tolerate Posted May 18, 2014 Share Posted May 18, 2014 Hi all, I have a 1977 280z with a 1982 rebuilt L28ET swap. I'm working on my tune, but I think I have vapor lock. symptoms I'm experiencing are: stalling at higher temperatures (> 180), even while idle cannot hot start even with prime pulse cycling cannot hot start even with a flood clear crank even when hot start works (after cool down) engine slowly stumbles and comes to life gradually and stalls out soon (3-5 minutes) I have tried clearing the line before cranking. Would love to find some tips to manage the heat or provide a couple of places I need to start with. I checked my fuel lines for leaks, and checked hte o ring pressure gauge (negligible drop in pressure after ~1 hour). However, when I came back to check the fuel pressure after an hour I noticed the fuel rail is still warm. Is that normal? http://imgur.com/a/ayrDw <------- engine bay pics. Car specs: L28ET with stock turbo MegaSquirt n Spark Extra EFI (fully programmable) Turbonetics (I think) T3/T04B turbocharger (internal wastegate) 260z intake manifold (no EGR) Intercooler with 2.5" aluminum piping Griffin aluminum radiator 16" electric fan Aeromotive Fuel Filter Russel fuel filter at pump 255LPH Walbro Fuel Pump MSD Blaster Coil 440cc Supra injectors (flow tested) JSK O-ring Fuel Rail Aeromotive Fuel Pressure Regulator Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 19, 2014 Share Posted May 19, 2014 Make sure your fuel pressure is not bleeding down after shut off (from something like a leaking check valve, etc...) Heat is your enemy, running a 160 thermostat helps quite a bit in keeping the fuel cooler. So does running a full tank. Heat Soak is Heat Soak. The two big answers are above, there are plenty more. Quote Link to comment Share on other sites More sharing options...
tolerate Posted May 19, 2014 Author Share Posted May 19, 2014 I checked the rail pressure, no bleed. My thermostat broke, so the fan relay is currently always grounded. the fan kicks in from on to off. I was running a half tank of 93 octane. Is there a way to check to make 100% sure its vapor lock? I checked the megalog and it looks like it stalled out around 165 degrees. Quote Link to comment Share on other sites More sharing options...
mattb3562 Posted May 19, 2014 Share Posted May 19, 2014 Keep in mind that your engine temp and fuel temp can be entirely different. Are you using the factory Cuts for your reading? Still have factory heat shielding? Turbo blanket and downpipe wrapped? Quote Link to comment Share on other sites More sharing options...
tolerate Posted May 19, 2014 Author Share Posted May 19, 2014 factory cuts?The heat shielding should be visible in the pics. ones between the intake and exhaust manifolds, and the others surrounding brake master cylinder. I dont have the 280zxt factory fuel rail blower thing. And I didnt wrap. I heard that accelerates teh rusting like crazy. would it be better to wrap the fuel rail? Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 19, 2014 Share Posted May 19, 2014 You got something serious wrong if it's happening at only 165! Shouldn't happen until 200-215+ I think "factory cuts" is an autocorrect of "factory sensors".... Make sure your EMS is not contributing. MS can have hot restart issues due to poor calibration of that table... Use one from someone who's got a reliable tune and hot restarts reliably. Should not be doing it anywhere near 160-170 at all. I think the issue is elsewhere... Quote Link to comment Share on other sites More sharing options...
tolerate Posted May 19, 2014 Author Share Posted May 19, 2014 thanks tony, I'll try a complete copy of Cygnus tune and update this post soon. And the sensors are in the factory locations, mostly. The O2 sensor is about 6" downstream of the turbo on the downpipe. Quote Link to comment Share on other sites More sharing options...
mattb3562 Posted May 20, 2014 Share Posted May 20, 2014 Yes that was meant to be 'factory CHTS'. Has it been calibrated to the MS? I understand the worry about rust, but I would strongly suggest running a turbo blanket and I would also wrap the downpipe. I, first, painted the downpipe with vht and it hasn't rusted in a year now. Quote Link to comment Share on other sites More sharing options...
mattb3562 Posted May 20, 2014 Share Posted May 20, 2014 Just curious, what's your intake temps getting up to? Quote Link to comment Share on other sites More sharing options...
Six_Shooter Posted May 20, 2014 Share Posted May 20, 2014 I'm not using MS, but I am running a non wrapped turbo and downpipe, and have done so for 5+ years. The only hot start issue I encounter is after the car is fully warmed up and I stop for between 5 and 10 minutes. Heat soak of the fuel rail causes a very lean condition, but the engine ALWAYS starts at hot start. I have also had reported coolant temps of over 230*, but this was most likely an air pocket because this only happens when the coolant is a bit low, but there was no stalling. I have seen hot restart coolant temps of over 220* (with topped up coolant) from the coolant baking after hot shut down, still the car started. My intake temps are usually around 160* F at this point (MAT sensor in place of the cold start injector). Because of this and other people's experiences with hot start I would say that this si something in your tune, that is causing the stalling at 165-ish and hot restart issues. What are your reported injector pulse widths when this happens? What is the actual cranking AFR? Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 20, 2014 Share Posted May 20, 2014 The CHTS being at 165 is way below any boiling point unless you are running a bad cap, and pure water! Nowhere near where you need to be to have the hot restart issues. My bet is your tune parameters. Quote Link to comment Share on other sites More sharing options...
skirkland1980 Posted May 20, 2014 Share Posted May 20, 2014 I only have this problem when I use fuel from QT. For some reason their fuel has a very low boiling point. I also had a fuel percolation problem on a carbed 350 chevy. The fuel was only 130 degrees. I've since been using chevron or bp. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 24, 2014 Share Posted May 24, 2014 This effect is not to be discounted as well! During "winter fuel" months in SoCal if you get an 80 degree day, you can get vapor lock from the evaporative characteristics of the re formulated greener fuel. Quote Link to comment Share on other sites More sharing options...
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