marlar98

Would anyone with the ability read my datalog for me please? I've finally been able to drive the car and datalog it since buying it in September of last year. It seems to run OK but gets a little rough at times. The O2 sensors are new. Throttle Position Sensor as well. MAF has been cleaned but the screen was removed by previous owner if all this helps with the numbers.

I'd appreciate the input. Thanks.

Injuneer

I'll try and download the file tomorrow.

marlar98

Thanks kindly. Much apprciated

Injuneer

Is there any specific operating condition where it seems more "rough"?

What brand O2 sensors did you buy? At idle they seem to hang up at rich readings (~900mV) for several seconds, when the should be switching back and forth.

Fans are running all the time, even at coolant temps as low as 183*F. Do you have a switch, or did you program them to run that low? What temp t'stat do you have?

System voltage seems low at idle -11.4 V. U/D pulley?

Does is always idle so high? Programmed idle is 800 RPM, but it's up around 1,200 RPM, and the PCM responds very slowly, pulling the IAC down to 60, and it's still at ~1,000 RPM.

marlar98

It runs a little rough at idle from time to time. Other times it's smooth as glass.

Both O2 sensor are AC Delco AFS75.

My car has a single fan. From what I could find out all z28 w/o a/c came with the single fan setup. I did program the fan to come on at 185*. I've put a 160* from hypertech and verified it does begin to open at 165. Before programming the fan to come on at 195 and off at 185, my temps would still reach around 215*.

I don't know if the car has an under drive pulley or not. I didn't put one on, and I wasn't told it had one but the guy I bought the car from didn't know much about the car himself.

It usually idles around 800. Do you think the IAC valve may need replacing?

Injuneer

Never saw a V8 with only one fan.... odd. Your data log shows the PCM is sending a ground signal to fan relay #1 and fan relay #2. If there was no relay #2 it would set a code. There is no wiring diagram in the factory manual for a single fan V8, only for a single fan V6.

The PCM responds to the high idle by reducing the IAC counts. As it reduces the counts the idle speed comes down. So the IAC is responding. It seems to happen very slowly. The car is stopped (MPH =0), the throttle is closed (TP% = 0), and the engine is at 1,100 RPM, and takes about 4 seconds to drop to 888RPM. There is no input to the PCM with regard to actual IAC position. The scan just tells you what the PCM is telling the IAC valve to do. Not a big deal, just not what I've seen before.

System voltage is not a problem due to an U/D pulley. Voltage is low all the time, ranging from 10.4 - 11.8 V. That's about 2 V lower than normal. When you get down that low, it can affect the fuel pump, injectors and PCM.

I'll focus on the parts of the data log that have extended idle period. It's a big log with almost 10,000 lines of data.

GaryDoug

I think the reason the idle doesn't drop is because the car is moving (at up to 104mph) almost all the scan. Still, I thought it odd that the target idle is at 800 throughout the whole drive.

marlar98

Thanks for your input.

Regarding the single vs dual fan, I thought it was a bit odd that a V8 would have a single fan instead of a dual fan set up, but I've read on other boards that this is common for non-a/c F-Bodies. I'd like to install a dual fan setup or even the Ford Taurus single fan/dual speed setup eventually.

Could the low voltage be due to the alternator going bad?

Thanks again

marlar98

Here's more info I found regarding the single fan/dual fan issue. Hope I'm not violating any board rules by linking another site:

"Standard equipment for all LT1 F-cars with A/C is a dual electric fan setup with primary (LH) and secondary (RH) fans. There are two different wiring schemes used for these fans, an early design that was used in '93-'94 and a late design that has been used from mid-'94 up. Note that non-A/C F-cars have a single primary fan which operates at a fixed high speed."

All about camaros

Injuneer

The details in the factory manual do confirm that. Learn something new every day. I guess the reason I've never seen one is because there are so few of them. Out of 119,799 Camaros built in model year 1994, 118,567 of them had option C60, air conditioning. Of the 1,232 non-A/C cars, 135 of them were the 1LE option, with no A/C (actually described as "A/C delete"). Is your car a 1LE? Odd that a package that includes upgraded suspension, conducive to track use would not have the two fans included.

The wiring diagram for a single fan is on a separate page from the wiring diagrams for the two variations of the dual fan control. But again, there is only one PCM pin for the ground for the single fan relay. Not sure how the PCM can command a second relay, when it shouldn't exist. Does your under hood fuse box have one relay or two for the fans? If both relays are there, replacing the single fan setup with the dual fan would be very easy.

Low voltage could be the alternator being weak, faulty voltage regulator, which is internal to the alternator, or a faulty 12V or ground to the PCM. The PCM is reading the voltage supplied to it. What does your dash gauge indicate at 800 RPM idle? Could be bad PCM grounds. Note - there was a typo in my post above. Minimum voltage was 10.8 V, not 10.4 V.

With regard to Gary's comment, I was only looking at idle speed in specific instances when the TP% = 0, MPH = 0, and fuel control Cell = 16. The minimum IAC position is a bit high at 49. I usually look for something in the range of 20-40 as being normal. IAC counts at idle can be adjusted with the throttle stop screw. Opening the blades slightly will drop IAC counts, but it will also increase throttle position volts. The most common number on an unmolested non-adjustable TPS sensor is 0.67 volts, and yours is 0.63 volts, so I would just leave everything alone. I was just curious where it idles, because looking at the very end of the data log, where it idled for several seconds before you shut it down, it never actually reached 800 RPM.

Target idle speed only applies to actual idling conditions mentioned above... MPH = 0, TP% = 0. Once you open the throttle, IAC counts are increased and minimum RPM is increased to prevent the engine from stalling on sudden closed throttle. I believe there is a "follower" table in the PCM that controls RPM vs. MPH on decel. Then there is decel fuel cutoff (DFCO) which shuts down the injectora at high RPM when the throttle closes, and doesn't turn them back on on decel until a specific, relatively low RPM is reached. If you have a manual trans, you can feel this happening if you concentrate. I doubt that it would be as noticeable with an auto trans, unless you had downshifted to a lower gear to allow some engine braking.

marlar98

At the moment I can confirm:

it is not a 1LE car, but it does have the a/c delete package according to the build codes in the glove box.

There's only a relay for fan #1 in the fuse box under the hood. I'd like to run the dual fan setup, but is it possible with just the single relay or would going with the Ford fan setup be easier?

I'll have the alternator tested, but it wouldn't surprise me if it needs replacing. I also should mention the car has an aftermarket stereo with two amps and a subwoofer which could be causing the drop in voltage maybe if the alternator isn't up to snuff.

I'm not sure if you were asking what the rpm gauge shows at 800rpm on my dash or the voltage, but I can tell you both. The voltage gauge touches the red slightly and the rpm needle is at or close to 1000, but on my Scanmaster the rpms are always at or near 800 rpms at idle.

I do have a manual transmission also if that means anything.

Thanks again for your help!