Rear wheel speed sensors

[Paul Higg]

Hey Junk, you were right. The speed sensors were COMPLETELY covered in gunk. I used purple cleaner and a toothbrush and paper towels to clean the and blew shop air through the hole and a lot of crap came flying out. The teeth on the spindle looked brand new but the sensors were a mess. I took some photos of them.

Thanks for your help.

 

[Paul Higg]

I test drove it and it still does the same thing. When I punch the gas in turns the wide open throttle stops the pedal from going full travel. I think it's an ASR problem because it didn't do it when I shut off ASR. I have no idea how this system works so I'll have to read up on it and as for adjusting, well the book says you need a Tech 1 and I do not know where to get one nor do I have the cash for one right now. Any ideas?

 

[jmccloud]

ASR

The ASR senses when the rear wheels turn at a different speed than the fronts or each other. If the difference is great enough, some rear brakes are applied to the faster spinning wheel(s). If the difference is greater yet, the mechanism in the engine compartment decreases the throttle setting (yes, actually pushes against your foot) to reduce/prevent slipping.
First time I felt it I thought the throttle cable had snapped or jambed - very disturbing. My kids owned Corvettes and explained the ASR to me.
The ASR is almost essential when driving in the rain or on slick roads or on roads with debris (gravel, sand, etc). I believe the car handles better with the ASR off when the track conditions are good.
And yes, I replace the rear brakes about 3 times as often as the fronts.
Enjoy

 

[Toms007]

I test drove it and it still does the same thing. When I punch the gas in turns the wide open throttle stops the pedal from going full travel. I think it's an ASR problem because it didn't do it when I shut off ASR. I have no idea how this system works so I'll have to read up on it and as for adjusting, well the book says you need a Tech 1 and I do not know where to get one nor do I have the cash for one right now. Any ideas?

Paul, I actually think what you are experiencing is the ASR in action. What you are describing is exactly how the ASR is supposed to work. With ASR off you can spin the tires easily and in a turn with ASR off, the rear end could come right on around.

 

[Paul Higg]

Thanks guys. That was my hunch, that it was working as it was supposed to. Did you know the Boeing 767's I used to work on had this exact same system? I used to work on it. Magnetic pickups with the same sensors. Different computers and no physical cables but same concept. When I first felt it I thought something was loose down there. It also feels like a brick is pushing against your foot.

I have no DTC's, no lights, so I guess all is well.

Thanks a lot for your help.

 

[jrogensk]

Does the ASR light come on when it happens? I think mine says 'ASR Active' when the pedal jumps.

 

[Toms007]

Thanks guys. That was my hunch, that it was working as it was supposed to. Did you know the Boeing 767's I used to work on had this exact same system? I used to work on it. Magnetic pickups with the same sensors. Different computers and no physical cables but same concept. When I first felt it I thought something was loose down there. It also feels like a brick is pushing against your foot.

I have no DTC's, no lights, so I guess all is well.

Thanks a lot for your help.

Paul, the first time it happened to me I was thinking WTF? A brick against the foot is an accurate way to describe it. And yes, as jrogensk says below, the ASR active light should come on. I know that the first two or three times it happened to me I was too "what's going on?" to be looking at the ASR active light. But I have since then discovered that yes, the light does come on during these "escapades".

Does the ASR light come on when it happens? I think mine says 'ASR Active' when the pedal jumps.

 

[Paul Higg]

I too have been too spooked by it to look at the gauges. If I get a chance I will have the wife keep an eye on the light. There are certain roads where I can duplicate it. It ALWAYS happens when I am stopped, and I am taking a left or right turn (mostly left) and I punch the gas--hard. Good call, I will look for that light. IF I get the light does that indicate that it is normal?

 

[LT4man]

Yes!

SAVE THE

 

[John Robinson]

When I accelerate hard even in a straight line the ASR comes on. The other thing that I have noticed is that the engine will act like it is misfiring if I am at WOT.:crazy

 

[Paul Higg]

I've never had that happen, when I accelerate in a straight line. I did have what seemed like a misfire for the first time the other night however. I was at a friend's house and when I started it and drove away it sounded like it was running real rough. I hit the gas a little and it seemed like it misfired or even backfired. It was real sluggish. Then half a mile later it was okay.

Whenever I drive it cold I have this noise coming from the left side under the hood. I brought it to my mechanic and he said the C4's have something that cuts out a part of the manifold or something until it reaches a certain temp. This guy knows everything about Vettes and I trust him and he seems correct because after half a mile or so it goes away. He said it is very common on this car. I just have to take it in and have it fixed. He said it is nothing to worry about.

 

[Hib Halverson]

(snip)

Whenever I drive it cold I have this noise coming from the left side under the hood. I brought it to my mechanic and he said the C4's have something that cuts out a part of the manifold or something until it reaches a certain temp. This guy knows everything about Vettes and I trust him and he seems correct because after half a mile or so it goes away. He said it is very common on this car. I just have to take it in and have it fixed. He said it is nothing to worry about.

I'm sorry, but your "mechanic" may know somewhat less than "...everything about Vettes...".

There is no system on an LT1 engine that "cuts out part of the manifold" while the engine is warming up.

The noise you hear from the left side of the engine during warm up may or may not be a problem, but typically, if your LT1 is in good condition and its accessories are functioning properly, you should not hear any noise that changes significantly (in loudness or pitch) as the engine warms.

 

[Paul Higg]

I wonder what it could be. It sounds funny till it warms up, usually a half a mile then goes away. I'll call him and see if he'll clarify what it is and get back to you. This guy is my age, about 48 and his Dad owns Corvette Country and he knows a lot about C4's especially. They overhaul Vettes. You should see this place. Him and his Dad have won dozens of trophies, been on many covers of Vette magazines, and they can take a Vette and totally modify the frame and put on another body, all that good stuff. Right now he's building his Dad a 78 anniversary edition. They have a brand new modified C5 chassis and he's putting on a 78 body with everything new. All from scratch. John can really paint. This car is going to be shown and then Ben (his Dad) is going to sell it later. The work they do is incredible. He has two Vettes in the showroom with brand new C5 chassises and brand new reproduction 68? bodies. The Vettes with the rear air scoops, anyway, he's selling them each for $200,000.

 

[Paul Higg]

Okay, I just talked with my mechanic friend at Corvette Country and this is what he told. First, I need a new exhaust manifold. He said that when the car is first started it is in what's called open loop mode. It uses preset fuel mixtures and base timing because the ECM is not making adjustments. The ECM needs to see a certain temp from the temp sensors and when it does it goes close trim or out of open loop mode. Hence the exhaust manifold making that noise then clears up when driven till it is warm enough.

Paul