Megasquirt - Assistance Needed, Very strange problem Options

[yarin]

I drove the car last thursday, ran fairly rough but had some power. Did some tuning, and had this very odd firing problem. I spent some more time today digging into this, here is what i found:

INJ1 bank hooked up to cyl 1 & 4
when either injector connector disconnected rpm goes up
when either spark plug removed no change

INJ2 bank hooked up to cyl 2 & 3
injector disconnect, seriousl drops rpm

Tried both combos. Alternating, 4 and simultaneous 2. reqfuel 9 / 4.5

So my conclusion is that all cylinders are getting spark, but only two are really firing. Furthermore a quick touch of the exhaust port shows that cyl 4 is running much cooler than cyl 3 after idling for a few minutes. I swapped the cyl 3 and 4 injector drivers and noticed an immediate change in head temp. It sounds like the cyl 1 & 4 are getting fuel, but not igniting. When those cylinders no longer receive fuel, the rpm goes up indicating no combustion, but resistance to compress the fuel.

Make any sense to anyone? I attached my .msq file. I double checked my setting, i made sure i'm only running off 1 table. I just took apart my MS box and can't find any obvious shorts, burns, etc. Keep in mind i'm only looking for this problem at 1000-1500rpm. It's not injector related, its driver related. (IMG:style_emoticons/default/sad.gif)

Anyone?

[DNHunt]

Yarin

Get someone to help you check spark. Make sure you have fire in each hole. I suspect you have spark but no fuel.

I believe there is an option in the fueling menus somewhere that lets you turn off 1 bank of injectors. Why they would have that I don't know. I got stuck on that once. If that's not the case start looking for problems with the hardware.

Dave

[lapuwali]

I think the one bank thing is if you're running all of your injectors off one driver, which you can certainly do with a four, and a number of people do so. If you're suspecting one driver is bad, try wiring all four up to the one good one, set this option, and run that way. Solves the alternating/batch question, too.

If this is so, then the driver FET may have let the smoke out...

[yarin]

I think the one bank thing is if you're running all of your injectors off one driver, which you can certainly do with a four, and a number of people do so. If you're suspecting one driver is bad, try wiring all four up to the one good one, set this option, and run that way. Solves the alternating/batch question, too.

If this is so, then the driver FET may have let the smoke out...

Can the driver handle 4 low impedence injectors with PWM on one bank? I'll try this tomorrow. (IMG:style_emoticons/default/type.gif)

Dave - I believe spark is OK based on my timing light. I get a consistent equally spaced strobing for each plug wire.

I might bring my MS to work tomorrow and hook up the injector outputs to a scope and see whats going on. Would be neat to capture the PWM waveforms.

[DNHunt]

Yarin check the menus. I think you can turn one of the banks off. At least when I had that prob I found some obscure option to deselect and all was well. Certainly worth looking for before you start taking stuff apart.

Dave

[yarin]

Yarin check the menus. I think you can turn one of the banks off. At least when I had that prob I found some obscure option to deselect and all was well. Certainly worth looking for before you start taking stuff apart.

Dave

I can't find anything. It might be an MS I option.

[lapuwali]

Yes, one driver can handle four low-Z injectors. This is how V8s run. I think one driver can even handle 8 low-Z injectors, so long as you use resistors or PWM properly.

You also don't have to turn off the driver. With no load across them, they can be triggered with no harm (assuming the "bad" FET isn't actually bad at all). People ask this regularly when trying to run MS as spark only. I believe Eric Fahl (author of MegaTune) is running at least one of his cars with all four injectors on one driver.

[yarin]

I moved all injectors to INJ2, set injector driver to simultaneous, 2 injection and reqfuel of 9. Started it up, noted the following:

Idles much higher, ~1700rpm, unstable idle
AFR jumps erratically between 14 - 16
Pulls much more vacuum ~27kpa
According to the timing light one plug doesnt fire consistantly, it misses which appears to cause the unstable idle.

My next step is to check the valves. Last time I checked them a year ago they were in spec. Might as well check them again for piece of mind even though I haven't really driven the car. Can't valve clearance issues be the cause of my problems?

[lapuwali]

Checking the valves wouldn't hurt, though I doubt that's the source of your problems. You changed plugs recently, I assume. When was the last time you changed plug wires? Cap? Rotor? How are you firing ignition right now?

[mightyohm]

I am sure you mentioned this somewhere, but are you using PWM or injector resistors?

I suggest injector resistors around 5-10 ohms per injector until you get everything figured out. PWM is risky in my opinion. Too easy to blow stuff up unless you know the settings in advance.

I agree with James, make sure your ignition system is totally working before you get too far down one troublshooting path!

[yarin]

I changed plugs, but the suspect cylinder looks fouled again. I have one plug left i'll change. Is there any way to clean the plugs? Sand the electrode a little?

Stock dizzy with mechanical advance.

PWM should work fine if its setup correctly which is easy to do. essentially 30%, 1.0ms, 1.0ms are your base settings. There is no need to go with inline resistors if your hardware supports PWM.

I'll try to throw my MS on a scope tomorrow and capture a few waveforms.

[JeffBowlsby]

I have only loosely followed your posts yarin, but wonder if you may be having EMI issues? What does the configuration of your harness look like? Did you use any twisted pair or shielded wiring? Is the harness physically routed away from the ignition wires? What is the configuration of your ground circuits?

[mightyohm]

Yes, but are you using a flyback board?

I don't think MS recommends driving 4 low Z injectors without the flyback board, especially if it's off one driver transistor. It's easy to burn up the board.

[yarin]

I spent some more time on the car tonight... here is my update. Anyone and everyone please chime in and give me your thoughts, i'm stuck.

I tried the suggestion of running all 4 injectors off one bank with the same pulse width modulation settings. ~20%, 1.0ms, 1.0ms, 66us. Car ran, a bit rough though. MAP dropped to 27KPA, no idea why. Idle wouldnt drop below 1400rpm either. I tried unplugging each injector one at a time, all caused a drop in RPM. Good sign.

I wasn't getting anywhere trying to solve the unstable / high idle issue with all injectors on one bank so I moved back to both banks.

The other day I brought my MS II to work with the stim and checked output on both injector banks probing off the LED to +12V. I captured the waveforms, will post tomorrow... bottom line is the signal coming out of my MS box looks perfect. PWM behaves exactly as defined on both channels. Of course I don't know how it performs under load.

When going back to 4 injectors split over two banks the following changed. Idle MAP back up to 37KPA. Idle dropped to 800rpm with idle screw all the way in. I even tried reflashing with firmware 2.33. I started from scratch with megatune as well, all new settings. SAME PROBLEM:

One injector drive signal causes the strangest problems. When disconnecting the injector, idle goes up. When disconnecting spark, nothing changes. This occurs for 2/4 injectors on the same bank. The other two behave as expected. When all injectors were connected to the same bank this did not happen. Which leads me to believe it is an injector driver problem. Tried alternating and simultaneous injections as well, same result. I know the "weird" cylinders arent firing properly because those two cylinders are cooler to the touch.

Strange right? Problem follows the injector bank. Spark is good, plugs are ok. timing light fires as expected when clipped to each spark plug wire.

Please give me anything you can possibly think of.

[yarin]

I have only loosely followed your posts yarin, but wonder if you may be having EMI issues? What does the configuration of your harness look like? Did you use any twisted pair or shielded wiring? Is the harness physically routed away from the ignition wires? What is the configuration of your ground circuits?

Jeff,

It's possible... The MS brain is mounted under the dash. My harness is running to the relay box in the engine compartment. No twisted pair. Shielded wiring only on the ignition wire from the dizzy all the way to the brain. The ignition is in the same bundle as the ignition wire. However i'm only getting a tach signal, i'm not firing a coil using MS yet.

Ground is going to a ground bus in the relay box which is bolted to the engine/tranny. No voltage spikes.

MS II V3.0 has built in flyback circuitry, so PWM with 4 low Z injectors is OK.

Also checked the valves the other day. The #4 cylinder was about 0.002" tight on both exhaust and intake. This is the cylinder that ran for a few minutes with an open injectors. I adjusted and checked everything else. No problems there. Also tried dual tables, still the same funky injector issue. ?????????

[yarin]

(IMG:style_emoticons/default/chowtime.gif)

[crash914]

Yarin, at this point, I am lost.

The only thing that I can suggest is eliminate the variable of the PWM by using a 10ohm resister.

This is the only way I have run mine. Give

it a try, nothing to loose at this point...good luck!

[yarin]

Yarin, at this point, I am lost.

The only thing that I can suggest is eliminate the variable of the PWM by using a 10ohm resister.

This is the only way I have run mine. Give

it a try, nothing to loose at this point...good luck!

I'm also running low on ideas here. Tonight i'll read the AFR off one cylinder and see what it says.

Here are the waveforms from each injector bank that I captured. Hooked up the scope to the LED output on the stim and +12V.

[drewvw]

yarin...I know your probably frustrated as hell right now but keep fighting the good fight. For guys like me that want to install a MS at some point, its wicked interesting and helpful to read your progress reports.

Seems like a real challenge.... (IMG:style_emoticons/default/beer.gif) (IMG:style_emoticons/default/givemebeer.gif)

[fiid]

Is there anything going on with your cold start injector? The one on the plenum?It should be unhooked and not leaking.

Have you checked that your fuel pressure is good? you could try removing all the injectors and firing them into jam jars to make sure it's fuelling right?

I'm also suspicious of your ignition system - is your timing right? Can you verify that 1&4 are firing correctly using the timing light (i.e. try clipping it to both those HT leads).

Do you have an oxygen sensor hooked up? What happens to the mixture when you see the effects you in your first post?