Another overheating fuel question

[Denvervet]

I've got a hesitation upon throttle...light or heavy...that seems to only be apparent when the engine compartment get nice and warmed up. Meaning that when the engine warms up but it cool outside it's much less apparent.I notice it most when it's warm outside and I idle for a long stop light. I ran my hard fuel lines on the inside of frame rail and up front the header collector is about 1.5 " away . I put some thermacool heat reflectant over the lines but doesn't seem to make much difference. The $64K question is whether I'm still heating up and thus causing bubbling or just still have a tuning issue. Fueling tables have been tweaked to keep this motor running pretty rich already( seems to run best there but may be just covering something up in my opinion)...12.5-13.5 AFR at cruise and accel...and trying to sort this out. My infrared gun shows fuel rail temp when occurring about 150-165 ish. Temps taken at fitting in engine bay down by header show 185ish. Is that temp at 58lbs pressure still enough to boil fuel? I've researched lots and not found a straight answer as to when gasoline boils. I know the different compounds that make up gasoline do it at different temps....but...sooooo..again...how hot is too hot in the lines to give symptoms? Basically, I am trying to decide whether to reroute line up front outside frame rail or just keep tuning.
I'm all ears.
Thanks

[parsonsj]

David, any idea what your AFR is during the hesitation/stumble? What sort of compensation do you have for CTS and IAT temps? That's what I'd look at first.

[Denvervet]

John
So, I take it that you don't think those temps are high enough to get too excited about? If so I'll get off that. I have an IAT adjustability. I haven't heard of CTS. My afrs during these areas aren't that exciting...to me anyway. I have a local tuner that went for a drive with me and he did a good job of smoothing some of those out by richening up spots on the table to where most of the time it seems to run best in the 12.5-13-5 range. The plugs are showing very rich...IMHO..Dark brown to black. Afrs when hesitating were maybe up to the 14 range and this is during like 25-50% throttle...nothing close to WOT. My tuner thinks my cam being a little agressive is why it likes to be so rich ( this crate motor though lumpy idle doesn't appear to be that aggressive considering HP/cubic inch standards). Sorry for the long winded reply.

[parsonsj]

CTS is coolant temperature sensor. If you are seeing an AFR of 14 during the stumble, and your engine "likes" 12.5 to 13 (which is pretty rich) than I'd look at MAP compensation. When you hit the throttle, vacuum drops and you need additional fuel to compensate.

I don't think it's fuel temperature. Sounds like tuning to me.

What EFI system are you running?

[CarlC]

Clamp a temporary heat shield in place between the header and the fuel line. Allow an air gap on both sides but keep it a bit closer to the header if needed.

[Denvervet]

Ok, I rigged up some to heat shields and we'll see if it makes any difference. I'll post up when I try it out...I hate it when I follow a post just to get to the end with no result.

[Denvervet]

The heat shields reduced fuel rail temps but still have a stumble to tune out. Moving on...thanks guys

[Mike Norris]

Looking at the pics I want to say I would move the lines quite a but further away. I would probably want 4-6" clearance just to be safe. Overkill? Maybe, but it will make it a non issue. I would run the line higher on the firewall and then to the out side of the frame rail with a debris guard.

Back to what John asked, what EFI system are you running? It could be a transient fuel issue that needs more at that temp.

Mike Norris

[MrForce]

The richness of your tune makes me think you may not have enough timing. +1 on the ECU brand as well as your timing curve.

Rob

[milehigh69]

Denvervet, I have had the same problem here in Denver. You should move the line out as far away from the engine, header as possible. I ran mine up over the outer fender. then down and to the front of the engine. Ethanol gas boils at around 100F so not very hot. Are you having problems with the vaporworx tank? Mine is in paint all summer so I was not able to run the new tank much yet.