Engine running rich, CEL is on

[justin_t_2]

I have a '95 GSX with pretty much stock motor with the T25. It has a AEM fuel rail with adjustable regulator, 3" downpipe, gutted cat, and 4" exhaust. There is a CEL and he car is running really rich and the idle fluctuates between 900-1200. Sometimes it will shoot up to as high as 1600 but it usually stay around 1000. Also my boost/vac gauge is not reading a vac when idling. I sprayed carb cleaner around the intake tract to try and locate if I had a vac leak somewhere but came up with no leaks. I also noticed that the rubber hose that led into the intake manifold has duct tape around it so I'm guessing that there must be a leak coming from there. Any of you guys have an idea or suggestion for what I can do?

I'm replacing the exhaust with a 3" exhaust and getting a new CARB legal cat.

 

[tsi4g63dohc]

have you messed with the regulator ?

 

[TurboTerror99]

Did it all of a sudden start running rich and threw a CEL or has it been that way since you bought the car? I'd say either a bad o2 sensor or vacuum leak are good places to start.

 

[delta448]

Check the front O2 sensor to make sure it oscillates between 0.2-0.8 volts, if it doesn't you'll need to replace it.

The stock UICP rubber hose leaves a lot to be desired. You'll get better performance and more reliability from hard piping (with as few couplers as possible) everywhere you can install it in the turbo system. It usually makes it a lot easier to check for boost leaks too.

 

[justin_t_2]

I bought the car from a friend. It was running rich and the CEL has been on even before I got it. I have not adjusted the fuel rail because I don't have a fuel pressure gauge yet. I don't want to adjust it blindly. I'm going to check the O2 sensor right now to see if it needs to be replaced. Also I'm going to buy aluminum intercooler piping that bolt on to the stock SMIC. Also does anyone know what the fuel pressure psi should be at if I'm running the AEM fuel rail and stock injectors?

 

[delta448]

The rail and injectors used doesn't matter.
With the FPR vacuum hose disconnected, fuel pressure should be 43.5psi.

 

[DSM1G90]

?..ecu...?

 

[90moneypit]

I don't think it's the ecu at this point. I think your first priorities are to get a fuel pressure gauge for that adjustable fuel pressure regulator (some one DID set it blind) or borrow one from someone local to you to get it set properly. The second thing is to replace that intake, duct tape isn't the best when it comes to rubber. Either replace it with a factory piece or one of the many hard pipe INTAKE options and make sure it has a recirculation port on it or you'll be running rich again (look up atmospheric dump on here). The golden rule with DSM's is to get it running right before upgrading performance parts so I'd wait on the hard IC pipes unless there are cracks/holes in them. Chances are, if you plan on making more horsepower, you'll end up with a front mount and your side mount pipes won't work. You'll end up buying parts twice which nobody likes to do. Think of it this way, the 2-300 bucks for hard side mount piping puts you half way to a much nicer FMIC from ETS, or almost covers a street FMIC from punishment racing. Personally I have the street from PR and WISH I'd held out for one from ETS as I've just about outgrown the PR unit.

Short hand version of above: Check your fuel pressure, fix the leaking intake before buying IC piping and make a plan for your ultimate power goals, stick to it and only buy parts once!

 

[justin_t_2]

Okay. Yeah sorry I meant to say that there is duct tape on the upper intercooler pipe that leads into the intake manifold. Also I'm running the factory bypass valve that's recirculated back to the intake tube. I don't have any plans of making some mad horsepower in the near future. So that is why I'm going to upgrade the factory IC pipes to aluminum. Also would having a 4" exhaust and gutted cat be a possibility for it running rich?

 

[90moneypit]

Okay. Yeah sorry I meant to say that there is duct tape on the upper intercooler pipe that leads into the intake manifold. Also I'm running the factory bypass valve that's recirculated back to the intake tube. I don't have any plans of making some mad horsepower in the near future. So that is why I'm going to upgrade the factory IC pipes to aluminum. Also would having a 4" exhaust and gutted cat be a possibility for it running rich?

Well not exactly but the second O2 sensor will need an anti-foul (for spark plugs but will work for this) adapter will fool the ECU into thinking there is still a cat in place. The 4" exhaust will just gut your bottom end power is all. For that setup I'd recommend putting the stock exhaust back on. Less attention from cops and more bottom end power. Put an electric cut-out in if you just want it loud "at the track".

 

[delta448]

Contrary to popular belief, putting a larger exhaust on a turbo DSM does not kill the bottom-end power.

Backpressure is never a good thing on a turbocharged engine. There is no real benefit from exhaust pulse tuning when the pulses are driving a turbine wheel before they reach the exhaust. The turbine creates a rather large restriction within the exhaust stream all by itself. If you eliminate restrictions after the turbine you will see only positive effects. Effects like quicker spool and lower EGTs. Quicker spool makes more boost available sooner, which will improve bottom end torque.

This well-written article may help explain it in further detail:
http://www.dsmtuners.com/forums/frequently-answered-dsm-questions/168578-exhaust-straight-scoop-backpressure.html

 

[justin_t_2]

Okay. So what do you guys recommend me replacing first? O2 sensors, cat, exhaust, fuel pressure, intercooler pipes?

 

[delta448]

1) Verify the fuel pressure is correct with a gauge and adjust it with your AFPR if it isn't.
2) Reset the ECU to keep the fuel trims from affecting O2 sensor output.
3) Use a datalogger or mutimeter to verify the front O2 sensor is cycling, replace it if it isn't.
4) Replace rubber UICP hose, preferrably not with another rubber or silicone hose.