hesitation
10-30-04, 06:12 AM
#46
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I disconnected my VAF today and all of the power is back. Car feels much stonger from idle to redline. CEL came on after I disconnected it and the car will stall when in park or neutral or drive (w/ the AC off). The car idles evenly with the AC on and in gear, which is fine by me for now. I'm guessing I've got a bad 02 sensor and its leaning out the mixture.
How many 02 sensors do our SC400s have?
How many 02 sensors do our SC400s have?
10-31-04, 11:52 AM
#51
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The Solution (I hope)
I have a 1993 SC400 with 104,000 miles and it has been hesitating since 90,000 miles or so. Mine is usually much worse when it's cold.
I have been following this thread to try and gain some insight into what the f*** has been happening with these cars to cause such a rash of hesitation problems. I think the key is the fact that disconnecting the MAF causes the engine to run better.
So, having the factory service manuals, I looked up the MAF and how it works, as well as the troubleshooting flow charts. Sure enough, under the symptom of hesitation, the second thing to check is the MAF (The first thing to check is the park-neutral switch). I ruled out my switch for various good reasons, and looked at how the MAF works on these cars. It uses a pillar in the airflow to generate vortices, and an infrared emitting diode & sensor to detect the number vortices generated per unit of time. The faster the airflow, the more vortices are generated per unit of time. If the sensor is sensitive enough to detect a tiny vortice of air, my guess is that ANY dirt or grime in this area will seriously impair its' ability to accurately measure air flow.
So I went to the car store, bought some electronics parts cleaner, took off my MAF, and CAREFULLY cleaned the inside of the thing. I re-assembled the mess and test drove it. The hesitation seems to be completely gone.
The MAF did not appear to be very dirty at all, but I'm sure it doesn't take much more than a tiny amount of dirt, oil, grime or other contaminant to spoil it's operation. I would reccommend not touching any of the parts, even if they are all plastic. I'm sure even a finger print from a "clean" finger would be enough to screw things up! Also, be sure to get a cleaner that's safe for most plastics. The first electrical contact cleaner I found was labeled as not suitable for most plastic.
Also, after spraying a bunch of the cleaner through the MAF, the parts get really cold and moisture condenses on them. I didn't dry it off for fear of contaminating the surfaces, and I didn't blow it dry with compressed air 'cause that has enough oil in it to coat those sensors. I re-assembled it and started it with moisture still on it. Wow. The engine wouldn't hardly idle, and stalled several times. The CEL and TRAC Off lights came on intermitently. After a few minutes of driving everything was back to better-than-normal as I thought it would be. The engine heat and air flow dried the moisture. This also tells me that this sensor is super sensitive to ANYTHING that gets on it! I cleared the memory by disconnecting the EFI fuse for a minute and it hasn't hesitated yet.
A cold start tommorrow morning will tell for sure.
Hope this helps!
I have been following this thread to try and gain some insight into what the f*** has been happening with these cars to cause such a rash of hesitation problems. I think the key is the fact that disconnecting the MAF causes the engine to run better.
So, having the factory service manuals, I looked up the MAF and how it works, as well as the troubleshooting flow charts. Sure enough, under the symptom of hesitation, the second thing to check is the MAF (The first thing to check is the park-neutral switch). I ruled out my switch for various good reasons, and looked at how the MAF works on these cars. It uses a pillar in the airflow to generate vortices, and an infrared emitting diode & sensor to detect the number vortices generated per unit of time. The faster the airflow, the more vortices are generated per unit of time. If the sensor is sensitive enough to detect a tiny vortice of air, my guess is that ANY dirt or grime in this area will seriously impair its' ability to accurately measure air flow.
So I went to the car store, bought some electronics parts cleaner, took off my MAF, and CAREFULLY cleaned the inside of the thing. I re-assembled the mess and test drove it. The hesitation seems to be completely gone.
The MAF did not appear to be very dirty at all, but I'm sure it doesn't take much more than a tiny amount of dirt, oil, grime or other contaminant to spoil it's operation. I would reccommend not touching any of the parts, even if they are all plastic. I'm sure even a finger print from a "clean" finger would be enough to screw things up! Also, be sure to get a cleaner that's safe for most plastics. The first electrical contact cleaner I found was labeled as not suitable for most plastic.
Also, after spraying a bunch of the cleaner through the MAF, the parts get really cold and moisture condenses on them. I didn't dry it off for fear of contaminating the surfaces, and I didn't blow it dry with compressed air 'cause that has enough oil in it to coat those sensors. I re-assembled it and started it with moisture still on it. Wow. The engine wouldn't hardly idle, and stalled several times. The CEL and TRAC Off lights came on intermitently. After a few minutes of driving everything was back to better-than-normal as I thought it would be. The engine heat and air flow dried the moisture. This also tells me that this sensor is super sensitive to ANYTHING that gets on it! I cleared the memory by disconnecting the EFI fuse for a minute and it hasn't hesitated yet.
A cold start tommorrow morning will tell for sure.
Hope this helps!
10-31-04, 12:01 PM
#52
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VAF sen
Thanks for reply. Mine always runs good for a while after disconnecting ECU but problem returns.
Let me know how it runs in a couple of days
Let me know how it runs in a couple of days
11-02-04, 03:37 PM
#54
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2 days, 200 miles and 6 cold starts later I still can't get it to hesitate at all. I REALLY hope it stays this way...
I'd like to know if yuz guys try this and it works or not.
Piece
I'd like to know if yuz guys try this and it works or not.
Piece
11-03-04, 12:16 PM
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The VAF must be removed from vehicle to clean it.
The grill at the intake of the VAF, which has all those honeycombed shaped holes, is only there to straighten the air flow, so there will be no vortices in the air as it enters the metering area. This is important because if the air is turbulent (not straight) inside the metering area, there is no sense in counting the vortices to determine the volume.
The next thing the air encounters in its path through the meter is the “pillar” or “Vortex Generating Object” as it is labeled in the manual. The pillar is a straight piece of plastic that passes across the air stream from one side of the VAF housing to the other. As the air passes over the pillar, vortices are produced on the downwind side of it. These vortices apparently move a mirror back and forth, and an infrared sensor counts these motions by sensing the light reflected off the mirror.
I don’t know and can’t see where the diode, mirror or sensor are inside my VAF, but I suspect they are embedded inside the plastic of the pillar. My VAF also has a plastic protrusion downstream of the pillar which may house one of the components.
Therefore, if my suspicion is correct, cleaning these plastic parts allows the VAF to function properly. Cleaning the surrounding metal housing and intake grill prevents the plastic from being quickly re-contaminated by the air flow moving the dirt from one surface to another.
So yea, I cleaned the grill and the entire inside of the VAF. I could see that a very light film of grime had been removed from the plastic and the honeycomb grill as I cleaned them because they were brighter and smoother looking. If you need to touch anything inside the VAF, do it before you clean them.
Also, it was the “Contact Cleaner” that I avoided because it was labeled “not safe for most plastics.” I used the CRC “QD Electronic Cleaner” because it was labeled as “Harmless to most plastics…”
Hope this helps.
Boy, will I be embarassed if my car starts hesitating again in few more daze....
But I look at it this way: It cost $6 and an hour of my time to clean it. If it doesn't work in the long run, it was still worth the cash and effort to know that the VAF isn't the problem. And if it does continue working correctly, it's a very cheap fix!
Piece
The grill at the intake of the VAF, which has all those honeycombed shaped holes, is only there to straighten the air flow, so there will be no vortices in the air as it enters the metering area. This is important because if the air is turbulent (not straight) inside the metering area, there is no sense in counting the vortices to determine the volume.
The next thing the air encounters in its path through the meter is the “pillar” or “Vortex Generating Object” as it is labeled in the manual. The pillar is a straight piece of plastic that passes across the air stream from one side of the VAF housing to the other. As the air passes over the pillar, vortices are produced on the downwind side of it. These vortices apparently move a mirror back and forth, and an infrared sensor counts these motions by sensing the light reflected off the mirror.
I don’t know and can’t see where the diode, mirror or sensor are inside my VAF, but I suspect they are embedded inside the plastic of the pillar. My VAF also has a plastic protrusion downstream of the pillar which may house one of the components.
Therefore, if my suspicion is correct, cleaning these plastic parts allows the VAF to function properly. Cleaning the surrounding metal housing and intake grill prevents the plastic from being quickly re-contaminated by the air flow moving the dirt from one surface to another.
So yea, I cleaned the grill and the entire inside of the VAF. I could see that a very light film of grime had been removed from the plastic and the honeycomb grill as I cleaned them because they were brighter and smoother looking. If you need to touch anything inside the VAF, do it before you clean them.
Also, it was the “Contact Cleaner” that I avoided because it was labeled “not safe for most plastics.” I used the CRC “QD Electronic Cleaner” because it was labeled as “Harmless to most plastics…”
Hope this helps.
Boy, will I be embarassed if my car starts hesitating again in few more daze....
But I look at it this way: It cost $6 and an hour of my time to clean it. If it doesn't work in the long run, it was still worth the cash and effort to know that the VAF isn't the problem. And if it does continue working correctly, it's a very cheap fix!
Piece
11-03-04, 01:15 PM
#57
WOW! I did mine a little differently than you did but achieved the same results, in under 15mins!!!
You'll need a phillips screw driver..
Electronic parts cleaner like CRC...
A hairdryer...
I removed the element from the VAF housing. by removing the 3 phillips screws.
I cleaned the element with cleaner and a paper towel.
I disconnected the plug and cleaned it, and used a hair dryer to dry all the connections.
I re assembled everything and no hesitation!!! without reseting the ecu!
lots of black grease came on the paper towel, and it didn't even seem visible.
Now i'm curious to know, of who has the hesitation... are you running BFI intake? I am. maybe an adverse side effect to doing the BFI
You'll need a phillips screw driver..
Electronic parts cleaner like CRC...
A hairdryer...
I removed the element from the VAF housing. by removing the 3 phillips screws.
I cleaned the element with cleaner and a paper towel.
I disconnected the plug and cleaned it, and used a hair dryer to dry all the connections.
I re assembled everything and no hesitation!!! without reseting the ecu!
lots of black grease came on the paper towel, and it didn't even seem visible.
Now i'm curious to know, of who has the hesitation... are you running BFI intake? I am. maybe an adverse side effect to doing the BFI
11-03-04, 05:50 PM
#58
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VAF
If you look on the back side of the pillar, theres 2 small passages going up to the mirror/diode/sensor. Did you spray up inside these passages? I was hesitant about doing that, so just cleaned the outside of the pillar. Mine still hesitates. Also, I put my friends VAF in my car and it didn't make a difference, his car runs fine so I know thats not my problem. Glad that fixed yours, mine has another problem. Wondering if I have a bad connector somewhere, they all look ok??
11-03-04, 09:36 PM
#59
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Fastflyer - what year is your vehicle? I'm thinking the design is different - I took mine apart a while back and all I noticed was a triangular shaped rod, which I cleaned with no observeable difference.