87fc3srx7

iTrader: (13)

hey guys new to this forum. just picked up an 87 na body with an 89 t2 13bt engine swap. problem is the afr is way off and i need a fix. any help?

RotaryRocket88

iTrader: (7)

What are the AFRs at idle / cruise / full boost?

Are the ECU, injectors, fuel pump, turbo & boost levels all stock, or modified?

87fc3srx7

iTrader: (13)

all thats in the car right now is an aem afr gauge, so at idle its reading rich then at cruise it swings back and forth, then at boost it goes way lean.
as far as i know the ecu is stock, it has bigger injectors (850cc i believe), turbo is a jdm s5, and the boost was at 8lbs. i'm not sure what the stock level is but it does have a turbo xs boost controler and bov, aem fuel presure regulator, and k&n air filter on a short ram

RotaryRocket88

iTrader: (7)

So this is a narrowband air/fuel gauge? The kind with no numbers; just LEDs to indicate lean/stoich./rich?

If that's what it is, then idle would be in the rich to stoich. range, and at cruise the LEDs should meter back and forth. But under boost, it should go to the very end of the rich range. If it's going all the way lean, it's wrong. All the way lean is about a 20:1 AFR, which would instantly kill the engine. You could try replacing the 02 sensor, and if that doesn't change it, I'd suspect the gauge has a problem.

Also, 8 psi is basically stock boost for an S5, and if the car has 850cc secondaries, a fuel controller such as an SAFC will be needed to tune the RPM range above 3800. Without any of that, you should be looking at excessively rich mixtures at high RPMs, which may have damaged the O2 sensor. A wideband air/fuel gauge would likely be showing that you are running a 10:1 or lower ratio under boost since the ECU will be allowing the secondaries to inject 54% more fuel than stock (850cc/550cc) under all mid to high RPM conditions.

87fc3srx7

iTrader: (13)

thanks a ton, you are right it is a narrow band a/f meter, and what you said makes sense. now to correct my own mistake, I got in touch with the seller this morning and found out that it is not an s5 engine it's a jspec s4 engine. he is suggesting that the plugs a fouled and to replace those. i'm gonna grab some hks iridium plugs with a 10.5 heat rating. it has 8.5 mm magnacore plug wires on it now but do you think i should up the ignition system too? also is there a good ecu upgrade for the s4 either a rom tune/reflash, or piggyback?

another7driver

Look into rteks.

RotaryRocket88

iTrader: (7)

The stock coils on an FC are actually very good. There are a lot of very high horsepower cars that still use them. Along w/ new plugs, I'd also replace the stock 02 sensor to see if it helps the narrowband readout. A new bosch sensor is $20 and will pay for itself in gas mileage.

The best chipped ECUs available are the Rteks from www.pocketlogger.com. The 1.7 version has adjustments to the fuel table to accomodate 550cc primaries and 720cc secondaries. But if you're running 850cc secondaries, you would need to get an AFC of some kind to pull some fuel above 3500 rpm (secondary transition point on Rtek 1.7). The other option is the Rtek 2.1; assuming you have an S4 ECU (N332, N333), this upgrade is available and lets you do almost everything a standalone EMS can, but with the benefit of the stock maps to build on. A palm pilot is used as a handset to adjust fuel & timing, as well as monitor and datalog all sorts of engine information.