Cold Start Issues

[jofwolves]

Howdy,

I recently got my first Datsun, a 280ZX from 1979. It runs great, but it has some cold start problems -- and I mean that literally. In the morning when I try it it cranks but won't turn over; when I get home after a day of it sitting in the sun I do have to give it some gas to get it up to idle but it eventually starts fine. I checked the oil and it isn't any more viscous than it should be. I've read that the stock air pumps from this model can sometimes result in this sort of issue and that it may be worth replacing if cleaning it doesn't work, has anyone else experienced something similar?

Thanks in advance,

Julian

[sblake01]

I saw you last week post on Z driver.com. Do you have a 1978 280Z or a 1979 280ZX? There are slight differences between the two mechanically that could effect the answer.

Howdy.

I just bought my first Datsun, a 280Z from 1978.

As a rule I figure adding a cold air intake is always a good first project for a new car. I noticed though, as soon as I opened up the hood, that the intake to the engine is extremely direct as is. For this reason, of course, CAIs are extremely cheap for old Datsuns; however, I'm wondering if it would make much of a difference.

Does anyone have any experience with this or ideally any figures regarding how much power it can add?

Thanks in advance,

Julian

[jofwolves]

Yeah it turns out it's a ZX; the guy I bought it from had his facts messed up and at the time I posted that I'd just gotten it and hadn't looked very thuroughly into it. Sorry about the confusion.

[zbane]

How's the car start after you've driven it for a while?

Have you any way to check the fuel pressure at the rail?

Have you changed out the fuel filter (not a bad idea anyway)?

Have you checked the little cone type filter in the fuel pump? Might be clogged.

I am a fan of running seafoam through the fuel system every few months; it may not help, but it certainly won't harm anything.

[jofwolves]

After I've driven it at any point durring the day it'll start fine, even if it's been off for a few hours. The first time I start it after it sitting for the night -- when it is indeed warm enough to turn over -- I have to give it gas immediately and keep it on for a while to get it to idle. Haven't gotten around to changing the filters, but last time I filled it up I did put in some additive that's supposed to help clean it out. This weekend I'm changing all the filters and rebuilding the mass air flow sensor; with any luck that should help but you never know with cars this old.

[Zed Head]

It sounds like your Auxiliary Air Regulator (AAR) is stuck closed (if it's still there,some people remove them). It is designed to let air past the throttle body to keep the idle up when cold.

Your engine has an Air Flow Meter (AFM). Technically it might be called a mass air flow sensor but that is not how they are known in the Z world. I have not heard of anyone rebuilding one themselves, but am interested in how you do with it.

Both of these items are covered in detail in the Factory Service Manual (FSM). It is worth reading at least the first few pages of the Engine Fuel section before diving in to engine problems.

[jofwolves]

Thanks, I'll look into the AAR later today with any luck. Cleaning out and rebuilding the AFM made a difference, but it still requires some gas after turning over. Coincidentally I'm currently waiting for a manual to come in the mail, and yeah, it's looking like I'm at a point where I might just end up waiting for it to get here before doing much else.