moespeeds

I just got done with a full rebuild on my 2000 FRC. Brakes were ok before I took it apart. Installed a new LS6 engine with a Texas Speed 228R Cam 112 LSA. Took the car out for a test ride last sat for about 6 miles and it was throwing a C1247 code and the brake pedal was very inconsistent. I had brakes all the time, but sometimes I wouldn't get pedal pressure until it hit the floor, and other times I would have it right away. Pumping up the pedal would bring the brakes back, but any amount of time off the brakes and I'd lose the pedal. Code will clear using the DIC and will stay away if I keep pumping the brakes, but any amount of time off the brakes and I lose the pedal and the code comes back. After the test drive I found the front left caliper locked up solid, and after taking it apart ended up replacing it with a new one. Just started the car on the lift, and still have the same problem. I pressure bled the system multiple times, no air is in the line. With the engine off I have a very solid, consistent pedal, but as soon as I fire it up the problem starts. I'm thinking it has something to do with the brake booster, and a buddy is telling me the cam could be causing vacuum issues. Any input is really appreciated, I've had a host of problems since getting this car back together, and this is the last gremlin and I really want to be on track next weekend! Thanks!

moespeeds

FYI during the test ride I got it into the ABS many times trying to get the whole system working, with no positive outcome. I've checked the whole system for leaks, and can't see any vacuum leaks. If I pull the differential plug on the portioning block the code will not come back, but still have the inconsistent pedal.

Hi Volts Z06

Did you bleed the system using a scanner to release any air trapped in the ABS unit?

You might want to also check all your grounds. I replaced my ABS unit after thinking the unit was bad but it ended up being a bad ground.

moespeeds

Cycled abs plenty during test drive. Bad ground wouldn't explain the inconsistent pedal..

froggy47

Original abs, how many miles?

moespeeds

Original abs 115k mi. Would abs or ebcm issue cause an inconsistent pedal while car is not moving?

crease-guard

Maybe this will help:

Circuit Description
The EBCM monitors the Brake Pressure Differential Switch to turn off Traction Control and Active Handling if a pressure loss is detected in the hydraulic brake system.

Conditions for Setting the DTC
DTC C1247 can be set anytime, if the EBCM detects the Brake Pressure Differential Switch has been grounded due to loss of brake pressure or a short to ground.

Action Taken When the DTC Sets
TCS/Active Handling are disabled.

• Indicators that turn on:

- RED Brake Warning indicator

- Car Icon (TCS indicator)

• Messages displayed on the DIC:

- Service Traction System

- Service Active HNDLG

Conditions for Clearing the DTC
• Condition for DTC is no longer present and scan tool clear DTC function is used.

• Fifty ignition cycles have passed with no DTCs detected.

Diagnostic Aids
• DTC C1247 could be set during a hydraulic brake system bleeding procedure if the ignition switch is in the ON position.

• It is very important that a thorough inspection of the wiring and connectors be performed. Failure to carefully and fully inspect wiring and connectors may result in misdiagnosis, causing part replacement with reappearance of the malfunction.

• An intermittent malfunction can be caused by poor connections, broken insulation, or a wire that is broken inside the insulation.

• If an intermittent malfunction exists refer to Intermittents and Poor Connections in Wiring Systems.

moespeeds

Bump I'm desperate

froggy47

I would focus around the abs, a std pressure bleed does not bleed the abs. Getting on the brakes hard to activate the abs is an iffy way to cycle/bleed the abs & if it does bleed the abs, then where does that air bubble go? Still in the system somewhere.

abs fixer does a recondition on these for a pretty good price (I have not had it done)

Check the wires & check the brake line connections at the abs.

This is all wag, so good luck.

fatbillybob

Sometimes guessing is not the best approach. Tec2 is my best guess if you have manually bled it the best you can.

Bill Dearborn

The C1247 code is pointing you to two things. Either a loss of pressure in either front or rear hydraulic brake circuits or an issue with the brake pressure differential switch. Since the purpose of the switch is to notify the driver there is a loss or pressure in one of the circuits I would go with the theory there is a pressure loss. That could come from a leak or a massive amount of air in one of the circuits that basically acts like a leak from a pressure standpoint.

The switch itself can't cause an inconsistent feel in the brake pedal but a small leak or air in one of the systems could cause it to trigger the light and code. I would make a very quick check for leaks, then I would try and bleed the two sub systems using a Tech 2. Something else that can cause an inconsistent pedal is a bad master cylinder. It may also cause pressure inconsistencies between the front and rear circuits thus triggering the pressure warning.

Bill

moespeeds

Tomorrow I will go over every connection again. I ordered a new MC and booster, as they are the last 2 important components left from the original car anyway. Phoenix is getting the car for suspension setup and dyno tune Tuesday, so I'll have them bleed it with a tech 2 while it's there.

Hi Volts Z06

Joe will get it straightened out for you. They are the best. I'm willing to bet you just have air trapped in the ABS system.

froggy47

My bet too.

BEZ06

You do have the calipers mounted with the bleed valves on top, is that right? If they're mounted on the bottom you'll have symptoms similar to yours.

Bob

moespeeds

Calipers mounted correctly.