Diag help needed -breaking up at 5500-6600 RPM under load, running lean

[91rs13]

Hello All,

I am looking for a little assistance. I just got back from Mt Tremblant in Canada from a track day/time trial with COMSCC. I had some major issues with the car breaking up under load /acceleration in 3rd/4th onto straights. When I got around 5500 RPM it would break up.

I could accelerate out of a slow corner in 2nd gear and pull right up to 7000-7500 RPM --but when shifting into 3rd --as soon as I got to 5500 --broke up again. Plugs look lean ( normally at the track it seems to run rich) -Pulled the O2 sensor wire off the sensor and could get to 6000 RPM

The car --240sx with CA18DET, GT28R Turbo, intercooler, 3 inch exhaust, mines ECU, running 9-10 PSI boost, Atmospheric BOV ( I know, I know but that should make it rich right?). --I am thinking FPR may be on its way out.

--Any other suggestions as to what it might be?

This was the 1st time at this track with the car ( has run at WGI, Lime Rock, NHIS --no issues like this)

Any help appreciated DJ


Modified by 91rs13 at 6:30 PM 8/1/2007

[Liquid_Neon]

the sensor made it run better when u disconnected it?

heh heh... try getting a sensor.. they arnt that expensive... or is it a wide-band?

[91rs13]

the sensor made it run better when u disconnected it?

heh heh... try getting a sensor.. they arnt that expensive... or is it a wide-band?

I only got 500 RPM more disconnecting it--The problem still existed, it just allowed me to run 1 practice session and the time trial. Since it was still lean, I do not think that was the issue ---but looking for comments from people better equipped than I to do so.

[mod_mastaz]

What MAF are you running? If it's the stock CA one, you might be outflowing it.

[91rs13]

What MAF are you running? If it's the stock CA one, you might be outflowing it.

Yup it is a Stock MAF. And I recently routed fresh air to the front of the Air Filter instead of picking up air just from the engine compartment.

[sil80ryan]

my car does the same thing but it stock and its boosting at 10psi and i have no boost contriler?

[BEST1TUNING.COM]

Do you have any Idea what the tune actually is set for? 5,000 is right around peak VE for a CA, that is where the motor takes in the best charge of air as long as you are fully spooled by then. It is also the point that requires the most fuel and if the tune is lacking fuel in this area you will get the lean misfire.

[Bwana]

I'd definitely be checking out your fuel pressure. The fact that it normally runs well and then suddenly begins to perform poorly when you haven't changed anything makes me think it's a part failure issue, not tune related. My first guess would be a dying fuel pump, are you still running a stocker?

[91rs13]

Do you have any Idea what the tune actually is set for? 5,000 is right around peak VE for a CA, that is where the motor takes in the best charge of air as long as you are fully spooled by then. It is also the point that requires the most fuel and if the tune is lacking fuel in this area you will get the lean misfire.

No I do not know what the tune is --bought off another member a few years ago shortly after installing the motor.

As for the 5000 RPM thing --it has not happened before at the track --and was fine this past weekend at an autoX. (1st and 2nd gear only)

I think I will add the fuel pump to the FPR and a new filter. Then I am going to have my buddy fab an intake pipe and upgrade the MAF and injectors. I picked up another ECU for this purpose but have been lazy about getting things done ( I hate it when work takes over my life)

Thanks for the input guys!

[BEST1TUNING.COM]

Oh ok I didnt catch that it just started happening

[91rs13]

Oh ok I didnt catch that it just started happening

Do you do tuning on CA's?