ignition cuts out at higher rpm

V8BUG · Post by **V8BUG** » Sun Jul 30, 2006 7:05 am

MSII embedded code 2.1, megatune 717, gm small cap 8 pin hei distributor, tuned port intake, 283 sbc, autolite 26 plugs.

The engine will fire right up and idle great when cold, and also restarts fine when hot. With the engine in park and no load it will rev fine, but if I slowly advance the throttle and slowly bring the rpm's up it starts to break up around 3000rpm. It does not break up bad enough where the engine dies, rather it just break up a little and keeps increasing in rpm.

When driving the car it has very good low end response, does amazing burnouts

, and cruises quite well. If I launch from a stop it will pull real hard up to about 3000rpm and then it will cut out, then a split second later it will come back to life and pull some more, then cut out again, then pull some more.......

I have tried every conceivable combination of ve tables from very lean to pig rich. I have also tried tons of different req fuel values. I a fairly certain it is not a fuel problem but a spark problem. I started with a msd blaster II coil, then switched to a coil off my father 69 gto, and now I am using a coil off his 92 buick roadmaster (which has a small cap 8 pin hei) None of the coils made a difference. I have the max dwell set at 2.5ms just like the manual says for remote coils. All the grounds to the distributor are good. The cap, rotor, and the module are new. I bought the distributor as a new replacement part.

Could the module be fried? I feel the wiring and hopefully the program are correct since it idles and runs at low rpm so well.

any suggestions/ help would be greatly appreciated!!

thanks,

Matt

mxmang · Post by **mxmang** » Sun Jul 30, 2006 10:32 am

hey man, you should add me on msn or aim or yahoo

mxmang@hotmail on msn
mxmang on aim
boredstoonguy on yahoo

i have this problem too and i think we need a dave cap but nobody seems to answer these q's and the mega manual says to consult the forum BOOOO

V8BUG · Post by **V8BUG** » Sun Jul 30, 2006 3:55 pm

well I went ahead and stripped out the module from my dads roadmaster and put it in my distributor. The car runs alot better, but still cuts out alitte, now at about 4000rpm. I am going to buy some msd super wires that are soppused to have like no resistance and still have tons of surpression.

I am hoping it was just a bad module. I will post with results in a couple days mxmang

thanks,

Matt

zguy36 · Post by **zguy36** » Tue Aug 01, 2006 6:22 am

sounds like your vb921 is fried...... swap itout with a new one and you'll have the problem licked. Look at my post (Direct Coil Control) and maybe you can get some help from the people who looked there.

Bernard Fife · Post by **Bernard Fife** » Tue Aug 01, 2006 8:11 am

Could the module be fried?

Matt,

It's possible. 3000 rpm is above the point at which the dwell begins to be cut back on a V8, so increasing the dwell won't help at all.

It's also possible that the distributor is 'out of phase'. All block chevs need to have the rotor and distibutor installed so that the rotor, and the #1 terminal on the distributor, is rougly in line (a line extended from the center of the cap through the #1 terminal) with the spark plug for cylinder #1 when the engine is near TDC for cylinder #1 (ideally about 20Â° to 25Â° BTDC). This is because the distributor drive gear has an odd number of teeth, and any other position will cause phasing problems at some advance values.

The Dave cap is a regular component on the V3 board (it's C30, you can find it on the schematics here: http://www.megamanual.com/ms2/pcb.htm), however the Dave cap should not be installed with the 7 or 8 pin HEI module (it causes a shift in the timing signal). It is used for triggering directly off the negative coil terminal.

If this were mine, I'd upgrade to the 2.36 code, and upgrade to the release version of MegaTune. Then I'd make a datalog and look to see what the tach signal and injector duty cycle looked like when the engine gets to 3000 rpm. Let us know what you find.

Lance.

V8BUG · Post by **V8BUG** » Tue Aug 01, 2006 2:55 pm

I dropped the distributor in at 10 dbtc pointing at number 1 with the "teeth" on the reluctor lined up.

I will load new code and run the new megatune, I probibly should have done that anyways.

I will let you know what happens.

Thanks,

Matt

V8BUG · Post by **V8BUG** » Wed Aug 02, 2006 5:52 pm

loaded the embedded code 2.36 and am now running the release megatune. The car runs absolutly amazing!!!! It ran well before except for the higher rpm, now it pulls right past 4000 up to 5500 where I set the rev limiter like an animal!!!! I think the smoothing factors or something are making the difference. I will try and make a datalog this weekend.

thank you very much!!!!