I just put a new motor in my car, rebuilt stock bottom end with a 306 cam. I had a valve job done on the heads with the crane 10308 spring package installed. It started up on the first crank, but its missing on the #7 cylinder. Adjusted the rockers with the motor running, b/c at first that is what me and a friend figured it was. That didnt help. So i pulled all the plugs, and the #7 is really black and sooty, but not oily. So I am guessing its not burning off all the fuel. So I put a new plug in it(NGK TR6) and it still did it. So I swapped the injector with the #1 and still did it. BTW, I know its the #7 b/c if I unplug the injector, it smooths out and quite missing. I checked for spark, and well it shocked the crap out of me, so I know its getting spark. It has a brand new GM opti on it. I am completely stumped as to why its missing. Anyone have any ideas? Maybe compression? I used the .029 impala head gaskets and torqued the heads down in 3 stages in the correct order. Someone please help, I dont want to drive the car with it like this. Thanks

Edit: Its a 96 and is not throwing a bank 1 sensor 1 02 sensor code. The car is tuned by MADZ28 for the cam. The header tube is getting hot so it is blowing some kind of exhaust gas out of it.

 

hows the plug wire look on #7

 

Wire is good, i checked for arcing in the dark, there was none. I am really thinking it may be on the whole drivers side, I just messed with it some more and it was still there with the #7 injector unplugged. It threw a code for a bad 02 sensor on that side, so maybe that could be it? The 02 was good before the motor swap though?

 

You said - "I know its the #7 b/c if I unplug the injector, it smooths out and quite missing."
When you unplug the injector on 7, the motor should stay the same roughness, not get better. Are you sure that you have the correct injector connector on the #7. Are 5 and 7 reversed? Try reversing. Same idea with the plug wire at the opti.

 

Put an old plug on the end of the #7 wire, ground the metal body of the plug and watch the spark. Shocking the crap out of you is not a definitive test. Compare it to another wire, if you need to. Also make sure all your plug wires are routed correctly.

 

I have checked and double checked the wires/injector harness. I am starting to think maybe I am a tooth off on my timing. I am using a cloyes double roller and have heard its fairly easy to do. The waterpump has a leak coming out of the end of the bolt, top on passenger sie. When I pulled the motor apart before the rebuild, that bolt broke off. I had it drilled out and helicoiled, think that could be why its leaking? Since its leaking, and I will be pulling it off, I might as well go a few steps farther check timing while I have it that far apart.

 

Also, every now and then, the car will backfire out the exhaust out the drivers side header. Sometimes it is hard to start, other times it is easy. Sometimes it idles great, sometimes it has problems staying alive. Tonight, I pushed on the connector that goes to the opti to make sure it was all the way connected, and it just died. I tired to re-start it but didnt have any luck. Had to crank it about 5 or 6 times and then it finally started up but still ran like crap.

 

I'd be looking really closely at that Opti connector. If you can wiggle it and get the car to stall again, (turn problem on/off repeatably) you have found a problem. It has an inline test connector at the LH middle of the intake, so you can unplug and test the harness by itself. Check continuity while wiggling, and look really closely at all the pins. Be careful not to damage the pins with your meter! The only connector problem I have personally found so far was actually caused by me sticking my meter probes in the female pins, spreading them, while testing.

Maybe borrow one from another car for a test?

 

How do the other plugs on the driver's side look?

EXACTLY which code did you get for the driver's side O2 sensor?

Sounds like it may be running excessively rich on the drivers side. Reading all 4 plugs would tell you if it is.

Pull the codes again and see if you are getting any for the low and/or high res Opti pulses.

 

I put a different 02 in it, and the code went away. It was a low res I believe. All the plugs were sorta black, but the #7 was excessively black. I am going to look more into that opti connector to. You dont think it could be timing do you?

Edit: It is not throwing any codes now.

 

5&7 plug wires crossed?


Easy to do, will have the backfire you speak of, firing with the ex valve open.



David

 

no we double checked the plug wires...

the code was bank1 sensor 1 low/no signal i believe, it was an o2 code not opti...

 

WOOOOOOOHOOOOOOOOO its fixed! After a long day/night of thinking about it, I finally decided to check the plug wires 1 more time. And sure enough, I labeled them wrong when I pulled the old motor out, and had the #5 and the #7 crossed. Swapped em, started it up, and now it runs like a champ! Thanks for all the help and info guys!

 

Awesome now go have fun.




David