Elusive First Start of BBC -*Started

[ddn]

I'm trying to get the first start of my 468 BBC (~10.5 CR). I'm running a MS2 3.0 board with 2.886. 60-2 wheel, MSD6AL box for ignition, and 8 port injectors for fuel.

Stupidly, I don't have the latest MSQ that I was testing today. I'm running 12* of advance, and experimenting with 7.5-9.5ms cranking pulses. The RPM signal is rock-solid around 110rpm.

Any suggestions for this motor? Am I way off base on timing or fuel?

[devastator]

The timing sounds ok, but the cranking pulses depends on the injector size and fuel pressure.

[ddn]

8 44lb/hr injectors and about 45 psi. I'm adjusting the -40 cranking pulse width, setting it to between 11 and 13. 160 is at ~3

[classic_chevy]

Can you smell gas in the exhaust? I would verify that you have spark and try using the led tester or a meter to verify the injectors are firing. Led tester is on this page http://www.megamanual.com/ms2/V3trouble.htm I used this and found it very useful. I would not recommend using the injector tester part of Megatune, I had problems with it getting stuck firing the injectors. Just crank and use the led tester to test your injector outputs from the cpu to the mosfet driver and finally to the mosfet itself... Verify fuel and its just a matter of time.

[krisr]

Is the trigger offset in sync with the balancer? Clip a timing light to #1 plug lead and verify. It'll tell you 2 things, where your offset actually is in relation to the crank trigger wheel and you're actually getting spark. Also feel the injectors to see if they "click" while you're winding the motor over too. When I setup the 36-1 wheel on my 400, I simple clocked the engine to 10*BTDC, mounted the wheel and fabricated the sensor so it's in the safest possible place away from the belts and just setup the teeth accordingly in megatune in relation to the position of the missing tooth.

[ddn]

I've gotten several backfires along the way, so I'm fairly confident that fuel is spraying. I'm not confident in the amounts though.

I'm also fairly confident in where the timing/offset is. I have the wheel at 9 teeth after missing at TDC, so I've set the delay to 7 which should set a base advance of 12* and I've set the trigger offset to 12 as well.

We didn't have a working timing light last time, so I will be triple-checking the timing next time I make it to the shop (hopefully today).

[krisr]

Which way was it backfiring? Out the exhaust or back up through the intake? Also which cranking trigger setting are you using - trigger rise or calculated?

I think it's best you v'fy with a timing light before doing anything, especially with a big motor! I know my 400 (true 10.5CR) was fun to get going properly but now it's an absolute dream!

[ddn]

Made progress. Still no timing light (that works).

I'vWe were however able to get the engine to run for a few seconds with starter fluid and the fuel pump completely off. I've taken spark timing away from MS and am using a standard distributor. I can only assume that my timing is within the zone since it ran with the starter fluid.

From there I went back to trying to get it to start with MS controlling fuel. After an initial cough, I made no progress. Finally in frustration I put the pedal to the floor and cranked it. Putting it into flood clear mode must have cleared out enough fuel to have it stumble a bit.

At that point the battery was too low to continue for the day. I have to assume at this point that my timing is close, but my cranking pulse widths are way too high. Anyone have advice on playing with pulse widths? How close do I have to be? The engine temp is about 80* F and I've only been touching the -40F cranking pulse width. Started at 3.2/12.2 and moved around there but no luck.

Thanks.

[SQLGUY]

OK. So right now you're working with stock ignition (known good) and MS fuel, is that correct?

One thing you could try is setting cranking pulses very low (.1 ms for instance), starting it with starting fluid, and then working on keeping it running from MS. If you can get it started and idling that way, the injector pulses you see when cold should give you an idea of where your cranking pulses should be (interpolated for ambient temperature). It can also be a lot less frustrating if you tune some of the running stuff now and fight with hot and cold start later.

My .02.

Paul

[SQLGUY]

OK. So right now you're working with stock ignition (known good) and MS fuel, is that correct?

One thing you could try is setting cranking pulses very low (.1 ms for instance), starting it with starting fluid, and then working on keeping it running from MS. If you can get it started and idling that way, the injector pulses you see when cold should give you an idea of where your cranking pulses should be (interpolated for ambient temperature). It can also be a lot less frustrating if you tune some of the running stuff now and fight with hot and cold start later.

My .02.

Paul

[ddn]

Correct. The stock ignition isn't exactly "known good" though as this is a brand new engine in a restored Corvette. Basically all new kit.

That's a pretty good idea, and I might have to give that a try tomorrow. Thats exactly where I'd like to get...tuning isn't an issue..but this initial start is killing me. Thanks.

[ddn]

http://www.youtube.com/watch?v=wekgrHqb6JQ

Solution: got a cheap non-digital timing light. Locked the timing in, and it fired right up. Still working on idle tuning. The GM IAC is giving me fits.

But NOW I'm having fun. Lesson: ASSUME NOTHING.

[krisr]

Once you get it starting and idling nicely, i'd try moving back to the crank wheel and have MS2 control timing now you have a timing light

Congrats!

[ddn]

Agreed.

Thanks for the help gents.