Any Mechanics in Pittsburgh?

[Pooky]

Hello All,  I "mostly" finished my '77 280z last Summer but I never did get it running right. I've searched this site over many topics and still haven't found the culprit. The car starts easily and idles nicely. It accelerates ok but holding a steady RPM causes the car to miss. At least that's what it feels like. The engine seems jumpy, like its running out of gas. It seems to get worse the longer I drive. Giving it gas seems to make it go away until I let off the accelerator again.

Car History: I bought the car almost ten years ago. Drove it home and don't recall having any running issues. For the ten years I was real gung ho at first but then the car took a back burner. Thanks to Covid and time off this year I was able to get it to where it is today.

Things I changed and checked include: Put a new ZX alternator in to go around the external regulator, fuel pressure seems to stay steady at roughly 35 psi and holds steady for a day or so when not running, I cleaned the injectors myself with an improvised spray can of cleaner and a 12volt battery. I believe they're all ok. Replaced all fuses. Replaced the coil with a flamethrower. This was a concern. I've since learned on YouTube that there are upper and lower limits that are important. My usual mechanic didn't think this would cause my problem. I've tried to check all my grounds and connectors. I replaced the temp sensor and the thermotime. Fuel filter. Battery. Cleaned my mass air flow chamber which I thought could be an issue. I have concerns that the distributor could be an issue. I question the wiring from the ceramic block by the coil. (I forget what its called) I did adjust my timing with a light. I used the light to also verify that all cylinders were firing and they were. My cylinders ranged from 48psi to about 57psi. A little low but I think in range according to my books. I have another computer that I haven't switched out yet.

I'm sure there are other things I've changed and checked that aren't coming to mind but I'm frustrated to say the least. A lot of you guys check this and that for resistance and so forth. I don't want to get into that depth unless its easily explained. I'm at the point where I just want to drive it! If you have any suggestions about what I may have missed, I'm all ears. Otherwise, please let me know if any of you know anyone in the Pittsburgh area who knows these cars.  Thank You Guys, Pooky

[Pooky]

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[S30Driver]

The ceramic block by the coil is the ballast resistor, only comes into play when starting, so you can rule that out.

Sounds like it could be a fuel issue to me,  after a drive with the car warmed up and after it has exhibited the misfire, stumbling issue, what is the fuel pressure reading?   Is there any way you can monitor it while driving during the misfire?

Maybe check the very important ground that the efi harness uses on the intake manifold.  Make sure its clean & tight.

[Pooky]

Thanks S30 Driver, I checked the things you mentioned. I took it for a ride today. So fun to drive! Can't wait to drive it once its running correctly. The Z ran half decent for the first 15 minutes. After a stop at my brothers house it ran like poo poo! Studdering and lunging.The grounds seemed tight enough. The fuel pump delivered an average 30psi while running. It would spike up to 33/34 when spiking and down to 28ish when idling at roughly 800rpm. I think my next step is to check vacuum. I've checked numerous times for leaks and found none or fixed what I found. I also believe I have an exhaust leak because the fumes keep coming into the cabin. Maybe that is part of my issue. I'll find it the next time I have it up. Another thing I noticed is that the car will stall out when I put on the high beams/electrical draw. The alternator puts out 14ish volts. Less at 800 rpm idle. Just throwing these things out in case it sends up a flag to one of the members. Thanks All,  Pooky 

[Captain Obvious]

Pooky, I'm not sure I understand the problem(s) you're having... How bad is the problem? Is the car drivable?

What's the worst of the problems? Maybe we can start there and knock them out one at a time?

Also, @mgood is and active member and he's in the Pittsburgh area. Maybe he has some input for local help?

Edited April 4, 2021 by Captain Obvious

[mailnome]

You didn’t happen to grow up in Somerset did you? Had a friend nicknamed Pook as a kid


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[Pooky]

Yes Captain, the car is drivable. I drove it to church this beautiful Easter morning. It drives like a cylinder isn't firing. When driving at a steady rpm, no matter what gear, the car is jumpy. Its a rough ride when driving along a straightaway. I pulled each plug wire one at a time to see if it made a difference but it doesn't seem to. The plugs never seem to be too dry, too oily, etc. I rechecked my compression and the results ranged from 112 to 120 psi on a cheapy Amazon gauge. I put a new muffler clamp on and the smell in the cabin went away. However, the fumes do have a peculiar smell. I'd say its running rich. A new theory I have might be to move the gears in the AFM a tooth or two. If it doesn't do anything I can simply move it back. 

No mailnome, I grew up right here in the southwest suburbs of Pittsburgh. A kid I used to work with years ago started calling me Pooky one day for no apparent reason. One day when I was trying to think of a login name it came back to mind. Now my screen name is Pooky,  Craig

[siteunseen]

It sounds like a fuel problem to me also. It may be the coolant sensor problem that is so common on the EFI  cars. I had to do mine and now it runs great. Here's a link that explains it. Mine ran like crap up to about 2,500 RPM then started pulling good the rest of the way up.

https://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

Have you installed a cheap clear plastic filter coming right out of the fuel tank to check for any trash in the tank? That's an easy way to see what kind of shape your tank is in plus it's another filter for these old cars. Here's the link I followed to do my '77. It goes before the pump so it's a cheap low pressure filter.

https://atlanticz.ca/zclub/techtips/fuel/g3filter/index.htm

Here's the Tech Tip page, very useful. Lots of good pictures too.

https://atlanticz.ca/zclub/techtips/

I haven't a clue about covering the hole on your throttle stop dash pot but I've always read it should be "open to the atmosphere"??? Anyway someone smarter will chime in and say. 

Engine bay looks great and welcome to classiczcars.com.  Cliff 

 

[Zed Head]

 

[Captain Obvious]

Have you done any of the testing from the EFI handbook (commonly called the EFI bible)?

https://atlanticz.ca/zclub/techtips/efisystem/280zfuelinjectionbook.pdf

Most of the testing there is done at the big ECU connector. I would be interested in hearing what your coolant temp sensor resistances are both cold and hot.

And about pulling off a plug wire to check for a misfire... Not good for the ignition system. A better way is to pull off the injector connectors one at a time and see if the idle changes.

Lastly, your compression numbers are definitely low. Did you block the throttle wide open while you cranked the engine for the compression test?

[Pooky]

Hey Cliff, the throttle stop is currently open to atmosphere. I think the picture was taken while I was trouble shooting. Good eye, though! Putting in another fuel filter is not a bad idea. I read somewhere on the forum there's also a screen type filter in the pump that should be checked. I've wondered about the internal condition of the tank. I'll revisit the coolant sensor as well. I replaced that and the thermotime in the Fall but I've questioned the wiring and connections. Thanks for the links. I'll check them out. Happy Easter, Craig

[siteunseen]

Here's a screen grab from the "efi and fuel" of the link I posted last. It's under the 2nd "fuel pump" heading. 

Thank you and I hope you had a nice Easter Sunday too.