No start, out of ideas/patience
07-13-2018, 02:57 PM
#31
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Year: 1995
Model: Cherokee
Engine: 4.0 inline 6
You know.. I had a similar problem a while back.. (No guages, engine wouldnt start, corroded battery wires) Turned out my problems were corroded battery cables, a toasted alternator AND ECU. They all three held hands and stepped off the cliff together at once.
Take a look at the thread.. maybe there might be something there than can help?
Hope you find the problem soon.
Take a look at the thread.. maybe there might be something there than can help?
Hope you find the problem soon.
Last edited by outersketcher; 07-13-2018 at 02:59 PM.
07-13-2018, 03:14 PM
#32
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Year: 97
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Have you just tried a new battery yet? If I missed this and you did forgive me...
Dodge had problems with this back in the 70's. They came out with the "electronic ignition" control box. And because they had a gear reduction starter, low voltage issues would pop up. The starter being gear reduced required less amps and volts to turn the engine over normal. So when a battery started to drop in voltage it was masked by this fact. What happened was the voltage would drop low enough while you were starting it that the Ignition box would not ignite the coil, yet there was no way to really figure this because it still turned over so fast from the gear reduction starter it appeared the battery was top notch and not an issue. But it was indeed the problem when drawing all the juice from a bad battery to the starter instead of putting enough to the box.
Dodge had problems with this back in the 70's. They came out with the "electronic ignition" control box. And because they had a gear reduction starter, low voltage issues would pop up. The starter being gear reduced required less amps and volts to turn the engine over normal. So when a battery started to drop in voltage it was masked by this fact. What happened was the voltage would drop low enough while you were starting it that the Ignition box would not ignite the coil, yet there was no way to really figure this because it still turned over so fast from the gear reduction starter it appeared the battery was top notch and not an issue. But it was indeed the problem when drawing all the juice from a bad battery to the starter instead of putting enough to the box.
07-13-2018, 07:53 PM
#33
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Year: 1999
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i did try a couple different batteries in it. a new one i had just put in a suburban and the one out of my wife’s car. same result with both.
I have a 74 Dodge Dart and this just happened to me the other day so it was on my mind.
07-14-2018, 07:24 AM
#35
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So, when I walked away from it last night my gauges worked and I could hear the fuel pump running for a second or two when i turned the key. Still no start but at least consistent. Went out this morning to work on it....no gauges, no fuel pump, and now the radio stays on all the time even without the key in it.....I don’t generally believe in the paranormal but I’m thinking either gremlins or something of that ilk.....
07-14-2018, 07:50 AM
#36
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So, when I walked away from it last night my gauges worked and I could hear the fuel pump running for a second or two when i turned the key. Still no start but at least consistent. Went out this morning to work on it....no gauges, no fuel pump, and now the radio stays on all the time even without the key in it.....I don’t generally believe in the paranormal but I’m thinking either gremlins or something of that ilk.....
07-14-2018, 07:34 PM
#39
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Year: 1998 Classic (I'll get it running soon....) and 02 Grand
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No that does NOT sound like a bad PCM.
The PCM does not control when the fuel pump turns on, and it would have to be completely dead to kill the gauges, which is an extremely rare event.
When there are weird or dramatic symptoms, people who do not understand vehicle electrical systems often point to the part of the system they least understand - the computer. They are almost always wrong.
07-14-2018, 09:00 PM
#40
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So, to test the ignition switch I remove the starter relay and test for power on socket 86 while having someone turn key to start, is that correct?
07-14-2018, 09:47 PM
#41
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No that does NOT sound like a bad PCM.
The PCM does not control when the fuel pump turns on, and it would have to be completely dead to kill the gauges, which is an extremely rare event.
When there are weird or dramatic symptoms, people who do not understand vehicle electrical systems often point to the part of the system they least understand - the computer. They are almost always wrong.
The other posters are correct - the ignition switch is the most likely explanation.
The PCM does not control when the fuel pump turns on, and it would have to be completely dead to kill the gauges, which is an extremely rare event.
When there are weird or dramatic symptoms, people who do not understand vehicle electrical systems often point to the part of the system they least understand - the computer. They are almost always wrong.
The other posters are correct - the ignition switch is the most likely explanation.
The symptons: fuel pump doesn’t engage. no voltage on gauge despite good battery. Crank but no start.
I was able to easily trouble shoot because I had another Cherokee of same year and when I swapped the pcm it fired right up.
Ive read a lot of your posts blueridge, and I respect your knowledge and contributions to this forum. You may be right. It may be the ignition switch. But if I had to bet I’d say it’s likely a bad pcm, based on my own experience and others that have had same symptons.
07-15-2018, 09:11 AM
#42
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Well, I tested the ignition switch, I believe. I removed the starter relay and tested voltage on socket 86 with the key off. No voltage. Had my wife turn key to start and had a reading of ~12v. Am I correct in thinking that this is how to test ignition switch? It is the information I gleaned from another thread on this forum...
Pretty sure I know the answer, but is there a way to test the pcm? I don’t have access to a known good one and the cheapest one I can find around me is about 75$. Don’t mind spending that if I know that is the issue of course, but likewise don’t want to just throw parts at it.
Pretty sure I know the answer, but is there a way to test the pcm? I don’t have access to a known good one and the cheapest one I can find around me is about 75$. Don’t mind spending that if I know that is the issue of course, but likewise don’t want to just throw parts at it.
07-15-2018, 09:21 AM
#43
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Well, I tested the ignition switch, I believe. I removed the starter relay and tested voltage on socket 86 with the key off. No voltage. Had my wife turn key to start and had a reading of ~12v. Am I correct in thinking that this is how to test ignition switch? It is the information I gleaned from another thread on this forum...
Pretty sure I know the answer, but is there a way to test the pcm? I don’t have access to a known good one and the cheapest one I can find around me is about 75$. Don’t mind spending that if I know that is the issue of course, but likewise don’t want to just throw parts at it.
Pretty sure I know the answer, but is there a way to test the pcm? I don’t have access to a known good one and the cheapest one I can find around me is about 75$. Don’t mind spending that if I know that is the issue of course, but likewise don’t want to just throw parts at it.
07-15-2018, 10:13 AM
#44
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SV Forty Two,
I try to resist jumping to the "bad PCM" as a cause on these types of problems, because it is rare that it is the actual cause. However, sometimes when many of the other checks have been performed, the evidence can lead in that direction. Both the ASD relay (for spark) and the Fuel Pump Relay (for fuel) depend on a ground being provided by the PCM to the control side of the relay (the coil side of the relay). To test, normally you would want to test the relay with a relay buddy or some other tool to confirm that the ground is never being provided by the PCM. Thus, the relay never closes. But, if the ground is missing at the relay, one still has to chase that wire to the PCM to test it at the PCM to see if it is a case where the PCM is producing the ground properly, but it never makes its way to the relay (perhaps due to a wiring problem between the PCM and the relay).
If the PCM originating grounds are missing at both the relay and at the output of the PCM, then that leaves 2 basic questions:
1. Is the PCM not producing this ground because it is failing internally?
2. Is the PCM not producing this ground because it is not receiving the information it needs from other sensors in order to enable this ground?
This can take a while to run down (especially #2). So many people at that point will decide that it makes the most sense to try and scrounge up a known-good PCM and see if the behavior changes. If no known-good PCM is available than the only alternative is to keep testing and collecting evidence.
I think if the ASD relay -and- the fuel pump relay are not seeing action, then the PCM is definitely in play as a source of the problem (by that, I just mean its a possibility). But if the ASD relay was implicated, but the fuel pump relay appears to be working and the fuel pump is seeing activity, I would be less inclined to think that the PCM was a source of the problem.
I will also correct previous posters, and remind that the PCM on a 96 XJ is very much involved with fuel pump operation. The PCM provides the ground to the control/coil side of the fuel pump relay. Without that signal from the PCM, the relay will not close, and the puel pump will not receive battery voltage. But, when turning the key on, the priming of the pump should occur, and this is not dependent on other signals (such as cam and crank sensor values) being read by the computer. So in some ways, if the key is turned on, and the fuel pump does not prime, this problem is simpler (in the number of variables) then trying to chase down the ASD relay because the ASD has far more variables involved (is the PCM good, is the relay good, is the connectivity between the PCM and relay good, is the PCM getting what it needs from the cam and crank sensors, etc).
I try to resist jumping to the "bad PCM" as a cause on these types of problems, because it is rare that it is the actual cause. However, sometimes when many of the other checks have been performed, the evidence can lead in that direction. Both the ASD relay (for spark) and the Fuel Pump Relay (for fuel) depend on a ground being provided by the PCM to the control side of the relay (the coil side of the relay). To test, normally you would want to test the relay with a relay buddy or some other tool to confirm that the ground is never being provided by the PCM. Thus, the relay never closes. But, if the ground is missing at the relay, one still has to chase that wire to the PCM to test it at the PCM to see if it is a case where the PCM is producing the ground properly, but it never makes its way to the relay (perhaps due to a wiring problem between the PCM and the relay).
If the PCM originating grounds are missing at both the relay and at the output of the PCM, then that leaves 2 basic questions:
1. Is the PCM not producing this ground because it is failing internally?
2. Is the PCM not producing this ground because it is not receiving the information it needs from other sensors in order to enable this ground?
This can take a while to run down (especially #2). So many people at that point will decide that it makes the most sense to try and scrounge up a known-good PCM and see if the behavior changes. If no known-good PCM is available than the only alternative is to keep testing and collecting evidence.
I think if the ASD relay -and- the fuel pump relay are not seeing action, then the PCM is definitely in play as a source of the problem (by that, I just mean its a possibility). But if the ASD relay was implicated, but the fuel pump relay appears to be working and the fuel pump is seeing activity, I would be less inclined to think that the PCM was a source of the problem.
I will also correct previous posters, and remind that the PCM on a 96 XJ is very much involved with fuel pump operation. The PCM provides the ground to the control/coil side of the fuel pump relay. Without that signal from the PCM, the relay will not close, and the puel pump will not receive battery voltage. But, when turning the key on, the priming of the pump should occur, and this is not dependent on other signals (such as cam and crank sensor values) being read by the computer. So in some ways, if the key is turned on, and the fuel pump does not prime, this problem is simpler (in the number of variables) then trying to chase down the ASD relay because the ASD has far more variables involved (is the PCM good, is the relay good, is the connectivity between the PCM and relay good, is the PCM getting what it needs from the cam and crank sensors, etc).
07-15-2018, 10:45 AM
#45
CF Veteran
Dude, you have much info here. Sit back a minute. What I see that catches my eye is that among other things:
The car continued to run with the key off
The radio played with the key off.
Both of these things point to a bad ignition switch or burned up ignition switch and or harness. Not so hard to take it apart, have you done this?
Your starter relay test is a good idea but you need to know what to look for, and it does not sound like you have that yet. Regardless if there is a problem there it might also indicate the starter switch. hope that heps.
Afterthought:
The scan tool does not communicate.
When it does you get a communication error wit the pcm.
These almost always point to the pcm or it's connections.
Have you had the 3 plugs off the pcm yet to look for corrosion?
The car continued to run with the key off
The radio played with the key off.
Both of these things point to a bad ignition switch or burned up ignition switch and or harness. Not so hard to take it apart, have you done this?
Your starter relay test is a good idea but you need to know what to look for, and it does not sound like you have that yet. Regardless if there is a problem there it might also indicate the starter switch. hope that heps.
Afterthought:
The scan tool does not communicate.
When it does you get a communication error wit the pcm.
These almost always point to the pcm or it's connections.
Have you had the 3 plugs off the pcm yet to look for corrosion?
Last edited by 97grand4.0; 07-15-2018 at 11:10 AM.