Hot-start issue with EFI - who has it, who doesn't

[siteunseen]

Could his fuel pump be overheating? Maybe clean and re tighten the terminals.

[Captain Obvious]

it seems like the injectors just refuse to open at all. could this be an electrical issue?? the odd thing is how it runs perfectly whenever it runs - just has this starting issue. is there a different control for firing the injectors during cranking vs. when it's running (like the fuel pump relay logic)??

There is an enrichment circuit built into the ECU which adds extra fuel while the engine is cranking. It tails off over the next thirty seconds or so after the key is released back to ON. But other than that, I'm not aware of anything different about firing the injectors between START and ON.

My money is on fuel, but just a quick test to make sure? Pull a vacuum hose and give a quick shot of starter fluid into the intake manifold? Should pop on that for a few seconds if there's spark.

Another idea would be to disconnect one of the bullet connectors going to the temp sensor (either one will work) and then try to start it. This will fool your ECU into thinking your engine is Antarctica stone cold and add extra fuel accordingly. Pull it and see if it will start then. It'll billow clouds of smoke if it starts, but while it's running you can then reconnect the sensor bullet.

Could his fuel pump be overheating? Maybe clean and re tighten the terminals.

Doubtful. He says the fuel pressure looks good even when the problem is occurring.

[rossiz]

i believe my problem is an EFI electrical issue which has somehow been exacerbated by or is simply coincidental to hot-start conditions, so i'm going to start a new thread to try and keep this thread on-topic.

let's just say today wasn't a banner day for the z...

Edited April 16, 2014 by rossiz

[siteunseen]

I had a thought :sick:. I put a ZX distributor on my '77. I have a black w/blue striped wire that's energized from the key at start then loses it when it clicks back to the on or run? notch. What if you wired the CSV to that wire? It would purge the fuel briefly and give it a shot of fuel on start up no matter how hot it was.

[txvepr]

In all this discussion of what 'it' could be, don't forget the value of having a fresh distributor cap and rotor. They do wear out, and Datsun said to replace them every 12 MONTHS in the manual. That, combined with a fuel check valve after the filter has helped my vapor lock problems here in Texas about 90% better. And it is vapor lock ,people.

[Zed Head]

Please give more definition of "vapor lock". I don't understand what you mean by the term. What, in detail, is happening?

[txvepr]

Zed, you funny

Vapor lock - Wikipedia, the free encyclopedia

[Captain Obvious]

txv, you funny too. Not hot enough back by the pump to vaporize the fuel.

Vapor lock - Wikipedia, the free encyclopedia

[txvepr]

To be clear, the fuel obviously vaporizes in the fuel rail and injectors, where the hot is(engine block). Mmkay? Not back at the pump. Once that happens, you are done until the fuel returns to the liquid state. That is the 'what' .

As to 'why', various reasons all boil down to the boiling point of the fuel in your fuel system, which can be controlled by pressure, temperature, and fuel blend.

Did I really type all that?

[Zed Head]

To be clear, the fuel obviously vaporizes in the fuel rail and injectors,

Now you're changing your story. Or you didn't read the link you posted, person.

From the Wiki link (bold italics mine) - "It occurs when the liquid fuel changes state from liquid to gas while still in the fuel delivery system. This disrupts the operation of the fuel pump, causing loss of feed pressure to the carburetor or fuel injection system,"

On a progressive (as in making progress) note, I'm 80% of the way to trying out some 1990 era injectors, of the four hole, high impedance type. Just to see if any design improvements happened along the way. I notice that the high impedance injector pop open with less voltage, even though resistance is higher. More windings, I think (another area I don't know well though, like transistors). If it's a mechanical binding problem, or solenoid resistance increasing due to heat, maybe more opening force will help. Hopes aren't high but I think it's worth a shot. I'm bypassing the resistor pack so there's a lot of new happening.

[txvepr]

Not my story, focus on temperature and pressure. The higher your fuel pressure is, the higher its boiling point is, just like a radiator. If the system does not hold pressure when its stopped, that gas boils, making vapor, and voila. No liquid.

I've watched gas start to boil in ambient pressure at around 140F. You can believe its at least that when the engine is stopped after 10 minutes easy.

Good luck with the windings.

[Zed Head]

Here's an interesting post I found while Googling around (this is not a reply or reference at all to the last 7 posts here),

ignition upgrade and timing bump (no 56K) - Page 106 - FSB Forums

Post #2108 (longest thread ever), bottom image with the diagram, talks about deposits on the single pintle design. Could help explain a pintle binding theory. Regardless, it's interesting reading, to me anyway.

I've been driving around with new injectors for the last 5 days, but am waiting for the next couple of days here in the Portland metro area to give them a true test, it's supposed to hit 80. But I've also changed to a straight-shot fuel rail so results won't be assignable to a single cause. But all of the changes combined seem to be working.