blake culp Posted May 5, 2006 Share Posted May 5, 2006 My car is having a high rpm miss at around 5000rpm. It only does it when i floor it, so if i hold it at half or 3/4 throttle it will rev smooth to redline. I was thinking this was related to boosting , but it will still boost full pressure at 3/4 throttle and still rev smooth. I have tried running different ve maps and still the exact same problem. The plugs are new and i am running the regular 4 prong gm hei. I did a datalog and made it miss and the only thing i saw that looked odd was when it was missing the o2 readings and the duty cycle would fluctuate pretty bad. Also, even though i was positively flooring the car, when it would miss the datalog would flip between 17 and 33 in the engine bit section, which im pretty sure means accel/decell. im going to try and figure out how to post the datalog and my msq. maybe that will shed some light on the problem. Im running MSnSextra set up exactally like the sticky. Any ideas? link to my msq http://www.ultimateuploads.com/file.php?file=cf03e4732e967c8922fbcd68179ce55d Quote Link to comment Share on other sites More sharing options...
mobythevan Posted May 5, 2006 Share Posted May 5, 2006 Definitely post the datalog and msq on the http://www.msefi.com MSnS_Extrra forum and here. Those guys may be faster to scan logs and settings to point out possible problems. The HEI module can charge the coil good well over 5000 rpm in 6 cylinder application. Mine worked to 6500rpm. My initial thought is that your AFRs are off at WOT at 5000. Even though the VE location may be the same for 3/4 throttle versus full throttle at 5000 and full boost in both cases, the amount of fuel delivered changes because the TPS reading will change. You don't have a wideband do you? Quote Link to comment Share on other sites More sharing options...
blake culp Posted May 5, 2006 Author Share Posted May 5, 2006 I do have a wideband, running the lc1. My ve table is rich about 10-1 under boost, butn im not really comfortable leaning it out yet because im still working all the little bugs out. However after some more searching both on here and msefi.com i decided to try and mess with the dwell settings. On MSnSextra you have the option for fixed duty or dwell controll, i had it on fixed duty with the minimal for hei4 selected. After changing the dwell setting to dwell control and then setting the running dwell to 3.5 and the ms. to .8 it seems to have completly cleared up the miss i had. I am not positive on what dwell is or what it does, am i going to fry anything with these settings? Quote Link to comment Share on other sites More sharing options...
mario_82_ZXT Posted May 5, 2006 Share Posted May 5, 2006 The miss/hiccup can actually be caused by your overly rich conditions. What are your spark plugs gapped at? Mario Quote Link to comment Share on other sites More sharing options...
mobythevan Posted May 5, 2006 Share Posted May 5, 2006 The dwell determines the amount of time the coil is charged between each spark, so it will certainly have an impact at high rpms. It is much better to run with dwell settings than to use the minimal HEI IMO. Sounds like the rich mixture is hard to light off. Looks like your on the right track. Quote Link to comment Share on other sites More sharing options...
Guest ON3GO Posted May 5, 2006 Share Posted May 5, 2006 im having the SAME problem as you.. its my fuel pressure, atleast thats what i think it is. my fuel pressure goes MAD and doesnt stay steady at all. down to my fuel pump, which i think it is. PLEASE post on what you find out. mike Quote Link to comment Share on other sites More sharing options...
z-ya Posted May 5, 2006 Share Posted May 5, 2006 Your fuel pressure should change with engine load (pressure). The regulator will keep the same pressure at the injector nozzle, so it must change as manifold pressure changes. The problem sounds like too rich a mixture. I had same problem with my turbo car after initial tuning. After an hour or so of tuning on the dyno, the mixture problem was corrected. Quote Link to comment Share on other sites More sharing options...
Guest ON3GO Posted May 5, 2006 Share Posted May 5, 2006 i know fuel pressure changes.. im talking it was going crazy... between 30psi and 65psi at any giving hard loads.. keep it to a slight pedal increase im load and fuel pressure would stay solid. werid.... Quote Link to comment Share on other sites More sharing options...
Clifton Posted May 5, 2006 Share Posted May 5, 2006 10:1 is way to rich. Adding a little extra fuel will help cool but you can only add so much before you start putting out the fire. 11:1 is plenty rich to start at and then lean it out from there. What are your plugs gapped at and how much boost? Quote Link to comment Share on other sites More sharing options...
blake culp Posted May 5, 2006 Author Share Posted May 5, 2006 yeah i know 10-1 is way rich, but hey, im paranoid and i want to make SURE this motor isn't going to go boom. Now that it seems to be running 100% right i will be leaning it out, from searching it seems that around 12.3-1 is the sweet spot, you guys agree? im getting it to the dyno soon, proabbly tomorrow. I found a shop that is 20$ a pull or 100$ an hour whichever turns out to be cheaper, and thats with wideband and tuning. My plugs are gapped at .35. on3go- i would play around with your dwell, try the settings i am using it fixed my problem instanatly. Im running 12psi with plans to turn it up to around 16psi. Assuming no detonation, about how much boost can i run relatively safetly? Quote Link to comment Share on other sites More sharing options...
Clifton Posted May 6, 2006 Share Posted May 6, 2006 How much boost you can run depends alot on timing. If you still have a miss under load after cleaning up the fuel, I would tighten up the plug gap to .028-.030. Quote Link to comment Share on other sites More sharing options...
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