Leaning Out at 3K RPMs

[pj23322]

Hey guys, I've got a 1998 GST (auto if that makes any difference) and within the last couple of weeks, at around 3,000 RPMs, I'm showing a very lean condition on my autometer A/F gauge when I normally would see the richest value. By very lean, I mean the first or second red LED is lit up when I'm at 3K. This happens if I have my foot down on the gas pedal or even when I'm cruising on the hwy between 75-80MPH. As soon as I bring the engine speed below 3K, the A/F gauge begins to cycle again. When I get on the gas, the A/F meter does light up the last green LED for about a second and they it slowly lights it way back to one of the first red LEDs. My autometer boost gauge shows I never go over 12-13 psi of boost when I'm at WOT. I originally had an intake, hard intercooler pipes, BOV, and a boost controller that I had been running for almost a year, but I took them off and put all the factory intake and intercooler pipes, even replaced the front o2 sensor, and I'm still getting the same problem. I am still using the stock turbo, but I do have a high flow exhaust manifold, ported o2 housing, RRE downpipe, RRE hig-flow cat, and Greddy catback. I have a FPR which I have set at 48 psi. I haven't been getting any CELs. Any ideas? Sorry to write a book...

 

[tom04841]

restated from your other post:

No offense, but that A/F guage is nothing more than a light show.

If you really want to know what the car is doing, get a logger so you can record what it is doing and post it up so we can do more than just GUESS.

I wouldn't put too much faith into your A/F guage

 

[DSM4me44]

Yeah, i have to agree with tom. Not to say that you can't get an idea of whats goin on from your gauge, but you can't tune or make tuning desicions with it. Get a hold of a cheap pocketlogger and go from there. Its pretty easy. I just recently got one and am working with it. There is a few great tech articles here that tell you all you need to know.

 

[pj23322]

I went out and got the Pocket Logger, v2.0 and pulled a couple of runs. Here is the data from one of the runs. Aside from the O2 sensor, I don't think it looks too bad for a mostly stock setup, but this is my first datalog, so I could be totally wrong. I replaced the front O2 sensor about 2 weeks ago.

Time RPM Timing O2 1
00:02.5 1992 15 0.06
00:02.7 2113 15 0.62
00:03.0 2188 15 0.24
00:03.2 2230 14 0.74
00:03.4 2289 14 0.6
00:03.7 2383 7 0.86
00:03.9 2621 5 0.9
00:04.2 3000 6 0.9
00:04.5 3137 8 0.8
00:04.7 3184 8 0.44
00:05.0 3633 9 0.24
00:05.2 3676 9 0.16
00:05.5 3805 8 0.12
00:05.8 3949 10 0.1
00:06.0 4047 10 0.1
00:06.2 4152 10 0.1
00:06.4 4258 10 0.08
00:06.6 4375 10 0.08
00:06.8 4477 10 0.08
00:07.1 4555 10 0.08
00:07.4 4680 11 0.06
00:07.6 4797 12 0.06
00:07.8 4875 12 0.06
00:08.0 4969 13 0.06
00:08.2 5035 13 0.06
00:08.4 5105 13 0.06
00:08.6 5195 14 0.06
00:08.8 5258 14 0.06
00:09.0 5336 14 0.06
00:09.2 5391 15 0.06
00:09.4 5477 15 0.06
00:09.6 5535 15 0.06
00:09.8 5617 15 0.06
00:10.1 5707 15 0.06
00:10.3 5824 18 0.06
00:10.5 5914 19 0.06
00:10.7 6004 19 0.06
00:10.9 6078 19 0.06
00:11.2 6164 19 0.06
00:11.4 6246 20 0.04
00:11.7 6270 34 0

Thanks for your help guys.

 

[dedlewamp]

First off, get rid of the O2 reading in your logs. The narrowband readings are almost worthless, and it will help with your datarate. Also, log knock in your next run. Really, all that you should be logging is RPM, Timing, Knock, and INJD.

It indeed looks like timing is being pulled pretty good at 2300rpm. I don't know what kind of exact setup you have, but if you have a SAFC, try adding some more fuel from 2300 to about 4600. Your timing starts coming back around 4600rpm. It also looks like you could afford to take out a little fuel in the upper RPM's, but don't mess with that until you see what your knock count looks like. Then make do another run and make sure you log knock. Post back with your results.

 

[pj23322]

Thanks for the info. Unfortunately I have a 2G and can't log knock with the pocketlogger. I am not using any kind of engine management. I am trying to figure out what could be wrong with the basically stock setup before I start trying to make my car go faster. The only mods on the car right now are a higher flowing exhaust manifold and a catted turbo back exhaust. I had the timing belt, water pump, plugs and wires all replaced about 6 months ago. About a month ago after I started to experience the lean condition on my a/f meter, so I replaced the front O2 sensor just in case.

So I guess now my real question are:

1. does the data log I posted appear to be normal for a stock 2G GST?
2. I know everyone keeps saying to ignore my front O2 sensor, but shouldn't the new sensor be reading close to .9 V and not drop off after 3K RPMs?