Abs light + dyno day= fail

[b_dike]

So a little back ground. My abs light started coming on intermittently last year, but for the last several months it comes on within minutes or even seconds of starting the car. It's not been a big deal really since I always manually turn off traction control.

I know with the abs light on trac control automatically turns off. So why when on the dyno would the car not rev past 4600 rpm... Every time (4 pulls).

Car runs great all the way through 6k on the street to and from the dyno, which is why I suspect the abs. Does it have something to do with the front wheels not spinning? Even though trac control is off.

Car made 426rwhp/ 480 rwtq @ 4600rpm

For comparison 3 years ago it made 455/501

How should I go about fixing this? Is there anyway to see which sensor is faulty or if its the abs module itself?

Thanks
Brian

 

[brian97cobra]

the abs lamp usually always comes on when on the dyno because the car sees the rear wheels turning and not the front. sounds like another issue honestly. what the heck did the tuner say.....?

 

[b_dike]

the abs lamp usually always comes on when on the dyno because the car sees the rear wheels turning and not the front. sounds like another issue honestly. what the heck did the tuner say.....?

The light has been on well before the dyno day. The tuner didn't know much about it. He just asked if my trac control was off. Of coarse it was... Has to be if abs lamp is on, correct?

It's not off in the tune though... Would it be possible to dyno the car all the way with the trac control disabled in the tune? Even with the abs lamp on...

 

[brian97cobra]

you can turn on the trac control with the button by the radio/shifter. that will not cause the abs lamp to come on

with the trac off in the tune the "trac control" lamp will always be lit up and that is fine. but again it will not cause the abs lamp to come on.

its as though you have some sort of neutral rev limiter active in your tune in my opinion. but there are other things it could be.

do you have a 2 step on the car? msd or accel coils?

 

[MalcolmV8]

To bad we don't know anyone local with an ABS code reader. You can unplug the harness from the ABS sensor and check it with an ohm meter. If it shows infinite amounts of ohms (no circuit) it's bad. Worth a shot. I'm thinking our cars have a sensor on each front wheel and one on the diff but I'd have to go look at my car to be 100% sure.
Might as well check them and if one of them shows open circuit replace it. Might be all you need.

 

[brian97cobra]

To bad we don't know anyone local with an ABS code reader. You can unplug the harness from the ABS sensor and check it with an ohm meter. If it shows infinite amounts of ohms (no circuit) it's bad. Worth a shot. I'm thinking our cars have a sensor on each front wheel and one on the diff but I'd have to go look at my car to be 100% sure.
Might as well check them and if one of them shows open circuit replace it. Might be all you need.

all 4 wheels have a sensor.

usually only some truck and some cars have the rear sensor in the diff.

but all 99-04 cobras have 4 wheel abs and sensors on all 4 wheels


I have a code reader but that does you no good im in Georgia.....

but you may try some parts places so may have a scanner that will read srs and abs codes.

if not go to www.obd365.com and search they are dirt cheap there....

our cars are known for the abs module to go bad. you can change just the electronics and not the whole unit for cheap. usually can get a used abs module for $75-150 bucks.



but back to the original problem I don't believe his abs is the culprit of the dyno "issue"

 

[b_dike]

What is a neutral rev limiter? I've seen this on my hand held, but just assumed it's just a rev limiter when the car's in neutral. Lol Which wouldn't be the case on the dyno...

 

[MalcolmV8]

all 4 wheels have a sensor.

usually only some truck and some cars have the rear sensor in the diff.

but all 99-04 cobras have 4 wheel abs and sensors on all 4 wheels

Well that'll make it much easier. I've never had to mess with the ABS on my car beyond moving the ABS unit up front back a little when fitting the Mishimoto radiator and ultimately ended up taking it out.
Although I've had to replace both half shafts on my car and don't recall there been an exciter ring or sensor at the hub. That's why I was thinking one in the diff. Guess I should pay more attention

 

[b_dike]

Maybe I should try and do a burnout. See if it let's me rev past 4600rpm... I wonder if there could be some kind of fail safe enabling trac control despite the abs lamp???

 

[MalcolmV8]

What is a neutral rev limiter? I've seen this on my hand held, but just assumed it's just a rev limiter when the car's in neutral. Lol Which wouldn't be the case on the dyno...

In the tune there are multiple rev limiter options, maximum output shaft speed and a host of others that don't all have very good help files explaining so it can be a little confusing. There is a rev limit in gear and a rev limit in neutral option so you can set them independently. However the help file in SCT PRP says not all car ECUs honor the neutral rev limiter and just use it all the time.
I've always set both of mine to the same 7k rpms and never tested if our ECUs honor the neutral option independently or not. I doubt that's your issue though or you'd have the same issue on the street.

 

[brian97cobra]

In the tune there are multiple rev limiter options, maximum output shaft speed and a host of others that don't all have very good help files explaining so it can be a little confusing. There is a rev limit in gear and a rev limit in neutral option so you can set them independently. However the help file in SCT PRP says not all car ECUs honor the neutral rev limiter and just use it all the time.
I've always set both of mine to the same 7k rpms and never tested if our ECUs honor the neutral option independently or not. I doubt that's your issue though or you'd have the same issue on the street.

not true if he has one on and the car does not think its moving... it would shut down cylinders like a "2-step"

if your using an sct then make sure those settings are off.

I suppose you can try to do a burn out before you turn it off and see of that does it. but the safe way to check would be to put the rear end up on jack stands and then run the car in drive and see if it still stops at 4,600 rpm's. then make sure the settings are off in the sct tune and try it again.

if you do it on jack stands id put run it thru the gears and then try it in 4th just like it was on the dyno.... but down flipping mat the gas as you wont have any load on the car and it will spin up very fast. don't want you to blow shit up.

just some good advise and a good start

 

[b_dike]

In the tune there are multiple rev limiter options, maximum output shaft speed and a host of others that don't all have very good help files explaining so it can be a little confusing. There is a rev limit in gear and a rev limit in neutral option so you can set them independently. However the help file in SCT PRP says not all car ECUs honor the neutral rev limiter and just use it all the time.
I've always set both of mine to the same 7k rpms and never tested if our ECUs honor the neutral option independently or not. I doubt that's your issue though or you'd have the same issue on the street.

I'll check that out tomorrow... See what it's set at.

 

[b_dike]

not true if he has one on and the car does not think its moving... it would shut down cylinders like a "2-step"

if your using an sct then make sure those settings are off.

I suppose you can try to do a burn out before you turn it off and see of that does it. but the safe way to check would be to put the rear end up on jack stands and then run the car in drive and see if it still stops at 4,600 rpm's. then make sure the settings are off in the sct tune and try it again.

if you do it on jack stands id put run it thru the gears and then try it in 4th just like it was on the dyno.... but down flipping mat the gas as you wont have any load on the car and it will spin up very fast. don't want you to blow shit up.

just some good advise and a good start

Thank you, yes it's a good start. I'll report back with what I find.

Hopefully that'll be it, but who knows...

 

[b_dike]

Way to curious to sleep, so I checked... Both rev limiters are set @7k

Looks like I may need to do a burnout at work tomorrow. Lol

 

[brian97cobra]

Way to curious to sleep, so I checked... Both rev limiters are set @7k

Looks like I may need to do a burnout at work tomorrow. Lol

I personally turn those off because ive seen them have issues on even at 7k....

 

[MalcolmV8]

Way to curious to sleep, so I checked... Both rev limiters are set @7k

Looks like I may need to do a burnout at work tomorrow. Lol

That's to long. Do a burnout right now in the garage lol Although I'm not sure what that proves. We already know when your front wheels aren't turning it cuts you out. You need to check the ABS sensors with a digital multimeter and find the bad one. Replace it and confirm your ABS light goes off. Not sure if a reset procedure is in order or not for the light to go out.

 

[brian97cobra]

That's to long. Do a burnout right now in the garage lol Although I'm not sure what that proves. We already know when your front wheels aren't turning it cuts you out. You need to check the ABS sensors with a digital multimeter and find the bad one. Replace it and confirm your ABS light goes off. Not sure if a reset procedure is in order or not for the light to go out.

no reset procedure just install new sensor. it self test when first started and then when driving and then when stopping.

but my money is not on a bad sensor but the abs unit itself. but again you can get just the electronic module and change it without even breaking open a brake line.


get the hoe scanned. but it will be tricky as sometimes it will not leave a hard fault when the lamp comes on and then goes off. if its on and stays on get it scanned and then report back the codes.

 

[brian97cobra]

if you pay pal me $200 bucks ill send you my scanner to borrow. when you send it back ill refund you $150. shipping with insurance will be about $25 bucks and ill pocket $25.

let me know if this will help you

my scanner does all obd 2 cars cel, srs, and abs.

 

[b_dike]

I personally turn those off because ive seen them have issues on even at 7k....

I didn't see an option to turn it off. I'll look again in the morning.

That's to long. Do a burnout right now in the garage lol Although I'm not sure what that proves. We already know when your front wheels aren't turning it cuts you out. You need to check the ABS sensors with a digital multimeter and find the bad one. Replace it and confirm your ABS light goes off. Not sure if a reset procedure is in order or not for the light to go out.

Lol I was just thinking how pissed my whole street would be if I was out revving the car this late...

I doubt a reset procedure would do anything since the neg cable was disconnected while I replaced the clutch. I do remember that when I first started the car the light didn't come on for a couple mins...

 

[b_dike]

I personally turn those off because ive seen them have issues on even at 7k....

if you pay pal me $200 bucks ill send you my scanner to borrow. when you send it back ill refund you $150. shipping with insurance will be about $25 bucks and ill pocket $25.

let me know if this will help you

my scanner does all obd 2 cars cel, srs, and abs.

I appreciate that... I may take you up on that offer. First I'm gonna go over the basics tomorrow with a visual inspection, and cleaning most likely.