Close
While driving my jeep jerks and then takes off like there was nothing wrong
1997 Jeep Grand Cherokee

While driving my jeep jerks and then takes off like there was nothing wrong

(1997 Jeep Grand Cherokee)
put on a new crank position sensor and still have the problem.Would a complete tuneup help or take care of my problem.
2 answers & 1 comment
Popular Answer
on February 15, 2009
I also repaired a Jeep recently which had this sympton. It turned out to be the Throttle Position Sensor. No codes were ever set. As I pulled out on the road, the thing would fall on its face and buck and jerk. It was a scary and sudden loss of power. I diagnosed it by looking at the scan tool data for the Throttle Position Sensor and when the Jeep acted up, the TPS value was frozen, even though I was giving more and more throttle. It was stuck at 20% when it should have been over 60%. This is different than a Crank Sensor failure because the Jeep never actually would die and it never set any codes. Crank Sensors typically will cause the Jeep to die completely and then it won't restart for a while. Often there are codes set. If you do replace the TPS, be sure to reset the idle air motor adaption and the TPS adaption or the engine will surge at stops signs when it is cold. Have your tech clean the Throttle Body as well before resetting the adaption. You need a pretty good scan tool for this.

Unfortunately, I have seen crank sensors NOT set codes as well as the TPS sensors. The error happens too fast for the computer to catch it. For the code to set, the computer usually has to see a condition for 1-4 seconds or longer. This is an eternity in a real time running engine. ( a cylinder fires in 3 1/thousands of a second )
One other thing. How is your exhaust system? I have seen a lot of weird performance problems related to the pattern failure of the 6 cyl Jeep engine exhaust manifold cracking. The fresh air hits the oxygen sensor and it really makes the engine run in a very erratic way, especially under power. I just had 1 yesterday. The exhaust manifold has to be replaced. You can see the estimate on RepairPal. The range is pretty wide. A good manifold can be had for about $300-350 with gaskets. The labor is about 4 hours. Of course if you go dealer, it will all be more.
Sign in to reply
on February 15, 2009
Thanks I will give it a try
General Diagnosis
$88 - $111 Learn More
on February 15, 2009
I also repaired a Jeep recently which had this sympton. It turned out to be the Throttle Position Sensor. No codes were ever set. As I pulled out on the road, the thing would fall on its face and buck and jerk. It was a scary and sudden loss of power. I diagnosed it by looking at the scan tool data for the Throttle Position Sensor and when the Jeep acted up, the TPS value was frozen, even though I was giving more and more throttle. It was stuck at 20% when it should have been over 60%. This is different than a Crank Sensor failure because the Jeep never actually would die and it never set any codes. Crank Sensors typically will cause the Jeep to die completely and then it won't restart for a while. Often there are codes set. If you do replace the TPS, be sure to reset the idle air motor adaption and the TPS adaption or the engine will surge at stops signs when it is cold. Have your tech clean the Throttle Body as well before resetting the adaption. You need a pretty good scan tool for this.

Unfortunately, I have seen crank sensors NOT set codes as well as the TPS sensors. The error happens too fast for the computer to catch it. For the code to set, the computer usually has to see a condition for 1-4 seconds or longer. This is an eternity in a real time running engine. ( a cylinder fires in 3 1/thousands of a second )
One other thing. How is your exhaust system? I have seen a lot of weird performance problems related to the pattern failure of the 6 cyl Jeep engine exhaust manifold cracking. The fresh air hits the oxygen sensor and it really makes the engine run in a very erratic way, especially under power. I just had 1 yesterday. The exhaust manifold has to be replaced. You can see the estimate on RepairPal. The range is pretty wide. A good manifold can be had for about $300-350 with gaskets. The labor is about 4 hours. Of course if you go dealer, it will all be more.
Sign in to reply
on February 15, 2009
Thanks I will give it a try
on March 12, 2009
I just went through this. All the forums pointed to crank position sensor. Dealer said it should give a check engine light if it is the problem. I was not getting a check engine light. He scanned for codes, and got a hit on the CPS and the coil.

After he replaced the sensor, the problem was still there (right away). So I limped home and replaced the coil, then everything seemed fine.

In retrospect, I think one failed and then the other because the first trouble was not firing the fuel injectors. Later, I could smell fuel, but no spark. A one-two punch.

Then a day later, the symptoms returned, but only once, and everything has been ok since. I am still waiting to see if it happens again (it's nerve rackng!), it hasn't even been a tank of gas yet. Before the new parts, it happened daily to every other day.

Often, after a sensor that communicates with the "computer" is replaced, it takes a good long drive to reset things (when the check engine light finally goes off). Correct me if I'm wrong because I don't understand this aspect. So I don't know if this was the case with my one-time recurrence, or if I have not solved the problem. If it happens again, I will try the cam position sensor next since its old and cheap anyway, then the throttle position sensor as the other post here refers to. (from dandd)

I have not heard the throttle position sensor remedy, but it sounds promising! (thanks dandd)
Sign in to reply

Similar Questions

View answers to similar questions from RepairPal's community of auto experts and enthusiasts.
Coolant light came on and was very low on antifreeze do i need to get it looks at?
I have had non-stop problems with the transfer case leaking.