​​​​​​​Thanks, do you think icm could be the reason? If I would drive further on with no tank refill at half tank, fuel temp would go so high that car would loss all power.. Fuel temp goes well over 130°F..And fuel starts to evaporate like crazy.. Thanks, Domen

 

Thanks, do you think icm could be the reason? If I would drive further on with no tank refill when half full, fuel temp measured on return and delivery fuel line would go well over 130°F, lot of power loss and fuel starts to evaporate like crazy.. Thanks, Domen

 

Any idea?

 

Have you checked for a clogged catalytic converter?

 

Hi, no.. I have all pre cats as well.. But i put new catback exhaust last yrar..

 

Good point.
Might be worth while to test temps of the cats when fuel temps get high.
Is the heat shield of the main cat still in tact?

 

Heat shields are there.. I can measure the temp and will let you know.. What could be the relation between cats and fuel temp?

 

Hello Domen,

If you have a plugged catalytic converter it will make the engine run hotter than normal. The simple test is to remove the oxygen sensor and see how much pressure comes out of the hole. It should leak a little here but no more than ~5 psi pressure. When a catalytic converter gets plugged they can get very hot and even glow red at times. When I put on my cat back exhaust I replaced the cat with a high flow modern version and it helped the Corvette make another 14 hp. When a cat gets plugged the engine is not able to get the exhaust through fast enough and this makes problems causing the engine to run hotter than normal.

How about your EGR valve? The EGR can easily make a normally running L98 run hot enough to experience detonation. The EGR can be tested by verifying the ECG Vacuum Solenoid (on the thermostat housing bolts) has power and a good source of vacuum going to it. Then using a hand vacuum pump try making a vacuum so the EGR diaphragm will move up and down while the engine is running, the idle should hunt around as the valve moves. If somebody removed the EGR valve then be sure it was removed from the software as well. It is not possible to remove the EGR properly without deleting it in the software as well and that requires a chip change.

I would give thought to replacing the fuel pump itself with it making the noise that you describe when half full. I have the same pump inside my C3 fuel tank and it is barely audible even at 1/8th tank full. The pumps will make more noise as they age, to me it is a sign of impending doom.

In my C3 with it's 427 and headers I have done the same thing as you did. I insulated the fuel line from the tank output to the fuel input on my EFI unit. I want cooler gasoline and have never had any issues with Hot gasoline however. My under hood temperatures are sufficient to make hot fuel after shut down. I only have one line coming from my fuel tank since the regulator is inside the fuel tank on my C3.

 

Hi, thanks for honts! I will check on this..the egr with the solenoid, just need to get hand vacuum pump.. Fuel pump is new, whining only when fuel gets hot.. Im about to order arh headers with no cats.. Underhood temps are really high compared to a normal european 4 cylinder cats.. Even brothers camaro v8 '78 has much much lower temps.. So the source of the heat to the fuel is fuel rail, which acheive such high temps.. I measured all possible area to define the source of the heat. And then the fuel goes hotter and hotter with the circulation tank/engine..

 

Hello again Domen,

You should check the fuel flow in your fuel "Supply" and fuel "Return" lines.

Many years ago I left my Corvette sit for a season and when I tried starting it the car would start and idle but not rev. I removed the fuel filter inlet and turned the Fuel pump ON and measured the flow in a big jug. The flow in my Supply line was seriously slowed down by a spot inside the fuel Supply line where the rust virtually blocked off the entire flow of gasoline. My Return line was fine compared to the Supply line. I ended up running a new Fuel Supply line and the car came back to life with the proper volume and pressure of fuel. Before the car could make the needed 43 psi but with extremely low flow rate, now it makes 43 psi and has the same flow it did when new.

If the fuel is spending too much time in the Return line that could be the cause of it getting hotter than normal. The only cause for that would be a blocked or partially blocked fuel Return line.

Another thing to keep your fuel cooler would be to put something very reflective on the fuel tank to repel heat. I have thought of doing it with my fuel tank as cooler fuel helps when you have higher compression. Cooler air and Fuel make the engine much happier. What circulation tank/engine are you talking about?

The idea of a Plugged Catalytic converter is still out there, have you verified that the Catalytic converter is flowing properly?

 

Hi! Thanks for all suggestions!

Yesterday after an hour normal drive I did measured 630 deg F temp on the catalytic converter.. Based on Google research it is way normal.. I havent measured the flow but based on the performance of the car Im sure its not clogged, at least fully clooged..
I did play with vacuum lines at the ecg solenoid- when I pulled the line off the idle started to go rough, when put back all back to normal.

Last year I did blow the fuel supply and return line with compressed air. from fuel rails to the tank.. Both seemd to be OK, air flow seemed OK- but I didn' t measue the flow rates.. So the idea of partially blocked line could still be the cause..

Do you think slow flow fuel rate would make fuel temp higher compared to fast flow rate, knowing the source of the fuel temp is hot fuel rail? If the fuel is too much time spending inside fuel rails it gets very hot.. If it goes thrue very fast it has no time to get hot, but it comes back again quicker..