Thumper Posted August 9, 2006 Share Posted August 9, 2006 I have had a problem with the car reving past a certain rpms. I just installed a msd 6a instead of a hei module. It still does the same thing. I have played with the dwell settings and they do make it better. At 75% it will not rev past 2800 and at 50% it won't rev past 3700. At the higher rpm the car's tachometer will start to drop off but the tach in megatune will not miss a beat so it is getting a good clean signal just not sending one. I have my 1k ohm 1/4watt resistor as a pullup as needed. I am running megasquirt v3.0 with a flyback and a relay board. Any ideas? Thanks Quote Link to comment Share on other sites More sharing options...
trwebb26 Posted August 9, 2006 Share Posted August 9, 2006 What coil are you runnin? Put a timing light on it and rev the engine. Make sure that the timing matches your timing map all the way thru the revs. That is the first place to start. Quote Link to comment Share on other sites More sharing options...
Thumper Posted August 9, 2006 Author Share Posted August 9, 2006 Already done. The timing will retard as timing goes up. Very little now that i have dwell at 50% and at 3800rpms the timing light will stop flashing alltogether. At 75% the timing would retard alot more. Thanks Quote Link to comment Share on other sites More sharing options...
olie05 Posted August 9, 2006 Share Posted August 9, 2006 maybe your distributor is not timed right with the crank? Maybe the rotor is sweeping past where you have designated timing, and it is causing that kind of behavior. unless the car was running fine before and all of a sudden it started acting up. n/m just read your post and it seems that the spark is cutting out completely. did you build it yourself? are you sure the vb921 is hooked up correctly? (are you using the vb921 coil driver?) Quote Link to comment Share on other sites More sharing options...
Thumper Posted August 9, 2006 Author Share Posted August 9, 2006 maybe your distributor is not timed right with the crank? Maybe the rotor is sweeping past where you have designated timing' date=' and it is causing that kind of behavior. unless the car was running fine before and all of a sudden it started acting up. n/m just read your post and it seems that the spark is cutting out completely. did you build it yourself? are you sure the vb921 is hooked up correctly? (are you using the vb921 coil driver?)[/quote'] The coil driver is not installed. I am running the msd to fire the coil. The only option installed is the flyback board. Thanks Quote Link to comment Share on other sites More sharing options...
sims76 Posted August 9, 2006 Share Posted August 9, 2006 I doubt this is your problem, but a few months ago my alternator belt was slipping under load causing a voltage dip and the symptoms you are describing. Of course it was even worse with the headlights on. Have you tried increasing/decreasing the value of the pullup resistor? At least with the tach input the following applies: smaller resistance = more sensitive to lower RPM but noisy larger resistance = less sensitive to lower RPM but less noise at higher RPM Quote Link to comment Share on other sites More sharing options...
Thumper Posted August 9, 2006 Author Share Posted August 9, 2006 I doubt this is your problem' date=' but a few months ago my alternator belt was slipping under load causing a voltage dip and the symptoms you are describing. Of course it was even worse with the headlights on. Have you tried increasing/decreasing the value of the pullup resistor? At least with the tach input the following applies: smaller resistance = more sensitive to lower RPM but noisy larger resistance = less sensitive to lower RPM but less noise at higher RPM[/quote'] That might be the case if this wasn't under no load. This is reving in neutral. Plus the the alternator is brand new is working perfectly verified with a volt meter. Thanks Quote Link to comment Share on other sites More sharing options...
Cal Poly Zmanaustin Posted August 9, 2006 Share Posted August 9, 2006 You might want to clean up all your connections, especially the grounds. I had the same symptoms and believe the problem (at least in my case) was the distributor was not putting out enough voltage. Good Luck. Quote Link to comment Share on other sites More sharing options...
trwebb26 Posted August 9, 2006 Share Posted August 9, 2006 I'm not sure I got the answer I was looking for... Does the timing you are getting with the light match the map? Quote Link to comment Share on other sites More sharing options...
Thumper Posted August 9, 2006 Author Share Posted August 9, 2006 Yes at idle it matches perfectly. Then as I rev higher it will retard away from the timing map. When I put it fixed at 25 degrees it will go to 20 degrees by 2k rpms and so on. Thanks Quote Link to comment Share on other sites More sharing options...
trwebb26 Posted August 9, 2006 Share Posted August 9, 2006 change the setting for "spark output inverted" to opposite of whatever you've got it at now. Quote Link to comment Share on other sites More sharing options...
mario_82_ZXT Posted August 9, 2006 Share Posted August 9, 2006 I still don't get your setup..... If you were running the 4 pin HEI before without the coil driver, then there should be no reason to set dwell. Like I stated before, 4 pin HEI's are smart dwell, aka they control it! Mario Quote Link to comment Share on other sites More sharing options...
trwebb26 Posted August 9, 2006 Share Posted August 9, 2006 You HAVE to set some kind of dwell setting in MS, though. For MSD's - the right setting is fixed - 50% dwell. Quote Link to comment Share on other sites More sharing options...
mobythevan Posted August 9, 2006 Share Posted August 9, 2006 You HAVE to set some kind of dwell setting in MS, though remember that in the beginning before MSnS_Extra was even available and we were just using Magnus' MSnS code there was no setting for dwell. The HEI modules had to be heatsinked well. Then as Extra code come into play the eventually added selections for 75% and 50%, then finally you could set dwell (cranking, running, minimum). Even with the magnus code my HEI module worked fine, I believe that was at 100%??? Quote Link to comment Share on other sites More sharing options...
Thumper Posted August 9, 2006 Author Share Posted August 9, 2006 Well I figured the problem was between my megasquirt and msd box. So it was either my relay board was messing up the signal or my megasquirt was sending a bad signal. So I bypassed the relay box and wired my white wire from my msd directly to my megasquirt fidle wire and presto its fixed. I truly don't know why it fixed it. Only that it did. I have guesses mostly bad put together of the relay board but don't really care why its fixed just that it is. So fyi if you have these symptoms bypass your relay box. Quote Link to comment Share on other sites More sharing options...
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