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Is this what you call lag or something else?

Scooby_Steve
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Scooby_Steve Community Regular

Scooby_Steve

Posted
Posted

Hi,

I put a cooler on my car approx 2mths ago and since then I noticed a flat spot from around 3500-5000 rpm. The piping is 2.5" back to both the standard piping

(ie routed behind the cooler). However, on the left end tank of the cooler (looking from front), I've got a 180 Deg Bend that was cut and modded (made it a mitred 180 Deg bend) to allow the bend (as i'm still using standard front bar) so i can route the piping behind the cooler. Would this be a problem for pressure and flow?

Also the size of the cooler is a 800x600x73 (i think 73 anyway). I've also got a 3" turbo back exhaust running 10psi boost.

Another factor is my coil pack were crappy at that very time as well and i have taped and siliconed them..No longer misfires but i have read that main "missfiring thread" and in that thread some people where getting flat spots roughly around that rev range.

As a result, my car is running slower than it was with just a stock cooler and 3"exhaust (9psi)

So is it my cooler size, cooler piping or is it the result of dodgy ignitor coils?

Any help would be great.

Tonba Rising Star

Tonba

Posted
Posted

++++

Greetings All.

I think you will find that the intercooler is too big...unless you DID mean a 600x300...other wise your cooler would be WAY too big for only 10psi...

Flat spot eh...over fueling issues...? Something to do with fuel or fuel delivery??

Cheers,

--Tonba

++++

Dale FZ1 Veteran

Dale FZ1

Posted
Posted

Why would the FMIC be too big?

They are essentially just a heat sink between the compressor and combustion chamber, so a larger heat shedding capacity = more reliable/greater power production.

I must say that my R33 running a 600 x 300 x 76 did suffer the std ECU flat spot.

Perhaps I'm missing something?

cheers

Ionos Community Regular

Ionos

Posted
Posted

Your mods sound the same to mine.

I suspect your ecu is richening the mixture and retarding ignition. Time for aftermarket engine management.

Whack it on the dyno if you want to really see what's happening instead of just guessing though.

Dale FZ1 Veteran

Dale FZ1

Posted
Posted

PFC plugged in with standard base maps immediately removed the flat spot - it did feel like ignition retard was the issue.

Perhaps a significant reduction in pressure drop (vs. the std R33 cooler + piping, + exhaust) means the engine was ingesting enough air to make the std ECU go into a fail-safe, even though the actual boost pressure was unchanged?

Sydneykid Grand Master

Sydneykid

Posted
Posted

You have removed a restriction, therefore more airflow (boost is irrelevant). The AFM is sensing more airflow and telling the ECU (AFM's are blabber mouths, just can't keep a secret). The ECU knows that much airflow is too much, so it hops onto Rich & Retard mapping to protect the engine. Time for some tuning, DFA, SAFC, PFC or equivalent.:D

Race__24 Experienced

Race__24

Posted
Posted

I'm suffering a simalar flat spot, after installing an EBC. I'm only running 9PSI but it gets there much quicker than before.

I'm guessing the computer sees AF/RPM. so in the mid-range where the boost is incresced it plays up but then over 4500RPM things are just about back to normal so she takes off again.

Well that's my theory........ :confused:

I'm hoping that playing around with the gain will help, if not i will be searching for a vacuum/pressure leak, and then look to the computer. Besides i don't have any money to buy a computer just yet!

Dale FZ1 Veteran

Dale FZ1

Posted
Posted
You have removed a restriction, therefore more airflow (boost is irrelevant).  The AFM is sensing more airflow and telling the ECU (AFM's are blabber mouths, just can't keep a secret).  The ECU knows that much airflow is too much, so it hops onto Rich & Retard mapping to protect the engine.  Time for some tuning, DFA, SAFC, PFC or equivalent.:cheers:

I'm happy that my deductions about the std ECU were correct - it really means Nissan engineers defined fairly tight engine performance parameters, enforced by a fairly tamper-proof brain. I've gone down the PFC trail, but what degree of success could be expected with an intercepter (eg. Jaycar kit) that fools the ECU into accessing different parts of the factory maps?

cheers

  • 2 weeks later...
Scooby_Steve Community Regular

Scooby_Steve

Posted
  • Author
Posted

Hi,

A mate of mine told me to clean the AFM so I cleaned and the car now seems to go alot better. I havent pushed it hard all through the gears (only 1st and 2nd) but the lag as mentioned between 3-5K rpm is now gone. I'll do more testing this weekend and let you all know the result.

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