GJSGS4

I have a '99 GS400 and it seems to have very little engine braking when coasting down a hill.

Going down a slight hill, with the cruise control off and my foot off the accelerator the car will gain speed quicker than it should. If I downshift to 4th and then go back to 5th the engine braking seems correct, but if I just tap and release the throttle the car will begin to pickup speed again.

Most fuel injection systems will detect an overhauling load, like going down a hill with your foot off the throttle, and shut off the fuel injectors, my car does not seem to be doing this.

Is this typical behaviour for GS4's? Any ideas on what could be wrong?

rickm430

Your GS will pick up speed going down a hill in 5th gear if its any kind of hill. You won't get much engine brake effect until the speed is well up there. Try this......apply the brakes when you are going down a hill over about 30 mph. Watch the Tach, the tranny will downshif for you. You will slow down. If you tap the gas, the tranny will go back to 5th, and you will start to speed up again. I bet when you gate shift to 4th, and then go back to 5th, it actually stays in 4th until you hit the gas again.

Rickm430

GJSGS4

I had a 12 hour trip to play with the braking.

I was expecting it to act like you described, but it would not down shift to 4th or cut-off fuel flow to the injectors when I was coasting or braking.

On a slight hill the car would coast to 90+ mph and then I would use the e-shift to go down to 4th, the rpm's would go up, and then immediately I would shift back to 5th, and the rpms would go down, but the car would continue to slow down, until I just tapped the accelerator and the car would start picking up speed again.

I think there is something wrong, but I wanted to hear if others have a similar experience.

rickm430

I can't verify this cuz the GS430 doesn't have eshift. Maybe thats the difference?