Pulse Widths (PW) suddenly dropped

[drholl]

A one time occurrence at 9325 ???

Our '59 Caddie runs absolutely beautiful and it gets really good mileage for a 10.25:1, 502 Chevy powering a 5,000 pound 59 Cadillac. It gets well over 20 miles per gallon on the new reformulated fuel we have around here for the summer, but it got over 25 with the regular gasoline before this years summer blend showed up at the stations. So I decided to touch it up for this new fuel, which probably has a bunch more alcohol in it, to see what I could get out of it.

So while data logging at about 75 miles per hour, and doing some retuning for our new reformulated summer fuel here, at 9324.9 seconds the MS suddenly commanded a Pulse Width (PW) of 1.454 ms, which is about the fuel for a good idle. It only did it for 1 second. But it felt like an eternity, as I was in the #2 lane of 5 lanes, with a not too heavy traffic condition. 4 lanes is a lot to cross with a dead engine. I was quickly looking for a break in traffic as it felt like the engine quit running, but for only 1 full second. Then it ran fine again.

I say commanded because there was no reset, the MS was still recording everything out to the laptop. The Duty cycle went from 24% to 12% with no cause for it that I could find in looking at all the other fields. Then, after 1 second, it went right back to 25% and ran fine. I tagged a whole bunch of marks (I freaked out for a moment) as I wanted to be sure I found this location on the log.

I looked carefully at the datalog, I only spotted results of the PW going to about ½ normal, nothing about what caused that drop in fuel delivery. First the PW dropped at the same time as the Duty Cycle, then the RPM started dropping, then the AFR topped out and finally the map went up a bit. My foot never moved on the pedal.

OK, my questions.
1) Have you ever heard of this happening to anyone before? Seems like the processor freaked out.
2) Any idea on what caused the commanded Pulse Width to drop? I don't have a clue.
3) Could this be a sign that my 5 year old MS-II is getting old and ready to fail? I doubt it, but it’s a thought. It’s sure more reliable than the old points systems though. And don’t get me started on carburetors…

It has always run as expected, except this one time. Nothing weird like this has ever happened to me before.

Thanks guys.
Holl

[drholl]

datalog201306190755.xls

Well, the "Pulse Width drop" happened again. Again for 1 second and again it dropped to about an idle mixture while driving, this time at 65 MPH.

It occurred when I was just ready to exit the freeway so my foot came up during the occurrence.

But here's 10 seconds of another one second of "Pulse Width drop" during the issue.

When I saved it I messed up and lost the complete data log off the thumb drive. I should have saved it as a different file name. Oops. So I'm unable to recover a longer session. Next time this happens I'll post a longer session like yesterday. Sorry.

I'll rebuild the MSQ today and see if it happens again. Maybe the MSQ has a small corruption in it.

Thanks Guys
I'll let you know what happens after I rework the MSQ.

Holl

[Bernard Fife]

drholl,

It looks to me like the PW is dropping when, and only when, Gve hits 128. There are no apparent triggers for the PW to drop (like decel enrichment, IAT or CLT changes, WUE, ethanol adjustment, etc.). So it sounds a lot like a roll-over issue in the code.

I'll try your MSQ on the bench, and alert Al once I can replicate the problem.

Lance.

[Bernard Fife]

drholl,

Looking at the datalog, it looks like you are almost constantly in accel enrichment mode (code 17). I believe this is caused by the MAPdot threshold being set down to 50kPa/sec. The datalog shows the pulse width dropping ~1.2 seconds after the latest MAPdot spike, and our settings are for 0.3 accel plus a 0.8 second taper, so that might explain it. (The pulse width drop could come from removing the accel enrich and subtracting the decel enrich of 30%.)

In any case, I was completely unable to reproduce the PW drop on the bench (maybe because I can't vary the MAP signal fast enough). That doesn't mean there's not a problem, just that we need more info to find it.

If this was mine, I would:
- upgrade to the latest 2.920 code. It has many fixes over the 2.886 code you are running, and is the starting point for any new fixes (i.e. it is 2.920 code that will get fixed, not 2.886, so you might as well upgrade now - it *might* have already have a fix for your issue).
- set the MAPdot threshold higher. I would go for 100 kPa/sec initially since that is a little above the highest of any of the values in the datalog (93 kPa/sec).

Then try it, and if the issue remains, please post another MSQ and datalog and we'll have a look.

Lance.

[drholl]

Wonderful answer Lance. Thank You. I'll make the changes you suggest. And "No news, is good news". I'll let you know, one way or the other.

I know engines, but I hate software ! ! ! - I'm afraid of software...

Ooo Kaayyy, I'll upgrade the software.

BTW, when I start using MS-3, I'll have to upgrade anyway? Right?

That'll scare me again.

Thanks Again Lance.
Holl

[drholl]

Ah, Yes. I didn't notice that when I changed the MAP Smoothing delay factor in the General settings back up to 100, that made a major change in the mapDOT area. Oops.

I guess I'll have to use the "Compare" feature more often.

Thanks Lance.
Holl