81 308 GTSi hard to start after it's hot

Here are a couple of threads on this issue.

http://www.ferrarichat.com/forum/showthread.php?t=141506&highlight=hot+start+problem

http://www.ferrarichat.com/forum/showthread.php?t=272174&highlight=hot+start+problem

http://www.ferrarichat.com/forum/showthread.php?t=322364&highlight=hot+start+problem

http://www.ferrarichat.com/forum/showthread.php?t=292644&highlight=hot+start+problem

http://www.ferrarichat.com/forum/showthread.php?t=291048&highlight=hot+start+problem

 

A bad thermotime switch will cause flooding of a warm engine and the test takes 5 seconds. Simply disconnect the cold start injector. If the problem goes away, it need not be reconnected until the switch is replaced. This need not be related to the previous similar symptoms and does happen to many of us.

 

sounds like the fuel system can not hold pressure

most probable culprits:

- check fuel pump/ leaking return valve

- check accumulator / leaking diaphragma aka return hose to tank

 

I bought a fuel pressure gauge kit with fittings just to diagnose my warm start problem. Gained an understanding about the system components and my problem turned out to be the thermotime switch but I still feel it was $100 well spent. Copper crush washers weren't included but needed (get a dozen) to insure no leaks afterwards. Since you've had fuel parts replaced earlier it's a bit surprising that the same symptoms are revisiting you but such is life. Since VW and MB also used the same Bosch injection system, there are many online pdfs with helpful details of the pressures involved.

 

MY QV is hard to start when hot if I don't hold the throttle at halfway while cranking. If I do that, it starts easily if not as robustly as when cold.

 

Pauly, a couple of ideas:

1. Injectors. You might consider replacing the injectors if your current injectors are old or have a lot of miles o them. The injector needs to be able to hold the pressure of the accumlator.....which it may not be able to do for more than a few minutes.

2. Compression. Have you run a compression test on your engine? If the compression is down and/or uneven that can make hot restarts more difficult.

Good luck and persist.

 

The accumulater is notorious for causing warm restart problems after sitting for several minuites. The internal diaphram slowly leaks fuel into the accumulator's interior, causing fuel pressure to drop over time.

On the other end of the accumulator is a vent tube with a 90 degree bend.

On US cars there is a hose connected to the tube. Pull the hose off of the tube. If fuel drips out of the hose or the tube then the accumulator is bad & is causing the fuel pressure to drop over time.

On Euro models w/o the hose, watch the vent tube for several minuites after the engine is turned off. If fuel drips out of the tube then the accumulator is bad & is causing the fuel pressure to drop over time.

Hope this helps.

 

My car was doing nearly the exact same thing, and I too was working the fuel system trying to fix it, until I finally bypassed the fuel pump fuse in the factory fuse box with a simple in-line fuse and... Problem Solved!! The original fuse boxes are bad for building up high resistence and heat which in turn means high electrical resistence in the fuel pump circut and the pump either doesn't run at all or runs poorly. I have since built my own replacement fuse boxes that don't have high resistence and also use more modern blade fuses and haven't had any hot starting issue in years. I've heard birdman sells a good replacement fuse box set up as well. Anyway, it is something too look into and is very easy to test by bypassing the fuse box with a simple inline fuse from and any autoparts store. Good luck!!

 

That's not the culprit; as noted earlier, the culprit is the accumulator. The switch you disconnected allows the fuel pump to run when the ignition is turned on but the engine is not cranking or running. It's a safety feature. You can leave it disconnected but the reason disconnecting it is helping is because the accumulator is bad. The culprit is the accumulator and replacing the accumulator is the fix. Replace it and re-connect the switch.

 

Purpose of that switch is so fuel can't be pumped onto/into a stopped engine...safety. Some carb cars had a switch under the driver's seat called a rollover switch to kill the fuel pump...similar safety concerns. There's no valid reason to disable it.

The accumulator keeps pressure in the system for many hours. With no pressure in the fuel lines AND a hot engine, after a few minutes vapor lock can develop requiring considerable time for fuel to again regain a path through to the injectors. Even with a cold engine overnight, fuel can empty the path and cause unnoticeable longer starts.

Warm start problems are attributable to either thermo-time switch or accumulator, and you have done the test ruling out the former.

 

If you have not seen these pictures they are the accumulator, filter and check valve.
http://www.flickr.com/photos/lonnie7777/5952780578/in/set-72157626099702794

The check valve is rubber and can cause a loss of pressure if it fails and the accumulator is a pressure relief valve that can stick and stay open or closed.

The problem is vapor lock and it is caused when the fuel line gets to hot and the liquid fuel becomes a gas in the fuel line. I'm not sure which would work better; Insulating the fuel lines from the heat or installing heat sinks. I have heard of attaching clothes pins to the fuel line or a grapefruit on the fuel pump.

 

The reason why unplugging the safety switch seems to be your solution is because without that plugged in the fuel pump can work for a while (and build up pressure in the system) prior to you turning the key to the start position and engaging the starter. With the safety switch plugged in you're cranking the engine while the pressure is starting to build and this takes a while.

 

Hi Pauly, I know this is a really old post, however I've got the same issue on my 1985 QV. Did changing the accumulator fix your issue? Cheers.