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Unread 07-08-2011, 07:48 PM   #1
hartnagle
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I dOnT gEt It! EnGiNe IsSuE!!! please helppp

okok.. new here folks as u can probably tell.... anyways...

i have a 96 Jeep grand cherokee straight 6 4.0 2wd.

it runs like crap... and im stumped!
it is running like its got low fuel pressure or a plugged injector.. heres what i have done so far, bare with me...

1. EGR is good
2. fuel pump is good (31 constant psi, 50psi for the 2 second prime)
3. changed the fuel filter
4. cleaned and switched up fuel injectors to dif cylinders to rule out an issue
5. switched fuel injector plugs to others and no change
6. changed plugs and wires, cap and rotor are good
7.

ok so heres the deal.. the trucks getting good fuel pressure......

cylinders 1 and 3 dont change any running condition of the engine when the injector is either unplugged or the plug wire is unplugged, but when i unplug cylinder 2, 4, 5, and 6, it falls on its face and runs even worse.. so no change in the running condition when i unplug cyl 1 and 3. but what boggles my mind is theres no water in the oil so pressure is there and head gasket is good, the plugs are not fouled they are firing and have the proper carbon build up so the cylinders (1, 3) are getting gas but theres no change in the way the engine runs..

also, theres no check engine light on until i pull one of the plugs from one of the good cylinders...

please please pleaseee help! think its something within the head? i sure hope not......

thanx ppl

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Unread 07-08-2011, 08:25 PM   #2
SAR-Swimmer
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A compression test might tell you something, a wild guess, but if you pull the plug/fuel injector on cylinders 1&3 and get no change in engine operation, you may have bad rings or valves on those cylinders.
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Unread 07-08-2011, 08:30 PM   #3
zander21510
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Well if I read this right...of couse if you unplug 4 of 6 cylinders its going to run like crap...I'm guessing you mean you unplugged them all one at a time...not sure what you're trying to do there but unplugging one of the cylinders is just asking for it to run like crap. And what exactly is your definition of running like crap? I also hope 'proper carbon buildup' means little or no carbon build up...if its idling rough your problem may lie in the throttle body, check for carbon build up there, clean it real good to where there is no carbon build up.

Try and list out your symptoms more in detail, since you eliminated just about every possibility in the fuel delivery and ignition system it must lie somewhere else. We can only help you if we know your symptoms in detail.
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Unread 07-08-2011, 08:40 PM   #4
TewSmooth18
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Quote:
Originally Posted by zander21510 View Post
Well if I read this right...of couse if you unplug 4 of 6 cylinders its going to run like crap...I'm guessing you mean you unplugged them all one at a time...not sure what you're trying to do there but unplugging one of the cylinders is just asking for it to run like crap. And what exactly is your definition of running like crap? I also hope 'proper carbon buildup' means little or no carbon build up...if its idling rough your problem may lie in the throttle body, check for carbon build up there, clean it real good to where there is no carbon build up.

Try and list out your symptoms more in detail, since you eliminated just about every possibility in the fuel delivery and ignition system it must lie somewhere else. We can only help you if we know your symptoms in detail.
I'm thinking he means he is unplugging the injectors 1 at a time to see if the jeep runs poorly when unplugging 1 at a time. so in other words, when he unplugged cylinder 1 fuel injector while it was running, there was no change at all, but when he unplugged cylinder 6 fuel injector, it started running more poorly then it already is, due to the injector being disconnected. so it sounds like there is an issue with cylinder 1 and 3 due to when unplugging each injector 1 at a time there is no change in the running
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Unread 07-08-2011, 08:44 PM   #5
zander21510
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ohhhh...I was confused. Sorry OP.
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Unread 07-09-2011, 12:00 AM   #6
ratmonkey
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31psi is low. A 96 should have 49psi constant.
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Unread 07-09-2011, 03:01 AM   #7
Boodyrider
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Originally Posted by ratmonkey View Post
31psi is low. A 96 should have 49psi constant.
With or without engine vac?

50 psi static less engine vac should be more like 40 psi at idle though, not 31. 20 inches or so engine vac at idle = about 10 psi. With engine vac to regulator plugged, 49 psi.
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Unread 07-09-2011, 05:28 AM   #8
ratmonkey
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Pressure reg is in tank and independent of vac.
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Unread 07-09-2011, 10:50 AM   #9
hartnagle
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Quote:
Originally Posted by SAR-Swimmer View Post
A compression test might tell you something, a wild guess, but if you pull the plug/fuel injector on cylinders 1&3 and get no change in engine operation, you may have bad rings or valves on those cylinders.
ill have to get a compression tester..

theres no "extra" oil though. the oil doesnt smell like gas, it doest back fire.. it just stumbles... like its running on 4 cylinders. the plugs are still firing too. ill have to take the valve cover off too and see if everythings moving as it should.
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Unread 07-09-2011, 10:52 AM   #10
hartnagle
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Quote:
Originally Posted by zander21510 View Post
Well if I read this right...of couse if you unplug 4 of 6 cylinders its going to run like crap...I'm guessing you mean you unplugged them all one at a time...not sure what you're trying to do there but unplugging one of the cylinders is just asking for it to run like crap. And what exactly is your definition of running like crap? I also hope 'proper carbon buildup' means little or no carbon build up...if its idling rough your problem may lie in the throttle body, check for carbon build up there, clean it real good to where there is no carbon build up.

Try and list out your symptoms more in detail, since you eliminated just about every possibility in the fuel delivery and ignition system it must lie somewhere else. We can only help you if we know your symptoms in detail.
if i unplug cylinder 1 and 3 theres no change in the running of the engine. it stumbles and runs like crap as it is.. when 1 and 3 are unplugged theres no change in the way the engine runs. when i unplug any other of the cylinders, it runs worse... ill get more detail for ya soon.
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Unread 07-09-2011, 11:36 AM   #11
ZombieJeep93
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If the pcm has been unplugged or batt disconnected, it looses the learned adaptive numerator. This is the value it stores as its basis for determining a misfire. If it isnt learned or learns it with a misfire, it will not detect any misfires. It probably learned 1 and 3 missing as normal condition. Here's a way to force the pcm to learn the value:
1) Place the transmission in low gear 2) Let the vehicle start rolling, open throttle until engine RPM is over 4000 RPM. 3) Lift foot off the throttle let engine/vehicle decel hard 4) repeat this process 5 times in a row without ever hitting the brake.
This should be done after the repair since you already know which cyl's are missing. Assuming you are not the original owner, it probably didnt get "revved" alot. There's a TSB about valve's not being able to rotate and getting carbon build up causing misfire. Basicaly your going to run chamber cleaner (or seafoam) through the engine per instructions on the can. Then drive hard the get the valves to rotate. Here's the procedure:

1. Operate the vehicle until the vehicle reaches operating temperature.
2. Remove the air tube from the throttle body
3. With the engine at an idle, spray the entire contents of Mopar Combustion Cleaner, p/n 04318001, directly into the throttle body. Allow the vehicle to load up with the cleaner to the point of almost stalling out.
4. Shut the engine OFF after the entire can is ingested.
5. With the hood closed and the vehicle parked inside the garage, allow the vehicle to soak for two to three hours. This will ensure that the engine will maintain its temperature and will allow proper solvent penetration.
6. **Drive the vehicle to fully warm up the engine.
7. If the vehicle is equipped with an automatic transmission, place the gear selector into L, if the vehicle is equipped with a manual transmission, place the transmission into first gear.
8. On a suitable road that will allow the vehicle to be driven safely at the posted speed limit, accelerate the vehicle until the engine reaches 4500 rpm.
9. Hold the engine speed at this rpm for 15 seconds.
10. Slow down and pull to the side of the road, then allow the engine to idle for five seconds.
11. Repeat Steps 7 through 10 two more times.

And your fuel press is low indicating a weak pump which needs to be replaced before it leaves you stranded.

Sorry for the lengthy post, hope it helps.
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Unread 07-10-2011, 01:26 PM   #12
hartnagle
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you guys are awesome!!! thanks sooo much for the advice.. ill try the seafoam treatment and let it sit longer.. can says to let it sit for like 10 minutes and rev the crap outta it.. ill put the whole can through it this time instead of breaking it up half in the gas tank and half in the throttle body.. ill keep everyone posted. im not sure if my pressure tester is any good at all. its a cheap one from harbor freight, so i may look for another one at advance auto or something..... thanx everyone
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