My 75 Z is running rough, please help

[graysonZ]

Hey guys, thanks for taking the time to help me on this issue. I looked at a lot of posts and I just need some general guidance not sure where to start. So I'll tell you the story what happened...

My 1975 280z has been running great since I bought it about 2 years ago. Drive it pretty much every week at least a couple of days or more. Changed the spark plugs about 4 months ago which helped the performance a little bit and a k&n filter. That is probably the only thing that is aftermarket on the engine.

It all happened after I changed the thermostat. It wasn't letting the coolant in so I replaced that. Probably was overdue. For a couple weeks of driving it would idle kind of rough in the morning and then when it warmed up it drove great. Then some times if I got on it a little bit it would cut out and act like I was letting up completely on the gas. It stalled on me at a light after I slowed down on one of those. Then for a couple weeks or so it ran perfect.

I then had my friend do a little body work and he drove it around a little bit. He actually put 91 in it when I always use 87. When I picked it up and drove it home I couldn't even go a mile. Idled really bad and stalled. I had to tow it to get it home.

I since changed the fuel filter and put new gas and fuel injector cleaner in it. Ran a little better but still cuts out. Once I turn it off it's hard to get started again. Black soot on the tailpipe and on spark plugs.

Any suggestions or what kind of mechanic i should go to would be great.

Thanks,

Grayson

[Zed Head]

Check your water temperature sensor. It's on the front of the thermostat housing. It might be loose or disconnected.

How do you know that the thermostat "wasn't letting the water in" (it actually lets water out)? Was the engine overheating?

[240260280z]

I concur. There are also bullet connectors ~ 1 foot from the thermostat that could have come loose. Take a look at the photos here to see what I mean: http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

As well, your plugs are probably very carbon fouled. Just take them out and spray with carb cleaner and brush off the electrodes with a brass wire brush.

[Willoughby Z]

I concur. There are also bullet connectors ~ 1 foot from the thermostat that could have come loose. Take a look at the photos here to see what I mean: http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

As well, your plugs are probably very carbon fouled. Just take them out and spray with carb cleaner and brush off the electrodes with a brass wire brush.

[photo]-The sensors themselves are mounted directly below thermostat. Check connectors for proper seating (clips), corrosion (accelerated by old/crumbly/broken rubber boots).

Stray coolant could have even contaminated AFM connector (bottom)

Don't ask how I know this...

[Willoughby Z]

I was trying to say "Yeah, what Blue said..." and this as well [previous post]

[cozye]

fwiw, when I had my coolant temp sensor unplugged, it wouldn't idle at all and I could barely get it to run. LIke already mentioned though it could be loose or corroded connection. you can test the sensor with an ohm meter, the values are in the FSM

What temp thermostat did you replace it with ?

[FastWoman]

Yupyupyup...

It's the same type of connector as on the injectors. If it's crumbly (which it probably is), go to a wrecking yard and get a quick release version of the connector from a Volvo (?) or some other car. The quick release connector releases when you squeeze the sides -- very handy for the front of the engine. While you're at it, grab a second connector for the thermotime switch next to the coolant temp sensor.