418% duty cycle, wth???

[pure insanity]

ok so sunday im driving home and my car starts acting realllly wacked and just wants to lean out and then go dead. it stranded me at a gas station for about 30 mins not wanting to run. it will crank and run for a moment like its burning off the prime pulse and as soon as that is gone it dies. sometimes it will start right back up and run a moment, or other times it will not start untill i turn the switch off and then on to get the priming pulse. at other occasions it will fire up let me rev a bit whilest its acting like it wants to clear out then will eventually die in a couple seconds. it acts like im running out of fuel yet my fuel pressure gauge on the fuel rail shows no change in pressure during all of this. more like the injectors arent injecting. during this whole thing, what really got my attn was a datalog during one of these spells was that i had a 418% duty cycle. how is this even possible? have i got a ms problem in the unit itself? any ideas are greatly appreciated.

[Matt Cramer]

The RPM reading is off the scale, and pushing the duty cycle off the scale too. What are you using for ignition input?

[pure insanity]

its off the neg. side of coil. this is odd, but it goes away as soon as the car decides to straighten up and act right. then everything will return to normal. for a while at least. the rpm off the scale is reminiscent of when i had noise issues. however those were resolved by the 24v zener diode in the tach line.

how about acceleration enrichments? do i have something weird going on there causing some of this? just a thought.

[pure insanity]

ok, it happened again tonight. it def seems as though something is shutting down the injectors. at this point i have no idea whats up but whatever it is gives me some wicked high rpms and some serious pulsewidths to go with it. i got another datalog, so maybe it will show something. thinking maybe its some sort of noise, but it doesnt make sense as it goes and comes without any pattern.

[Matt Cramer]

its off the neg. side of coil. this is odd, but it goes away as soon as the car decides to straighten up and act right. then everything will return to normal. for a while at least. the rpm off the scale is reminiscent of when i had noise issues. however those were resolved by the 24v zener diode in the tach line.

how about acceleration enrichments? do i have something weird going on there causing some of this? just a thought.

It's not the acceleration enrichments, it's tach noise you need to filter out. When the duty cycle goes to 400%, you're also seeing around 10,000 RPM or more. Try jumpering XG1 to an unused pin on the DB37 and running that pin to an engine block ground, see if that cuts down on the noise.

[pure insanity]

matt, any thoughts as to why this noise comes and goes. i can drive fine for a while, then other times it just shows up, creates havoc and then will go away.

[Matt Cramer]

The negative terminal of the coil can be a real pain to get a good signal from. It seems like the noise amount ranges from a little too much for your filtering, down to enough to almost make it through the filter but not quite.

[pure insanity]

im gonna try the jumper as you suggested but how about a stronger zener diode ? what effects would that have? and how about putting a filter in the 12v source to ms ? any suggestions on what size, watt, brand or etc. ? any other places that i can do something to get rid of this noise once and for all ?