Excessive cylinder misfires.

 

Could these be ignition misfires as controlled by the ecm or usually coilpack/wires/plugs related?

 

Its a misfire. What can cause misfires? Lots of things. Bad plugs, bad ground, bad fuel, bad injectors, crappy tune, shitty fuel, lose ground, low voltage, mid-term elections, you name it.

Get Hptuners and start logging misfires by cylinder and begin troubleshooting.

 

Do you keep the HPTuners tool in the OBD-2 port and allow it to log while running? So my understanding with HP tuners is that you can use it as an interface to modify your tune? I would be hesitant to change my tune personally fearing I would mess it up being a novice.

Am I correct in this? New to HPTuner.

 

A larger cam is also known to trigger erroneous random misfires which can be compensated for in the tune (which a good tuner knows how to do).

 

Were specific codes logged? What code were logged?

 

No codes, just a momentary flashing that went away.

 

the fact that your car is modded with a different engine and cam complicates things.

the light could be blinking because of a legitimate misfire condition. as steelchicken said, there is a lot of things that can cause a misfire. weak/no spark, poor fueling, mechanical failure, etc.

could be because you swapped in a different engine and never did the crankshaft angle variation relearn.

could be because of the cam and the tune hasn't had the misfire tables edited to desensitize them in the correct rpm range, or the values entered are still too low.

the ECM calculates the presence of a misfire using the crankshaft position sensor. it can accurately sense when the crankshaft accelerates due to a power stroke. if the speed of the crankshaft is "off" based on the values it has, it will think a misfire has occurred.

 

This is the first time I have seen this so I don't believe it the tune. I agree with you there is a possibility of a "perceived misfire" by the ECM. I will see if it returns in another run. It may be a component starting to go bad. How long will the light flash after a perceived misfire goes away?

 

well, hptuners is an excellent tool if you don't own it yet.

you can use VCM scanner to log just about every engine parameter you can think of.

and then log all of the misfire PID's for each cylinder. Misfire counts for cylinder 1-8, and misfire history for cylinders 1-8.

then log away. if it happens again, you'll see what the conditions are when it does.

 

FYI, a high misfire rate will cause the CEL to start flashing. If the ECM thinks the misfire conditions for catalytic converter overheating are present, the CEL will flash. I.E. it flashes during, not after.

You will generally have an accompanying code, such as P0300 which is general misfire condition, or P0301-P0308, which are misfire conditions for specific cylinders.

 

Man it sure seemed to be running correctly during and after the hard pulls.

 

hypothetically, if it only happens during WOT, i lean more towards a fueling or spark issue, heavily towards fueling.

do you have a wideband? if so, how was your AFR during the pull?

 

I'm not sure which O2 sensor I have. It is the one that was in it when I bought the car. Is there a way to tell by looking at it?

How would I record the afr during the pull? With an HPTuner? I have a decent code reader that will show the readings too but I don't think it has a record feature.

 

I'm assuming that you have double valve springs. Pull your valve covers and look for the broken spring.

 

Thanks for the advice. I'm going to do another test run to see if it repeats and then if it does I will inspect that. I've not taken the valve covers off yet. They are Patriot Performance Stage 3 heads which have double springs.

 

i'm starting to think you're in over your head.

maybe stop driving it and have a professional look at it.

 

Yeah ur off track with that. Just haven't used HPTuner before.

 

Sarcasm aside, just do some basic checks before you take it on another drive. Please?

Checking for broken valve springs, or any other valvetrain issue evident when you pull the valve covers, checking compression, checking your spark plugs.

Fuel pressure and fuel trims. These can be checked at idle with a fuel pressure guage and with your current scantool, without driving, and definitely without flooring the engine. You might even try using an old school vacuum guage on it and see what you find out at this point.

You might feel it excessive, but i've had/seen engines run "perfectly fine" with mechanical damage.

The CEL flashed for a reason that needs to be addressed. Never have i seen it not.

After you rule some serious stuff out, maybe move on to data logging.

Anyway, i'm out. Good luck i guess.

 

Sarcasm aside, just do some basic checks before you take it on another drive. Please?

Checking for broken valve springs, or any other valvetrain issue evident when you pull the valve covers, checking compression, checking your spark plugs.

Fuel pressure and fuel trims. These can be checked at idle with a fuel pressure guage and with your current scantool, without driving, and definitely without flooring the engine.

You might feel it excessive, but i've had/seen engines run "perfectly fine" with mechanical damage.

The CEL flashed for a reason that needs to be addressed. Never have i seen it not.

After you rule some serious stuff out, maybe move on to data logging.

Anyway, i'm out. Good luck i guess.

Ok thanks. I'll take your advice and let you know . You are right to be cautious.

 

Sorry if i came off harsh. I just don't want anyone's engine blowing up, lol.

 

No Man its cool

 

I've had dual PRC springs break before. The reason you are not asking for engine recommendations is because the valve is still being controlled below a certain RPM by the spring that is not broken.

I got lucky and only had some nicks on the piston and a bent valve.

Please take the 15-20 minutes to pull the valve covers and visually inspect. All springs are good? You are out and hour of your time. Then we will teach you how to soften the misfire tables.

I would also take this time to read up on how the LS computer calculates misfires, what physically causes them. It's kinda cool and will make sense why adding a performance cam will require those tables to be changed.

But again, please bust out your deep 10mm for the coil brackets and the 8mm for the valve covers. You won't even need to replace the gaskets. Look at both inner and outer springs. Please post pictures of each spring if it is not obvious. Just want to try and save you a boat load of money in case I'm right.

 

You got it and great advice. I've been very busy and had to prioritize tasks. I had to tear down the engine in my other toy this Sunday so I will get to it in the next couple of evenings. Honestly, I haven't had the time to even put a code reader on it yet or pop the hood to look at wires etc. I'll read codes, visually inspect, and probably pull a valve covers to check for damage, all in hopes of seeing something obvious. I'm fortunate that this is just a toy racecar and don't need it for a vehicle...no stress!

 

I think this should be a lesson in how to respond to advice here.

We're all used to knuckle heads asking for advice but then not listening.

Then this guy comes along and ends up being completely reasonable.

 

Thanks!