1984 Corvette

When coming back I stopped at different places with the motor HOT. At Walmart it restarted without any problem.
At Home Depot it started but shut down immediately after gaining some RPM’s again. Started again with some pressure on the gas pedal and it is like it choked itself then.
Tried again and indeed it started up with a lot of sputtering and I got the gas pedal pressured enough to stay running. After a couple seconds the problem goes away and the motor runs terrific again! It does it only when it is warm outside and with a hot motor.
Ones it runs no problem anymore.

 

Does your 84 still have the factory Crossfire Injection? If so, that system is known to be problematic. I don't know much about them myself. There are people who do but not many. To me it seems like the symptoms you described would be fuel related.

 

https://www.google.com/search?q=crossfire+injection+hot+start+p roblems&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari

 

The aren't any more problematic then the millions of tbi equipped GM cars & trucks. I'd get it hot, pop off the air cleaner, & look at the injector spray pattern. You want to see a nice cone shaped pattern with no big drips. You should also check for weak spark, low fuel pressure, & things like tps voltage. Any codes?

 

This kind of hearsay is useless--especially when you admit to knowing nothing about the system. Two injectors, two throttle bodies, very easy to work on...everyone hears Bubba complaining about it, but Bubba hasn't taken 5 minutes to read up before forming an opinion & spreading it like lice.


Why do his symptoms sound like they're fuel-related? Without an explanation you are just blowing smoke and not being helpful, so let's stop throwing guesses and start diagnosing. I know why I'd look at fuel first. In excessive under-hood heat conditions, fuel can boil in the lines & cause difficulty starting. This is known as vapor lock--injectors can't work with a vapor supply, just liquid...no (or very little) spray, no start. Then once you've turned it over a few times & removed the vapor pressure (which keeps liquid out of the line), and cooler liquid fuel from the tank reaches the injectors, you're running again. Like other TBI designs, the fuel system is not designed to hold running pressure after shutdown, but that doesn't prevent some fuel from absorbing heat & remaining as lightly pressurized vapor.


I don't know of a specific test for this, but you CAN test fuel pressure, and as suggested above, injector spray pattern. Start there Kint Daniel; try to check it hot & reproduce the problem while you're testing. Keep in mind winter gas can aggravate this issue--it is formulated to vaporize much more easily, as doing so is difficult on frigid winter mornings. If there's a chance you still have some in the tank, try to run it dry before you fill up again.


Your problem may be fuel-related, but I'd venture an educated guess that your solution lies not in part-swapping, but in reducing underhood temps & running gasoline more appropriately formulated for the season. Allowing the fan to bring coolant temps down in the parking lot before shutoff (while the water pump is still spinning & directing coolant to the radiator) can be helpful, and may even save you a head gasket on super hot days.

 

Sounds fuel related to me.

 

Nobody was responding to help the guy, so I got the ball rolling and now he's getting help. So the will for the attack on me results in the guy getting help.

I'll take it.

 

Yes, it still have the original factory Crossfire Injection. We are living in Houston, TX were it is hot, hot!

 

Op - you didn't mention "location" and actual outdoor temps. That might be critical. I believe "fuel related" also but it requires systematic diagnostics as mentioned earlier to an extent. Winter blend? Likely doesn't help if that's what you have BUT maybe your problem is very basic "vapor lock" sorta - it's thought that submersible electric pumps eliminated that (a friend disputes that) when dealing with TBI that requires much lower pressures that the TPI.

Fuel cap, vapor lines. fuel return and fuel pressure checks I'd think are a must and the "first to do". Fuel pressure regulation is confused by some and I believe I might have seen a recent thread where it was maybe explained incorrectly.

Rely upon comments and thoughts by L83 owners (two have posted to this thread). Both post frequently and likely understand very well the system.

OP - I was typing I guess while you were mentioning LOCATION

 

Not an attack...just would like people to think about whether their post helps the OP, or sends him on a wild goose chase, or spends his money needlessly, or gets him nowhere...or even all of the above. You are by no means the worst offender, so don't take it personally, but think about it. In this case you're probably right about a fuel issue, but unless you provide an informed basis for your hypothesis, and/or instruct the OP what to test and why, he is no farther along than before.

As for posting when nobody else will help...maybe wait a day before you worry about bumping a topic to the top. I'd have given my two cents regardless--1984 model year in the title usually gets my (and others') attention.

If there was an attack, it was you bringing in the "because Crossfire" generalization, which misinforms everybody who happens to read this thread.

Apologies to the OP for planting my soapbox in his topic.

 

I would look at the fpr pull the hose off and smell for fuel. It sounds like it is flooding might just be the fpr diaphragm. Smell your oil for fuel too.

 

A friend would mention not to rule out perhaps the distributor module. Lots of diagnosis required I'd think before as "84Z51J" mentions just "throwing parts at it".

This is an L83 car

 

To explain vapor lock a bit more...it's akin to submerging an empty water bottle in a bathtub, mouth-down. The pressure from the trapped air prevents water from entering. In this case there are two small holes in the top of the bottle (your injectors) which, when pulsed, will bleed off this vapor pressure and eventually allow flow to resume.


Thinking on this, a system designed not to hold running pressure after shutdown is probably more likely to develop vapor lock, even with a submerged pump (which does help prevent introduction of air into the system). The reasons as I see it are twofold. A pot full of water on the stove will take longer to boil than a splash at the bottom of a pan, for one...more mass will tolerate/absorb more heat before changing state. Also, keeping the ID of the lines packed with liquid fuel leaves little to no room for the expansion in volume that takes place when liquid absorbs heat & shifts to gas/vapor form. If fuel begins to drain out immediately post-shutdown, and pre-cooldown, that creates room & conditions for this expansion.


Drippy injectors can allow air to enter the system & cause or aggravate this problem as well; fortunately they are super easy to inspect


Verify proper spray pattern, address the fuel formulation, and monitor/manage underhood temps...I'd bet your problem goes away. If not, we'll be here when you report back!

 

Enough said. I'm cool

 

I don't suppose you could explain vapor lock in a system that has a return fuel line and an electric fuel pump ??? I believe this is the setup on the car in question.

 

After shutoff, thanks to gravity and cohesion (fuel sticking to itself), fuel drains to the tank from both the supply and return lines, leaving the system largely vacated/unpressurized...but the little puddles & drops that remain due to adhesion to the inner walls of lines & tubes can then absorb heat very quickly.


Add enough heat and the fuel will expand/vaporize, which takes up space in the lines, effectively eliminating the "slack" that was left. A gas/vapor takes up a LOT more physical space than a liquid. The pressure from this phenomenon fights the flow of liquid fuel as it attempts to re-enter the supply line, which is what causes long cranking and an eventual start once that resistance is eliminated.

 

And what IF the return is obstructed. There's I believe flexible hoses at both ends. Just askin' I mentioned "sorta" and that's the way years ago my friend (best I recall) explained to me.

***"84Z51J" - I was typing/thinking I guess when you posted. My friend didn't go on to explain but I'm thinking I'm good with your explanation. I might ask him. He's sometimes got some very interesting comments.

 

You must realize that the very presence of the return line means its impossible to contain the evaporated fuel in a way that would prevent the electric fuel pump from priming the system. Using your earlier analogy about the bottle submerged in water inlet side down, you know as well as I do that you couldn't develop pressure in the bottle if there is a hole in it on the other end.

I'm going to give you the point about how if all the fuel back flows into the tank after shutdown that would set up the conditions for vapor lock. This is very generous on my part since the fuel wont flow back into the tank of a c4 corvette unless your on some sort of incline.

 

Yeah if the return line is obstructed then yeah, but that would be a return line problem.
I was fine with the way you worded your post earlier. I thought you described vapor lock (in this case) as more of a symptom than the underlying cause. I can agree with that.

 

Envision a straw in a glass, completely submerged by water. Naturally, the straw will be full of water too. Remove some of that water in the glass, and the liquid level in the straw will drop, remaining even with the level in the glass. In these conditions, unless you raise the bottom of the straw above the waterline, or remove enough water to leave the bottom of the straw effectively dry, the water level in the glass and straw will remain even. Unless air pressure above exceeds the water pressure below, the system remains static. This is the bottom of your supply line--it stays submerged, sealing one end, and vapor pressure isn't high enough to force its own way out.


Now put your finger over the top of the straw. If you lift it out of the glass, it will lift the water with it. Similarly, if you start with the straw only partway into the glass, seal it with your finger, and press down, no new water will enter the straw. You've just simulated a very basic form of vapor lock. Substitute trapped air in this analogy for fuel vapor; it isn't there to start with, but heat causes isolated pockets of leftover liquid fuel to expand, vaporize, and take up space. There is neither enough pressure to overcome the liquid reservoir which remains in the bottom of the supply line, nor to pass the regulator at the top (vapor pressure would have to exceed regulated fuel pressure @ ~13psi to enter the return line, which it won't), so even though the system won't retain running fuel pressure, it will hold vapor pressure.


Expanding gas will effectively be sealed inside the supply & crossover lines, and only escape if A) fuel drops below the end of the pickup line in the tank, allowing pressure equalization to occur, B) vapor pressure actually exceeds the force that the liquid in the tank is exerting to remain in the line (like blowing bubbles with your straw), or C) the injectors are pulsed, forcing the gas out the top and/or to the return line with pump pressure.


Option A is (hopefully) designed out for a reliable pump prime at low fuel levels, and B is not realistic, so you end up with C and a long crank. The orifices of the injectors are extremely small compared to the ID of the line, so it takes a few turns over to clear the vapor and start feeding the injectors liquid fuel.


It doesn't help that the throttle bodies are plumbed in series, and fuel must pass through an accumulator to reach the regulator, and by extension, the return line--that may be the source of your confusion. Drain-back isn't directed or limited to the return line, which has no standing liquid to seal the bottom end, and thus wouldn't hold vapor pressure. The problem occurs in the partially-drained supply line, which is isolated from the return by the the regulator in the 2nd throttle body as soon as the injectors & pump are inoperative.