my mistake I didn’t keep up with the plugs or boots I took it to the mechanic cause of the service engine light on and he replaced the spark plugs & boots at 150k and he told me driver side of my engine the coils needed to be replaced just because he saw some built up & passenger side was clean. The mechanic cleaned the coils and I drove it home with a better improvement. Now at 160k my car has the service engine light on turning on/off with codes P0316 & P0304 at idle I did noticed fuel odor and on driver side the rear pipe puffs of smoke. This car will stay with me and I’m planning to improve it a little at a time this is just the beginning of the replacements I have to do

 

i have 1999 mustang gt with only 45,500 miles. after sitting for 8 years I have brought it back to life ($1400 later) but have rough idle and seems like a small loss of power. I get codes p0300, P0302. i checked #2 cylinder and seems I am not getting any voltage to the coil pack. Checked other coils and volts are very erratic and all over the place. Goes to 1.5v down to 0.6v. Was told I should be getting 10 to 12 v at the coils. P0300 I know is random misfire and I think the low voltage could be my problem. I can drive the car no problem but it hesitates a lot and runs rough. I would think with that low voltage to all the coils that the car would barely run but it idles at a steady 750 rpms just engine is running rough. Any help with be great. Never seen this happen before.

 

How did you check the voltage at the COPs?

With the Key On and Engine Off (KOEO) there should be 12 VDC between the red wire at each COP and ground.

With the engine running the +12 V (between the red wire and ground) will still be there however the fly back voltage in the primary windings will be superimposed on the 12 VDC--it looks like this on an oscilloscope:



The trace shows the primary voltage at idle where the PCM fires each plug three times in a rapid sequence, it does this up to 1200 rpm or so to help idle smoothness and emissions. The base line preceding and following plug firings is at 12 VDC (the vertical scale is 20 V/division, the green arrow at the right indicates the ground setting).

The other wire at each COP is controlled by the PCM to charge and fire each COP at the appropriate time--the voltage on those wires will be 0 V when the PCM is charging the coil and "undefined" (actually quite high and mimicking the the firing pattern seen in the primary (in the 'scope trace above).

Reading between the two wires at each COP with a multimeter and the engine running will produce the sort of readings you observed, with the displayed voltage range dependent on the meter's sampling rate and response time...

 

Cliffy! Thought we lost ya, good to see you back around bud.

 

Cliffy what happens above 1200 RPM, single fire? and is this due to less time between strokes/cycles?

 

Yup...

And yes it is due in part to the shorter cycles, and that it is unneeded at higher engine speeds and charge velocities..

 

I had a stroke in May of 2014 that affected my left side--it took a while to get back on track...

 

You are still the man!!!, i have done your COP conversion on my 98

Thanks

 

Yeah I recall a post you made a couple years ago where you mentioned some health stuff you were dealing with and not to expect your presence much here anymore. Glad to hear it sounds like you're bouncing back from that, hope all's good with you.

 

Man Cliff, sorry to hear about the health issues, glad to see you are making a come back. You have really added some great info to this thread since I have been gone.