JEEP Question

SpinnerBait_Nut

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1996 Cherokee 2DR 4X4.<br /><br />Love this Jeep, but need some input on a problem I am having.<br />It started the other morning.<br />It had been running fine up to this point.<br /><br />It acted at first like it was running out of gas, but never quit.<br />Just bogged down real bad.<br /><br />I took it to Advance Auto,(I'm cheap), to have them pull the codes on<br />it and it said, Random Misfire in number 6.<br /><br />So, I bought all plugs/wires/cap and rotor and put on.<br /><br />No good.<br />Next I changed fuel filter. No good.<br /><br />Next I checked fuel pressure.<br />Key on, 44Lbs.<br />Running 48LBs.<br /><br />Turned off motor with gauge still hooked up.<br /><br />Checked in 15 minutes, still at 46Lbs. so not much of a drop.<br /><br />Now this evening we were out in it doing stop and go, we run a paper<br />route, and it started missing and did quit once.<br /><br />Started back up and run like a scalded dog.<br /><br />Now I am stumped. Don't know what else to do except the pump thing.<br /><br />Could it be the #6 injector misfireing at times?<br />How do you check them?<br /><br />Is it possible to change it without dropping the tank?<br />I noticed it came out the front of the tank instead of the top.<br /><br />Sorry for all these questions, but I really need to get it fixed<br />cause I use it ever day.<br />Thanks<br />SBN
 

jimchere

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Re: JEEP Question

SBN first how many miles on the gal. Second, do a compression check to rule that out. Maybe some carbon on the valve seats etc but first rule that out. You could have some junk in the injector and no, you don't have to dump the tank to do clean/replace it. Might be a sporadically firing injector. Need to trace the wiring from home to ground to get to it and rule that out. Believe it or not the Haynes manual for this vehicle is fairly decent as far as the FI system, schematics, and PCM codes go and darn near every auto parts outlet has it.<br />Do a comp/vac test, and check the wires per a Haynes schematic for the NR6 INJ and see what you got from there. I bet its a crappy electrical connection if the symptoms you described are pure.
 

SpinnerBait_Nut

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Re: JEEP Question

Thanks Jim.<br />It has 120k on it and was running like a champ and all of a sudden started running crappy.<br /><br />I did notice that all the plugs were nice and clean when I changed them.<br /><br />Also noticed today when I changed the filter some nasty looking, almost red looking stuff came out of it.<br /><br />Maybe I have sucked something up into the #6 injector.
 

snapperbait

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Re: JEEP Question

I'd bet an injector is fouled or the connection is bad...
 

JRJ

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Re: JEEP Question

A Jeep I had a lone time ago did what your's is doing, and the gas cap wasn't venting fast enough.<br />Hope your problem is cheap to fix.
 

tylerin

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Re: JEEP Question

SpinnerBait, what motor do you have, inline? I had a similar problem on a truck and it ended up being my fuel pressure regulator. It was a diaphram that was vacuum operated and it was sucking gas through the vacuum line. I had a friend check the codes and came back w/ misfire in x cylinder. Check for vacuum leaks as well. This regulator regulated the flow to the injectors.
 

SpinnerBait_Nut

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Re: JEEP Question

Yes it is inline 4.0L.<br />The regulator is suppose to be attached to pump inside tank.<br />Other regulators are on the fuel rail.<br /><br />Also have found out a high pressure reading like I am getting, (48psi) is an indication of bad regulator also.
 

JasonJ

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Re: JEEP Question

I just replaced the ECM on my 93 Jeep Grand Cherokee with 4.0 6 banger, $1185 installed. It had all sorts of wierd symptoms, difficulty starting, just dying for no reason, running bad, then running good, and it finally died for good. It never showed any fault codes. This was after I replaced the $260 in-tank fuel pump and replace the filter.<br /><br />I had to drop the tank to replace the pump, it was a pain, but not horrible. The red stuff is a problem with the chemical composition of the plastic fuel tank. There was a number of years where the tanks would break down over time, which would clog the fuel filter, which would put too much stress on the fuel pump and cause it to fail. I thought replacing the fuel pump would fix my problems but it didn't. Now I have a new pump in the rig that I didn't need and an old pump in the box that I don't need. Oh well....
 

SpinnerBait_Nut

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Re: JEEP Question

I don't know about your pump set-up in a grand, but mine comes out the rear and not the top, so I can get mine out without taking the tank off.
 

SpinnerBait_Nut

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Re: JEEP Question

no ebb, I have done nothing to the pump/regulator yet.<br /><br />I just am thinking that maybe that is where my problem lies because of high line pressure.<br /><br />They say a bad regulator will cause that and low pressure means a restriction somewhere.
 

Skinnywater

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Re: JEEP Question

When it starts running bad do a power balance test to identify what cylinder is misfiring. Some vehicles DTC's indicate #6 as being #6 in the firing order. This would be an excellent time to identify if its a secondary ignition problem. If your power balance test reveals the secondary ignition is in order and you've identified the offending cylinder, swap that injector to another cylinder. Repeat the power balance test, if the problem followed the swap, replace the injector. With that being SFI (Sequential fuel injection) diagnosis is easy.<br /><br />A simple pair of insulated spark plug wire pliers ($6-8)and a noid light ($6-8) goes a long way against an scope.<br /><br />Also, the fuel pressure regulator may have a vacuum line to it. Check it's integrity, as it may be responsible for the slightly high reading.<br />However, slightly high won't give your driveabilty symptoms.<br />A normal to high pressure reading doesn't warrant replacement of the pump either.<br /><br />BTW, brake problem on the truck a couple months ago? A/C problem last week? <br />Howabout some feedback.
 

NOSLEEP

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Re: JEEP Question

what is fuel pressure suppose to be at?<br />high pressur in tank fuel pumps run at 70 psi.
 

SpinnerBait_Nut

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Re: JEEP Question

Update, went out this am and run it in the stop and go and it ran like a champ for about an hour or so and then the gremlins showed up again.<br /><br />Skinnywater said;<br />
When it starts running bad do a power balance test to identify what cylinder is misfiring.
It won't do it at idle, Skinnywater, just under a load and not all the time.<br /> <br />
BTW, brake problem on the truck a couple months ago? A/C problem last week? <br />Howabout some feedback.
Sold truck with brake problem, an going to wait till spring and have a regular A/C guy work on it. :) <br /><br />NOSLEEP said;<br />
what is fuel pressure suppose to be at?<br />high pressure in tank fuel pumps run at 70psi
NOSLEEP, my Haynes says it is suppose to be 31psi with hose off regulator and 39 with it hooked up, so I don't know if 48psi is considered high or not.<br /><br />It just has me confused cause at first start and go, you could not ask for one to run better.<br />Even under extreme load, no falter for about an hour and then it will sputter and miss and then straighten up for a while and then right back at it again.<br /><br />Really intermittent kinda deal.
 

tylerin

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Re: JEEP Question

SBN, I was just thinking, I pulled a fuel pump out of the tank on a few differant occasions and if I remember correctly it has a filter screen attached to it. Might be ok at first but as you begin to drive maybe it starts sucking more crud. I'm probably just reaching for straws here
 

SpinnerBait_Nut

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Re: JEEP Question

Yea ty, a strainer or soc as I call them.<br />In the old days when you would have a problem with the strainer on one, you could take compressed air and blow back through the gas line and blow it off and then install an inline filter and have at it, but them times are gone. :D
 

KennyKenCan

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Re: JEEP Question

Hey SBN,<br /><br />Make sure to check the Mass Airflow Sensor (MAS).<br /><br />A freind of mine had a similar problem, and the sensor ended-up being the problem.<br /><br />The only way to determine if it is the MAS, is you have to hooked it up to one of those diagnostic computers!<br /><br />Otherwise, IMHO, you will be wasting time and money on parts that are not the problem.<br /><br />Take it to a quality repair shop that can do a computer diagnosis for ya, let them tell ya whats wrong, and then ya can purchase the part and repair it yourself.
 

KennyKenCan

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Re: JEEP Question

Hey SBN,<br /><br />Make sure to check the Mass Airflow Sensor (MAS).<br /><br />A freind of mine had a similar problem, and the sensor ended-up being the problem.<br /><br />The only way to determine if it is the MAS, is you have to hooked it up to one of those diagnostic computers!<br /><br />Otherwise, IMHO, you will be wasting time and money on parts that are not the problem.<br /><br />Take it to a quality repair shop that can do a computer diagnosis for ya, let them tell ya whats wrong, and then ya can purchase the part and repair it yourself.
 
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