GSL-SE Vapor Lock
 

I was having a problem with vapor lock over the weekend. I did it when it was very hot in traffic at high altitude. The car is an '84 GSL-SE that is completely stock. Fuel pump is new and good and the fuel filters have been replaced.

It seems like the problem is at the fuel lines under the intake are sitting right on the motor. Is that normal? I'm thinking that insulating the hoses will fix the problem. Under normal driving in the heat the fuel tank is building a bunch of pressure. I think the pressure is caused by the vapor lock.

I did blow out the vent lines with a compressor and inspected the rollover valve and charcoal canister. All looks good now. If I blow through the lines with everything hooked up, I can feel some restriction. Is that normal?

The vent line could be clogged. It was on PercentSevenC's 83. His tank would blow up like a balloon. His temporary solution was to unhook the vent line near the tank and removed his charcoal cansiter. Or maybe he just unhooked the charcoal cansister. He'll have to chime in.

I actually did unhook the vent line at the tank for the trip back hoping that would fix the problem and it still happened. I'm thinking the problem I'm having with the vent is most likely the roll over valve. I can blow through the valve with it removed just fine so I'm not sure. I'm going to try blowing out the hard line again and see if that helps.

cannot possibly be vapor lock. what it could be is a clogged charcoal cannister. this incorporates the tank vent, so when they get clogged, the car does all kinds of weird things.

actually what can happen with a clogged tank vent/charcoal canister is that it can draw a vacuum on the gas tank (the 83's put pressure on the tank, there was some kind of fix for that), and with a vacuum on the tank, the fuel pump can't pump!

take the gas cap off, and see if it changes

It happened with both the charcoal cannister connected and disconnected. When I had the vent system completely hooked up, it built so much pressure that it sprayed gas out the gas cap when I removed it. I did blow out the lines and it was still building pressure. I tried just disconnecting the vent at the charcoal cannister and it still built pressure. The vent problem has to be between the tank and cannister.

With the tank just venting to atmosphere before the valve, it didn't build any pressure at the cap. It still vapor locked though.

I have two other charcoal cannisters that I can try. One is off my '83 and I know I never had any problems with it.

Subscribed! My 83 and my 82 both build up pressure so I'm interested in seeing what the reolution to this one ends up being.

weird. time to disconnect the vent line at the tank and see what happens. i think the vent line just goes right to the canister. the roll over and there is another valve (i think) under the car could be problems.

The line goes from the tank to the roll over valve to the hard line to the charcoal cannister. I disconnected the line between the tank and valve and drove it like that. I still had the problem.

I know part of my problem is the vent not working right and the pressure building but it isn't the real problem.

The hills I was driving up are some of the hardest in the country, this isn't normal traffic. I'm talking huge elevation climb and starting at high altitude. Vail pass goes from Vail (8022 feet) to the summit (10617 feet). And this was in really bad traffic, it was basically a parking lot. There were cars overheating and vapor locking everywere. I got stuck in a spot with 2 other cars with the same problem. I would say there were over 100 cars that overheated that I saw. I'm really happy my car wasn't overheating, it acually stayed right where it should.

The intake got really hot, I couldn't even touch it. I made it to a mountain stream so I cooled the intake down and that really helped. I also drove the rest of the way over the pass with the hood popped open so I could get more airflow.

hmm...i gotta keep an eye on this...i'm planning on bringing my rx7 to the springs next year..from washington...thinking about driving it...if i do..it might be easier to go through utah and I-80 than try to go through I-70

You're probably fine as long as the traffic isn't bad. Also this may just be a problem with my car.

What actually happens? Does the engine die suddenly while at idle? Does it die while you are pressing the throttle? Does it run rough, then die?

Since the problem happened at high altitude, have you checked the atmospheric pressure sensor? It is on the plate under the passenger carpet with the ECU. If it is not working the car would run rich at higher altitudes. Hard to believe it would cause the car to die. Just a thought.

From the 84 training manual and the 84 FSM...

https://www.rx7club.com/attachment.p...1&d=1310154382

https://www.rx7club.com/attachment.p...1&d=1310154575

It feels like it would if it was running out of gas. It will be running fine than it will start to stumble when I push the gas but still idle. Once that starts about a minute or so later it will stall. If I start it back up, it'll start right up but stall immediatly. No smoke at all on startup.

I haven't checked the almosperic pressure sensor yet but I'll check that.

Vapor lock is almost non-existent on fuel injected cars, because the pump is not in the hot engine compartment. Back in the day (pre 80) carbed engines often had a mechanical fuel pump attached to the engine. When the car was idling the fuel would move slowly in the fuel lines and pump. Since the fuel pump was higher than the tank the fuel between the tank and pump was being sucked all the way to the pump. That means the fuel is under less pressure (lower boiling point) and, when the flow slowed, it could get hot enough to vaporize in the lines. When the vapor bubble reached the fuel pump it could stop pumping.

All RX-7s have a return fuel line and an electric fuel pump near or (FC and FD) in the tank. That means it is pushing the cool fuel from the tank to the engine and any fuel not needed returns to the tank. So the fuel flow never really slows down. It doesn't have a chance to heat up. If a bubble formed after the pump, the flow from the pump would just push it through. You might have a hiccup, but it wouldn't break the prime in the pump.

The other reason that I think it is vapor lock is that when the car started to stall the pump would start to make a ton of noise like it was running out of gas. Now that i think about it, This happened when I was on a steep grade of over 7%. The first time it happened was on floyd hill wich really isn't any higher than colorado springs, just very steep. That was the time the tank built so much pressure that when I opened the gas cap it sprayed close to a gallon of gas out.

I was doing some looking online at fuel injection cars with vapor lock. What I found is that it is rare but it does happen. The reason that they moved the pump to in tank was mainly because it prevented problems like this.

Posible causes for the car stalling that i found:
-bad temp sensor (already replaced)
-weak pump (less than 6 months old)
-clogged fuel filter (replaced about 3 weeks ago)
-bad pressure regulator (haven't looked into)
-fuel line getting way too hot

any ideas of what could be causing the problem?

if the pump got really noisey during the problem time this would indicate starvation(ie lack of fuel to the pump) drop the tank and check the pump sock for dedris. while you have the pump out replace the sock, cheap. it could be you were just fuel starving the pump and everything else is just a fluke and not related. just a place to start. at high altitude there is a lot of demand on the pump due to lack of air in the fuel system. just a thought

I actually don't have a filter in the tank. I couldn't find a replacement so I have a filter between the tank and the pump. The first time it happened, I pulled the filter to see if it was clogged and it was fine.

My 85 GSL has been building up a lot of pressure in the tank, too. Runs just fine if I remove the gas cap, but if I have the gas cap on, it builds up pressure.

I would clean out the vent lines, check the valve, and check the charcoal cannister. Your problem is most likely one of those.

I'm going to swap out the check and cut valve on Friday because I have a good one and I think this is part of my problem. I'm also thinking about replacing my pump because this could be the problem and the one a have is still under warranty. The other possibility is the fuel pressure regulator so I may be swapping that out as well soon.

Mine was doing the same kinda thing here in town lol!!! I checked the sock that snivley whiplash was talking about and it had some debris in it. I have a about 30 miles or so and no vapor locking so far. I also changed my fuel filter.Im here in springs to and think I seen you cruising around the other day.Traffic was lame so I couldnt get to you.

I actually had that problem in the past before I had my tank dipped. I'd going to see about getting a new fuel pump this weekend. I'm hoping that fixes my problem.

Also I PM'd you.

I swapped out the check and cut valve with the one off my other car. I also replaced the fuel pump under warranty over the weekend.

I need to get a hold of a fuel pressure gauge that I can use to check and see if my pressure regulator is working properly.

The fuel tank is still pressurizing. Yesterday it was about 95 on the way home and when I got home I could hear a wine coming from the filler neck. I removed the cap and a bunch of pressure existed the tank.

Talked to SIMPLESOUND and he is having the same problem. Maybe he will chime in.

He said he talked to Pineapple Racing about this. Basically he said that it is actually vapor lock and it happens on these cars when it is a combination if high altitude and very hot. They said the fuel is boiling at the fuel rail and recommended having a fan blow on it to cool it off.

So I now really plan to insulate the hoses and fuel rail.