Help with diagnosing
Thread Starter
Heel & Toe
Joined: Jul 2023
Posts: 18
Likes: 0
Help with diagnosing
I have a 89 C4 auto and it has a few problems. The car was bought with basically everything I wanted done to it already done, which was a bonus but I knew it was risky. Anyways, it is cammed with LTH, full exhaust. I believe it has a shift kit. It also has some sort of rear conversion going on as its on 315mm rears and coils. Maybe different gearing but not sure. I don't have the specs or build sheet for any of that, just what I've found from driving and looking at the car.
The problems:
The car will go from a stop to 30 mph and upshifting from first without any throttle (not a problem just interesting). The brakes work very well at speed, but as soon as I get to first gear its like they barely work, ABS turns on almost every time I stop, and I have to go pedal to the floor to fully stop. While doing highway speeds there is a noticeable whine, it gets louder the faster you go, and changes based on throttle. The car seems like it wants to launch from a stop, but it doesn't squeal tires AT ALL until it shifts from 1-2 (maybe this is normal, not sure). I can't get the car to do a burnout but I blame that on the brakes.
I have other problems but they don't seem to be related to any of this so won't bother mentioning. I guess my question is are these all connected to one part being faulty? They seem pretty related to me. My mechanic thinks my brake issue is vacuum based, but I don't buy it. I've thought about it for a while and I'm thinking it might be a possible Torque Converter issue? I'd like to hear some opinions from people who actually know things.
The problems:
The car will go from a stop to 30 mph and upshifting from first without any throttle (not a problem just interesting). The brakes work very well at speed, but as soon as I get to first gear its like they barely work, ABS turns on almost every time I stop, and I have to go pedal to the floor to fully stop. While doing highway speeds there is a noticeable whine, it gets louder the faster you go, and changes based on throttle. The car seems like it wants to launch from a stop, but it doesn't squeal tires AT ALL until it shifts from 1-2 (maybe this is normal, not sure). I can't get the car to do a burnout but I blame that on the brakes.
I have other problems but they don't seem to be related to any of this so won't bother mentioning. I guess my question is are these all connected to one part being faulty? They seem pretty related to me. My mechanic thinks my brake issue is vacuum based, but I don't buy it. I've thought about it for a while and I'm thinking it might be a possible Torque Converter issue? I'd like to hear some opinions from people who actually know things.
Burning Brakes
Joined: Aug 2008
Posts: 825
Likes: 216
From: Tampa, FL
I have a 89 C4 auto and it has a few problems. The car was bought with basically everything I wanted done to it already done, which was a bonus but I knew it was risky. Anyways, it is cammed with LTH, full exhaust. I believe it has a shift kit. It also has some sort of rear conversion going on as its on 315mm rears and coils. Maybe different gearing but not sure. I don't have the specs or build sheet for any of that, just what I've found from driving and looking at the car.
The problems:
The car will go from a stop to 30 mph and upshifting from first without any throttle (not a problem just interesting). The brakes work very well at speed, but as soon as I get to first gear its like they barely work, ABS turns on almost every time I stop, and I have to go pedal to the floor to fully stop. While doing highway speeds there is a noticeable whine, it gets louder the faster you go, and changes based on throttle. The car seems like it wants to launch from a stop, but it doesn't squeal tires AT ALL until it shifts from 1-2 (maybe this is normal, not sure). I can't get the car to do a burnout but I blame that on the brakes.
I have other problems but they don't seem to be related to any of this so won't bother mentioning. I guess my question is are these all connected to one part being faulty? They seem pretty related to me. My mechanic thinks my brake issue is vacuum based, but I don't buy it. I've thought about it for a while and I'm thinking it might be a possible Torque Converter issue? I'd like to hear some opinions from people who actually know things.
The problems:
The car will go from a stop to 30 mph and upshifting from first without any throttle (not a problem just interesting). The brakes work very well at speed, but as soon as I get to first gear its like they barely work, ABS turns on almost every time I stop, and I have to go pedal to the floor to fully stop. While doing highway speeds there is a noticeable whine, it gets louder the faster you go, and changes based on throttle. The car seems like it wants to launch from a stop, but it doesn't squeal tires AT ALL until it shifts from 1-2 (maybe this is normal, not sure). I can't get the car to do a burnout but I blame that on the brakes.
I have other problems but they don't seem to be related to any of this so won't bother mentioning. I guess my question is are these all connected to one part being faulty? They seem pretty related to me. My mechanic thinks my brake issue is vacuum based, but I don't buy it. I've thought about it for a while and I'm thinking it might be a possible Torque Converter issue? I'd like to hear some opinions from people who actually know things.
- The car will go from a stop to 30 mph and upshifting from first without any throttle (not a problem just interesting).
What is your rpm at idle? When The car is in park, and just sitting there... is the idle above 1,000 rpms? Generally, a healthy idle is around 900-1,000 rpms. If you have a vacuum leak, that increases the speed of the engine RPM at idle. It's like pushing the gas down, though you're not adding more fuel too so it's actually running a bit lean. Either way, that can lead to what you're seeing. If a car can accelerate on it's own, it means it's getting enough throttle to do so, and the transmission of course will shift once it gets to the proper speed. The ONLY other thing it could be is that you have a really low-stall torque converter that's engaging right off idle, but I'm kind of doubting that.
- The brakes work very well at speed, but as soon as I get to first gear its like they barely work,I'm inclined to agree with the mechanic here. A leaking power brake booster, or one that has a leak where or from where it's connected (as in, not getting vacuum), it means you're not getting any boost, and it has to rely purely on the mechanical pressure of your foot pressing down on the brake / master cyl. It could be other things of course... like a leaking caliper that's getting oil on the rotors, etc. Does the car pull at all... or it does brake proportionally... but just can't stop?
- ABS turns on almost every time I stop, and I have to go pedal to the floor to fully stop.Not sure I know what this could be... but the ABS works off a combination of wheel / speed sensors, and if they're misaligned or you've gone with different axles and the tone ring is off, or cracked... that could cause it too. Do you get an ABS warning light?
- While doing highway speeds there is a noticeable whine, it gets louder the faster you go, and changes based on throttle.This could be any number of things. Since it's speed related, it could either be gear whine from improperly installed differential gears, or it could be a failing wheel bearing.
I think some of them could be related (accelerating on its own, and failing brakes). Sounds like a leaking brake booster to me... but I'd need to know what your idle rpm typically is...
