Fuel pump priming ISSUE
11-22-2019, 08:24 AM
#1
Newbie
Thread Starter
Fuel pump priming ISSUE
Hello everyone,
We got a 1996 Grand Cherokee Laredo 4.0L AWD that we are trying to bring back to live. My Dad and I are pulling our hairs off and we can seem to find a solution. We hope you can help us to save some money and get this going. Any idea will be deeply appreciated. Thank you in advance...
The problem: Cars stay priming for minutes at times before pump stop and car starts. If we tried to start the vehicle before the pump stop it wont start; so my dad open and closes the switch several times and that seems to shorten the time that the pump stay priming. My Dad has left the pump run without interfering and it has taken close to 30min to stop. It is worst in the AM; during the day the longer it seat the longer it take to start. If you try to start it right after you shut it off, it will start right up. We got a fuel tester and fuel pressure was at 50; although, we had to turn the switch to on twice before we got the reading at 50 first time stayed at zero! I have listed below some of the parts we have replaced so far:
Part replaced:
Fuel pump brand is Boch. Tank was cleaned
Fuel filter
We cut the fuel line and added a none return one way check valve after considering the one in the fuel pump was defect.
Spark plugs and wires and distributor cap
Cam sensor
New battery
We got a 1996 Grand Cherokee Laredo 4.0L AWD that we are trying to bring back to live. My Dad and I are pulling our hairs off and we can seem to find a solution. We hope you can help us to save some money and get this going. Any idea will be deeply appreciated. Thank you in advance...
The problem: Cars stay priming for minutes at times before pump stop and car starts. If we tried to start the vehicle before the pump stop it wont start; so my dad open and closes the switch several times and that seems to shorten the time that the pump stay priming. My Dad has left the pump run without interfering and it has taken close to 30min to stop. It is worst in the AM; during the day the longer it seat the longer it take to start. If you try to start it right after you shut it off, it will start right up. We got a fuel tester and fuel pressure was at 50; although, we had to turn the switch to on twice before we got the reading at 50 first time stayed at zero! I have listed below some of the parts we have replaced so far:
Part replaced:
Fuel pump brand is Boch. Tank was cleaned
Fuel filter
We cut the fuel line and added a none return one way check valve after considering the one in the fuel pump was defect.
Spark plugs and wires and distributor cap
Cam sensor
New battery
Last edited by Jswfla; 11-24-2019 at 07:53 AM.
11-23-2019, 07:50 AM
#3
Newbie
Thread Starter
The vehicle cranks and there is no check engine light either. I would assume that any bad sensor or relay will throw a check engine light. We did look at the fuel pump relay and it seems to be working; you can hear it clicking. I will check the ADS relay. Thank you
11-23-2019, 01:26 PM
#4
Newbie
Thread Starter
ADS relay seems to be working fine. My Dad this morning before turning the key on he check the fuel rail for fuel reassure and it was empty. After key was turn on several times, the system got fuel back and the car started. He also notice that the fuel gauge doesn't mark the fuel level until the lines get pressure back on. I stood outside the vehicle as he kept turning the key on and off, I heard the bussing of the fuel system and lines get pressurize, fuel pump will stop, and vehicle will start.... This is driving us insane!
11-23-2019, 02:39 PM
#5
CF Veteran
Join Date: Oct 2018
Location: United Kingdom
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Year: 1995 RHD
Model: Cherokee (XJ)
Engine: 4.0l
Don't always assume that a fault will throw a CEL.
Past that, this is in the 95 FSM:
If your pressure if 50 psi it could be way too high as your engine is flooding itself, when the pump turns off and the pressure drops it could start to fuel correctly. So I'd suggest that you take a look at the pressure regulator on the end of the fuel rail and if the vacuum line looks cracked, replace it and also follow any other vacuum lines up to the manifold. A vacuum leak will stop the regulator from working properly.
When the system is depressurised it may also be worth pulling the fuel return line and checking that fuel is able to flow back to the tank freely, a restriction would also increase rail pressure.
Past that, this is in the 95 FSM:
Fuel system pressure is maintained at approximately 214 kPa (31 psi). This is when the pump is operating and vacuum is supplied to the fuel pressure regulator. If vacuum is not supplied to the pressure regulator, fuel pressure will be approximately 55-69 kPa (8-10 psi) higher. This may be due to a broken or clogged vacuum line. When the fuel pump is not operating, fuel system pressure of 131-269 kPa (19-39 psi) is maintained for approximately 2 to 6 hours. This is done by the fuel pump outlet check valve and the vacuum assisted fuel pressure regulator.
When the system is depressurised it may also be worth pulling the fuel return line and checking that fuel is able to flow back to the tank freely, a restriction would also increase rail pressure.
11-23-2019, 09:00 PM
#6
Newbie
Thread Starter
Don't always assume that a fault will throw a CEL.
Past that, this is in the 95 FSM:
If your pressure if 50 psi it could be way too high as your engine is flooding itself, when the pump turns off and the pressure drops it could start to fuel correctly. So I'd suggest that you take a look at the pressure regulator on the end of the fuel rail and if the vacuum line looks cracked, replace it and also follow any other vacuum lines up to the manifold. A vacuum leak will stop the regulator from working properly.
When the system is depressurised it may also be worth pulling the fuel return line and checking that fuel is able to flow back to the tank freely, a restriction would also increase rail pressure.
Past that, this is in the 95 FSM:
If your pressure if 50 psi it could be way too high as your engine is flooding itself, when the pump turns off and the pressure drops it could start to fuel correctly. So I'd suggest that you take a look at the pressure regulator on the end of the fuel rail and if the vacuum line looks cracked, replace it and also follow any other vacuum lines up to the manifold. A vacuum leak will stop the regulator from working properly.
When the system is depressurised it may also be worth pulling the fuel return line and checking that fuel is able to flow back to the tank freely, a restriction would also increase rail pressure.
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11-24-2019, 04:51 AM
#8
Old fart with a wrench
What's a Drank Cherokee? Are you talking about a GRAND Cherokee? AWD sounds to me like a 249 t/case found only in a Grand. The fuel pump is supposed to be on a TIMED cycle to only charge the fuel rail with pressure for about 2 seconds. IDK why it's running for 30 seconds. It's not a pressure cycle, just a timed cycle. I think I have a leaky injector because if my XJ sits for longer than 24 hours, I have to cycle the key 2 or 3 times before it starts right up without cranking for a long time. Mine may be a bad pump check valve, but I need to replace the injectors anyway. I'm getting rid of the squirt-gun single holers and going to 4-port ones.
11-24-2019, 12:46 PM
#10
Banned
You potentially have a seriously difficult problem to diagnose. You possibly have two or three issues occuring simultaneously. I would venture to say there may not actually be three faults though? What I mean by this is there may only be a single fault needing to be fixed. If you are able to find possibly this single primary specific fault, then the other problems you are seeming to experience may dissapear and go away on there own after fixing the primary fault?
This is why it is difficult to diagnose. Because, how do you know where to start looking? You could chase your tail trying to look for a fix to your crank no start condition you are experiencing at times, when there is actually nothing really specifically wrong to be hunting down there to even fix.. You could do the same trying to hunt down focusing only on trying to fix the abnormal continual priming that is occuring with your fuel pump.. looking only on the fuel pump specific electrical circuitry. Same thing for trying to chase down the nearly zero fuel pressure you've been seeing at the fuel rail in the mornings as well etc...
Either way, you have to begin looking somewhere. The fuel pump should not be priming for thirty minutes. That is a big fault! I say start there, and totally ignore the occasional crank no start and your Jeeps fuel rail pressure issue for the moment. They are all clues to keep in mind though... The fuel pump we know should be priming only for two seconds with the key turned to run, and then it should be done priming if you are not sending crank signals via the ignition turn key input to start. So, why is it staying on when you are not turning the crank, or running the engine? This is where I would want to first focus all of my attention to figure out what is the reason for the fuel pump to be continuing to run like that.
Do you know how to use a voltmeter to check a ground circuit? If you don't? You are going to want to learn. I personally believe you have a short to ground. The only thing is.. On the Chrysler systems, there is a lot to contend with for on your ASD, independent Fuel pump, and the ignition circuitry. Many of the components all tie into each other.. I have not begun to look things up to be 100% sure right now... However, a short to ground on any one of the components that are tied into the circuitry here may result in a problem to occur elsewhere. For example, since you have a crank no start condition. This means a faulty intermittent short to ground that occurs at your crank sensor (CPS) may possibly be able to energize the ground for your fuel pump to continually prime like it is doing (when there is actually nothing wrong with the primary ground wire directly involved with the fuel pump itself), since it may only happen to be effected by a fault that may be occuring actually as a primary fault directly at the CPS sensor circuit wires. To continue with this first one example... Something like that could possibly also explain why you are having the crank no start condition too, you see (but it would probably not be the reason for the low fuel rail pressure issue). Also, a faulty CPS has been known to cause issues of the fuel gauge to not work correctly to give readings. Whats worse.. is that I believe the opposite is also a possibility to be true. A fault in the wiring or ground specific for the fuel pump has the ability to make the CPS look like it is working incorrectly based soley off the diagrams, should a short be causing confusion to the ECU's..for it to look like it is bad and has a fault when it does not. It could effect the fuel gauge too, as the diagrams I've seen in the past also has this tied in powered thru the same relays. The ASD and fuel pump relays. They are seperate relays sure. But, they are both still driven by the same thing from the PCM. It's basically like they are still as they were in the past on the much older designs being on the exact same circuit because of this...
There are a lot of possibilities. Some of the voltmeter tests needing to be done are not the easiest tests to be performing, even for an experienced mechanic or auto technicians to accomplish them correctly. It is easy to be fooled if you do not know precisely what you are doing. AND, to know why you are doing them...
If you want to try and chase this down? I will attempt to help you. I would need to study some of the diagrams again though. To be sure and know exactly whatever it is I am trying to correctly and accurately say to you before proceding. Maybe someone else will know of something better than what I can come up with?
You never know until you try.. It could turn out to be something rather simple? Maybe being the first thing you check will be the one and only reason? This is why you have to try and think about going at it as logically as you possibly can.. What is the most likely reason(s), and go there first. For example, a PCM is not a likely reason. They are kind of resilient components PCMs are, overall... But still, a driver or other aspect of the PCM could definitely be a reason for why you are having these problems to consider. I wouldn't recommend trying to replace the PCM as a first way to test and resolve the issues though. When there are some other much more likely possible reasons to explore first.
My advice is for right now to totally forget about the fuel pressure and the crank no starting issues until you find out what is keeping your fuel pump turned on continually priming. Find this out first, and then move on when and if needed...
I am almost certain to me it sounds like it is some sort of grounding issue. Since the fuel pump continually primes like it does. The ground here would be the ground I want to check out to do testing on it first.
Do you know how to check a ground? You have to apply battery power to it. Then, look for VOLTS. If you see anything more than 100 milivolts distal and after the power being applied to the grounding wire. That is how I would recommend for you to test. For you to know it is a faulty ground is when you see that kind of reading being greater than 100 milivolts. You may have to do this for every wire tied into this group of circuits - on the ASD, fuel pump, and in the ignition circuit groups. There is the O2 sensors, alternator, starter, ignition coil, fuel pump etc all to be suspected in this group right now, and there may be more? You will have to start ruling each of them out systematically.
I would start first by verifying what exactly is going on with the ground for your fuel pump. I would go ahead and disconnect this ground from its stud wherever that is located (Probably it is located either hidden behind the drivers side door panel? Or, maybe behind the back panel where the spare tires get put sometimes?). Connect one lead of the dvom to the stud (or any good grounding point really) and the other dvom lead to the now disconnected fuel pump grounding wire. Set the dvom to measure for geting a reading of AMPS. With the key turned to the off position you should see zero, right? Turn the ignition key to the run position, and see what it does? Normally, you should see something like 3 - 4 amps for approximately two seconds after you turn the key into run. Then, it normally shuts itself off if you do not advance the ignition key to start and crank to turn on the engine. I suspect you will continue to see current, or amps on the meter, with your ignition key turned and remaining in the run position.. since you say the pump is continuing to go on priming like it has been doing for up to thirty minutes straight.
Then, apply power to its ground wire with the key in the off position while looking for a reading with the dvom now being set to pick up in the VOLTS setting. Anything above and greater than 100 milivolts indicates having a bad ground. You have to trace it back and forward along the wire(s) depending on what you see where...
I read that you say toggling your Jeeps ignition key several times sometimes helps to make things operate more normally for you too? How so does this exactly happen as you notice? Since you say this.. I suspect this maybe will be the problem ground within the ignition circuit as a very highly likely suspected area to fully investigate further...
Let me know what you think.
I promise I will come back to try and help if I am able. This week coming up is going to be keeping me particularly busy though.. I have three 12 - 15 hour days coming up, then I will be taking a flight home for the Thanksgiving Holiday later Wednesday night.. To catch another flight early Friday morning to be back and working another long day on Saturday.
This is why it is difficult to diagnose. Because, how do you know where to start looking? You could chase your tail trying to look for a fix to your crank no start condition you are experiencing at times, when there is actually nothing really specifically wrong to be hunting down there to even fix.. You could do the same trying to hunt down focusing only on trying to fix the abnormal continual priming that is occuring with your fuel pump.. looking only on the fuel pump specific electrical circuitry. Same thing for trying to chase down the nearly zero fuel pressure you've been seeing at the fuel rail in the mornings as well etc...
Either way, you have to begin looking somewhere. The fuel pump should not be priming for thirty minutes. That is a big fault! I say start there, and totally ignore the occasional crank no start and your Jeeps fuel rail pressure issue for the moment. They are all clues to keep in mind though... The fuel pump we know should be priming only for two seconds with the key turned to run, and then it should be done priming if you are not sending crank signals via the ignition turn key input to start. So, why is it staying on when you are not turning the crank, or running the engine? This is where I would want to first focus all of my attention to figure out what is the reason for the fuel pump to be continuing to run like that.
Do you know how to use a voltmeter to check a ground circuit? If you don't? You are going to want to learn. I personally believe you have a short to ground. The only thing is.. On the Chrysler systems, there is a lot to contend with for on your ASD, independent Fuel pump, and the ignition circuitry. Many of the components all tie into each other.. I have not begun to look things up to be 100% sure right now... However, a short to ground on any one of the components that are tied into the circuitry here may result in a problem to occur elsewhere. For example, since you have a crank no start condition. This means a faulty intermittent short to ground that occurs at your crank sensor (CPS) may possibly be able to energize the ground for your fuel pump to continually prime like it is doing (when there is actually nothing wrong with the primary ground wire directly involved with the fuel pump itself), since it may only happen to be effected by a fault that may be occuring actually as a primary fault directly at the CPS sensor circuit wires. To continue with this first one example... Something like that could possibly also explain why you are having the crank no start condition too, you see (but it would probably not be the reason for the low fuel rail pressure issue). Also, a faulty CPS has been known to cause issues of the fuel gauge to not work correctly to give readings. Whats worse.. is that I believe the opposite is also a possibility to be true. A fault in the wiring or ground specific for the fuel pump has the ability to make the CPS look like it is working incorrectly based soley off the diagrams, should a short be causing confusion to the ECU's..for it to look like it is bad and has a fault when it does not. It could effect the fuel gauge too, as the diagrams I've seen in the past also has this tied in powered thru the same relays. The ASD and fuel pump relays. They are seperate relays sure. But, they are both still driven by the same thing from the PCM. It's basically like they are still as they were in the past on the much older designs being on the exact same circuit because of this...
There are a lot of possibilities. Some of the voltmeter tests needing to be done are not the easiest tests to be performing, even for an experienced mechanic or auto technicians to accomplish them correctly. It is easy to be fooled if you do not know precisely what you are doing. AND, to know why you are doing them...
If you want to try and chase this down? I will attempt to help you. I would need to study some of the diagrams again though. To be sure and know exactly whatever it is I am trying to correctly and accurately say to you before proceding. Maybe someone else will know of something better than what I can come up with?
You never know until you try.. It could turn out to be something rather simple? Maybe being the first thing you check will be the one and only reason? This is why you have to try and think about going at it as logically as you possibly can.. What is the most likely reason(s), and go there first. For example, a PCM is not a likely reason. They are kind of resilient components PCMs are, overall... But still, a driver or other aspect of the PCM could definitely be a reason for why you are having these problems to consider. I wouldn't recommend trying to replace the PCM as a first way to test and resolve the issues though. When there are some other much more likely possible reasons to explore first.
My advice is for right now to totally forget about the fuel pressure and the crank no starting issues until you find out what is keeping your fuel pump turned on continually priming. Find this out first, and then move on when and if needed...
I am almost certain to me it sounds like it is some sort of grounding issue. Since the fuel pump continually primes like it does. The ground here would be the ground I want to check out to do testing on it first.
Do you know how to check a ground? You have to apply battery power to it. Then, look for VOLTS. If you see anything more than 100 milivolts distal and after the power being applied to the grounding wire. That is how I would recommend for you to test. For you to know it is a faulty ground is when you see that kind of reading being greater than 100 milivolts. You may have to do this for every wire tied into this group of circuits - on the ASD, fuel pump, and in the ignition circuit groups. There is the O2 sensors, alternator, starter, ignition coil, fuel pump etc all to be suspected in this group right now, and there may be more? You will have to start ruling each of them out systematically.
I would start first by verifying what exactly is going on with the ground for your fuel pump. I would go ahead and disconnect this ground from its stud wherever that is located (Probably it is located either hidden behind the drivers side door panel? Or, maybe behind the back panel where the spare tires get put sometimes?). Connect one lead of the dvom to the stud (or any good grounding point really) and the other dvom lead to the now disconnected fuel pump grounding wire. Set the dvom to measure for geting a reading of AMPS. With the key turned to the off position you should see zero, right? Turn the ignition key to the run position, and see what it does? Normally, you should see something like 3 - 4 amps for approximately two seconds after you turn the key into run. Then, it normally shuts itself off if you do not advance the ignition key to start and crank to turn on the engine. I suspect you will continue to see current, or amps on the meter, with your ignition key turned and remaining in the run position.. since you say the pump is continuing to go on priming like it has been doing for up to thirty minutes straight.
Then, apply power to its ground wire with the key in the off position while looking for a reading with the dvom now being set to pick up in the VOLTS setting. Anything above and greater than 100 milivolts indicates having a bad ground. You have to trace it back and forward along the wire(s) depending on what you see where...
I read that you say toggling your Jeeps ignition key several times sometimes helps to make things operate more normally for you too? How so does this exactly happen as you notice? Since you say this.. I suspect this maybe will be the problem ground within the ignition circuit as a very highly likely suspected area to fully investigate further...
Let me know what you think.
I promise I will come back to try and help if I am able. This week coming up is going to be keeping me particularly busy though.. I have three 12 - 15 hour days coming up, then I will be taking a flight home for the Thanksgiving Holiday later Wednesday night.. To catch another flight early Friday morning to be back and working another long day on Saturday.
Last edited by Noah911; 11-24-2019 at 01:08 PM.
11-24-2019, 01:23 PM
#11
Newbie
Thread Starter
Thank you so very much for taking the time to replied. I will follow your advice and get to work. I will definitely need to learn how to used a voltmeter, and the wiring schematic of the vehicle. Again… thank you for your time and advice. I will keep you posted.
11-24-2019, 01:42 PM
#12
Banned
Good luck. It sounds like there may be a learning curve involved. I will check back to see your progress and for the consensus of the forum. It may not turn out to be all that difficult, but it sounds like it does have the potential. You just have to stay focused on the task at hand in front of you. Before you know it, everything may start to come together for you to see the reason(s) for the problems... after they begin to show their faces. There are lots of videos to be found online for learning the meter. It may probably actually be a super simple fix? It just sounds like it may possibly be a hard one tracking it down to me.
11-24-2019, 02:04 PM
#13
Banned
Our model has the regulator in the pump, which we replace thinking it will solve the problem but it did not; we also added an external pressure regulator to the line thinking that the one provided was defective, and nothing. I believe my Dad already look for a return line and there isn't one!!!
Did the fuel pump priming issue staying on running like you say.. Did this start after you guys replaced the pump? Or, was this also happening before you replaced the fuel pump?
11-24-2019, 02:12 PM
#14
CF Veteran
Join Date: Mar 2016
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Year: 96
Model: Cherokee (XJ)
Engine: 4.0
I have '96 as well. I believe there is a check valve in the fuel pump assembly that can cause issues
you may also have a problem with the ASD or fuel pump relay or associated wiring, substitute them
I agree they should prime for 2 secs, then go quiet till the engine is running, at which point you can hear it whine with your ear next to the fuel tank
slightly possible you a downstream fuel pressure issue, like a bad injector
you may also have a problem with the ASD or fuel pump relay or associated wiring, substitute them
I agree they should prime for 2 secs, then go quiet till the engine is running, at which point you can hear it whine with your ear next to the fuel tank
slightly possible you a downstream fuel pressure issue, like a bad injector
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Jswfla (01-13-2020)
11-24-2019, 11:53 PM
#15
Old fart with a wrench
Switch the ASD and fuel pump relays around and see if it still primes for a long time. I'm thinking it may be a sticking pump relay that will drop out when you turn the key off but stay tripped while it's still on.
The ASD relay controls the ignition and injector circuits while the fuel pump relay only controls the pump. They are both energized when the PCM gets a CPS signal showing the crankshaft is actually turning, as in cranking.
The ASD relay controls the ignition and injector circuits while the fuel pump relay only controls the pump. They are both energized when the PCM gets a CPS signal showing the crankshaft is actually turning, as in cranking.
Last edited by dave1123; 11-24-2019 at 11:56 PM.
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Jswfla (01-13-2020)