ryan95i4 Posted September 12, 2012 Share Posted September 12, 2012 I've been trying to track down this issue for some time now. 73 240Z w/ L28ET Swap (essentially stock swap). Car runs rich at idle, around 11:1-11.5:1, but extremely lean under boost, will go 18:1 or leaner in first 3 gears, 4th and 5th still lean, but will drop to 15:1 give or take. AFM checks out by FSM test, but Ive tried another with same results. Dizzy/CAS is fine, but again, have tried a second with same results. CHT checks out. TPS checks out. Base timing is at 24* adv and is rock steady at 2000, 3000, 4000rpm. Just installed new stock turbo injectors, all 6 fire. Fuel pressure is good, 34psi at idle, ~50psi at full throttle (aftermarket pump and surge tank setup). Car starts, idles and cruises fine (other than the rich idle). Perfect compression, pulls 18-20in-hg vacuum at idle, ~650rpm. The idle adjustment screw on the AFM doesnt seem to effect idle a/f much, if at all. Im running out of ideas on what to look for next...is it possible to have a bad ecu and still drive fine under light load (81 turbo auto according to the parts number lookup), how do you check the ecu if so? Anywhere else I should be looking? Thanks for any insight! Quote Link to comment Share on other sites More sharing options...
cgsheen Posted September 12, 2012 Share Posted September 12, 2012 Is your A.A.C. functional? It supplies bypass air at idle to correct the AFR. If it has no vacuum it'll cause a rich condition at idle. The stock ECU can't really correct the idle AFR without it. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted September 12, 2012 Share Posted September 12, 2012 (edited) If your AFM checks out using the service manual specified tests, that doesn't mean it couldn't be out of adjustment. Perhaps the springs are too tight, that could give the symptoms you describe. Edited September 12, 2012 by SleeperZ Quote Link to comment Share on other sites More sharing options...
ryan95i4 Posted September 12, 2012 Author Share Posted September 12, 2012 Is your A.A.C. functional? It supplies bypass air at idle to correct the AFR. If it has no vacuum it'll cause a rich condition at idle. The stock ECU can't really correct the idle AFR without it. No A.A.C. -- intake manifold is shaved and polished, sorry didnt mention this. This is part of the "essentially" stock part, as car also has a 60mm TB from a 240sx. Other non-stock bits: aeromotive 1:1 fpr and aftermarket fuel rail. If the rich idle and lean under boost are in fact separate issues and if the lack of AAC explains the rich idle, then I am less concerned with that than I am with being lean under load. If your AFM checks out using the service manual specified tests, that doesn't mean it couldn't be out of adjustment. Perhaps the springs are too tight, that could give the symptoms you describe. Is it likely that two different AFMs would have the same problem? I havent taken the inspection lid off one, but the second one I tried still had the original glue "globs" in place. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted September 12, 2012 Share Posted September 12, 2012 Only other thing that comes to mind is the pressure regulator, but 50psi at boost is appropriate (for 8 psi boost). I can't see an untouched AFM causing it either. But the ECU has got to be getting an inaccurate air measurement, or it would fuel properly with that fuel pressure. Quote Link to comment Share on other sites More sharing options...
NewZed Posted September 12, 2012 Share Posted September 12, 2012 (edited) Maybe your AFR reading is incorrect. Jumped on to Google and found this interesting article - http://www.mpsracing.com/instructions/Daytona/WEGO2_NB_Instructions.pdf Page 3 describes erroneous reading causes. Edited September 12, 2012 by NewZed Quote Link to comment Share on other sites More sharing options...
ryan95i4 Posted September 12, 2012 Author Share Posted September 12, 2012 Only other thing that comes to mind is the pressure regulator, but 50psi at boost is appropriate (for 8 psi boost). I can't see an untouched AFM causing it either. But the ECU has got to be getting an inaccurate air measurement, or it would fuel properly with that fuel pressure. Just to confirm, it is running off the stock wastegate, 7psi. I wanted to get it running perfect as is before adding anything else. I suppose I could try adjusting one of the AFM's and seeing how it reacts. Quote Link to comment Share on other sites More sharing options...
ryan95i4 Posted September 12, 2012 Author Share Posted September 12, 2012 Maybe your AFR reading is incorrect. Jumped on to Google and found this interesting article - http://www.mpsracing.com/instructions/Daytona/WEGO2_NB_Instructions.pdf Page 3 describes erroneous reading causes. I wish that were the case. Car falls on its face like a lean condition. The original narrow-band a/f that was in the car when I bought it also pegged out lean. I'll pull the new plugs to be sure, but the car feels acts like its starving of fuel in boost. Quote Link to comment Share on other sites More sharing options...
ryan95i4 Posted September 12, 2012 Author Share Posted September 12, 2012 Update: I did try adjusting the AFM to see how the car reacted. I tried adjusting the AFM small bits at a time at first with little change, then made large adjustments, so large the car idled extremely rich. Rich enough to peg my wideband (only shows down 10:1, so likely beyond that), car idled poorly obviously, but even then, as soon as the car is under load/boost, car goes way lean just as it had before. I returned the afm back to where it was previouly, then a tooth or two leaner. AF at idle is now better, around 13.5:1 or so, but still same lean condition in boost remains. Not sure where to go from here. Quote Link to comment Share on other sites More sharing options...
cgsheen Posted September 13, 2012 Share Posted September 13, 2012 Just to confirm, it is running off the stock wastegate, 7psi. I wanted to get it running perfect as is before adding anything else. I suppose I could try adjusting one of the AFM's and seeing how it reacts. Sorry, using the stock ECU there will never be a "running perfect" without all the parts it's expecting to be there. It's just not that smart. You may be able to "fiddle" with what's left and get things closer... It make take quite a bit of trial-and-error. If your plan is to get even further away from stock, you need a different engine management system - one that's smart enough to keep up with your changes. Quote Link to comment Share on other sites More sharing options...
ctc Posted September 13, 2012 Share Posted September 13, 2012 Double check the afm connector and wiring back to the ecu. I had a similar problem on a Bosche L-jet system ( very close to Nissan system), that would cause the ecu to recive a different signal than the afm was putting out. Only found it when we installed a custom break out box at the ecu, to see real time ecu signals. Also might need to ohm out all the afm to ecu wires. Quote Link to comment Share on other sites More sharing options...
ctc Posted September 13, 2012 Share Posted September 13, 2012 Second thought, what is you fuel pump voltage doing at full throttle. Might have pressure, but not flow? Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted September 13, 2012 Share Posted September 13, 2012 Second thought, what is you fuel pump voltage doing at full throttle. Might have pressure, but not flow? If you've got the pressure at the rail, the only thing that would restrict the flow are the injectors. Quote Link to comment Share on other sites More sharing options...
ryan95i4 Posted September 13, 2012 Author Share Posted September 13, 2012 Sorry, using the stock ECU there will never be a "running perfect" without all the parts it's expecting to be there. It's just not that smart. You may be able to "fiddle" with what's left and get things closer... It make take quite a bit of trial-and-error. If your plan is to get even further away from stock, you need a different engine management system - one that's smart enough to keep up with your changes. Perfect may have been too strong of a word. "Able-to-actually-go-WOT" would have sufficed lol Quote Link to comment Share on other sites More sharing options...
ryan95i4 Posted September 17, 2012 Author Share Posted September 17, 2012 Double check the afm connector and wiring back to the ecu. I had a similar problem on a Bosche L-jet system ( very close to Nissan system), that would cause the ecu to recive a different signal than the afm was putting out. Only found it when we installed a custom break out box at the ecu, to see real time ecu signals. Also might need to ohm out all the afm to ecu wires. I havent got a chance to work on the car since my last reply, but I guess this will be my next investigation Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted September 17, 2012 Share Posted September 17, 2012 It's a good suggestion. Check all the vital connections to the ECU and AFM, clean them with electrical contact cleaner. Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted September 18, 2012 Share Posted September 18, 2012 If everything checks out electrically, you can do some air flow meter stuff. If you have gotten the mixture correct for driving but have idle mixture issues, there are air bleeds in the air flow meter that you can adjust to bypass the flap. Screw them in for richer idle and unscrew for to lean. What you are doing is closing the bypass with the screw. There will be a 1/2 inch or so round aluminum plug you have to remove unless you already have a hole there. This is only for idle mixture. Still......a stock engine should run ok without fiddling with either the flapper spring tension or the idle air bypass. Quote Link to comment Share on other sites More sharing options...
ryan95i4 Posted September 21, 2012 Author Share Posted September 21, 2012 Update: Everything checked out because everything was fine. The issue is either a loose pin or solder point in the ECU connector or the ECU itself. Going through the ecu connection now to find the exact point, but a quick jolt to the ecu (read: knocking the ecu in the footwell with your foot) and the car took off Thanks to everyone for their input, but it looks like we found the culprit. Going though the connectors now and checking all pins and fixing as needed. Hopefully this clears it all up. If nothing else, the search has gotten me familiar with the FSM and how to check every sensor in the car. If the issue still persists, ill be back (and probably asking megasquirt questions instead... ) Quote Link to comment Share on other sites More sharing options...
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