Quote: Number: 84-174 Section: 6C Date: July, 1984 Subject: REDUCTION IN PERFORMANCE UNDER HARD ACCELERATION ON 5.0L HIGH OUTPUT V8 4BBL ENGINES (L69) Model and Year: 1983-84 CAMARO To: All Chevrolet Dealers Some Camaros with the L69 engine may experience a reduction in performance in the form of hesitation or sag under hard acceleration. This condition usually occurs at high ambient temperatures when the engine is hot and may be due to fuel vapor lock. Vapor lock is temporary fuel starvation that is most likely to happen upon acceleration after a short soak or extended idle period. To repair this condition, it will be necessary to install vapor lock fix kit, P/N 14085385. This kit utilizes a low pressure (3 psi) electric in-tank pump. The fuel vapor fuel fix kit has detailed instruction sheets for installing all parts found in the kit and for reworking existing grommets on the vehicle. The instruction sheets do not show parts that have to be removed in order to install kit parts. Use the appropriate shop manual procedures where indicated. anyone have one of these kits? My 85 L69 needs one, dealers don't have them anymore. Has anyone seen this kit in person?

All that is, is GM adding a 'helper' electric pump to the fuel tank to go with the mechanical one on the block. From what I remember, all '84+ carbureted cars had this? That could be incorrect though.

Just a note that has little, if nothing, to do with the question: There was also an underhood, passenger-side mounted fan, yes, fan, that was available at some point, to reduce vapor lock.

http://www.thirdgen.org/techboard/te...lock+fan+vapor (Fan?)

JamesC

Incorrect. All later L69's, and '87 LG4's.

If you have a real '85 L69, perhaps your problem is the in-tank electric pump has failed.

All 87 LG4s had the in-tank helper pump although it shows a different part number than the 85 L69. A sawzall at the yards may be the easiest way to get the associated pieces/parts to install a pump on a carb'd vehicle that didn't come with one. Don't forget the oil pressure switch on the rear of the block and associated relays.

Although if I was there, I'd probably install an in-tank electric that was large enough to work without the mechanical pump on the block.

I thought the '85 L69s came with one too.

Oh, and I've still got the little aluminum heat sink that was (I'm told) dealer installed on my 85 LG4.

I've heard different stories, such as the L69 in-tank electric started mid-year '84, the L69 in-tank electric started model year '85, etc. But, either way, an '85 L69 should have the in-tank electric fuel pump. If it isn't operating, vapor lock problems will be worse than if there was no electric pump at all.

The "HO 350 Camaro Conversion Kit" included the in-tank electric pump and a fuel pressure regulator. However, I can't put my hands on the parts list right at the moment.

What's "the little aluminum heat sink?" I haven't seen or heard of that.

You made me dig it out and clean it up. It's definitely NOT a production piece although it was certainly intended to dissipate heat. It was on the 85 LG4 that was otherwise unmolested- the tamper-proof plugs were still installed on the carb. The PO said it was installed by a dealership, which could, I suppose, be true.

I've always suspected that the return style pump was the 'vapor lock' culprit and not the carb. When I first installed the fuel pump on the 87 (used it as a return regulator-no fuel pump bore) I ran a clear filter so I could observe the fuel flow. When shut down hot you could see the fuel boiling back through the filter. When this happened the fuel pump itself was much hotter than the carb. 'Course the fuel pump stays relatively cool to the touch while the engine is running and fuel is constantly cycling thru it.

Cooling the carb may keep fuel in the bowl from vaporizing as much. This may give the mech pump a little more run time to catch up, but it's got to be negligible. Any dealer installed carb cooling system had to be, IMO, a quick, easy way to get the customer out the door with something shiny attached to the motor.

I have never seen nor heard of that piece before. Wow.

Is their any "dead give away" that there is a electric pump in the tank with out pulling it?

Yep my Z28 had a fuse in the fuse box for fuel pump. Simple way to check is to look in the fuse box.

That aluminum piece looks almost homemade. I have used this aluminum piece. But now use this Phenolic one.

Yes, it was apparently fashioned from some aluminum stock.

I have an 84 T/A L69 and I don't have either of those "Helper" kits installed. I always thought my "bogginess" was from how the carb wasn't tuned right. Perhaps all this time I've been dealing with vapor lock instead?

Your bog is probably real bog. The vapor lock I've experienced would let the car start after sitting hot then try to die as it struggled to get fuel back through the line. Once the fuel started flowing again all was fine.

From the text above, "Vapor lock is temporary fuel starvation that is most likely to happen upon acceleration after a short soak or extended idle period."

Mine does it when it is hot after driving awhile and I get on it. I make it threw first, second and third, and then half way threw 4th (around 4,000 rpm) it lays down/bogs. I can let off for a few seconds and it comes back.

When I first bought the car back in 92' it would only do it if the tank was almost empty and it was hot, then it would start doing it in 3rd by 3,000 rpm.
I learned to keep it at least a 1/2 tank. Years later and a few years of not taking it out of storage it got worse. I changed the filter and mechanical pump so far and it's better but it's still there. I am not looking forward to pulling the tank but I think that is my next step.

I don't think that is the cause of the vapor lock problem. If anything, it's going to happen in first or second because of the heat on the fuel. By the time you're in 4th and 5th, you already have the cooler air flowing over the engine and carb and cooler fuel from the tank. If you have the origional metal fuel line running up to the carb, make sure it's not touching anywhere on the motor. That goes for any aftermarket fuel line.

The line is clear and not touching anything.

If I understand the vapor lock theory correctly in this case, it is a fuel starvation caused by fuel vapors, caused by high temperatures, building up in the line before the fuel pump causing a drop in fuel volume and pressure to the carburetor. This causes the float bowl to empty out during high consumption conditions (i.e. hard acceleration). The factory fix to this was to add another fuel pump at the tank to assure that the mechanical pump was always supplied with liquid fuel not fuel vapor.

I am basing my understanding on the information in the tsb "Some Camaros with the L69 engine may experience a reduction in performance in the form of hesitation or sag under hard acceleration. This condition usually occurs at high ambient temperatures when the engine is hot and may be due to fuel vapor lock. Vapor lock is temporary fuel starvation that is most likely to happen upon acceleration after a short soak or extended idle period."

When mine does it, it feels just like it is running out of gas. If I let off the accelerator for about 1-2 seconds it comes back and it accelerates through 5th gear. It will do it again if I hold it at high rpm in 4th or 5th for an extended period of time and it will still come out of it if I let for a few seconds. I am planing on doing a fuel pressure test for a base line and again after pulling the tank adding/replacing the in-tank pump and possibly going to the 1LE style baffled tank.

Feel free to correct me if you think I am looking at it wrong

Vapor lock happens when the fuel in the line starts to boil. When that happens pockets of gas form, the suction of the pump is wasted in expanding these gas pockets, and liquid fuel flow is greatly reduced. It can cause fuel starvation under demand or it can cause the engine not to run entirely, depending on the severity.

The boiling point of fuel in the line is actually lower than the boiling point of fuel in free air because the block-mounted pump puts the line under a slight vacuum between the tank and the block. The helper pump in the tank puts the line under a slight pressure, which raises the boiling point higher than in free air.

In extreme cases there can still be a problem when the fuel reaches the carb bowl. When the fuel enters the bowl, pressure drops from 6 PSI or so above atmospheric to atmospheric, and the boiling point drops. If the bowl is hot enough, the fuel will start to boil in the bowl.

"Vapor lock is temporary fuel starvation that is most likely to happen upon acceleration after a short soak or extended idle period."

This sentence is what makes me think that the bog in 4TH/5th gear was not related to vapor lock. I'm wondering, if it's vapor lock why not in 1st/2nd?

I would think it depends on much gas is available in the fuel line and carb bowls before the vapour lock prevents refilling the fuel supply.
I run a carbed 350 which has a fuel line which passes directly over the bell housing and then along the frame rail to the mechanical pump. After a few passes at the track and several minutes in the staging lanes, the car will come out of the hole hard and then lay down at the top of the first gear. A second later it'll pick up and run hard through to the end.
I've tapped the fuel rail on the carb and run a return line back to the tank. The thinking is that the vapour will be purged from the system even though at idle in the staging lanes there's not much demand for fuel. It's handy in that the car was originally a TPI with an OEM fuel line.
So far so good.