine computer of a non-50 state emissions XJ and you'd be set. Unfortunately, this is illegal at the federal level.

Of the band-aids you described, the fan timer is the one tried-and-true fix I've heard discussed. Hood vents helped some people, but not all.
 
The heat soak on mine has been completely eliminated. All it took was to install an electric water pump...

The basic problem is the heat rising off of the exhaust manifold is cooking everything it can get it's pudgy little hands on. The heat must be moved somewhere else. Either run the fan for air cooling or run the water pump for liquid cooling. On my rig, the pump runs for two minutes after shutdown and, if the Heep is at 93C or above, both electric fans run as well. I have zero heat soak issues.
 
The heat soak on mine has been completely eliminated. All it took was to install an electric water pump...

The basic problem is the heat rising off of the exhaust manifold is cooking everything it can get it's pudgy little hands on. The heat must be moved somewhere else. Either run the fan for air cooling or run the water pump for liquid cooling. On my rig, the pump runs for two minutes after shutdown and, if the Heep is at 93C or above, both electric fans run as well. I have zero heat soak issues.
Yeah, both solid solutions that I've considered but again, they're workarounds - I'm after the root cause :)

Supposedly, the issue is caused by either a failing check valve or leaking injector that leads to enough pressure loss that vapor lock is possible.

Yesterday, I did as scientific a test as I could:

  1. Got the car nice and hot on the way home from work. Highway speeds, AC on, etc.
  2. When I arrived at home, I immediately popped the hood, connected the fuel pressure tester, and closed the hood. Started the car and ran it AC on (idling) for about 5 minutes and shut it off.
  3. I quickly popped the hood and clamped the fuel line connected to the fuel rail, and immediately shut the hood.

Upon doing so, I waited about 15 minutes (right when heat soak is guaranteed under these conditions) and went to check the pressure at the fuel rail... It was steady at 50 psi. At 30 minutes, it had dropped to 28 psi, but I assume this is due to the engine (and really the fuel in the rail) cooling off and pressure going down as a result of this. After an hour, it was below 20 psi.

If the same amount of fuel remains in the fuel rail, what kind of pressure drop can I expect as temperatures drop? Does the result of the above test indicate that my injectors are not leaking? I guess I just don't know the relationship between gasoline temperature and the resulting pressure it exerts.

*EDIT* (Follow-up thought) I'm going to do basically the same test again today, but without the pressure gauge... Get home, pop the hood, clamp the fuel line, close the hood, and wait 15 minutes... At the 15 minute mark, I'll remove the clamp from the fuel line and start the car to see if the vapor lock/heat soak issue is mitigated. If so, I'll turn my attention to the rest of the fuel system upstream of the fuel rail (i.e. the check valve).
 
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I have a '88XJ, '96XJ, '98TJ, and had a '98XJ - NO heat soak problems

I have a '01, always been in GA and came with pre-cats had serious heat soak issue last year. Ditched the pre-cats - no more problems.

Its the the pre-cats, no question in my mind
 
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I have a '01, always been in GA and came with pre-cats had serious heat soak issue last year. Ditched the pre-cats - no more problems.

Its the the pre-cats, no question in my mind

Care to share the details? I'm interested in this.

I've had a stupid Check Engine P0432 code since I picked up my '01 Used about 7 months back. I'm not convinced the Pre-Cats are bad... but I don't want to spend the money to replace those when perhaps I could just get rid of them all together. Guess I'd have to swap out the PCM or something to compensate for those O2 sensors.
 
Yup.
IBTL-Shining.jpg


NAXJA doesn't want to get in deep ca-ca with Big Brother... (It's understandable that they just want to legally protect themselves).
 
Off road only?

And, I still run the federally mandated catalytic onverter downstream. Its been through the emissions process and it is well within spec for the year and vehicle. The pre-cats only help in initial startup
 
Off road only?

And, I still run the federally mandated catalytic onverter downstream. Its been through the emissions process and it is well within spec for the year and vehicle. The pre-cats only help in initial startup

Agreed ... Offroad only. :)

I'd still be running the downstream converter either way. PM me info if you'd like... I'm interested in knowing the ins-outs of doing something like this on my '01.
 
Thanks guys - please keep that whole topic to PMs not only due to the questionable nature of it, but also because it's not what this thread is about (FYI: a thread of mine discussed this very topic not too long ago, so look up my history).

Do we have any chemists in the house that can better explain the relationship between gasoline pressure at operating temps vs. cool? I'm really curious as to whether or not my fuel rail pressure tests say anything conclusive about the health of my injectors.
 
The pre-cats are an issue, but, IIRC, my 01 just started doing this at some point. Off the lot it was fine. So, root cause and all...

In the abstract it is hard to comment on the pressure/temp issue, as it involves alot of variables. Given a space of fixed volume though pressure varies directly with temperature, especially if you are talking about a liquid that can enter a vapor state.

Pressure would decrease with temperature, but you have no direct way of measuring temperature, or, without lab tests, you don't know how much heat it should shed and how fast in the complex system it is in...all you could do is try to keep temperature at a constant to try to eliminate it as a variable.

You don't know volume, you can't determine fuel temp in the lines reliably...all you can measure is pressure...you need to fix another variable, and volume (ie. a leak) is essentially the question, so you need to fix (or measure and determine the normal behavior of gasoline) temperature.
 
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The pre-cats are an issue, but, IIRC, my 01 just started doing this at some point. Off the lot it was fine. So, root cause and all...
Agreed. Something degrades or changes about the affected XJs over time, as few seem to experience it from day one. Which is exactly why I'm hell-bent on determining the true root cause (Chrysler's response of installing an insulator sleeve on injector #3 was utter BS, IMO).
 
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