What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

76’ 400ci overheating bad

CraigFulton said:
This is a fun ride to be on! Haha. I will get it Wally warmed up and get more temp readings. Ordering the exhaust wrap next. I’ll do that and the EFi all at once.
Click to expand...
1 THING AT A TIME ! :deal: or you can go in circles fixing a problem you have no idea were it started .

what efi kit you thinking of ? and plans for pump and tank ? lots of us use stock efi tank from 87-up and sender . then swap on a ep381 pump for plug / play no mods 60psi fuel pressure . https://www.rockauto.com/en/moreinfo.php?pk=90717&cc=1053380&jsn=493 .
 
sweetk30 said:
1 THING AT A TIME ! :deal: or you can go in circles fixing a problem you have no idea were it started .

what efi kit you thinking of ? and plans for pump and tank ? lots of us use stock efi tank from 87-up and sender . then swap on a ep381 pump for plug / play no mods 60psi fuel pressure . https://www.rockauto.com/en/moreinfo.php?pk=90717&cc=1053380&jsn=493 .
Click to expand...

I picked up this new unit Holley just started making Sept 14. https://www.holley.com/products/fue...sniper_efi/sniper_efi_quadrajet/parts/550-869

I have a new tank. Going to put an ‘87 sending unit in it with holleys 60psi in tank pump for the ‘87. Running all the Earls vapor guard high pressure fuel lines, Holley regulator on the return, and an earls pressure gauge at the inlet.

This is the fuel pump. https://www.holley.com/products/fue...efi_fuel_pumps/efi_in-tank_pumps/parts/19-369
 
Anyone know the purpose of this line? It’s has a little bell like piece on the tank side with a ball on it. I was planning to cap it in this EFi conversion. Was also going to cap the return because I don’t think it’s big enough for this amount of flow and add a 3/8” return on the tank.

1315F9B9-8E4D-4954-8367-E5F0F85855C9.jpeg
 
How important is it that the tank has the baffle in it?

I feel like I know the answer to this already. Damn another $100. How do I adapter the filler hose to fit this neck?
 
Last edited:
CraigFulton said:
How important is it that the tank has the baffle in it?

I feel like I know the answer to this already. Damn another $100. How do I adapter the filler hose to fit this neck?
Click to expand...
On the street, the baffle probably won’t be missed

The tank hose and filler hose sizes that different?
I slipped a section of my old 77 filler hose inside the filler hose for the 89 tank
 
Bent77 said:
On the street, the baffle probably won’t be missed

The tank hose and filler hose sizes that different?
I slipped a section of my old 77 filler hose inside the filler hose for the 89 tank
Click to expand...

I’d prefer to not upgrade the tank if I don’t have to, but I bought it anyway.

Someone on the review of the tank said that they had to adapt the filler hose on their ‘79 to fit the neck on the tank. That it’s smaller on the tank.
 
Last edited:
GM did change the fill neck diameter at some point. AFAIK however that was done once they went to the hidden fuel cap, so I don't think it will be something you can just swap out like you can with the hidden cap setups, since the metal fill portion is interchangeable.

GM did not send these things out vapor locking, running fuel lines outside the frame is at best a bad idea IMO. I have ripped wiring off that was run outside the frame rail, and that's not four wheeling, there is no way I'd run fuel that way. If your EFI uses a return line, that can HELP with a vapor lock issue (as well as the pressure), but it uses the tank and lines as cooling, so any heat dumped into the fuel along the way will heat the tank and raise the fuel temp.

Run a tank breather. The best method is through a vapor canister (EVAP) and back into the throttle body, but theoretically it can be vented anywhere. My experience with this is that if you just vent it, you will smell fuel often. My experience with a vented gas cap on the K5 is that when the tank is full, fuel can/will leak out when it sloshes, or if climbing a relatively steep hill.

FWIW the spring in the lower radiator hose is a factory deal, because they used to fill them with a vacuum system, and the hose would collapse. It is not needed in a pressurized cooling system, factory configuration, working properly.
 
dyeager535 said:
GM did change the fill neck diameter at some point. AFAIK however that was done once they went to the hidden fuel cap, so I don't think it will be something you can just swap out like you can with the hidden cap setups, since the metal fill portion is interchangeable.

GM did not send these things out vapor locking, running fuel lines outside the frame is at best a bad idea IMO. I have ripped wiring off that was run outside the frame rail, and that's not four wheeling, there is no way I'd run fuel that way. If your EFI uses a return line, that can HELP with a vapor lock issue (as well as the pressure), but it uses the tank and lines as cooling, so any heat dumped into the fuel along the way will heat the tank and raise the fuel temp.

Run a tank breather. The best method is through a vapor canister (EVAP) and back into the throttle body, but theoretically it can be vented anywhere. My experience with this is that if you just vent it, you will smell fuel often. My experience with a vented gas cap on the K5 is that when the tank is full, fuel can/will leak out when it sloshes, or if climbing a relatively steep hill.

FWIW the spring in the lower radiator hose is a factory deal, because they used to fill them with a vacuum system, and the hose would collapse. It is not needed in a pressurized cooling system, factory configuration, working properly.
Click to expand...

Great input! Thank you. So I should add a charcoal canister on the 1/4 vent on the sender. Where should the other port on the canister go? What if I don’t add one at all and block the port on the sender? I am running a return line from the throttle body back to the tank and adding the by-pass regulator on the return as recommended by Holley.

Im not dead set on running the lines outside the frame rails. I did buy some
Exhaust wrap to help with heat on the downpipe.

I think my vapor locking is happening because of what you described. It’s heating up near exhaust and returning to the tank and heating all of the fuel.

I’m going to keep the gas cap that’s on it. It has a spring loaded vent in it. I’ll adapte the filler to the tank neck with proper hoses.

Thoughts?
 
Someone here (Forrest?) I want to say measured fuel tank temps. You could do it after it sits for awhile, should be ambient, then after the drive. I assume you have a return style system.

"out" canister port should go to a spot on the throttle body, I'd ask the manufacturer what they recommend. If you plug it the tank will expand and *hopefully* vent out the cap, but unless a really old cap, they don't vent until 16PSI, which is a lot of pressure for the types of clamps, seals and fittings used in the fuel system.

Is the float level set high enough? It sure sounds like a lean condition if the exhaust is stock, in the stock locations, and working properly, but getting as hot as you describe. I had an issue in the past where the float level caused issues as the truck warmed up. Ran fine until the carb got hot.
 
dyeager535 said:
Someone here (Forrest?) I want to say measured fuel tank temps. You could do it after it sits for awhile, should be ambient, then after the drive. I assume you have a return style system.

"out" canister port should go to a spot on the throttle body, I'd ask the manufacturer what they recommend. If you plug it the tank will expand and *hopefully* vent out the cap, but unless a really old cap, they don't vent until 16PSI, which is a lot of pressure for the types of clamps, seals and fittings used in the fuel system.

Is the float level set high enough? It sure sounds like a lean condition if the exhaust is stock, in the stock locations, and working properly, but getting as hot as you describe. I had an issue in the past where the float level caused issues as the truck warmed up. Ran fine until the carb got hot.
Click to expand...

I’m installing the Holley sniper EFI. There is nothing on the throttle body for a tank vent. I can buy a charcoal can and add it. I guess I would just run the line into it and that’s it.

The gas cap is a brand new cap. It definitely works. If I apply slight vacuum to it it opens.

What you describe at the end is EXACTLY what I’m thinking. I feel it’s running lean at times. Carb is getting super hot. I rebuilt the carb and set the float ever so slightly lower than required. Maybe that was a mistake? Regardless I’m over the carburetor and ready to be on EFI.
 
Does that intake have the exhaust crossover in the middle? Maybe the exhaust passage is heating up the carb more than normal due to a blockage or something.... Just a thought:dunno:
 
shady said:
Does that intake have the exhaust crossover in the middle? Maybe the exhaust passage is heating up the carb more than normal due to a blockage or something.... Just a thought:dunno:
Click to expand...
It has the crossover. In one of the measurements and pictures. I showed that the choke is there and that part of the intake is hot as hell. 238 degrees.

Which brings up a good point. I need to block that passage for the EFI.
 
Last edited:
That shouldn't get that hot under the carb.. think your on to something there
 
Is the EFE (assuming it has one) stuck shut? I would *think* one side would be exponentially cooler than the other if that was the case, but they can stick, this much I know. Which would dump a lot more heat under the carb.
 
Da
dyeager535 said:
Is the EFE (assuming it has one) stuck shut? I would *think* one side would be exponentially cooler than the other if that was the case, but they can stick, this much I know. Which would dump a lot more heat under the carb.
Click to expand...
Damn this could be it. Because wrapping the fuel lines did nothing. Points to a hot carb being the problem. But last thing I want is that heat on the new Holley.

Where is the EFE located? Is that at the passenger side exhaust manifold where the down pipe is attached? I see some kind of valve there.

Does the charcoal can just go to a manifold vacuum port?

I think I’m going to install new intake gaskets and seal off the crossover ports. Thoughts on this too?
 
Last edited:
CraigFulton said:
Da

Damn this could be it. Because wrapping the fuel lines did nothing. Points to a hot carb being the problem. But last thing I want is that heat on the new Holley.

Where is the EFE located? Is that at the passenger side exhaust manifold where the down pipe is attached? I see some kind of valve there.

Does the charcoal can just go to a manifold vacuum port?

I think I’m going to install new intake gaskets and seal off the crossover ports. Thoughts on this too?
Click to expand...
I think that is contributing to the vapor lock but the transmission being 360, next to the exhaust is a separate issue that is a big deal.
You can kill the transmission with that much heat.
I think you found the causes for both issues you have.
The valve might be the cause for the hotter than normal exhaust.
I have my exhaust that close to the transmission and it's never this hot.
I removed the valve on my truck
 
So that valve on the exhaust manifold just where the downpipe connects could be partially close and causing this? Jesus. Lovely. Then I wonder if more exhaust than normal is going over that crossover because of that because it has no where to go.

How do I remove this valve? Google says it’s an exhaust heat riser valve.
 
Last edited:
I think you can just check the valve. I've never played with then, but they work off heat, I'm assuming they should move freely when the engine is off and cold.

Ask Holley how to run EVAP. It's technically a vacuum leak, and it can add a minute amount of combustible gas. GM normally ran a solenoid on efi setups, so the ecm "knew" what to expect but switching it, I assume in terms of loss of vacuum and potential fuel addition
 
You must log in or register to reply here.

Latest Posts

Top Bottom