‘98 TJ goes into safe mode when ambient heat is 85+ degrees

Stump Jumper

Stump Jumper

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Joined
Jul 29, 2021
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21
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Colorado
‘98 TJ 2.5 Manual Trans stock motor, no mods…runs great until the outside summer heat goes above 80-ish degrees. The engine starts to sputter and will not go over 2,000 rpm. This is after running for 10-15 miles. I have replaced nearly every sensor, cleaned the intake, replaced the intake manifold gasket, replaced the cat, to no avail. This has been a three year endeavor and only does it when it is hot summer weather. At first there were codes out the a## but after chasing them down and changing out all the sensors, I have a box full now, there are no codes anymore but the issue continues. Yes, it runs like a champ any other time of the year and is my go to for winter driving. Any further suggestions or ideas that I might need to try is appreciated.
 
Welcome to the forum SJ! Does your TJ run good right after starting it in the morning, before the engine starts to warm up? Have you replaced your upstream O2 sensor, and if you did was it with another NTK or NGK brand?
 
Geez 80 ish is almost winter daytime temps where I live!
I cant see 80 degree outside temps causing problems, sorry no help but just saying :)
 
Jerry Bransford said:
Welcome to the forum SJ! Does your TJ run good right after starting it in the morning, before the engine starts to warm up? Have you replaced your upstream O2 sensor, and if you did was it with another NTK or NGK brand?
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Thank you Jerry! Yessir, the TJ runs good after starting in the morning and runs good as long as it’s not hot outside. The upstream O2 was replaced with an NTK.
 
Have you replaced the IAT (intake air temperature) sensor yet? It's screwed into the air intake manifold. It's recommended to avoid any store brand sensors.
 
Have you tested fuel pressure? It sounds similar to a vapor look issue. There’s a TSB for that on later 4.0s, but it might be worth insulating your injectors to see if anything changes.
 
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Yes I replaced that as well with a duralast sensor. Along with other AutoZone sensors. Including the Camshaft sensor, intake sensor, thermostat sensor, TBS, MAF, and others.
 
Duralast from Autozone is the very last brand part I'd go with. Store brands usually scrape the bottom of the quality and reliability barrel.
 
RMETeeJay said:
Have you tested fuel pressure? It sounds similar to a vapor look issue. There’s a TSB for that on later 4.0s, but it might be worth insulating your injectors to see if anything changes.
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Yessir, I insulated the injectors, rail, and the regulator in hopes for a difference but no change to my issue.
 
Jerry Bransford said:
Duralast from Autozone is the very last brand part I'd go with. Store brands usually scrape the bottom of the quality and reliability barrel.
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I had anticipated your answer since I've read many of your threads in this forum before I joined. That said, I have many things in my Rock Auto cart right now and everything is MOPAR with the exception of the IAS. They don't have MOPAR part available for the IAS so I have a NTK selected. Is it ok to go with the NTK for this sensor?
 
Stump Jumper said:
I had anticipated your answer since I've read many of your threads in this forum before I joined. That said, I have many things in my Rock Auto cart right now and everything is MOPAR with the exception of the IAS. They don't have MOPAR part available for the IAS so I have a NTK selected. Is it ok to go with the NTK for this sensor?
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Jerry Bransford said:
Duralast from Autozone is the very last brand part I'd go with. Store brands usually scrape the bottom of the quality and reliability barrel.
Click to expand...
The MOPAR sensors I have in my cart right now are the MAP, IAC, TPS and CPS. I will order them and change them one by one to see if the OE parts make a difference with my issues.
 
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If your IAC is the OE Mopar, I would just clean it by spraying throttle body cleaner into the throttle body while the engine is at idle (only) rpms. This floods the IAC with cleaner so the engine will die. Just restart it and keep at it until you have used 1/3 of the can. Don't raise the engine rpms to prevent it from stalling, that would cause the cleaner to bypass the IAC.

Doing it this way gets it and its orifice in the throttle body clean better than if you remove it first. This normally restores it to good operating condition.
 
Jerry Bransford said:
If your IAC is the OE Mopar, I would just clean it by spraying throttle body cleaner into the throttle body while the engine is at idle (only) rpms. This floods the IAC with cleaner so the engine will die. Just restart it and keep at it until you have used 1/3 of the can. Don't raise the engine rpms to prevent it from stalling, that would cause the cleaner to bypass the IAC.

Doing it this way gets it and its orifice in the throttle body clean better than if you remove it first. This normally restores it to good operating condition.
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Jerry, thank you for the info. Tomorrow I will replace the original IAC since I had changed it with a duralast and give it a try.
 
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Update; I replaced the IAC with the original MOPAR part and cleaned it as Jerry said. I also put a Poison Spider vented hood skin on it. I plan to take it to the Mountains this weekend so will update again with the results.

AAB88056-34F6-42A0-A6F1-5B5399AB6BEE.jpeg
 
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Jerry Bransford said:
Just don't try to convince me the vented hood was the cure since Jeeps don't need that to run well in even very hot weather. :)
Vasq said:
I found the problem...
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TJ Gurus. I totally agree and understand the humor, I am not under the impression it would run any better with the vented hood, but releasing any trapped heat at a stoplight can’t hurt a thing. My hacking up the original hood should be a sign that I’m seriously looking for a fix to my TJ seemingly going into “safe mode” only on hot days and in heavy stop and go traffic.

Is there supposed to be a heat shield at the top of the headers/intake to shield the injection rail?
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I’ve worked on this issue for three years and am tapping into this forum for “expert advice”…if I needed any crap I would have joined a humor blog. JS
 
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Vasq said:
I found the problem...
Click to expand...

TJ Gurus. I totally agree and understand the humor, I am not under the impression it would run any better with the vented hood, but releasing any trapped heat at a stoplight can’t hurt a thing. My hacking up the original hood should be a sign that I’m seriously looking for a fix to my TJ seemingly going into “safe mode” only on hot days and in heavy stop and go traffic.

Is there supposed to be a heat shield at the top of the headers/intake to shield the injection rail?
 
Jerry Bransford said:
Just don't try to convince me the vented hood was the cure since Jeeps don't need that to run well in even very hot weather. :)
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I wouldn’t even begin to try and convince you nor anyone else that it made a difference. JB, I replaced the IAS with an NTK and threw the duralast away. I also changed the duralast IAC with a MOPAR. Now it idles at 2k rpms…it was at 5-700 before I changed the IAC. Any further recommendations? Thank you.
 
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