Introduction and a plea for help

[z_scout]

Hi everyone,

I've posted once on this site but never properly introduced myself.

About four years ago I found a 1978 280z on craigslist for cheap. I was lucky enough to find the ad about 2 hours after it was posted. I called the owner and made an appointment for the next day. The following day I was really surprised by the condition of the car. The body was near perfect with no rust and two small scratches on the hood. The interior was completely original and showed very little signs of its age. It looks like it had been repainted but it still looked fairly new. Unfortunately, the engine wasn't as good. The Z had been sitting in storage for 12 years and was hardly driven. I took her home and started the engine restoration project. While I was at it, I installed a Tokico HP set up with energy bushings, new foam and uphostery, new carpet, etc... The list goes on. It's now in great condition. Except for one thing - which is where the plea for help comes in.

I found that I had to replace a lot of different components in the engine in order to get it running right. This included replacing all sensors, injectors, exhaust, fuel pump, and gave it a good tune up. It now runs like new ... except for a nagging hot start condition. (I think someone w/ a ZX just recently posted the same condition).

http://classiczcars.com/forums/showthread.php?t=22613&highlight=hot+start

Basically the engine starts right up when cold. But once it warms up to a normal temp, and I shut off the engine, it sputters like it's flooded. The condition returns to normal once the engine cools down.

I've followed the EFI bible like it was a ...bible and all tests checked out fine. I thought for sure it would be caused by a faulty water temp sensor, faulty pickup coil, or a leaking cold start valve but they are all brand new and passed the resistence tests. Not only did I run the test from the ECU connector, I also ran them on the actual sensors.

If anyone can offer any help, it would be very appreciated. Thanks and sorry for the long post.

Andre

[zbane]

Andre, congratulations on the find and on your persistance.

Don't apologize for the long post, providing more information rather than less helps those with more knowledge than I give you more helpful information by knowing what you have already tried or done.

Regarding your mention of a similar post-

The jist of that line ended up being a discussion of Vapor Lock or other problems as the cause of the problem. No consensus was reached.

I wish I could be of more help on this, but I am still learning about these things myself.

As a general suggestion, have you tried using the "search" feature on this website?

I have found it to be quite useful, enlightening and entertaining.

welcome to the forums,

david

[DatsunZsRule]

So let me get this straight, It runs or idles rough when you re-start it after it sits for a short time correct? then smooths back out again when cold or as you give it gas or drive it?

Sounds like you have already done a lot of testing I'd test the fuel pressure after the filter if you haven't already. Should maintain 36 PSI at idle. If that checks out good then I'd test the Thermotime Switch again, if you haven't already.

Good luck

[sblake01]

Does it take a long time to start when it's warm or not start at all when it's warm? Have you checked the fuel pressure while it's exibiting this condition? The answers to these questions would lead me in a direction of how I solved a similar problem on my 810.

[z_scout]

It will actually start but only if I give it a little gas. Once it starts, it has a really rough idle and if I let go of the gas pedal it will die. I can actually drive it for a while like that but I haven't driven far enough to see if the condition will go away. The only thing that really resolves the issue is if I let it sit for about an hour.

As for the fuel pressure, it's getting around 35 to 40 psi which I think is within spec.

I also ran the thermotime test from the EFI bible. Basically, while the engine was hot, I unplugged the thermotime switch and it had the same problem. I also measured the resistence on the thermotime and it was within spec.

This may be a dumb question but could heavy carbon build up in the fuel rail or in the block or head produce this type of condition? Also, there is an air temp sensor in the AFM but the EFI bible doesn't include this in the hot start tests. Could this be the culprit?

[Chris280Z]

I had the same problem on my 78. Turned out to be the magnetic pick-up coil in the distributor was gapped too high. Started great, drove great, turned it off had to wait til it cooled then all was good. Then on a 100 degree day in a parking lot, it wouldn't start for 2 hours, called triple A, got a tow, dropped it in the driveway, started right up.! Doh! Use a brass feeler gauge. Can be a pain to get the reluctor wheel lined up with the magnet but a very easy fix/check.

Good luck Chris

[TomoHawk]

Also check that none of the connections/connectors to the sensors are exposed and touching bare metal. BTDT.

[sblake01]

As for the fuel pressure, it's getting around 35 to 40 psi which I think is within spec.

Have you checked the fuel pressure while the car is in the hard start/no start condition? Are you using an OEM fuel pump or and aftermarket replacement?

[dnicol]

an Ignition coil could have the same symtoms.