Mods, I posted this here because FI guys run e85 more than anyone else.

Before you jump on me, read the symptoms and the conditions of the issue. Vapor lock is very rare on an injected car due to the pressures in the fuel system.

Symptoms: Car missfires under light throttle between 1500 and 3000 rpms when hot.

When first started with a cold engine, car runs and drives fine, no issues under any driving conditions. As the engine heats up to 180ish degrees a missfire starts to happen under light throttle low load. It's not very bad but noticeable. If I stop the car for a few mins after it's over 180 degrees and restart it, it's difficult to start and when it does start it idles at 1.12 lamda vs 0.91. After a few mins of driving the idle lamda will return to 0.96. The car also develops major missfires and becomes very annoying to drive. If I take a drive on the highway an do a few quick 65-110 pulls the problem starts to lessen and after a few more minutes usually goes away. If I then park the car and let it sit for a few minutes, the problem comes back with a vengeance. The car does not have any issues under heavy loads (boost).

Last night after a drive I parked the car and let it sit for about 1.5 hours, hood down. It started hard, had the missfire after giving someone a ride. After coming back I opened the hood for 30 mins, then left and the problem was gone, but returned after about 2 mins of driving and didn't go away until after 10 mins of highway driving.

My fuel system is still a stock dead head with 95lb/hr injectors run by a megasquirt and dual in tank walbros. I'm thinking that the fuel is gassing out in the rails after heat soaking in a hot engine bay causing inconsistent flow. Seems unlikely, but it seems to fit the symptoms. The cooler the outside temperature the less problems I seem to have.

I don't know what the vapor pressure of e85 is compared to e10 gasoline but I suspect it's the problem. I'm trying to burn off the last of it and go back to 91 oct to see if the problem dissipates.

I suspected plug/wires at first and have changed the plugs, but not the wires yet and am reluctant to due to the behavior of the problem with heat. Current daytime temps are 100-110.

 

good reasin to go to a return setup but i think you may be right

 

I was thinking the same thing, that if vapor lock is the cause that a return setup should fix it. Just don't have the fundage at the moment. I'll be switching back to 91 octane later today or tomorrow so that should let me know if it's the E85 or a bigger problem.

 

Any chance the heat from your turbo heat up the fuel in your tank by any chance and thats why after you do a 65-110 pull it lessens because it gets mixed?

 

Ok, filled up with 91 octane... Problem seems solved. No more miss firing. Looks like I'm boiling the fuel in the rail. At least that's the theory I'm going with at this point.

Aggravating, but solvable.

As for the turbo heating up the fuel tank it probably contributes a little but heating 5-15 gallons of fuel with a small heat source in one location vs heating the tiny capacity of the fuel rails in a 200+ degree environment.

 

prolly cause it doesnt recirculate...just sits there in the rails till it gets used

 

yeah, that's my thought too. Sucks that a return setup is so damn expensive to do. Not going to waste my time unless I can do a sumped tank so I can get enough e85 to the engine. Dual intank walbros just don't cut it on e85.

 

Remember that the engine runs open loop before it is warmed up. It sounds like you might start running poorly right around when it switches to closed loop. The fuel wouldn't heat up that fast after a night of sitting. Worth checking - this may not be a vapor issue, could be a tuning issue or sensor.

Jim

 

Open loop... Megasquirt II controls my fuel. During summer my coolant temp is 135ish after 4 hours of sitting during the day and takes about 2 mins to get to 180 and another 3 to get over 200 with the a/c on. Overnight in the garage it will drop to 100ish.

I was hoping the problem would be something else simple besides this, but it looks like it's the fuel sitting in the super hot fuel rails at this point. Driving the car again during the day tomorrow so I'll see if the problem comes back.

 

Changing to a return setup isnt that expensive if done right. Use the stock feed as your return and do 1/2" hardline for the feed. Only need 1-2' of -8AN braided at each end for where it comes out the tank and where it goes to the rail/regulator. Its less than $100 to make the change over if done correctly. Summit 1/2" hard line thats 25 ft long is $23. Summit even sells a kit that has the line and the -8an braided and the fittings for $64

 

Same thing 1320 suggested to me a long time ago and probably what I'll end up doing so I can run e85 in summer for driving around now that I've slept on it. Rails/Regulators are pretty reasonable as well.

 

I went with a return style setup, and plumbed a B&M Supercooler into the return line. Mounted it up behind the rearend, and added the Aeromotive pump controller that cuts my pump duty cycle to 50% at low rpm. With both mods my fuel heating problem was reduced from "can't touch the pump after a hard run" to pump gets warm but not hot.

When I installed the fuel lines (used braided steel), I also put an Earl's fire sleeve on the areas that run near hot stuff:



Good luck on this.

Jim

 

NTK L1H1/L2H2 Sensors FTW! Love them over the POS Bosche die every few months sensors. My first NTK sensor I bought 7 years ago still works good even after several hundred gallons of leaded gas.