Serban Posted June 23, 2014 Share Posted June 23, 2014 Here's the scenario, 1975 CA base model, EGR equipment has been removed, cat has been removed, air regulator has been removed, and 7th injector is not hooked up. I had a custom rail made using Ford 19lb injectors, and stock fuel pressure regulator. Car ran great everything described above, even a little rich, so I adjusted the AFM to lean it out a bit. Lately, once it gets to 4k or higher in the rpm, it runs real lean, this is verified by an AEM wideband gauge installed/ Sensor is located where the cat used to be. I adjusted the TPS as per the instructions on atlanticz, and it helped a little bit initially, but now it does the same thing. I even adjusted the AFM back to factory position, and it seems the only change is it runs real rich at idle, and part throttle (in the neighborhood of 10:1 - 11.5:1 air/fuel). Unfortunately, the fuel pressure gauge that came with the rail is busted, and no longer reading accurately, so I'll need to change the gauge. Could the fpr be bad? What else should I check for? Could the ECU be doing something goofy, and not providing enough fuel at the higher rpm range? Quote Link to comment Share on other sites More sharing options...
NewZed Posted June 23, 2014 Share Posted June 23, 2014 No gauge, it's all guessing. Quote Link to comment Share on other sites More sharing options...
Serban Posted June 23, 2014 Author Share Posted June 23, 2014 I realize it's guessing, but any reason it would just start going lean at wot? By the way, it is in the neighborhood of 15.5:1 - 16.3:1 on the wideband. Quote Link to comment Share on other sites More sharing options...
Serban Posted June 23, 2014 Author Share Posted June 23, 2014 (edited) I put a new gauge on and here's what I got at idle. Revving it I'll get around 30-33 or so but if I hold the throttle, it drops back down. Edited June 24, 2014 by Serban Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 24, 2014 Share Posted June 24, 2014 once the AFM flap is opened, or the throttle position closes the WOT contacts around 33% open, or you are over 3500 rpms, the things that affect fueling are few since it's on the preprogrammed map. It has X Pulsewidth plus small (I mean REALLY small) air temperature or coolant temperature compensations. The fueling should pull back after 4,000 somewhat as that gives best power past peak torque. A turbo would go to 13.8-14.7, I can see an N/A doing similar, but since they start 12-13 to begin with, and not 11-12 14.8-15.8 doesn't seem too lean. Other than the gauge telling you something that appears to be correct, were there physical manifestations such as surging or bucking at speed that indicated it was 'too' lean? 18:1 is NOT 'too lean' in some cases, especially under low/no load. Quote Link to comment Share on other sites More sharing options...
NewZed Posted June 24, 2014 Share Posted June 24, 2014 Your 25 psi at idle implies 22 inches of intake vacuum, which is very high for the 280Z, I believe. And you should have seen 36-37 psi when blipping the throttle. Disconnect the starter solenoid wire and turn the key to Start. The fuel pump will run but the engine won't turn over. Or disconnect the vacuum hose to the FPR while the engine is running. You'll get full pressure on the gauge, it should be 36-37 psi for a stock regulator. Why not use the FSM or the Electronic Fuel Injection Guide to know that the TPS is right? The early one was written for your car. Test at the ECU connector. http://www.xenons130.com/reference.html Those Ford injectors are one lb/hr higher rate than stock. You should be running rich. Are they low or high impedance? If they're high, did you bypass the stock resistors in the power circuit? Maybe the injectors aren't opening correctly. Just some possibilities. Quote Link to comment Share on other sites More sharing options...
Serban Posted June 24, 2014 Author Share Posted June 24, 2014 At full throttle when it starts to go lean, I feel a power loss. If I keep it at part throttle on the highway, even after 4k, it will maintain 13:1 ratio, as soon as I go wot, it jumps to 16 almost 17. I've browsed through the fuel injection guide, but I'll go through it again. The ford injectors are high impedance, I was told by the guy who built the rail for me that I could run them without any I'll effect. Quote Link to comment Share on other sites More sharing options...
Serban Posted June 24, 2014 Author Share Posted June 24, 2014 Vacuum at idle is a very solid -19, fuel pressure with th e hose off the fpr is about 38 psi Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 24, 2014 Share Posted June 24, 2014 At full throttle when it starts to go lean, I feel a power loss. If I keep it at part throttle on the highway, even after 4k, it will maintain 13:1 ratio, as soon as I go wot, it jumps to 16 almost 17. I've browsed through the fuel injection guide, but I'll go through it again. The ford injectors are high impedance, I was told by the guy who built the rail for me that I could run them without any I'll effect. You have a plugged fuel filter. Quote Link to comment Share on other sites More sharing options...
Serban Posted June 24, 2014 Author Share Posted June 24, 2014 You have a plugged fuel filter. I'll check it, its an Aeromotive filter, pretty sure its got a stainless element that I can clean out. Quote Link to comment Share on other sites More sharing options...
NewZed Posted June 24, 2014 Share Posted June 24, 2014 (edited) Where is this Aeromotive filter? Before the pump or after? The stock Nissan pump is huge so that it can pass enough fuel to support the engine while still filtering. You might have the wrong filter. The high impedance injectors won't hurt anything but if you left the resistors in place you're running less current through the system, including the ECU, than designed. Your pressure and intake vacuum numbers don't add up but 38 psi would be sufficient pressure to make things work right. 19 inches of vacuum is 9.3 psi. 38 - 9.3 = 28.7. Your picture of the gauge at idle shows 25. Probably just two bad gauges, combined, or the camera caught a bounce. Who knows. If the lean-out happens even when you work up to 4000 at part-throttle then the TPS probably isn't a factor. Edited June 24, 2014 by NewZed Quote Link to comment Share on other sites More sharing options...
Serban Posted June 24, 2014 Author Share Posted June 24, 2014 (edited) Filter is located near the factory location, I can't remember what micron size the element is, I'll take it apart and check. I used the same filter on a couple previous cars I've owned, and never had any issues with it. I'm not getting any bounce on the new gauge, it's liquid filled and very steady. Old one was a dry gauge and it only lasted about 4 months before it failed. Here's a few pictures I took this morning at idle, and with the vacuum hose off the regulator, and my intake manifold vacuum. Fuel pressure at idle this morning was slightly higher, looks to be about 28. Manifold vacuum was also very steady, it held at 19 until I blipped the throttle, then came back down to 19. ::Ninja edit:: The wideband gauge is a dual purpose gauge, wideband, and boost/vacuum. I changed the settings to show vacuum in the center. Another thing I left out, I'm using an Odyssey PC680 battery, and if you know that battery, it's small compared to a full size car battery. Could the small battery be causing my problem? I'll try a full size battery and see if anything changes. Edited June 24, 2014 by Serban Quote Link to comment Share on other sites More sharing options...
NewZed Posted June 24, 2014 Share Posted June 24, 2014 The simplest test for you would be to view fuel pressure when the problem happens. Get the vacuum number from your dash gauge and the fuel pressure number from another and you'll have numbers that tell you something. The standard practice is to T in a service gauge and run the hose out of the partially open hood to where you can see it while driving. Your idle numbers don't show anything wrong. But, more to the point - does the engine run differently above 4000 RPM? You never really said. Or are you doing all of this work because your AEM gauge shows a number? You might just have an exhaust leak. Quote Link to comment Share on other sites More sharing options...
Serban Posted June 24, 2014 Author Share Posted June 24, 2014 I feel a substantial loss in power. Previously when the gauge was indicating low to mid 13s AF the car felt like it had more power all the way to redline, now I don't even chance revving that high. It doesn't break up or stumble or anything of that sort, just low on power. Cap, rotor, wires, plugs have all been changed in the last 6 months, so I may be able to eliminate them as culprits. Quote Link to comment Share on other sites More sharing options...
Serban Posted June 25, 2014 Author Share Posted June 25, 2014 (edited) Tony D, you may be right about the fuel filter. There was an obscene amount of rust in there. At least it's the 10 micron element so it may have stopped some of that rust from reaching the injectors. I'll report back once I get a new filter element in there. Edited June 25, 2014 by Serban Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 25, 2014 Share Posted June 25, 2014 10 Micron is big... If it persists, before doing anything else I'd reverse-flow clean your injectors to flush the individual inlet screens of anything that went past the filter. The symptoms of what you described (that I quoted) were classic clogged/restricted filter problems. Runs fine but not at WOT at high speeds. Let up on the throttle a bit and the car comes back alive and will sometimes run all the way to redline---just won't do it WOT. That's been the same from carbs onwards. I think you will likely find you're back to your former power levels, and it explains the gradual loss. Pray your injectors inlet screens are clear! They can do the same thing. JeffP lost his forged bottom end when the Z31 ECU switched from 2 squirts to one at 5225 rpms. Up to that point, with the injectors only flowing half the required fuel for full power everything was fine. Go to 5230 rpms and it was like the engine was on a rev limiter "rm-rumm-rm-rummm-rum-rum..." He'd unknowingly blown a cellulose based fuel filter and the loose shards of the fibers got into his injectors. When they were called to deliver that fuel flow in ONE injection pulse per timing event, they flow limitation was presented. Below that point you could get 10:1 AFR's easily. 5 rpms, and they went from 11.3 to 16/19/22.0:1 before Clark could lift. Fine to a point of high load WOT then after that no matter what, couldn't get more fuel. And it wasn't that way before! Sound familiar? Quote Link to comment Share on other sites More sharing options...
Serban Posted June 25, 2014 Author Share Posted June 25, 2014 Dirty/clogged fuel filter was the culprit! New filter element is installed, car is back to its slightly faster self. AF maintains 11.4:1 all the way to redline. I'll have to adjust the AFM again and lean it out slightly. Thanks again Tony for the suggestion. The filter wasn't in that long, but got dirty real quick, would have never thought that was the problem. I'll have to check it every few months now. Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 26, 2014 Share Posted June 26, 2014 Yes, it will do that continually... You may want to just take the time and drop the tank--clean it out with Muriatic Acid, plug any leaks that pop up after the cleaning, possibly coat the interior and be done with it! Quote Link to comment Share on other sites More sharing options...
Serban Posted June 26, 2014 Author Share Posted June 26, 2014 I may have to check it again. I dropped the tank when I bought the car last year. I drained out about 4 gallons of fuel, but it came out clean. Could the fuel line be producing so much rust? Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 27, 2014 Share Posted June 27, 2014 Not that size. I'd pickle the two fuel lines with muriatic acid, and flush liberally with water afterwards. But I really doubt its in there.On a ZX, you got a swirl pot and a strainer in the tank...I'd open it and pull your pickup out to take a look. Something is inside there. I've seen bad gas tanks in podunk desert towns pump enough clay silt to sidline every car in a convoy by the end of the driving day... So the source could be almost anywhere. But likely it's the tank. I'd have a look at your strainer and swirl pot for sure...that's fairly easy to access. Quote Link to comment Share on other sites More sharing options...
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