97 LT4

Can these O2's be bad and not set an SES code. Car still running rich and has a slight surge/miss. I changed TPS and had no significant change. Can the sims be wrong or not working? the LED on the sims blink is this right?

LT4 Kit w/hot cam, Fast chips Program and sims.

shoebox

Yes, they can be working poorly and not set a code. Monitoring them with a scan tool or software would give some idea on what they are doing.

Injuneer

It's possible for a pre-cat O2 sensor to be providing bad data, and not be setting a code.

Confusing.... first you ask about pre-cat O2 sensors, then you start talking about sims. Are you possibly attempting to run sims in the pre-cat position?

97 LT4

No I checked the sims are on the rear position. I bought new pre-cat O2's and have not yet installed them. Just wanted to know if it was a good $100gamble to install them. Car is definatly rich and I am just chasing possible problems. Any suggestions on what else might be causing the issue. I have been told that the car is running in closed loop and this is why it is dumping fuel. Thanks for the Help.

Injuneer

Appears from your "name" that you have a 97. If that's the case (why not add a "signature" with year, model, engine, tranny and any major mods?), you should be getting indications of a misfire. A "scan", using a tool that can access GM enhanced parameters would allow you to identify the misfire count by cylinder. That might help identify the source of the problem. A misfire can cause it to run rich, or running rich can cause a misfire. Need some more info.

Why did you change the TPS? What lead you to that conclusion?

Do you have headers? Extensions on the O2 sensors? Does the "LT4 kit" include the heads and intake? Any mods beyond what you listed? Under exactly what operating conditions do you feel the "surge/miss".... at idle, at part load cruise, at WOT, all of the above? What indicator tells you its running rich - exhaust smell (have you deleted the cats, since you are going for sims?), wide-band exhaust check, poor fuel mileage, all of the above?

97 LT4

It is a 97 M6, Lt4 Kit, wHot cam, Hydra rev spring kit, LT's, no cats. Car smells really rich and is averging around 18 mpg (42 miles one way to work 30 on the interstate). Scan showed no misfires, inspection station (3 trys) shows not ready on emmissions parameters. Car feels like it has more of a slight surge while cruising. Highway at 1800 it surges just enough to be a pain. does not like to be driven around under 2k rpm. somtimes difficult to take off from a dead stop in normal driving or stop and go traffic. WOT runs really good and pulls hard all the way to 6500.

I will work on the sig

Thanks for the help Injuneer.

Darrell N
TX

97 LT4

Changed TPS because car would not come back to idle quickly. It hangs around 1800 rpm for 5-10 secs then drops slowly. TPS voltage was showing .57 and I was told the target was .67 volts. Helped very little but thought for 40 bucks I would give it a try. Car feels more like a surge rather than a miss. Almost like a vaccum leak. Also car idles at 1100 rpm. Should I put those O2's on or save my money. And I do have o2 extenders.

Injuneer

You need the O2 sims to get rid of the SES light and codes. That will also get rid of the "not ready" flag on the cats. There are other "not readies" for thinks like EGR and AIR. Do you remember exaclty which "not ready" flags you failed on?

The PCM will correctly accept a TPS signal ranging from 0.20-0.90V at closed throttle. Some people claim 0.67V is the "sweet spot".... but I think that's just because that's what you find on most totally stock, factory setups. There is no logical reason 0.67V would be any better than 0.57V.

If it idles too high, its getting air form somewhere its not supposed to. Either the blades are stuck open, the IAC motor is stuck open, or the throttle stop screw is out too far, you have a vacuum leak, etc. Put a scanner on it and check the IAC counts..... I'lll bet they are bottomed out at "0".

Solve the obvious problems first.... high idle speed, codes for after-cat sensors, etc. Then get a scanner on it and look at the long term fuel corrections, for an indication of what's causing it to run rich.

97 LT4

I have sims on the car now, just dont know anything about them. I do not have an SES or any codes from a scan. The only code I have had was for the TPS after I changed it. I can not remember the not ready codes, only that there were only 2 ready. Got to ask what is IAC?

Injuneer

IAC is the idle air control valve. Its located in the base of the throttle body, and controls idle air flow by moving a small pintle valve in and out with a stepper motor. A scan will tell you how many steps ("counts") the valve is being told by the PCM to position to .

Shoebox has a pic of it on his "tech pages":