Uneven Injector Firing? - Very Odd Problem

[yarin]

MS II V.3.0 2.33 firmware. Megatune 2.25.
Porsche 914 2.0L, stock low Z injectors (~2.4Ohms). Fuel only, triggered off stock distributor with Pertronix. 2 bar fuel pressure (stock for D-Jet). MS II under dash running to relay box in engine compartment. Shielded tach wire.

I've taken the car out, driven it.. but noticed something very interesting. I suspected some cylinders weren't firing properly. So I walked around the car pulling each injector connector off one at a time. Two produced expected results.. drop in RPM. Two actually increased RPM, (900 -> 1300). When pulling the spark plug wire on the good cylinders the rpm dropped as well. However nothing changed when pulling the spark plug wire on the suspect cylinders.

I tried running all four cylinders off one bank, this problem dissapeared. But MAP dropped from 37KPA to 27KPA, idle increased from a min of 900 to 1400rpm. Also noticed erratic WBO2 readings and an inconsitent idle.

I tried Alternating and Simultaneous in both injector configurations. Same result. I checked INJ1 and INJ2 with 12V lamps at the relay box, they pulse as expected.

I even stuck an oscilloscope on INJ1 and INJ2 when connected to the stim. The PWM waveforms looked identical to one another and behaved exactly as expected.

Any ideas? The problems follows the injector channels, not the cylinders/injectors. Could this be an EMI issue?

Please give any suggestions... i've been trying to get these simple issues solved for two weeks now. I've changed several injectors and 3/4 injectors. I threw a timing light on the spark plug wires and confirmed spark. The plugs do look fouled, black. I changed the suspect plugs. Still no luck. However when I drove it last week it felt like I was driving on all 4 cylinders. Maybe this issue only shows up at idle. HELP!

[grippo]

This sounds like you have a bad INJ2 driver. You may have other issues with getting 4 cylinders running on one bank - but I suspect they are tuning issues, but you really want to run 2 injectors off each bank. The driver isn't completely dead because you say it drives a test light and the scope outputs on each banl are identical. But if you put an injector there do you feel the injector clicking on both drives ? If not I would try replacing your driver (on the main board).

[yarin]

Valid point. I verified that the injector is firing to some extent. I have a feeling it is due to the increase in RPM when the injector is disconnected. To me it sounds like some amount of fuel is entering the cylinder and not combusting properly. Identical issue with both cylinders injected by this bank.

I'll try to tune all 4 injectors on one bank, then move it to the other bank and see how it runs.

Thanks

[yarin]

UPDATE:

4 injectors off 1 bank isn't working out. I can't get it to idle properly at all. AFR jumps around and idle rpm is not constant. Is it possible one injector channel can't handle 4 low impedence injectors? I tried various different combinations of PWM%, injector open time, etc.. from 15% to 30%, open time from 1.0 to 1.3ms.

I verified the issue with INJ1 channel numerous times. Any injector that is connected to that bank displays the following symptoms: Disconnect injector -> RPM goes up. Disconnect spark -> no change. The injector outputs look perfect on an oscilloscope using the stim outside the car. Continuity between DB37 connector through relay box and injector connectors.

Any suggestions?

[yarin]

Still fiddling with this problem.

The engine idles a bit rough with all injectors on one bank (INJ2). When i switch them all over to INJ1 it runs pig rich, black out the exhaust, MAP up to 50 from 27KPA, needs a lot more air to maintain a really rough idle.

I just pulled apart my relay box, its all good. Continuity from injector connectors to DB37 at the brain is good. I even checked impedence looking into the brain through the cabling across the+12V source and signal with the power off. Equal.

I haven't driven the car with the existing setup since last week. But at idle when i rev the engine the AFR goes to max lean on decel. Even when rev up slowly and let off AFR goes near lean. When I had the injectors evenly spread across both banks i never had this issue. Not sure what it could be. Sadly it idles so much better on two fully functioning cylinders.

I'd really like to figure out why the 2nd bank doesn't work. I even checked the injector outputs on the stim using an oscilloscope. They look perfect.

What to do?

[jsmcortina]

I wondered if you might have dual table turned on by accident, but this doesn't show in the MSQ.

Have you tried re-flashing the firmware? Simple and worth a try just in case something got corrupted.

Also, you've fairly large injectors but you are running 4 squirts per cycle, this is likely to cause idle tune difficulties (even with the increased precision of MS2 I think)
Reduce that to 2 or 1.

If the two injector outputs still behave differently after a reflash then I would do as Al advises and replace some components on the board - something must be faulty to have differing fuel per channel.

Have you confirmed that the current limiting PWM is the same between the channels?

James

[yarin]

I tried reflashing, same problem. I checked that dual tables are turned off, even tried with it enabled and did notice a change.

I'm running 2 squirts per cycle 9 / 4.5ms simultaneous. My unstable idle issues also take place high up in the rev range.

Does MS2 provide for different injector parameters per bank? Check out the 2nd attachment from my first post. I captured the waveforms from both channels, they are identical.

The one parameter I never touched was pulse width period. It's set at the default 66us. Maybe I need to step up or down? How far do I dare go?

Thanks for your response, your help is most appreciated.

[grippo]

Does MS2 provide for different injector parameters per bank? Check out the 2nd attachment from my first post. I captured the waveforms from both channels, they are identical.

The one parameter I never touched was pulse width period. It's set at the default 66us. Maybe I need to step up or down? How far do I dare go?

Thanks for your response, your help is most appreciated.

Do NOT change anything in the data - it is fine as shown by your scope pulse shots and your datalogs, and the fact that one bank runs fine. PW1 and PW2 are equal in the datalogs - the slight differences are due to timing of the data capture, but the differences are insignificant. MS2 it putting out equal pulses to both banks, and I believe you said that if you reverse the hookup of inj1 and inj2, the bank hooked to inj2 is always bad. That tells me that you driver chip for inj2 is not able to drive the injectors because it is broken/ defective. There is no sense playing with MS2 inputs as they give the same perfect outputs on both banks. The pwm parameters apply equally to both banks.

The only additional data you could get is a scope shot of the injector voltage. I expect this will be quite different between banks.

[jsmcortina]

The only additional data you could get is a scope shot of the injector voltage. I expect this will be quite different between banks.

Or, if you have the injector current limiting resistors in place (those two wire devices on the heatsink) scope the voltage across them as that will show the current flow. As Al says, I would expect to see some strangeness on inj2 indicating that the output electronics are damaged.

James

[yarin]

I ordered both Q3 and Q9 (Tip42, Tip125). Is there anything else I should replace on the faulty channel?

I don't have injector resistors.

Thanks for the help!