Z dies after warmed up 77 Z Drives For About 10 To 15 Minutes,then Dies.

[240260280z]

Is the fuel pump stopping? Listen by the passenger wheel well to see if it is the problem. This is a weird one.

[Zed Head]

it only runs for about 10 seconds. It will start up again after another 10 to 15 seconds.

Sounds like a corroded contact point, or bad ECU component.  Too bad you're not a hoarder yet, you'd have a spare ECU to try out.

 

Another thought  on diagnostics - light bulbs in parallel on suspect circuits.  If the light goes off, that's a sign.

 

On the positive side - you only have to wait 10 to 15 seconds before you can try something new.  20-25 seconds round trip.  You can check everything in one hour.

[Crazy477280Z]

  I went through EFI tests today and got a couple of readings that were off. Water temp sensor resistance at 50 degrees was 2134- Fuel inj. relay should have continuity... I have a tone on my multimeter that sounds when continuity has been made. All I could get when test probe is on number 20 on ECU connecter,and neg. probe is to vehicle ground, was barely a chirp that cut off right away...on cold start system test, I got battery voltage instantly. No battery voltage at pin 34 for\at air regulator. Air flow meter resistance #2 should read continuity[small resistance]. I have it reading 185.2 ohms. I think that might be a little much for small resistance. Also air temp sensor resistance was 2476 at 50 d Anyway, even though I had just replaced EFI relay, it looks like I get the pleasure of doing it again as fuel pump now appears to not be working.I cant seem to find any kind of voltage at fuel pump and aux. air regulator are on the same circuit. Seeing as how I just replaced EFI relay,and water temp. sensor,and just cleaned my air reg,should I be thinking that something is causing these things to fail prematurly? Ive got a Bosch 332 514 120 combo relay coming in morning.95 bucks!!!!! Every thing electrical for Z cars is priced like they are gold.but I guess they areni or they would conduct better. I will fix and replace what I can, andlet you know where Ime at after Ime finished. Thanks to Rossi and Blue for your comments on possible fuel system problems.

[240260280z]

EFI on early 77's has a vane switch on the AFM that sometimes does not work properly. It it one of those things that you can pop the cover off and watch it work (or not) when a friend cranks the car.

[siteunseen]

I bought my 1st Z, '76 280 in 1987 for $1,000 because it would only idle.  Trailered it to a mechanic that popped that cover off and tapped that sweeper vane loose from being stuck because it sat for awhile.  Ran like new. 

[EuroDat]

Did you end up fitting a pressure gauge in the fuel system? That would show any problems with the fuel delivery. If it stops, just pop the hood and check the pressure or run the gauge out and tape it to the windscreen during during your test runs.

Any gauge capable of reading up to 50psi will do the job with a tee fitting to tap into the flex line between the filter and the fuel rail. Fuel pressure is normally betwwen 25 and 36psi depending on manifold vacuum.

Chas

[siteunseen]

I did what Chas is saying but zip tied it to the driver's side wiper blade.  If you get an 1/8 NPT threaded gauge it'll screw down into 5/16" fuel line then put a clamp over that.  Just for testing, the cheaper low pressure fuel line worked for me.  About 4 or 5 feet with a gauge like this, http://www.lowes.com/pd_199191-1003-PG550_0__?storeNumber=0252&selectedLocalStoreBeanArray=%5Bcom.lowes.commerce.storelocator.beans.LocatorStoreBean%4031c031c0%5D&productId=3151541

[Zed Head]

. Air flow meter resistance #2 should read continuity[small resistance]. I have it reading 185.2 ohms. I think that might be a little much for small resistance. Also air temp sensor resistance was 2476 at 50 d

Be careful on interpreting "continuity".  For some reason, Nissan broke the testing up in to continuity and real numbers.  That 180 ohm number looks like the right number for one of the circuits on the AFM.  180 is small compared to thousands.  The real numbers are shown later in the FSM chapter, where removing and testing is described.

 

The air sensor reading is close.  Wouldn't cause a no start condition.  

 

It's great that you're digging in to the details of all of the tests but you're skipping over the basics, like "is there fuel" and "is there spark".  With all of your test numbers, and the answer to those two questions, you can then step back and look at the complete picture.  I think you might be buried in trees right now.

[Crazy477280Z]

I have found that ime getting no fuel because fuel pump is not working due to no power at pump.I will check air flow meter also just to make sure everything is working correctly.Ime going out to work on it in a bit.Will stay updated till solved. Thanks for tips!

[siteunseen]

There's some different safety cutoffs to the pump.  I know one is in the oil pressure sending unit and MAYBE the '78s are in the AFM???

 

You can get some small alligator clips and speaker wire and straight wire the pump to the battery, bypasses all the safety switches.

[Zed Head]

site makes a good point.  I think Nissan changed from the AFM to the oil pump/alternator switches in mid or late 77.  Which EFI relay do you have, the big silver 1x1x2 combined EFI/pump one or the smaller one?

 

 

Note - in past posts I think I've said that I had a 78 with the older EFI/pump relay.  But I was confusing ti with AFM's.  I had a 78 with an AFM that had the switches, but not used.  But the 78 pump relay was separate from the EFI relay.

[Crazy477280Z]

I have narrowed problem down but I dont know whats causing it. Apparantly EFI combo switch[EFI and ignition switch] loses power. I unhooked solenoid energizing wire,and could hear fuel pump running with old EFI relay. I hooked solenoid back up,and it started right up. It ran for about 5 minutes,then died. I unhooked solenoid again and fuel pump was not working again. I instantly changed EFI combo relay,and still no fuel pump noise and no power back at fuel pump. On the safety cutoff at switch...Are you talking about oil pressure sending unit? And I will try hooking up fuel pump direct and see what happens.OOh, and my oil pressure sending unit is working fine while running.