RockLobster

iTrader: (7)

Need some ideas from those with experience...

I have a strange lean condition. It seems to be sporatic.

Over the last couple months i have replaced a ton of stuff on the car and have been trouble shooting it since i got it back togeather a couple days ago.

I have a AEM wideband sensor in place of the stock sensor (which has an output for the ECU).

The car has:
-All new vacuum lines.
-Rebuilt/Cleaned stock injectors (marren service)
-New Fuel/Air Filters
-All fresh fluids
-All new hoses including fuel/coolant/etc
-New primary rail with new FPD.
-All emissions associated with the cats, air pump, ACV, & AWS removed and blocked off.
-RB full turbo back exhaust.
-374 ECU with reprogramed for no fuel cut for overboost, speed limiter, RPM cut.
-Stock fuel pump with stock wiring
-Compresson is good with 7.8-8.0 all faces.
-No smoke or other evidence of bad engine internals.

The car seems to run fine at idle, It is a little rough but I think that is because timing needs to be adjusted. It shows a solid 11.8 AFR at idle. I dont have anyting to show me vacuum yet as the stock boost solinoid is removed and i havent hooked up the boost controller/gauge (E-boost2) yet. Idle usually dosn't hunt to bad or at all and is steady at 750 rpm.

I checked the TPS, it checks out fine via the sweeping ohm test.

The car seems to want to sporatically run lean under crusing speed & RPM and light low RPM accelleration. It dosnt do it all the time but i can tell its not right because even at steady state throttle it will surge when the AFR drops to where i think it should be. I have only boosted a little bit and only below 4500rpm but it seems that that also will surge and hesitate randomly. It seems to run rough under any throttle condition.

AFRs durring these lean times of light throttle are int the low to mid 15s. When i give it more throttle it will drop them to mid to hight 13s. Then with 1/2-3/4 throttle and when the car begins to boost it will be mid to high 12s. But will not stay constant and will jump into the 13s. Sometimes the lean condition is even worse and sometimes it is better.

I have not driven the car much and only driven it gingerly when I did to prevent damage.

I am thinking either i have a small vacuume leak or something with the vacuum system is hooked up incorrectly or i have a fuel delivery problem. It cant be the HP (main) fuel filter as it is new but I have not checked the pickup screen.

I have not checked fuel pump voltage but that is next on my list allong with fuel pump regulated rail pressure.

Any other thoughts?

Edit: My alternator is a new FD alternator that is putting out close to 130 amps. I was hoping that this would help with the voltages the fuel pump sees and avoid a rewire. I have a Walbro pump ready to install but I was wanting to see where the car was at as far as AFR and how it ran before installing it to avoid an overly rich condition, (ghetto tunning).

RockLobster

iTrader: (7)

I would think it is not likely the fuel pump itself as they typically just quit when they are bad. From my experience it is rare for a pump to be bad but still kinda work at low pressure.

SureShot

You're on it - check the fuel pump & it's supply voltage.

Also check the AFM plunger for smooth action with no rough spots.
My AFM had tar residue in it from a previous bad air filter.

RockLobster

iTrader: (7)

Anyone else?

Also, what vac should I see at idle things being as they are listed above.

myfc3s

iTrader: (2)

Try Grounding you engine? I.E Get a big wire. Bolt it on to your engine and bolt the other on the negative side of the battery. I had the same problem prior and this work for me, hope it would work for you?.

RETed

Are you describing a rythmic cycling when under light load driving???


-Ted

JBrotor

I know this thread has been dead for a while but my car is doing the exact same thing. My AEM UEGO A/F Meter sweeps from 14.1-almost 16.1. It goes away under boost and heavier throttle. It also stops when cruising over 3200 rpms. I have adjusted TPS, BAC, FPR, and Lean/rich resistor. THe car idles at 12.5 to 1. Any ideas??????

boost_its_what_for_dinner

fuel pump check them my gas tank had bad gas in it when i bought it and it was full of trash and the trash clogged the filter sock on the pump.... so i pulled it and cleaned it and suck everything out of the tank and now it runs good just a stupid slight lean problem at 2700 ish but just for a second no biggie since under boost its rich like 2or 3 green bars rich on a narrow band af gauge

JBrotor

Its strange though b/c under boost the car runs 11.1-12.1. I have a streetport, TD02, cosmo fuel pump, Engman modified waterpump and thermostat. It gets jerky under very slight uphill loads only when I'm under about 3200 miles. My AEM UEGO a/f meter with bosch 5 wire o2 is calibrated to send the readings to my stock PCM. My original narrow band o2 still had the same results. Ideas??

SureShot

A worn out AFM or TPS will cause that.
Pull the plug & clip on an ohmmeter.
The TPS should give a nice smooth sweep with no drop-outs.
The AFM readings should step up & down with no drop-outs.

JBrotor

I have checked the TPS, I will test the AFM tonight. Thanks for your advise. Do you still have your TII?

JBrotor

I didn't read entirely. I am sorry for your loss..

HAILERS

It's nothing more than the ECU going into closed loop. Remove the 02 sensor input to the ECU.

I say this because what I read was all about gentle/light throttle.

JBrotor

Does disconnecting the 02 sensor cause the computer to go into failsafe mode? I would prefer to repair my issue rather than put a band aid on it.

gxl90rx7

iTrader: (1)

+1

sounds like normal closed loop operation, mine will do the same thing, scoll back and forth around 14.7.

my question is this: when in closed loop, if let off the throttle slightly, the afrs will drop to 12's and down to 10's as i slowly ease more off the throttle. Then let off all the way, it will fuel cut and the afr will to 0 (which I know is normal). usually cruising, it will be in that pre-closed loop rich state, and only go into closed loop if i am slightly accelerating. Makes for backfires when cruising, especilaly after boosting, and i would assume lower gas mileage. I suppose i should just lean it out under no boost more, but you would think that they would want to stay in closed loop until decel (fuel cut)?

HAILERS

I think some of what is being experienced is part of *closed loop* being engaged/disengaged.

But, I've thought about it a bit more. Even if the 02 sensor is unpluged you will experience some of the traits given in this thread. If your at a constant speed and look at the AFR, THEN just barely step on the throtte a smidge, the AFR will go richer about a full AFR point. Like from say 14.2 to 13.2 give or take.

In my opinion, that is the ECU acting like an accelerator pump on a carb engine. It's to keep the engine from stumbling when you hit the throttle by giving it a little squirt of extra fuel.

I've had my mixture too lean for a given steady throttle and what results is a bit of surging because it's too lean. Make it a bit richer with whatever device your using and the lean stumble should go away.

That part about how at PARTIAL throttle you say you see the AFR not being consistant........I believe that is going to be a normal condition. You step on the throttle about three quarters and see the afr go say to 11.5 AFR, and a few moments later the AFR goes a bit leaner. That's normal in my opinion, because initially you had a Load but as the engine speed came up it posed as less of a Load so the ECU now leans the mixture out. I'm talking PARTIAL throttle, not Full throttle.

To me that's odd what you say about going into closed loop under light throttle. Maybe I need to refresh my memory, but if memory serves, if I accelerate while in closed loop, the ECU will usually go OUT of closed loop while accelerating, even light acceleration. Like I said, maybe I need to go out and refresh my memory.
Disclaimer: I am NOT a Tuner. I have a birth certificate that shows both mother and father, unlike a Tuner......humor.