Bad city MPG
Team Owner
Joined: Sep 2003
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From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
See if the trend follows them or not.
Thread Starter
Race Director
Joined: Oct 2011
Posts: 16,089
Likes: 819
From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
As a reference point using my Tech,1 I always show in closed loop a pulse width of ~3.3 - 3.4ms on both banks. Yours seems very high for idle.
My 94 (stock) is an automatic which gets lower mileage then manual. My dash shows about 25 m/g under 65 mph. around town and mixed expressway I might average 20. But my dash says when strictly around town is around 15 - 18 m/g and of course it varies with conditions. A lot of time the darn m/g is sitting at 16.
Replaced my O2s last year and think I pulled the originals. Using my Tech1 they swung fine and with the new ones everything is still good and no real improvement (172,000). I replaced them cause I was chasing another problem at the time.
The BLMs look OK but what are they while driving at a steady speed?
This is just me, had the car since 03 and not much has really changed in performance. Digital readout seems to pretty much agree when I do a real mileage using actual miles and fuel.
Thread Starter
Race Director
Joined: Oct 2011
Posts: 16,089
Likes: 819
From: Dallas Texas
2025 C4 of the Year Finalist - Modified
FYI - Just saying
As a reference point using my Tech,1 I always show in closed loop a pulse width of ~3.3 - 3.4ms on both banks. Yours seems very high for idle.
My 94 (stock) is an automatic which gets lower mileage then manual. My dash shows about 25 m/g under 65 mph. around town and mixed expressway I might average 20. But my dash says when strictly around town is around 15 - 18 m/g and of course it varies with conditions. A lot of time the darn m/g is sitting at 16.
Replaced my O2s last year and think I pulled the originals. Using my Tech1 they swung fine and with the new ones everything is still good and no real improvement (172,000). I replaced them cause I was chasing another problem at the time.
The BLMs look OK but what are they while driving at a steady speed?
This is just me, had the car since 03 and not much has really changed in performance. Digital readout seems to pretty much agree when I do a real mileage using actual miles and fuel.
As a reference point using my Tech,1 I always show in closed loop a pulse width of ~3.3 - 3.4ms on both banks. Yours seems very high for idle.
My 94 (stock) is an automatic which gets lower mileage then manual. My dash shows about 25 m/g under 65 mph. around town and mixed expressway I might average 20. But my dash says when strictly around town is around 15 - 18 m/g and of course it varies with conditions. A lot of time the darn m/g is sitting at 16.
Replaced my O2s last year and think I pulled the originals. Using my Tech1 they swung fine and with the new ones everything is still good and no real improvement (172,000). I replaced them cause I was chasing another problem at the time.
The BLMs look OK but what are they while driving at a steady speed?
This is just me, had the car since 03 and not much has really changed in performance. Digital readout seems to pretty much agree when I do a real mileage using actual miles and fuel.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Is it all stock?
Those pulse widths are even high for a cold engine in open loop.
Any sensors feeding the ECM could impact the pulse widths.
I have hear LT1s have had intake manifold gasket leaks causing a lean condition. The ECM would then increase the fuel to get the A/F mixture correct.
Also check the EGR for a leak. May have to pull to get a good check on it.
It may be worth it go get a smoke test on the intake system just to make sure there is no leak.
I know on the 94 never to touch the throttle adjustment screw. The earlier Vetts had a procedure on how to adjust. But I would not mess with it if it says not to.
I assume you are reading long term fuel trim (BLM) rather than short.
I also put some new gaskets on the throttle body last year.
I would have to review some notes I have but I think if there is a vacuum leak, the IAC counts will be lowered and can be "0".
Does it ever fall out of closed loop once it goes into closed loop?
Those pulse widths are even high for a cold engine in open loop.
Any sensors feeding the ECM could impact the pulse widths.
I have hear LT1s have had intake manifold gasket leaks causing a lean condition. The ECM would then increase the fuel to get the A/F mixture correct.
Also check the EGR for a leak. May have to pull to get a good check on it.
It may be worth it go get a smoke test on the intake system just to make sure there is no leak.
I know on the 94 never to touch the throttle adjustment screw. The earlier Vetts had a procedure on how to adjust. But I would not mess with it if it says not to.
I assume you are reading long term fuel trim (BLM) rather than short.
I also put some new gaskets on the throttle body last year.
I would have to review some notes I have but I think if there is a vacuum leak, the IAC counts will be lowered and can be "0".
Does it ever fall out of closed loop once it goes into closed loop?
Thread Starter
Race Director
Joined: Oct 2011
Posts: 16,089
Likes: 819
From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Is it all stock?
Those pulse widths are even high for a cold engine in open loop.
Any sensors feeding the ECM could impact the pulse widths.
I have hear LT1s have had intake manifold gasket leaks causing a lean condition. The ECM would then increase the fuel to get the A/F mixture correct.
Also check the EGR for a leak. May have to pull to get a good check on it.
It may be worth it go get a smoke test on the intake system just to make sure there is no leak.
I know on the 94 never to touch the throttle adjustment screw. The earlier Vetts had a procedure on how to adjust. But I would not mess with it if it says not to.
I assume you are reading long term fuel trim (BLM) rather than short.
I also put some new gaskets on the throttle body last year.
I would have to review some notes I have but I think if there is a vacuum leak, the IAC counts will be lowered and can be "0".
Does it ever fall out of closed loop once it goes into closed loop?
Those pulse widths are even high for a cold engine in open loop.
Any sensors feeding the ECM could impact the pulse widths.
I have hear LT1s have had intake manifold gasket leaks causing a lean condition. The ECM would then increase the fuel to get the A/F mixture correct.
Also check the EGR for a leak. May have to pull to get a good check on it.
It may be worth it go get a smoke test on the intake system just to make sure there is no leak.
I know on the 94 never to touch the throttle adjustment screw. The earlier Vetts had a procedure on how to adjust. But I would not mess with it if it says not to.
I assume you are reading long term fuel trim (BLM) rather than short.
I also put some new gaskets on the throttle body last year.
I would have to review some notes I have but I think if there is a vacuum leak, the IAC counts will be lowered and can be "0".
Does it ever fall out of closed loop once it goes into closed loop?
I did have a code for the egr, May 2016. Now, with the new one, I can stall the engine by pushing on the EGR at idle. Makes me think EGR has no leaks?
I know that on a speed density engine, like mine, a vacuum leak would be a high idle. My desired rpm and actual rpm are at the most, plus or minus 100 rpm. To me, that indicates no vacuum leak. Even though the IAC is at zero. But, I will block off the throttle body and see if it stalls or not. Nor does the idle surge.
Yes correct, I am looking at long term fuel trim.
I'm not sure if it ever falls out of closed loop once it's already in closed loop. Will have to verify that.
Last edited by 1993C4LT1; Jan 14, 2017 at 07:03 PM.
Thread Starter
Race Director
Joined: Oct 2011
Posts: 16,089
Likes: 819
From: Dallas Texas
2025 C4 of the Year Finalist - Modified
A dumb question, at idle my TPS voltage is .57
And TPS percentage is 0, at idle. Since it's at 0% in idle, it's safe to say the throttle plates are not open too much?
And TPS percentage is 0, at idle. Since it's at 0% in idle, it's safe to say the throttle plates are not open too much?
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Burning Brakes
Joined: Mar 2005
Posts: 1,082
Likes: 115
From: Richmond Hill Ontario
You have to take a reading of your IAC and see where it is at idle. A good number for idle is between 40 - 60. Anything above that indicates that the throttle blades are too closed.
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Burning Brakes
Joined: Mar 2005
Posts: 1,082
Likes: 115
From: Richmond Hill Ontario
That means that the blades are too open. The IAC is trying to compensate at idle to adjust idle down, but is out of room to adjust. I suggest you read the IAC at idle and adjust the blades until IAC reads between 40-60
Thread Starter
Race Director
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
So even though my desired idle RPM vs actual RPM, are plus or minus 50 to 100 RPM at most. I would say it is adjusting it because the idle is not high? Not trying to argue, just trying to learn. There really are no vacuum leaks, so if I have to adjust the throttle blades I will. Will the blades being open too much cause a lean condition at idle only, or driving around as well? Or would it even cause it to run lean?
Burning Brakes
Joined: Mar 2005
Posts: 1,082
Likes: 115
From: Richmond Hill Ontario
internet hearsay suggests that having your throttle blades open at idle such as in your situation causes split BLM at idle. The belief / reason is that at idle the majority of the air entering the engine should be feed from the IAC passage and not from the Main intake manifold plenum. Whether this totally corrects split BLM or not is still questionable..but it is noted that it does help to some degree.
I say adjust your blades to put your IAC counts at idle around 40 counts and tell us the results
I say adjust your blades to put your IAC counts at idle around 40 counts and tell us the results
Last edited by FrankieD; Jan 15, 2017 at 11:35 AM.
Thread Starter
Race Director
Joined: Oct 2011
Posts: 16,089
Likes: 819
From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Screw it, Ill do it tomorrow. I would do it now, but it's too rainy. Don't want the car idling in the garage till it warms up either.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
internet hearsay suggests that having your throttle blades open at idle such as in your situation causes split BLM at idle. The belief / reason is that at idle the majority of the air entering the engine should be feed from the IAC passage and not from the Main intake manifold plenum. Whether this totally corrects split BLM or not is still questionable..but it is noted that it does help to some degree.
I say adjust your blades to put your IAC counts at idle around 40 counts and tell us the results
I say adjust your blades to put your IAC counts at idle around 40 counts and tell us the results
Thread Starter
Race Director
Joined: Oct 2011
Posts: 16,089
Likes: 819
From: Dallas Texas
2025 C4 of the Year Finalist - Modified
It did stop raining for a while yesterday. So I checked for vacuum leaks again by blocking off the throttle body. I used 5 microfiber towels and my hand. The car did stall. So I believe it's safe to say no vacuum leaks.
Thread Starter
Race Director
Joined: Oct 2011
Posts: 16,089
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Car runs great, that's for sure. But the IAC at 0 I need to fix. Going to ohm the IAC valve to be sure. I guess if I mess with the TB screw, I can put it back in the factory position if it doesn't bring the counts up. Will mark it before I move the screw. Whenever I have time.
Last edited by 1993C4LT1; Jan 17, 2017 at 12:38 PM.