5.0 engine problems and questions

[NcTurnL]

Hello, Im new to posting on this forum but ive lurking around for a little while looking at all the good info there is on here. I haven't been able to find anything for this problem though...

The motor is a 92 5.0, mods are: E7 heads, ported and milled with compression bumped to about 9.8:1, GT40 intake, bbk headers, Pro products FPR and a e303 cam.
My problem is this, I have an AEM UEGO wideband, it took place of bank 2 o2 sensor and im currently running the analog output to send the signal to the ecu. ( im using the P0 calibration on the gauge), At random times, The engine will lean out pretty bad, ( The idle note even changes). And just as random as it happens, it then goes back to stoich. I found out that raising fuel pressure actaully helps the engine stay out of lean, but didnt actually fix it, fuel pressure it now at 55psi with the vacuum line disconnected and about 40 with it connected. No air leaks either. Any ideas??

My other problem, after driving the car for a while with light to medium throttle, once I get on it (WOT) it will slightly stumble. After the first pull, at WOT, the pulls start getting more clear until it wont break up at all anymore. Any ideas on this?

Thanks guys!
-Jon

 

[f8tlfiveo]

Who put the wideband sensor in place of the o2 sensor? When I put my innovate wideband in I added a bung to put it in.. Not sure, but the wideband sensor might not be the best to use in place of an o2 sensor. If you have tuning software you can turn off that bank and use 1 sensor instead of 2. But I didn't see that in your post.

 

[jrichker]

Using anything but the stock sensor to feed information to the computer is a sure way to have problems. The stock sensors do not have a linear (straight line) output. The reason is that the O2 sensors "switch" between .2 volt lean and .6 volt rich with a curve that looks like the drop off a high cliff. The curve is almost straight up and down, so the voltage shoots from .2 to .6 and back down again 2 or more times a second at cruse. The computer program knows this and watches to see that it happens. When it does not, then the computer cannot calculate the correct air/fuel mixture.

 

[NcTurnL]

I see what your saying. I was under the impression that the Em could emulate the signal but I guess not. I'm going to disconnectthe o2 and run the car and see how the afr is. I'll update on how it goes.

 

[jrichker]

You need correctly working stock O2 sensors on both sides to make the computer happy and the engine to run right.

 

[ID89GT]

Yep, the computer uses the info from the o2 sensors to adjust the fuel trim numbers for the engine. If the car has no o2 sensors, then the computer has no idea how to compensate the fuel amounts

 

[NcTurnL]

The car does have a stock o2 sensor on bank 1 of the engine. Bank 2 is the one where the AEM wideband is, and where im trying to use the analog output signal. I disconnected both o2 sensors altogether and drove around, found that it wont punch lean anymore, but does idle around 15-15.8 afr. Keep in mind this is no o2 sensor and 55psi at idle ( with vacuum line disconnected). All the research ive done show me that idle fuel pressure should be at 40psi with vacuum disconnected, is this correct? Its odd because at stock fuel pressure, my afr just sits in lean 17.0-19.0. Also, I drove very light footed for about 5 miles, drove the car hard right after and I felt a a couple of misses at high rpms. The more I pushed it, the less it missed until it was gone altogether and drove perfect. Im running Autolite copper A25, I believe, gapped to .035. Should I widen the gap. I also have autolite platinum I think ap24, gapped to .045, should I install those?

 

[NcTurnL]

Update: found out that for sure the aem analog output to the ecu is not enough for the stock ecu and.does not like it. With o2s unplugged, I was able to turn down the fuel pressure to about 43psi and now she runs awesome with good afrs.