flames_187 Posted June 2, 2008 Share Posted June 2, 2008 hi guys I been battling a misfire for a while now and have some basic questions. 1.) i noticed the fuel pressure at 30 psi when in the on position then dropping to 20ish psi once started. If i was to rev it to about 1700 and hold the fuel pressure would increase then drop back down.Does this point to the fuel pump (FP) or regulator (FPR)? I tired to trick MS to add more fuel thinking it would increase the pressure. It added more fuel (can hear the difference in engine) but pressure was still at 20 psi. 2.) my A/F guage and MS2 gauge reads a 12.5 ish A/F ratio where it is set in the AF table for 13.5. This is at 1200 rpm(ish). Shouldnt MS be trying to match that if my threshold is 1000rpm. setup: stock 83zxt inovative lc-1 A/F setup stock FP and FPR MS2 V3.0 code 2.885 may 31.msq.zip Quote Link to comment Share on other sites More sharing options...
mobythevan Posted June 2, 2008 Share Posted June 2, 2008 Remember that your fuel pressure in the rail is independent of megasquirt. That pressure is based on the fuel subsystem (pump, fpr, clogged filter, etc). Increasing fuel in megasquirt only changes the time the injectors are turned on/off. What is the history of the pump and fpr? Are they both stock? The fuel pressure in the rail should be higher when you unplug the vacuum line to the FPR (same situation as turning the key on so the pump runs, but not starting the engine). When the engine is started and the vacuum line is connected to the FPR then the pressure should drop. If this is a stock pump and stock FPR then follow the directions in the manual for checking fuel pressure. Quote Link to comment Share on other sites More sharing options...
mobythevan Posted June 2, 2008 Share Posted June 2, 2008 my A/F guage and MS2 gauge reads a 12.5 ish A/F ratio where it is set in the AF table for 13.5. This is at 1200 rpm(ish). Shouldnt MS be trying to match that if my threshold is 1000rpm. The short answer is NO. MS will only compensate up to the authority limit you have set in your EGO settings. You set up iginition events per correction, step size and authority. If it needs to correct 80% to meet the AFR you put in the table and your authority is only 50% then it will never make it. Quote Link to comment Share on other sites More sharing options...
Clifton Posted June 2, 2008 Share Posted June 2, 2008 Disconnect your vacuum source and see if the fuel pressure goes back up to 30. I wouldn't run fuel pressure that low. You should be 10 psi higher. If you can drive the car it's not the fuel pump. If it can't keep up at idle, no way it will at load. Quote Link to comment Share on other sites More sharing options...
flames_187 Posted June 2, 2008 Author Share Posted June 2, 2008 Thank you that clears up alot...I will follow the manual steps to check the fuel system... [EDIT] It idles but misfires throughout so my first thought was check timing then check spark plugs and they looked fouled (blackened) so i thought the car was gettting too much flow then noticed the my fuel pressure gauge reading 20 ish psi at idle so i started to think maybe the regulator is going bad since the FP is a year old. Its the stock FP (aftermarket oem) and stock FPR so i will check it once i get done with this food safety seminar :-/ Quote Link to comment Share on other sites More sharing options...
flames_187 Posted June 9, 2008 Author Share Posted June 9, 2008 so i finally got time to work on the car... I checked the FPR based on the manual and got about 4-5psi difference (lower). I unplugged the vacuum hose and started the car at it stays at about 32psi...but i am still getting this annoying misfire at all rpm but more noticable at idle. my wideband is not steady at all and looks like its trying to catch my afr setting. I tired lowering my afr settings but that didnt help. (included datalog of jumpy afr at idle) would a faulty FPR cause a misfire? thanks guys! Quote Link to comment Share on other sites More sharing options...
Clifton Posted June 9, 2008 Share Posted June 9, 2008 would a faulty FPR cause a misfire? thanks guys! If the fuel pressure is constant, your afr should be too. So, not in your case. If it's too lean it will cause a misfire though. What is your idle afr? Your pic is too small to make it out. Quote Link to comment Share on other sites More sharing options...
flames_187 Posted June 9, 2008 Author Share Posted June 9, 2008 sorry didnt realize the pic was small... AFR is set at 13.2 AFR fluctuates from 12.2ish to 13.5 ish i attached the datalog and msq file (megatune ver 2.885) I also tried to hear if the spark plugs are missing and it doesnt sound like it... ROUGH.msq.zip rough datalog.xls.zip Quote Link to comment Share on other sites More sharing options...
Clifton Posted June 9, 2008 Share Posted June 9, 2008 sorry didnt realize the pic was small...AFR is set at 13.2 AFR fluctuates from 12.2ish to 13.5 ish . You say afr is set at 13.2. It sounds like you are having MS control afr. I don't know what code you are running but on 2.36 it needs to have a small correction factor. On 2.67 it is termed different but it needs to pull small amount at each correction to keep the afr from jumping around. I would turn off the correction, set the idle bins to were it will idle at 13.2 and see how stable it is. Quote Link to comment Share on other sites More sharing options...
Noddle Posted June 10, 2008 Share Posted June 10, 2008 Not sure if this has to do with anything, (I'm new to MS and still not sure of what is best), but I see your spark table is very low, i.e. 7 degrees at idle, and 6 degrees at the top end. I take it you are using MS to do the timing ?. I've included a pic of your config for others to see Nigel Quote Link to comment Share on other sites More sharing options...
X64v Posted June 10, 2008 Share Posted June 10, 2008 +1 on what clifton said. Run an open loop idle (no O2 sensor input) and see what that does. Quote Link to comment Share on other sites More sharing options...
flames_187 Posted June 10, 2008 Author Share Posted June 10, 2008 hey nigel... thats my safe setting...i thought my spark table was too advanced and causing the misfire...now i know its not the cuase but my car did like the detuned settings at idle (stock turbo motor) i fouled my spark plugs so cant do anymore realiable testing for the misfire i did get around to lowering my lamda averaging lag factor 10 to 20 % or the lamda correction (MS2 codes call it differently) seem to lower the flucutation but i am still getting a misfire...i tired turning it to 0 % but then the afr doesnt do any correction and i still get the misfire...i need to get some new plugs 2morrow. I wish i had a spare CAS to see if that could be the problem b/c i really dont think ms is causing it. Quote Link to comment Share on other sites More sharing options...
Clifton Posted June 10, 2008 Share Posted June 10, 2008 Your timing is more than safe off boost, I run around that at 30 psi. I would ramp up to 38* by 3000-3500 at 100 kpa and under. You can run a little more at cruise if you want but anything more than what you have should wake it up a bunch. You have to be getting horrble mileage too. Quote Link to comment Share on other sites More sharing options...
1 fast z Posted June 10, 2008 Share Posted June 10, 2008 Wow that is REAL conservative. You will have overheating problems with timing pulled back that far also. Quote Link to comment Share on other sites More sharing options...
flames_187 Posted June 10, 2008 Author Share Posted June 10, 2008 thanks for the info guys, I didnt realize turning down the spark timing have a negitive effect I will go back to my original table and get some new plugs in the car. P.S. i only drove it around the neiborhood cause of the misfire its a slight misfire but happens consistently...its still noticable to me and drives me crazy...im going to change the ground point to the battery of the car and see if that helps (grounded to body of car right now) ...been searching quite a bit and seen people having to get a better ground. Quote Link to comment Share on other sites More sharing options...
flames_187 Posted June 16, 2008 Author Share Posted June 16, 2008 just to update...my misfire is 99% gone...what i did was turn down the lamda and rpm averaging lag factors...it seems if they are too high , the signal jumps around more...I also tuned the VQ tables and timing table better with wideband...i noticed i was leaning out badly in certain areas... I still have to tune my cranking pulse width...everytime i seem to have it set close and try to start it up the next day its like i am back to square one...its real touchy.. I also had to turn down the warmup enrichment...it was making my idle too rich ...finally time to put on my intecooler and up the boost to 10psi...cant wait! thanks for the help guys Quote Link to comment Share on other sites More sharing options...
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