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Misfire/jolt at 3k rpm only


Baconsarnie

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Hi guys new to the forum so still learning, lol.

 

Got a bit of a weird problem here. I fitted Japspeed decats about a week ago and everything was completely fine. (not sure if these are linked to the problem, thought I'd mention it).

 

Part throttle driving, 1/4 throttle, 1/2 throttle pulling up the rev range there is no misfire.

 

Full throttle, foot to the floor there is no misfire.

 

But

 

At about 3/4 throttle when pulling from around 2k rpm, as soon as it hits 3k rpm, I get a sudden splurt, jolt, misfire, but as soon as I pass 3k it's fine. It's mostly noticeable in 3rd.

 

It's on 40k miles and due for a plug change, but surely if it was plugs it would happen all across the rev range.

 

Also I have lambda sensor sims fitted to the decats which already have a spacer welded on them. I had a quick look under the car and the sensor wires are pretty low, and look like the may have rubbed on bumps but haven't jacked it up to have a proper look.

 

Could this be a lambda sensor fault from possible wire scraping or does it sound like something else?

 

Or are there issues with the stock map when fitting decats and not having a remap?

 

The rest of the rev range it feels ok, maybe a bit down on power but that could be me being paranoid.

 

Cheers guys :thumbs:

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I spoke to somebody the other day about this with japspeed decats. The decats have bungs already installed and dont require the spacers as the also hit the ground.

 

Dont have any info on the jolt but, what fuel are you using?

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95 regular. But Just filled right up with shell vpower incase it was a a fuel issue. Do these HAVE to be run on super? I thought uk models could accommodate 95 Ron?

It - HAS - to be run on Super (98RON in handbook/filler cap, but 97 is ok). You will be running the high det map and probably getting knock from 5k to redline, if not below when the knock sensor does not work. The knock sensor only works up to 5k RPM on the 350z.

 

Hopefully you havent done any serious damage.

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95 regular. But Just filled right up with shell vpower incase it was a a fuel issue. Do these HAVE to be run on super? I thought uk models could accommodate 95 Ron?

It - HAS - to be run on Super (98RON in handbook/filler cap, but 97 is ok). You will be running the high det map and probably getting knock from 5k to redline, if not below when the knock sensor does not work. The knock sensor only works up to 5k RPM on the 350z.

 

Hopefully you havent done any serious damage.

+1 especially with decats, breathing enhancements cause the car to run lean etc and can cause det/knock problems.

 

A car should be remapped when being fitted with decats etc as the car will eventually revert the map back once it see's the afr's have altered. This results in absolutely no power gains until remapped with uprev.

 

Running 95ron has shown severe engine failure as mark @ abbey found. The cars have no knock control after a certain amount of revs.

 

Check abbey motorsports sub forum or search for this.

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If it is a hard misfire/cut out I would say it will be electrical, so maybe spark pplugs/coils or even crank trigger/ cam trigger problem or even a Air flow meter problem.

 

I doubt that fitting De-cats will cause this problem thou.

 

Where are you based? are you local to us @ Abbey?

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Any way of testing the afm?

 

Where abouts are you based mate? As I'm interested in getting a remap, just want to get the inlet spacer before aswel.

 

 

click on abbey's sig pic and it will take you to there website where you can find the address

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Ahh, that's not far at all!! I'll have to give you a call mid week to get booked in with you mate! (don't drive the car much, usually once or twice a week).

 

Are there any checks I can do at home with a multimeter? Or are they all live tests rpm related so require a diag laptop and driving?

 

Cheers for the help mate!

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strange fault this one. weird how its only at 3Krpm. reminds me of my Evo, fitted new spark plugs, gap was too big, as soon as you come on boost, the boost blew the spark out causing a miss. but obviously theres no boost to blow out the spark on these :lol:

 

could it not be spark plugs/coils breaking down as the engine gets loaded up? especially if its only a splutter? surely if it was the MAF, it would be jerking around all over the place and not just a miss at 3k as it can control the airflow?

 

get under it and check your lambda sensor wires if it looks like theyve been rubbing. and remove your sims from the decats. i fitted the sims from zmanalex to my japspeed decats, then lowered the car, had a random look under the car to see how low the exhaust was and noticed the 02 sensors were really low. going to remove them on my days off, so im using the derv at the mo.

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strange fault this one. weird how its only at 3Krpm. reminds me of my Evo, fitted new spark plugs, gap was too big, as soon as you come on boost, the boost blew the spark out causing a miss. but obviously theres no boost to blow out the spark on these

 

I doubt this will be a spark plug issues but I haven't seen or heard the problem myself, these cars just misfire on a cylinder all the time when the plugs are worn out or if the car has the wrong plugs fitted , we had a car in last week fitted with wrong plugs that caused a full cylinder misfire but this also caused a CEL for a misfire

 

could it not be spark plugs/coils breaking down as the engine gets loaded up? especially if its only a splutter? surely if it was the MAF, it would be jerking around all over the place and not just a miss at 3k as it can control the airflow?

 

We have seen cars with a stumble being caused by AFM , you can see this on the dyno the car was going ultra lean just before the stumble was felt

 

get under it and check your lambda sensor wires if it looks like theyve been rubbing. and remove your sims from the decats. i fitted the sims from zmanalex to my japspeed decats, then lowered the car, had a random look under the car to see how low the exhaust was and noticed the 02 sensors were really low. going to remove them on my days off, so im using the derv at the mo.

 

The post cat lambda's don't control fuelling at all they only measure the exhuast gas to tell the ECU if the cats are doing there job , that's why the cars throw CELS when removing the cats, its the pre cat lambda's that control the closed loop fuelling, you can disconnect the post cat lambda's and the car will run the same but just with a constant CEL up

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really appreciate all the help guys. Theres no CEL up nor does it flash as it splutters at 3k.

 

how much is a AFM sensor? im wondering if its worth just chucking one on? is it just the sensor peice thats bolted into the intake pipe, or is it the casing aswel?

 

cheers :thumbs:

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