Pulled almost all of my hair out. Still running rough.

[thousandlegs]

Ok, here's the deal...I have a 96 Infiniti I30 that is running rough at low rpm and idle. This began just a couple of weeks after I got the car. This is what it does: very soon after warming up it will start to run rough. this is especially noticeable at lower rpm with the car in gear. it feels kind of like it is missing or running out of gas. the codes are for misfire on cyl 4 and knock sensor. I have, since the rough idle began, done the following:

replaced spark plugs with autolite platinumreplaced fuel filterreplaced cyl 4 fuel injectorreplaced cyl 4 coilchanged oil and filled with full syntheticrunning on premium gassea foamed the intake and in the gas

What do you think could be the problem? ANY HELP would be appreciated.

[brianw]

And the codes for cylinder 4 misfire still persist after replacing the injector and coil pack?

Could be a bad ECU, but at this point I would take it to a good, trusted Nissan expert and have them look at it.

As for coilpacks, I assume you've checked the resistances on them and they all come up ok? Because if #4 really did go back, you can be assured the other 5 are also on their way out and should be replaced together as a precaution.

You checked to make sure the replacement plugs are gapped correctly? Most strongly recommend sticking with the factory NGK PFR5G-11's or 6G-11's if memory serves...

if those codes are now gone then there are some other things to check...

[coolhand]

Check compression on the no. 4 cyl. Make sure you unplug all the coil packs so the engine will not start. If the compression is around 120 -150 psi, the injector seals may have torn during installation. If psi is lower, engine problems.

[thousandlegs]

Yes, the code is still present. There was no change when I replaced the injector or the coil. The tool to check the compression...is that one that I can get as a loaner from autozone or pepboys? Also, does anyone know if there is a computer that can diagnose the problem more precisely than the one that just reads the codes?

[MinisterofDOOM]

Yeah, you should be able to find a compression tester at Autozone or Pep Boys.

A Nissan Consult MAY be able to give you more answers, depending on what is wrong.

[lightsout]

i just went through all this.my bad cylinder was #6.

take it to a dealer, and have all your sensors scanned through their scanner for open circuits. i had 6 bad sensors. primary ignition control unit(not a sensor, but computer problem)bank 1 Oxygen sensorbank 2 Oxygen sensorbank 3 Oxygen sensorcamshaft sensorcrankshaft sensoridle control sensor(on bottom of throttle body)....all were replaced and cleared.

i had all 6 coil packs that were worn out, and all spark plugs were tired too...in addition my primary ignition control unit needed to be reprogrammed.

Nissan recommends that if you have a misfire you should replace all coil packs, spark plugs, reprogram your primary ignition control unit, and clear the codes........so that was done and she drives like a dream!! I let the dealer replace the rear coil packs and spark plugs because i was not willing to take apart the upper intake manifold and remove all the electronics to get to them.

my problem was;as i replaced 2 sensors at a time, and the PCM could read the car better and showed that other sensors were a problem, so i got a 2 sensor codes at a time...and spent more time scanning it at autozone than actually working on the car, but i saved LOTS of money by doing most of it myself.

i would highly recommend taking it to a dealer and paying the $100 to have the dealer scan all your engine sensors for open circuits...then buy the parts through pepboys/autozone/napa like i did, and replace the ones that you feel comfortable doing. I'm sure U have a couple oxygen sensors that are bad...if you get a "open circuit" on those, I'd replace them first. Also, take off your intake components that are located just in front of your throttle body, take a look and see if your throttle body is grimy/oily/sutty...if so, take out your throttle body and clean it with DEEP CREEP(made by sea foam, get it at NAPA only) or another good name brand throttle body cleaner. Feel free to wipe around inside the throttle body with a shop rag and Qtips...while you've got it out check your Idle Control Sensor(at bottom of throttle body) for an oily plug. cleanse accordingly with the proper cleanser for electrical connections.

keep me posted because I WANT TO HELP!!

good luck,Lightsout

PS please post all the cods you have been receiving from your OBD2 scanner from autozone. thanks

Modified by lightsout at 3:29 AM 8/17/2007

Modified by lightsout at 3:29 AM 8/17/2007
Modified by lightsout at 3:34 AM 8/17/2007

[lightsout]

if you have a bad knock sensor....replace it...it's hard to get to b/c i believe its under the upper intake manifold.

lightsout

[lightsout]

thousandlegs,

i'm wondering what happened sitll...update me!!

thanks!!

Devin

[thousandlegs]

I am going to have to go to a shop so that they can scan/diagnose the problem. I still dont have the cash for that yet though. I'll post the problems when I find them...I'm sure I'll have to get help with one or more of the fixes when I find the problems. Thanks for the concern and interest.

[lightsout]

no problem!!

[robo_geek]

Check compression on the no. 4 cyl. Make sure you unplug all the coil packs so the engine will not start. If the compression is around 120 -150 psi, the injector seals may have torn during installation. If psi is lower, engine problems.

Sorry to sound old-school, but test for vacuum leaks too. A leaky air control valve, or just a split vacuum hose can cause rough idle. Don't forget to clean out the throttle body. I would also listen to each fuel injector with a stethescope....sometimes a bad injector resistor, or some other fault makes one injector go wonky.