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View Full Version : Hard start caused by coolant temp sensor?


smallredxj
November 26th, 2017, 14:47
Hey guys. Earlier today my Jeep started having rough starts. It will crank for about 10 seconds and then "sputter" to life. It idles rough for about 5 seconds and then it's fine. I can hear the fuel pump prime so I'm guessing it's not that- although I have not tested the check valve/ fuel pressure yet. I also know a dirty IAC sensor can cause this- but mine looked okay after cleaning. My main question is could this be caused by a bad coolant temp sensor? Mine went bad about a week ago and the Jeep has been starting fine until now. If it's not any of these things- what else could it possibly be? Thanks for the help.

old_man
November 26th, 2017, 16:22
In order to help you need to provide more info. What year model, transmission, and engine is it? When the problem happens, is the engine warm, has it been started recently or is it cold?

Fidget360
November 26th, 2017, 17:24
I would say that it certainly could cause that. I had a car a while back that had the same condition and it was all due to the coolant temp sensor. If the ecm doesn't see the coolant temp, then it will assume the worst and go as rich as possible to make sure that it has enough fuel to start. I'd bet that it's also killing your gas mileage.

smallredxj
November 26th, 2017, 18:04
99 4.0 auto
140,000 miles

smallredxj
November 26th, 2017, 18:18
I would say that it certainly could cause that. I had a car a while back that had the same condition and it was all due to the coolant temp sensor. If the ecm doesn't see the coolant temp, then it will assume the worst and go as rich as possible to make sure that it has enough fuel to start. I'd bet that it's also killing your gas mileage.

That's what I was thinking- the temp sensors failure put it in limp mode.

smallredxj
November 26th, 2017, 20:15
Well I hung it up for tonight but after testing stuff a little more I think I may not be getting spark- or it's at least intermittent. The truck reeks of gas so I know I'm getting fuel- not to mention I tested the pressure, however it's still a b***h to start. I can crank for 10-12 seconds and get nothing. I know for sure I'm changing coolant temp sensors, and my IAC because it was dirty as crap but what else should I be looking at? Maybe my CPS? I'll test for spark tomorrow I just ended up running out of daylight. I'm pretty stumped so help would be greatly appreciated.

Ralph77
November 26th, 2017, 22:18
I had a buddy with a '96. Was running like crap so he tuned it up. New wires, plugs, cap, rotor, and fuel filter. No change. Drove him nuts until he figured out it was the temp sensor in the thermostat housing.

cruiser54
November 27th, 2017, 05:11
Ya know, if the vacuum line to the MAP sensor has a split, cut, or leak, the thing will run pig rich and act just like you're describing..........