car hesitates at around 3700 rpm?

[808state]

after my second run of logging, i've analyzed using megalog viewer, then imported it into my megasquirt (msii, 3.57, firmware 2.67). i should have adjusted some of the values to make it more gradual, but didn't. was too giddy with excitement. went for my third run. did wot and i think at around 3700 rpm, car just hesitates all of the sudden. i let off, continued to datalog and went back to analyze. this is the first time i've gone above 3500. if you go to the max tps (1st one) @ 216secs, i think thats where it hesitates.

basically, if i'm reading the logs right, is the hesitation a combination of the below?

1) rpm reading went crazy (3712 to 9302), which then sent the fuel cut off to kick in. what caused this?
2) afr went super lean, also could have cause it to hesitate.

car didn't die after it hesistated, but was wondering if i'm analyzing this hiccup correctly. i'm going to try rev up with no load to see if there is also some kind of rpm pickup problem at higher rpms. anything else i should do or check?

[devastator]

Your lean condition is probably the reason for your hiccup, not the result. The lean condition could have been due to the crazy RPM reading triggering your rev limiter which is set to fuel cut. First thing to do here is find the source of the RPM jump.
If the max TPS reading triggered the ACCEL that could have made it lean out and hesitate. If so, raise your settings so that ACCEL is not triggered until you get your VE tables tuned better. If not, try smoothing out the tables a bit as you might have dipped to a leaner VE bin accidentally. I didn't have time to review the log, sorry.

[808state]

thanks for pointing out the ACCEL enrichments. i should have disabled it until i got my ve table better. or better yet, read the megamanual better on this part. i haven't touched the ACCEL enrichments settings at all, mainly because i'm not exactly sure what it does. i thought what triggered the rpm jump was maybe a rpm gremlin or something. but now you pointed out something else to consider as the culprit.

If the car does not buck under acceleration, you are close to correct settings. If it bucks and stumbles, then it is going too lean and you need to richen that part of the table. Before tuning decel [or accel], make sure you have your VE table close to correct first! One way to do this is to get the VE table set up by setting the TPSdot threshold setting very high (250 kPa/sec or 250 %/s, something like that) so that TPS enrich/enlean never kicks in. Then, (in steady state) set up VE table.

[re-animator]

I have this same problem and I've been chasing it around for a couple of years. It only happens under load, under light throttle, it doesn't happen. I've tried adjusting the fuel, but it's still there, just not as bad. I've found datalogging to be a complete pain, so I'm renting some dyno time this winter. Keep trying, you'll get it!

good luck.

[devastator]

I looked at your log today, and at around 216 like you mentioned, the RPM went haywire. The Accel was triggered, but what's strange, is that the PW and the duty cycle went to zero. I think you have a wiring or electrical problem since Accel shouldn't shut the injectors down completely. Not even the rev limiter will do that.

I have this same problem and I've been chasing it around for a couple of years. It only happens under load, under light throttle, it doesn't happen. I've tried adjusting the fuel, but it's still there, just not as bad. I've found datalogging to be a complete pain

How do you tune the VE table without a datalog?

[808state]

i checked my wiring to the relay board, looks to be ok. not sure what other wiring i should look at. i pretty much ran all the wiring, soldered connections since this is carb to efi conversion and most of the stock wiring was pretty bare.

in any case, for these erratic rpm jumps, since i have firmware 2.687, if i changed the firmware to a 2.8 version, do you think the tach mask would help with these erratic jumps every once in awhile. mind you i don't get it all that often. i set the accel to 25.5 (max) so it wouldn't trigger. my setup is also fuel only, no timing, and triggering off the negative terminal of the coil. my smd 3.57 board already had to be fixed because of the hot coil (i've since changed the coil though).

http://www.megamanual.com/mt28.htm#ib

[devastator]

I wish I could help you with the electrical stuff, but I am almost clueless in that area. I think that upgrading to the latest code would help you as there are filters that you can change around to your liking.
My concern is that a tach spike should have spiked the injectors for a split second as well, but that is not the case according to your datalog. You might try posting this in the electrical forum and see if you get any feedback there as to a possible electrical problem. It might not be the cause, but the PW going to zero during a tach spike seems opposite to me. It's also possible that the ignition scheme you have chosen simply ignored this spike since it was not a normal event, but that still does not explain why the PW went to zero.

[808state]

installed msd6a, blaster2 coil, pertronix ignitor (already existing). solved the problem. instead of taking the tach signal off the negative of the coil, the tach output of the msd6a is hooked up to the megasquirt tach input. appeared to have cleaned up the signal.

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