misfire at high rpms?
12-02-2008, 05:46 AM
#1
TECH Apprentice
Thread Starter
iTrader: (1)
Join Date: Oct 2005
Location: VA
Posts: 339
Likes: 0
Received 0 Likes
on
0 Posts
misfire at high rpms? I've been experiencing misifre on my Z above 4k when I'm under WOT. It backfires loudly and acts like its hittng the rev limiter. The previous owner has a receipt for new plugs but it's running "rich" at idle and drives at normal conditions just fine. Idles a little low and may stumble slightly on takeoff from time to time. Drove it 4.5 hours back home when I bought it 2 months ago with no problems. I'm thinking it needs new O2 sensors, but wanted some imput before I drop a hundred bucks on it. Already have new plugs for it too as I'm sure they're near the fouling point. Any info is greatly apprecaited.
12-02-2008, 08:25 AM
#3
TECH Fanatic
iTrader: (12)
Join Date: Aug 2007
Location: Cornfields near Pontiac, IL
Posts: 1,818
Likes: 0
Received 1 Like
on
1 Post
yeah, i have the same problem, it almost acts like a rev limiter is being hit, but its in 2nd or 3rd gear and the trans isnt being manually shifted. i figured maybe the timing may be off or something.
12-02-2008, 12:09 PM
#4
Man Ive been having the same problem since I got the car in March but it would come and go! Sometimes I could unplug and plug back in the Pigtail to the coil and it go away for awhile...
Hell since yesterday my car hasnt started, think it finally took a crap on me... Ill keep you updated after I replace my coil and let you know if it fixes it...
Hell since yesterday my car hasnt started, think it finally took a crap on me... Ill keep you updated after I replace my coil and let you know if it fixes it...
12-02-2008, 05:44 PM
#7
On The Tree
Join Date: Nov 2008
Location: South Carolina
Posts: 117
Likes: 0
Received 0 Likes
on
0 Posts
i had a possibly similar problem over the weekend. my car would sputter above 3k and would backfire alot, but would be just fine in between 2-3K. i ended up having a broken fuel pressure regulator vacuum line. it goes from the pass. side of the manifold to the regulator on the back of the intake. the plastic it was made of was brittle. probably from the age of it. i hope this helps, because all i needed to fix it was some small diameter vacuum hose, quite cheap.
Trending Topics
12-02-2008, 07:22 PM
#9
TECH Resident
Join Date: Oct 2008
Location: Redondo Beach, CA
Posts: 968
Likes: 0
Received 0 Likes
on
0 Posts
i had a possibly similar problem over the weekend. my car would sputter above 3k and would backfire alot, but would be just fine in between 2-3K. i ended up having a broken fuel pressure regulator vacuum line. it goes from the pass. side of the manifold to the regulator on the back of the intake. the plastic it was made of was brittle. probably from the age of it. i hope this helps, because all i needed to fix it was some small diameter vacuum hose, quite cheap.
12-02-2008, 08:04 PM
#10
On The Tree
Join Date: Nov 2008
Location: South Carolina
Posts: 117
Likes: 0
Received 0 Likes
on
0 Posts
the miss was so bad it seemed like the cam was off by a tooth, but the chain is new and has just beyond cam break in on it so i just ruled that out. i have worked on cars with vacuum related idle problems, i didnt know what the line went to until i realized it went to the Fuel Pressure regulator, it then made sense, it explained my extremely rich idle, stalling, and wrong fuel amounts at higher rpms. i was just looking under the hood, and found a broken vacuum line. after i made sure of where it went with a shop manual diagram, i fixed it, and it worked.
Heres a vid before i fixed the vacuum line.
Heres a vid before i fixed the vacuum line.
12-02-2008, 08:48 PM
#11
On The Tree
iTrader: (2)
Join Date: Jan 2008
Location: DFW, TX
Posts: 158
Likes: 0
Received 0 Likes
on
0 Posts
does your z have a dump on it? if so, when i take mine off and stretch it out there is so little backpressure in my exhaust, it just back fires like crazy and likes to lunge also.
12-05-2008, 07:18 AM
#13
well if the coil is new. how about your wires? if they are pretty new then lets look at your plugs..what kind and are they gapped right? You could pull them out and gap them .005 smaller. if both of these are knocked off the list then i would check fuel pressure and then unfortunately lean towards the opti.
12-06-2008, 06:19 AM
#16
"high rpm miss" can be almost anything. Cap and rotor should be checked if their age is unknown. You said the plugs were new but what plugs are they?? Wires can rub through fast if improperly routed. As said vacuum line troubles are another possibility, as are fuel delivery troubles, might be worth putting a fresh fuel filter on. One car I help work on turned out to have a cotter pin for a coil tower, ran fine for the first few years they had the car and only once the pin got rusty did it act up only at high rpms. Wacky stuff happens with used cars.
On modified cars worn out valvesprings often cause troubles described as "high rpm miss".
On modified cars worn out valvesprings often cause troubles described as "high rpm miss".
12-06-2008, 06:48 AM
#17
TECH Apprentice
Thread Starter
iTrader: (1)
Join Date: Oct 2005
Location: VA
Posts: 339
Likes: 0
Received 0 Likes
on
0 Posts
"high rpm miss" can be almost anything. Cap and rotor should be checked if their age is unknown. You said the plugs were new but what plugs are they?? Wires can rub through fast if improperly routed. As said vacuum line troubles are another possibility, as are fuel delivery troubles, might be worth putting a fresh fuel filter on. One car I help work on turned out to have a cotter pin for a coil tower, ran fine for the first few years they had the car and only once the pin got rusty did it act up only at high rpms. Wacky stuff happens with used cars.
On modified cars worn out valvesprings often cause troubles described as "high rpm miss".
On modified cars worn out valvesprings often cause troubles described as "high rpm miss".
I'm changing out the plugs today(NGK TR55) and inspecting all vacuum lines. I'm getting a fuel filter today as well. I want to replace all the uncostly items first and hope it fixes it...lol I pray that it isn't the opti. So, can I rule out O2 sensors?
12-06-2008, 07:16 AM
#18
O2 info is ignored in open loop which includes WOT, BUT depending what they were reporting before WOT the computer can still use the info they were providing to adjust fueling. It is possible but to check that I would use a scanner and see what the BLMs are, if they show it adding a lot of fuel it will keep adding even more at WOT, would have to be severe for it to show up like this but possible.
Do you have a laptop? Datamaster($90) and a $50 ALDL cable are the best money you can spend if you want to drive and modify these things. Takes a lot of guesswork out of maintenance and repairs even without CELs being set.
Do you have a laptop? Datamaster($90) and a $50 ALDL cable are the best money you can spend if you want to drive and modify these things. Takes a lot of guesswork out of maintenance and repairs even without CELs being set.
12-06-2008, 07:46 AM
#19
TECH Apprentice
Thread Starter
iTrader: (1)
Join Date: Oct 2005
Location: VA
Posts: 339
Likes: 0
Received 0 Likes
on
0 Posts
O2 info is ignored in open loop which includes WOT, BUT depending what they were reporting before WOT the computer can still use the info they were providing to adjust fueling. It is possible but to check that I would use a scanner and see what the BLMs are, if they show it adding a lot of fuel it will keep adding even more at WOT, would have to be severe for it to show up like this but possible.
Do you have a laptop? Datamaster($90) and a $50 ALDL cable are the best money you can spend if you want to drive and modify these things. Takes a lot of guesswork out of maintenance and repairs even without CELs being set.
Do you have a laptop? Datamaster($90) and a $50 ALDL cable are the best money you can spend if you want to drive and modify these things. Takes a lot of guesswork out of maintenance and repairs even without CELs being set.
12-06-2008, 09:39 AM
#20
My car had been acting up last few day doing the same high rpm studdering... Then wouldnt start again this morning.. I think it was my ICM pigtail... I unplugged it and tried to bend the prongs in the pigtail and re-installed it and it started right up!
AND
the sputtering is gone.... FOR NOW.. Ill keep you all updated..
AND
the sputtering is gone.... FOR NOW.. Ill keep you all updated..