RPM's dropping on the highway.
- Thread starter dlundblad
- Start date
- Status
I can't help but smirk at myself when somebody suggests clogged catalytic converter when the engine suddenly quits while on the highway.
Come on, I mean don't they teach you logic somewhere in the school anymore?
You are losing the ignition. A bad ignition switch which temporarily cuts the ignition wire would behave exactly like that. You have no spark firing and the tachometer which measures the ignition pulses will read zero. If the contact is re-established quickly, you are not presented with the Christmas tree light show on the dash. There is enough momentum in the flywheel, so the car starts immediately.
Concentrate on the ignition switch and wires.
Come to think of it, start the car and just wiggle the key and see if you can reproduce it.
Come on, I mean don't they teach you logic somewhere in the school anymore?
You are losing the ignition. A bad ignition switch which temporarily cuts the ignition wire would behave exactly like that. You have no spark firing and the tachometer which measures the ignition pulses will read zero. If the contact is re-established quickly, you are not presented with the Christmas tree light show on the dash. There is enough momentum in the flywheel, so the car starts immediately.
Concentrate on the ignition switch and wires.
Come to think of it, start the car and just wiggle the key and see if you can reproduce it.
Originally Posted By: Vikas
I can't help but smirk at myself when somebody suggests clogged catalytic converter when the engine suddenly quits while on the highway.
Come on, I mean don't they teach you logic somewhere in the school anymore?
You are losing the ignition. A bad ignition switch which temporarily cuts the ignition wire would behave exactly like that. You have no spark firing and the tachometer which measures the ignition pulses will read zero. If the contact is re-established quickly, you are not presented with the Christmas tree light show on the dash. There is enough momentum in the flywheel, so the car starts immediately.
Concentrate on the ignition switch and wires.
Come to think of it, start the car and just wiggle the key and see if you can reproduce it.
+1 I doubt it is a clogged cat. These year Jeeps also have two cats on the manifold that are monitored by O2 sensors, so they have 4 total O2 sensors. If the cat was failing the sensor would most likely tell you before they got bad enough to stop the engine. Mine were going bad (they were so fun to replace) and it threw a code. They looked fine upon removal, but apparently they were losing efficiency.
The ignition switches in these aren't really prone to failure. A common failure on this vehicle is the crank position sensor, which will show similar symptoms when it begins to fail. When the crank sensor fails it cuts spark to the engine. It will start doing it intermittently, which can cause strange issues like this. Soon it will cut spark altogether, causing stalling and no start problems. My bets are on that being the problem.
I can't help but smirk at myself when somebody suggests clogged catalytic converter when the engine suddenly quits while on the highway.
Come on, I mean don't they teach you logic somewhere in the school anymore?
You are losing the ignition. A bad ignition switch which temporarily cuts the ignition wire would behave exactly like that. You have no spark firing and the tachometer which measures the ignition pulses will read zero. If the contact is re-established quickly, you are not presented with the Christmas tree light show on the dash. There is enough momentum in the flywheel, so the car starts immediately.
Concentrate on the ignition switch and wires.
Come to think of it, start the car and just wiggle the key and see if you can reproduce it.
+1 I doubt it is a clogged cat. These year Jeeps also have two cats on the manifold that are monitored by O2 sensors, so they have 4 total O2 sensors. If the cat was failing the sensor would most likely tell you before they got bad enough to stop the engine. Mine were going bad (they were so fun to replace) and it threw a code. They looked fine upon removal, but apparently they were losing efficiency.
The ignition switches in these aren't really prone to failure. A common failure on this vehicle is the crank position sensor, which will show similar symptoms when it begins to fail. When the crank sensor fails it cuts spark to the engine. It will start doing it intermittently, which can cause strange issues like this. Soon it will cut spark altogether, causing stalling and no start problems. My bets are on that being the problem.
You are absolutely right. CPS would be more likely scenario on this particular vehicle.
My jab was at the guys who think cat converter would suddenly clog up cause a momentary stall and then miraculously unclog itself in fraction of second.
My jab was at the guys who think cat converter would suddenly clog up cause a momentary stall and then miraculously unclog itself in fraction of second.
Originally Posted By: Vikas
A bad ignition switch which temporarily cuts the ignition wire would behave exactly like that.
Originally Posted By: jeepman3071
The ignition switches in these aren't really prone to failure. A common failure on this vehicle is the crank position sensor,
Originally Posted By: Vikas
CPS would be more likely scenario on this particular vehicle.
Come on Vikas..make up your mind...ignition switch, crank position sensor or muffler bearings?
A bad ignition switch which temporarily cuts the ignition wire would behave exactly like that.
Originally Posted By: jeepman3071
The ignition switches in these aren't really prone to failure. A common failure on this vehicle is the crank position sensor,
Originally Posted By: Vikas
CPS would be more likely scenario on this particular vehicle.
Come on Vikas..make up your mind...ignition switch, crank position sensor or muffler bearings?
Before removing the CPS, I figured id give the fuel pressure a check. With the key on, it was about 10 psi. With the engine running, it was about 58 psi. IIRC, the 4.0 should be idling at about 49 psi?
The fuel filter was replaced about 6000 miles ago FYI.
The fuel filter was replaced about 6000 miles ago FYI.
- Status
