No start with Force GDI

[Scott33]

I'm trying to get a motor running with Force GDI.  I haven't gotten it to start yet, though I have verified that injectors and spark work.  I wanted to verify a few assumptions before I push forward.  It's a street car motor without any internal modifications - a BMW N26 if it matters.  Unfortunately I don't have much technical data to go off, so I'm trying to derive as much data as I can from the motor itself.  I started with the VW GTI map and have been making modifications along the way.

1. The MAP sensor never reads much vacuum when cranking.  The lowest I've seen is around 60kPa at 270RPM.  Is that normal?  I assume more vacuum is generated at proper idle and especially at high RPM.  Because of this, I added an extra column to the fuel map at 400 RPM so I could enter much lower VE %.  Otherwise I was getting "injector duty cycle too long" error messages, which is what led me to think that 60kPa is actually not normal.  I did open valvetronic up (before that, MAP read 97-99 kPa).

2. Is it possible to run a GDI motor without controlling the GDI pump? When I run the fuel pump, I see both the low and high pressure gauges read 5 bar, which tells me fuel is getting to the injectors even without controlling the pump.  I recognize I won't be able to run at a high RPM or open throttle but it should be enough to start and idle, right?  If it matters, I adjusted injector timing to be 180, so that the injection happens when there is relatively little pressure in the combustion chamber.

2b. If I get a "GDI pump failed to maintain pressure" error, will the ECU still try to run the motor or will it give up?  AFAICT it was still trying to inject fuel but I just wanted to make sure.

3. What's a ballpark injector duty cycle for start at 5 bar on a 2L 4 cyl?  I recognize this heavily depends on the injector flow rate (which, of course, I do not have), but I know an N55 (same injector, but 6 cyl instead of 4 cyl) has a duty cycle of around 1.8ms at idle.  I scaled that up assuming idle is at 50 bar to be 5-6ms at 5 bar.

 

I guess my next step after this is to get a timing light.  I was hoping to avoid it but I'm running out of things to check/fix and it's still not starting.  I've attached my attempt to start log in case anything jumps out (note this one has the injector pulsewidth at around 1.5-2ms instead of 4-5 but I've tried bumping it 20% at a time up to 10+ms and it still didn't fire).

Do you have a log file from starting a GDI motor, and if so could you post it?

Attempt Start Log 2020-03-31 5;38;56 pm.llg

[Adamw]

1. It is normal to not see much (if any) vacuum during cranking.  
2. No, you will unlikely get it to fire without something close to normal DI level pressure.  Typically 50-80Bar at cranking and idle.  Looking on google that engine looks like it has a fairly standard HDP5 NO type pump so it needs to be energised to create pressure.  First thing to check is if you have 12V at the DI pump while cranking.  You could also try setting polarity to high in the software in case the control logic is reversed.  Some engines if sitting around for a while seem to take a long time to build pressure, I dont know if they get air trapped somewhere or what.   

2b. When the GDI pump is in error the pump output is disabled.  In the GDI pump error settings you could try setting the low pressure to something very low and the blanking time to max to stop it tripping while trying to get pressure for the first time.  Usually once you have everything working correctly the pressure will come up near instantly during cranking.   

3.  I cant really find any relevent logs in my data.  I have one from a N54 engine (which is quite different and uses a async PWM pump), it has 8% dutycyle on the injector with 57bar FP while cranking. 

[Scott33]

Thanks for the responses.  My take away is I need a whole lot more fuel.

I had hope I could run it without high pressure.  I haven't characterized the pump or the cam profile at this point, and was hoping to do it through deduction on the running motor (see what duty cycles are needed to maintain the right pressure at various angles, and use linear regression to estimate the profile).

I have gotten pops and even had it run for a second or two after I ran the injector test.  I think the residual rail pressure was enough that the cylinders got some fuel.  But maybe the injector time limit of 20-24ms will be too short to get enough fuel when the rail is at 5 bar.  Given the occasional pops I've heard I also think I've gotten the air out of the system by now.

Do you have any crank/start logs from the VW GTI GDI or Ford Ecotec GDI motors?  I'd take anything at this point just to understand what "normal" is.

 

[Adamw]

You need to calibrate the pump somewhere close first and you will need near normal DI rail pressure before it will run.  Stroke and number of lobes is easy to determine by removing the pump and looking/measuring through the hole in the cam cover.  Bore dia is normally 9mm on the HDP5 pumps.  You can get a rough pump calibration by marking 5, 10 , 20, etc deg marks on the crank pulley and measuring the lobe height through the cam cover with the crank sitting on those marks.  

 

7 hours ago, Scott33 said:

Do you have any crank/start logs from the VW GTI GDI or Ford Ecotec GDI motors?  I'd take anything at this point just to understand what "normal" is.

I dont sorry, most of the DI engines I have been working on are combined DI/Port so they use port injectors for starting.

 

[Scott33]

Thanks for all your help.  I don't want to remove the pump as I have to replace a $70 fuel pipe if I do.  Not sure why, but the factory manual says so.

I looked at pictures of a cam on ebay and estimated the lobe angle.  I also guessed that the lobe is a perfect sine wave.  After that I started getting fuel pressure.

I had guessed at the timing based on pictures from the factory manual on the position of the trigger wheels at TDC, combined with what I saw in the trigger scope.  Something somewhere was wrong (either the factory picture, the Link manual on missing teeth + cam level, or my interpretation of one or the other) but once I reversed it 360 degrees it fired up every other time.  I also lost GDI pressure.  Then I realized since I changed the definition of TDC, I had to change the GDI cam lobe position and now it starts and runs perfectly.

Now on to the fun stuff!