reading scanner question - NJFBOA - Home of New Jersey's Camaros and Firebirds

grazi · 12-23-2011, 02:49 PM

94 TRans am...So I just logged about ten minutes on Datamaster and I'm trying to analyze why my car is stumbling and missing at half throttle. Why are certain boxes such as LTerm counts and EGR DC highlighted pink and or yellow sometimes? Should I ever have spark retard???
Thanks

WildBillyT · 12-23-2011, 03:00 PM

Pink in an Lterm means you are running rich. What do your Sterm counts look like?

grazi · 12-23-2011, 03:04 PM

Theyre generally the same as LT around 125 average number

WildBillyT · 12-23-2011, 03:54 PM

Can you take a screenshot of datamaster and post it up? Or host the file online and post a link?

grazi · 12-23-2011, 04:19 PM

I'd love to, Just have to figure out how. Give me a few minutes. Appreciate the help

grazi · 12-23-2011, 04:41 PM

Sorry cant figure out how to do it now. Anytime im under 50% Throttle position, LT is almost always around 120. At full throttle they are both 129....The Injector voltages went up to 86 and turned pink also if that means anything

grazi · 12-23-2011, 07:54 PM

I was just running the histogram on Datamaster. It shows I'm running really rich around 1600-2000 rpm when MAF sensor reads 20-30 gps. That is exactly when I'm having my missing, stumbling problems. I ran it for awhile with the MAF unplugged with no change at all. Does anybody have any ideas as to what may be causing this.

WildBillyT · 12-23-2011, 08:11 PM

It is definetly running rich

Couple basic questions just to get them out of the way:

1.) How old are the plugs, what type and gap?
2.) How old are the O2 sensors?
3.) No tears in the intake tract?
4.) Can you hear any exhaust leaks?
5.) Did you trace for any vacuum leaks?

For other guys, here is his scan:

http://www.njfboa.org/WBT/AutoLog_001.uni

grazi · 12-23-2011, 08:17 PM

Dont know much about the plugs.
O2 sensors are most likely original (102,000 miles)
Definitely no tears in intake. Stock bellow-SLP cold air intake
NO exhaust leak
Almost positive no vacuum leaks.

JL8Jeff · 12-24-2011, 08:45 AM

If the EVAP stuff starts going bad, it could basically act like a constant vacuum leak. Maybe try plugging off the EVAP hose. But it could be time for new O2 sensors as well. Do you know if there was any type of custom tune installed?

grazi · 12-24-2011, 08:52 AM

All of the vacuum lines going to the charcoal canister were bad so I replaced them. Could the canister be bad or plugged??. Im pretty sure there wasnt any tunes on it, an woman owned it since 95 or 96.

grazi · 12-24-2011, 08:58 AM

To plug the EVAP hose should I just unplug from TB and put avacuum cap on TB? Should I plug hose, too?? I didnt know I could run like that

sweetbmxrider · 12-24-2011, 03:22 PM

Just on the throttle body will do it, the other line will still vent fumes though. I let mine dump at the tank. I don't think that is 100% your problem though but I don't have datamaster on a working computer at the moment.

S.J.SLEEPER · 12-24-2011, 04:51 PM

stock ecm/pcm? stock chip? tuned?

grazi · 12-24-2011, 06:26 PM

No mods. no chips. no tunes. no nothing besides slp cold air intake. So if I unplug evap line and still runs rich and misfires would that rule out entire evap system??

JL8Jeff · 12-26-2011, 11:38 AM

Quote:

Originally Posted by grazi

No mods. no chips. no tunes. no nothing besides slp cold air intake. So if I unplug evap line and still runs rich and misfires would that rule out entire evap system??

That would rule out a vacuum leak in the EVAP system. Go over all the vacuum lines like the power brake booster, the PCV, etc. Maybe try swapping the MAF out with someone else to see if that is going bad. If the MAF is faulty, the stock programming may cause it to run rich to protect the engine from leaning out.

grazi · 12-26-2011, 03:19 PM

I have a spare MAF that I can swap.But I have the same runnung rich problem when I disconnect my MAF. Doesnt that rule it out?? Is it possible to have a vacuum leak from brake booster internally. maybe i can idle and wave around an unlit torch around booster to see if it changes idle

JL8Jeff · 12-26-2011, 09:59 PM

Quote:

Originally Posted by grazi

I have a spare MAF that I can swap.But I have the same runnung rich problem when I disconnect my MAF. Doesnt that rule it out??

Actually, I would think it should run differently with the MAF disconnected. It sounds like you're running in speed density mode or it's in limp home mode. The computer should be making changes based on the MAF readings, so no MAF readings and the same result sounds like the MAF could be bad. I would swap to a known good MAF and see what happens.

grazi · 12-27-2011, 05:31 AM

Good point. Ill try that later on today. Thanks

WildBillyT · 12-27-2011, 09:11 AM

Quote:

Originally Posted by JL8Jeff

Actually, I would think it should run differently with the MAF disconnected. It sounds like you're running in speed density mode or it's in limp home mode. The computer should be making changes based on the AMF readings, so no MAF readings and the same result sounds like the MAF could be bad. I would swap to a known good MAF and see what happens.

To Jeff's point, even if it's not throwing codes the MAF can be bad. I had that happen to me.

If the O2s are still original you may want to replace them just because you are due. Denso or AC Delco only though.

Pampered-Z · 12-27-2011, 11:38 AM

If you don't have any codes stored I'd start with a basic tune-up. Stumbluing at part throttle is also commonly caused by a stuck EGR or PCV valve that causes a basic vacuum leak and they won't throw a code.

Plug the hose between the ERG and the relay ( golf tee works nicely ) so that the ERG is blocked off. See if that helps. Also check the PCV valve is working properly.

Yes, you will always see some spark retard.

grazi · 12-27-2011, 03:50 PM

The PCV valve is working. One thing I noticed about my EGR when I took it off to clean it the other month, when i manualy squeeze it together, the shaft binds a little bit. I will try to block it off though.
When I talk about stumbling and missing at part full throttle, its not like a light miss or non noticeable type thing, sometimes it pings real bad and shutters like crazy.Its pretty undriveable. I will try to log on datamaster when it does it bad. The log that is on this thread hardly cut out that much on me.

sweetbmxrider · 12-27-2011, 08:05 PM

Try sticking a fuel pressure gauge on it? What kinda of fuel have you been using?

grazi · 12-27-2011, 08:08 PM

I cruised around with fuel pressure gauge the other day. Have 40-42 at full throttle and mid 30's at idle and cruise. Going off memory

grazi · 12-27-2011, 08:10 PM

Ive been using premium 92 or wahtever it is. I dont drive the car often so it has been sitting for maybe a couple months but happens even with good gas.