Vapor Lock!

[Hodgeee]

My neighbor has a 2009 tahoe and we started talking about our trucks. He has had a vapor lock issue for three years since moving to vegas.

His trucks on 80 plus degree days drives perfectly, until he stops somewhere for a while. When he then gets back in to drive, his rpms go all over the place, and he has a similar lunging problem at slow speeds, or when coming to a stop. After about half a mile of driving it goes away, unless of course he stops and lets the vehicle sit for a while. We in Vegas had about 4 days where the weather was low 70s, and he said it went away, and never comes back until the hot weather returns. He was told by the dealership that it was Vapor Lock and was common on 07 to 14 GM trucks and SUVs out here. Mine does this a little, but only when it gets into the 90s, but its not bad.

Ive been told by others in forums that they never hear about this. Ive also read that since they got rid of the return fuel lines on the fuel rail, that this problems started. I have been researching to see if there is a fix, to no avail. Very few posts, and next to nothing on this forum when searched.

Does anyone have an idea what could help? I have thought that maybe wrapping the fuel rails, and removing the bueaty cover could help, for mine does it exactly under the same condition, of sitting after the motor has warmed up. I drove his truck and its pretty bad, does it constantly if you stop for just a couple of minutes like to get a pop to drink or something at a convenience store. He said on 100 degree days, it just does it all the time.

I have noticed that when working on mine under the truck, that the radiator emanates a ton of heat, and also that they fuel rail goes right bye the catalytic converter and transmission. Was thinking of strapping an aluminum heat shield on the driver side cat, to see if this would help.

Appreciate any ideas.

 

[Dustin Jackson]

@Hodgeee I think I was the one that said that I've never heard about vapor lock being an issues with these vehicles.

I live in Redding, CA and when I compare the weather of my city to yours we have hotter days over here. I've had my Tahoe about 4 years and have driven it all around the western US at the peak of summer and haven't experienced what you are describing. Nor have I ever heard of a 2nd hand account of another person having a similar problem.

Curious if you have E85 where you are at and if you are up to testing with that to see if it changes anything.

 

[Hodgeee]

Interesting, ive driven a couple of these trucks, and some do it, most dont, its odd. Ive only read of a couple other people on forums with the same problem, but no solutions. Mine is very minor, hardly noticable. My neighbors is real bad. Im gonna try the wrap and report on it. I have now had two GM techs that say its common out here. I just dont know why some have the issue. I dont care about mine, but the nieghbor, if mine was like that, i would probably trade it. This is my third Tahoe, first time with probs. Ive read also that others had this with first and second gens too. So uncommon with any vehicle today.

 

[OR VietVet]

So, an answer to the E85 question, @Hodgeee?

 

[Hodgeee]

Found e85 station, gonna have him fill up
Today. Should be hot enough today.

 

[petethepug]

That’s also the behavior of an LS motor needing a tune up. The tech will clean the throttle body and run a fuel injector cleaner, add new plugs & leads.

Running a tank of e85 will also act as a tb cleaner and scrub any carbon deposits from the system.

 

[Dustin Jackson]

@Hodgeee I don’t think E85 is a cure all but it’s just a bit different than gasoline and I’m curious if your Tahoe behaves differently with it. I believe E85 has a higher evaporation temp than regular gas so in theory if vapor lock is occurring then E85 should react differently.

When I search the internet for “Chevy 5.3 vapor lock” I don’t get many results and the posts I have come across just mention possible fuel pump or tank venting issues so I’ll be curious what this ends up being.

 

[strutaeng]

It's probably something else going on. I've never heard of "vapor lock" before, and I would consider myself an intermediate, or maybe even advanced DIY-er (courtesy of YT diagnostics channels, LoL).

The way the ECU monitors fuel trims, O2 sensor data, spark advance, pwm fuel pump duty, etc, I would think it will throw the money light on if it detects something really out of wack. Maybe something intermittent?

Google says vapor lock was a larger issue with carburators and low pressure fuel systems. Carburators was before my time, so I don't know...

 

[Geotrash]

Can't be vapor lock at 43-45 psi on the fuel rail. The RVP of gasoline at 100ºF is no more than 9 psi in the US, and in places like Phoenix they formulate it for 7 psi in the summer. Gotta be throttle body, vacuum issue or something else.

 

[OR VietVet]

Having been in shops for 35+ years, I saw my share of vapor lock concerns with carbs. When the high pressure fuel injection systems came along, the concern with vapor lock, went away. So many components monitoring and making bunches of adjustments, per second. Correct fuel octane and clean fuel are important. There is always a reason that a manufacturer dictates a certain fuel in the owners manual and it is not because they are getting a kick back from the major oil companies. In this case, a tank full or two, of E85 is worth the effort and see what happens.

 

[Hodgeee]

Very interesting. Mine does it a little also, and mine has all new components and vacuum lines plus all new evap components on the tank. I have read that sometimes it still happens with fuel injection vehicles, but very rare. Im real curious to have him fill up with the E85 and see if it fixes the problem. I was surprized also when two different techs at two different Chevy dealerships told me they run into this often out here.

After doing some research i found it is very common on earlier fuel injected jeeps. And they have specific fuel rail kits with heat wrap and heat shields. Also found that guys that have offroad LS fuel injected engine race vehicles have heat soke issues and they wrap their rails and fuel lines. This is where i got the idea of doing the wrap.

Might be jumping the gun here, gotta wait and see. He stated he ran no ethanol gas from maverick but made it worse on recommendation from dealership. Looking it up, 10% ethanol gas boils at 140 degrees, non ethanol can start to boil at 110 degrees. E85 is 173 degrees F. I have heard the gas boiling on older muscle cars out here durring the summer. Its crazy when you can hear it, like a pot of water on the stove.

 

[Dustin Jackson]

@Hodgeee Another test you can do, drive it for a while and get it nice and hot and then bring it home and pop the hood and put a fan on it for 5 minutes to cool the top of the motor down and try and see if the problem persists.

 

[Geotrash]

Very interesting. Mine does it a little also, and mine has all new components and vacuum lines plus all new evap components on the tank. I have read that sometimes it still happens with fuel injection vehicles, but very rare. Im real curious to have him fill up with the E85 and see if it fixes the problem. I was surprized also when two different techs at two different Chevy dealerships told me they run into this often out here.

After doing some research i found it is very common on earlier fuel injected jeeps. And they have specific fuel rail kits with heat wrap and heat shields. Also found that guys that have offroad LS fuel injected engine race vehicles have heat soke issues and they wrap their rails and fuel lines. This is where i got the idea of doing the wrap.

Might be jumping the gun here, gotta wait and see. He stated he ran no ethanol gas from maverick but made it worse on recommendation from dealership. Looking it up, 10% ethanol gas boils at 140 degrees, non ethanol can start to boil at 110 degrees. E85 is 173 degrees F. I have heard the gas boiling on older muscle cars out here durring the summer. Its crazy when you can hear it, like a pot of water on the stove.

I have no doubt that they theorize that vapor lock is the root cause of the problems they're seeing, but it would defy the laws of physics. There has to be another cause.

 

[Hodgeee]

I wouldnt say it defies the laws of physics, if it gets hot enough it can still happen. Ive now found that it does happen from time to time on all different vehicles. Also these have non return fuel lines, that causes direct pressure, leaving no room to push out the vapor. So i can see it as an old used to be mechanic.

I watched a video on youtube, with a rally truck ls motor, where the guy swapped his fuel system to a return line rail due to power loss from fuel vapor.

 

[petethepug]

What’s the service / tune up history on the motor?

Have you pulled any DTC off it yet? Bottom line is you’ve gotta work off data. The dealer telling you “vapor lock” is really weak sauce. That’s typically a blow off to customers (up’s) that don’t seem to have something easy to fix or make a quick buck on.

 

[Hodgeee]

Ok, he got back with me. After his 20 minute drive home, he parked the truck for 20 minutes, then went to drive it. He stated that the issue was still there, but the mildest its been in this weather. He then drove for 20 more minutes and parked again, waited 10 minutes and went for a drive. He stated it would badly fluctuate for about a mile of driving, but seemed like it settled way faster. He says he will continue to use this, as its a dollar a gallon less than regular, and he said the truck really livened up. He told me before when the temps are in the 70s it doesnt do it at all.

I think i will try it tomorrow since its time for my refill also. I found this very interesting. Mine doesnt do it unless its in the 90s temp wise, but if it makes more power, ill try it once.

So if this is working, or at least helping, maybe it is Vapor Lock. I thought the same, that it was a dealer blow off, instead of spending hours to diagnose the problem for just a diagnosis fee.

Mine didnt do it bad unless it was in the 100s. Now with this cooler weather it doesnt seem to do it at all.

No check engine lights, and i used my xtool d8, no dealer codes either???? Freakin wierd. I had mine checked and they said they couldnt reproduce it, but since its pretty mild, i just dont care, ill live with it.

 

[petethepug]

Order a new oem carbon canister for the fuel system. Replace it. It’s time, no matter what. If the carbon pellets fall out when replacing it, you’ve got your answer, contaminates in the fuel pump, fuel lines, fuel tank & vacuum system.

It won’t throw codes. It’s intermittent with the only constant being, the lower the fuel level goes, the more the pellets can obstruct things. Of course, when the motors off, the fuel pressure stops sucking them around, so a completely different kind of obstruction occurs on the next drive. AKA: gremlins.

There’s a fix, but won’t get into it until you verify if the carbon canister is compromised. It sounds like the e85 wiped away a lot of the petroleum and carbon residue.

 

[Geotrash]

Ok, he got back with me. After his 20 minute drive home, he parked the truck for 20 minutes, then went to drive it. He stated that the issue was still there, but the mildest its been in this weather. He then drove for 20 more minutes and parked again, waited 10 minutes and went for a drive. He stated it would badly fluctuate for about a mile of driving, but seemed like it settled way faster. He says he will continue to use this, as its a dollar a gallon less than regular, and he said the truck really livened up. He told me before when the temps are in the 70s it doesnt do it at all.

I think i will try it tomorrow since its time for my refill also. I found this very interesting. Mine doesnt do it unless its in the 90s temp wise, but if it makes more power, ill try it once.

So if this is working, or at least helping, maybe it is Vapor Lock. I thought the same, that it was a dealer blow off, instead of spending hours to diagnose the problem for just a diagnosis fee.

Mine didnt do it bad unless it was in the 100s. Now with this cooler weather it doesnt seem to do it at all.

No check engine lights, and i used my xtool d8, no dealer codes either???? Freakin wierd. I had mine checked and they said they couldnt reproduce it, but since its pretty mild, i just dont care, ill live with it.

I’m telling you…it’s not vapor lock. I would sooner suspect a bad fuel pump, than vapor lock.

 

[Hodgeee]

Thank you. Mine has all new vapor system and pump, and it does the same thing, just in hotter weather. New injectors, plugs, wires, coils, TB, and new sensors.

This was all done at 140,000 miles when i bought it. I depend on my truck to not strand me when i go hunting or camping, out in the middle of no where. It may be much, but i like renewing all these items regardless at 150,000 miles, even if they are fine.

As for my nieghbor we are looking into it. My canister was fine, and i blew out all the hoses for the reason you described. Mine were fine, and it doesnt do it at all on cooler weather. We are gonna work on his this weekend to see if thats the problem.

 

[intheburbs]

I'm very familiar with vapor lock. Used to live in Colorado, and we had an 85 S-10 Blazer (carbureted). We did a lot of wheeling at high altitudes.

I've similarly abused my Suburban at high altitudes and high temperatures. The lower barometric pressure at those elevations is much more likely to induce vapor lock than simply high temperatures. And I've been in situations where the engine was operating at higher-than-normal temperatures and opening the hood felt like opening a blast furnace. The picture in my avatar is our last trip to Canyonlands, and the temperature that day was 100°, and we were driving slowly with the A/C on.

I'd start by replacing the purge solenoid. When mine went bad, I'd get the exact same behavior described by OP after filling the tank. It's a cheap part and simple to replace.

As others have said, the laws of physics say the fuel can't boil off under the pressures typical in a modern fuel-injected system.