Megasquirt EFI conversion

[snakeoil24]

I have waited years to take the plunge. I look at the writings about various systems on the market like ez and MSD, Each has their issues. Would you start all over using MEgasquirt. I see alot of leading edge racers in california swear by Mega squirt??

 

[dpstark2]

I would use Megasquirt, but if you're not familiar with electronics I wouldn't recommend it. If you want the most flexibility and are willing to invest the time and gain the skills, go Megasquirt. If not, go with one of the many new off the shelf systems. In any case, expect problems and a learning curve.

 

[Bone]

As an FYI I recently read a great book on tuning called Designing and Tuning High Performance... by Greg Banish
He has a walkthrough on a tune using your system at the end of the book
Great reference in general for tuners and people who are thinking about going to EFI

 

[dpstark2]

Looks like a book I should buy! Thanks.

While my Dart is laid up, I've been spending more time driving the Charger and letting it tune. I found that the default AFR table had some areas that were too lean (15.5:1 or more). The motor just doesn't seem to like that at cruise around town and developed a lean surge. I was pleased to see that enriching that table only took one tuning session to correct and get things running properly.

Cold starts are still a problem- mostly because in order for cold starts to work properly, you have to have your idle fuel delivery correct. And my idle, I believe due to the throttle body injection, is really hard to get perfect across temperature and all conditions. In some cases, the same VE sets AFR at 14.5:1, and in others, it settles in around 12.0:1. I don't have much of an explanation for that, and I'm still looking into it. That situation leads to an occasional cold start that hits a ridiculous 10:1 AFR and causes a lot of issues. It's also looking more and more like 160F is "warm enough" for normal operation instead of the 180F I set it to.

The best news is that closed loop idle control is working. The computer can now successfully navigate idle RPM from cold starts, in gear, and out of gear to a healthy RPM. I think I still need to address my distributor curve a bit (or remove it entirely and go computer controlled) because it seems to advance a bit early and sometimes settle in a bit higher than it should for a while before coming down.

Just more info for anyone interested.

 

[Bone]

I am excited to hear how it all goes. getting ready to take that plunge myself

 

[dpstark2]

I watched a video about setting idle fueling with EFI. The video's author stated that for an engine like I have (batch fire, dual plane manifold, etc.) idle AFR should be near 13.3:1. It can be leaner on sequential motors, and probably should be richer on TBI (also my situation) motors. The author suggested watching manifold pressure and only paying passing attention to the AFR ratio. Instead, just set the fueling to produce the highest manifold pressure and go from there.

There are some reasons to believe this, but the primary problem with tuning AFR at idle is that cam overlap can trick your O2 sensor. Any crossover from the intake directly to the exhaust will create an artificial AFR reading. It can go either way- lean or rich- but you'll primarily get an artificial rich condition as it detects unburned fuel passing directly from intake to exhaust. By tuning based on manifold pressure, you're trying to find the point at which the engine is "happiest" with the fueling.

I believe the issue I was having (14.5:1 going to 12:1 on occasion) was due to it being too lean and getting loaded up and getting a bad burn at times, therefore seeing extra fuel in the exhaust that should not be there. I temporarily changed the fueling to get it into the low 13's or high 12's and that was better. However, tuning based on manifold pressure got me an extra inch of vacuum and a much steadier motor running more like 13.6:1. And it doesn't seem to get this extra rich cycling any more.

Is that the end of idle issues? Not really. One issue is going from park to drive- the vacuum drop nearly kills the motor at times. Some compromises may have to made in the table. There is also a "wall wetting" function that helps smooth out large vacuum transitions I need to look into. The warm up table and cold idle is still far from perfect, too. It's all trial and error. I also found I was adjusting the wrong parameters to try get a better start. I got that better sorted so cold starts happening in a couple revolutions, not 4-5s.

At least the motor seems happier this way!

 

[dpstark2]

I had a great time tuning the Charger this weekend while forum member Meep-Meep flogged it around town and down the freeway. There are still definitely some issues with idle that I really need to look into. One fueling issue that has crept up three times now is a lean misfired at about 1800 rpm just cruising steady. It goes by so quickly you won't notice it unless you really isolate those conditions.

Tuning that lean condition was troublesome. The problem was that the AFR table was (probably) much leaner than it should be for that condition. As the computer tuned, it would go lean, get a misfire and see a rich condition. The lean misfire shows as rich (sometimes) which causes the computer to further lean out the fuel mixture. The solution to the issue was to not only change the target AFR, but to manually add fuel to the areas around the misfire. Eventually it settled in and it seems to be fine. However, that's just another lesson how the computer can be too smart for it's own good.

Anyway- my driver was fairly impressed with the response and steady pull of the motor. It's not a high horsepower motor, but it's definitely a steady pull to 5500 rpm. It's been a long road, but the results are pretty satisfying at this point.

 

[Meep-Meep]

Charger flogging is just another service I offer - free of charge! Thanks for the MS tutorial by the way. EFI is in my future once I clear my plate.

 

[dpstark2]

On Tuesday, my dad, brother, and me got together for some drive time with our cars. More on that in another post in a few weeks- there was a reason we were out in these cars, without A/C on a 100F+ day. After some 80-ish miles of driving, I can definitely say there is a benefit to EFI I hadn't entirely considered.

It was hot. My car normally runs 195-200F on hot days. It easily topped 205F in normal operation and got closer to 215F in traffic once. When I had done this sort of drive carbureted, those conditions would cause all sorts of loading up and RPM cycling. Bucking, poor response, gas smell... It would recover when I got moving and temps came down, but it was pretty unpleasant.

And forget about it starting easily if you parked it...

The motor never flinched once under these conditions. Fueling was as good as it is any time- which is not to say perfect, but pretty good. I was pretty nervous when the motor temp would climb up like that, but at least I quickly learned it wasn't going to stall, bog, or stutter. It just ran like it usually does.

It's not perfect. Never will be. But it sure ran well and it never gave me the slightest trouble. And boy does it like the freeway. We had wide variety of driving conditions and I think I averaged around 10mpg, including a couple runs up to near a 100mph. I'm pretty happy with it!

 

[Seventy]

I have a mega squirt on my turbo hayabusa running a secondary set of injectors mounted in the air box, makee 420 hp and weighs less than that in #'s... They make good stuff...

 

[Mr.SpeedFreak]

Charger flogging is just another service I offer - free of charge! Thanks for the MS tutorial by the way. EFI is in my future once I clear my plate.

I may need to take advantage of that service one of these days as well haha. Bring Doug up for the Crescent City run this fall, too, I'd love to see megasquirt working on a car up close in person!

 

[dpstark2]

One of the issues I've had since I got the MS3 TBI going was an unpredictable idle. Idle was rough, the IAC made little difference, and changing the table had little to no effect the actual AFR produced. I blamed all of this on the TBI, thinking it was likely not sized correctly for the motor. It is, after all, a unit intended for small block Chevys.

I'm pretty sure I was wrong.

It all started when I uncovered a weird response at 1600 RPM while cruising. AFR would start normal, but over 5-10s, it would lean out until it misfired. I tried adding fuel to the table at 1400 and 1700RPM as these were the only columns in the table (it uses math to create the 1600 RPM fuel numbers). All this did was richen those RPMs and not fix the 1600 RPM problem. So I changed the table to have entries at 1400, 1600, and 1800 RPM. I ended up adding 30% to the fueling at 1600 RPM to get it stop misfiring noticeably, but it was still lean and logs still showed AFR oscillating a lot. That didn't make much sense to me. I would expect adding 30% to fueling out of desperation would cause a pretty rich condition.

After explaining the problem to a multiple people, I was pretty convinced something was fundamentally wrong. Doing some research, I found a note regarding fuel pressure and the pressure regulator vacuum reference. It turns out that for TBI motors, the vacuum reference should be left open to atmosphere. I had it plumbed to manifold vacuum.

While I still can't explain things completely, I can say that the motor behaves much better and more predictably with the vacuum reference open. I had to heavily modify my tables, but after that, it came up and ran so much better. Idle is much smoother, and changes to the table actually have an effect!

The point of the vacuum reference is to adjust fuel pressure so that the differential pressure across the injector is constant. That is, that the injector sees a constant pressure relative to the spray side of the injector. In MPFI, the injector is in the manifold so the spray side see manifold pressure. In TBI, it sees atmospheric pressure. By referencing manifold pressure, I was reducing pressure across the injector under all conditions. At cruise, fuel pressure would have been as low as 30psi. I believe this led to a poor spray and unpredictable amounts of fuel.

It's so much better now. WOT has always been really good. It's nice to have predictability all around though.

 

[440roadrunner]

I had "scored" a Commander 950 TBI system pretty cheap---under 400, complete. I ran it one summer, but was never able--by myself--to fully get the tuning just right, although I DID get it "very" drivable. Minor cold and "extreme" hot start issue. I was somewhat happy.

I wanted auto tune, and "nearly" went with MS, but after adding up "all the extras" it was nearly as cheap ---a bit over 1K -- to buy the Holley HP and harness to upgrade the Commander system. I would STILL like to play with an MSII if I could get into it cheap enough.

I disagree somewhat, with the complaints made earlier a bout TBI. While there is no argument that MPFI is "better" in many many ways, TBI can be VERY VERY drivable. Considering the simplicity, I see no downside as one more alternative.

Glad you finally found your fuel pressure problem. Heh.......there are so many details when DIY

So far as your idle problems and cam overlap, Holley (I'm not an expert) talks about running the thing in alpha -N at lower RPM instead of the normal system. Can you do that with MS? Migiht be something to check into

 

[dpstark2]

I believe you can blend alpha-N and speed density. And my complaints about TBI were probably unfounded. MPFI must be better but I think the issues stemmed from the fuel pressure. I think. I hope.

My cam is pretty mild. From what I've seen, it's responding well enough. I'm just happy to be on the right track now.

 

[dpstark2]

I was finally able to get the MS3 computer to control the ignition timing. There were a few hiccups, but now the computer triggers an MSD box just like a set of points would. The computer controls advance entirely. There is still a distributor sending spark to each cylinder, but the MS3 does the timing. I had to swap in a locked out distributor and carefully set the rotor phasing, but once it got dialed in, things were good.

The computer has a table that sets advance based on manifold vacuum and RPM, just like the distributor would. However, it gives you infinitely variable curves. I started by making very basic table that advanced with RPM, like the mechanical part of a distributor. In the pictures below, the Y-axis is manifold pressure. WOT would be near the top, idle is about the "60" row, and cruise is near the bottom. I settled on this table:

There is no vacuum advance on this table. All I tried to do was get a consistent ping and misfire free acceleration through the gears at medium throttle. My motor seems to like close to 10 degrees near idle, but a pretty fast advance rate after that. Beyond that, I really don't know what I'm doing here.

Here is a table generated by a tool online that makes some assumptions based on cylinder head design, bore diameter, idle speed and vacuum, etc. I'm not sure what's going on here, so if anyone has theories, I'm happy to hear them.

What I can say is the motor didn't like this table very much. Cruising, idle, etc., were all pretty good. Acceleration was not. Minor misfires and surging happened a lot, as well as really lean readings on the O2 sensor. I think it's a reasonable start but I'll need to adjust it to match the first table along the path that would describe normal driving. I hope to do that and smooth out this table and try it soon.

The beauty is these changes don't even require opening the hood. You can do it with the car running. To get the first table, I started with 10 initial and 32 at 2500 RPM. Then I bumped columns a degree either way until things smoothed out, then interpolated the rest of the table. In half an hour. Without opening the hood.

Response is so much better too. It's pretty impressive. I do hope to do individual coils at some point, but it's not going to be soon.

 

[dpstark2]

I started collecting parts to convert to multi-port fuel injection a while back. Well, I finally had them all and the time to do the swap. Over the last two weekends, I swapped from the Edelbrock Performer RPM manifold to a multi-port Edelbrock Victor manifold. I reused the throttle body I had been using, just left the injectors in place and unconnected. The kickdown cable worked as before, but my throttle cable came up about an inch short. I managed to cobble something together, but it will need a new cable. Fuel lines needed modification, but eventually it all came together.

The car runs marginally better. Idle quality is noticeably better. Response is better. Cruise and normal driving isn't much different. However, what is most amazing to me is that in gear idle is nice and steady at 750 rpm whereas before it would always cycle a bit no matter what I did. I attributed this to the TBI unit. I expected to trade that issue for some others issues with the big single plane manifold, but there really aren't any. I can only conclude that there was some kind of fuel distribution issue with the dual plane manifold and TBI. I guess it makes sense if you think about it a little, but I didn't expect such a difference. The car also had a lean spot at 1600 rpm that I couldn't explain. That is also gone now.

There is one issue remaining- the second hand injectors I picked up turn out to be much smaller (flow-wise) than advertised. I will need to replace them with larger, appropriately sized injectors before much more driving happens. I calculated something around 42 lb-hr injectors should be required. The ones I have were supposed to be 36 lb-hr, which I could compensate for with higher fuel pressure. What I have seem to be 20-22 lb-hr injectors... Way too small. The motor can't do much more than 3krpm with these injectors. Fine for driving around the block, but not for much else.

Hopefully I'll find some injectors this week and get back to tuning. I think things are finally on the right track.

 

[66chargerpat]

Glad to hear it's running better. Are you running sequential now or still batch. Thank for the up date. Pat

 

[dpstark2]

It's running semi-sequential. I need a cam sensor to get to full sequential. I don't intend to ditch the distributor any time soon, so I will be working up a cam sensor based on a points distributor in the future. I can switch between batch fired and semi-sequential, and I can say that as things stand, idle is very VERY slightly noticeably better in semi-sequential. I don't know if it makes a difference anywhere else.

I found some genuine Bosch injectors on eBay remanufactured and flow tested for $140. Hopefully they arrive within the week. I don't really trust the Chinese knock-offs and these come with full flow sheets too so I can eventually do injector trim tables, if necessary.

- - - Updated - - -

Here's a link to a movie of the car running. I had not re-tuned idle yet and it does cycle a little. However, it's way better than the TBI/Dual plan combo.

 

[dpstark2]

Remanufactured 36 lb-hr injectors arrived last night. They are going in TONIGHT!

 

[dpstark2]

Got the injectors in and the car fired off last night. I'm pretty impressed. After tuning idle and doing some driving, my fuel map is finally starting to look normal. I think there were some issues with the combination of the TBI and dual plane manifold. I'm still using the same throttle body, but without the injectors in it. MPFI is definitely an upgrade in this situation. Idle control is actually working correctly.

The car idles much better than it did on TBI, and I'm surprised it idles well at 700-750 rpm with this single plane manifold. Response is good, although having made this swap, I now need to retune virtually everything. The accelerator pump function is pretty far off. Cold starts, cranking pulse width, and even the timing need some adjustment.

One annoying thing I found that must have been there from the start is that I'm not actually getting full WOT. The travel at the throttle body lever is a bit longer than the travel at the pedal, so I will have to deal with that at some point. It's not like it's that far off (probably 95% of WOT) but if I can have it, I want it.