The engine has had problems with hunting for a while. Everytime I do something it seems better then goes back to its old ways. Cleaned the AIV and it ran smoothly for a while. Replaced a vacuum hose and it ran smoothly for a while. The engine, under no load, idles spot on (750 with a/c off)for a couple seconds, then slowly increases the range of hunting until rpm drop to zero. I am thinking perhaps it's the oxygen sensor (it's been on there since I bought the car three years ago and looks like crap. Was going to replace it, but I haven't had a chance yet to break through all the rust and I'm afraid maybe the socket is fubar anyways.) I also ran a compression check a while ago, between the time I cleaned the AIV and replaced the hose, none more recently. I had low (120) compression on the #4 Cyl., others were very good. It has since been getting rougher at idle aside from the hunting, and at low speeds is jerky; almost like the clutch is slipping, but I don't think it is as it's fairly new. Then this morning I noticed black exhaust for the first time. Is there possibly a bad piston ring, or maybe a cracked piston? I think I also need a valve job. Or perhaps a long block
Modified by 420sxse at 7:36 AM 10/8/2005
ka24de hunting and smokingobems with hunting for a while.
Black exhaust smoke tends to mean rich fuel condition. This coupled with low compression on #4 and a slow dieing of the engine suggests to me you possibly have a # 4 injector leaking fuel into the cyl. There is a couple things you can do to test here. Dont just start throwing parts at it. First redo your compression test. Do it this way exactly. Warm the car to operating temp. once it reaches operating temp, while its running, pull the fuel pump fuse and let the car run till it dies, crank the car over a few more times to be sure all the fuel is drained from the fuel lines. pull your fuel cap off [ to prevet pressure from building in the tank pushing fuel in the rail while testing] Remove all 4 plugs, install your compression tester , start with number 4 and work forward. get in the car hold the throttel to the floor and crank it over for 5 secs [count it off]. Do that on all 4 cyls. See what kind of readings you get now. The reason you are redoing this in that fashion is if your fuel injector was leaking it would wash the cyl walls down giving you false compression readings.
The next test you can do is a fuel leak down test. This is done with all the compression conditions reset to allow the car to run. Tee in a fuel pressure gauge inbetween the fuel filter and the injector rail. once installed and tightly sealed turn the key to the on position [dont start the car] the gauge should pop up to around 40 psi and hold. If after the pump shuts off [about 5 secs] the gauge starts to fall off rapidly or more then 10 psi in 10secs you have a leak down somewhere in the system. you now need to repeat the process but pinch off the fuel line between the fuel filter and your pressure gauge as soon as it reaches pressure. if it continues to leak down you have now eliminated the fuel pump check valve and your problem lies in the rail or the pressure regulator. If it didnt leak down you have a fuel pump check valve problem but that would not cause the problem you have. Just a leak down test diagnostic. If leak down still occured you now need to do the test again , this time pinch off the return line. If it still leaks down you need to redo the test and pinch both the lines . If at this point it still leaks down you have a leaking injector. If when you pinched the return line and it didnt leak down your pressure regulator is leaking, again that would not be the cause of your problem just leak down diag info. If you determine during this test you have leak down on the injectors I suspect #4 is your problem and that could be the cause of your run problems.
Now about your O2. Only after those 2 tests if you dont find anything wrong. then conduct this simple test to see if the O2 is causing a problem. simply disconnect it and see if the problem still exists. If it goes away and the car runs stable just slightly rich your O2 is likely phase shifted reading lean and is cauing the ECM to flood the enigine out to stall.
Unless your driving a 75 chevy I doubt you need a valve job. Nissans are not all that common for needing valve jobs.
The next test you can do is a fuel leak down test. This is done with all the compression conditions reset to allow the car to run. Tee in a fuel pressure gauge inbetween the fuel filter and the injector rail. once installed and tightly sealed turn the key to the on position [dont start the car] the gauge should pop up to around 40 psi and hold. If after the pump shuts off [about 5 secs] the gauge starts to fall off rapidly or more then 10 psi in 10secs you have a leak down somewhere in the system. you now need to repeat the process but pinch off the fuel line between the fuel filter and your pressure gauge as soon as it reaches pressure. if it continues to leak down you have now eliminated the fuel pump check valve and your problem lies in the rail or the pressure regulator. If it didnt leak down you have a fuel pump check valve problem but that would not cause the problem you have. Just a leak down test diagnostic. If leak down still occured you now need to do the test again , this time pinch off the return line. If it still leaks down you need to redo the test and pinch both the lines . If at this point it still leaks down you have a leaking injector. If when you pinched the return line and it didnt leak down your pressure regulator is leaking, again that would not be the cause of your problem just leak down diag info. If you determine during this test you have leak down on the injectors I suspect #4 is your problem and that could be the cause of your run problems.
Now about your O2. Only after those 2 tests if you dont find anything wrong. then conduct this simple test to see if the O2 is causing a problem. simply disconnect it and see if the problem still exists. If it goes away and the car runs stable just slightly rich your O2 is likely phase shifted reading lean and is cauing the ECM to flood the enigine out to stall.
Unless your driving a 75 chevy I doubt you need a valve job. Nissans are not all that common for needing valve jobs.
Thanks for the thorough reply! The injector possibility had never occured to me. Perhaps I was using the term "valve job" incorrectly. My mechanic (before I started having these problems) thought it sounded like the shims might need checked. The engine's very noisy up top. (I don't believe he used the term "valve job". that was me).
A funny thing happened when I pulled the fuel pump fuse (I am absolutely positive it was the right one...I quadruple checked) while the engine was idling at operating temperature...the engine immediately stopped hunting and stayed at 750 with a tiny waver every now and again. When I plugged the fuse back in it idled like that for a couple minutes then began hunting again. I also let it run fo 15 minutes+ and it didn't die. I don't recall it taking nearly that long the last time I did this. Also, about your fuel injector test: If I let it run to get to operating temp won't the Cyl. wall already be washed with gas if the injector is leaking? Could I send you a couple mp3s to listen to (about 500KB total or less)? My engine is really starting to sound like crap. My e-mail is [email protected].
Modified by 420sxse at 10:22 AM 10/10/2005
Modified by 420sxse at 10:22 AM 10/10/2005
OK, so I finally got around to actually following your instructions, made sure every last waft of fumes was out of the lines...and whaddaya know, I got 176 psi on #4 (I was incorrect, I found my notes from the previous...It was 130ish before) #'s were 1=183, 2=185, 3=180, 4=176 not bad for 190k miles, but as it has been running rich (after looking at the plugs I'm pretty sure the 02 sensor was contributing to the overall richness of the system) I wonder if those #'s are above spec because there is buildup in the cyls? Am I thinking right here? So, then I did a leakdown and after pinching off both lines It is still leaking! I've never been so happy to probably need a $130 part (always Bosch). I also got the 02 sensor changed finally, after a day of spraying Penetrating Blaster every half hour, tapping with a wrench and working off the rust with a toothbrush...I used like 1/3 of a can. Thanks again for the help, your suggestions were much appreciated.
So you gotta throw in a #4 injector. I would think the other plugs would have been whiteish in color since the O2 would have been trying to lean it out. But if they were black then it probably was reading on the lean side or the coolant temp connection is a bit corroded causeing the ecm to think it is colder then it really is causing it to richen up. Higher compression readings generally indicate carbon build up on the cyl head and piston top surface. This will cause a car to fail for nox due to high pressure.