Just bought a 280Z, engine will not run properly. Help!

[HSL]

Do the fuel return line check that Zed Head mentioned. If the FPR checks out OK then I would be looking at the tank. It could be a lot of dirt and rust floating around in the tank and clinging to the fuel pick-up stainer and eventually blocking it enough to reduce the pressure. Your tank might be the cause of it all.

Chas

The inside of the tank looks good, not any rust as far as I could see. I checked if it was something blocking the outlet from the tank by using compressed air and blocking off all lines except the outlet but a good amount of air came through. I have a fuel cell lying around so I might test that one just so I can possibly rule out the fuel tank.

[alternativez]

The 280z has a ecu? I'm not so familiar, but I'm assuming it does. The ecu is the heart. Do they ever fail? Wild chance, I suppose, but I spent a month once with similar problem, different car. Checked and rechecked everything related, components, circuits, absolutely drove me nuts. Finally, i hit on the thing all manuals say to leave alone, the ecu. I took it apart, and of course it looked fine. Then I discovered my other car had the same ecu. Swapped them; car ran perfectly. I figured luck was on my side, so I judiciously reflowed some solder on the "mother board" and it was fine. Not prescribing this as your route, just maybe to say, don't overlook old electronics and the central component. Good luck!

[siteunseen]

Just so happens to be a thread going now on ECU drifting out of specs and a way to tweak it with potentiometer, http://www.classiczcars.com/forums/fuel-injection-s30/50946-sorry-redundent-help.html. It gets good around post #31.

I have one on mine, and for $5 I now have a strong running car. No stumble at all, steady pull.

Edited November 21, 2013 by siteunseen

[EuroDat]

Sometimes good to go back to your first post and read it again. Your description in the first section makes me think its too lean, but your plugs are sooting up.

Thinking out of the box. Could it be a blocked cat. or other part of the exhaust?

I had that with an old Escort before I restored it. The muffler colapsed internally and caused similar problems.

It doesn't explain the strange fuel pressure behavior, but you might have more than one problem haunting you.

Chas

[Willoughby Z]

Lean mixtures can cause sooty plugs, as can a cold range plug. Also a weak ignition.

[HSL]

I've done some more troubleshooting and now is the problem described in post #1 also occurring when the engine is cold. I have not replaced anything only change is the air temperature, winter is coming to Norway Also a lot of backfiring both through exhaust and afm, especially right after start up. Fuel pressure is good.

Can someone tell me if the measurements below are ok (from the EFI bible)? Electrical isn't my strongest side

Test #1 - (3b) Air flow meter - resistance #2. Should read - continuity (small resistance.) My test result gave 293 ohms, is that acceptable as small resistance?

Test #1 - (5) Air flow meter fuel pump contacts. This test fails. My fuel pump is running all the time, I guess this is the reason for that? But will this error cause other problems?

Test #1 - (7) Fuel pump relay circuit. Should read - continuity. My measurement gave 60 ohms, acceptable?

Test #1 - (8) Air regulator and fuel pump circuit. Should read - continuity. My measurement, 60 ohms, acceptable?

[Willoughby Z]

Because you stated that electrical concepts are not your strong suit, start with visual /manual checks related to the fuel pump contacts inside the AFM cover.

"When the engine is not running the flap in the AFM is closed and the fuel pump control switch in the AFM is OPEN. When the key is turned from "OFF" to "RUN" there is no continuity through the fuel pump switch in the AFM and the fuel pump should not run. When the key is turned to "START" the engine turns over AND the fuel pump relay closes which starts the fuel pump. As air is sucked past the flap in the AFM it opens and the FUEL PUMP contacts in the AFM close. When the engine starts the air flow through the AFM keeps the fuel pump running because the switch is closed. If the engine stops / stalls the flap in the AFM closes and the fuel pump control switch in the AFM opens thereby shutting off the fuel pump." - Atlantic Z Tech Tips

Read, understand and check/adjust TPS:

"The TPS is just a switch connected to the TB Valve. It senses when you got the gas pedal tramped (Wide Open Throttle WOT) or when your foot is off the pedal (Idle). The ECU adds more fuel when the TBS says "Go like hell". This extra rich mixture give you more power. The ECU also adds more fuel when your foot is off the gas to make a smoother idle. The TPS also does a fuel cut mode to save gas... if you are going over 3200rpm and take your foot off the gas, the TPS sends an Idle signal and the ECU says "Damn I 'm gonna turn off the fuel if he just lifted his foot off the gas at this speed!... must be the fuzz".... but when the RPM's drop to 2800rpm, it turns the fuel back on.... "must of passed them by now". Note that if the TPS switch gets shorted with water, it The ECU will always thing your foot is off the pedal and go into fuel cut mode. This results in the RPM's brick-walling at ~3000rpm." -Atlantic Z Tech tips

[Zed Head]

Also a lot of backfiring both through exhaust and afm, especially right after start up. Fuel pressure is good.

Can someone tell me if the measurements below are ok (from the EFI bible)? Electrical isn't my strongest side

Test #1 - (5) Air flow meter fuel pump contacts. This test fails. My fuel pump is running all the time, I guess this is the reason for that? But will this error cause other problems?

Test #1 - (7) Fuel pump relay circuit. Should read - continuity. My measurement gave 60 ohms, acceptable?

Test #1 - (8) Air regulator and fuel pump circuit. Should read - continuity. My measurement, 60 ohms, acceptable?

The popping is a typical sign of lean mixture and the fact that it's worse as it gets cold fits.

The fuel pump contacts are only for the relay and will not cause problems since yours runs all the time.

60 ohms is about right for a relay, but in your case the relay is not being used so it doesn't really matter.

60 ohms is also about right for the AAR citcuit. That is the resistance of the heater wire inthe AAR. looks good.

What you need to measure is Pin 8 to Pin 6 (180 ohms) and Pin 9 to Pin 8 (100 ohms). Measure at the ECU connector if you can. IF you're using the 1980 EFI Handbook, they would be tests #1-3A 1975-78, and test #1 3C 1975-78 Those are the circuits that control the fuel mixture. I have a theory that as long as the ratio of those two is 1.8 the AFM will work correctly, but if you're way off, typically the engine will run lean, causing popping and backfiring.

[HSL]

The popping is a typical sign of lean mixture and the fact that it's worse as it gets cold fits.

The fuel pump contacts are only for the relay and will not cause problems since yours runs all the time.

60 ohms is about right for a relay, but in your case the relay is not being used so it doesn't really matter.

60 ohms is also about right for the AAR citcuit. That is the resistance of the heater wire inthe AAR. looks good.

What you need to measure is Pin 8 to Pin 6 (180 ohms) and Pin 9 to Pin 8 (100 ohms). Measure at the ECU connector if you can. IF you're using the 1980 EFI Handbook, they would be tests #1-3A 1975-78, and test #1 3C 1975-78 Those are the circuits that control the fuel mixture. I have a theory that as long as the ratio of those two is 1.8 the AFM will work correctly, but if you're way off, typically the engine will run lean, causing popping and backfiring.

I've done all the tests, and those listed above are the ones that did not meet the requirements. The rest of the measurements on the AFM are ok, except for the test where I check the flap.

And if your theory is correct the AFM should work correctly, I have measured Pin 8 to 6 at 182 oms and Pin 9 to 8 at 101 ohm so should be ok.

[Zed Head]

Checked the fuel pressure gauge and pressure had dropped to about 25 psi. As I kept letting the engine run fuel pressure decreased even more ending up at about 18-20 psi.

When you came back with AFM testing I assumed that you had fixed the fuel pressure drop problem. I'm guessing now that you did not. The EFI must have proper fuel pressure to work correctly. There's no way around it. 26 psi is probably the lowest pressure number you should ever see on these engines. Don't get distracted by the new pump or the recently cleaned tank. Something is still wrong with your fuel system.

[HSL]

When you came back with AFM testing I assumed that you had fixed the fuel pressure drop problem. I'm guessing now that you did not. The EFI must have proper fuel pressure to work correctly. There's no way around it. 26 psi is probably the lowest pressure number you should ever see on these engines. Don't get distracted by the new pump or the recently cleaned tank. Something is still wrong with your fuel system.

Strange thing is that I had good fuel pressure. When I measured the fuel pressure and got appr 20 psi the engine was warm and it was ok when cold. But now the engine was having trouble both starting and running when cold but had 35-40 psi fuel pressure.

I have replaced some of the vacuum hoses but will go through the entire system. Is failure of the intake gasket a common problem on the l28?

[Zed Head]

So is the popping and backfiring still there or does it run poorly in a different way? What's the current state of engine operation? You might have problems masking problems, or a problem that comes and goes which is what your first post suggested.

If the engine runs well sometimes then you should probably hold off on big things like manifold gaskets. It's unlikely that they would vary between bad and good.