Hi!

I’m new here and I own an original ‘86 corvette C4 for three years now. I have read lot of posts here on your forum- got nice know how about these cars.
Here my C4:



I use the car only as a summer car- here in Slovenia summer means approx. 3 months per year-no daily driver.. and also spring+ autumn time when no rain..


Perhaps someone could help me with a problem I am dealing with since I bought the car. Fuel temperature gets so high that eventually car stops. I read many topics here about this issue with a simple solution- never run less than half-full tank so fresh fuel cools down the temp. In my case also this doesn’t help..

How it all began:

Soon after I bought the car, fuel pump started to become noisy. With each additional mile noise level increased, car got more and more loss of power and eventually car stopped. After half hour car started again and run poorly. Pressure in gas tank was enormous.. Next day, when all cooled down, story repeat.

After testing and testing fuel pump went broke.

I changed the pump and I thought I solved the problem. It was better but after 80 miles driving it started all again.. It was better only as the pump was new and had better performance.. rest the same.

Then I figured out/ got hint on the forum- when fuel level goes to half tank, I should fill it up. I tried and it was better. I was able to drive like 150miles with refilling after 100miles, but no chance to drive in this way for example 300miles. Fuel temperature gets to high even with refilling each 100miles.

As a next step I did wrap the gas lines in engine bay with temp. resistant tape- especially in area of exhaust manifolds.. I mounted also a fuel cooler/ radiator on the fuel return line from engine to tank/ reservoir.

It has improved a bit but still my range is approx. 200 miles.

All this at the environment temp 86°F- 100°F

Is there something I have missed or somebody has same problem as I do. For example I would love to go for a 1000miles 3 day trip with the car but no chance right now. Other than that the car is in healthy and perfect condition.
I would be grateful if you could help me in this case.


Greetings, Domen

 

I've driven my 86 many miles and in high ambient air temperature and never had a problem with the fuel being too hot. Unless it is boiling, I think the pressure in your tank is really the problem. The tank is vented to the charcoal canister and should not build up any positive pressure while driving. Air does enter the tank through the fuel cap, and if the wrong cap is used, a high negative pressure can result. My vent line was plugged. I found it by disconnecting the tank vent valve by the charcoal canister and hooking up my mityvac to the tank line. I could pull a high vacuum and it would hold all day. It was plugged solid, took me many hours to clear it. It should not hold any vacuum. If you can build a vacuum try loosening the fuel cap. If it then drops you have a defective or wrong fuel cap. Hope this helps you.

 

You have other issues besides fuel temp. No one has fuel temp issues

 

Hi Domen
nice car and nice location. It’s pretty clear that the issue is the pressurization of your fuel tank. So is the tank being pressurized or is it holding a vacuum? Either way it could be a blocked line. There is a fuel feed line, a fuel return line and a vent line. I would blow all three out with compressed air. Disconnect both ends of each line and blow them out. Also you could replace the fuel filter while you are at it. The fuel filter is located under the car on the RHS just forward of the door.

 

Hi,

Thanks for replys! I did change fuel pump, filter and injectors last year but didn't checked if any of lines are blocked. I Will clean them using compressed air as you said. Actually I have an overpressure in the tank.
So the issue could be that the fule does not return to the reservoair fast enough due to blocked fuel line and gets heated up in the engine bay too much. After miles of driving, fuel temp goes very high and pressure is being created in the tank. Both lead to power loss and car stop. This sounds logical.. Actually my fuel starts to boil in the rail- this I noticed as the car started to struggle on highway like if there was no fuel at some moments.. And later also fuel pump died. Once I put my finger inside filler neck and got almost burned.. The fuel from return line was all in bubbles already- almost boiling.. You think the slow circulating of fuel between reservoair and fuel rail could be the source of the heat the fuel gets?

Thanks, Domen

 

I had a problem with pressure in the fuel tank. I bought a cheap locking gas cap (vented) on ebay and all problems went away. Dan

 

gasoline boils at 395F so there won't be an "almost". It will be burn city. IT will be hot obviously since it has to go through the rail on top of the engine. To test your theory out, the fuel pressure should be higher since the return line is blocked. So check the fuel pressure when it is happening and report back. I think you have other issues.

 

Hi, I already use fuel cap which can release pressure. It helps to reduce intank pressure, but due to high fuel temp, fumes that are getting out are big amount. So still my problem is heating of the fuel... I will test fuel lines and measure pressure.. Like you said perhaps there is other issue that im dealing with, do you have any idea? What could be the reason for this high temp of the fuel.... Thanks, Domen

 

Also double check that there is no kink in the fuel lines inside the tank. I had that happen and it built up a ton of pressure and car quit til it cooled down.

 

I might add...the kinked line was causing the fuel pump to superheat in turn causing the pressure buildup. The pump was new, the hose was too long and kinked.

 

Hi, thanks on that. Yesterday I did blow the lines with compressed air and at same time checked the lines from fuel rail to the gas tank for any damage /kinks.. All looks ok and seems to work.. When I exchanged fuel pump I remember no kniks there as well, all intact.
Today I bought a IR laser temp gauge and played a bit measuring temp all the way from fuel rails to the tank. After approx 2h of driving (140mph on highway &#128513 and some cruising + idle all at ambient temp 95 °F with less than half full tank, fuel pump starts to become very very noisy.. Temp measured :fuel rail 176°F, fuel lines in area of fuel filter 140°F, fuel lines in the back before rubber lines to the tank 127°F, and tank filler neck inside 122°F.
If I would continue driving without gas refill the pump would go bad and shut off.. Fuel pump can't cool itself with fuel temp above 122°F. No unnormal pressure inside tank.. I was thinking to add a high capacity fan on the fuel coller I installed last year. I found a 210m3/h fan with small diameter of only 100 mm /4''.. In my opinion it would also help to install a fuel pump with better cooling performance.. I saw some high performance fuel pumps but not sure if colling is also better or is it only higher fuel capacity /pressure. What do you think? Currently I run New airtex fuel pump.. There must be something better.. Thanks, Domen

 

I'm not sure that for a stock car that a fuel cooler is worth it or thst the temperature you got is a big deal. Maybe the pump is on the way out?

 

I've got a 96 c4 with similar issues. Hard start, slightly rough idle and no power as you accelerate. Really rough over 55. I want to thank the forum for the detailed posts. Some of the checks posted, I've already done, some I haven't. I've got a long weekend and a lot of testing to do. I recently replace the plugs, wires and opti. I think I'll start by checking the firing order at the opti. I also want to check the temp at the cat. I have an 84 camaro Z28 that I can take a part and reassemble in my sleep. The 96 Vette is a very different animal. I'm learning a lot on this forum very quickly. Thank You

 

Hi Guys,

Thanks for your inputs!

Finally I made a break through and solved the issue J I did reroute both fuel lines between fuel filter area and fuel rails. Original fuel lines were very close to exhaust headers (?!) and all along the engine block.. I have measured temperature of the lines in that very area- definitely this was the greatest heat source which caused my problems. Based on this I pulled complete original lines and made new ones in a way to fully avoid the area of this heat source.. Fuel temperature measured now is much much lower compared to before (return 105°F at the filter area- before ca 140°F).

After modification I did test driving in total 600miles (500 miles one road trip- two days) .. no problem with fuel temp on very long distances, fuel reservoir filled up only when almost empty.. now I can enjoy driving J

If you have similar problem with fuel temp- that’s what’s going to do the trick..



Few pics from the trip..

 

Hey Domen
Thats great news. Interesting, I take it that your car has aftermarket headers that are too close to the original fuel lines. My car has aftermarket headers but they clear the fuel lines but quite a bit. There is also a bit of clearance where they are routed up the front of the engine. Anyway it good to hear that you have sorted it out and it’s great to see pictures of that beautiful Vette in Europe.

 

Hi GregMartin! Thanks on that. Actually headers are all original as well as were the fuel lines.. That was also main reason why I tried to beleive the lines here shouldn't be a problem.. Thus it turned out opposite.. Now all clear and I can focus on other things.. like driving 😉
​​Here in Slovenia, summer season is ending up slowly.. Domen

 

Hi GregMartin, thanks on that. Actually headers are all original as well as were the fuel lines. That's also reason why I tried not to beleive that's the case.. But now all clear and solved. I can now focus on other things.. driving Here in Slovenia, summer season is slowly getting over.. Domen

 

Yeah wow that’s even more interesting any all good now.
Just coming into summer here is Australia. My wife and I traveled round Europe for six months in a combi van back in the 90s and always planned to Go to Slovenia. Car trouble in Italy changed our plans. No making it to Slovenia is one of the few regrets we have from that trip it looks lovely.

 

Hi again,
I did some long nice trips this year.. Perfect ride 😀 I enjoy! See pic from today..

Thus the problem with high fuel temp is not fully solved as it seems.. The fuel on return line is getting hotter and hotter with each mile I drive and eventualy the fuel gets so hot that I loose power.. Higher the fuel temp lower the octanes.. After 2h driving, fuel is already on 127 °F.. Fuel rails constantly on 165 °FI changed already all possible parts of fuel system.. What is fuel temp on your return line? Any help highly appriciated. Domen

 

I would look elsewhere. The temperature of the fuel rail you are measuring is ambient underhood temperature, not the temperature of the fuel. Fuel pressurized at 40psi will not vaperlock. I would look at the ignition control module which is known to malfunction under hot conditions.