Yamae

It would be the best to use an oscilloscope but a multi-meter with an AC voltage mode + a DC cut capacitor can be used in most of the case. This doesn't show the peak to peak voltage nor the higher frequency components though. As far as I use this method, most of middle class multi-meters can be used for this purpose.

The ECU is detecting different analogue signals from different sensors. Most of those sensors are biased by the DC 5V. I'm sure you can imagine what will be happening when the DC5V has ripples. Sensors signals become dirty with those.

For an example, when the ECT is sending the temperature level to the ECU, the level is unstable by the ripples and the ECU detects the temperature sometimes too high and sometimes too low in a very short time. This certainly disturbs the ECU to work accurately.

When the ripples become too much and reach the digital thresh hold level, the ECU can't work any more. Sometimes leaked liquid disables the ECU to work.

Loganlion4

Well I have been planning to pull the ecm and check for bad caps any way and replace them on the principle that after 25 years any e-caps will have gone bad if only because the electrolyte dried up and it would be nice if this fixes odd code 14 / 15 but running fine I did also have a high reference voltage at the maf but I figured that might be caused by my high b+ it was 6.74 on two of six wires of the maf

Loganlion4

Well I just pulled the ecu to check which caps I needed and found to my surprise all the brown caps have been replaced however I am unable to verify which brands or types where used. I am wondering should I go ahead and get the new correct caps and replace the replacements assuming previous person used incorrect caps or should I go looking at the 237 ignition control module

Yamae

Why don't you judge measuring the ripple?
Or simply replace those unknown capacitors since you have good low ESR ones.
Non low ESR capacitors don't have the capability to remove ripples well.

dicer

I have not done it yet. But we need an easy place to check the ripple without cutting into a wire or digging so deep for it. Gen 1 is what I'm talking about. How about at EGR or something? Maybe the TPs? Need some alternatives.

Yamae

LOL, not yet? Why don't you do it? A man cannot be comfortable without changing his own ECU capacitors.

Better now than later. I have seen many poor slow movers regretting crying over spilt milk. The dark milk kills the board, as you know.

You'll be amazed how good the engine runs after replacing capacitors.

dicer

Yamae, I will be doing it. I just have so many things I have to do, not just working on my cars. What I meant is I haven't yet done a ripple test. I will just need to find the time. Hmmm if I spent less time on this computer and this web site maybe I could do it. LOL

Loganlion4

Well just did the ripple test and after my multimeter settled from first connection it said 0.020 volts a.c. and I had it on 2 volt scale because I got nothing on the lowest scale. So looks like I get to replace a Icm now. I think I know what killed it one of my connectors for the icms has lose wires so when you pull on it the wires might pull out I think someone may have previously wired it wrong damaging the icm I say this because when trying to reset the wires at one point I put two wires in backwards and car wouldn't run.