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

[FastWoman]

I usually don't have hot restart issues, but it happened today.  While I was out on errands and let the car sit for maybe 15 min, the engine fired up, died, fired up again, and ran roughly for several minutes.  The car had been sitting for several months and had a full tank of winter blend gasoline.  Today wasn't especially hot, but I guess it was hot enough.  Reminder:  All stock '78 with FJ3 injectors, fuel pump priming switch, and light insulation on the fuel rail.

[Zed Head]

Bummer!  Hope it doesn't last for you, it gets old real fast.

 

I made some injector insulators from old cellulose sponges (so they wouldn't melt, and because they're low heat conductors when dry) and the problem went 98% away.  I understood when Nissan went to those plastic one piece injector mounts over the cool looking two piece mounts after seeing that.  Might also explain some of the differences people see in addition to fuel.

 

Later, and recently, I filled up with premium fuel over the usual 89 octane I get.  So I'm back to no problems even though we've had some high 80's days here.  I think that I might have been filling from the same big tank of 89 at my usual station and it was a funky winter blend.  I'm sure that 89 doesn't turn over as fast as 87 and 90.

 

Anyway, try some insulation around the injector bodies and see what happens.  I had also placed some Mylar film between the injectors and valve cover just to buy a degree or two of radiant heat deflection, and found that the hole in the center of the manifold between three and four gets very hot.  Enough to cause the bubble film to deform there.  Your 78 probably has the webbed manifold with the little screwed-on sheet metal cover, but that's the hot spot I think.  

[S30Driver]

Ya, I'm thinking the modern ethanol blend gas is at least 50% of the problem.

On my recent road trip, I had many 15 -25 min. restarts for gas & food... never had a problem.

I attribute my heat coated heat shield to part of the solution.

 

A perk of my new location is the flexibility to buy pure gasoline, less that a mile from my house ...

 

[Chickenman]

Just had a really bad case of Hot Start syndrome. Only 2nd time I've had it with this car. Both times temps were in the 90's and AC was running. 

 

Long cruise up to Whistler area this morning. Stopped in Pemberton at around 11:00 AM. Fairly cool on the way up and no Traffic. No stops on way. No AC required.

 

Edit: After lunch, the Sun had cleared the Mountain tops and the ambient temps soared. 95 degrees F. Ran the AC all the way back and had fairly heavy traffic. We stopped after about 90 minutes driving, in Britannia Beach for a Rest Break. Really hot outside. Stopped almost exactly 20 minutes and there was no way the Z would start again. Engine bay was like an oven. Popped the hood, poured some water over the fuel lines and waited another 15 minutes or so. Finally got the SOB started and it ran rough for about a minute or two before she cleared up.

 

1: Chevron 94 fuel. No ethanol.  Bought in Coquitlam BC ( Metro Vancouver ).

 

2: Headers, but no thermal wrap nor are they Ceramic coated. Soon to be changed!!

 

3: Factory heat shield in place.

 

4: 1976 model so has no hood vents.

 

5: N47 head with exhaust liners.

 

6: AirTex Fuel pump. 1 year old.

 

Edit #2: I think I may have a leaky Cold start valve. Something I will have to check further. I have it electrically disconnected ( for testing ). I wonder if having that disconnected made the Hot Start situation worse?

Edited June 8, 2015 by Chickenman

[Captain Obvious]

The temperature threshold for the cold start valve actuation is pretty low (below about 70F). If the engine bay is hot, the cold start wouldn't be expected to actuate anyway. In other words, once the engine is warm, there's no difference between having it electrically connected or completely disconnected.

 

[Zed Head]

 

3: Factory heat shield in place.

 

My 76 with the non-webbed intake has a pretty big hole in the heat shield above the 3 and 4 exhaust ports.  Seems like it's a natural channel for a lot of heated air to pass up and by the 3 and 4 injectors.  Nissan made the webbed intake for 1978 (maybe 77 too) and blocked that hole with a small heat shield (it has to be opened to reach the top-center manifold fastener).  Must not have wanted any air at all coming up from below.

 

Check out the link in #107 to see what Chrysler did for their hot injector problem.  Might help to insulate 3 and 4, if not all of them.

Edited June 8, 2015 by Zed Head

[rossiz]

interesting fix chrysler did - looking at the picture it seems that the injector is downward angled, so the heat flowing up would really cook it. if the heat transfer is "flowing" up (hot air) or if it is radiant (line of sight) than a heat shield from something like this would definitely help: 

 

 

but if it's transmitting up through the metal from the exh. port around the intake and through the threaded connection at the base of the injector than a shield won't do much...

 

[Zed Head]

I placed reflective Mylar bubble film in various places (standing up along the valve cover, for one) to reduce radiant heat (I measured temperature with an IR gun to see what was hot) and saw no effect.  It did deform right where that hole above 3 and 4 is though,  That was an affirmation of the hot air tunnel.  I pondered better pintle caps for the conductive pathway but couldn't come up with anything.  My injectors don't have the plastic pintle caps like the stock ones do so the metal-to-metal conductive path could be in play in my case, if an injector was misaligned.  But the stock injectors have a plastic barrier, although it is thin.

 

The insulators I made from plain old kitchen sponges had a significant effect.  We're up in the high 80's and 90's here and I've been out (sweaty rides with no AC) a few times, restarting in the critical 20 minute window, and not seen any more hot start problems.  The sponges are multi-color and look way out of place but compared to the problem, are worth keeping there.  I have some thoughts for better covers, for when I next take the injectors off.  It's not broke though, so no fixes planned.

 

 

I wonder if the super-flammable North Dakota crude could be the part of the cause.

[Chickenman]

Yeah..I'm going to be looking at all the fixes. Seems like Plastic injector holders, sealing hole in Heat shield under #3 and #4 and a Fuel Pump priming switch may be the things I try first.

 

Later on, if I go Mega squirt, I may go with an aluminum fuel rail. Right now I'd like to keep the factory fuel rail system due to restoration value.

 

Edit: Ceramic coated headers will be on the cards as well. When I get those, I'll probably add some a reflective Thermal insulation to the back of the factory heat shield.

Edited June 8, 2015 by Chickenman

[Chickenman]

Well I did some poking around the hood and discovered a few things. I have an non webbed Intake manifold, but my heat shield is full coverage with no holes between # 3 and # 4... so that was a nice find. Might be a ZX heat shield as it's an F54 block with N47 head. PO had chromed the Heat shield so it should be nice and heat reflective.

 

Injector holders are Phenolic or " Plastic ". Not sure if those are a factory revision or not, but nice to find. From their " as new " condition, it looks like they've been replaced at some point. BTW, my car is a 1976 Arizona car ( 48 State, non-Catalyst, non EGR )

 

Also, I did find that the " old " alternator ( LT150 ) was weak. I've suspected that for a while. I did a load test on it with a known good V/regulator ( new ). At cruise rpm with AC and headlights on, blower fan at #4, alternator was barely able to maintain 12.2 volts. So that's an actual discharge rate. 

 

With slow cranking rate and low fuel pump pressure/volume due to partially discharged battery, I think that was enough to prevent the Fuel Rail from being purged of Vapors.

 

I have a new 60 amp alternator ready to be installed. With that and a Fuel Pump " Prime " button, I'm hoping that this Vapor Lock issue will be solved.

Edited June 11, 2015 by Chickenman

[FastWoman]

Chicken, I have a priming switch on my Z, and I can tell you it doesn't really help to resolve the hot restart issue.  I think the problem is that the cool fuel won't dribble into the injectors just with gravity and therefore won't cool them.  Instead, you have a stubborn pocket of fuel vapor inside each injector that doesn't really budge from where it is.  The only way to get rid of that pocket is to inject vapor into the intake.  Then fresh/cool fuel enters the injector, flashes, and must be injected as a vapor.  Eventually this happens enough that the fuel vaporization, combined with cool air rushing through the intake (perhaps a more significant factor), carry away enough heat that the fuel no longer flashes inside the injector.  And that's when the engine evens out.

[Mark Maras]

Concerning the hot start issue. Has anyone tried spraying the injectors, lines, etc. with something cold such as pressurized propane or CO2(better option) to condense the fuel? In theory it seems as if this would be a good way to get going without the wait.