letitsnow Posted October 8, 2011 Share Posted October 8, 2011 (edited) Engine: fresh L28ET lower end, stock p90a(unknown miles), stock t3, 750cc injectors, MS2, walbro 255, AEM regulator, evo 8 IC, 2.5" downpipe, 3" exhaust, optical dizzy, new NGK wires, new cap/rotor, new plugs @.040" gap, and an MSD blaster 2 coil. Here is a burst datalog of it happening in 3rd. Because the AFR looks perfect and the power loss is smooth, I'm thinking it's a mechanical problem and not a tune problem. Valve float or hydraulic lifter problems maybe? It might not be entirely clear from the picture, but the car did not have the power to go past 5300. 2011-10-08_15.58.54.zip Edited October 8, 2011 by letitsnow Quote Link to comment Share on other sites More sharing options...
Pyro Posted October 8, 2011 Share Posted October 8, 2011 Your graph is hard to read. A stock turbo cam is done by 5000. A weak alternator can make the power fall off sooner than it should. Quote Link to comment Share on other sites More sharing options...
DuoWing Posted October 8, 2011 Share Posted October 8, 2011 I remember on my stock ZXT with auto tranny by the time you were rolling up onto about 5500 RPM there wasn't much left, it'll be interesting to get out and really see how it does with the N/A cam in my L28ET when I get a chance. Quote Link to comment Share on other sites More sharing options...
Tennesseejed Posted October 9, 2011 Share Posted October 9, 2011 Pull up SparkAdv on your data log . . . . goes from 40 deg at 2200rmp to 20 deg at 5200. ? Might be that Megasquirt is not reading spark advance properly, so the reading is meaningless, but curious nonetheless. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 9, 2011 Share Posted October 9, 2011 Valve float is not an issue unless you got some serious valve spring issues. SERIOUS valve spring issues, like forgetting to assemble it with inners or something like that... Quote Link to comment Share on other sites More sharing options...
letitsnow Posted October 9, 2011 Author Share Posted October 9, 2011 (edited) It feels like it might be misfiring, and sometimes it seems to run poorly after a WOT pull, you can smell unburnt fuel when it does run poorly. The odd thing is that it doesn't seem to show up on the wideband trace. It doesn't do this unless you go past 4500-4600, if you stay below, it runs fantastic. This feels like a large unnatural power loss, not like the engine just running out of steam. The thing that really bothers me the most, why does the power just disappear but the datalog looks perfect? I have datalogs of it breaking up at 4500, then continuing to run like crap for 30 seconds more, the afr's on the log look fine, the only telltale sign is that it took more throttle to keep the car going than normal. Spark advance is around 40 degrees in the low load cruise areas, at 12psi it's closer to 20. Megasquirt is controlling spark, it's set up firing the coil directly. I didn't put the head together, so I'll check and make sure the springs are all there. Could a set of worn or poorly maintained hydraulic lifters/lash adjusters cause odd problems like this? Compare this to the 1st pic, notice that it doesn't fall off. This one went to 5500 easily. Edited October 9, 2011 by letitsnow Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 9, 2011 Share Posted October 9, 2011 I can't see the photos... Quote Link to comment Share on other sites More sharing options...
letitsnow Posted October 9, 2011 Author Share Posted October 9, 2011 (edited) Rehosted on hybrid z, they were on imageshack before. Edited October 10, 2011 by letitsnow Quote Link to comment Share on other sites More sharing options...
Pyro Posted October 9, 2011 Share Posted October 9, 2011 I would run about 25 degrees of timing with 12 psi of boost on a 7.4:1 cr engine (stock turbo compression, with 93 octane fuel) What octane fuel are you using? I feel 4500 rpm is right at the most sensitive detonation period of a L28. I recently had a similar issue with power falling off, I couldn't find the problem and lived with it for a month or two, then the alternator failed, I replaced it and the "power fall off" went away. Same thing was happening to a friend of mine with his retro fit turbo Z, so he had his alternator checked and it was only putting out 30 amps. Quote Link to comment Share on other sites More sharing options...
letitsnow Posted October 9, 2011 Author Share Posted October 9, 2011 93 octane, kameari 1mm head gasket, so compression should be very close to stock. The power loss seems related to boost pressure, the more boost, the worse it is. Under 10psi it doesn't seem to happen. I'm not sure it's spark blow out either. Last night I was helping a friend with his subaru, we loaded a mail order tune and adjusted the boost, at 18psi it would 'skip' every now and then at wide open, at 16 psi this didn't happen. AFR was alright on both, I believe this was spark blowout, that's not like what I'm feeling. I wish there was a better way of describing it, reminds me of fouling a sparkplug on my snowmobile, like it drops a cylinder or 2. Quote Link to comment Share on other sites More sharing options...
letitsnow Posted October 9, 2011 Author Share Posted October 9, 2011 I've decided to completely rule out issues with the HLA's and fuel pressure. I ordered the timeserts to convert to mechanical lash adjusters and a pressure transducer so I can datalog fuel pressure. As a plus, now I can toss in my extra N/A L28 camshaft. Total cost for timeserts and transducer, $77. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 10, 2011 Share Posted October 10, 2011 Can you datalog both upstream and downstream of the fuel filter? I agree with Pyro, there is a lot of fuel that can be thrown at an L-Series at peak torque, and that's usually around 4500, after that point you can pull fuel like crazy (I have seen mid 13's on boost!) and you just keep making horsepower. Then again, I guess you have to be able to pull through peak torque to the point where you can pull fuel, eh? Quote Link to comment Share on other sites More sharing options...
letitsnow Posted October 10, 2011 Author Share Posted October 10, 2011 I only bought one transducer, if the pressure seems wrong at the fuel rail I can investigate further. I have the filter on the suction side of the pump, it's a generic, but fairly big, 3/8 steel body filter from autozone. If it were fuel pressure related, wouldn't we see it going lean on the log? I guess I'll find out next weekend. Quote Link to comment Share on other sites More sharing options...
Pyro Posted October 10, 2011 Share Posted October 10, 2011 don't use a regular filter on the suction side. These filters are around 40 microns which is too small for decent flow with suction. buy a 100 micron filter from summit racing. The bigger the better. Quote Link to comment Share on other sites More sharing options...
letitsnow Posted October 10, 2011 Author Share Posted October 10, 2011 I didn't have a filter on the suction side until recently a little bit of the tank sealer I used flaked off and plugged the screen in the pump. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 11, 2011 Share Posted October 11, 2011 OhOh.... If you have large seives in the line for catching (as the tech instructor in Block 10 said:) 'sharkshit and little children' be advised the VERY FINE screens at the inlet of the fuel injectors MAY be clogging with fine debris which is bypassing your fuel filters. This is EXACTLY what happened on JeffP's engine. They will flow fine...to a point. Then the engine is like it hits a rev limiter. And that would be at or around peak torque like you're seeing. Take the time to pull off your injectors and reverse-flow them. Put them in the fuel rail backwards and simulate some load to cycle the injectors with cleaner flowing backwards through the bodies and see if afterwards you get better results. It may be you indeed DO need finer filtration on the downstream side of the pump (you can always run several filters in parallel to get the flow you need) to prevent the filter inlet screens on the injectors from fouling and restricting flow when you really start using the injector capacity. We may be on to something here.... Quote Link to comment Share on other sites More sharing options...
letitsnow Posted October 11, 2011 Author Share Posted October 11, 2011 I'll give that a shot this weekend if I can, I'm super busy this week with school. But once again, shouldn't the wide band show lean? Is there a good way to hold the injector in the rail? I suppose I could use one of the extra manifolds I have laying around. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 11, 2011 Share Posted October 11, 2011 Depends what injector you have. If you have the o-ringed style, they may spin round in the rail/intake and you van try a run that way... Don't know about wiring connecto clearance in that configuration. If they are barbed it's almost as easy to send them in for a flow check and cleaning as it is to make the apparatus. Quote Link to comment Share on other sites More sharing options...
letitsnow Posted October 11, 2011 Author Share Posted October 11, 2011 deka 14mm o ring injectors. I've got an extra manifold I could just stick them in, but I don't have a separate pump, so at best I'm going to best able to flush them with gas. There is a local shop that does cleaning and testing pretty reasonably, but cash is running low until I start my new job near thanksgiving. I could toss the stock injectors back in, they look like they should work up to ~12psi, but they'll be nearing 100% DC. Quote Link to comment Share on other sites More sharing options...
CamH Posted October 12, 2011 Share Posted October 12, 2011 I had a similar issue on my setup. It turned out to be an "on the way out" coil. One day, I was out messing with the tune, and it failed entirely and left me stranded. After picking up an MSD Blaster SS coil and installing it, the car would rev to about 5500 (on hydro adjusters and stock hydro cam, but with a bigger turbo.) Might be worth your time to swap out coils if you have an extra sitting around. After that I converted to solid adjusters and MSA Stage II turbo cam and the car revs to just over 6500RPM and pulls hard all the way up! Quote Link to comment Share on other sites More sharing options...
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