HeatRaveR Posted September 7, 2008 Share Posted September 7, 2008 Here's the setup: '82 280ZXT with MS-I V3 (29V coding) running fuel-only (stock ECU still controls spark, fuel pump relay, emissions, etc). I have 370cc RC Engineering injectors, and pretty much everything is basically new. The engine is tuned and running smoothly when driving. However, I'm having a devil of a time trying to get it to *crank* smoothly. The starter will be spinning, but I have to pump the peddle until it finally turns over. When it finally does start, it frequently smells a bit gassy for a moment. The strange thing is, this cranking hesitation doesn't occur when it's started for the first time in the morning (so when it's fairly cold). Can you guys please take a look at my settings and see what I might need to tweak in order to get it starting good? There seems to be so many possibly-related settings to tweak that I'm at a loss on which to fiddle with. I'm actually on road trip right now and experiencing these problems, so I'd really, really appreciate any suggestions in fixing this ASAP so I can have some peace of mind for the rest of my trip. ^^ Thanks! Also, I don't know if it's a related matter, but when it's "cold" (meaning, hasn't been run recently), the engine will frequently choke/stumble/stall if I try gently applying the gas pedal (such as when leaving my garage). This forces me to rev up and then slip the clutch to get going. But once it's warmed up, the stumbling disappears. Is this related, and if not, what should I tweak? Quote Link to comment Share on other sites More sharing options...
Matt Cramer Posted September 8, 2008 Share Posted September 8, 2008 Here's the setup: '82 280ZXT with MS-I V3 (29V coding) running fuel-only (stock ECU still controls spark, fuel pump relay, emissions, etc). I have 370cc RC Engineering injectors, and pretty much everything is basically new. The engine is tuned and running smoothly when driving. However, I'm having a devil of a time trying to get it to *crank* smoothly. The starter will be spinning, but I have to pump the peddle until it finally turns over. When it finally does start, it frequently smells a bit gassy for a moment. The strange thing is, this cranking hesitation doesn't occur when it's started for the first time in the morning (so when it's fairly cold). Sounds like your high temperature cranking pulse widths need to be adjusted, and from your description, they're probably a little bit too rich. Also, I don't know if it's a related matter, but when it's "cold" (meaning, hasn't been run recently), the engine will frequently choke/stumble/stall if I try gently applying the gas pedal (such as when leaving my garage). This forces me to rev up and then slip the clutch to get going. But once it's warmed up, the stumbling disappears. Is this related, and if not, what should I tweak? This one's an issue with the warm up enrichment - try adding a bit more of it at low temperatures. This may make you have to turn the after start enrichment down by a proportional amount. Quote Link to comment Share on other sites More sharing options...
HeatRaveR Posted September 9, 2008 Author Share Posted September 9, 2008 Sounds like your high temperature cranking pulse widths need to be adjusted, and from your description, they're probably a little bit too rich. Thanks for the response. I just tried adjusting the 130F and 160F cranking pulse width settings all the way down to 1.5, but it still experiences the same cranking problem. Just how much lower should/can I go? Or would one of the other cranking settings, such as the Standard Priming PW (mS) value or Priming PW Source be the culprit? Since the car does start good when it's cold, I was almost wondering if I should actually *increase* the hotter Pulse Width values to match the cold values. But since it smells a bit gassy when it finally does start after cranking while hot, that does support the too-much-fuel diagnosis. Or is it only smelling of gas because the lengthy cranking is injecting lots of fuel with each crank? So I don't know what to think about which direction to tweak it. As a side note, I just changed the sparkplugs tonight, hoping that might make it better, but it didn't help. This cranking problem never happened when the injectors were still under the control of the stock ECU, so it seems doubtful it's an ignition or other such problem, I would imagine. Quote Link to comment Share on other sites More sharing options...
Matt Cramer Posted September 9, 2008 Share Posted September 9, 2008 I suspect it's the cranking pulse width. It is likely it's rich but it could be so lean it misfires. You can go as low as zero, though values below the injector opening time won't do much good. Quote Link to comment Share on other sites More sharing options...
HeatRaveR Posted September 10, 2008 Author Share Posted September 10, 2008 I suspect it's the cranking pulse width. It is likely it's rich but it could be so lean it misfires. You can go as low as zero, though values below the injector opening time won't do much good. A thought just occurred to me: is the Standard Priming PW supposed to be the same value as the PWM Time Threshhold from the Constants page? Just to confirm, I reconnected the injectors back up to the stock ECU, and sure enough, it fires up right away, so Megasquirt is definitely the culprit. Quote Link to comment Share on other sites More sharing options...
Matt Cramer Posted September 10, 2008 Share Posted September 10, 2008 A thought just occurred to me: is the Standard Priming PW supposed to be the same value as the PWM Time Threshhold from the Constants page? Not necessarily. Some people use it to blow any air out of the lines and others use it like a small shot of starting fluid. It can take some trial and error to get it adjusted, but in your case I'd start by adjusting the cranking pulse. Quote Link to comment Share on other sites More sharing options...
HeatRaveR Posted September 12, 2008 Author Share Posted September 12, 2008 Ok, I've got some new data about this problem. If I was running on MS and swap back to stock, it will still have trouble cranking for the first time. And if I was running on stock, and switch to MS, it will start ok. This suggests that the MS cranking settings are not the fault. It seems that MS is somehow doing something when I shut the engine off that makes it difficult to crank again (unless it's left for an extended period like overnight), regardless of which engine management is at work. It's as though MS might be flooding the engine or something just as the engine is being shut off. But if that's what's happening, what setting could cause/cure that? Quote Link to comment Share on other sites More sharing options...
HB280ZT Posted September 12, 2008 Share Posted September 12, 2008 Try doing a search in the MegaSquirt thread on heat soak. I have been running the MS1 V3 for about 3 years now and when I restart the car after it has been running for awhile it starts and runs really bad until the fuel cools the fuel rail down again. This is caused by heat soak of the fuel rail and causes the car to run really lean for a few minutes, 19:1 or so. Hope this helps some. HB280ZT Quote Link to comment Share on other sites More sharing options...
HeatRaveR Posted September 13, 2008 Author Share Posted September 13, 2008 Ok, I'll do some research on that heat soak problem, but although some of the symptoms sound similar, I'm doubtful that's the culprit. The fact that the stock ECU will start it up good tends to rule that out. It's been very consistent that if the stock ECU was just in control that either ECU will crank it up good the following time; and that if MS was just in control, that both ECU's will have a difficult time getting the engine going. Yes, it is true that if MS was running the engine and left overnight that it will start up the engine good in the morning, but I suspect it's something more related to time (something dissipating perhaps) than temperature. Oh, here's another thing I've noticed on these difficult starts. In addition to the gassy smell once it cranks, sometimes it will even belch out a puff of black smoke once it does fire up! I don't know if this' related too, or not, but I've also noticed that sometimes the idle will be very good and steady, and then other times, it will fluctuate as if it can't decide how much fuel or what rpm to hold it at. I haven't yet deciphered the pattern of when this idle issue occurs, but I wonder if it might be related to the cranking issue. Like maybe the time idling before parking is somehow doing something that makes the subsequent cranking difficult? Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted September 14, 2008 Share Posted September 14, 2008 Sounds as if you could be too rich at idle. This is helping your (theoretically lean) cold starts the next morning but making your (theoretically rich) hot starts even worse. (On a side note, I've never seen a map come from a California car have proper (really) COLD start enrichment. They usually need beefed up quite a bit.) Likewise, your after start enrichments seem too high to me. Also, don't "pedal" the gas when trying to start. I am not sure if the megasquirt does any AE while cranking, but if it is, you are only making things more confusing for yourself. If the car won't drive about while cold it could be either after start enrichment, coolant enrichment or your base fuel map. Get the base fuel map dialed in really good when it's at operating temp. Particularly at those very high load points at idle rpm and above. Don't try to tune it while sitting still on a hot day with the hood closed, though. It'll hit the high load points more when it's cold so they are crucial to get dialed in before trying to drive around a parking lot with it cold. Hast thou a wideband? Quote Link to comment Share on other sites More sharing options...
mario_82_ZXT Posted September 14, 2008 Share Posted September 14, 2008 I'd look into heat soak again. My friend's car has this problem as well and it's because the IAT sensor (which the stock setup doesn't have) gets severely heat soaked. Mario Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted September 20, 2008 Share Posted September 20, 2008 I'd look into heat soak again. My friend's car has this problem as well and it's because the IAT sensor (which the stock setup doesn't have) gets severely heat soaked. Mario Yeah, the S30 heatsoaks like a mofo. I had to use Fyresleeve on my fuel line and I am thinking about putting something reflective and insulating on the fuel rail itself as well. I try to tell everyone about the IAT (and installing it in the engine bay) but it's evidently a touchy subject with some people. I always install them on the outlet endtank of the FMIC. Quote Link to comment Share on other sites More sharing options...
HeatRaveR Posted September 22, 2008 Author Share Posted September 22, 2008 I have the IAT sensor mounted after the intercooler, about 7" before the throttle body. Should I wrap the part of it sticking out of the piping in some kind of insulation? Quote Link to comment Share on other sites More sharing options...
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