Hard Start, Rough Idle, No Temp Gauge

[jakehobbs]

97, 4.0, Auto, 135K, 4WD

Long time lurker, first time poster. I have a 97 Sport that I have been having random starting problems with. I am no master mechanic but I like to tackle most of the issues on the jeep myself. This one has been plaguing me so I think I am ready to seek some advice from a professional to at least rule out some of the possible problem causers.

When I go to crank the motor over it will just turn and turn until I press on the gas pedal. It will run rough for a few seconds and then its fine. The temp gauge is also not registering which leads me to believe that the thermostat is sticking open, this also causes it to idle as if the motor was cold. I checked the fuel rail and there is pressure, not sure how much though since I didn't use a gauge. Over the past year or so I have replaced every part of the cooling system including the coolant temp sensor and two different thermostats. Thats why I am stumped on why it is not registering on the dash.

So based on the above, and info from searching the forum, I have it narrowed down to the following:

-Bad CPS
-Bad Fuel Pump
-Bad Coolant Temp Sensor
-Faulty Thermostat

Any advice? Thanks in advance.

 

[joe_peters]

97 the CTS in the thermostat housing feeds the PCM, the PCM feeds the temperature gauge in the dash.

I would recommend you start with testing the CTS.

 

[Digger87xj]

So, no CEL? odd with no temp reading.... does the gauge move at all or??

another thought is a failing sensor that is dragging down the 5v ref signal. Groups of sensors share the same 5v wire. A faulty MAP or CPS can cause weird things if they are causing a low 5v line.

 

[jakehobbs]

No CEL. The gauge might move 1/1000th of an inch but it gets no where near the first line at 100 I believe.

 

[CaliGold]

Like Joe Peters said, a faulty temp sensor will make your rig run like kaka. Make sure the temp gauge is working since the signal is shared with the PCM.

 

[JJacobs]

You say you have to push the gas pedal to start- how far? All the way to the floor activates clear flood mode and turns off the injectors. Less than to the floor, disregard.

 

[Eli Lilly]

CTS is super-easy to test...

 

[jakehobbs]

Whats the easiest way to test the CTS?

 

[jakehobbs]

Update: Replaced the CTS and it fixed the starting issues and now the temp gauge is registering again. However, now I have a new problem. Shortly after replacing the CTS I took it to dinner to test it on the freeway. On the way back, 25 mile round trip, it overheated on me. No coolant spewing everywhere but the temp gauge went into the red zone. I waited for about five minutes then the needle went back to one tick to the right of 210. The radiator, cap, thermostat, waterpump, fan clutch, and thermostat housing are all under a year old. Could my cooling system be clogged? Should I take it to a radiator shop? Any recommends? Thanks for everyones help.

 

[JeeperMatt]

Was there steam, smoke, etc... Any other indications of overheat? Just curious - I recently replaced my CTS and now my gauge will creep up, then drop down. Hits maybe 215*, then drops to ~170* over two or so seconds. Only does it for the first 20-30 minutes into a drive, and only when it's up to temperature. Long drives, it'll quit doing in period and stay right at 180*. No overheating issues at all, just a weird gauge deal. Wondering if there was a faulty batch of sensors or something...

 

[Digger87xj]

take a look at this thread:

The sensor from NAPA was out of range causing the PCM not to engage the electric fan

 

[joe_peters]

Curious if you ended up with an air bubble in the system after changing the CTS.

 

[JeeperMatt]

'97, open systen - bubbles shouldn't be an issue

 

[joe_peters]

'97, open systen - bubbles shouldn't be an issue

While open-systems are "self-burping", it can take a number of heat/cooling cycles to get air out of the system. I have dealt with some systems so poorly designed--in an attempt to fit components into "sleek" body styles--we had to put the front tires on a lift and raise the front end to get air out of them. Not all "self-burping" open-systems are created equal.

As jakehobbs hasn't posted back we might just be spitting into the wind, but if it turns out to have been a one-time issue then it was most likely an air pocket that has finally cleared.