91 Prelude Electrical Issue

My daughter is reporting some strange electrical behavior with her 91
Honda Prelude.

Sometimes when she does one thing electrical, then it affects other
electrical things as well. For example, when she lowers the window or
turns on the wipers, then the radio is affected and lights dim. Today
when she pressed on the brakes, the car died (she only was slowing
down some).

She has had no trouble starting the car and the voltage at the battery
is over 12v (I can't remember what I saw when I tested it) when no
load and not charging, and 14.2v when the engine is running. The
battery was bought last July, and the alternator was replace last
summer too. I could not find any wires that were grounding out in the
engine area. The fuse box under the hood did not show any signs of
moisture or arcing.

I'm not sure where to look next to solve the problem. Could it be an
electrical relay.

Any ideas might help.

Thanks

Jerry

 

You might look around for ground points and clean the connections,
starting on and around the engine, and then the interior. A factory
electrical troubleshooting manual shows all the ground points. The
manuals can be found cheap on ebay.

Just a thought.

dan

 

That makes sense. I have already purchased the manuals
online last summer so I'll check all the grounds next.

Jerry

 

Let the engine running at idle. If the idle speed drops under
electrical loads, then the throttle angle sensor (aka throttle
position sensor or TPS) might be out of adjustment

 

rubbish!!! never touch the tps - it's set at factory and never needs
adjusting.

 

Either way, I don't see this behavior anyway.

I did find that one ground was only held on by a partially stripped
nut on top of the engine, near the alternator (that was replaced
by a local repair shop last summer), I tightened it with a new
nut.It might have been the issue since it was slightly tighter
than finger tight. I also cleaned up the connection if a wire
brush.

I don't know if this fixes it or not yet because I never experienced
the problem, only my daughter has. I drove it for about 20 minutes
after that, playing with all the electrical devices I could and it
worked
fine. Nothing got dimmer or reacted like it had any problem when
something else electrical was being adjusted or operated. It might
be fixed now or it might not be fixed. Only time will tell.

Jerry

 

oh my bad!! the sensor is made of magnesium alloy and it's welded to
the throttle body!!

muahahhaha...

 

Then you can check for ground connections.
When the engine is not running, measure the voltage between the
battery terminals and compare it with the measurements you get from
the

(+) terminal to the valve cover
(+) terminal to the engine block
(+) terminal to the transmission housing
(+) terminal to chassis

voltage drops should be no more than 0.05 - 0.1 volt

make sure you check and tighten the nuts on the alternator terminals
too!!!

Was the rear defogger on when she experienced the problems? the
defogger typically draws 25A !!

Still, i don't see how the engine dies when the brake is applied, if
the TPS is good, i would suspect vacumm leaks or other causes of
mechanical malfunctions

 

that's because its not the tps!!! apart from anything else, tps gives
you code.

that's more like it.

welcome to psychic car care 101.

 

Except for the signal it receives from the TPS, the ECU has absolutely
no other reference to the position of the throttle plate.

The signal from the TPS is in form of electric voltage, and falls into
a certain range (corresponding to the throttle positions at idle and
WOT) The ECU only throws a code when the voltage it receives is out
out range, and then defaults the throttle to a certain position. Your
car will start, but will not be drivable as the gas pedal will not
work. Note that the ECU is completely blind to how you calibrate the
TPS to the physical postion of the throttle plate.

The links you sent regarding the codes for TPS doesn't work. But
thanks for the turkey dog treat recipes. My dog loves it!!

Cheers

 

it doesn't know enough to understand "out of range" - all it checks for
is whether there's any connection. three leads - one at each end of the
carbon track and one for the brush - just like a potentiometer. if the
track is broken, code. if the brush is worn and doesn't contact, as
happens at high mileage where a spot wears on the track, code.

the throttle position is entirely mechanical, so no change in actual
throttle position. as for assumptions, if it doesn't get tps signal,
injection stops.

that's not my experience - it cuts completely.

you are not supposed to touch the calibration. period. the eacv exists
entirely to remove the need to ever go near tps calibration. that's why
it's shear-bolted into position - so as to be non-adjustable.

you can of course adjust the throttle plate's idle position, but the
throttle plate and the tps remain synced and in calibration.