AEM Wideband and AEM Adjustable Fuel Pressure Regulator

My motor did NOT come with a factory oxygen sensor. I had changed my fuel pump to a Walbro 190LPH unit a long while back after the stock pump failed.

Motor is stock.
No idea where the ignition timing is currently set at.

With the stock regulator:
Idle - 38psi
Blip throttle - 46psi
Cruise at 80km/h - 14.6 (AFR)
Light acceleration - 14.1 (AFR)
Medium acc - 12.7 (AFR)
Full throttle - 12.6 (AFR)
Regular driving was often in the 13.x range (AFR)
Spark plugs got black / sooty after a while of use.

With AEM AFPR installed:
Idle - 38psi
Blip throttle - 48psi
Cruise at 80km/h - 14.1
Full throttle - 11.7

Idle adjusted to 32psi
Blip - 42psi
Cruise at 80km/h - 15.0
Full throttle - 12.6
Regular driving hovered around 14.6-14.8

From my understanding, the AFR at the 32psi (idle) fuel pressure settings are more ideal for a daily driven vehicle. It did feel as though I lost some power by reducing fuel pressure to achieve the desired AFR..

What do you all think of the results so far? Is 32psi safe for this motor even though it appears to be running fine?

I am planning to the ignition timing properly checked soon..

My main goal is motor longevity and fuel efficiency.

I am currently averaging 18 - 19mpg with the walbro pump and stock regulator.

I'm curious to see what I get now with the new settings..

Ignition timing can and will alter your A/F almost as much as changing the fuel pressures, really both will need to be adjusted at the same time for optimum performance.  Also you can adjust the camshaft timing with offset keys to help optimize your powerband.

I don't know if you're aware of this, but on the OBD1 ECUs without the O2 sensor, there is a potentiometer that adjusts the AFR - flip the glove box out and look to the left of it.



This is what you're looking for.

When you say 18~19 mpg is that imperial or US gallon?  It seems a little on the low side.

Potentiometer! Wow, how convenient! Thanks for that one, never knew it had that..

I generally get around 500kms to a full tank of petrol (about 61L). I usually attribute that to the extra weight I carry around, the slightly taller than stock tyres and the engine running on the rich side.

(side story, I had dropped my GV at our local Suzuki dealer about 2 years back, and one of their mechs had 'tuned' something for me to get more power.. I never knew what he did but the GV did feel more lively afterwards.. Now I am suspecting he just used that potentiometer to enrich the AFR abit.. I will look for it)

500 kms on 61 litres - say 12+litres/100km - thats about what I get - but mine is low because of the drive pattern, mostly short trips - if yours is different, then you should be able to get more out of tank than that.

Is your odometer calibrated in miles or km?

My two Suzukis have odometers in miles, two Mitsubishis have odometers in km.

My odo is rated in Kms. My driving is a mix of city and highway driving. Vehicle gets driven around 45kms a day, plus another 100kms or so on weekends. My driving style is generally light on the throttle with a few full throttle bursts in between when overtaking slower cars etc.

I also have ~277,000kms on the motor.

Potentiometer! Wow, how convenient! Thanks for that one, never knew it had that..

This should be adjusted at each service, it replaces the O2 sensors function of compensating for long term wear. You already have the advantage of no emission equipment which gives you 5-10% better fuel efficiency 

I've always been curious about that - 5~10% better fuel efficiency - why should it be better, it's always in open loop.

Theory dictates that with a conventional EFI system (one with an O2 sensor) that it runs rich in open loop (warm up and wide open throttle) and is more efficient in closed loop - I have to assume that these "full time open loop systems" will have a "warm up" map that is based on coolant temp, and where the conventional system switches to closed loop, these perhaps have an "operating temp" map.

Am I making sense here or is there something I am overlooking?