e38 cranking help

[ringram]

Ok any help appreciated. Engine is 440 cube LS7 with LS7 top end. Cam is 230/238. Injectors are scaled ok as closed loop and stft are not miles off.

Main issue at present is starting. If I crank it fires almost immediately then instantly dies. It seems the more cranking air I add the better it fires, but it still dies. I have bumped up min idle airflow and once its running it holds idle ok, though it likes to swing a bit past the right level sometimes like too much cracker and follower decay etc. (Except those tables dont exist!)

I read Swingtan's cranking threads and have messed about with most stuff, but am trying the open loop IVT table with some more fuel in the AM.

So I need to figure out why its not firing and catching, I can get it to fireup if I crank it a while with the throttle down a way. It almost caught a day or so back when I had thrown shed loads of cranking airflow, like 20g/sec style of thing.

So if anyone can help that would be great, like a few hints on the best sequence with these controllers and key tables.

Many thanks :)

[swingtan]

Hi Ringram,

I was talking to someone about this sort of thing last week.

Have a look at B8062 and "REDUCE" the % value for the cranking. I haven't put a lot of thought into why this works, but it seems to help a lot with larger cams. I think the guy I was talking to tried values around 75% to start with, and then jumped to 50%.

The other table would be B5119. For some reason, GM decided to put some weired steps in the spark map for cranking. I removed the -VE values, added some timing as the RPM rose and smoothed the lot out.

Hopefully this helps a bit.

Simon

[ringram]

Hi mate, thanks for the comments, interestingly enough I had got rid of the -ve stuff anyway in the cranking spark table. I tried 75% in that cranking ve table ages ago, but good to hear it helped Ill have another go with it. Cam has some definate overlap so both valves will be open causing VE to drop at low RPM, so that makes sense. It might not be getting enough fuel/air which might explain why making cranking air table mega numbers helps.

[GMPX]

The other table would be B5119. For some reason, GM decided to put some weired steps in the spark map for cranking. I removed the -VE values, added some timing as the RPM rose and smoothed the lot out.
People have told me that when that table (B5119) has those values removed the engine knocks at start up just as it fires. It looks dumb but it does seem to serve a purpose.
Richard, sorry but I can't offer any practical advice on your problem, maybe I need a 440 for R&D?

Cheers,
Ross

[ringram]

Yes I recommend it Sir :)
The -ve timing is only over 100*C in that table in any case. But thats good info. We will see how we go today.

[ringram]

Have a look at B8062 and "REDUCE" the % value for the cranking.

Good man, 50 bonus points.

My last attempt to use that table failed, (I set it at 75%) probably due to issues in other area's. I have tried to return most of the tune to stock when I have gone too far away from "normal" values to save myself getting lost in the forrest.

I have added 10% more timing to cranking timing, ~30% air to cranking air (27% more displacement) and set the cranking ve to ~70% plus added a similar ~30% air to min idle airflow. Now things are working nicely, or at least it cranks, fires and maintains idle now anyway. I reset open loop IVT table to stock as it was too rich.

Its not fun stalling in multi story car parks and needing to reflash with people stuck behind you :)

[swingtan]

Excellent! I've been on the side of the road flashing a tune and had every car that passed me hit the brakes thinking I was a speed camera.... Was very funny

[ringram]

Ok turns out this worked but not for the right reasons.. Im now at 90% and might even make it back to 100%
Low rpm min idle airflow seems to be my new best friend.

[hymey]

I had similiar issues with 230 cams, I had to command a lot more min idle airflow then stock. It was worse when hot. Increasing cranking air and min idle air cranking timing. and B1845 multilply that by -50% reduces hunting a lot. I would imagine being a big cube engine it would need a lot more air.

[TuneMaster]

Post your tune so we can have a look.

[ringram]

I had similiar issues with 230 cams, I had to command a lot more min idle airflow then stock. It was worse when hot. Increasing cranking air and min idle air cranking timing. and B1845 multilply that by -50% reduces hunting a lot. I would imagine being a big cube engine it would need a lot more air.

Yep pretty much exactly what Ive done. She eats shedloads of air :)
Im still progressing ok, so will post up if/when I get stuck

[calais-346]

Hi Ringram,

I was talking to someone about this sort of thing last week.

Have a look at B8062 and "REDUCE" the % value for the cranking. I haven't put a lot of thought into why this works, but it seems to help a lot with larger cams. I think the guy I was talking to tried values around 75% to start with, and then jumped to 50%.

The other table would be B5119. For some reason, GM decided to put some weired steps in the spark map for cranking. I removed the -VE values, added some timing as the RPM rose and smoothed the lot out.

Hopefully this helps a bit.

Simon

After going around and round in circles changing cranking idle air and timing, i tried this, i reduced B8062 cranking ve to 75% and now have perfect starting!

Safe to say i'm a very happy man now,:cheers: i was getting sick of putting my foot on the throttle to start the car:bad: