No injection pulse cold -- possibilities

[Wade Nelson]

Hey all, it's MY time to need some help!

Before I bailed out of Colorado to take care of sick family members, I used a NOID light to diagnose my Z's hard starting in very cold weather.

It simply came down to this. In sub-freezing weather I am sometimes NOT getting main injector pulses

Let it warm up a few degrees outside, and everything operates fine.

This was AFTER installing new injectors, a check valve, new cold start injector, diagnosing the thermotyme circuit, cleaning the AAR, and every OTHER possible source of hard starting problems. She starts instantly now -- except after a cold soak.

One time I finally caught her "in the act." Cranking, but no injection pulses. A minute later she was fine. Then I caught her again a few

days later.

I need some ideas as to what could be causing this.

Possibilities I've thought of include:

Worn or corroded contacts on main injection relay (voltage drop 'em?)

Temperature-sensitive Ignition module not sending signal to ECM so it's squirting (try hot air dryer?)

Voltage drop in main ignition switch signal controlling main injection relay?

What else should I look at as a possible cause of NO MAIN INJECTION during CRANK?

[Zed Head]

I think that the ECM gets its signal from the negative post of the coil, not the ignition module.

Are you sure that you're getting spark? No spark = no ECM signal = no injector grounding through ECM transistors.

Of course though, the same applies for spark - no reluctor pulse from distributor to ignition module = no spark = (see previous).

That's the chain of events, assuming that you have distributor-controlled timing and not a CAS (you have a ZX right?).

[Wade Nelson]

280ZX, and I confirmed spark during a crank no-start event. She immediately started upon application of starter fluid.

But I should probably re-confirm spark NEXT time I catch it "not injecting" since the problem is so intermittent.

Temperature-related is the clue....

[Wade Nelson]

* fake post intended only to get thread listed on home page again and hopefully spur some comments*

[Mikes Z car]

Is there a possibility of heating suspected components with a heat gun one sub freezing morning one at a time to see if it will then start? Easy for me to say I don't even have a car with an ignition module!

Edited January 12, 2013 by Mikes Z car