I'm About Done With The %**&ing Efi

[rossiz]

i feel your pain - spent a ton of time tracing through the system and replacing parts, many trips home by tow truck, but when it's working correctly the system is actually pretty darn dependable and runs well. patience and you will get there...

[siteunseen]

Did it run any better before the ZX distributor swap?

[mjr45]

OK folks I will try to answer the questions in order:

       Blue:

        the injectors were new about 18 mos. ago, don't remember the type, but know they wern't for a turbo or high flowing.

        the whole wiring harness has new connectors and the ones that couln't be cleaned were replaced, male/female etc

        the FPR is new and fuel pressures: idle no vacuum 36-37 psi with vacuum 30-32 psi

        the TPS points lighhtly cleaned and adjusted per FSM, not sticking etc.

        the AFM is stock and the number on it checks out as correct, has new harness connector

        don't know about the Air Temp Sensor

        CTS is new and checked per the Bible at the ECU connector and the CTS wiring, OK'd

        the ground on the EFI harness is ? since I can't find a ground wire after peeling open the entire harness back to the 

        firewall, I know its supposed to be there and ground out on the harness holder.

        the ECU looks good and the connections are all clean

        ignition has a good nice blue spark with a new Crane coil, dizzy cleaned up, has no vacuum advance, the vacuum line

        has been deleted.

        new battery

        new NGK plugs and wires

 

        Haz:

Right on Brother! Carbs in my humble opinion are so much easier, but I really want to keep this at least semi-original.

 

        Zed:

Resistance readings on #1 test pg 49 of the Bible were 189 ohms, #2 test was 218 ohms and #3 test 112.4 ohms, thus the 12% wrong number. Also see answer above about the CTS.

 

        Captain:

I changed to another ECU I have and no difference. As for the injectors, they were sold as for the 75-78 280Z, but I can't remember the name or the number, so they could be wrong. I also wish you were closer

 

        rossiz:

I agree, I had a 76 and it ran like a charm topped it out one nite a long long long time ago at about 170mph on a "dark deserted highway."

 

       site:

It ran well when I bought the car, but that engine took a crap on me so I have a 79 block with a 75 N 42  head(rebuilt by a guy who does nothing but head work) so its hard to make a comparision.

 

As I have said, the car runs well now, starts right up hot or cold except if it's started cold and left to idle, after about 5 minutes, the idle drops down to about 500 instead of the 900 I have it set at and if driven to warm up the idle stays at 900 so I never let it sit and warm up.

 

I truly truly do appreciate all you guys and women (won't say gals, not poltically correct) that have given me so much help over the last couple of years. I'd been lost and much deeper in debt without you. Thanks.

 

Mike

Edited March 19, 2015 by mjr45

[hr369]

I was recently  working on my 280 and had to remove the efi harness off the engine. When I put it back I didn't tighten the ground good enough and it ran 

rough at higher rpm's. Fortunately for me I knew everything was good before I worked on it. Just checking connections narrowed it down real fast. What surprised

me was the bolt to the ground wasn't that loose. I wiggled it and tightened it more.  In the 17 years of having my 280, the hardest thing to find and fix was the bad fpr.

It had a small leak in the diaphram and when i shook it i could hear gas sloshing around inside.

Edited March 19, 2015 by hr369

[Zed Head]

It's not common but have you confirmed that the CSV is closed and not leaking while the engine is running?  It's fairly easy to remove, pull it out and run the fuel pump and see what it does.  Or block the hole and start the engine.

 

I had a similar problem diagnosing my bad FPR and I've seen others with the same.  The pressure will read correct, but the diaphragm leak allows fuel to pass through and in to the vacuum hose, on to the intake manifold.  In my case, the FPR was only malfunctioning when it got hot.  I never did figure out what, exactly, was causing it.  But when mpg dropped to 15, in one day, I swapped FPR's and fixed it.

 

Do you have a performance cam in that head?  Head work, plus cam, plus no vacuum advance = low mpg, poor low RPM performance.

[mjr45]

hr369, I've looked and looked for that ground wire and the FPR is new, look at my reply to Zed.

 

Zed,there is no cam, just stock. The FPR is new but that's not to say it can't be bad, my fuel pressure drops to zero in about 8 minutes after shut down, so its loosing pressure somewhere, I suspect there is a microscopic hole in the fuel rail under the #1 injector, there is some brown goo dried on the heat shield that I've cleaned off a buncg of times but keeps coming back. With all that said, that shouldn't cause it to run rich I don't think. The CSV is new, but could be a problem, maybe its leaking, but taking it out of the circuit electrically doesn't make a difference, Thanks

Mike

[FastWoman]

Considering all that you have done, and especially considering that your CTS measures correctly at the ECU connector, and your TPS is adjusted correctly, I think your problem would likely be a misadjusted or faulty AFM.

 

You identified three resistance tests; however, I'm not 100% certain what you tested.  I think I'm understanding this:

 

Pins            Should be         You measured

 

6-8                180                        189

7-8                low reading            218

8-9                100                        112

 

If I understand these correctly...

 

I wouldn't worry too much about the first and third readings.  I think they're close enough and set up the voltage ladder about correctly.  If you want to get persnickety, you could solder 1680 Ohms of resistance in parallel with R0 between pins 8 and 0, to give you an effective R0 of 105 Ohms, which would put your voltages in the correct proportion.  However, I don't think this is your problem.

 

The more likely problem, if I'm understanding you correctly, is your 218 Ohm reading between pins 7 and 8.  This is the resistance between the "near" end of the potentiometer trace (at zero airflow) and the wiper.  This value should be less than 6-8 (your reading, 189 Ohms) and should actually be maybe several Ohms.  This indicates to me that your wiper and/or trace are dirty/oxidized and/or that your wiper isn't making good contact with the trace.  I would try cleaning the trace and the wiper and then repeating your measurements.

 

Once you've cleaned the wiper and the trace and confirmed a low resistance between 7 and 8, you can power the meter up by hooking +12 to terminal 9 and ground to terminal 6.  Hook a voltmeter between 7 (neg) and 8 (pos).  Then move the vane back and forth slowly.  You should see the voltage reading vary smoothly as you do this, with no jumps or gaps.  This is the acid test.  If you've got good voltages, your AFM should be fine.  (By "fine," I don't mean that your clock spring is necessarily calibrated to spec.  That's obviously another issue.)

 

Another issue with the '75 AFM is that it has no backfire valve in the flap (vane).  A '76 AFM has this feature and might be substitute for the '75, depending on fuel pump shutoff circuitry.  (I can't remember for certain whether these are compatible.)  Without this valve, a bad backfire can cause the vane to bend, so that air flow turns the potentiometer a bit more than it ordinarily would.  This can cause a rich-running condition.  If your vane is bent, you can actually bend it back with a bit of care.  I did this on my '75, long, long ago, as a kid, by inserting the end of a wooden block into the throat of the AFM to serve as an anvil, and then tapping it out carefully with a hammer.  (I think I had to insert another wooden block through the other end.)  That solved a rich-running issue I had.

 

BTW, "guys and gals" is perfectly acceptable language, at least to me. 

 

And PS:  Be very careful of fuel leaks!  You can burn up your car and/or burn down your house that way (if your car catches fire in the garage)!

Edited March 20, 2015 by FastWoman

[rcb280z]

Not 100% sure but I believe you have an "altitude switch" correct? Have you checked it?

 

My 77 FSM Says altitudes over 3,675 energizes the switch leaning the amount of fuel by 6%. Not a lot but if you have this switch and its malfunctioning along with no vacuum advance your fuel mileage will be poor IMHO.

 

Just something else to eliminate.  

 

 

NEVER MIND, just found my 75 manual and it is NOT listed for your model. Probably hence the reason it wasn't talked about yet. Sorry.

Edited March 20, 2015 by rcb280z

[240260280z]

Maybe tighten the AFM spring even more.

[Zed Head]

Considering all that you have done, and especially considering that your CTS measures correctly at the ECU connector, and your TPS is adjusted correctly, I think your problem would likely be a misadjusted or faulty AFM.

 

You identified three resistance tests; however, I'm not 100% certain what you tested.  I think I'm understanding this:

 

Pins            Should be         You measured

 

6-8                180                        189

7-8                low reading            218

8-9                100                        112

 

If I understand these correctly...

 

I wouldn't worry too much about the first and third readings.  I think they're close enough and set up the voltage ladder about correctly.  If you want to get persnickety, you could solder 1680 Ohms of resistance in parallel with R0 between pins 8 and 0, to give you an effective R0 of 105 Ohms, which would put your voltages in the correct proportion.  However, I don't think this is your problem.

 

The more likely problem, if I'm understanding you correctly, is your 218 Ohm reading between pins 7 and 8.  This is the resistance between the "near" end of the potentiometer trace (at zero airflow) and the wiper.  This value should be less than 6-8 (your reading, 189 Ohms) and should actually be maybe several Ohms.  This indicates to me that your wiper and/or trace are dirty/oxidized and/or that your wiper isn't making good contact with the trace.  I would try cleaning the trace and the wiper and then repeating your measurements.

 

 

That's a good catch.  I only see the 180 and the 100 when I look at people's AFM numbers.  I have several AFM's I can measure just to see what my 7-8 numbers are.  Might hook a battery and meter up too.

 

The level of the problem, the rich mixture and super-low mileage, doesn't make sense, from the other information given.

 

 

Edit - I don't find any indication of "should be low reading" on 7-8 in the FSM.  Some would consider ~200 ohms to be low.  7-8 is only called out as continuity, but not detailed later in the FSM.  Anyway, I'll see what mine show, they all worked.

Edited March 20, 2015 by Zed Head

[Zed Head]

I measured my two spare AFM's, which have both been on my engine and both run a hair lean (fixable with the potentiometer) and they both measure 175 ohms on 7-8.  One was 180 and 100 on the other two circuits,the other was 202 and 112.  Both divide out to 1.8, if that means anything.  I don't have a good picture in my head of how the ECU uses the split voltage.

 

Didn't connect the battery since there's no numbers, just a continuously decreasing voltage spec.

 

Nothing obvious showing...

[240260280z]