Diagnostic help
03-29-2018, 01:08 PM
#1
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Diagnostic help
So hopped in the Jeep to head to work Tuesday morning and it would crank but wouldn’t start. Tried to fire it up in neutral but to no avail. Finally got a chance to work on it today and low and behold it fired right up. Had the battery, alternator and starter all tested because those are all easy and free and they all tested fine. I’ve started it probably 20 times since and can’t get the issue to reappear.
I was having intermitten rough idling and a bit of a stutter when quickly accelerating a few weeks back so I replaced the TPS and haven’t had those issues since but as I said they were intermitten and not at all consistent.
Any ideas on where to go next?
Possible fuel pump issue?
Loose connection?
CPS?
I was having intermitten rough idling and a bit of a stutter when quickly accelerating a few weeks back so I replaced the TPS and haven’t had those issues since but as I said they were intermitten and not at all consistent.
Any ideas on where to go next?
Possible fuel pump issue?
Loose connection?
CPS?
03-30-2018, 12:24 PM
#2
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Year: 1997
Model: Cherokee
Engine: 4.0L
Drive it a while before messing with anything else. When you change too many things at once and the issue stops, you dont know which one actually fixed it. It is quite possible the TPS was the culprit. But did you use Mopar or aftermarket? Aftermarket can be hit or miss when it comes to longevity and reliability.
03-30-2018, 01:44 PM
#3
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You need to include information about your vehicle. Year, make, model.
TPS erroneously presenting high values can cause this problem. It will make the computer think you have the pedal on the floor, and disable the fuel injection pulses, causing a crank-no-start (this is what the manual calls "clear flood" mode).
Intermittent failure of the CPS can cause this problem, and often the first signs of failure look like what you have experienced. Stumbling, rough idles, misfires at higher RPMS...and the random crank-no-start that gets progessively more common until starts always fail.
A failing ASD Relay can cause intermittent crank-no-start conditions. Typically not involved with rough idle or stumbling issues though.
A failing fuel pump can cause intermittent crank-no-start conditions as well as rough idles and stumbling, particularly while accelerating or when under load. Like any motor depending on the position it stops in, it may not want to start again, then sometimes....it just will.
If the crank-no-start has happened since replacing the TPS, I don't think that is your primary culprit.
I think your two top troubleshooting priorities will be the CPS and fuel pump. Both, you may have to wait until the problem is a little more present to get a handle on. You could change the CPS pre-emptively if the original one is very old (go Mopar), but I don't think I'd change a fuel pump preemptively until I knew it was the problem.
TPS erroneously presenting high values can cause this problem. It will make the computer think you have the pedal on the floor, and disable the fuel injection pulses, causing a crank-no-start (this is what the manual calls "clear flood" mode).
Intermittent failure of the CPS can cause this problem, and often the first signs of failure look like what you have experienced. Stumbling, rough idles, misfires at higher RPMS...and the random crank-no-start that gets progessively more common until starts always fail.
A failing ASD Relay can cause intermittent crank-no-start conditions. Typically not involved with rough idle or stumbling issues though.
A failing fuel pump can cause intermittent crank-no-start conditions as well as rough idles and stumbling, particularly while accelerating or when under load. Like any motor depending on the position it stops in, it may not want to start again, then sometimes....it just will.
If the crank-no-start has happened since replacing the TPS, I don't think that is your primary culprit.
I think your two top troubleshooting priorities will be the CPS and fuel pump. Both, you may have to wait until the problem is a little more present to get a handle on. You could change the CPS pre-emptively if the original one is very old (go Mopar), but I don't think I'd change a fuel pump preemptively until I knew it was the problem.
03-30-2018, 02:00 PM
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You need to include information about your vehicle. Year, make, model.
TPS erroneously presenting high values can cause this problem. It will make the computer think you have the pedal on the floor, and disable the fuel injection pulses, causing a crank-no-start (this is what the manual calls "clear flood" mode).
Intermittent failure of the CPS can cause this problem, and often the first signs of failure look like what you have experienced. Stumbling, rough idles, misfires at higher RPMS...and the random crank-no-start that gets progessively more common until starts always fail.
A failing ASD Relay can cause intermittent crank-no-start conditions. Typically not involved with rough idle or stumbling issues though.
A failing fuel pump can cause intermittent crank-no-start conditions as well as rough idles and stumbling, particularly while accelerating or when under load. Like any motor depending on the position it stops in, it may not want to start again, then sometimes....it just will.
If the crank-no-start has happened since replacing the TPS, I don't think that is your primary culprit.
I think your two top troubleshooting priorities will be the CPS and fuel pump. Both, you may have to wait until the problem is a little more present to get a handle on. You could change the CPS pre-emptively if the original one is very old (go Mopar), but I don't think I'd change a fuel pump preemptively until I knew it was the problem.
TPS erroneously presenting high values can cause this problem. It will make the computer think you have the pedal on the floor, and disable the fuel injection pulses, causing a crank-no-start (this is what the manual calls "clear flood" mode).
Intermittent failure of the CPS can cause this problem, and often the first signs of failure look like what you have experienced. Stumbling, rough idles, misfires at higher RPMS...and the random crank-no-start that gets progessively more common until starts always fail.
A failing ASD Relay can cause intermittent crank-no-start conditions. Typically not involved with rough idle or stumbling issues though.
A failing fuel pump can cause intermittent crank-no-start conditions as well as rough idles and stumbling, particularly while accelerating or when under load. Like any motor depending on the position it stops in, it may not want to start again, then sometimes....it just will.
If the crank-no-start has happened since replacing the TPS, I don't think that is your primary culprit.
I think your two top troubleshooting priorities will be the CPS and fuel pump. Both, you may have to wait until the problem is a little more present to get a handle on. You could change the CPS pre-emptively if the original one is very old (go Mopar), but I don't think I'd change a fuel pump preemptively until I knew it was the problem.
The crank no start only happened since the TPS was replaced I didn’t have the issue before just the occasional rough idle and acceleration missteps.
I also noticed the fuel gauge takes a good 1-2 minutes to find the current fuel level once started. It will show it being below a quarter of a tank with the low fuel warning light on then slowly move up until it finally settles at what I think is the actual fuel level then the low fuel light goes off.
03-30-2018, 02:10 PM
#5
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If you have a voltage gauge, do you also see weirdness with that when the crank-no-start is occurring?
Weirdness with fuel gauge and the voltage gauge are often coupled with a failing CPS. Especially if disconnecting the CPS causes them to return to normal when the key is on.
A TPS that is producing the wrong voltages can cause your problem as well.
Disconnect your CPS and see if there is a change in the fuel gauge with the vehicle in the ON position (it won't start with the CPS disconnected).
Weirdness with fuel gauge and the voltage gauge are often coupled with a failing CPS. Especially if disconnecting the CPS causes them to return to normal when the key is on.
A TPS that is producing the wrong voltages can cause your problem as well.
Disconnect your CPS and see if there is a change in the fuel gauge with the vehicle in the ON position (it won't start with the CPS disconnected).
03-30-2018, 02:19 PM
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The voltage gauge does the same thing. It will start at a low reading then return to normal after a short period.
It’s still firing right up so it’s hard to diagnose without the problem present.
I will unplug the CPS once a have chance shortly and watch the gauges.
The TPS I used is a duralast I bought from Autozone hopefully it’s not failing already
It’s still firing right up so it’s hard to diagnose without the problem present.
I will unplug the CPS once a have chance shortly and watch the gauges.
The TPS I used is a duralast I bought from Autozone hopefully it’s not failing already
03-30-2018, 10:35 PM
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Tested the CPS with a meter and I’m getting an OHM reading across the B and C leads in the CPS. If the sensor is good I should be getting an open reading across all, is this correct?
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