2G MAS in 1G. Very lean even with 550's

[Antilles]

I have a 90 FWD with 16g, 2G MAS, 550cc injectors, 255hp pump and AFPR at 43psi.

The car starts and idles just fine, with AFR's at about 14-15:1 on the wideband. At cruise the car sits at 18-19:1 AFR's!! The car seems to respond appropriately to boost because afr's drop quite a bit during spool, I want to say like 12:1 or so but I only just barely spooled the turbo for fear of damaging the engine.

Anyone know what could possibly cause the car to idle fine and seem to run ok under boost but cruise so ridiculously lean? I have no secondary tuning(ie AFC) at the moment. The car will be getting an EPROM tune shortly, but I don't want to pay someone else to chase issues while it's sitting on the dyno. If it just needs a tune then fine, but this seems like something else.

 

[Spoolin18]

I have a 90 FWD with 16g, 2G MAS, 550cc injectors, 255hp pump and AFPR at 43psi.

The car starts and idles just fine, with AFR's at about 14-15:1 on the wideband. At cruise the car sits at 18-19:1 AFR's!! The car seems to respond appropriately to boost because afr's drop quite a bit during spool, I want to say like 12:1 or so but I only just barely spooled the turbo for fear of damaging the engine.

Anyone know what could possibly cause the car to idle fine and seem to run ok under boost but cruise so ridiculously lean? I have no secondary tuning(ie AFC) at the moment. The car will be getting an EPROM tune shortly, but I don't want to pay someone else to chase issues while it's sitting on the dyno. If it just needs a tune then fine, but this seems like something else.

Cars always run a little leaner at cruise to conserve gas, it should be tunned though.

 

[habitatguy187]

Sometimes the injectors don't flow exactly what they say. I'd first do a boost leak test to find any vacuum leaks, if there aren't any then I'd bump the base fuel pressure up a little until your afr's straighten up.

Lean during cruise is fine but not THAT lean. Also your WOT is too lean also considering that stock maps aim for 9.2:1 afr under wot pulls. The setup you have will lean that out a little (which is a good thing) but shouldn't lean it out to 12.1:1. Low 11s should be good.

Do you have a logger to see what your fuel trims are up to?

 

[donniekak]

A 2g mas, and 550's is not an acceptable method to tune a car, no matter what anyone says. At least buy an old afc.

 

[Dsmj89]

You can't just run a 2g maf in a 1g out the box and expect it to run good.
You must have some form of a tuning device to re-tune the new higher flowing maf sensor.
An safc or 2 would be good enough.

 

[Antilles]

I don't expect the car to run perfect, and I'm not putting a SAFC on the car. It'll be tuned via EPROM chip. I just want to sort out whether this is most likely a tuning issue, install issue, or other mechanical issue BEFORE I go pay to put this car on the dyno and have the EPROM chipped.

I'll check the fuel trims when I get a chance and post back.

 

[habitatguy187]

I've been running a 2gmas and 550s for almost a year now with no other tuning compensation, not even an afpr. Car ran great, hardly ever saw knock this summer with a 14b at 20psi on stock sidemount.

Honestly some people have great luck with it and some have problems. At least you have an afpr so you'll be able to get a decent tune on it, of course it won't be perfect, but it will be good enough unless you're trying to absolutely max out your setup.

 

[z24frank]

I have a 90 as well with a 2g mas evo injectors and a ebay 16g and my car runs rich.Im going to find someone to install my safc soon.But point being im not running lean at all so I think they are right every car gets different results so just tune it.

 

[Yngvar]

couldn't you turn the screw in the maf to get it a little richer

 

[Oldsid]

Try increasing the fuel pressure slightly on your FPR and see what air-fuel you get at cruise and under boost. More pressure will make the injector deliver more fuel for the same injector pulse width. Start increasing slowly and see if you can get the "correct" air-fuel ratios. I would still recommend to use a proper tuning device (AFC, Ecmlink..etc).

 

[JayRolla]

Get yourself a cheap used SAFC. Can be found for under $100