Some Honda models, for instance, are known for O-ring failures that cause the steering pump to draw atmospheric air into the pump reservoir. With the engine running, inspect the fluid in the reservoir for signs of aeration or foaming. If the fluid is dark black, the system might have a problem with deteriorating seals in the steering rack or with power steering hoses that are deteriorating from the inside out. Most commonly, the fault lies with a seized support bearing in one of the front MacPherson strut assemblies.ĭiagnostic Summary When diagnosing an assist or noise problem with a power steering pump, always begin by inspecting the condition of the power steering fluid. In these cases, the steering gear or rack might have a failed compression disk or similar steering sensitivity device in the metering valve assembly. On rare occasions, power steering assist will be stronger in one direction than the other. In contrast, worn metering valves in steering racks tend to provide sluggish assist when cold and return to normal assist as the assembly warms up and returns to operational tolerances. In most of these cases, the cam ring develops a rippled surface that allows fluid pressure to leak past the vanes or rollers. In general, worn pumps usually provide good assist when cold, but tend to provide less assist as the power steering fluid warms up. In this case, the loss of steering assist will be instantaneous and a loss of fluid recirculation will be apparent at the power steering reservoir with the engine running. The only exception to this would be the relatively rare instance when the pump input shaft breaks at the impellor assembly. Power Steering Symptoms Most power steering pumps provide ample warning of impending failure. The EVO system, for example, uses vehicle speed, steering wheel position and other inputs to determine the amount of modulation necessary to produce the required steering wheel sensitivity.Īs with any application-specific pressure modulation system, diagnostics require a scan tool capable of accessing the power steering data stream and retrieving diagnostic trouble codes. As axle shaft speed increased, the modulator increased steering sensitivity by reducing power steering fluid pressure to the steering rack.Īlthough a number of steering pump modulation systems have been produced over the years, auto manufacturers have now developed computer-controlled, electronic variable orifice (EVO) power steering pumps that help adapt steering pump pressure to driving conditions.īefore attempting to diagnose any late-model power steering system, it’s important to access service data describing the operation of the system and how the system should be diagnosed. There are people firmly in both camps, it seems.Power Steering Designs The problem engineers struggle with on power steering is the tendency of the hydraulic boost to insulate the driver from sensing the road surface through the steering wheel on ice-covered roadways or while driving in high-speed road course events.ĭuring the 1980s, Honda addressed this problem by introducing a relatively simple power steering pump pressure modulation system mounted on the transaxle output shaft assembly. Lift the front wheels off the ground, and cycle the steering stop to stop with the engine off? Or with the engine on? Do it first with the engine off, then with the engine on? Four Wheeler magazine has a great write-up here, but they seem to be in the "cycle with the engine running" camp, and some folks say that this can cause pump failure if you let it cavitate too long while bleeding the system with the engine running. I am going to bleed the system tomorrow, but I have been looking online and there's a lot of debate about what the best way to bleed a PS system is. So, I topped off the fluid, and ran the engine for a few minutes to get things all warmed up - and the fluid is still foamy as hell and the steering feels like there's a ton of air in the system. I thought maybe it was just cold, and a little low on fluid. It HAS been sitting in the snow without being started for weeks. I started it, and the power steering pump whined like crazy and the steering felt like the fluid was very low. After sitting for a few weeks in the snow, I finally finished the repair and put the steering column back together. I had the steering column torn apart to replace a cracked sector and a worn rack. 1990 YJ, 2.5L with the standard integrated reservoir PS pump.
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