no bus dead gauges. cps replaced last month
06-06-2011, 07:10 PM
#1
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Model: Cherokee
Engine: 4.0 HO
no bus dead gauges. cps replaced last month
Title says it all.
Went to go leave today. And it starts. Runs for 3 secs then dies. Instantly I assumed the cps. Same symptoms as last time. But it shouldn't go out this fast. What could be causing this?
Went to go leave today. And it starts. Runs for 3 secs then dies. Instantly I assumed the cps. Same symptoms as last time. But it shouldn't go out this fast. What could be causing this?
06-06-2011, 07:15 PM
#2
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Year: 1987
Model: Cherokee
Engine: 4.0 liter RENIX I-6, DIY Cold Air Intake, 2.5 FM Exhaust, 3 Core Radiator
My son learned the hard way that his CPS wiring was routed too close to the exhaust pipe. 2 CPSs later, he figured it out. With a proper re-route and some heat shield he was good to go.
06-07-2011, 03:57 PM
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Year: 1999
Model: Cherokee
Engine: 4.0
There are 2 types of NO BUS
1. You see the NO BUS message, but engine runs fine (this is a dash cluster cleaning issue)
2. You see the NO BUS message and the engine won't run.
Yours is number 2. This is not a cluster issue. It is usually that one of the 5 volt engine management sensors shorts out. Many times, it is the crank sensor, but theoretically it could be any of the 5 volt sensors. Or even the computer.
What I do to troubleshoot this is one by one, remove the connector for each of those sensors. Then turn the key ON to see if the NO BUS message is gone. Start with the crank sensor. Removing the connector removes that sensor from "the bus". If the message is still there, reinstall the connector and move onto the other 5 volt sensors, like the cam sensor, TPS, etc.
Just because that crank sensor is newer doesn't mean it can't fail. Especially if it is an aftermarket crank sensor, where early failure is not at all unusual.
There is a connector for the crank sensor near the firewall / #6 injector which is easier to get to than the one on the sensor itself, so I'd disconnect the crank sensor there.
Let us know what you find!
1. You see the NO BUS message, but engine runs fine (this is a dash cluster cleaning issue)
2. You see the NO BUS message and the engine won't run.
Yours is number 2. This is not a cluster issue. It is usually that one of the 5 volt engine management sensors shorts out. Many times, it is the crank sensor, but theoretically it could be any of the 5 volt sensors. Or even the computer.
What I do to troubleshoot this is one by one, remove the connector for each of those sensors. Then turn the key ON to see if the NO BUS message is gone. Start with the crank sensor. Removing the connector removes that sensor from "the bus". If the message is still there, reinstall the connector and move onto the other 5 volt sensors, like the cam sensor, TPS, etc.
Just because that crank sensor is newer doesn't mean it can't fail. Especially if it is an aftermarket crank sensor, where early failure is not at all unusual.
There is a connector for the crank sensor near the firewall / #6 injector which is easier to get to than the one on the sensor itself, so I'd disconnect the crank sensor there.
Let us know what you find!
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