Power Fc Driveablity Problem......

[USRB25S13]

Hi,

First let me list my setup;

92 240sx

Series II RB25DET Motor with a larger turbo/FMIC

480cc s15 topfeed injectors

Q45 MAF

Nismo FPR

Walbro high pressure pump

The problem that I have been having ever since I had the Power FC is when I am driving down the road trying to hold a constant speed the car surges. It's kinda faint but passengers in my car can tell. I have a wideband O2 sensor and it shows the car going rich/lean and the surging goes at the same pace as that. So to keep this problem from happening I turn off the 02 feedback on the PFC. But my car gets terriable gas milage this way. I tried another O2 sensor and that didn't help.

Would hooking up the speed input do anything? I didn't hook it up with the stock ECU so I wouldn't have fuel cut. Other then that I am lost. I may just get an AEM EMS if I can't figure this out.

[BHDave]

The stock nissan ecu and the power fc seem to sweep through the af ratio on cruise as you have stated when looking at an a/f gauge. The funny thing is, when running a data logger i never saw a wave pattern when i logged cruise.

My rb25 has a slight surge, similar to what you are describing but at really low load, light throttle, and no where near as prononced as yours. I had put mine down to using 550cc single pintle injectors.

What you can do before splashing out on a new ecu is get a tune done in the mid and low range part of the map with the closed loop control switched off and get your mixtures as close to stoich as possible. That way the ecu isn't having to swing as far trying to correct the cruise mixtures.

Edit: Hook up your speed sensor. It has all sorts off effects on power steering weight and hicas and could well be part of the problem. I assume you have the hicas locked (if you have it).

Edited December 22, 2005 by BHDave

[Sydneykid]

My 20 cents........

1. The Q45 AFM is a bit big for your application, its metering at very low airflows may be an issue. Check the AFM voltages.

2. Does the surging stop when you turn closed loop off? If so, tuning the maps at low airflows will help a lot. Also the PFC default O2 aim is set at 1.047 lambda (15.2 to 1), try droppin that down to 1.0 (14.7) and see if it helps.

It has been my experience that you will not fix this problem by changing ECU's, only the standard ECU is better than a Power FC at light load running. It's a tuning problem, not an ECU problem.

Hope that helps, please let us know how you get on

cheers

[USRB25S13]

My 20 cents........

1. The Q45 AFM is a bit big for your application, its metering at very low airflows may be an issue.  Check the AFM voltages.

2. Does the surging stop when you turn closed loop off?  If so, tuning the maps at low airflows will help a lot.  Also the PFC default O2 aim is set at 1.047 lambda (15.2 to 1), try droppin that down to 1.0 (14.7) and see if it helps.

It has been my experience that you will not fix this problem by changing ECU's, only the standard ECU is better than a Power FC at light load running.  It's a tuning problem, not an ECU problem.

Hope that helps, please let us know how you get on

cheers

<{POST_SNAPBACK}>

Thanks for the replys

My Q45 MAF will hit 5v's @ 15 psi of boost. I plan to run more boost once I get larger injectors. My turbo good for 650hp. So that is why I have the Q45 maf

When I turn the o2 feedback off the car runs pretty rich at cruising speeds. between 12-13:1.

I was looking at the sensor check screen while driving. Nothing looks out of place.

As for the EMS I am still considering getting one since I can get one for $1300 USD and sell my pfc for 850. I would then have a map based standalone with boost controler that plugs into the stock harness.....But that's just a though and I would rather get what I have working better.

Another quick question. When I check my timing the PFC will show 15 degree's timing on the comander but the timing light shows 25. Is it supose to be double the PFC's reading? If I adjust the timing to 15 on the crank the car runs really bad.

[USRB25S13]

As for changing the 02 aim settings I need a datalogit to do that correct?

Also I though of some thing else. My Airflow settings are 93% at low voltage and 83% @ 5.12v.

I need a good guide to seting up a PFC. Where can I find one?

[maximajim]

Thanks for the replys

As for the EMS I am still considering getting one since I can get one for $1300 USD and sell my pfc for 850. I would then have a map based standalone with boost controler that plugs into the stock harness.....But that's just a though and I would rather get what I have working better.

Another quick question. When I check my timing the PFC will show 15 degree's timing on the comander but the timing light shows 25. Is it supose to be double the PFC's reading? If I adjust the timing to 15 on the crank the car runs really bad.

<{POST_SNAPBACK}>

good luck selling the pfc, I can't even get $425 for it.

As for timing, pull #1 coil, install a spark plug lead and attach the timing light to the lead. Make sure your IACV and TPS is disconnected and make sure your base idle is correct. The PFC is supposed to read what the Timing light reads.

[gawdzilla]

i had a very similar problem with this surging effect. mine was pretty pronounced. felt like i was throttling/lifting off the whole time while trying to keep constant throttle. keep an eye on your MAF voltages and see if they are steady when the surging occurs. my voltages jumped around pretty significantly. replaced the maf and everything is ok now.

[paulr33]

what are the afm voltages at cruise and at idle out of curisoity?

can you change to another afm temporarily to see if this helps?

[USRB25S13]

what are the afm voltages at cruise and at idle out of curisoity?

can you change to another afm temporarily to see if this helps?

<{POST_SNAPBACK}>

I had the stock MAF and the problem was still there. No I have the Q45 MAF on and no difference. The MAF voltage looks good (steady) while it is surging.

[carl h]

perhaps this is a case where a blowthru setup could solve some problems?

where is the maf positioned as ive found that if any air can be blown on or near the maf then it will surge and do all sorts of odd things.

running blowthru on my car has been sweet so far, might be worth a go.....