1JZ Flat Spot... Help??!!

[Danners]

Hi Guys,

I recently bought a MiNE’S computer for my 1J and have since noticed a flat spot in the middle of my rev range that never used to be there before. I am not sure if this due to an incompatible tune in the new computer ie too much fuel, or that the timing is not right

Any suggestions? I’ve thought of purchasing an S-ITC to correct the timing (if it is even out) but how can I tell?

I also have an Apexi AVCR and SAFC which are both already installed.

A mate suggested that it could be that my spark plugs are gapped incorrectly now that I’m running 1.05 bar. I believe I’m using NGK plugs gapped to 8mm but am not sure of the model.

To top all of this off, theres a chance that my o2 sensor is stuffed because I was only getting around 300km’s per 70L tank on the old ECU

I really appreciate any comments on the situation guys.

P.S One of my stock turbos is starting to make a whistling noise and I assume it is also on its way out! I’m looking to go big single, but want to fix this flat spot issue before I feel I’m able to move ahead

[JZA70 R]

you really should have had it on a dyno when you first put the ecu in, you dont know how lean or rich it is. It could be running way lean causing the flat spot and pinging too. Then again it could be running way rich at that point causing the flatspot, either way you should have had the AFR's checked by now. SAFC should be zero'd out with the new ecu too.

The o2 sensor can cause bad fuel economy, you could always disconnect it and monitor fuel economy.

[Danners]

Yeah, i always knew that in the back of my mind but i wasn't sure if it was even worth putting it on a dyno with a dodgy 02 sensor. Wouldn't it muck up the readings?

[JZA70 R]

Nope. o2 sensor only influences cruise and light throttle conditions...

[Vios-GT_07]

just so you know, the dyno would have their own 02 sensors they'd shove into the exhaust.. this applies for even the basic dyno dynamic and links dynos

and yea it's worth it to fix up the 02 sensor or get an aftermarket 02 wideband to monitor the A/F ratios ..

[JZA70 R]

just so you know, the dyno would have their own 02 sensors they'd shove into the exhaust.. this applies for even the basic dyno dynamic and links dynos.

Didn't you read my post?

[Danners]

Car is going on the dyno today. I'll update results tonight!

[chris davey]

Good idea.

300kms to 70L does sound very much like dead 02 sensor or possibly coolant temp sensor although I haven't heard of these failing often.

what Jza70r said is correct. Most people with Mines/blitz/whatever ecus end up using a SAFC to trim them as the japanese tend to tune stupidly rich for some reason?

I am guessing that your ecu may have come off a car with bigger turbos and the flat spot you are experiencing is AFR's heading WAY rich as the engine is spooling up. Dyno will tell the story though and as long as their isn't other factors besides the ecu then they should be able to sort it out.

[Danners]

What do you guys think?

Flat spot is clearly evident.

[JZA70 R]

i would be refitting the factory ecu asap. that is a very lean tune.

the flat spot (to me) looks familiar, when boost stops climing and the fuel pours in but according to your afr's thats not the case, it actually gets really lean at that point.

whats worrying is the leanest point is at the top end of the rev range!

i see what you or the tuner is trying to do with leaning out the first half of the scale, it is somewhat rich where it could be leaner but it stays lean all the way now, it should start at 13:1 as power starts climbing and work its way down to 11.5 or so at the end of the scale.

see if you can add fuel from half way thru the run and add more down to redline.

[Danners]

I was silly, and sold the factory ECU... so i'm goinhg to need to fix this with the SAFC.

The red run is what the SAFC is currently set to.

[chris davey]

Did tuner have knock sensing headphones on?

Did he hear any knock?

If blue is before and Red is after and his o2 sensor is reading correctly it looks very strange. I think the blue afr's are much safer. I would be quite worred about the red ones. But the common thing is the general shape of both afr curves.

Also, for a mild modded 1j it is very weird to have the afr's going lean like that in the upper rev range. It sort of looks to me like you have a fuel restriction up top and if you add fuel via SAFC and it doesn't get much richer then I think that would confirm that) FYI my afr's are 12:1 from about 3500rpm and making boost until red line.

I would be checking fuel pressure, fuel pump (how new are these?) Looks as though the SAFC settings are a blanket setting ie. taken out 3% from 4000 to 7000 just based on those afr's.

The flat spot I think is to do with not enough fuel at peak torque, possible inaudible detonation setting off knock sensors and ecu pulling timing.

It is strange that it makes the flat spot better with the lean afr's though. That dyno looks like a 2jz in sequential mode.

Also, pull plugs and check for any speckles on the porcelain. This inducates knock. (google how to read spark plugs from dragstuff.com)

Hope that helps

Chris

Also, go and get your settings from SAFC and post em up. Heaps of SAFC gurus around here.

[Danners]

After my last post I started doubting whether or not the red one was the 2nd run.... i'm now pretty sure that it wouldn't be, going by the file name of the dyno and the colours of the 005, and 007 run on the left.

Fuel filter, fuel pressure (regulator I assume you mean?), and fuel pump are all original items. I've never changed any of them. I do have a new walbro pump in the garage but haven't fitted it yet because i'm a bit of an electrical tard. I'm also not sure if i need to get an aftermarket fuel regulator if I put the pump on (its a 255lph i beleive)

I've never heard the engine knock before... and i do listen out for it after owning a 7M

[Danners]

BTW i'm not sure if the tuner had any headphones on. The car went in there simply for a dyno run as he didn't have time to tune it. He did some VERY rough stuff on the SAFC to richen things up a bit. I've looked at what he did and it is a very simple few percent increase starting at about 2Krpm at 3% or so and works its way up to 8Krpm and 13%

[Danners]

Installing my fuel pump this weekend guys. Can anyone recommend a FPR for me to get at the same time? Do i need a rising rate one?