My valve covers needed to be replaced. I could smell the oil residue running down and burning on the headers. I bought the valve cover gaskets and picked up some autolite double platinum spark plugs. I replaced the gaskets and the plugs. Then I started the car,it was running really rough. It sounded like 2 cylinders just weren't firing. I took it to Advance Auto Parts and they scanned it to pull codes. All he gave me was P0300, but I saw another code that popped up. I didn't catch much of it. I asked the sales guy what it was and he told me it was most likely caused because of the P0300. Well, P0300 is multiple misfires. While driving I noticed my, "service engine soon," light was blinking. I went back home and proceeded to pull out my spark plugs. Plugs 1,3,5 were in good shape. Spark plug 2 is fine, 4, 6 had fuel on them, but the electrode was clean/unfired. I assumed it was the plugs. They had been sitting since March waiting on me to install them, so I pulled them all and replaced them with ngk laser platinum. I rechecked them and the gaps were a little off. I reset them at .043, reinstalled them and and proceeded to start the car. It won't start, it'll turn over and you can hear it try to fire, but it just won't start. This may be a problem on it's own, but my battery is dead. I charged it and I'm only getting 13.9v. So I'm not sure if the battery issue is related or not, but I'm including it. I pulled the plugs again to look at them and it seemed they were all the same. I checked to make sure I was getting spark on every plug and the coil packs are firing. No damage seems to have occured to the coil packs. I had a friend of mine tell me it sounds like my car has a vacuum leak. I replaced the intake manifold gasket in the plenum and in between the upper and lower intake manifold. I'm thinking a vacuum leak so big that the car can't start, has to be noticable. Does anyone have any suggestions that I can try? BTW, I'm broke for the most part.

Parts I checked and replaced was the coolant bypass hose, spark plugs twice, upper intake manifold to lower gasket, and intake plenum gasket. All appropriate electrical plugs where reconnected and checked several times. The only think I noticed odd was the vacuum hose on the passenger side, that looks like a goofy looking question mark, hissed when I disconnected it from the intake manifold.

 

the goofy looking hose is the brake booster vacuum hose. if u think u have a vacuum leak buy the kit from z1 motorsports. itll replace all the intake related vacuum hose at a much lesser cost than oem.

u sure u installed the plugs for the spark plugs in the right order? its hard to do it wrong but ive read of people doing that here. also the spark plugs are pregapped. not sure how u couldve gapped them better than the manufacturer.

 

Make sure that all the coil pack plugs are in the right order, when I changed my plugs and started it, it ran really rough because I had 2 of them in the wrong order because they will fit on either pack. Check that for that problem on the other problem I'm not sure without seeing or hearing the car.

 

I've checked the plug firing order and have verified all the electrical plugs on the coil packs correctly. I'll try to get a video of it. I'll look into z1 motorsports. Like I said I'm broke.

 

Here's and update. I finally got it started. A friend of mine, that owns a shop, stopped by and looked it over. He tapped on the throttle body and disconnected and reconnected the plug. It fired right up, but still not firing on 4 and 6. He checked out everything I did. I pulled a spark plug from 4 and told him, "this is what 6 looks like too." Under the advisement of the electrician, at my job, I replaced the COP boots on 4 and 6. It didn't do any good. At this point, I'm at a loss. It has thus gone to the shop. I will keep this thread updated as news is handed to me.

 

Probably time to scrape some change together and go to a mechanic for help, sadly. Sometimes you have to know when you are in over your head.

 

did you check the condition of the wires themselves? if any of them are cracked i would replace them. Also you can try using oem spark plugs. i had misfires when i tried to use aftermarket plugs, they seem to work once i switched back to oem.

 

in for updates...

 

Subscribed to try and help if possible... The only thing I can think of is the harnesses are plugged in incorrectly. This would cause a misfire, but they should ALL still be firing. Make sure all of your harnesses don't have exposed wires and are all connected.

Good luck!

 

Update from the mechanic wasn't so good. Actually it's pretty bad when he says to me, "I have no clue what the hell is wrong with your car." My car has multiple misfires and the tps is trying to adjust fuel BC he believes there is an air leak. His computer is saying the misfires are all over the cylinders. Lost I am. I didn't see any loose or exposed wires.

 

Now for an update. The mechanic has been threw the car. He has replaced the TPS, believing that was the cause of the problem. He reset the ECU so it could relearn the new throttle body. No change at all. Guys, I'm lost. He really doesn't know what else to try. I've suggested that look at the wires, but that's about it. Again, it's still misfiring across all cylinders. Please I need help. It's been a month w/o my car.

 

Crank sensor?

 

Since you had just replaced valve covers, I'm inclined to believe something didn't get reconnected, or the connectors to the coils on 4 and 6 are flipped. It's easy to get them plugged into the wrong coil on that side. (search replacing spark plugs, a lot of people have made that mistake) This thread has good pictures of the coil harness wires. https://g35driver.com/forums/engine-...ug-change.html

Also, the coils are pretty sensitive, so if they were "shocked" somehow (ie dropped, bumped together, etc) then they could be damaged.


From the FSM:

You really need to go over all of your work and verify everything is connected in the correct spot and FULLY inserted.

 

Don't think so. Wasn't a listed code. As a matter of fact I was just handed the list of codes. These were recorded after the TPS was replaced and the ECM was reset. 0300, 1121tp out of range, 1122,1123 and 0123. I am trying to verify that the ECM is being reset according to how Infinti does it (by VIN and build date.) If it isn't, the car will be going to infiniti. If it is, my mechanic will be attempting to monitor the voltage on the TPS and the camshaft position sensors. Depending on whether it's one or the other, hell or all three at this point, they will be replaced and could be the cause of my problems.


This is been a damn nightmare.

 

It is not on 2 cylinders, the misfire is, "jumping" around on all cylinders. I have checked the plugs and an ASE certified mechanic has undone all my work and reassembled it. I understand that forgetting to plug something up is very easy to do. I check my work thoroughly, then an actual mechanic does the same thing. I'm inclined to say it's not just a plug unplugged, but I'm really hoping it's not an electrical issue.