Popping / misfiring

HOTSIX

Ran outta hand cleaner
I'm glad that the new motor is finally in running condition and soon (Tues) it's off to the body shop. I have been ironing out some minor details....IAC set, TPS set, up-pipe sealed, idles great, new coil / module installed with good gnd, new cam sensor set, new crank sensor set, etc.

Problem is I rev it in park from an idle and I get a slight popping or misfiring when I do so. This happens after it's warmed up for awhile. Did the MAF tap test (passed) and checked fuel pressure - all good. New wires, new plugs. I read a thread after doing a search on this and someone suggested to check the motor to body GND from the head to firewall....

Don't know what else to check...no SES light on either.....
 
Just put a new engine in mine. Low mileage on it. It seems to miss fairly regularly at hot idle (very subtle and not very much). It's sort of like non-constant pulse, best heard from around the tail pipes. I'm just assuming it's a miss.

I get the same thing when powerbreaking for any length of time, it's sort of like the studder feature that the trasher chips have, but my car doesn't "studder", just sort of randomly misses. This is at low-rpm, not building any boost or anything.

I've got a big cam in mine... 214/214 (maybe too big), so I dunno, that may be the reason. The car drives fine and pulls pretty hard (only 13 psi of boost so far, still need to tune it).

So I dunno... Does your car have any trouble driving? Or I guess you haven't driven it yet. I have no idea how serious it may be compared to mine (I'm not at all worried about mine). So there ya go, just thinking out loud here.

Dave
 
Geez...thx Dave.

I am a bit relieved here. I too only get a lil bit...seems identical to your misfiring. So just to claify, nothing at boost right ? I have everything stripped off it 'cause she's going in to body shop Tuesday so I haven't driven her as yet.

Maybe it's my cam doin' it..... I got 92 Octane in her.... or maybe the plugs...the 44's

I'm gonna maybe try the 42's (or whatever) that everyone else uses and is recomended on Gnttype.org in spring cleanup (I think...) What say...? What plugs u have in urs ?
 
No prob hotsix. Keep in mind a "miss" and a "misfire" are two different things (I think). Mine's a miss, not a misfire. Like you say, a misfire is more of a pop. I'm not getting that. Mine seems more like it's just not firing on some cylinder once and at a random point in time.

I'm using 94 octane and I think I have delco 44 plugs (whatever ones it says to get for our cars in the canadian tire book). real cheap plugs. I gapped em at 0.04 (canadian tire book said 0.045 for our cars and 0.035 for 86/87s).

No I don't notice my "miss" problem when driving at all, not even under boost.

The only time I've heard a misfire from my car was when I had a huge vacuum leak (bolt fell out of the turbo) and it was idling like complete sh!t (500 rpm or so). Definitely heard some poping.

Does your car misfire if you hold the rpms a little higher?

Hope you get to drive it soon!

Dave
 
I'm just gonna take a shot in the dark here:

Is it possible your rockers are setup too tight? If so, the valves could be floating slightly when the oil pressure & revs come up(?)
 
Try 43's gapped at .035 or .032. My car dosn't like 44's it eats them literally.



Dave85
 
I'll try the 43's....see what that does. Just to be clear here - sorry I meant miss not misfire. It only seems to do this when I get the revs up slightly. Like when my VAC/BOOST guage goes up from 15 Hg (idle) to like 5 to 0 Hg when I rev it. Just before it starts to make some boost. It's parked in my driveway when this is done don't forget...so it's hard to tell if it will continue at boost.

BFH - I'm hoping it's not my rockers....are they even adjustable tho ? I have only ever heard that they are not - but I don't have a clue tho. How do I tell / check this ? Would it get worse at higher revs ?

It seems to be quite small tho and I am hoping it is just my cam / plugs combo....
Any opinions on that ?
 
As far as the misfiring I have a very little bit at idle. and as far as plugs I'll swear by the NGK UR5
just my .02
 
Rockers aren't adjustable.....could the IAC be out of wack? Does it stumble off idle. What fuel pressure are you running, if you are over 40 - then your probably fouling plugs.
 
No stumble...revs fine since I adjusted the IAC. Used to do the 'ol 'hunting' idle thing...up and down up and down...but that's settled.

My FP is 35-38 PSI at idle with vac line off. Today I ran it for a bit...closed loop...then I reved it a bit - nothing. Thought it went away...till I put her in "D" and stayed in the same spot with foot on the brake only. It poped a 'lil...not too much tho...and only every so often. It is not super noticeable but its there.

Sumpthin's up
 
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