Occasional Hesitation, 1500-2500 rpm, 80+kPa

[Digger]

I've been tuning a Microsquirt for ~6 months now in my '69 Bronco. This was my first time diving into Megasquirt/Tunerstudio. I've had my share of struggles, but I'm at the point where a have a decent driver. Certainly a fare cry better than the old Holley carb.

One of the last wrinkles to iron out is an intermittent problem. When it kicks up, I'm cruising between ~1500-2500 rpm. If I roll into the throttle, I start getting a hesitation /bucking of the engine when I exceed ~78 kPa MAP. (For reference, I'm in Colorado. WOT is only 85 kPa here) Looking at the gauges, bucking seems to flare up when the AFR is in the 13:1 range. Above or below that, no problem. If I stab the throttle, no bucking, AFR usually jumps to 12:1.

Likely related, but sometimes when I lift throttle quickly, I get a short shutter from the engine in the same 1500-2500 range.

Initially, I started adding ignition timing at high MAP which seemed to fix the problem, but it occasionally comes back. I'm a little scared to add more time. I seem to have a lot of advance the way it is. It's not pinging, but its ingesting 20-40 F air, so ping really hasn't been a problem.

Engine Specs:
1994 Ford 351W roller block bored .030" over
Forged pistons/rods
Aluminum heads, 2.02/1.65" valves, 9:0 compression
Weiand Stealth intake, FAST 4bbl throttle body, 4x 71lb injectors
Mild Comp Cams roller cam, 1.6 roller rockers.

I'm confident in the VE map's accuracy. The VE table peaks out at the cam's stated peak torque. Steady cruise at various rpms/loads yields an AFR that is right on commanded AFR with no EGO correction. Engine is peppy other than stated problem.

[Matt Cramer]

It looks like the log attached doesn't go over 61 kPa?

[Digger]

Sorry, I got a little trim-happy trying to get that file down to 1Mb

I played around with advancing the timing. It quelled the problem a little, but it was still present. Torque had noticeably dropped. I reduced timing 10% at low rpm/high MAP and re scaled the ignition table. Torque came back and it felt like I was back on MBT for that region. There is still a slight hesitation, but it is mostly gone and stutter when lifting throttle is gone.

The problem doesn't manifest itself on the log, but I'll let you guys look and see if you spot something I missed.

New msq and msl attached.

[CRSTune]

You mentioned that the maximum MAP reading you'll get is 85kpa (log shows 84kpa). You may want to consider switching to percent baro as your fueling and timing algorithm. If WOT is 85kpa, then your AFR target is 14.1AFR at that point. That is far leaner than I'd ever intend an engine to be at. The log on the other hand does not match that as when you approach that load point, the AFR is 12.0AFR. In fact, it's consistently richer than your target.

You have enhanced acceleration enrichment enabled. Is this tuned? If works for the most part out of the box when enabled but can cause the bucking and stumbling you're describing if not calibrated.

You data is highly smoothed in the general settings. 20 isn't going to make the sensors very response. Was this to compensate for sensor noise? It also doesn't help the EAE algorithm.

[turbo conversion]

I agree with CRSTune about EAE, if your VE AFR and SAT are not really tuned well EAE will cause these issues.

I would suggest turning EAE off until your tune is much closer than it is now.

I would also set Decel Fuel Amount to 100 instead of 95.


David

[Digger]

You mentioned that the maximum MAP reading you'll get is 85kpa (log shows 84kpa). You may want to consider switching to percent baro as your fueling and timing algorithm. If WOT is 85kpa, then your AFR target is 14.1AFR at that point. That is far leaner than I'd ever intend an engine to be at. The log on the other hand does not match that as when you approach that load point, the AFR is 12.0AFR. In fact, it's consistently richer than your target.

You have enhanced acceleration enrichment enabled. Is this tuned? If works for the most part out of the box when enabled but can cause the bucking and stumbling you're describing if not calibrated.

You data is highly smoothed in the general settings. 20 isn't going to make the sensors very response. Was this to compensate for sensor noise? It also doesn't help the EAE algorithm.

I hadn't really considered %baro, but that might be a better solution for my commanded AFR problem. I will look into that.

It's hard to capture accurate AFR in the log file unless I can linger a long time in one region. I spent a lot of time tuning EAE. 3 months of driving around in the evenings to be exact. I did all the EAE work with the AE TPSdot cranked up so I wasn't seeing artificial enrichment from the AE. AE could use probably use some work. Right now, quick stabs of throttle require me to "over shoot" the target AFR to prevent hesitation 100% of the time. I assume it's because I have a large intake with central port injection and long runners, but it takes the engine a long time to settle from transient conditions. (10sec+) This may be because during AE too much of the enrichment shot is sticking to the intake vs evaporating into the air stream.

The FAST throttle body has little pins pushed into the path of the injectors that disrupt the fuel shooting out. It seamed odd, but I thought there may be been a reason. I asked a FAST representative at a trade show about this. They didn't have an exact answer, but eluded that this feature might have been more about avoiding a patent infringement than actual function. I may knock the pins out to test this theory, but for now they seem to cause splattering of the fuel instead of a nice mist of fuel.

Yes, sensor signals are smoothed a lot. It seems happier that way. Not so much for noise, but it helped EAE. The throttle is very touchy at low throttle position and the EAE needs to have aggressive change in that region to properly match the engine. Air in the throttle body is a little turbulent and needs averaging for a clean signal. I have tried settings from 10 to 90. Settings near 10 work better, so I left it at 20 for now. I may back it off some and see if it helps.

Turbo - Are you suggesting changing Decel Fuel to 100 to deal with hesitation during quick lifts of the throttle?

[turbo conversion]

Yes.

David