ll77 Posted March 1, 2011 Share Posted March 1, 2011 hey guys. so ive been having smog problems recently. i got a tip from a smog station that my afm might be the problem b/c its running lean at idle and very high on CO at speeds above idle. so i took the afm and ran some tests w/ an ohmmeter and it failed both potentiometer tests. these 2 were from the fsm when i ran this test (as seen on http://www.atlanticz...fm/index.html): Measure the resistance across pins 7 and 8 while moving the flap. It should change. (though it may be jumpy) Repeat this but between pins 6 and 7 while moving the flap. the resistance only dropped a little bit when i began pushin the flap back, but stopped dropping about a quarter of the way in. resistance went from continuty to approx. 0.4 ohms. it checked out on the rest of the tests. my mechanic friend tells me he doesnt trust ohmmeter tests b/c he's seen parts that fail resistance tests work fine, but I was thinking it would make sense that the potentiometer was bad b/c that could make the flap open, but not all the way. so at low engine speeds, it could get too much air, making it lean, and at higher speeds, too little, making it rich. is that good logic? also, it seems my car will not rev past 3500-4000 rpm, and its got a rough idle. perhaps related? also, any ideas of what else could be causing my car to run rich would be helpful. the technician mentioned a couple things, but i didnt write them down ( i know, i should have). i think he said my cold start valve shouldnt be the problem, i didnt understand why. also, my fuel pressure is registering about 40-41 psi at idle, and jumps to about 43 when i rev it, and i know that the fuel pressure should be at about 36 psi. so im thinking about the fuel pressure regulator too. could also be that the gauge is faulty or inaccurate, it is installed on the fuel feed line, but i have heard that this doesnt indicate the "true" fuel pressure as that should be measured from the fuel rail? also, i am in the market for an afm, and i might make a trip to see a guy with a couple of them tomorrow. he has 2 280zx afms, but only 1 280z afm, all used, not tested yet and have been tweaked for air/fuel ratio adjustment. so i was wondering do 280zx afms work in 280z's too? i know they both have l28's so they should right? but if not, i think i'll go for a remanufactured one instead off zccjdm.com. so what do you guys think??? thank you soo much!! Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 1, 2011 Share Posted March 1, 2011 It says rough on the zccjdm page that the 280Z AFM won't work on a 280ZX. The inverse should be true. Did you measure the resistance across pins 6 and 8, and 8 and 9? What were those numbers? Your fuel pressure is high, as you noted. If the gauge is between the filter and the rail, there would not be much pressure drop to the injectors. If it's before the filter you could get a high reading. High fuel pressure will richen things up. The main reason to "tweak" an AFM is because an engine wasn't running right. Sounds like buying someone else's problems. By the way, nice formatting on your message, but a few capital letters might help you get more responses. Effort returned proportional to effort in. Just my opinion. I think the mods have given up on grammar policing, they're overwhelmed. No caps really only works for e. e. cummings... Quote Link to comment Share on other sites More sharing options...
ll77 Posted March 1, 2011 Author Share Posted March 1, 2011 Oh ok sorry, I'm just so used to it. But thanks for the tip, I'll be sure capitalize in all my posts from now on. But yes, I did also perform those tests. I can't remember off the top of my head what the results were, but they were unsatisfactory. They did not read 180/ 100 ohms like they should have. The gauge is located after the fuel filter, before the fuel rail, so the reading should be accurate if the gauge is ok? Thanks for the help! Quote Link to comment Share on other sites More sharing options...
ll77 Posted March 1, 2011 Author Share Posted March 1, 2011 So today I put on the afm w/ the connector off to see if it was actually working or not. It started up, but would die immediately. I plugged in the connector, and it started right up. So I guess the afm is working. However, I'm thinking that it is not a 280z afm, because I noticed that the holes on the bottom of the afm did not match up with the holes in the mounting bracket. I also think that 75-76 models had a blowback valve in the flap of the afm, and mine does not. So, I'm thinking that the previous owner tried to use a 280zx afm on my car. Do you guys think this adds up? would using a zx afm in a z explain the problems I'm having right now? Pics coming soon! Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 2, 2011 Share Posted March 2, 2011 REalisticallly any AFM can be used in any AFC Controlled car if you alternate the pins to match the inputs reequired by the ECU. Idle enrichment is done through the TPS, not the AFM. If the contacts on the TPS don't close, you run lean at idle. If someone dorked with the AFM to richen it up at idle (since it should be near or completely closed and only running air through the bypass) then you would run lean at idle, and rich most everyplace else. What does it do over 3500RPM. The biggest problem I see with people doing ohm checks is they use a digital ohm meter, and disregard the settings in the FSM. If it says "RX1000" then that should be manually selected. This will give you no 'right of decimal' numbers in your readout, and your 0.4 now becomes '0'... and the FSM usually says 'any reading but infinity or 0' meaning you have intermittent shorts in the resistive trace. This may or may not cause a problem, but if the wiper lands on one of those spots it definately will screw up your ECU outputs. I manually select (usually) Rx1 or Rx1000 when doing tests with my Fluke. I was once held up 8 hours on a job because an electrical engineer had us searching for a phantom supply voltage to a mercoid switch: "Nope, there's still voltage there!" Finally after 8 hours I looked at what this degreed engineer was doing, and it was connecting his Fluke to the connections and was getting '127' just like our supply voltage to the switch. Problem was it was an AUTORANGED 127mV, instead of a 127VAC! Sure, from an 'electrical engineering standpoint' there was 'voltage present' --- from a practical OSHA Lockout Tagout Perspective, that was dead as a chicken in a pot... Just because you get a reading doesn't mean it's good or bad, you have to use the correct scale. "Autorange" was an invention so people using the equipment needed less training. Not necessarily a good thing IMO. I'm old school Simpson A/N PSM-37 Meter Trained: Select the appropriate range for the circuit you're testing, and that gives you reliable results. That means, of course, you need to know the circuit you're testing and what you should get....but it's a small price to pay to 'troubleshoot through system knowledge'! Good Luck! Quote Link to comment Share on other sites More sharing options...
ll77 Posted March 2, 2011 Author Share Posted March 2, 2011 Thanks Tony. But what do you mean by what does it do over 3500? Scratch the part about it not revving past 4k, it's actually fine, just takes longer than I expected it to. A bit sluggish on the throttle response. And I am using a analog ohmmeter, and there is only one setting on it, "x1k." I am not very good w/ electrical know how, I can only do whatever manuals tell me to do. Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 2, 2011 Share Posted March 2, 2011 I think that Tony D might be trying to point you to the TPS. The TPS tells the ECU when the throttle is at idle position. At idle, the ECU adds enough fuel to allow the engine to idle. At about 3/4 throttle it adds a lot of fuel so the engine can go. I haven't tried but I've read that the engine should run, at least idle, without the AFM connected. Yours doesn't so the place to look is the TPS. My 76's AFM number is A31-060-001. Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 2, 2011 Share Posted March 2, 2011 How did you get a 0.4 ohms reading on an RX1 scale? Is the meter properly zeroed? I am pointing to the TPS for your idle problem. The 3500 reference is due to the fact that by 3K-3500 rpms the AFM is all the way open and the ECU is running on a "WOT" map that is based on rpms and fixed program. For the record the WOT switch closes closer to 30% throttle than 75% as well. NewZed kinda nailed it: if it doesn't run with it disconnected, then likely that's not the issue. Try the same with the TPS, it's very common they get misadjusted, drift, or crud up and don't work properly. Quote Link to comment Share on other sites More sharing options...
ll77 Posted March 5, 2011 Author Share Posted March 5, 2011 Oops forgot to check the thread. Sorry Tony, I don't know what and RX1 scale is. Correct me if I'm wrong, but is the TPS inside the black box on the side of the throttle body? Yeah, so I definitely have the wrong afm, the vendor told me so too. Today, I made the adjustment for less fuel (since it's running rich) and maybe I'm mistaken, but the throttle seems snappier. I also advanced the igntion timing to 12 BTDC, b/c I heard that advancing would give the mixture more time to burn. The car dies after a bit when I disconnect the afm. So I guess the afm is OK. I will begin researching the TPS. Thank you everyone! Quote Link to comment Share on other sites More sharing options...
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