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What are you using for Q5, the specified IRFIZ43n?

That device cannot handle much kickback from the injector, but maybe it's enough. The coil drivers I'm looking at will handle 100 times as much. I'll try to go thru the datasheet for my injector drivers and see what they are spec'ed at.

R38 is used to sense the current in the injector circuit so that's why it's useful to look at the voltage there. It says it is .05 Ohms. Looking at it some more it looks like it makes more sense to look at the voltage across Q5. An IRFIZ34n has an on resistance of 0.04 Ohms, so it is about the same as looking at R38. In addition if you look across Q5 you will also be able to see the action of the circuit around Q12 and Q13.I know you pulled that stuff off or disabled it, but maybe it's still on the other bank so I'll describe some more.

So at 4 amps of injector current across the resistance of Q5, .04 Ohms, you should see a voltage of 0.16V. What you would see on the scope is 12V when the transistor is off. When it's turned on the voltage will drop to 0 and then gradually rise to 0.16V over a couple of milliseconds. If you unshort R38, you would get twice as much voltage to read if you measure across both R38 and Q5. You will also be able to see the action of the Q12 and Q13 circuit when the injector is turned off and the voltage rises to 12V again. The part in the schematic would allow a spike to 55V or so.

I find the PWM circuit fix to be a bit confusing. I don't understand how the two flyback circuits work together really. So if you have high impedance injectors, leave out that PWM stuff ( which you have now removed ).

Someone in the MS thread commented that the flyback circuit affects the injector dead time. What it does is affect how quickly the injector will close after the switch turns it off. It is required in some form or other to protect Q5. Many times this is included on the transistor itself. The IRFIZ43n includes an internal diode that will clamp at 55V, if it's installed the right direction. If it's in backwards it will work but require the external flyback circuit.

So this flyback thing - if you just installed a simple diode to provide flyback protection everything will work, but when you turn off the injector the current from the collapsing magnetic fields will recirculate around in the injector and thru the diode until it dissipates in resistance of copper wire and the diode. All the while holding the injector open. So on your scope you would see the voltage rise above the normal amount for a short while and then gradually descend to 12V ( 14V is I suppose but you get the idea ).

If you use a 40V Zener diode the voltage will have to climb to 52V to recirculate thru the injector. It will be dissipating 40V thru the diode instead of the 1V for a normal diode. That will kill the current much faster and allow the injector to close. You can easily see this on your scope.

I'd be happy to drop by and visit one of these days. Drove by Duxbury a couple of times this week to visit people on the cape... Finishing a weeks vacation so I may be available this weekend, but not sure yet.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

Marcus,
If you want to swing by this weekend, I am available and can use another set of eyes. My address and phone numbers will be in a PM.
Thanks,
Paul

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Parts left out cost nothing and cause no problems!!

Well... after much screwing around and some serious concerted effort along with my son we tracked down the problem. It turned out that there is a wiring fault between one of the spark IGBT's and the relay board. It was not a fuel problem at all. You could actually see the insulation break down and the channel get weaker and weaker on the oscilloscope as it started to die then finally the signal would drop to the point where the coil no longer fired. We have a jumper wire soldered in going around the entire problem since tracking down the now disconnected wire is going to take some real work as it is buried somewhere in the wiring harness inside the tunnel. I will find it over the winter.
The car is traveling the roads of New Hampshire for the next couple of weeks as I lent it to my son and he has put hundreds of miles on since the repair making us both confident it is fixed.
This problem must have been causing a weaker spark than needed for a long time as I have had to adjust the fuel tables since it was running rich since the repair. Anyway...its all good now!!!

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Parts left out cost nothing and cause no problems!!

Congratulations on trouble shooting it.

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

That was a tough one! Good find and fix, congratulations.

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Larry in Seattle

that's a really edifying result, and is -sort of - congruent with my experience with the B-3 donor the year I stopped riding it (late 2006). it weould misfire badly across all three cylinders over 4000rpm, and I chased it around as a fuel problem for the rest of the '06 riding season. didn't understand that it was simply the coils dying until I tried starting it at the beginning of the '10 season, (when I began the B-3 project) and coils didn't fire at all.

new coils, VROOM.

funny how ignition faults can present as fuel issues at times.

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The B-3 build log: http://www.locostusa.com/forums/viewtopic.php?f=36&t=13941 unfortunately, all the pictures were lost in the massive server crash

The beginnings of the Jag Special,
https://www.locostusa.com/forums/viewtopic.php?f=36&t=19012
Again, all pictures were lost.

So that's interesting. I think it's normal to use a low side switch for the coils, so the ground side is turned on and off. It sounds like your saying the low side wire had a fault. The fault should be an open though or there would have been a blown fuse or a fire. So it shouldn't be insulation, I don't think. On a printed circuit board if there is a crack in a trace as the board warms up it will open the trace ( or a via ). It takes a good amount of heat though, the board expands the most when it gets near the glass transition temperature.

Did you bypass the relay board completely?

The driver IC I am using in my project is a Freescale MC33810. It drives the injectors directly and the gates of the coil drivers. It measures the current going thru the coils with a very small resistor so it can tell some faults, like a bad coil wire or plug. I think it will also flag if the coil current doesn't reach a nominal amount.

I still need to understand the spec for frequency on the injector drivers for you. Here's a dta sheet though if you're interested.
http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MC33810

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

Hi Marcus,
That is correct. Coil fires by grounding. Relay board is in the circuit. The jumper is running from the IGBT to the relay board connection. I have disconnected the old cabling at the DB37 on the Megasquirt itself. Its really weird, I know...but it appears to be rock solid now. Its the season to use the car, so thats the plan since we have done hundreds of miles since the fix. I will certainly let you know what I find when I tear it apart come snow time.
I will check out the FreeScale stuff this week.
Paul

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Parts left out cost nothing and cause no problems!!

So, I told my son he could borrow the SeVen for a few weeks as I had other family stuff going on and it was just going to sit anyhow. He took it up to NH (it is titled at his NH address in any case) and it was his daily driver. He put 1000 miles on it in 3 weeks!
When he brought it back today, the 2 of us put together a to-do list for it (mostly minor and not keeping it from driving, but should be addressed)...Oh yeah, it passed NH inspection!
the list:
1. minor oil leak in pan where I welded a patch on it. I will fix this next oil change which is nearly due.
2. really minor exhaust leak in header. You would not even know except that it leaves a bit of soot on the paint.
3. gas tank vent gets fuel in it with a full tank and in a hard left hand turn...will reroute vent hose across the tank so that it cant do that. I thought that the roll over valve would address that, but no.
4. squeaky urethane bushings in rear suspension. OMG....that got loud in last 3 weeks, needs addressing soon.
5. front fenders hit the headlights at full lock...not sure how to address yet, probably shim the lights up a little bit.
6. screws that hold the front fenders need loctite. I have already tightened and he needed to retighten so blue Loctite.
7. better velcro to hold the rear cover on. the Velcro works great, but the adhesive on the Velcro gets soft sitting outside in sun.
8. time to drill some drain holes in floor in strategic spots
9. reinstall oil pressure gauge sender with a better mount. the brass "T" that it came with cracked.
10. look at one of the rear brake calipers as one side of the parking brake does not hold properly. I guess they missed this in inspection.
11. as a winter project, I am going to connectorize the wiring harness to make it neater and easier to service...also track down that MegaSquirt harness issue.
12. fuel starvation in long right hander if under half tank of fuel...this needs addressing real soon. I will start a new thread on this.

Anyway, the car performed great for him. It now has around 2200 miles on it and its continues to entertain all!

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Parts left out cost nothing and cause no problems!!

Good catch on the oil sender line crack. I've read that before, the copper fatigues - just not a good place to use it. I was curious so I just figured out that since an I4 engine vibrates at twice it's RPM it produces a million cycles every 3-4 hours or so. I was surprised.

If you hadn't caught that it would have made a very big and also very flammable mess...

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.

Woohoo!!!
First drive of the new year. Still kinda chilly but at least the roads don't have salt on them anymore. Sand...that's another story. I had sand in my hair, shirt, pants, shoes, you name it. The car was of course similarly inundated with the stuff. I don't care!!! Totally worth it.

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Parts left out cost nothing and cause no problems!!

I think the Seven got its moniker from the 7 pounds of sand and gravel picked up from a short drive. Congrats on the first drive of the year. I had mine last Saturday taking grand-daughter and DIL for a drive and let my son drive a short bit. All on a calm, sunny 38 degree day. It was chilly, but oh-so worth it.

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

Wow, up here in the great white north it was 68 degrees today. I took mine out for the first time today too. It was my son's 4th birthday and we took a quick trip to grandma and grandpa's place while my wife and daughter were in town.
Kristian

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V6 in a book frame build. Now registered.
viewtopic.php?f=35&t=7587
viewtopic.php?f=33&t=18172

Hodgepodge passed inspection today for the second time! (to be honest, they don't really check it that thoroughly). My son and I plan to take it to an autocross this weekend. That should be interesting as I have never truly thrashed it and I am sure my son will. As for me, it has been years since I have done autocross...I just want to be respectable. I have reminded my son that it would be good if we could drive the car back home rather than having to get it flatbedded or trailered.
On a side note...it collected its first squirrel yesterday. Smells bad with roasted squirrel on the headers.

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Parts left out cost nothing and cause no problems!!

Not much meat on a squirrel... They do make a good gravy though. Now, get a few rabbits and half-a-dozen squirrels and you got a good stew!!!


JD "Used to Live in WV" Kemp

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JD, father of Quinn, Son of a... Build Log
Quinn the Slotus:Ford 302 Powered, Mallock-Inspired, Tube Frame, Hillclimb Special
"Gonzo and friends: Last night must have been quite a night. Camelot moments, mechanical marvels, Rustoleum launches, flying squirrels, fru-fru tea cuppers, V8 envy, Ensure catch cans -- and it wasn't even a full moon." -- SeattleTom