RNH524

So doing a ripple test on my a 1995 Lexus ls400.
We used a 1.0uF does that make a difference? Also when we did when it was cold it was around 80-90 mV and once it started to warm up it dropped down a bit. (Not sure if the multimeter as the right settings but I'll try and post a little video of it. But where should the reasings be when doing these test?

RNH524

This was my setting... 200m


This was how I had it in there...


This is the reading it was at... It would bounce around from there to 52 when warming up (drops when getting car getting warmer)


That reading was at this temp....

Aeok18109

Difficult to make out, can you get a clearer shot?

RNH524

I know sorry my phone takes horrible pictures... I found a post just like mine and the guy was getting the same readings as me and everyone told him the ecu was good.. Thanks though!

Yamae

It looks like a PP film capacitor and your 1.0uF is good to use. It provides your DVM a bit more lower frequency ripples.

There are two reasons why the reading results change as temperature goes higher. One is the resistance change of the thermal sensor R(t). It is a Thermistor and it reduces the resistance as temperature goes higher. It is pulled up by a resistor R(p) in the ECU box. The ripple voltage V(r) at the DIAG connector is calculated as below. Also the real ripple voltage in the ECU is bigger than that.

V(r)="Real ripple voltage in the ECU" X R(t) / R(p) + R(t)

As the value R(t) reduces, V(r) also reduces.

Another reason is the characteristics of a electrolytic capacitor. It decrease the capacitance as temperature goes down. In other words, the capability to reduce the ripple becomes poorer when cold and better when warm. It is natural that you get a bigger reading value when cold and smaller when warm.The "Real ripple voltage in the ECU" is reduced when capacitors are warm.
These are the reasons why you have different reading results as temperature changes.

Anyway, judging from the figure 61mV, it's time for you to replace those capacitors.

RNH524

When I took the ECU out everything looked perfect and my buddy tested them and they call came back good.. How long you think they will last? And where they're at right now you think it could throw a code of the crank sensor ? They can't be that bad to where they are throwing random codes..

Yamae

The answer is at the thread.

RNH524

The answer is not at the thread... I understand that bad caps can throw faulty codes but I found a post just like mine, the guys mV were as high as mine at cold start and lscowboy told him his caps were fine for now... If my caps are fine at this very moment would it or would it not throw faulty codes ? I want to know before going to pay for a crank sensor or not... My exact symptoms are Car sometimes runs perfect at first but that only last for about 10-15 seconds then it will take off normal but if you only give it little gas but if you try to floor it it acts like its not getting enough gas sorta like if it has a bad EGR and its running lean and it takes a good 10-15seconds for the RPMs to get up to 2k but once it does it will start picking up as normal again.. It only happens if I have it in a higher gear say keep it in D and take off from a stop but if i take off in 1st gear its fine.. and the codes that came up were p0715 & p0336 which are crank sensor and input turbine speed sensor circuit which would explain why my ECT light blinks sometimes.. I just don't want to waste my time pulling the ECU all out again if the caps are fine at the moment.

python

iTrader: (4)

so what ur implying is this, a bad capacitor is in fact the only reason for a fault code?
or...would a good ecm cause a faulty code?
either way ur statement is ambiguous and im not sure what ur line of thinking is
btw the guy u want to be involved in the thread is, so u might wanna clarify this

RNH524

Did you not read everything? I don't understand how you don't understand lol. He's telling me its time for my caps to be changed but i found another post where the guy had the same ripple readings as me and was told his caps are fine. I'm simply asking if where my caps are are they low enough to where they would throw a code or not because if they are to a point where it would throw a code then i don't want to waste my time and money spending it on replacing a crank sensor.. He's not giving me a direct answer to my question.

python

iTrader: (4)

p0715 is a speed sensor circuit in the tranny is it not?

RNH524

Yes it is.

RNH524

Could the crank sensor cause that to go off ? The car doesn't have any problems shifting when it shifts, it shifts fine and how its suppose to. It doesn't jump through gears. I don't know anything about these types of cars. I'm just trying to get it to run right before I sell it. If it were your car what first step would you go towards replacing..

midwest2

You got an answer from the ECU guru, the very man, I believe, that brought us the ripple test. I wouldn't worry about some other thread that you found.

RNH524

So I just got done changing out the Caps.. Seems to be running a little better but still having the same symptoms.. hmmm..