vapor lock TBI on 350 small blk

[BGoodale]

Hi guys; I'm having a problem with vapor lock that I cannot figure out. My other toy is a 78 CJ-7 with a chevy 350. It was installed by me 2 winters ago. During the summers vapor lock occurs often. I have rerouted the fuel lines, wrapped the pump, and on and on. I have a howell fuel system with the pump on the inside of the frame about 1/3 of the way up the tank. I have heard the fuel boil in the tank before! Would putting a spacer between the intake and throttle body help? Do I need to put the pump in the tank? The dual exhaust does come quite close to the tank . I have wrapped the exhaust and put a shield between the tank and exhaust. Any ideas. Thanks, Brett.

 

[JR]

How hot does your engine run? I've seen a hot engine (usually from advanced timing) create vapor lock once or twice. Also a lean mixture Can possibly cause it, but you would have likely noticed that by poor running conditions and by plug color. The most common cause I can think of is poor placement of fuel lines, and low fuel pressure, but it sounds like you've got them routed away from heat.
How can you tell your fuel is boiling in the tank? It is at the rear of the vehicle right? Your positive it's venting properly, not creating a vacuum (or pressure)?

 

[Wayne M.]

Hey Brett. From what I'm reading, I don't think you have a vapor lock problem where you think you do. If I understand properly and that the fuel pump is mid way up from the tank and likely above mean fuel level, I'm betting the pump is losing prime.
I remember years ago doing an install on a similar Holley pro-jection kit. they wanted the pump low on the frame, near the tank, and a loop going up on the inlet side. This way the pump would never go dry.

The Howell stuff is cool. Does it have O2's and run in closed loop?

 

[LNaugle]

Also... Does your intake still allow the heat riser to work? If so it is heating the underside of the TB. Get a set of FEL Pro gaskets that block the heat crossover, injection doesn't like it!

 

[leaky gasket]

You may want to try a phenolic spacer between the throttlebody injection and the intake manifold. This will help greatly with the heat transfer. You all you also may want to try to put some lovers in your hood or space up the back of the hood just a little bit.

 

[Wayne M.]

I disagree with any vapor lock in a pressurized gasoline FI system. If anything like that were to happen on say- a hot soak, then the injectors will purge on start up. Anythings possible though. With carbs when you're heating a float bowl and storing un pressurized gasoline, then vapor lock is a real problem.

On the OP. you can hear gas boiling in the fuel tank??

 

[BGoodale]

Thanks for the reply. I have heard the fuel boiling in the tank. This last trip we took, it started to vapor lok at about 10,000 ft. We live at 7000 ft. and frequently jeep at 12 to 13k feet. The venting issue has had me vent properly to no vent to try and push the fuel. Now I'm using a cap that vents in but not out and the vent tube is closed off to the filter canister. That scares me a bit but one of my buddies has a 350 in his toyota land cruiser and does the same. Any other thoughts? Thanks, Brett

 

[BGoodale]

Hi Wayne; Thanks for your reply. It does run on closed loop and does have o2 sensor. The pump is low in relation to the tank but is a ways from the tank. I had it on the cross member just out of the tank but that was too high so I've relocated it so that the pump is lower now. Thanks, Brett

 

[BGoodale]

Thanks LNaugle; It does not have a heat riser, but the next thing I'm going to do is buy 5 gaskets silicone them together and install them under the throttle body. Thanks, Brett

 

[B.G. Smith]

I would guess the pproblem has to be before the fuel pump and is causing the pump to vapor lock. How much line is exposed between the tank and the pump? What pressure does the pum put out when normal? If the return line from the pressure regulator is not insulated the hot air from the engine/radiator will vaporize or at least het the fuel returning to the tank caausing the problem to be worse. What is the material you used for the shield between the tank and the exhaust? If it is metal it probably is not doing a very good job. All the fuel liones under the vehicle need to be insulated from the tank to the engine. There are some materials available where you can wrap and then mud the line/tank that really work well, you might have to find an industrial insulation place to find them. bg

 

[B.G. Smith]

You need to get the pump as near the tank as possible. bg

 

[MGreer]

Brett; Do you still have the original metal fuel tank or have you added a plastic replacement tank?

 

[Wayne M.]

Thanks for the reply. I have heard the fuel boiling in the tank. This last trip we took, it started to vapor lok at about 10,000 ft. We live at 7000 ft. and frequently jeep at 12 to 13k feet. The venting issue has had me vent properly to no vent to try and push the fuel. Now I'm using a cap that vents in but not out and the vent tube is closed off to the filter canister. That scares me a bit but one of my buddies has a 350 in his toyota land cruiser and does the same. Any other thoughts? Thanks, Brett

IIRC the throttle body has the regulator built in? Maybe at 7000' you might have to raise fuel press a bit.

 

[leaky gasket]

Wayne brings up a good point. I went to the Howell website to check out their systems, Looking out the universal TBI kit they use GM 86 to 92. If memory serves right I think GM had vapor lock issues withthis particular TBI also. It would be great if we can go back and look at technical service bulletins from that era. But I believe what they did to fix it was up the fuel pressure from 18 pounds to 23. Also are you running headers or cast-iron exhaust manifolds and what about your intake aluminum or cast iron? I think your idea of adding gaskets to try and help insulate is a great idea and will go a long ways. You have a lot of heat in a very tight compact area anything you can do to insulate what would be to your benefit.

 

[Wayne M.]

Been thinking about the boiling in the fuel tank. Perhaps the pump is cavitating or similar and sending air back to the tank via the return? Just a thought.
Newer vehicles have returnless fuel systems where there is no return and the line deadheads right at the rail with no regulator. This not to be confused with the Chrysler system that had the regulator with the pump in the tank. I know Ford started about 10 years ago and they were controlling the pump via Pulse Width Modulation and using a pressure sensor in the rail as a feedback. They did this to figure on the engine's demand, and also to raise the rail pressure when temps got hot under the hood. I'm sure they had a factor for altitude too.

 

[JR]

IIRC the throttle body has the regulator built in? Maybe at 7000' you might have to raise fuel press a bit.

I briefly touched on that in my first post, and after seeing where he is in elevation I would definitely check into the f. p. closer. Growing up in Laramie which is considered a valley at 7000 ft, we would often ride our dirt bikes and snowmobiles up to the summit which is over 10,700 ft. We were constantly re jetting to stay ahead of lean/rich conditions. I also remember having a problem with an AMC that was giving us fits on hot days, long story short replacing the weak 20 yr old pump solved our problems







I'm wondering how the gas can actually be boiling in the tank? I've seen it once before on my 450 dirt bike that was overheating in a bad way, and obviously with the tank sitting overtop of the engine it was like a boiling pot of water. Just trying to wrap my head around it boiling in a tank at the rear of a vehicle with no heat source... . strange

 

[Hoefler]

When I installed a 383 Stroked Stroker in my 83 Chevy Pick Up, I installed Edelbrock port fuel injection. I was experiencing similar problems with mine. I found that the intake air temperature was getting way too high, especially when traveling at low speeds or after a hot start up. The temps were as high as 230* and would never really come down. I was running a K&N open air filter. I went back to the factory filter housing and snorkel to the radiator support. While I still experience the hot start temperatures, after starting, the air temperature quickly went back to ambient in a matter of seconds. This allowed me to dial up the timing and lean it back out. The second issue I was having, was hot fuel return. With a 20 gallon fuel tank, the fuel in the tank would get to the boiling point. I looked into fuel cooling cans, but decided that the need for ice to keep it cool was not very practical out on the highway towing a trailer. Since the A/C was in use when I had the most problems, I came up with the notion of possibly using it to cool fuel. I wrapped 3/8" copper tubing around the accumulator/dry about 6 times and used stainless hose clamps to keep it tight to the dryer. Then I hooked up the return fuel line to my new cooler. Went for a heavy tow with about a 1/2 tank of gas, it was in the mid 90's, and never experienced any power loss or anything.

 

[rscurtis]

IIRC, a certain vintage of V-12 Jaguars required fuel cooling from the AC system. If the AC was non-functional, the car would not run properly.

 

[Wayne M.]

Yes. More recent, and what I've experienced. The last of the 4. 0 Cherokees liked to boil the fuel in the rail when idled in hot traffic too much. This would cause the MIL to come on and misfire codes set.

 

[Wygate]

Return line? Working?
Didn't see it listed.
I got so fed up w/ issues like this I transplanted a stock TBI pump into my CJ tank, 7,8 years on it now, now vapor lock issues again
Is the heat shield on the lines spaced off, if not eventually everything will become the same temp. Lean will hurt like has been pointed out.