Misfire after high flow cat install.

[vxsr33]

I just swapped my cat (unknown highflow cat) to a venom 100cell highflow, 3 inch inlet and outlet,5 inch body.

 

I also changed my bov to a turbosmart plumb back.

 

Prior to this the car would never misfire under load. But now its misfiring at around 5k rpm. The coilpacks and spark plugs are in good condition, i recently cleaned all the coilpacks thoroughly and put dielectric grease around all the connections.

 

What could be causing the misfire? Could the new cat have affected the tune?

[KiwiRS4T]

More likely to be the BOV. What kind did you have before? Or could be totally unrelated cause.

[vxsr33]

More likely to be the BOV. What kind did you have before? Or could be totally unrelated cause.

Had the stock bov but it was blocked off.

I bought the turbosmart as i thought the stock bov wasnt working properly, was sick of the flutter and was hoping for better response . Turns out the stock bov was probably fine the previous owner had stuffed a bottle cap in one of the hoses.

I was thinking the extra flow of the new cat could cause the motor to run leaner. Which could cause misfiring?

The old cat looked pretty restrictive. Looked like it was 400cell

[admS15]

Possibly due to less restriction you are making more boost and power at that rpm and it's just enough to cause misfire. What plug gap are you running?

[vxsr33]

Possibly due to less restriction you are making more boost and power at that rpm and it's just enough to cause misfire. What plug gap are you running?

Im running NGK coppers pre-gapped to 0.8mm. Plugs are only around 5000km or less old

[admS15]

How old are the coilpacks? Try some new plugs. If it still does it, try gapping to 0.7

[vxsr33]

Coilpacks are probably around 15 months old and are splitfires. I dont think they are faulty though.

Im ruling out the bov as i drove with the new bov installed but not the cat, and did a few hard accelerations but no misfire. It only started after the new cat.

[admS15]

Fit new plugs

[KiwiRS4T]

Do you have a boost gauge? What kind of car/engine have you got? As suggested above "excessive" boost can cause misfiring.

[vxsr33]

Fit new plugs

Ok i will get new plugs, only around $20 anyways.

[vxsr33]

I have a boost guage, the car runs around 16psi of boost although i did not check the guage when i was getting the misfire so maybe boost levels have increased.

The car is an r33 gtst with rb25det and is running a power fc

[KiwiRS4T]

1 hour ago, vxsr33 said:

I have a boost guage, the car runs around 16psi of boost although i did not check the guage when i was getting the misfire so maybe boost levels have increased.

The car is an r33 gtst with rb25det and is running a power fc

OK so boost should not be a problem (so long as you haven't still got the original turbo). Have you had a tune in recent times? May help with performance and pick up any problems.

[vxsr33]

OK so boost should not be a problem (so long as you haven't still got the original turbo). Have you had a tune in recent times? May help with performance and pick up any problems.

Im running an op6 hypergear highflow and xpurt 1000cc injectors.
The car was tuned about a month ago at chasers motorworks and has been running perfect ever since, until the cat install.

Right now im thinking after i give the car a service(oil, filter, plugs) ill take it back to chasers for a touch up tune and hopefully they can fix it.

[Dose Pipe Sutututu]

Take it to someone else.. there are some interesting tunes from said workshop. 

In have a Nistune file for a R33 they did, interesting at the very least. Jono would have seen the same tune as well.

 

For now pull back your boost before you lean out a lunch a motor 

[Kinkstaah]

Or just put the cat back in, see if the issues really do follow the cat converter... Or in reality and exhaust restriction/moar boost as others are saying

[vxsr33]

Yeah i might just take it for a retune somewhere else. Chasers seemed good but i would rather Chequered tune it, they seem to be the best and they also deal with hypergear turbos all the time. Im making sure to drive the car like a grandpa and not hit much boost.

To be honest i really cant be bothered putting the old cat back in. Also when i shake it bits of catalyst fall out (not huge pieces but little crumbles) so im guessing its not in the best nick.

I was thinking of getting an ebc before the retune, any suggestions? I was thinking the turbosmart eboost street.

Also i noticed my canon muffler actually reduces to 2.5 or 2.75 inch piping inside, it has the jasma label. I was thinking of maybe swapping with a true 3 inch muffler.

[vxsr33]

Just in case anyone runs into a similiar issue, i lowered the boost to 15psi by installing a turbosmart e-boost street EBC and that has completely stopped the misfire.

[KiwiRS4T]

On 15/02/2017 at 0:06 AM, vxsr33 said:

Also i noticed my canon muffler actually reduces to 2.5 or 2.75 inch piping inside, it has the jasma label. I was thinking of maybe swapping with a true 3 inch muffler.

They do that. Ditch it and get a locally made 3in all the way item.

[vxsr33]

Has anyone had any experience with the xforce dual tip mufflers? (part number MP01 - 3)

I like the look of them, just not sure if they flow well.