Mercury Electric hydraulic brakes no power assist

[Blayze]

I have an 89 Mercury Cougar XR7

Problem is there is no power brake assist.

Power assist was working for a while then I noticed the brake pump motor would stay running after I turned the engine off.
A few weeks later the power assist stops.

ABS light and Brake light are illuminated. Cant find anywhere to connect a tester to and the lights arent blinking I dont know if an obd port was installed for this year or not.

Power assist did come on for me randomly once so I know the motor is still good and possibly the accumulator.
Since then I’v tried cleaning the WSS. Only one was noticeably dirty. Not sure if those would be related to shutting the brake assist off or not.

I’m pointing more towards the ABS control module being bad, but would like some help in any diagnostics that could be checked or if theres anything I could be missing.

And also if the control module is most likely bad, would this have to be reprogrammed or anything special prior to install. Or would I just be able to purchase from rockauto plug and play?

Any help is appreciated Thank You

Topic

[Nathan Richards]

You should check all your vacuum hoses. The power brakes rely on a vacuum on your engine. A vacuum hose may be cracked or disconnected. OBD is unfortunately on only on cars 1996 and up. There is a special procedure for older makes. I’m not quite sure how it is does but when done correctly the engine light would flash and give the code through flashes. if there is not lean code, this is probably not your problem

[Andrew Harris]

As Nathan stated before 1996 which is when the OBD2 mandate was initiated it was free game. Car makers had free reins to do whatever they wanted with their computer controlled monitoring. Their was no set standard. Unfortunately to retrieve codes from the ABS system you need an outdated tool called a super star 2 to retrieve the codes.
Again as Nathan has stated the Booster is called a vacuum assisted booster because it works with engine vacuum to provide assist. their should be a hose coming off the engine going into the brake booster. make sure the hose is attached and is not split or cracked. The vacuum hose connects to a one way check valve. this can also fail. to check run the engine for a few minutes and then shut off. then disconnect the valve from the booster. you should hear a hiss as the vacuum leaks out. if not either the valve is bad or the booster diaphragm is damaged. to check the booster itself you would need a vacuum pump like a mightyvac and apply vacuum to the booster and see if it can hold a vacuum. If you find that the booster is bad make sure you check and make sure the master cylinder isn’t leaking fluid into the booster from the rear seal.

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