MicroSquirt.com read only forum (Jan.15,2018)

I'm still having trouble with the low-impedance injector. With settings of 75% and 1.0ms it workes ok, but after some test driving the engine will start to cough. This was occuring very early a while ago when I had slipped the default time threshold of 25.5ms into play. So I think something is still causing the injector to heat up, etc...

So to tune the injector should I first start with the PWM current limit and set it as low as I can. After that the same thing with the time threshold or should it be done vice versa?

The injector is a bosch 0 280 150 651 with impedance of ~1.3 ohms. One odd thing is that after I played with the time threshold A/F started to go VERY rich (plugs went pitch black)). I had it around 0.6-0.7 and I could not tune the engine leaner anymore?!. This is also weird becaude I made some calculations today and realized that I have used a way too low req_fuel value.

The injector flows 611.4 g/min (80.87 lb/hr) @3bar (43.5 psi) 100% duty according to one source (not bosch). I'm using only 1-1.2 bar (14.5-17.5 psi) of pressure so it should flow around 50 lb/hr at 100% duty. Lower it to 80% duty it should flow around 40 lb/hr.

In a 1.3 liter (75hp) engine it will give 5.2ms of req_fuel. I have been using 3.0-4.0. How can the engine go richer after lowering req_fuel and PWM time threshold?!

It's probably possible that the injector took some beating after the HIGH time threshold setup. Maybe I'll go and buy a new one... I was thinking of buying a less flowing injector. With the calculations above I should get idle pw around 1.5. The same injector is used in a 75 and 90 hp Golf 1.8 engine and also in a 1.6 Seat 70hp engine. So how big role does the displacement play becaude I have 75hp but 1.3 liters?! I could get the injector from a 60hp 1.4 Golf that flows 29 lb/hr @1bar and 80% duty (446 g/min @ 3bar 100% duty) or a 1.4 liter Fiat 32.5 lb/hr @ 1bar 80% duty (506 g/min @ 3bar 100% duty). These could give me around 1.6-1.7 ms idle pw. Sounds good but a injector size calculator gives a maximum of around 50-55 hp? Where am I calculating wrong?!

Any opinions how should I proceed?! Thanks a lot of your help!

AriK,

You do both at the same (nearly) time. So you move the PWM% down a bit (say 5%), then check all is okay by making sure the engine idles properly and revs cleanly. Then move the PWM time threshold down a bit (say 0.1 msec) and check again. Then move the PWM% down some more, then the opening time, etc.

At some point, moving one of them (say the time threshold) down will cause a problem with the engine running or reving. So you up that variable a bit (say increase the time threshold by 0.2 msec) and continue working on the other variable (PWM%, in the example) until it causes a problem with the running/reving - at which point you move it up 3% to 5% and you are done.

You do it this way because these variables interact, and you need to work back and forth to get them both right.

Lance.

Thanks, Lance!

I tried to set the injector today and also increased the req_fuel value. It runned ok with 65% and 0.7ms. But still after a couple of short test drives the engine started to cough again.

I will buy a new injector tomorrow to see if it's the part that is causing me trouble. It can't be the spark because I run about 3.0ms dwell at the moment and the coil doesn't heat up that bad.

Weird things happened again. I now have a new injector that is smaller and has 7.2ms of req_fuel. Idle pw is about 1.6-1.7ms. I tried to drive with the new inj, but the same weird coughiness occured at idle and cruise when the engine got hot.

So, because I use only one injector output I decided to try the the other one. To my suprise the engine didn't start at all?! I disconnected the injector and plugged a scope to the outputs. Both channels gives a spike, but I think the original is higher?! I checked the MS board and connections are ok on both FET:s. So, no luck there... Any ideas?

Because I was using the Fidle output for spark I decided to swap it to the LED output, because I wan't to test my idle stabilizer system using MS on/off idle signal. I took off the led and jumpered it and swapped the 330ohm resistor to 1k. Then connected the jumper to the X12 output (X11 used in hall signal).

Then I fitted the MS back to the car I plugged the scope back to take a test drive to see what signal is wrong when the engine starts to cough. BUT, after some test driving I just couldn't get the engine to cough anymore?! It was 2pm at that time, so I decided to do some more driving next day. I hope the coughing is history (knock knock...), but I will find out soon...

Edit: I also used a separate battery on MS to see if the powerline is noisy, but no difference...

I'm continuing my monologue ;). I was a happy bunny today and drove a nice 30min without any hick-ups. I didn´t take a longer trip because the car is not inspected and I did´t want a ticket for it ;).

Anyway, things got worse and the damn coughing got back again. The most weird thing is that you can drive around without any problems, but if you stop the engine, wait for a 15min and start it again it will cough and hickup like hell??? why, oh, why??

I wanted to investigate the signals again, but my journey was short because I accidentally zapped the injector signal to ground with my probe. This caused the injector to stuck open. The thing is just numb, no clickety-click anymore. Swapped the old injector back and drove the car back to the garage.

I rechecked the injector banks with a scope (injector not connected) and why is that the signal on the second one is way too weak? It won´t open the injector at all? If I look at the signals on a scope the spike on the other one like 1/5 too small? There is no visible damage on any components on the board?

My head is empty, so any ideas are welcome. Maybe I heed some exorcism on the system.

Ok, enough chit-chat, let´s open a beer. I think i'm going to have plenty tonight!

More debugging today and it seems that the problem is ignition related. The injector signal is ok, but still the other bank is dead (weak signal).

Also the ignition signal shows no missing spikes, etc... But the timing light goes off when hickup occures. So, next I wil go and get a new ignitionamp and see if it cures the problem.

I will continue in the ignition forum ;)... If someone has an idea why the other injector bank is weak let me know!