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'83 280ZX Turbo runs like crap when cold, bucks, pops with CHTS connected.


HRH

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Ok, so on to the new turbo car.  1983 280zx Turbo.  Start it up in the cold, runs like dog shit.  Can barely hit the throttle, it'll just die.  If you slowly advance the throttle it will sort of respond but be all pissed off, starts backfiring and spitting/popping but through the intake, not out the tailpipe.  Just horrid.  However, if I disconnect the cylinder heat temperature sensor, it puts the car into open loop and she revs up just fine, no issues.  Other than she idles at about 1800 rpm at that point.

 

Things I've done:

 

1.  Replaced vacuum hoses, sprayed with carb/brake cleaner all over trying to find a change, nothing.

2.  Replaced CHTS.  This one is on the back of the head like the Maxima, doesn't go into a water jacket.  Has a little tapered fitting.

3.  Replaced O2 sensor.  Found car will not start with O2 sensor disconnected, interestingly.

4.  Unplugged fuel pressure regulator to increase fuel pressure, no dice.

5.  Checked my coolant filter. ;)

6.  Read up on various forums that these sorts of issues are common on these cars.  Found threads saying CHTS fixed it, cleaning connectors fixed it, and burnt spots on ECU resoldered, then fixed it.

7.  Scratched my head.

 

So I'm going to rule out plugs/wires/fuel pressure issues as when it's in open loop rich mode, it runs just fine.  That leads me to think it's electrical.  This system is very unique in the 280 turbo.  The distributor is a crank angle sensor, not a matchbox like the regular L28.  There is no idle adjustment other than the throttle plate.  Idle is changed by various vacuum cans with inputs from the ECU on when and where to bleed vacuum to control idle.  It does have the thermistor type bi-metallic spring unit found on the L24 and L28, but no adjusting screw in the body of the AFM or on the side of the intake like the L24/L28.

 

I'm going to test the original CHTS here in a second to see if it matches the ohm requirements it's supposed to.  If it does, seeing as the new one is in there, that will tell me the sensor itself is not the issue.

 

So here's the other thing:  When the car has finally gotten warm, she runs pretty well with the CHTS connected.  Still runs better without, but no bucking and snorting, it revs up mostly like it's supposed to though I feel a little bit of hesitation that shouldn't be there.  But point is, it runs ok, enough that the issue seems to be gone.

 

Any thoughts?  If I can't figure this out, I'm just yanking the motor and either carbing it like my original plan or running a megasquirt and building my own harness.  Carbed turbo is certainly cheaper, but then again, I've been wanting to do MS for quite a while, just been intimidating.  I know this motor is fine, just management is old and sucky.

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Exactly, but removing the lead to the CHTS put the system into open loop.  Which is interesting since in regular open loop it has the issue.  I'm trying to think of any significance of that.  A buddy of mine suggested the fuel pressure regulator since it was problematic and he got a lot of good cars that way.  Tomorrow I will put a pressure gauge in line and test that theory.

 

As for the CHTS, I just ohmed it out at a couple different temps, it's fine, nothing wrong with it.  So it seems just the removal of it is what's making the system better.  Which makes me think it could well be lean popping from not enough fuel due to the regulator being wonky, and then richening up the mixture by removing the CHTS lead solves the issue.  Hmmmm.  Still doesn't explain why it wouldn't run well when bone cold then, but perhaps gremlins?

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Interesting!  My vote is megasquirt! haha  

 

I always for some reason like to kink the return line just enough to know the fuel pressure has gone up a bit and see how it acts.  Doesn't that setup have the big trap door air sensor thing?  Those are magic and scary to me.  Maybe you should swap the 300zx turbo ECU and harness on it!  

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Yes, well if I can't make this old system work I don't want to try and cobble another old system on it.  In which case it's carbs or megasquirt.  However, it runs decently enough, which means I should be able to figure the thing out and make it work with it's existing management.

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Have you stuck a noid light in each of the injector leads to make sure they are actually working??

 

Have to tried banging ( tapping ) ECU while it's running to see if there's a loose connection??  

 

  There is a fuel pump regulator thing that sits up above ECU that will give you fits if it's not working properly... I don't know exact name as i can't find my factory repair manual right now... 

 

Always keep the inside of the car DRY ,,,,,  ALWAYS!!   Our 83 zx turbo electronics hate to be even a little damp and cold.

 

 

 

 

 

This thing,,,,,,,,, my extra

 

IMG_2173_zpspdf9u8qd.jpg

 

 

It sits above ECU ,, here's mine that i ran an extra ground to and the ECU ( all those extra green wires)  is electrical taped because i soldered the big resistor in it since it had come loose,,, and had been running almost exactly as you describe

 

ONION014_zps70a0936c.jpg

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Good tips, I'll check those hamuck, however, I do believe I've found the issue.  And it's so retarded you wouldn't even think to look for it.  As for damp electronics, the wonderful t-top design of the 280zx allows water to drip from the seam between the t tops and fall right onto the driver's seat.  So it makes a nice wet environment for everything inside.  Snowing, raining, whichever.  Bah.  Wish it was a hardtop, wouldn't have that issue.  I'm sure factory replacement seals would be the fix, but even so, it's a crap design.  Make it convertible or make it hardtop.  Don't do t-tops.  Waste of roof architecture.  And problematic when they get old!

 

As for the fix, I'm making lunch.  I'll upload a video later here.

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And to double confirm, I just watched Quantum of Solace (Bond, James Bond) after a late lunch.  Car was bone cold, just started her up, purrs like a kitten.  Amazing the TPS could affect so much.  Think it would have been easier to find on the Maxima system since it doesn't have computer feedback to adjust idle.  And it looks like my eyes are closed on the video thumbnails, lol.  I changed the one, we'll see if it updates or not. ;)

 

On greater pontification, being the tps told the ecu it was in midrange, it gave it too much fuel, which over-richened the mixture, which pissed off the O2 sensor, which then sent data to shorten the injector pulses, and there you go, like it was running out of fuel when it was too rich.  Goofball shit.  The simplest problems.

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  • 3 weeks later...

Update:  Still pissy when cold on occasion.  Have to wrap it up into 6000 rpm a couple times or more before it gets less pissy.  When I yanked the motor, I did find a stud broken off the downpipe, surmising a leak there might have irritated the O2 sensor until it heated up and expanded.  Not sure, but as I go through it to prepare it for the Z, I'll probably find more little issues that need fixing.

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