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  #1  
Old June 21st, 2011, 07:55
anthrax323 anthrax323 is offline
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Chasing the root cause of heat soak (2001 XJ)

I know that the most common solution implemented to correct heat soak (the issue in which injectors 3 and/or 4 going into vapor lock when the car is shut off for 5 to 30 minutes while warm, then started) is to install a fan timer, which is not a bad solution... But in all honesty, I'm now more interested in diagnosing the source of the pressure loss that allows vapor lock to occur.

I've been doing some research and it seems as though this is what I'll want to do:
  1. Check the fuel pressure on the fuel rail after a solid drive and monitor for pressure loss... Just a general way to make sure there is even an issue.
  2. Remove the fuel rail, but keep all injectors connected. Turn the ignition to "On" to engage the fuel pump and look for any visible leaks (derp!). Somewhat dangerous due to the presence of gasoline, but seemingly manageable so long as I'm not a moron.
  3. If no injectors are visibly leaking, inspect the fuel line all the way back to the gas tank.
  4. If no line leaks are visible, drop the gas tank and replace the fuel pump check valve (is that even the right word?).
Am I on the right track here? If I'm missing any other diagnostics that I should perform, please chime in. Thanks!
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  #2  
Old June 21st, 2011, 08:48
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gradon gradon is offline
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Re: Chasing the root cause of heat soak (2001 XJ)

You're on the right track. That check-valve is a common issue on 97+XJs. The heat soak from the 00-01s might make it fail sooner. When you turn off the Jeep with the fuel pressure tester already on the rail, it shouldn't drop below 30psi. If it keeps on going down, you need to look at the check valve.
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Old June 21st, 2011, 08:51
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DrMoab DrMoab is offline
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Fighting the same issue which seems to be getting worse as time goes on. One thing to consider. If the check ball in the tank is going bad, it will be hard to start after it's sat awhile, not just when it's hot.
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  #4  
Old June 21st, 2011, 09:03
anthrax323 anthrax323 is offline
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Re: Chasing the root cause of heat soak (2001 XJ)

Good tips, thanks guys.

DrMoab - on occasion, it will be hard to start (very rarely though - maybe once every two weeks). I need to buy a fuel pressure tester so I can check it immediately next time it happens.
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  #5  
Old June 21st, 2011, 09:28
O-Gauge Steamer O-Gauge Steamer is offline
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Re: Chasing the root cause of heat soak (2001 XJ)

Do you have the insulator installed? It sets into the spaces left open by the intake partially blocking the heat from raising off the exhaust manifold. If it is not there, it should be added. I have the 99+ manifold on the 98 and also had heat soak issues with it. Adding the heat shield helped. When I installed the electric water pump, I removed the sheild and have not had any issues with heat soak. The pump runs on for two minutes after engine shut down. Drops the engine temp by 5 degrees C. If the engine happens to be at 93C, the electric fans run also which gives an even greater drop in temps.

I am running a 90C (194F) setpoint on the controller so the fan does not kick into high until 3C over setpoint.

According to the 98 FSM I have...

Fuel Pressure Leak Down Test
Use this test in conjunction with the Fuel Pump Pressure Test and Fuel Pump Capacity Test.
Check Valve Operation: The pump outlet contains a one-way check valve to prevent fuel flow back into the tank and to maintain fuel supply line pressure (engine warm) when the pump is not operational. It is also used to keep the fuel supply line full of gasoline when the pump is not operational. After the vehicle has cooled down, fuel pressure may drop to 0psi (cold fluid contracts), but liquid gasoline will remain in fuel supply line between the check valve and the fuel injectors. Fuel pressure that has dropped to 0psi on a cooled down vehicle (engine off) is a normal condition.When the electric pump is activated, fuel pressure should immediately (1-2 seconds) rise to specification.
Abnormally long periods of cranking to restart a hot engine that has been shut down for a short period of time may be caused by:
~Fuel pressure bleeding past a fuel injector(s).
~Fuel pressure bleeding past the check valve in the fuel pump module.
(1) Disconnect the fuel inlet line at the fuel rail. Refer to Fuel Tubes/Lines/Hoses and Clamps in this section of the group for proceedures. On some engines, air cleaner housing removal may be necessary before fuel line disconnection.
(2) Connect the appropriate Fuel Line Pressure test Adaptor Tool (number 6539, 6631,6541 or 6923) between the disconncted fuel line and the fuel rail.
(3) Connect the 0-414 kPa (0-60psi) fuel pressure gauge to the test port on the adaptor tool. The fittings on both tools must be in good condition and free from any small leaks before performing the proceeding test.
(4) Start engine and bring to normal operating temperature.
(5) Observe test gauge. Normal operating pressure should be 339 kpa +/- 34kPa (49.2 psi +/- 5psi).
(6) Shut engine off.
(7) Pressure should not fall below 30 psi for five minutes.
(8) If pressure falls below 30psi, it must be determined id a fuel injector, the check valve within the fuel pump module or a fuel tube/line is leaking.
(9) Again, start engine and bring to normal operating temperature.
(10) Shut engine off.
(11) Testing for fuel injector or fuel rail leakage: Clamp off the rubber hose portion of the Adaptor Tool betweent he the fuel rail and the the test pot "T" on Adapter Tool. If pressure now holds at or above 30psi, a fuel injector or the fuel rail is leaking.
(12) Testing for fuel pemp check valve, filter/regulator check valve or fuel tube/line leakage: Clamp off the rubber hose portion of the Adaptot Tool betweent he the vehicl fuel line and the test port "T" on the Adaptor Tool. If pressure now holds at or above 30psi, a leak may be found at a fuel tube/line.If no leaks are found, one of the check valves in either the electric fuel pump or filter/regulator may be leaking.
Note: A quick loss of pressure usually indicates a defective check valve in the filter/regulator. A slow loss of pressure usually indicates a defective check valve in the electric fuel pump.

The electric fuel pump is not serviced separately. Replace the fuel pump module assembly. The filter/regulator may be replaced separately on certain applications. Refer to Fuel Filter/Fuel Pressure Regulator Removal/Installation for additional information.

Fuel Filter/Fuel Pressure Regulator
The combination Fuel Filter/Fuel Pressure Regulator is located on the fuel pump module. The fuel pump module is located on the top of the fuel tank.

The filter/regulator may be removed without removing the fuel pump module although the fuel tank must be removed.

WOW! It goes on from there but removal is very straigt forward. Clean befor you disassemble. Disconnect the fuel line at the filter/regulator. Remove the retainer clamp (simple snap into tabs) and pry out the filter/regulator using a couple of screwdrivers.

Toss the gasket. It also says to inspect the o-rings. I think I would just replace them on GP. Then install new part.

Part Number is 4798301 $141.00 from Jeep.

Hope this helps!
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  #6  
Old June 21st, 2011, 10:13
anthrax323 anthrax323 is offline
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Re: Chasing the root cause of heat soak (2001 XJ)

Quote:
Originally Posted by o-gauge-steamer View Post
(lots of good info)
Thanks a ton for the details buddy. One thing I'm not entirely sure of in the diagnostic procedure, though, is whether or not it's really necessary to disconnect the fuel line from the fuel rail in order to connect a gauge. Since mine's an '01, can't I just use the pressure test port? It seems like the behaviors described would still be relevant (as I could still clamp off the fuel line to verify whether or not any injectors are leaking).

20 minutes after shutting off the hot engine, fuel pressure dropped from 49 PSI to 24 PSI. Should I consider that to be acceptable?

Also, part 4798301 you mentioned looks like a complete fuel filter assembly. Is the check valve/regulator contained inside that same assembly?
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  #7  
Old June 21st, 2011, 11:26
anthrax323 anthrax323 is offline
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Re: Chasing the root cause of heat soak (2001 XJ)

I found that same procedure in my 2001 FSM... Still a bit confused. The fuel inlet is on the very front of the fuel rail, whereas the test port is in the middle. Is it really necessary to get the special tool and read the pressure in-line like they describe? Logically, it seems as though leaving the fuel supply line connected to the fuel rail and using the test port would accomplish exactly the same thing.
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Old June 21st, 2011, 12:17
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Tim_MN Tim_MN is offline
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Re: Chasing the root cause of heat soak (2001 XJ)

Quote:
Originally Posted by anthrax323 View Post
.... interested in diagnosing the source of the pressure loss that allows vapor lock to occur.
A failed Check Valve is the most common cause of hard starting and Vapor Lock on the 97-01 Cherokee.

Use a pressure tester that will attached to the Schrader valve in the center of the fuel rail.

POSSIBLE CAUSES

• Failed check valve on the fuel pump in the gas tank.
• Leaky fuel injector(s) may be the true cause of your problem, but more likely they are simply contributing to the check valve issue.

Testing of the fuel injectors should show if any are faulty and are allowing fuel to drain into the cylinder. Either problem can allow heat soak to vaporize the remaining fuel in the fuel rail and you may be dealing with a bit of vapor lock as well, especially in warmer weather.

1. Connect the gauge at the fuel rail and start the engine. The gage should read 49 psi plus or minus 5 psi.

2. Turn the engine off and immediately clamp the fuel line just ahead of the fuel tank. Watch the pressure gage and see how long it takes to loose pressure.

If the pressure remains at 49 psi for an extended period of time then the problem is in the tank - probably the check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably a leaky injector.

There are a few solutions to the problem –

1. Turn the key to ON for 5 seconds and let the fuel pump prime. Turn the key to OFF, turn the key back to ON for 5 seconds, start the engine.

2. Crank the engine for 3-5 seconds, pause, and crank the engine again. It will almost always start on the second try.

3. Replace the fuel pump assembly in the gas tank. The check valve is not a separate part and cannot be serviced. This is both expensive and time consuming because you have to remove any hitches and skid plates and then remove the gas tank from the vehicle.

You can use solutions 1 or 2 for as long as you want to, they do not harm anything and the fuel pump will continue to function for many more years.


If you do replace the fuel pump assembly, purchase a high quality OEM style unit. Some cheap aftermarket fuel pump assemblies, like Airtex, don’t hold up and fail completely within 12-18 months.
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Quote:
Originally Posted by bimmerjeeper

I spent a few hours researching how to jack up an XJ, but even this is more complex than a normal car.
.
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  #9  
Old June 21st, 2011, 13:31
anthrax323 anthrax323 is offline
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Re: Chasing the root cause of heat soak (2001 XJ)

Thanks for the additional info - I'm buying a proper hose clamp here in a bit to avoid damaging anything (plus I've really need proper clamps several times in the past).

I guess my questions that remain are as follow:
  1. With the fuel line clamped, how long should the injectors hold pressure on a hot engine? Indefinitely, or only until the engine is cool?
  2. Same question, but with the check valve. It seems as though the baseline established here is that it should hold at least 30 PSI for 5 minutes.
Thanks again guys. This is unfamiliar territory for me (though not totally alien).
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Old June 21st, 2011, 13:53
O-Gauge Steamer O-Gauge Steamer is offline
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Re: Chasing the root cause of heat soak (2001 XJ)

The factory test tool sits between the chassis fuel flex line and the fuel rail. The rubber it is made out of allows you to be able to choke off pressure from either side of the T fitting that holds the gauge. Allows the system to be split into two halfs (rail/injectors and all the rest) in order to diagnose. I think it possible to build as long as you can find the quick disconnect fittings.
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  #11  
Old June 21st, 2011, 14:46
anthrax323 anthrax323 is offline
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Re: Chasing the root cause of heat soak (2001 XJ)

Makes sense, thanks for straightening that out for me.

I guess testing from the fuel rail will allow me to do half the diagnosis and rule out leaking injectors, but only be able to speculate on the condition of the check valve.

If the injectors are not leaking, I'll probably go ahead and buy a new fuel filter and drop the tank as part of the 170,000 mile maintenance I plan on doing (i.e. replace the timing chain, water pump, transmission filter/gasket, engine mounts, transmission mount, and throw on a Rigid FbG since everything will be torn down anyway). Really looking forward to that weekend
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Old June 21st, 2011, 15:00
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Milford Cubicle II Milford Cubicle II is offline
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Re: Chasing the root cause of heat soak (2001 XJ)

In my experience, that stock insulator that goes between the intake runners helped greatly. I mistakenly threw it away, before that however I never had any heat soak issues. Unfortunately though, I have no idea where to get another one. I'm guessing it's a dealer part.
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Old June 21st, 2011, 17:01
anthrax323 anthrax323 is offline
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Re: Chasing the root cause of heat soak (2001 XJ)

Are you referring to that foil mat sitting on top of the intake manifold? If so, I stillhave that in place.
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Old June 21st, 2011, 18:29
badron badron is offline
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Re: Chasing the root cause of heat soak (2001 XJ)

((((((IMO)))))))))
The real problem is two fold.
First them 2 dam pre cats and the cast iron manifold releasing tons of stored up heat well after key off. This heat generates excessive fuel pressure in the rail, injectors etc.
2. todays fuel systems with the regulator in the tank. That lets the pressure build up after key off until it finds or it makes a weak point.
The older system had a bleed off regulator under the hood. By bleeding off excess pressure this would keep more fuel moving and a lot more cooler fuel in the rail. Acting like a coolant system for rail, injector etc. So at key off the system was cooler to start with but if the fuel did heat up after key off the reg was still active and would not let excessive pressure build.
I vented my hood this fix the problem for me.

Last edited by badron; June 21st, 2011 at 18:58.
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  #15  
Old June 21st, 2011, 20:28
BrokenSockets BrokenSockets is offline
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Re: Chasing the root cause of heat soak (2001 XJ)

Is it the actual temperature on the fuel rail that is the issue? what about a heat sink or heat pipe with remote heat sinks to cool the actual problem area?

I don't have this problem, but I have seen all these posts and I am just wondering if this could be a permanent solution - to passively cool the fule rail itself.
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