So i installed my AEM UEGO wideband today.. and well lets just say im really not happy with the results... i knew i had a miss but i was hoping it was a wire/plug related thing.... but instead i think it might be lean miss...

my idle AFRs are so lean to were the wideband cant read them (18+:1)
and at WOT i get about mid 13s to low 14s in second gear
Third gear is a better with high12s to low 13s and First is just too bad to bring up....

What i have is a 88 gm truck 350tbi on a 90 camaro RS that had a 305tbi (i bought it that way) WELLLL my guess is the previous owner didn't bother changing any of the Fuel Mapping from the old 305 tables.... and with a MAP sensor that means the added displacement wont be read by the computer so it wouldn't know to give more fuel... right?

Also the headers were swapped to a set without an 02 sensor hole. i know in some cars this can make the computer revert to a really safe AFR map and timing But it wouldn't be making the engine run lean would it?

Well this sucks because right now this is my daily driver, i planned on switching to carb in the summer, should i just bump those plans up so i can tune it myself?

 

What's your question here? it seems like you already know you're lean, and you need to adjust it. So tweak it, add more fuel and you're done.

I must be thick about TBI, but I thought it would take an O2 sensor measurement, and add fuel as needed. Aside from the knock sensor setup, it shouldn't know if you've got 305, 350, or 327 cubes under it, it can only sense air in the exhaust and add more fuel right? So something isn't right there.

 

In closed loop, the ECM will adjust itself to a point by using feedback from the O2 sensor. I don't know if it will be able to make the almost 20% adjustment without throwing a code though. Since the OP has a speed-density system, the ECM "calculates" how much air is going in based upon the MAP sensor. To make this calculation it has to know the correct displacement of the engine. Since a MAF based system measures the actual air flow, it handles engine displacement changes more automatically. At least that is how I understand this stuff to work.

 

oh right, I remember Fast355 correcting me on that before. TBI is smarter than I give it credit for (being MAP rather than a MAF system). My personal preference is towards MAF since it's simpler. Heck, my true preference is to carbs, but that's not really here nor there for this thread
So the punch line is bigger injectors?

 

Since Im running really lean under part/moderate throttle, would it be safe to assume that EGT's are going to be high, and the likelyhood of burning an exhaust valve could be somewhere in the distant future?

Obviously WOT driving while lean is far more dangerous than a low load condition, which concerns me considering the fact that im almost half to a whole point off (air to fuel charge).
Im scared of damaging the motor, and I cant get a compression tester in the spark plug holes to check compression since the exhaust manifolds and related items are in the way!

Any quick fix to this problem?

As mentioned before, im switching to carb here hopefully in the summer, so all of this PCM controlled stuff is going out the *******, but until then I dont want to damage my bottom end or valve train!

Let me know!
thanks

 

No, your exhaust will be cold since you're on the verge of lean misfire conditions. "Lean" refers to stoich, under high load. If you're lean of stoich it'll run cooler. If you're rich of stoich you'll run cooler. Rich of stoich is still full power, just cooler. Lean of stoich is down on power, and cooler.
So "just right" is RICH of stoich, and "running lean and hot" refers to being very close to stoich.
(let the flaming begin...)

Go buy a carb and put it on! It's not like you're redoing the bottom end, a carb can be installed and set up in an afternoon, don't wait that long for it. Visa gives you a month of grace, go nuts!

Or just drive it really gently until then.

 

I don't think the 18+ readings are "real". If the system is idling in closed loop it can't be that high. This may have something to do with the AIR system putting air into the exhaust manifolds when it shouldn't.
Where is the WB O2 sensor in relation to the factory O2 sensor?
I'm assuming that since this is your DD that it has a complete exhaust system, right?

 

well it cant be the AIR system because i removed that a long time ago. the WB02 is about a foot after the Y-pipe meets (which means its way away from the factory 02 which was only on one set of headers)

No i do not have complete exhaust at this time, i was "in the process" of redoing it all (just slowly) The exhaust dumps after the y-pipe

Why i think the WB might be right is because the original owner swapped the cars 305 for a 350 and i think he left the original 305 fuel mapping (im full tbi still so its all EFI)

 

There's the problem. The WB is seeing the air bouncing in and out of the end of the pipe at idle. When the exhaust stream picks up velocity above 1/2 throttle it keeps the air out.
Granted the fuel map needs to be corrected, but the closed loop will keep the mixture close to normal.

 

The fact that you don't have an O2 sensor is a big problem. Any exhaust shop or muffler shop can weld a bung into the header collector no problem. You might also want to re-locate that wide band (or fix the exhaust by putting a cat or something after the open y-pipe) and see if it changes anything. Are you running long tubes or shorties? If you're running shorties get the NB02 bung welded into the driver side collector and the WBO2 downstream of that into the top of the exhaust 'down' pipe just before it goes under the oil pan. If long tubes then put the NBO2 into one collector and the WBO2 just a few inches downstream of the collector after the flange into the exhaust pipe.

 

That's exactly right. Don't even bother reading those results, it'll just make you paranoid. Once you get a full exhaust on it, leak free, you can start using it again. Keep it running (heated) so it doesn't die on you, but don't bother reading it. (or take it off and put it on a shelf).

 

It way to late for the post but you need to make sure you change the setting on the aem gauge to p03 so it will send 0-1v not 0-5v to the o2 sensor wire otherwise it maxes out making the computer run the car super lean.

 

thank you for the reply Anthony. Just about 6 years late haha that is very true about the aem o2. However I was hooked up directly to the UEGO gauge and not the pcm. In the end I just did a carb swap and msd 6al as I did more engine mods than the factory set up could have supported.

 

And just for the people who said it was the air pulsing back into the exhaust I put full exhaust on and it made no changes. Thanks for the input though

I love when a thread for an old car comes back. Brings back memories

 

Haha yeah. Glad to see you didn't give up on the car and did something with it. I just recently started tuning and did a computer swap to a newer one. I had to re pin a lot of things and make the two may relay circuits. I'm not going to lie I almost cried a few times in anger haha. I almost gave up and went carb as well and 454 but the gas prices are crazy.