Scope pattern anylyst needed

[plus2]

Can someone tell me if these cam and crank patterns are in time and look good. and what would cause my coil driver pattern to do this?
93 3.9L V6 Dodge magnum
Yellow=Crank Green=Cam Blue=#6 injector Red=ignition coil driver

Can't upload 1039KB LSM scope movie file.
Can I send this to someone through email, please
Thank you

[greasybob]

Here's some 3.9 screen shots I have in my library, it's kind of hard to tell cam/crank relation because crank lines don't show up that well. Instead of uploading the move try uploading a screen shot.

[plus2]

My crank signal looks different than all I can find, but does not change when running fine. My coil driver will randomly spike down to -20V. I don't have the modis this weekend, can I send file?

[greasybob]

Do you have a low amp probe you can check the coil with, this would show if the coil was short internally or if the problem was on the PCM side. At what point in the ignition cycle do you see the downward spike. I included here a screen shot of a coil with current ramp ontop of the ignition probe around the coil wire. I also included a shot of the negative side of the coil being backprobed and the ignition probe around the coil wire, I was surprised how similar the wave forms were. The coil I current ramped was from a 91 F150 and is current limited.

[plus2]

93 3.9L V6 Dodge magnum
Yellow=Crank Green=Cam Blue=#6 injector Red=ignition coil driver

[David Green]

I am by no way an expert on American type vehicles, but the type of ignition waveforms provided look like our vehicles over the water when I used to scope them some twenty years ago. The square waveform which I take it is your cam sensor signal, not definitive but I would not think the cam signal amplitude should increase with engine speed. The spikes operating within the square wave signal to me look like interference from another source, i.e. the ignition patterns seen don't look good.

I might want to look at the ignition secondary side of things, i.e. leads, cap,rotor etc, does not look to good.

David

[plus2]

All secondary ignition is new
Yellow=Crank Green=Cam Blue=#6 injector Red=ignition coil driver

I have all 4 signals at different zero heights on the screen. Is that what you mean by amplitude? Cam and crank both switch from 0 to 5v. Can you tell me if there timing looks correct?

[greasybob]

Sorry, but I was not able open the file.

[plus2]

Disregard, wrong screenshot, see next post

Yellow-Crank Green-Cam Red-Coil driver(looks white in screenshot)
If my cam and crank look good what would cause that to the coil driver?

[plus2]

Disregard last screenshot

Yellow=Crank
Green=Cam
Blue=Coil driver(looks white)

If my cam and crank look good what would cause that to the coil driver?

[David Green]

Disregard last screenshot

Yellow=Crank
Green=Cam
Blue=Coil driver(looks white)

If my cam and crank look good what would cause that to the coil driver?

Hi This blue coil driver indicated by colour white to me does not look good at all, why on the samples shown are there spikes going off vertically downwards on some parts of the trace?

The ignition patterns shown although you do say all items are new indicate a fault condition to me, maybe in the primary side, i.e. amplifier ground etc, If it were me I would be looking at some comparable data of another vehicle or scope patterns and doing a comparison. In our day when investigating scope faults for ignition related faults or queries, I sometimes found that the distributor shaft had corroded into the engine block and gave a poor earth return signal, also a poor earth wire on the base plate to the body of the distributor. To me there is a lot of interference on those scope patterns indicating a fault condition.

I cannot give a definitive guide as I would need to get the old books out of the archives and re valuate the situation

David

[plus2]

I thought the yellow(crank) and green(cam) look good. They look like that all the time. The Blue(coil driver) is what changes. I'm not sure what would cause this. My guess is a PCM. What else should I scope?

[David Green]

Hi,

The blue coil driver picture six looks like one circuit has a fault present to me. I am saying the blue line, the green line to me may have a fault because there appears to be no coil windings present, i.e. high resistance in the circuit. Picture eight, top scope trace producing a negative switching trace looks like a fault or interference present just before switching off.

Ideally what you require is a test criteria for the PCM pins in/out, thus checking the individual circuits using the scope.

It is difficult for me to explain what I mean properly as firstly I am not familier with American cars, and secondly I don't know what ignition system you are working with.

Another option you have on this forum is, you could send a PM to diagnostic nick who works on American cars and he may be able to give you some advise. Give him a PM you have nothing to loose, if you cannot then resolve your problem, let me know and I will dig out my old notes and load up some scope patterns of typical inputs/outputs of a PCM to give you some extra help if I can.

David

[plus2]

The green signal is my cam sensor/in distributor. I think that looks fine. I think that I got a bad PCM. I can't think of what else controls the spark timing, but the crank/cam sensors and the pcm. It don't look like the cam or crank change enough to make the coil driver do that.

[David Green]

Have you checked the ignition advance curve, is it single or double stage. under the base plate inside the distributor will be one or two weights, they probably look like small plates with springs attached, these plates should be forced out against centrifugal force as the engine speeds up, thus the springs pull them back. To check ignition advance as you already know, just connect a strobe light to the ignition system and point at the timing marks, then rev the engine, if the timing marks advance you know the spark timing is advancing.

However, based on the scope read outs, I don't think that area will be of concern, but if you feel differently, please do give it a go.

David