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Old 12-07-2011, 05:38 AM   #1 (permalink)
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Default Need OBD-II Live Data comparison readings 1997 3.0 Vulcan(pushrod)

1997 GL 3.0 Vulcan (pushrod-OHV)

My altitude is 700ft, outside temp is 15 F, IAT Sensor is showing 17 F in motion at 45mph.

I'm having a problem with a high idle (1200 RPM) at cold start, this has been happening since back into the summer. I usually wait SEVERAL minutes until it revs down to about 1000 RPM before I shift into gear, but when it's this cold out, it takes even longer to rev down, and even at 1000 RPM I still don't like the idea of the sudden shock to the tranny. I have some Live Data Sensor readings that I hope someone can give me their results in a relatively close altitude and temp.

at Idle, MAF shows .691-.732 lb/min
at 45mph, MAF shows 2.1-2.6 lb/min

TPS with foot off pedal shows 18.8%, at full press, it shows 92.5%

Shouldn't the TPS range be 0-100%? The linearity between 18.8-92.5% is smooth and consistent, no dead spots....

I unplugged my MAF and it brought the idle down, so it seems like an obvious bad MAF, but i would still like to hear other peoples readings of TPS and MAF. thanks to anyone who can take the time to help.
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Old 12-07-2011, 08:43 AM   #2 (permalink)
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Quote:
Originally Posted by 97glinkc View Post
1997 GL 3.0 Vulcan (pushrod-OHV)

My altitude is 700ft, outside temp is 15 F, IAT Sensor is showing 17 F in motion at 45mph.

I'm having a problem with a high idle (1200 RPM) at cold start, this has been happening since back into the summer. I usually wait SEVERAL minutes until it revs down to about 1000 RPM before I shift into gear, but when it's this cold out, it takes even longer to rev down, and even at 1000 RPM I still don't like the idea of the sudden shock to the tranny. I have some Live Data Sensor readings that I hope someone can give me their results in a relatively close altitude and temp.

at Idle, MAF shows .691-.732 lb/min
at 45mph, MAF shows 2.1-2.6 lb/min

TPS with foot off pedal shows 18.8%, at full press, it shows 92.5%

Shouldn't the TPS range be 0-100%? The linearity between 18.8-92.5% is smooth and consistent, no dead spots....

I unplugged my MAF and it brought the idle down, so it seems like an obvious bad MAF, but i would still like to hear other peoples readings of TPS and MAF. thanks to anyone who can take the time to help.
TPS can not be zero or 100%

Has to be ~15-90. Exact numbers not required.

System learns what is there.

High idle often caused by IAC or PCV system leaks, or other vacuum leaks.

-chart-
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Old 12-07-2011, 10:43 AM   #3 (permalink)
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What are the long term fuel trims for each bank at idle and at crusing speeds?
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Old 12-07-2011, 02:43 PM   #4 (permalink)
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Chart - After more thought, I see the logic now of the system learning the TPS limits, would allow looser manufacturing tolerances with the sensor without requiring "lab-grade" accurancy during production. The IAC was my first thought too, but once I unlugged the MAF and it idled good it kind fo shifted my suspicions. About 3 years ago I had an identical 97 3.0 vulcan, and it exhibited the EXACT same problem, on that car I replaced the IAC and no improvement. Remembering that just made me assume more then likely that I would have the same issue with this one. Not that it relates to this topic I started, i've only had one car with a verified failed IAC, it was a 90 SuperCoupe Tbird, I was sitting at a Sonic Drive In eating with the engine idling and all at once the engine revved to 3500 RPM and wouldn't back off for anything, all the carhops went running away thinking I was crazy and about to ram them! Spent the next few hours walking to an autoparts store and popping the hood while in the bay at Sonic... How embarassing.... I saw your 'test procedure' on another post relating to idle problems, i tried it; engine warm, in Neutral, A/C Off, Lights off. With the Live Data scanner plugged in, my RPMS in Neutral were 900, put into Drive and RPM's dropped and then stabilized at 715.

Jeff -

@ 45 mph on cruise, mild up-n-down hills, engine warmed in closed-loop:
LTFT B#1 ran from 2.3 - 7.0, seemed to hover around 6.2 mostly.
LTFT B#2 ran from 2.3 - 7.0, seemed to hover around 5.4 mostly.


@ idle, in Park, engine warmed in closed-loop:
LTFT B#1 ran from -2.3 - -0.7
LTFT B#1 ran from -2.3 - -0.7

The overall ranging of the the two banks is identical, but they never stayed the same with each other during testing, they were all over the place when compared to each other, but after recording the high and low of each they ranged the same, is that normal that the overall range is the same yet they never agree with each other at any one moment?


Thanks for the replies from both of you, any help is much appreciated.

Last edited by 97glinkc; 12-07-2011 at 08:56 PM. Reason: accidentally type STFT B#2 @ Idle and mean to type LTFT.
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Old 12-07-2011, 08:29 PM   #5 (permalink)
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If unplugging the MAF makes the car run better, it usually means you have a vacuum leak or the MAF is dirty/bad. I'm leaning more towards a dirty MAF because they overestimate airflow at idle and underestimate airflow at higher speeds and your fuel trims support this. Get a can of MAF cleaner and clean your MAF.

Those LTFT's aren't real bad, but they are starting to get a little high. Again, clean the MAF, do a clear trouble codes with the scanner to reset the fuel trims, then drive it a while and see if the LTFT's improve.

The engine will stay about 1000 rpm for several minutes when it's cold out until it warms up enough. Shifting it into gear at that speed won't hurt it. Your warm idle speeds are normal, so I think the IAC is okay for now. You can replace it if you like.
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Old 12-07-2011, 08:47 PM   #6 (permalink)
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Behlinla - Good point you make about the fuel trims corresponding to a dirty MAF. I will try to clean it and see what happens. In trying to decipher my fuel trims (new at Fuel Trims) it appears the ECM thinks the car is running rich at warm idle and therefor decreasing fuel delivery, and running lean at cruising speed and richening the fuel?

Does clearing codes reset trims(By the way, no codes except when i unplugged the MAF for testing)? I was under the impression that I would have to disconnect battery power for a period of time to do a Hard-Reset on the trims?

Does MAF play a role in Idle Speed during Open Loop Startup?

Approximately how long from the time the car is started until it enters Closed Loop? Is it entirely dependent on the O2's getting to temp? Or combination of O2's and ECT?
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Old 12-07-2011, 09:02 PM   #7 (permalink)
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By the way, what is the component of the MAF that gets 'dirty' and needs cleaning? Is it the heated wire element that gets a gunky coating on it from small debris that make it through the filter, or is it more like an oxidation of the wire element? I know your not supposed to ever touch the wire, nor should you use oiled-filters (K&N) because of the oil vapors collecting on it. I'm having severe money problems right now, as seems everyone is, do you think i could take a Q-tip and some 91% rubbing alcohol and clean the element or would that be about as effective as a fart in a tornado?
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Old 12-07-2011, 09:19 PM   #8 (permalink)
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Ditch the Q-tips! Do not touch the wire with anything but solvent since it is extremely fragile. You will break the wire with the Q-tip. Also, Q-tips leave little cotton fibers behind. The bottle of MAF cleaner is a lot cheaper than a new MAF. If you're really in a pinch, find a way to gently squirt the IPA on the sensor. Let it air dry only.

The MAF heated wire gets dirty from oil and soot that works it's way back from the PCV. Granny cars and cars driven in the city usually have more deposits since the PCV is spewing more crap into the intake. If this is the case, your throttle body might also be a little dirty (especially the throttle backside).
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Old 12-07-2011, 09:29 PM   #9 (permalink)
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Quote:
Originally Posted by 97glinkc View Post
Behlinla - Good point you make about the fuel trims corresponding to a dirty MAF. I will try to clean it and see what happens. In trying to decipher my fuel trims (new at Fuel Trims) it appears the ECM thinks the car is running rich at warm idle and therefor decreasing fuel delivery, and running lean at cruising speed and richening the fuel?

Does clearing codes reset trims(By the way, no codes except when i unplugged the MAF for testing)? I was under the impression that I would have to disconnect battery power for a period of time to do a Hard-Reset on the trims?
Yes, clearing codes usually resets the fuel trims. The battery method is more common because people don't have code readers to do it properly.

Quote:
Does MAF play a role in Idle Speed during Open Loop Startup?
The MAF has an indirect role. When you first start the car, the PCM wants to maintain the high idle speed first and foremost. It might use the MAF to roughly estimate the A/F ratio until the O2 sensors are warmed up enough.

Quote:
Approximately how long from the time the car is started until it enters Closed Loop? Is it entirely dependent on the O2's getting to temp? Or combination of O2's and ECT?
Some scanners will tell you if your car is open or closed loop. On newer cars, you can be in closed loop in as little as 10-15 seconds on cold car thanks to O2 sensor heaters. If your O2 sensors are a little worn and take a little longer to heat up, then maybe a minute. It's faster than you think. The car will still maintain a fast idle until the car is completely warmed up some minutes later, but it's running in closed loop.
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Old 12-07-2011, 10:39 PM   #10 (permalink)
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Quote:
Originally Posted by 97glinkc View Post
Chart - After more thought, I see the logic now of the system learning the TPS limits, would allow looser manufacturing tolerances with the sensor without requiring "lab-grade" accurancy during production. The IAC was my first thought too, but once I unlugged the MAF and it idled good it kind fo shifted my suspicions. About 3 years ago I had an identical 97 3.0 vulcan, and it exhibited the EXACT same problem, on that car I replaced the IAC and no improvement. Remembering that just made me assume more then likely that I would have the same issue with this one. Not that it relates to this topic I started, i've only had one car with a verified failed IAC, it was a 90 SuperCoupe Tbird, I was sitting at a Sonic Drive In eating with the engine idling and all at once the engine revved to 3500 RPM and wouldn't back off for anything, all the carhops went running away thinking I was crazy and about to ram them! Spent the next few hours walking to an autoparts store and popping the hood while in the bay at Sonic... How embarassing.... I saw your 'test procedure' on another post relating to idle problems, i tried it; engine warm, in Neutral, A/C Off, Lights off. With the Live Data scanner plugged in, my RPMS in Neutral were 900, put into Drive and RPM's dropped and then stabilized at 715.

Jeff -

@ 45 mph on cruise, mild up-n-down hills, engine warmed in closed-loop:
LTFT B#1 ran from 2.3 - 7.0, seemed to hover around 6.2 mostly.
LTFT B#2 ran from 2.3 - 7.0, seemed to hover around 5.4 mostly.


@ idle, in Park, engine warmed in closed-loop:
LTFT B#1 ran from -2.3 - -0.7
LTFT B#1 ran from -2.3 - -0.7

The overall ranging of the the two banks is identical, but they never stayed the same with each other during testing, they were all over the place when compared to each other, but after recording the high and low of each they ranged the same, is that normal that the overall range is the same yet they never agree with each other at any one moment?


Thanks for the replies from both of you, any help is much appreciated.
See pic of chart of long term fuel trims. This from '01 DOHC which is running as perfect as it gets. That period is normal driving, and my '03 DOHC looks very much the same.

Long term is not exactly a good name. In that chart the sample is every 5 seconds. Long term is maybe a few seconds per adjustment. Now, when running at a constant speed, constant throttle, that chart settles down, but jumps when the throttle is moved quickly.

-chart-

Last edited by chartmaker; 06-27-2014 at 10:20 PM.
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