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post #1 of 43 Old 10-09-2007, 07:39 AM Thread Starter
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hot starts

I have a 1980 308 GTSi that I am continuing to have issues with hot starts. There are no issues starting the car when cold. Also, it will start when hot if you restart immediately. If not, it will take over a minute to get the car to start. It seems as if it is not getting the needed fuel or air mix. I have had the fuel injection checked and appears fine. Suggested were clogged injectors or valve clearance? Any thoughts?
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post #2 of 43 Old 10-09-2007, 01:43 PM
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I had a problem with a chevy back in late 1970's that had a problem like that. I don't know if it relates to your issue. Turned out to be a bad coil. Worked good enough when cold but heat reduced the effective output to a voltage not good enough for a hot spark. I don't recall how I tested it. Worth checking anyway.

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post #3 of 43 Old 10-09-2007, 02:35 PM
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I also was going to suggest looking over the ignition system. On my Jeep once I had a bad connection that would cause the Jeep to actually stall and not restart when hot. Let it cool down for 10 minutes and it would start right up.
I'd start with the basics, be sure all electrical connections are clean and tight. Electrical resistance goes up with temperature. A marginal connection may let enough juice pass through to start a cold engine and keep the engine running but once the connection heats up you may have a higher voltage drop that is insufficient to fire the engine right up.

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"Time is what prevents everything from happening all at once."
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post #4 of 43 Old 10-10-2007, 10:06 AM Thread Starter
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thanks

Thanks for the information, I will go back and have the system checked. This is a great site and forum and I have enjoyed the educational banter from the group. Capt…what are you flying?

gk
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post #5 of 43 Old 10-10-2007, 11:49 AM
 
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Hi Guys - Years ago I had a problem with hot starts on my 308GT4 (really hot-here in Phoenix). Problem was vapor lock. I talked with Bill at GT Car Parts, and he suggested a larger replacement Fiat fuel pump, which fit pretty well in place of the original. That completely solved the problem. If you don't find an electrical problem, and think the problem is related to hotter weather, you might want to call GTCP and talk to Bill or Dave. I'm sorry... I don't remember the Fiat part number. Good Luck!

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post #6 of 43 Old 10-10-2007, 11:56 AM
 
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Hey Again - After my last post, I remembered I still had some of my old receipts, and I found one with the pump on it. It was in 1993, and the GTCP number listed was 1304213. After all these years, their inventory numbering system may have changed, though. At the time it was $87. Hope you find an easy solution!

Rick
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post #7 of 43 Old 10-10-2007, 01:32 PM
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Not sure about the GTSi, but on many modern cars that can be a sign that the ECT (Engine Coolant Temp) sensor is faulty.

HTH.
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post #8 of 43 Old 10-10-2007, 06:36 PM
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I would say vaopr lock is the issue.

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post #9 of 43 Old 10-11-2007, 02:55 AM
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I've never experienced vapor lock but my understanding is that can only happen in low pressure systems. it is virtually a bubble of air that forms in the fuel line that must be "cleared" by vent or flow. It would be nearly impossible to experience vapor lock on a injected system.

Am I wrong?

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post #10 of 43 Old 10-11-2007, 05:23 AM
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Quote:
Originally Posted by ggk View Post
Capt…what are you flying?
gk
Not Flying.....Floating. Drilling for oil so I can keep all these Ferraris going.
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Capt. Pete
'79 308 GTS, '82 Jeep CJ7 Jamboree
"Time is what prevents everything from happening all at once."
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post #11 of 43 Old 10-11-2007, 05:36 AM
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Quote:
Originally Posted by Saint Bastage View Post
I've never experienced vapor lock but my understanding is that can only happen in low pressure systems. it is virtually a bubble of air that forms in the fuel line that must be "cleared" by vent or flow. It would be nearly impossible to experience vapor lock on a injected system.

Am I wrong?
You are correct. Vapor lock is not the issue with this car. When you lower the pressure on a fluid you lower its boiling point. On cars with an engine-mounted fuel pump that "sucks" the fuel from the tank, the fuel line is lower than atmospheric pressure and the boiling point is lowered. If the fuel line is run close to a hot spot the fuel can boil in the line and the fuel pump can't pump a vapor. You have to let the car cool off so the fuel can condense. On the Ferrari the entire fuel system is under pressure so the boiling point is raised.

That is also the reason why we have pressurized cooling systems. Water boils at 212 degrees F at atmospheric pressure, but at 15 psi it boils at 250 degrees.

Capt. Pete
'79 308 GTS, '82 Jeep CJ7 Jamboree
"Time is what prevents everything from happening all at once."
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post #12 of 43 Old 10-11-2007, 06:34 AM
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Vapor Lock

Unfortunately, Capt. Pete and Saint Bastage, it is quite possible to vapor lock a fuel injected car. Here's the Cliff's Notes version of what happens. When the car is running, the Bosch K-jetronic fuel systems run at 5 bar pressure, or about 75 psi. Because fuel is always recirculating back to the tank, fuel in the lines is pretty cool, usually no more than 100 degrees. The problem occurs after the engine is shut down. All the heat from the exhaust, coolant, and oil heats up the fuel in the fuel lines and injectors. The peak temperature at the injectors occurs at about 45 minutes after shut down, and the temperature can reach as high as 235 degrees. If the pressure in the system is zero, about 85% of the fuel turns to vapor. When you try to restart the car, all you get out of the injectors is vapor - and a no start. Now, as Capt. Pete knows, if you raise the pressure in the lines, you will keep more of the fuel as a liquid. The higher the pressure, the less fuel will be vaporized. It is for this reason that it is critical for the system to hold at least 50 psi for about an hour after shut down. Even at 235 degrees, only about 10% of the fuel turns to vapor. When you shut down the engine, the fuel pressure regulator at the engine, and a check valve in the fuel pump are supposed hold pressure in the lines for at least an hour. After that, the fuel system starts to cool down, and holding pressure is not so important.

As for diagnosing, you need to install a fuel pressure gauge in the line, run the car, then shut it off. It should read 50 or so psi for an hour. Typically, what happens to a regulator over time is that the seat gets warn, and can't quite seal. Old regulators sometimes bleed pressure down in seconds.

At school, this was part of a three hour lecture I did on this very subject. If you'd like, I can elaborate.

Steve Julius
General Motors fuel systems engineer (retired)
Automotive Instructor (retired)
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post #13 of 43 Old 10-11-2007, 07:05 AM
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Wow Steve, Awesome stuff!! I stand corrected, vapor lock could be an issue with this car. The situation you describe fits perfectly. It would make sense that the check valve would be worn on a 20+year old car.

Still, I check the basics first. I remember way back (22+ years) on my Opel when after several hours of diagnosing why it wasn't getting any fuel to the engine the problem turned out to be that there was no fuel in the tank.

Capt. Pete
'79 308 GTS, '82 Jeep CJ7 Jamboree
"Time is what prevents everything from happening all at once."
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post #14 of 43 Old 10-11-2007, 07:31 AM Thread Starter
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wow

This is excellent feedback and diagnosis. I will take the information back and have both the ignition system and fuel system checked. But I think you guys are on target with the vapor lock issue. It does occur on FI systems, it is a common problem with Lycoming airplane engines that have the FI distributor on top of the case. They become very difficult to start hot and you need to follow specific procedures.

Much thanks!

GK
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post #15 of 43 Old 10-11-2007, 08:09 AM
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Hey Capt. Pete,

Please note that I never said that vapor lock was the problem with this particular car, only that vapor lock can occur on fuellies. I agree with you completely that one should always start with the basics. Trying to diagnose a car from the other side of the country often backfires (pun intended), but if I can be of assistance, ggk, feel free to ask. -Steve
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post #16 of 43 Old 10-11-2007, 08:19 AM
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Of course Steve. But you definately provided a lot of useful information for consideration.

Capt. Pete
'79 308 GTS, '82 Jeep CJ7 Jamboree
"Time is what prevents everything from happening all at once."
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post #17 of 43 Old 10-11-2007, 09:55 AM
 
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Actually guys, I have never owned a FI car, and didn't really notice you were talking about an injected system. But glad to have Steve chime in with the technical facts... so it sounds like FI systems have a different fuel pump. No doubt that if the fuel lines do not hold enough pressure, substantial vapor may form. But always best to check the simple stuff first.

Rick
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post #18 of 43 Old 10-11-2007, 10:26 AM
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I come bearing an Apple for the teacher

I understand Pete's point about cavitating a pump with vapor but I need to know more about Steve's point. Where is the fuel pump on this 308. I assume the pump is located in or near the fuel tank and therefore not subject to dramatic heat issues. Vapor near the injector would seem a very minor problem. Pump cavitation should not be an issue since the pump is in a cooler environment and far away. Flow and recirculation should clear the vapor bubble rapidly. In addition, isn't it the purpose of the injector to convert the fuel into a burnable form (spray into a compressed air environment, these are not throttle bodies...are they?)

Hmmm...Please educate me further ohh masterful Yoda

eewwww...I can't beleive I just said "throttle bodies" in a Ferrari forum

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post #19 of 43 Old 10-11-2007, 11:05 AM
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OK, class is back in session . The fuel pump on a 308GTSi is located down on the frame below the front distributor. That's pretty close to the clutch, and not too far from the front header. It does get hot. However, it's not the pump vapor locking that's the problem here. The pump doesn't really have to suck from the tank because the hose comes out from the bottom of the tank directly to the pump. The pump is fed liquid fuel essentially by gravity. It is a high speed roller vane pump that then sends high pressure fuel to the engine.

I think you said that "Vapor near the injector would seem a very minor problem." Well, actually, that is precisely the problem. Here's the reason: Once fuel gets past the K-jetronic distributor, there is no way out except through the fuel lines and injectors. The injectors are supposed to spray liquid fuel, which turns to droplets. In the vapor lock scenario, you have less dense vapor spraying out to even less dense vapor. There are a lot fewer BTUs of energy in a cc of vapor going through an injector than there are in a cc of liquid fuel. The engine is being fed a very, very lean mixture and won't run.

A lot of newer fuel injection systems drastically reduce the volume of these "dead end" lines, and thus have fewer vapor lock problems. How would you go about designing such a system?

Whew, my brain is bleeding. I need to go eat some cold pizza...

Steve
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post #20 of 43 Old 10-11-2007, 12:50 PM
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Thanks

I think I get it now

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