MS1 PCB3.0, SBC TBI - blown injector circuit

[toyotaspeed90]

Something very strange just took place.

I've been setting this up for a while - I'm not new to MS. I recently rebuilt the DB37 with all new wiring - I know the wiring is better than good (I used the 23" DIYAutotune kit then incorporated it into the engine harness using male/female connectors so I can unplug and test/diagnose any wire at any time).

The recent change/addition is an LC2 wideband/controller (without gauge). It's wired in properly and I calibrated it (and tested the circuit I built before connecting to MS). I had tried to follow the instructions for changing the project to Wideband (except they are slightly incorrect) and at first wasn't able to get the AFR target table to populate. The MS had burned values for the wideband, but not the AFR target table. I played with tunerstudio, disconnected, and found the AFR target values located within the Lambda setting, not th EGO controller - so I made the changes in Tunerstudio.

I started the truck in the garage as a test fire and all went well. Shut it down - attached the air filter.... (there have been many test fires, running at idle, etc in the past - maybe 20+ starts and some runs upwards of a minute, but didn't leave it running long as it was in the garage).

Then I connected the laptop - Tunerstudio saw a difference between what was in the MS and what was in Tunerstudio.

I allowed Tunerstudio to make a change, and was going to back the truck up into the driveway.

Went to start, heard a bang (like a tool had fallen and got caught in the drivebelts).... I found fuel seeping below the fuel filter.

I pulled the air filter off, turned the key to 'on' to see 1 (of the 2) injectors spraying fuel - instantly shut it down. (Reminiscent of a V1 2.2 board that failed injector circuits and just about killed an engine by leaving the injectors wide open (circa 2005) in an attempt to start the vehicle.)

Checked wiring - 12V+ and ground at the injector when key set to on. So I worked my way back - other injector is fine, checked the wiring from the male/female connection point to the injectors - no ground continuity.

Knowing that the *only* change was to the wideband and AFR stuff, I turned the wideband off, went back to narrowband settings, turned off the AFR table, and no change.

The 'failed' circuit had ground continuity when the key was on or off.


R15 seems to have blown, and unsure what else may have done so.


Doing a little research online I have found a diagram but not much else in mentions to how/what R15 is connected to the system.


Normally I wouldn't blame software, but that is the only change that took place after quite a lot of successful starts and countless 'key on' situations.

Any help would be appreciated.... attached is the MSQ with only O2 related changes back to narrowband...


Any thoughts on the cause?

How can I properly test all pieces of the injector 1 circuit to find out what failed and what didn't?

[toyotaspeed90]

I had the resistor (spare) and replaced it.

I am getting continuity across all pins of Q1 and Q14....

I am not getting continuity across all pins of Q11 nor Q15, which seems to be for the injector bank that didn't fail.

I have an old (unused) mosfet chip with "IRFIZ34G" on it, digikey says it's obsolete and new number is IRFIZ34GPBF-ND, which is the Q1/Q11 pieces..... I see one contains lead, and one doesn't..... is that the only difference?

http://www.digikey.com/product-detail/e ... -ND/352408
http://www.digikey.com/product-detail/e ... -ND/812106

[slow_hemi6]

This is a good walk through of testing the injector drivers. https://www.diyautotune.com/support/tec ... or-driver/

[toyotaspeed90]

I've ruled out U4, but the instructions really only help narrow down to Q14 or Q1.... no mention of how to identify which failed, or if Q1 has all 3 pins grounded (without stim) what that means (since this only happens on Q1).

The flyback circuit is also fine (injector 1 stuck on even with D5 desoldered).

Also unsure how it happened to only 1 injector circuit.... something is afoul....

[toyotaspeed90]

Like I said - wiring in the truck and to the MS is all good with no shorts.

Injector 1 ohms at 1.6, Injector 2 ohms at 0.5 (concerning since the other 4 spares I have all ohm at 1.6). However circuit 1 is what failed and the flyback circuit is fine.


I'm hard pressed to blame Tunerstudio, but it's also extremely convenient that it asked to make a change, and the next instant is when it failed - the only changes being to the Wideband.

Although I've orederd 10 spares of each Q1/14 components, I don't want this to happen again - I had a hell of a time making an old MR2 be reliable on MS V2.2 due to bad injector circuitry and I thought the PCB 3.0 resolved those.

Is there any chance that somehow the higher voltage of the wideband affected the injector 1 circuit?

[toyotaspeed90]

Q1 definitely failed, Q14 I'm unsure of.

Removed Q1 and all 3 legs have continuity. Haven't tried the above mentioned spare part.

The Q1 points on the board now only have 1 leg with continuity to ground, matching Q5.

[toyotaspeed90]

An update, though I doubt anyone is following.

U4 was fine until I did some testing and jumpered something I shouldn't.... so ordered some of those.... plan to get an 8 pin dip ic socket so they won't have to be soldered...

Going back to the V2.2 days where the injector circuitry isn't reliable, extremely disappointed. If I had known this was still an issue I probably would have bit the bullet and incorporated a stock TBI ECU instead.

To mitigate the problems I've done some testing - each injector seems to be fine with independent firing (without MS, just grounding), but if I fire both, a fuse up to 15a blows - I had a 20a in place when the ECU went. As stated above, there's a variance in the resistance between them but the concerning injector isn't the circuit that blew. I have extra injectors so I will swap them.

I also have a Toyota resistor box, so I might wire that in to raise the resistance MS sees.

I'm guessing the problem is either when the MS is turned on it batch fires both injectors - which overloaded the circuit.... or something with the wideband was reading something invalid and MS was trying to compensate by dumping fuel, blowing the circuit.

[billr]

Oh, I'm following... just can't help much because this is MS1

SBC TBI injectors are nominally 1.2 ohms, I think. So, the first issue is what yours actually measure. Low values like that can be hard to measure accurately, you have to dig in the probes hard enough to "bite through" oxides that are on most metals, even when looking shiny. Or, do some accurate V/I measurements, but don't try to hit them with 12V, these are definitely injectors that want " P&H" drive. I would think 5V or less would be more appropriate for continuous power on them.

Do you have each injector connected to a separate mainboard driver? If so, then the drivers on a V3.0 board should be happy, no matter how much they are turned on. Yeah, "both on" may blow a fast 20A fuse, but the driver circuits should be OK. I think adding resistors is going to cause more problems than you want, with dead-time that may be nearly unpredictable.

[toyotaspeed90]

Only 5v for testing, or always? Isn't the factory wiring setup with a constant 12v?

The resistance on the "bank 2" (arbitrary, but just for continuity in diagnosing) is 0.4-0.5.... tested with power, without power, at the wiring, at the injector, and with probes dug in...

[billr]

5V only for testing, when applying continuous power to the injector. Are there two injectors, in parallel, on each bank? I would measure each injector coil individually.

[toyotaspeed90]

It's GM throttle body injection - it has two 55lb injectors, I wired them together on 12v, but separately to MS. They are meant to run alternating, and have them setup that way.

I have 6 injectors, 4 are not installed in the vehicle (2 are spare 55lb units, 2 are smaller from a V6 2.8L), was using them as a comparison for resistance testing.

[toyotaspeed90]

Reading online and I'm unsure which direction to go.

PWM act as a voltage "limiting" circuit to the injectors, which is used for low ohm injectors. The purpose is to effectively lower the voltage by, very quickly, sending signals and dropping voltage - at 30% it should drop from 14v to around 4.2V... which is what I have it set to.

The MS is sending a priming pulse, and from what I've read, PWM isn't in effect when cranking - which means that the injectors get a full 12V signal - which I would assume that any load/draw from the injectors is put on both the 12V signal (from a relay) and on the megasquirt..... This thinking is exactly in line with the problem - when both injectors are held open with full voltage, a fuse 15A or under blows. Now - this could be an issue with the injectors that I can't seem to test.... but, the logic to me seems a bit off - if the injectors are most happy with a "limiting" voltage scenario - isn't the entire system put at risk under a cranking load?


Further in my reading - the resistor pack is only used to limit the voltage, then you set PWM at 100% (or depending on the new resistance it may have a higher PWM).....


So maybe I don't understand - aside from the prime pulse/cranking pulses, why would using a resistor pack to reduce voltage have any different effect than using PWM?

[slow_hemi6]

The PWM time threshold applies the full 12v to open the injectors before the pwm is applied and voltage is lowered. It's Peak and Hold. Using resistors means you don't get a Peak period of full 12v so when using them, your dead time will likely be longer than when peak and hold driven. No big deal really.

[DaveEFI]

Early injection systems used low impedance injectors with series resistors to limit the maximum current to one both the injector driver and injector can handle. To drive them without those resistors (which in theory are a bad idea as they slow down how fast the injector can react to a change from closed to open) you need to use either PWM or a peak and hold board.
I've been using an MS2 V3 using PWM and low impedance injectors for many years with total reliability.
I've always assumed the priming pulse was also PMW, one you had selected that in software. I have four injectors per driver which would take a vast amount of current if fed with plain 12v.

[toyotaspeed90]

I might be coming to the realization that the problem is far too simple...... I can't imagine since this setup should technically run upwards of 8 injectors, but....

Power is fed to the injectors from a relay with a single fuse..... unsure if I mentioned it above - if I have a 7.5A fuse in there, apply 12V, and ground out the other side (not holding long, just taps) there's no issue - but if I run a wire to both 'negative' side wires, and tap that, the fuse blows (up to a 15A fuse). I had a 20A fuse in the system when it happened.

Looking at a relay board the INJ1 and INJ2 run off a common relay, but are then fused separately. I'm wondering if there's somehow excessive draw that overloads the circuit when both are running that would be resolved if I fused them separately with a lower rated fuse. Though to be honest, I may be grasping at straws, because without something like a diode in place, I'm not sure how they wouldn't affect one another still.....