Okay, just buttoned up my 97 ss with a 9 inch rear swap, th400 swap, walbro 255 fuel pump, new optispark along with a cc306 cam swap. Did first start up and took me a while playing with the throttle but i got it to idle and it sounded amazing. Problem is the first time i got it to idle and took a video is backfired at first once out the intake and the rest out of the exhaust but once it would idle it was as smooth as pie. I started it yeaterday and now it wants to backfire more and die sometimes. Still have to play with throttle to idle.i left stock injectors in till i get a tune. I called my tuner and he says that a yune wont do anything about the backfires. Im really out of ideas. PLEASE HELP.

 

Are you absolutely sure the valve lash is adjusted properly?

Are you sure that no plug wires are on the wrong cylinder(easy to get them crossed up if you are not careful)?

It would be hard to index a 95-97 opti wrong on the cam, but I think I've seen that a couple of times too.

 

You can get the opti wrong lol. My first shot I missed the dowel hole and made it into one of the reliefs. I foolishly assumed it needed to press fit a little bit and used the bolts to get it pushed tight and since it went tight thought all was good. I remembered it didnt push tight after I had starting troubles.


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I am absolutely positive that the opti is indexed correctly. And i have been told about the valve lash but what gets me is that if anything they could have to be too tight because they arent clattering but if a couple valves were adjusted a lityle to tight wouldnt that make it run bad and never idle properly? I mean i got this thing to run perfect for at least 7-8 min before i shut it off and its gotten worse since. The motor didnt shake or anything for those 7-8 min and it was smooth as could be. Now the motor is shaking a little like its an intermittent misfire and it will backfire out the exhaust a few times and out the intake like once.

 

On the valve lash question only...an over tightened rocker will cause it to run poorly, enough of the too tight and it won't run at all. Too tight causes valves to stay open. No compression. Kinda like trying to start it with the heads off. Okay, not THAT bad lol. Just trying to paint a picture Example: an intake valve not properly seating will cause exhaust pressure to be forced out the intake, creating the intake backfire.

 

And i totally understand that but my question is can you adjust the valves to tight and then the car idle without backfiring for ten minutes? And why has it gotten worse the second day as opposed to the first? I dont have a problem taking the valve covers off and redoing them but it just seems pretty intermittent for a valve to be too tight

 

I'd check your valves first since that was all just messed with. A lot of guys will mistake the lash feeling because some of the lifters didn't have oil in them when installed, so they got adjusted too tight. In that case the lifters may not have been pumped up when you first started the car so the idle was OK. When you started the car, the lifters pumped up and now the valves are hanging open. I'm not sure if you replaced them or not or what all you did when you did the cam.

Once you are sure your valves are good and if you are still having problems, maybe pull your plugs out and take a close look at them. There might be a clue if you have a dead cylinder. Also make sure you don't have a cracked plug or burned or half-connected wire although that will usually just cause it to idle rough and lose power.

If it turns out that it is heat related, then look at the ICM and coil, although if they were good before, they are still probably OK. Other things - opti cable corrosion or rotor screws coming loose (not usually this soon). Double check all electrical connections to the engine. Maybe scan it if you can and make sure all sensors are reporting in with numbers that make sense.

Good luck fixing it & Let us know what you find.

 

Im going to dig into the car in the morning. First thing im goin to do before i mess with these PITA canton valve covers is check all my plug wires and make sure one of them isnt a little loose on the opti cuz it seems like #2 was a pain and i never heard a good "click" also, when i was reconnecting the harness one of the wires on the TPS pigtail broke really close to the connector so i tried to put another wire to connect the two ends and maybe that is screwing with me so i bought a new pigtail that i will hook up tomorrow as well. If none of that works i will pull the covers and loosen up the valves and readjust them. Will update after tomorrow. Any more input is appreciated.

 

UPDATE!!!
Pulled valve covers, readjusted valves, changed plugs, changed tips pigtail started car and same problem, then dug into plug wires and found that #8 & #4 were crossed. Fixed that started car and was better but still backfiring so I started looking over everything and realized that I forgot to plug in the MAF. Plugged it in and car started and idled. Ran car for ten min. Definitely running rich and it seems like right when you first hit the gas it is just a touch slow but once you get into rpm's it is smooth and feels good.

 

I assume once I send my ecu to ion at mad tuner and have it tuned and then put my new injectors in hopefully the richness and throttle response off idle will be better. Any input?

 

Also this is my first cam swap and don't really know what to expect but at idle it definitely seems like it shakes a bit. Is that normal? I know stock it was smooth as could be. I guess the overlap of the cc306 cam will cause that?

 

Definitely give Ion all your info and get the tune, then give it another try. Without the tune, everything the PCM has to go by is your previous setup, and it will definitely cause it to be a little off. I just got done fine tuning some things on mine, and now it idles great. But if you start trying to make adjustments without a tune, it will be very frustrating, as you may not be able to attain anything because the PCM will fight you, as in fighting to bring itself back to what it BELIEVES to be correct after ANY tweaking you may try. Sounds like you are very close now, the tune may be all it needs. Needs it no matter what, so it's a good direction to go at this point, IMHO.

 

CC306 for sure will need a tune. My CC503 idled with absolutely no issues on a stock tune(already had tuned PCM, but tried stock for the heck of it), but the CC306 is more aggressive in the lift and duration than the CC503.

What injectors are you running?

 

Im going with SVO 42lb injectors so i will have plenty in the future for anything i do besides boost plus i got a good deal on them. Obviously now i still have the stockers in it because the stock ecu definitley wouldnt like the 42's. Is a cam that size gonna shake the car? Like at idle or should it be as smooth as before?

 

If you have any way to datalog would be helpful for your tuner. Changing the pump alone can raise fuel pressure a fair bit if it was weak before. My pump and hotwire kit has me at 49-50 psi. I would also get the pressure for your tuner(every bit helps). My injectors were a little off from rated flow and that made a big difference getting that accurate. What im getting at is the pcm can compensate for changes but it has its limits and the closer to right on in the areas that matters the easier it adjusts and the more precise it is and quicker to respond. I have spent alot of time driving while logging the last several months and the further off the tune is the more eradic car behaves. As I get closer to dialed in the smoother it gets. My cam is a little bigger that the cc503 . I wouldnt expect it to be as smooth as stock and honestly your logs can tell you more than anything if it isnt smooth. I bet alot of people dont have their car dialed in and dont notice or when they do the pcm has lost power and its learned corrections. I dont know alot yet but improvements get me excited. I have gained over 4 mpg while getting closer as well and nothing has reaaly been changed except in the fueling(from my baseline tune for all my mods). If it were up to me my next moves would be with datalogging. The only other things I would do is look for any vaccum leaks, exhaust leaks near or before o2sensors(consider replacement depending on age)


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