After replacing Stator and switchpacks on 150.

[llyons]

I have been working on my 87 mercury which came up lame a month ago. I was able to determine that the Stator was bad by doing impedance and dva tests. I just finished putting a new stator back on in the same orientation. I also changed out the 2 switch packs with newer switch packs. So stator and both switch packs are new. We started it up to see if it would fire up and run and it did. It ran fine for a minute or two then the RPMs dropped. When I gave it a little more throttle it picked up and ran normal again. I keeps doing this.. Running ok and then a big drop in RPMs. I decided to put a timing light on the spark plugs to make sure they where all firing. What I noticed is when the motor is running fine, all the spark plugs are firing with a good repetitive frequency. When the motor would suddenly start running at much lower rpm I noticed the spark plugs on the 2,4,6 side where all firing well although the frequency was less.. On 1,3,5 side the firing became eratic and sometimes no fire. When we gave it very small amounts of throttle just to bump up the rpms, all the cyclinders would start firing like they should.

What might cause the engine to suddenly lower in RPMs (probably because 1,3,5 cutting out) but when adding a little throttle brought them all back in? The idle stabilizer and high speed spark advance where both disconnected during this experiment.

Here is the youtube video so you can hear what I am talking about. The oil level in the reservoir was half way full causing the oil alarm you can hear in the back ground.

https://youtu.be/mhPz3F5Zask

Thanks in advance for any guidance
Lance

 

[Faztbullet]

This is usually a stator...new dont mean it cant be bad especially if a CDI unit.

 

[llyons]

Thanks for responding. The stator still has good readings... 2300 ohms from the blues to ground and 52 ohms for the reds to gnd. I did not do a DVA test.

Would a stator that cuts out like this, start working when the throttle is bumped a little (a little gas)?

 

[Faztbullet]

Yes......as seen it several times.

 

[tommarvin]

Hook everything back up for testing,idle stabilizer and high speed spark advance.
Does your motor have a trigger,if so test it .
Do you have a malfunction indicator light to read error codes.
Are the coils ok, or is that the new switch packs.
Get a factory service manual to study the ignition system its complicated.