West-se

So I pulled my engine out yesterday, peek into the exhaust port on the front rotor coudlnt really see any visible problems or signs of broken seal or damage. I will be breaking it apart this week and finding out for sure.

My friend came over to help me pull the engine who I sold my old secondary 550cc injecters. He told me after he got them he installed them and his car ran like crap. So he tested and came back 1 hi imp and 1 low imp... wtf ? I thought must have gotten mixed up when the previous owner had my car. Well long story short when he came over he wanted to test my primaries to verifiy a hunch he had, and what do you know 1 of my 550 primaries was hi and 1 was low, the hi was on the front rotor which has the problem. Now either the guy i bought my car from installed the mixed injectors by mistake or the guy who replaced my seals (3 days after i bought it) mixed them up, now considering that last time it failed it was the front rotor too the guy who replaced my seals most likely pulled the primary rail and left the injector alone. Or he installed them mixed by mistake but this I doubt.

Now my question is this, what are the implications of running mixed injectors on the same rail. My limited electrical knowledge would tell me that the hi impedance injector would not receive enough amps to run correct producing a intermittent spray or possibly not spray at all. Can anyone with more experience explain what would/could happen from this. I guess I am wondering how likely is it that this Hi Imp injector has caused a lean issue and caused my seal to fail ?


-Sean

muythaibxr

It really depends. What year is your car? Are you still using the stock harness or did you build your own? Did you set up the MS for Low-impedance injectors (assuming you don't have a resistor pack)?

It could also be that if you didn't set up the MS for low impedance injectors, and you're not using a resistor pack, you may have fried the low-impedance injector too.

Maybe before you rip apart the engine, you can make both the primaries high-impedance, and start up the car to see if it runs right? Depends on whether you're sure you blew a seal. If you're pretty sure after looking through the exhaust port that you didn't blow a seal, then you shouldn't be able to damage the housings by starting the car back up.

You should be running either all high impedance or all low impedance with the MS; it's not good to mix and match them since the MS can't control the PWM settings on the 2 injector channels independantly with the staged injection code. (I think it can do that with the dual-table code).

West-se

No need to dumb it down here Ken

my car is low impedance, Im still using the factory harness for my injectors. I have the resistor packs still in use. The front rotor is toast no question.

My question is what is the implication of running a high impedance injector in a low impedance circuit. I know you can run mixed as long as its in the same bank and you bypass the resistor pack. This isn't the case, this is running both in the same bank on the primary rail. What would be the expected outcome ? How will the Hi impedance injector flow ?

SirCygnus

iTrader: (1)

dang mang. sorry to hear that.

muythaibxr

I don't really know how it'd flow.

Your theory is probably correct though now that you've told me how you were running it. I'm willing to bet that injector wasn't opening all the way, or its opening time was WAY longer than it should've been. Either way that rotor would've been running quite lean.

Oh and I wasn't trying to dumb it down, just didn't know the answer based on the info given, so I was trying to cover a likely case...

Eagle7

The low impedence injector harness has a resistor in series with each injector so that with 12 volts applied it will draw about 1 amp. A high impedence injector with that resistor in series will only see about 6-7 volts and draw about 1/2 amp. It will be slow to open and may not open fully, which would give you the rotor-eating lean condition.

scotty305

iTrader: (2)

If you had a high-impedence injector in a circuit that was designed for a low-impedence injector, all your hardware should be OK. It's impossible to feed a high-impedence injector too much current, because the higher impedence won't allow as much current to flow. Impedence is nearly identical to resistance, so we'll treat the injectors as if they were resistors, to avoid complex mathematics.


For instance, if you connect a 2 ohm injector directly to your 12V battery, the current flow will be:
current (I) = voltage(V)/resistance(R) = (12V) / (2ohm) = 6A
6 amps of current will fry your injector if you leave it connected for too long. I'm not intimately familiar with the megasquirt's ignition driver circuit, but if it's designed to run low-impedence injectors, then it will be able to handle that much current. It will also have a 'peak-and-hold' circuit, which will vary the amount of current supplied to the injector to avoid burning it out.



Let's try the same thing with a high-impedence injector. The impedence should be 15-20 ohms. Let's assume 20 because it's easier to do the math. Current draw will be: I = 12V / 20ohms = 0.6A. Even if we somehow got a high-impedance injector that only measured out at 10 ohms, it would only draw 1.2 A of current. So it's very very unlikely that you've fried your circuitry or your injectors.


The problem would be if you used a low-impedence injector in a circuit that was designed for high-impedence injectors. You would probably fry both the injector and the transistor used to drive it.


Some more info:
http://www.asashop.org/autoinc/nov2004/techtotech.cfm

-s-

muythaibxr

what I was saying that if he wasn't using resistor packs, and didn't set up the MS for PWM peak and hold operation for the low impedance injectors, he would've probably fried the low impedance injector.

The injector drivers can be short circuited and sit there at 14 amps of current and not burn out (on the v3 board)

There isn't a peak and hold circuit really unless you're talking about the flyback circuit.

renns

Looks like you found the source of your problem. Sorry to hear it took out the engine...

Eagle7 answered the question. The front high impedance injector never sees the full 14v to snap it open due to the series resistor. That will result in much slower opening times as compared to the rear rotor. Commanded pulse width (signal from MS) front to rear will be the same, but effective (actual time injector is fully open) will be much less up front.

muythaibxr

by opening time I mean the time it takes the injector to open, so pretty much all of our responses have said more or less the same thing.

That's an expensive mistake to be sure! Hopefully you get it fixed up soon.

West-se

Thanks alot for all your responses very insightfull. It confirms my theory with some actuall science thanks. Im hoping to break open the motor tomorrow and see how bad the damage is inside.

Shifting gears here, does anyone know where I can find a good techinical write up on dowelling the housings, I've got access to a full machine shop and some skilled machinists. If I can find a good write up on how its done and such I can hopefully dowel my engine while its apart.

West-se

I am back!

It only took 5 months to get my engine rebuilt. Turned out that I cracked an apex seal which then machined the rotor housing for me and destroyed the other 2 seals in the process as well as a few corner seals. It wasn't pretty, so a new rotor housing later and alot of seals and countless hours its back in the car and running.

While it was out I've added a few things (pictures) I added a TD07 mitsubishi turbo said to make 425-450 @ 15psi an HKS cast manifold, HKS 40mm wastegate, I also uppped my primaries to 720cc, also added new AN-6 fuel lines with parrallel feed system as per fc3spro.net shows with aeromotive a1000-6 regulator. And a new front mount intercooler.

I fired up the car over the weekend without the intercooler piping so effectivly running as an n/a and it fired right up. Check all the vitals and everything is operating Ok. Last night I took it for a drive around the block in n/a mode and I still think I've got issues with my secondaries it was stumbling hard during the transition, mind you I didn't drive it hard or far, I just took it up to 4500 slowly, I am wondering what is the best way to test my secondary driver ? remove the transistor and test or will the stimulator be able to test it to see if its working right ? I've got a suspision that the transistor is dead after having crossed polarity on the secondaries before I broke my apex seal in the spring.

muythaibxr

if in doubt, just replace that transistor... however, if you are slowly revving up then the throttle might not be open wide enough to get enough airflow by the secondaries.... so that could cause your stumbling too.

Or it could be settings..

West-se

I've tested with the stim and show INJ2 working fine and now dc2 and pw2 actually work with this version 29q since I was using an earlier version and those 2 values didn't work with staged injection. Considering my VE1 is totally wrong for what I'm doing combined with a couple vacume leaks there's good reason to believe these are the culprits for the stumble. I will triple check my secondary wiring since I rewired them myself this time around.