big-phil Posted October 12, 2008 Share Posted October 12, 2008 I think its been a month now that I've had this problem. It all started after a night of tuning at 20 lbs of boost and getting the revs above 6k rpm. All went perfect, until the next morning while dropping it into 4th to take an exit. I felt a stumble. Also that morning my turbo (holset) started smoking. Rebuilt the turbo that week no more smoke but the stumble is still there. Let me define the stumble. It feels like I'm hitting a rev limit. and seems to only happen above 14lbs of boost. But sometimes it does not happen at all. If I lower the boost to say 12lbs, the car will rev to 65k rpm. During the stumble the tack stays in place does not jump around, fuel psi builds and holds steady does not drop off, wide bands goes LEAN during stumble, but the injector pulse width and duty cycle hold steady. Sometimes it will pull through, so rpm holds at say 48k rpm, fuel builds to say 50lbs and holds. But then boom the car takes off as though nothing was wrong. I've changed the cap and rotor with Nissan parts. check the plug wire ohm's, new plugs. put a test light on fuel pump before and after the relay. test light on coil, neither losses power. Nothing has changed from that tuning night a month ago. I've ohm'd the injector wires, signal wire from dizzy, TPS wire, put noise filters on all 12+ going to megasquirt. And I've rewired the CLT and IAT sensors with shielded wire. I'm left thinking its my turbo? I rebuilt it but did not have it balanced. I've done that before on my other holset but I've checked EVERYTHING and thats what I'm left with? Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted October 13, 2008 Share Posted October 13, 2008 sounds like Acceleration Enrichment's possibly? I also have slight issues with my car stumbling too.. are you TPS or MAP accel tuned? I dont think it would be the turbo at all.. if you had a turbine jet engine I would say its a symptom of compressor stall.. but in an automotive application this doesn't apply from : WikipediaA compressor stall is a situation of abnormal airflow resulting from a stall of the aerofoils within the compressor. Stall is found in dynamic compressors, particularly axial compressors, as used in jet engines and turbocharged reciprocating engines. Compressor stalls result in a loss of compressor performance, which can vary in severity from a momentary engine power drop (occurring so quickly it is barely registered on engine instruments) to a complete loss of compression (compressor surge) necessitating a reduction in the fuel flow to the engine. Symptoms in a turbocharger in a recip engine are not as wild as jet engine stalls.. but a sudden surge or "stall" in performance is applicable Quote Link to comment Share on other sites More sharing options...
jeffer949 Posted October 13, 2008 Share Posted October 13, 2008 Does it do it in between shifts like if your doing a 2nd-3rd-4th run? mine does it at the track some when i shift and then slam my throttle back down during shifts. Ive messed with the Accell enrichment and its gotten better. I just havent taken the time to mess with it more. Ive also heard that switching to MAP dot enrichment might be the way to go with my set up. Quote Link to comment Share on other sites More sharing options...
Thumper Posted October 13, 2008 Share Posted October 13, 2008 I think its been a month now that I've had this problem. It all started after a night of tuning at 20 lbs of boost and getting the revs above 6k rpm. All went perfect, until the next morning while dropping it into 4th to take an exit. I felt a stumble. Also that morning my turbo (holset) started smoking. Rebuilt the turbo that week no more smoke but the stumble is still there. Let me define the stumble. It feels like I'm hitting a rev limit. and seems to only happen above 14lbs of boost. But sometimes it does not happen at all. If I lower the boost to say 12lbs, the car will rev to 65k rpm. During the stumble the tack stays in place does not jump around, fuel psi builds and holds steady does not drop off, wide bands goes LEAN during stumble, but the injector pulse width and duty cycle hold steady. Sometimes it will pull through, so rpm holds at say 48k rpm, fuel builds to say 50lbs and holds. But then boom the car takes off as though nothing was wrong. I've changed the cap and rotor with Nissan parts. check the plug wire ohm's, new plugs. put a test light on fuel pump before and after the relay. test light on coil, neither losses power. Nothing has changed from that tuning night a month ago. I've ohm'd the injector wires, signal wire from dizzy, TPS wire, put noise filters on all 12+ going to megasquirt. And I've rewired the CLT and IAT sensors with shielded wire. I'm left thinking its my turbo? I rebuilt it but did not have it balanced. I've done that before on my other holset but I've checked EVERYTHING and thats what I'm left with? Sounds like you are blowing out the spark. Especially the part where you can run lower boost and not higher. Tighten the gap to something very small. Quote Link to comment Share on other sites More sharing options...
Matt Cramer Posted October 13, 2008 Share Posted October 13, 2008 Sounds like a classic case of spark blowout to me, too. What are you running for igntion? Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted October 13, 2008 Share Posted October 13, 2008 Unburnt fuel will make the O2 read lean. Quote Link to comment Share on other sites More sharing options...
jeffer949 Posted October 13, 2008 Share Posted October 13, 2008 Im pretty sure he is running the same as me MSNS v3.0 using the internal coil driver to fire his msd 6a then his coil. I know a few weeks ago he was running BPR7ES-11 Quote Link to comment Share on other sites More sharing options...
big-phil Posted October 13, 2008 Author Share Posted October 13, 2008 MSD 6a my gap is .028 I have run .025 in the past I can try putting it back down to .025. Again I have run the same setup with no trouble for months. At one point I turned the accel enrichment off. I'm going to try putting the gap at .025. plugs are NGK bpr7es-11 Quote Link to comment Share on other sites More sharing options...
big-phil Posted October 13, 2008 Author Share Posted October 13, 2008 Unburnt fuel will make the O2 read lean. that was my big question. I started thinking it was fuel because it went lean. But I don't think its fuel or coil. Quote Link to comment Share on other sites More sharing options...
ktm Posted October 13, 2008 Share Posted October 13, 2008 What are your target AFRs at 20 psi? Quote Link to comment Share on other sites More sharing options...
big-phil Posted October 14, 2008 Author Share Posted October 14, 2008 What are your target AFRs at 20 psi? 11.5 with methanol Quote Link to comment Share on other sites More sharing options...
big-phil Posted October 14, 2008 Author Share Posted October 14, 2008 well I feel stupid. I just set the plugs to .024 and beat the hell out of the car for about 30 min at 16lbs with out one stumble. I could of swore I tried .025 with no luck. But I've rewired so much stuff, cap, rotor, test lights everywhere..... I had them set at .028 when I took them out of the car. Now.. its run great in the past, and then went all to hell the next day. So time will tell. so far problem fixed. Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted October 14, 2008 Share Posted October 14, 2008 well.. i defin over thought that one ughm.. lets pretend I didnt say what I said Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted October 14, 2008 Share Posted October 14, 2008 Excellente! Quote Link to comment Share on other sites More sharing options...
big-phil Posted October 14, 2008 Author Share Posted October 14, 2008 well.. i defin over thought that one ughm.. lets pretend I didnt say what I said I went a month overlooking it:? I just hope it still runs great in the morning Quote Link to comment Share on other sites More sharing options...
jeffer949 Posted October 14, 2008 Share Posted October 14, 2008 I know how you feel Phil. I changed my alternator to a 240sx unit today and it started working much better.. We will see what happens tomorrow. Quote Link to comment Share on other sites More sharing options...
Thumper Posted October 14, 2008 Share Posted October 14, 2008 I went a month overlooking it:?I just hope it still runs great in the morning FYI 1. When the spark plug gets too hot it can adjust its gap by itself. If this happens get a colder plug. 2. What Thumper says is always right:twisted: Quote Link to comment Share on other sites More sharing options...
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