4SrU

1984 5000S always started easy in the morning. BUT then if the car was run for soem time and up to temp. when you shut it down and resart immediatly it starts fine, BUT if you shut down and let it sit for 5min+ then try to start, it starts fine but immediately shuts down, you have to start it give it gas and hold it for about a minute for it to idle on its own. If the car cools completely no problem starting.

And just recently it is getting a little harder to start from cold (needs a few cranks, but not always).

Any thoughts?

Ofeelya

In my V8, the culprit was the RPM sensor. Both the RPM and Crank Position sensors will cause the car to do that when heat soaked. Audiqv8 knows the specifics of how they work, but basically they lose their magnetic properties when bad. The crank position sensor senses a pin on the flywheel that ultimately sets the ignition sequence. I replaced both sensors and have had no problems since. Hope that helps.

tonyj

Sounds like leaky injectors.

Restart soon after running - the injectors haven't has time to leak very much.

Let sit for a while and the engine is flooded.

Let sit overnight the flooding drains down to the crank case so starts fine.

Try a couple of treatments of injector cleaner.

My second '84 had the same symptoms.

Tony
'91 100Q 5spd

Ofeelya

The reason why it will start after letting it sit for only a few minutes (after it's been running and is hot)is because the ECU stores the injector firing sequence. It will start again after 20-30 mins. because the crank position sensor has cooled. The car will continue to drive fine once its running because the crank position sensor is only used for starting. I would think that if you had a leaky injector(s) you'd have other driveability problems. But I could be wrong.

Ofeelya

Sorry, meant injector sequence not "ignition sequence"

audiqv8

On a Audi 5000 the crank and speed sensors are located on top of the bellhousing and away from the exhaust mainfold. The heat from the exhaust manifold is what destroys these sensors on the V8's.

Hard start when hot on a 5000 is either leaky injectors or fuel pump check valve. Do a fuel pressure test to determine which one is causing the problem.

4SrU

Thanks for the quick responses. I have a fuel pressure gage, so I'll check for the check valve or leaky injectors (I thought these were the problem areas but wanted to see what anyone else would come with). The sensor theory is intresting.

I think it's the check valve, as I had pulled out the injectors to check the spray patterns and they all looked OK, I left them out after testing the spray patter to see if any would leak but they all remained dry. I will have to confirm if it's the check valve but I have been putting it off as I don't like the idea of digging around in the fuel tank to pull out the fuel pump ( I geuss the good news is that the check valves are only $27.00).

thanks again, for everyones input, I'll let you know what I find out.