Low O2's @ light acceleration

[MCDEVOE]

Hello and thanks for your help. I have a 87 GN and am currently experiencing low O2's at light acceleration. The O2's are around 180 to 220 and the car sometimes sputters. The car will continue with low O2 readings until it go's into PE mode, at which time, from my understanding, it begins to omit the O2's senor's reading and reads off the ecm chip (Red Armstrongs). When entering PE Mode the O2 readings come up to 880's to low 900's and the car runs fine. I am monitoring O2's with direct scan software. The fuel pressure normally increases when you accelarate, approximately 1 pound per boost. Fuel Pressure set @ 42lbs idle vacuum off.

The following are the mods on the car. 60# injectors, TE45A ptrim turbo, Iron aftermaket heads (Webber Racing), Adjustable fuel press reg, stock plenum and throttle body, 3 inch down pipe.

I have replaced the following items in an attempt to repair the promblem, with no change; O2 sensor, TPS, Egr, fuel pressure reg., plugs/wires, map sensor, fuel filter, coil pack, ECM. All wiring seem to be in good conidition.

Thanks again for everyones help, this has been an ongoing promblem for about three months. Two mechanics and several hundreds of dollars later and no change. :rant:

[kenmosher]

A few suggestions to try to isolate the problem ...


Unplug your DirectScan, reset the ECM (disconnect orange power wire at battery for 30 seconds) and then drive it for a bit at moderate/light acceleration. It could be RF noise on the DS cable.
Do an IAC reset and make sure the TPS is also reset to specs.
Try another chip ... might just be a tweak in the off-idle/transition cal for your combo
Change the O2 sensor with an AC Delco (not a Bosch) ... possibly contaminated or failing.

[MCDEVOE]

I've ran the car without the directscan, just a scanmaster. If you think the scanmaster may be causing rf then i'll disconnect and run. The O2 is a new heated one (forgot to mention). I've done a IAC and TPS reset and am sure they are set correctly. The car was run on a dyno with a wideband O2 and the monitoring equipment show the car leaning out just like the directscan showed.

Thanks for responding so quickly,

Mike

[kenmosher]

ScanMaster won't cause any problems, but a loose or noisy DirectScan cable will.

Given what you've said, I'd try a new STOCK one wire O2 (cheap at $25) and then I think I'd try another chip and see if the cal might be a bit off for your combo.

I've had problems like you describe when using the Bosch/MotoCraft heated O2s.

[MCDEVOE]

thanks, i've tried a one wire O2 and the 107 red armstrong chip as well as the 93. These chips were burnt by Red when I order the injectors from him. The car run a little on the rich side when going into PE mode.I'm wondering if these new 60# injectors would cause it to lean out in AE mode. I've changed alot of thing on the motor like heads injectors and cam at one time then stated noticing the promblem. I'll check the Direct Scan cable, I'll unplug it from the ECM completely and see what happens. When I first put the 60# in I was getting a rich exhaust code, then I lower the fuel press. The promblem went away, then other mods were made, like heads, roller cam 212 206. Thanks again for responding. I'll let you know about the Direct Scan cable.

[kenmosher]

The 60s are very linear and predictable (and the curve has been provided to the chip makers, including Red).

If it is going lean when you under boost, then either the wrong cal is in the chip or your fuel system (pump, lines, etc) aren't keeping up with the demand of the motor. I found that I had to run TWO pumps on the engine dyno to keep up with my motor, and it has a flat tappet cam, iron ported heads, and a TA61.

[cherrypie]

Hey Mcdevoe, sounds like you might have a faulty cam from the sputtering sound. My car was doing the exact same thing and it turned out to be the cam shaft. One of the lobes was misground.

[MCDEVOE]

No luck with the direct scan cable unpluged. I tried changing the chips again and still no change. I have Red's Double Pumpers in the car now. This problem is very strange in the way the car runs lean when using the O2 sensor to adjust fuel delivery through the ECM (this from my understanding is from idle to a certain TPS reading, at which it goes into PE mode and starts referring to the chip for fuel management and timing at what time the car runs fine and O2's come up from low 200's to mid to high 800's.). Do you know what may be omitted from the circuit when it changes from AE to PE mode. I can watch a recorded pass with my direct scan and as soon as the car changes states AE to PE the O2's come up immediatley. Thanks for your help.

[cherrypie]

Do your lifters have a eractic clacking sound, like a flutter sound when you are running at part throttle? Does it sound like popcorn popping? When you had your ace mechanics look at it, what did they tell your problem could be?

[MCDEVOE]

The rockers are Hartland roller and are a little noisey, but nothing unusual. It doesnt seen like it could be something mechnical due to the disappearing of the problem when changing modes. I'm currently looking for shop manuals for the car in order to get wiring diagrams.

[kenmosher]

Some diagrams can be found here:

http://www.gnttype.org/techarea/electrical/electricpage.html

That said, I'd be surprised if it's in the wiring. Sounds a lot like something in the chip cal. Do you have another brand of chip?

When you go from AE to PE, there is a change in where the ECM is calculating the fuel trims and it could just be a table is skewed just enough for your combination to be unhappy.

Try someone else's cal and see if it persists ...

[cherrypie]

Since you have tried two chips, a race and strip they would have different calibrated enrichment settings. You might have a sticking injector or a bad injector wire harness. You know the injector wires get old and break. How many mile does the car have on it?
Are there any local competent GN racers that live in your area? :idea: