RPM oscillations

[Eds]

I am having an issue with a rpm oscillation. I hope someone can look at the attached log help me address the issue. With help I was able to get my 3.4L v-6 up and running. What we have not been able to address is a rpm oscillation that occurs between 1100 - 1400 rpm. It does not matter if the vehicle is sitting still or moving.


'94 3.4L hybrid, Comp Cam 260H, 1227727 ECM, $A1

Ed

[steveo]

for some reason the $A1 ads i have at work wont load so i can't view it, but here's some questions just to help shed some light..

by feel, does it feel like surging where the vehicle actually oscillates torque or does it seem like some oddball timing jitter?

could be something shitty going on in your distributor pickup?

how many rpms is it surging?

does it get worse when the engine warms up?

does it occur across the MAP range (does it happen regardless of load)?

is it the stock timing map?

it's a pretty small cam, but since i don't know that engine and what its stock timing map looks like, maybe you've run into some surge?

if i suspect cam surge, i generally drop 'bout 4 degrees from the affected area and flatten/smooth the timing map for that range, if it doesn't help, i just put it back and start looking for other causes..

[Eds]

1. It oscillates torque. In the early part of the log {1:48-2:03) I was in 1st gear under light load.
2. No distributor. DIS ignition system.
3. Oscillates about 200 rpm.
4. Oscillations start after going into closed loop.
5. It is more noticeable under light to no load (approx. 40KPa). It is quite noticeable when slowing to a stop and I push in the clutch and still rolling.
6. It is not a stock timing map. I do not believe it is a timing issue.

Thanks, Ed

[steveo]

Oscillations start after going into closed loop.

ok, that sticks out a bit.

so now you have to figure out;

- do the occur only if closed loop happens, or is it just a coincidence (i.e. unplug an o2 to prevent closed loop, does the problem ever occur?)

if it happens only in closed loop; there are a few possibilities..

the extra fuel from open loop is behaving as a band-aid for something that extra fuel would solve. this happens more often than you think, often dumping fuel at a mechanical problem like a weak cylinder will smooth it out.

closed loop configuration is incorrect, causing heavy AFR fluctuations, such as a totally inappropriate BLM rpm hysteresis causing fluttering between blm cells in that range, or prop gains too high.

something is horribly wrong with how the o2 itself is behaving, causing fueling to be all over the place in that range, but i doubt it, never see o2 sensors do that...

if i might ask, since i still cant view your log for some reason, how much timing advance is logged in that rpm range when the problem seems to occur?

[Eds]

With the rpm oscillating between about 1100 & 1300 rpm the spark advance is varying between 16* & 18*.

A little more info: engine is fresh with approximately a thousand miles total so no weak cylinders. I did play around with the fuel tables in this rpm range but there were no changes as to the oscillations. I will try to load the log again.

[steveo]

its not the log.. do you have an adx that works for $A1? i guess i cant find one

[Eds]

ADX attached

[delcowizzid]

looks like closed loop is on and its rying to swing the o2 back and fowards but its rich like idle mode. tps volts is high probably not even going to idle mode .35% throttle is the lowest i saw

[Eds]

In the log, I also noticed the .39 tps% at idle. I don't know why that happens sometimes in the logs as the tps is new. I have several other logs where the tps% is zero % at idle yet the rpm oscillations persist.

[delcowizzid]

if you watch item list veiw when it does it its tripping in and out of idle mode and commanded step change is going up and down on the iac either close the throttle a little or adjust the TPS to get closed throttle volts down under 0.5 so it has 0% at idle

[Eds]

I re-adjusted the tps. Had to slot the mounting holes and was only able to get it to .53 volts and 0%. The oscillations unfortunately are still there. I made another log.

I did make a mistake earlier in as much as the oscillations do occur in open loop as noted in the log @ times 1:23 - 1:31.


The oscillations occur under light load @ 3:39 - 4:30 & 4:25 - 4:30. At 6:16 - 6:26 I am coasting to a stop with the clutch in so there is no load on the engine.

Ed