Hey guys,

The short version is:
misfire under vacuum, cant free rev in neutral past ~2000 rpms without it start to miss (havent even tried boost as the motor has less than 50 miles on it)
New motor from Forged, so its not compression/leaking etc....
Haltech with roughed in tune
2 sets of plugs swapped, no change
good idle

*with no codes, how does one tell if the crank or cam sensors are causing misfire?

*Can a bad cam sensor car misfire, or is that 100% crank sensor? Chris had a bad CKP but his his car would die, mine doesnt https://my350z.com/forum/forced-indu...some-help.html Would the car always die with a bad/failing crank position sensor?

*Does anyone know off the top of their head if the coils have a separate grounding point (how many) or does it ground thru the ECU?

*On my Haltech log watching the Ign1 Angle it seems to go crazy jumping to 100- 600*. Not sure if thats pertinent or not as the misfire counter isnt seeing a miss, but you can feel it and see the AFR drop


*Other things to check??? Other details needed?

More details/ Longer version-- reposted from the Haltech thread with RCDash's explanation:

"It Misfires mostly just high vacuum while the car sits and you raise rpms above 2500 or so. Also when driving, the AFR will transiently dip to 11, 10 etc but I don't think it happens as frequently while driving or as badly but it still occurs. The fuel tables I think are ok. I sat in the car watching afr for various cells and it would be spot on one second then 2 pts too rich the next. Str8dum1 has base maps from my car I think and he's due to be tuned by Sharif soon. Trying to make the car driveable enough to get down there 6 hrs and put some miles on the engine. My theory was his C2 cams in conjunction with very short downpipe dumps (no exhaust!) is causing some issues at high vacuum but that doesn't seem that likely under light load to still cause trouble. I have no experience with cars with no exhausts like that.

He's breaking in the engine so rev limiter is set to 5000 and overboost fuel cut is set at 1 psi. This is all happening under vacuum with rpms above 2k. Just suddenly the car will get diarrhea and fart out a bunch of gas. (sorry str8dum, but that's what it sounds like!)"

--What do the afr's do when you slooowly sweep through the rpms at no load?

"They hover around 14.7 until the car starts misfiring. Then they dip transienty to 10-12. Then might be ok for 15 secs, then dip again, etc. It doesn't happen at idle. Only above 2k rpms as I recall. Fuel pressure I think was constant. I know he has a gauge in there but I didn't actually look at it. All gauges read ok (oil p, fuel p, temps etc).

By the way closed loop feedback is OFF. It was causing all sorts of headaches with the misfiring going on. To top it off I think the wideband is reading outside air (the distance from wideband to open air is likely no more than a foot!). I told str8dum1 he might not be able to turn closed loop feedback on until he gets some longer pipes on there.

I wonder if the stock ECU, which is controlling timing (copy through set for low loads) is screwed up with the AFRs reading lean because of the short dump to open air? Maybe str8dum1 should eliminate all the copy through cells? Doesn't hurt to try - might start idle hunting, but no biggie.

Now that I recall I was watching the stock ECU timing and it was reading 30-40 degrees advanced at high vacuum when the misfiring was occuring. Not sure if that's the cause... I have copy through for high vacuum on my car but I have an exhaust!"

 

What are indications that you are misfiring (how to tell?)

 

AFR dips as the car emits unburnt gasoline.

 

bump for any other experience with misfires on a new build..

 

Weak coil? Which cylinder(s) is misfiring?

 

How about tossing stock injectors back and run factory ecu. Sometimes it's easier to troubleshoot if u start from a known good state. Give it a try?

 

I am getting the generic P0300 random miss code as well as P0132 and P0152 high primary O2 sensor voltage

but if i try to hold say 2000 rpms the AFR will be stable and then it will stumble so bad that the BOV will pop and the AFR drop 2-3 points rich.

I know the injectors are not the problem as I swapped those already.
Its not a vacuum leak as I sit at -19-20inches HG at idle.

I could try the stock injectors and stock ECU. I'd like to try someone elses crank position sensor as well.

 

I believe the O2 codes may be thrown with excess fueling and are secondary to the misfiring (so not helpful).

 

the best way

 

ya i need to swap in a known good crank sensor before I try stock injectors/ecu.

 

I lost a O2 sensor and the other had a weak signal and it ran almost exactly as you described without throwing codes. Once I poped in new O2 sensors the car came back to life without any problems at all. For what it's worth, I had a cam sensor go bad a few years back and it was kind-of the same but from what I read above I'm betting O2 sensors are bad. Just my .02.

 

both set of my O2 sensors are in my downpipes after the turbos now. I think thats pretty standard for turbo kits.

How would failing O2 sensors cause misfire, unless they are telling my Haltech copy thru cam timing to go way outta whack?

 

Vacuum leak is a pain to troubleshoot. This happen to me and my vacuum HG was also stable at idle but my A/F will lean out randmomly and will generate a misfire. It really depend where your Map sensor is located but in my case my catch can was the source of the leak and that is after the Map sensor so the map didnt pick up the the minor change in vaccum. Random Mis-fire is a pain to troubleshoot.

 

my haltech logs dont indicate the AFR leaning out before a miss though.. Its not so much random as I can reproduce it at will and the cause must be something global to all the coils/injectors.

I am running a drilled out PCV to a breather and a breather on the other drivers side valve cover. But thats no different than most anyone else.

I can try running a hose from the passenger PCV back to the manifold as well...

The only leak that could possibly affect the MAP sensor would be a leak after the Cosworth plenum.

The misfire at high vacuum is what is puzzling because misfires happen under load, not under no load

 

good advice. sometimes you need to start with the most basic setup and then add one thing at a time until you figure where the problem lies.

 

If you need a crank sensor, I have an extra one. Its new.
Just a few ideas about the misfire...
Did you calibrate the tps? is the injector dead time set up correctly?
Where is your map source?
When i was having crank sensor issues, the tach was jumping around and the vdc and slip lights were on. It was due to a bad encoder on the jwt flywheel though.
What plugs/gap are you running? I believe all the coils are grounded to the same place, have constant power, and a ground pulse from the ecu to fire them.
Have you messed with ignition dwell time? Ignition decay rate?
I would run a compression test just to make sure, but it shouldn't be an issue.
keep us updated

ross

 

so it runs fine until 2k rpms...........? .....make sure your aux rev limiter is disabled.

 

+1 on the rev limiter
also as far as grounds.... some say the grounding kits don't help but when I was having crank issues, it helped TONS, and basically eliminated the problem until i changed the trigger wheel. So if there is a bad ground somewhere, that could eliminate it.
oh and the crazy ignition numbers during copy through are supposedly not an issue. that freaked me out the first time I saw it on my haltech...

 

its not the aux rev limiter (it's not enabled). the main rev limiter is set to 5000 for break in. str8dum1 is examining all the grounding points per the FSM - that's a possibility esp given the wire tuck. It's weird that it doesn't affect idle though.

 

Thanks! going to try the stock ECU/injectors this weekend/monday.

The noise I thought was my BOV popping is not. I unplugged my BOV and I still get this sneeze sound when the car misses. Compressor surge?