1997 Jeep Grand Cherokee - TPS or electrical?

InvalidUserID

Thread starter
Joined
Aug 23, 2004
Messages
793
Location
Bay Area, CA
So I have a 1997 Jeep Grand Cherokee 4.0L V6 that doesn't get used much, usually once or twice a month (always gets up to highway speeds when it does run) that I had to take in to get emission tested. Passed with flying colors EXCEPT the emission systems were not "ready". Smog tech asked if I replaced the battery or cleared the codes (I hadn't) and showed me that the systems weren't ready.

BUT I remember when the tech went to start the car, it started and then heard it sort of die and then he went to restart it. When I got in the car after it had failed the test, the VIC was flashing to reset the date/time so that explains why the systems weren't ready.

I know the vehicle has issues sometimes where it will die (from a start) if I don't hold the gas down and keep the RPMs up. Looking it up, it sounds like it's a common thing and is the throttle position sensor. Since the car hadn't been started for a while, I hooked up a multimeter to the battery and it was 12.4 off and 13.7 running. Planning to remove the battery, let it charge to get back up to full and see if it holds a full charge before I drop $200 on a new battery (though it is 5 years old). Thing is though, it has never not started right up.

Just wanting some thoughts if I low/weak battery could cause the "system" to act that way or even if a faulty TPS can or if it sounds like something else.
 
Joined
Feb 20, 2007
Messages
6,586
Location
Southeast
so… it’s probably an inline 6, not a V, so get ready for some friendly heckling.

two things I’d look at. First, that engine as a motorized valve built in to the side of the throttle body called the idle air control valve (iacv). It’s supposed to do for you what you were doing with your foot. They get dirty and clog. Yours can typically be removed and cleaned out by hand. Google “jeep 4.0 IACV cleaning”

second, and it’s less likely, but your engine has a vacuum-modulated fuel pressure regulator on the end of the fuel rail. Failure is usually marked with long crank times but not always. It could be getting tired.

i can see why you’d question the voltage. Something like that was needed to throw that code. 12.4 is reasonable, and it does crank the car so I don’t think it’s a weak battery. However, a bad ground, bad (+) somewhere or possible failing solder joint on the ECU, or other intermittent connection, could cause this.

id start there.
 

InvalidUserID

Thread starter
Joined
Aug 23, 2004
Messages
793
Location
Bay Area, CA
so… it’s probably an inline 6, not a V, so get ready for some friendly heckling.

two things I’d look at. First, that engine as a motorized valve built in to the side of the throttle body called the idle air control valve (iacv). It’s supposed to do for you what you were doing with your foot. They get dirty and clog. Yours can typically be removed and cleaned out by hand. Google “jeep 4.0 IACV cleaning”

second, and it’s less likely, but your engine has a vacuum-modulated fuel pressure regulator on the end of the fuel rail. Failure is usually marked with long crank times but not always. It could be getting tired.

i can see why you’d question the voltage. Something like that was needed to throw that code. 12.4 is reasonable, and it does crank the car so I don’t think it’s a weak battery. However, a bad ground, bad (+) somewhere or possible failing solder joint on the ECU, or other intermittent connection, could cause this.

id start there.
Thanks for your thoughts. You know, I neglected to put in it was a 4.0 and as I was typing in the "V6", something felt off. I guess I'm so used to putting V6 for six cylinders, my fingers were working before the brain. ;)

Thanks for your suggestions. I'm pretty sure I replaced the IACV valve before (I watched a video, looks familiar) but not the throttle position sensor as those two were the most suggested fixes for the symptoms I was having.

I think easiest path, just to get it smogged, is drive it around until the emission systems are all "ready", take it to the shop to get resmogged and make sure it doesn't shut down before it gets tested. Once it starts, it never gets that memory cleared, only on startup.
 

InvalidUserID

Thread starter
Joined
Aug 23, 2004
Messages
793
Location
Bay Area, CA
That generation Jeep is VERY sensitive to weak batteries. If your VIC reset, that means all the memory in the vehicle reset.

Test that battery and clean all the connections first.
It's in the garage charging and I'll clean the posts and connections before hooking it back up.

Yeah, VIC reset and the radio stations/time all reset when this sort of thing happens. Not sure if it's related to the weird throttle issue but when that happens, the memory all resets too.
 

InvalidUserID

Thread starter
Joined
Aug 23, 2004
Messages
793
Location
Bay Area, CA
Update: Bought a fresh battery at Costco, installed, and it's been fine since. Have driven it for about two weeks straight, 500+ miles, no issues.

Typically, it gets driven infrequently but due to my DD Civic having seperate issues, Jeep has been my DD. Once Civic gets fixed, will put a solar charger on it to keep the battery from just sitting and getting stale. Thinking that might have contribute to it.
 
Top