AtlantaZ Posted September 12, 2011 Share Posted September 12, 2011 I finally have my 1976 280z with a freshly rebuilt L28ET swap up and running. It drives okay under low load, but I feel like it is at only 50% power. Under 7psi boost and/or WOT, I am getting intake backfires. My wideband O2 sensor is showing healthy AFRs under all operating conditions. Compression check shows 135-145psi across all six cylinders. I pulled the spark plugs and observed whitish firing ends on five out of six plugs. However, plug #4 definitely looked darker and fouled. These plugs all have less than 500 miles on them. I've looked at several spark plug diagnosis charts, and it definitely looks like a classic fouled plug to me. But I'd love to hear what you guys have to say! Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 12, 2011 Share Posted September 12, 2011 (edited) Wow, EXACTLY the same symptoms that I got last week, when I thought I blew my engine again....let me go find the post. http://forums.hybridz.org/index.php/topic/101991-half-power-sputtering-turbo-surging/page__view__findpost__p__955106__fromsearch__1 Edited September 12, 2011 by cygnusx1 Quote Link to comment Share on other sites More sharing options...
AtlantaZ Posted September 12, 2011 Author Share Posted September 12, 2011 Hah, just read your thread before you posted! I didn't think to check the timing - will probably do that first thing tomorrow. Still, shouldn't all six plugs look similar? Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 12, 2011 Share Posted September 12, 2011 Similar, I suppose, but those are far from fouled enough to cause trouble. My plugs never all look identical...that is something I got over with some help from meditation J/K it's probably related to injector balance, air flow balance, and condition of valve seals. Quote Link to comment Share on other sites More sharing options...
AtlantaZ Posted September 12, 2011 Author Share Posted September 12, 2011 Head got new valve seals when I rebuilt it 800 miles ago, so hopefully they're good. Where in the wiring was your issue? PIP/SAW? Quote Link to comment Share on other sites More sharing options...
jasper Posted September 12, 2011 Share Posted September 12, 2011 5 look lean, one looks very rich, possibly causing the seemingly good afr's. Check for a bad injector. Swapping the suspect injector to another cylinder, and a road test, could confirm this suspicion. Ignition is also suspect. Swap plug, wire, and injector to differnt cylinders. See if problem follows any component Quote Link to comment Share on other sites More sharing options...
AtlantaZ Posted September 12, 2011 Author Share Posted September 12, 2011 That's exactly what I came up with - sticking injector or misfiring plug. I'll shuffle the wire and injector, install new plugs, and take her for a 30-minute road test. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 12, 2011 Share Posted September 12, 2011 (edited) Yeah SAW wire was giving me intermittent connections, so the car was going from 0-btdc to whatever the Map called for at random spurts. Definitely caused all of the symptoms you describe. Edited September 12, 2011 by cygnusx1 Quote Link to comment Share on other sites More sharing options...
AtlantaZ Posted September 12, 2011 Author Share Posted September 12, 2011 I can see where that would make timing go crazy. I'll definitely check that too. Thanks gentlemen - hope to have update tomorrow. Quote Link to comment Share on other sites More sharing options...
AtlantaZ Posted September 13, 2011 Author Share Posted September 13, 2011 (edited) Ok, put in a fresh set of BPR6EY-11 plugs, gapped to .030. I moved the #4 plug wire to #6 and moved the #4 injector to #1. Took it for a 20-minute test drive and pulled the plugs. Now all six look lean. #2 also looks like it has a burn mark, but I think that is from a spot of copper anti-seize that made it onto the insulator during installation. None of the electrodes had a wet appearance. My Supra MkIII turbo injectors are port-injecting into a stock 280zx turbo manifold, so I don't think there's a problem with the spray pattern itself. Fuel is supplied by a Walbro GSL392 inline pump, pushing fuel through the stock hardline and up to a -8AN braided stainless line in the engine bay, on to a Pallnet rail, and regulated by an Aeromotive FPR with a mechanical pressure gauge. Return feeds into stock return hardline. Reading 45psi fuel pressure at idle. My AFRs still look dead on. I get intermittent intake backfiring at full throttle, but my WBO2 shows 13-14:1. It still feels flat through the power band, but idles great and pulls fairly well under light throttle. I parked the car and hooked up a cheap timing gun. The white dot I painted on the crank wheel definitely advances when I hand-throttle the engine, so at least some sort of advance is being commanded. But maybe at higher RPMs I'm getting signal noise and the SAW signal is dropping out? I think if the SAW weren't commanding advance at idle, I'd be in limp-home mode and only seeing 10*BTDC. But I'm not sure how I could be getting interference on the SAW wire, as the EDIS module and the Megasquirt relay board are only 6" apart inside the glove box, and I don't recall seeing any high current wires passing near them. Fuel pressure looks good when the car's parked and I hand-rev the engine, but maybe it's dropping out under load...? Need to figure out a way to read mechanical fuel pressure while driving. Other thoughts? What's going on here? My 0-60 time is something like 7-8 seconds. Even for a daily driver, that is unacceptable! Edited September 13, 2011 by AtlantaZ Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 13, 2011 Share Posted September 13, 2011 (edited) If fuel pressure was dropping out, AFR's would reflect that. Can you run some datalogs and post them? Also run a calibration cycle on your WBO2 sensor if you can. Edited September 13, 2011 by cygnusx1 Quote Link to comment Share on other sites More sharing options...
AtlantaZ Posted September 13, 2011 Author Share Posted September 13, 2011 (edited) I can definitely run datalogs! But the mean old forum won't let me "post this type of file"...? I ran a free air recalibration on my WBO2, and recalibrated the AFR tables, yesterday. I'm using an LC-1 and setting the Wideband O2 in Tunerstudio to "LC-1 Default". Edited September 13, 2011 by AtlantaZ Quote Link to comment Share on other sites More sharing options...
AtlantaZ Posted September 13, 2011 Author Share Posted September 13, 2011 (edited) I am attaching my ignition and AFR maps. Also note that my VE map looks awfully flat (the areas above 100kPa and 4000RPM aren't tuned, so ignore those areas). *EDIT* Is it possible that I have something incorrectly wired on the Megasquirt board? I have a good tach signal and the advance seems to be moving as commanded by Megasquirt, so everything seems okay. But maybe I'm missing something... Edited September 13, 2011 by AtlantaZ Quote Link to comment Share on other sites More sharing options...
jasper Posted September 13, 2011 Share Posted September 13, 2011 Is it possible your heat range is off? You went to a hotter plug. They look even "leaner", or too hot. Quote Link to comment Share on other sites More sharing options...
AtlantaZ Posted September 13, 2011 Author Share Posted September 13, 2011 I know. I went with the coldest NGK plug that the local Autozone had in stock. Maybe I should try a non-projector BR7ES plug... but wouldn't that lead to lean AFRs? I'm wondering about the discrepancy between the plug appearance and the WBO2 reading. Quote Link to comment Share on other sites More sharing options...
AtlantaZ Posted September 13, 2011 Author Share Posted September 13, 2011 My tune fine and a recent log: AtlantaZtune.zip Quote Link to comment Share on other sites More sharing options...
mario_82_ZXT Posted September 14, 2011 Share Posted September 14, 2011 What's your elevation? Are you running barometric corrections? If you're running 13-14:1 AFR at full throttle you're way too lean. Your AFR map seem a little on the lean side as well. In boost on a street car I tune for Low to mid 11s under full boost. Atmospheric Baro is about 75kPa here, and I'm usually in the mid to low 12s (AFR) then. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 14, 2011 Share Posted September 14, 2011 I agree that some of the AFR areas are a bit lean. I have recently begun to throw fuel efficiency ideas out the window, and richened up my maps. It runs much better that way. 14.2:1 would be about as lean as my setup will smoothly tolerate under cruise. Everywhere else go rich or go home....I will try to get a look at your datalog and msq files tonight. It has been a rough few days so I haven't had any downtime. Quote Link to comment Share on other sites More sharing options...
AtlantaZ Posted September 14, 2011 Author Share Posted September 14, 2011 Thanks for helping with this, everyone. I visually inspected the wiring, and the SAW wire looks okay. Will double check tonight. Ran BR8ES plugs but no real change in performance... Quote Link to comment Share on other sites More sharing options...
Lazeum Posted September 14, 2011 Share Posted September 14, 2011 Maybe a stupid idea but have you check for leaks? you might have some air going thru the engine at some point. 14.2:1 seems very lean to me as well, I would expect at WOT around 12.5 at Max torque & 11.5 at redline as a baseline. Quote Link to comment Share on other sites More sharing options...
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