Rough idle, tried everything
02-16-2017, 12:41 PM
#1
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Year: 2001
Model: Cherokee
Engine: 4.0
Rough idle, tried everything
Ok so thanks in advance to anyone who takes time out of their day to read about my problems and even more thanks to anyone who tries to help lol. I've tried everything (that my father and I can think of) to solve this issue and I've gotten to the point where im desperate. I have an 01 4.0. The issue: rough idle (not like its going to stall, more like RPMs fluctuate) and I have NO power when I step on it but once past about 1500 RPMs, runs like theres nothing wrong with it. When I do try to step on it, the check engine light flashes and my rev limiter kicks in. I usually put it into neutral, turn the jeep off, turn it back on, holding the key a bit longer than normal and most of the time it goes back to no power when accelerating but rev limiter doesn't kick in (all while rolling down the road.) The check engine light is on, drawing codes of P0303 and P0304 (cylinder 3 and 4 misfire.) We've put in a new head, new intake manifold, new exhaust manifold, just put in all new lifters (did not change the cam when we changed the lifters), rods, got a valve job done professionally, all new sensors on the throttle body, new upstream o2 sensors, cleaned every wire and plug in the engine compartment, new injectors and fuel rail, new coil pack.... I think thats everything. (feel free to ask about any other thing and I'll tell you if its been cleaned or if its new.) I'm sure im forgetting a few things but please any advice on what we should try next would be greatly appreciated. Our next step (as of right now) is most likely down stream o2 sensors and then fuel pump. Thanks again in advance for any and all advise you guys have for me. I've tried to look on this forum and every other forum for issues that are even remotely close to mine, and usually changed another part of the motor as a result but nothing has worked so far.
02-16-2017, 02:35 PM
#2
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Welcome to the forum.
You sure went all out trying to solve this. Does this have coil packs? How about a compression check? What is the fuel pressure? You are familiar with the dreaded head issue on these, right?
You sure went all out trying to solve this. Does this have coil packs? How about a compression check? What is the fuel pressure? You are familiar with the dreaded head issue on these, right?
02-16-2017, 02:51 PM
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Year: 2001
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Yeah I have gone all out lol it does have coil packs and we replaced it already (twice actually). Compression test was done 4 days ago, everything looked good there. Haven't checked the fuel pressure yet but from what I've read on other threads is that people have checked the fuel pressure, gotten good readings and still had the issue till they changed the fuel pump, but I will probably test the fuel pressure anyways within the next week. When I got the head gasket job done professionally, he got a new head and had it checked for and kind of crack or imperfections so I know the head is good.
02-16-2017, 03:00 PM
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You put a scan tool on it, to check the function of the O2 sensors? The upstream one is the one that might cause that kind of thing. Also it will tell you a host of other stuff. The long term fuel trim reading should be low, almost 0 ideally, if it's more than about 2 or 3 one way or the other it means it is compensating heavily for a lean or rich, which usually points to the o2 sensor. Downstream one just makes sure the cat is doing it's job, not involved in fuel trim. Lots of infor for a $40 ebay scanner that would show you graphing of the o2. Sounds like you have a nice mill there, would like to see it run nice for ya.
02-16-2017, 03:03 PM
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I have a scanner but honestly don't know how to use it besides the basic function of reading the codes. I should read up some more on the functions of it. If you tell me what information might be helpful then I'll figure out how to read it with my scanner! I appreciate all the input
02-16-2017, 03:46 PM
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Year: 2016
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I have a neighbor who rebuilt the 4.0 in his 99 XJ. It had roughly 195k miles at time of rebuild. When he reinstalled it and fired it up, he had a number of idling issues and went through pretty much what you are going through. Turns out that while the engine was rebuilt, the drive accessories were not. The Distributor shaft bushing was shot and allowed the main shaft to wobble in the housing. At low speed the shaft wobbled causing all sorts of issues. At high speed the shaft balanced itself out and ran pretty good. He replaced both the Distributor assembly and Cam sensor and that solved his issues. I am not saying that this is your culprit but neighbor Bill threw all sorts of parts at the same problem your having and this is what worked for him.
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02-16-2017, 04:08 PM
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I have a neighbor who rebuilt the 4.0 in his 99 XJ. It had roughly 195k miles at time of rebuild. When he reinstalled it and fired it up, he had a number of idling issues and went through pretty much what you are going through. Turns out that while the engine was rebuilt, the drive accessories were not. The Distributor shaft bushing was shot and allowed the main shaft to wobble in the housing. At low speed the shaft wobbled causing all sorts of issues. At high speed the shaft balanced itself out and ran pretty good. He replaced both the Distributor assembly and Cam sensor and that solved his issues. I am not saying that this is your culprit but neighbor Bill threw all sorts of parts at the same problem your having and this is what worked for him.
02-17-2017, 07:25 AM
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Year: 1996
Model: Cherokee
Engine: 4.0
I have a neighbor who rebuilt the 4.0 in his 99 XJ. It had roughly 195k miles at time of rebuild. When he reinstalled it and fired it up, he had a number of idling issues and went through pretty much what you are going through. Turns out that while the engine was rebuilt, the drive accessories were not. The Distributor shaft bushing was shot and allowed the main shaft to wobble in the housing. At low speed the shaft wobbled causing all sorts of issues. At high speed the shaft balanced itself out and ran pretty good. He replaced both the Distributor assembly and Cam sensor and that solved his issues. I am not saying that this is your culprit but neighbor Bill threw all sorts of parts at the same problem your having and this is what worked for him.
I just went thru this as well.... took me a minute to figure it out. New dizzy and all was well again.
02-17-2017, 10:52 AM
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02-17-2017, 10:52 AM
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I have a neighbor who rebuilt the 4.0 in his 99 XJ. It had roughly 195k miles at time of rebuild. When he reinstalled it and fired it up, he had a number of idling issues and went through pretty much what you are going through. Turns out that while the engine was rebuilt, the drive accessories were not. The Distributor shaft bushing was shot and allowed the main shaft to wobble in the housing. At low speed the shaft wobbled causing all sorts of issues. At high speed the shaft balanced itself out and ran pretty good. He replaced both the Distributor assembly and Cam sensor and that solved his issues. I am not saying that this is your culprit but neighbor Bill threw all sorts of parts at the same problem your having and this is what worked for him.
02-17-2017, 10:55 AM
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You put a scan tool on it, to check the function of the O2 sensors? The upstream one is the one that might cause that kind of thing. Also it will tell you a host of other stuff. The long term fuel trim reading should be low, almost 0 ideally, if it's more than about 2 or 3 one way or the other it means it is compensating heavily for a lean or rich, which usually points to the o2 sensor. Downstream one just makes sure the cat is doing it's job, not involved in fuel trim. Lots of infor for a $40 ebay scanner that would show you graphing of the o2. Sounds like you have a nice mill there, would like to see it run nice for ya.
02-17-2017, 06:42 PM
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Year: 2016
Model: Grand Cherokee (WK2)
Engine: 5.7l HEMI
According to a few other forums the 2000-2001 doesn't have a distributor.. "2000 and 2001 have a coil on plug design" correct me if I'm wrong! (i didn't know if you'd receive a notification if i didn't reply to your comment too thats why i copied and pasted from the comment above)
You are right as there is no distributor in the sense that we normally know. These models have what amounts to be a distributor with the cap cut off. The Cam sensor is mounted to the top of the distributor shaft housing so it receives the signal from the camshaft then tells the coil packs to fire in order. My neighbors problem was the Cam sensor was sending erratic signals to the coil packs causing idle issues. This smoothed out above 2000 rpm.
02-17-2017, 07:04 PM
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You are right as there is no distributor in the sense that we normally know. These models have what amounts to be a distributor with the cap cut off. The Cam sensor is mounted to the top of the distributor shaft housing so it receives the signal from the camshaft then tells the coil packs to fire in order. My neighbors problem was the Cam sensor was sending erratic signals to the coil packs causing idle issues. This smoothed out above 2000 rpm.