cant figure it out. its a 98 ls1 with a big cam, tune from hpe a couple years ago. i noticed it seemed rich a couple months ago and now its really rich at idle, smells like fuel real strong. no codes, etc. its bogging pretty bad as well. idles right where it always has. cant figure it out. sparkplugs would throw a code wouldnt it? it also will backfire a little on decel from WOT. car feels gutless, and i want a little affirmation on sparkplugs before i go through that headache. what plugs should i go with seeing as i do also spray 150 shot wet from time to time. Stock injectors btw. thanks!!!

 

Depending on the tune, the maf and o2 sensors can be changing the original a/f to what the sensors "think" the engine wants in the way of a/f ratio.

 

NGK TR6 gapped .038-.040

 

hmm. it has a granatelli maf on it, o2's are pretty new. o2's would pull a code wouldnt it? i wish the damn car would pull a code so i'd have some freaking idea. i'll be pissed if i sweat and swear over changing the plugs and it doesnt do anything (or fouls the plugs out again)

 

What are your LTFTs and STFTs? If your performance is down, but you don't have any DTCs have you don't basic old school tests(vacuum at idle and 2500RPM and a snap throttle, compression and leakdown). Once you have those things verified you can dig deeper.

 

compression is good on all cylinders. it doesnt lose a drop of oil over 5k miles (mobil1 syn) vaccum check is a good idea, what should it be pulling at the different levels? i'll check tomorrow.

it feels more like a fuel/spark issue then an actual motor issue. sometimes it'll pull hard like it should and other times (especially when its humid) it's super sluggish and really struggles until about 3-3.5k and then it pulls, but still not as hard.

 

Read the thread title and first thought in my head was, "Since when is getting rich a bad thing and why would he need our help to hinder this great thing that I wish was happening to me."

Didn't even read one word in this thread, so I'm no help.. Just thought I would share.

 

First thought was start looking at your injectors. I'd really like to see a picture of each spark plug though.

 

Went back and read...

I would say O2s.. Is it loading up in the lower RPMS? 1500-3500?

 

Well, I read the words "big cam" + "stock injectors". My guess is that your injectors are too small. Injectors should run at no more than 80% duty cycle WOT. On a fat cam it's easy to peg the injector duty cycle over 100%.

This lack of fuel is noted by the PCM and it "adds" to the LTFT (Long Term Fuel Trim) tables to compensate. For example, an inadequate injector might trigger an addition of 10% or more to the LTFT to compensate. NOW, when you go WOT, the O2 sensors are ignored and the computer calculates fueling based on the PE table (enrichment table) + the LTFT's at the time you stomped on the gas.

SO..... if the PCM is adding fuel all the time (say 10%) for small injectors when cruising through town, it will ADD that 10% to the commanded air/fuel ratio when you go WOT. End result = running pig rich. That leads to the back-firing you are describing + loss of power.

Trust me. Been there/done that.

 

80% is what people strive for.. It is not easy to be there though is it?

 

injector theory is interesting.. but wouldnt that have manifested itself a couple years ago when the cam was installed? bigger injectors is on the honey to do list anyway. it does explain alot of the symptoms im having. i think ill just deal with it for another month or so, buy bigger injectors (dunno what size yet) ls6 intake, new plugs and get it retuned and see what happens.

 

Hows your water temp guage looking? I had a bad sensor one time and it made the cpu think it was Winter(below 0) when it was 98 degrees outside and it was adding fuel. Your 98s Water temp sensor is like the corvettes 3 wires instead of 2 and the 98 has the non idiot gauge. Have you cleaned your MAF lately? A can of MAF cleaner isn't but about $5.00. Also pull out your air filter, especially if you have done the free air mod or have a bottom breathing ram air system and make sure you haven't sucked up a plastic bag or two in front of the radiator. It never hurts to reset your cpu either and let it relearn it's operating parameters again. I'm still on stock 98 injectors also. But I don't use the NOS.

 

how do you reset the cpu? just unplug the battery right? i have the k&n cold air intake that sits right on top, and its clean. ill try cleaning out the maf. water temp is good, no issue there. i wasnt too worried about the injectors originally, i spray wet so it gets enough fuel, and on motor is only about 400-ish to the wheels through the stock ls1 intake.. i plan to change out the injectors eventually anyway when i get a good set of heads and get up around 450-500 to the wheels.

 

my injectors are running at 73% DC... still smells rich as hell