Hot Start Problem - a new clue and a work-around

[Captain Obvious]

Zed Head and Willoughby Z, Thanks for the reality check! I didn't even think of the possibility that a previous owner took that stuff off my 77! I already saw that someone before me pulled the EGR system off, and it now seems they pulled the TVV and that heater block off as well.

I'm not a fan of the fan either. Here's my plan A... Like I said, I've not yet owned this 280 through a summer yet, so I'm going to play ostrich and hope it doesn't get me. If that doesn't work, the second thing I'm going to try your trick of fooling the ECU into a richer mixture.

[FastWoman]

Here's my totally wonky idea: How about an electronic circuit that would literally "buzz" the injectors to shake any fuel vapor bubbles out of the tip of the injector? I'm thinking maybe of a warm-start push-button. The circuit would need to drive a bank of power transistors that would ground the injectors. It could be wired safely in parallel with the ECU wiring to the injectors. There might be a bit of smoke out the exhaust on that first fireup, but then the engine would run smoothly.

[cozye]

I think it cleared up faster for you due to the injectors being opened longer which cleared out the air. My observations I can always hear a ton of bubbles getting recirculated though the fuel return line when open up the throttle some (more vacuum), it's the stranges sound coming from the passenger side floor.

I did a ton of Internet searching on this subject, and this is what I came up with.

1. Lots of efi z owners started having the problem around the same time a few years ago. It was difficult to find because those are some really old posts. Before then, everyone said they never had the issue. This was like 10 years ago maybe.

2. Around the same time, various other classic car guys where having vapor lock issues that had not had them before (old hot rodders, etc). I found a few posts on this on some street rod forums where guys had original fuel systems.

Some of these other classic car forums suggested that the addition of ethanol and reformulated gasoline was the culprit. One guy that seemed to have a pretty good chemistry background claimed that they had estimated based on some calculations that the boiling point of gasoline had been lowered about 15 degrees.

Now consider that Nissan made some improvements in later years to keep the injectors and fuel rail cooler (injector fan), I would think that there were some reported hot start issues early on, but this must have been in very hot conditions. Maybe it was just a rare occurance in very hot climates under certain conditions.

My point being that if the fuel rail was just shy of boiling most of the time, that would not have been discovered as an issue in early testing and for most drivers. But lower the boiling point of fuel 15 degrees and you have pushed it over the edge. The gas we buy today is very different than what was available in 1978' or 1988 for that matter.

This is the conclusion i have come to, and the fact that in 10 years no amount z enthusiast have ever come up with a definitive cure supports this. I think the only way around it is to find creative ways to keep the fuel rail cooler.

[cozye]

Oh, one more thing on the ethanol. I know ethanol has been in gas for a long time, but I believe that oil companies are putting more in than they claim. I recently had some work done on my wife's Honda relating to the cat converter, the service manager was telling me that they had been having problems with low quality gas. They had some tested out of couple of cars and found that it was way over 10% ethanol, they had one test come back at 40% !!! There is no telling what we get for gas these days

[inmocean]

When I swapped manifolds, to a non-webbed N42, from a webbed N47, my hot start issues went away. When I did the swap I also added a piece of Mighty Mat 1/2" insulation with a foil backing to the top of the manifold heat shield. (should be visible in my garage pics.) Before the swap, when the issue would arise, the fuel rail was hot to the touch. Now, the Fuel Rail is cooler than the surrounding metal, and only a little warmer than the air. I believe the webs on the original manifold acted like a heat-soak, and that heat transferred to the fuel rail. Just my observations. I also noticed a benefit to the 280zx cooling fan, although it was not a complete fix. I happen to have an unused one with a thermostat and complete wiring harness to fit a 78, if anyone wants to experiment. I set the thermostat so the fan would kick on when the car wasn't running.

[grantf]

One thing I have noticed: Last summer I changed out my intake/exhaust manifold. Being lazy I never got around to putting the heat shield back on. Since then, my hot start has gotten worse. Time to put it back on. Bad me, I should know better.

Wondering if I should insulate it and were I can find insulation locally.

Edited February 21, 2012 by grantf