i just recently installed a LT4 hotcam and 1.6RR's on my car, and now the computer is throwing a "RANDOM CYLINDER MISFIRE" code

any idea to what this code could be?
I know the timing chain is right and i seriously doubt the opti is bad, because i took extra special care when i removed the water pump and also did not change the plug wires or plugs...

i thought about this being due to the computer pulling out timing because i have the regular knock module in the PCM and i am about to order the LT4 knock sensor. Would this cause the engine to "missfire" or throw the code?

if you guys can give me ANY idea as to what this could be, i would GREATLY appreciate it...

Im about to put the car on the scanner(auto tap) and find out what cylinders are misfireing and taking timing out..

but please help me with any information you guys may have

Thanks,
Greg-

 

roller rockers could cause the false knock you're getting, that's why factory LT4 engines got composite valve covers and the knock module. composite valve covers contain some of the noise.

 

Get the LT4 knock module, and your PCM programmed. Your computer's just picking up on the new roughness and thinking it's a misfire

 

sweet, im going to do that in the morning, i figured that its picking up the fase knock

if anybody else has any other ideas as to what this could be, let me know..

thanx
greg-

 

Same thing happend to me, I did what spinner said. Damn thing runs flawless!

 

when you threw the code, did the car run like it was actually misfireing?

i get it at idle, cause down the road when im driving, it runs decent..just at stop lights is sux bad

greg-

 

also, another thing ive noticed, is that when crusing, it wont go into lock up, could this be due to the computer detecting a "misfire"?

i never once did anything with the transmission
i think the computer is preventing it from locking up the converter because the "random missfire" code is on

could this be a reason?

 

Forget knock sensors and modules.

The problem is related to OBDII and your crank sensor. What's happening is that the relatively rough (compared to stock) low rpm running of your engine is being sensed by the PCM through the crank sensor.

Since the PCM "thinks" the engine is misfiring (due to the cam) it won't allow the torque converter to lockup. This is all explained under the P0300 code in the factory (Helms) shop manual.

I've tried extensively to modify spark tables to eliminate this condition to no avail. Your only options are to wire up a converter lockup switch (which works fine) or to have the "random misfire" feature disabled in the PCM (LT1 Edit v2.2 does this beautifully).

I had to endure the manually modified lockup switch for about a year until the guys at Carputing (LT1 Edit) came out with the version that eliminated it by PCM.

 

try kicking the idle up to ~850 - 900 rpm and raise your closed throttle spark advance (28 - 30 deg) and see if that helps any with the misfire code.

-Tony

 

Greg,

Be sure to keep this thread updated on your problem. I have a 96Z I plan on adding the hotcam and 1.6 RR's soon. I would like to know if you get your issues worked out. Also, how you got them worked out as well.

From the research I've done, programming is really needed. PCMforless seems to be the ticket. They have the hotcam program nailed from what I've read. I already have the LT4 KM. If you don't have one I'd recommend it. Good luck and please keep us OBDII boys updated!!!

 

hey man no problem, tomorrow im going to call the guy at PCM forless and talk to him and ask him the questions, ill keep in contact with you as to what needs to be done via PM or email..

ill send you a OM and give me your email adress, id gladly let you know what needs to be done once i find out for sure

as for the others, ill keep you guys yupdated on the situation...
thanx again for all your help guys

 

my email is: erorrer@adelphia.net

Thx Greg!

 

I had the same problem. Programming is a right way to go if you don't feel real engine miss.

 

where in houston you at greg? and what color is ur car?

 

I installed the kit around 2000 I think, installed the KM at the same time and never had a misfire code (even when I had stock programming).

30k miles on the kit without having to crack a valve cover, I'm pretty happy with it.