cobrakilling101

I recently bought a 94 Z28 with a 383,32#injectors,cam mild,and a 2800 stall,,how ever it will not idle in gear it dies. When I give it gas in a feather like pattern it pops and just does not respond until 3000-3500 rpms the guy I bought it from said it might have to have the computer reflashed does anyone know how much this will cost or have any other thoughts as to what it could be...plus looking to make good horse power anyone willing to give me suggestions would be greatly appreciated

Injuneer

Who tuned it for the cam, injectors and displacement change? Do you know where the tuner set it to idle?

Check pcmforless.com for tuning rates.

cobrakilling101

I have no clue how or where to set the idle...also I recently noticed that the o2 sensor is unplugged I don't know if I wanna plug it back in

cobrakilling101

it still has the pain in the butt obd-1 computer in it as well....its expensive to plug it in around my area money is tight at this point in time as long as I;m not doing any damage to my motor I will run it just a bit...ah and I forgot to mention it sat for a year so i'm running Lucas oil fuel injector cleaner through it right now as well

Injuneer

The idle speed is programmed into the PCM. You can't really adjust it externally, without screwing up the ability of the idle air control (IAC) motor to control the idle speed.

Plug the O2 sensor in. PCM can't control the A/F ratio accurately without it. It prevents the PCM from going into closed loop, where it "learns" what it needs to do to control the fuel.


I would disagree the the 94 OBD-1 PCM is a "pain in the butt". Much easier and less costly to program, and you can scan it easily for the cost of a connector cable. Use Scan9495, which was written specifically for the 94 and 95 OBD-1 PCM's, not only reads codes for the engine, trans, air bags and ABS systems, but allows you to do a data log that we can review to try and pin down the source of your problems. Its a free download, and a quality, ready-made cable to connect to a laptop is not very expensive.

Go to the "sticky" at the top of this forum for more info:

https://www.camaroz28.com/forums/com...95-lt1-874306/

The author of the software (GaryDoug) is a regular on this site and can walk you through any download, install, comm port, etc. problems. Once you get a data log, I can interpret it, as can Gary and several others.

If you are running extremely rich at this point, you can wash down the cylinder walls with excess fuel, contaminate the oil, and do serious damage to the rings and bearings. I would not recommend continuing to drive it without know that is has a good tune, and all the control systems are operating correctly.

cobrakilling101

First off I would like to thank all of you for the help...I really appreciate it a lot guys.....Ok so I plugged the O2 sensor in and its runs a little bit better.... and now my air fuel gauge works but I don't know what it means so I tell ya what it reads when I get on the throttle half way it goes to 18 when i'm doing a constant speed its at 15 and when I push it to the floor it pops and goes way down to 10-11.....and at about 4500 to 5000 rpms it starts to like fart and pop my thoughts would be that it is not getting enough fuel at high rpms now so today i'm getting it scanned and cleaning my maf sensor

Injuneer

Is your A/F gauge connected to the stock narrow band sensor? When the engine is idling, fully warmed up, does the gauge swing rapidly back and forth between rich and lean?

Or is it an additional wide band sensor?

10-11 is very rich - getting too much fuel. At WOT with a naturally aspirated engine, you typically want the A/F ratio in the rnge of 12.8 - 13.2:1. At normal, part throttle cruise, should indicate 14.7:1. Leaning out to 18 when you move to 1/2 throttle could indicate a problem with the programming or TPS sensor.

cobrakilling101

no there is no bouncing its maxed out at 18 until I give it gas..there is a set mark on the gauge at 13 it never goes there for more than a second... then when I set the cruise control at 68mph its at about 15 -15.5. i'm not losing hope but it seems like this is going to be an expensive tune...to return to stock settings is 110.00$ and then the tuning is going to be more....went to go get it scanned today but the guy forgot that he lent out his 12 point boot so Friday I will find out whats really wrong hopefully if you want injuneer you can give me a call 507-351-0093 my name is Tom and if you want to just keep in touch on here that's fine to

cobrakilling101

beings how I have no serious mechanical skills this is a situation that I bit off more than I could chew

cobrakilling101

the air fuel gauge is a AEM 52mm wide band

Injuneer

When the engine starts, it will be in "open loop". The O2 sensors will be cold, and will read about 450-500mV (~14.7:1). If you still have an AIR pump working, as the sensors heat up, they they will drop as low as 4mV with the AIR pump on. That would certainly max the A/F ratio on the wide band to 18 (very lean). Not really running lean, the sensor is just reading the excess air that the pump is forcing into the exhaust.

When the O2 sensors get hot, coolant warms up, and a timer (205 seconds) times out, the PCM should enter closed loop. While operating under idle or part load conditions, the PCM is hard coded to maintain 14.7:1 stoichiometric A/F ratio. But it does this by rapidly switching the A/F ratio back and forth from rich to lean.

This allows the cat to break down the oxides of nitrgen (NOx) and store the oxygen to be used to oxidize CO to CO2 and unburned hydrocarbons to water and CO2. In doing this, the stock band narrow O2 sensors will swing back and forth rapidly from 0xx mV to 900+ mV. The actual range of the A/F ratio when this is going on will stay around the 14.7:1 average, so your cruise condition sounds normal.

Check the rubber inlet elbow for a tear, or the bottom of the boot not being over the bottom of the throttle body.

Where is your wide band O2 sensor mounted?

cobrakilling101

when I start the car the f/a is usually around 15-16 when its cold when its warm 17-18 the car is not chipped does that make a difference......I bought a new maf sensor it seems to be running a little bit better but not much it also back fires is in the throttle body when I feather the gas..how ever it doesn't do it all of the time just 90% percent.. would that mean the timing is off..... and when I rev it the a/f guage goes down to 11 then to 18 and that's where it stays till the idle balances out

Injuneer

What do you mean by "not chipped"? 94 and up does not have a removable chip.... has to be flash programmed.

And to repeat my question, where is the wide band O2 sensor located?

cobrakilling101

I don't think I have a wide band o2 sensor but the a/f is plugged into the o2 sensor right off the exhaust under my feet.....sorry for not answering your ? i'm gonna download that 9495 program today

cobrakilling101

Oh yeah my buddy sold his 94 Camaro because he says you can't flash the obd1 computer.....he said he did a bunch of research but he don't know what you guys know....I have a question too how can I flash my computer if I don't know the size of the cam....Im not a very good mechanic sorry