hot start issue

Based on your description of "hot running fine except for restarting" (which is goodness for almost everything), the first thing to confirm/deny IMO is if the fuel system is holding pressure after shutoff -- by measuring the supply fuel pressure when running (should be something like 5~5.5 bar) and then seeing what is does after shutoff (the supply fuel pressure should not drop quickly to "0" -- it remain above ~2.6 bar for at least ~20 minutes).

If you fail this test, a likely culprit is the check valve mounted in the fuel pump outlet (but there are other causes too) -- if you can find a shop (Mercedes, Volvo, etc.) who knows Bosch CIS injection they should be able to make this pressure measurement without much effort/$, or, if you are a DIYer, the test gauge set-up for this is ~$100 IIRC.

 

Don't do that! GeesohPete that's hard on lots of internal components. Please, if you have to hack at the car, instead of hitting the darn ignition key 10 or 15 times in a row, buy a $2 can of starter fluid and spray into the air intake for a couple of seconds, then start.


OK. So you've got your $2 can of starter fluid. Good. Now your car can start.

Start it up when the motor is cold. Run it until it is hot. Now turn off the motor and as soon as the motor stops, try starting it.

Does it start right up, even without starter fluid, right then when the motor is hot?

If so, your problem is likely as Steve suggested above...a problem with holding fuel pressure.

Now wait 5 minutes. Is it now difficult to start without starter fluid while the motor is hot? If so, then almost certainly Steve is correct above.

Spray in your starter fluid, start her up, and drive home.

To *fix* the problem, begin looking at fuel components (fuel pressure regulators and check valves are notorious for failing...if your car has one).

 

There can be two types of hot/warm start problem.
(if you do a search, look for 'warm' start problems as that's what's often called)

In one case, the engine doesn't get fuel after starting. That's what you seem to describe and its
often trouble shot by looking at fuel pressure to the distributor. Problem can lie with the
fuel pump, accumulator, and back flow valve.

In the other case, the engine is flooded by the cold start system malfunctioning.
This is best trouble shot by disconnecting the connector to the cold injector valve.
Problems here can lie with WUR, ThermoTime switch etc.

So best determine which kind of non-start problem you have.

 

I had the exact same thing last year with my 80 GTBi. I pulled my hair out for 2 weeks dealing with it. Turns out I was losing fuel pressure, the fuel lines were getting hot from the engine heat and causing vapor lock. Here's an easy way to check it that I discovered by accident. When the engine is hot and it wont start , pop open the engine compartment and remove the cover from the air filter box, remove the air filter, now turn on the ignition so the fuel pump is running, look down in there and you will see a large round disc that will be closed from the bottom/up, gently push down on the disc about 1/2" or so and hold it there for about 3-5 seconds. Don't push it wayyyyyy down and make damn sure you don't drop anything down in there! You should feel and hear the system purging air and eventually it will push the disc back up under more pressure when the fuel gets there. Now start the car. If the car starts right up, YOU've got a vapor lock problem.

Before doing this, I replaced the accumulator on the advice of Fchatters which turned out not to be the problem. That was OK because it needed to be replaced anyway from age. After trouble shooting fuel lines, cold start valve and anything else I could find, I put a set of gauges on the fuel system. I discovered the fuel pressure dropped to zero within seconds of shutting down. The fuel system should hold pressure until the engine cools down to avoid vapor lock. After talking to Larry (the Fchat fuel distributor expert) and checking a small valve in the side of the fuel distributor (cant remember what its called) which holds the pressure at the distributor end, I replaced the check valve at the other end of the system at the fuel pump. I put the pressure gauge at the fuel distributor input line and the system held pressure for over an hour.

Sounds like you are losing fuel pressure and getting vapor lock. If you don't have a set of fuel pressure gauges and since youve already replaced the accumulator, check for fuel leaks at the fuel filters. If that looks ok, replace the check valve at the fuel pump. Thats what did it for me. The check valve is an easy thing to replace and not expensive. You just have to drain the fuel out of the tank before removing the valve. Hope this helps. Joe

 

That's a great post. If you 308/Mondial guys have some sort of 308/Mondial Primer, that post should go into it. It should be archived, indexed, and searchable.

 

If the fuel pump was not working I don't think it would start even cold? If I recall correctly the fuel pressure is held in place by the check valve at the fuel pump end and a small valve at the fuel distributor end. You need to chat with Larry Fletcher. If you are losing pressue and the check valve is good, its got to be going out the other end at the fuel distributor. If you don't see any obvious fuel leaks you need to get a set of gauges on the distributor to see what's going on. You've trouble shot about all you can and now you'd be just replacing parts blindly till you find the right one. That's expensive and frustrating. There's also a haynes fuel injection manual that I found very helpful with my issues. you can get at a local parts store and it breaks down the Bosch systems in pretty simple terms. The manual part number is 10215 and I think it was around $20. But before I did anything else, Id talk with Fletch. He hangs out on here so odds are you'll year from him. Good luck. Joe

 

Not necessarily -- see page D43 in the Mondial8/QV WSM for some other causes. However, I'd confirm/deny if losing the fuel pressure after shutoff is really the root problem before replacing any (more ) parts.

 

I had the same hot start issue, and replaced the fuel accumulator. That was my car's bandaid, and I thought it would be yours too. I hope you get it fixed soon. Good luck.

 

Read my earlier post. You must ascertain the nature of the problem first...you're just throwing parts at it. Disconnect the cold start injector electrical connector and go from there.

 

The cold start injector may have a mechanical failure as well, and be stuck open/partially open.

 

John, have you checked to make sure you have good compression? Low or uneven compression can make hot starts difficult. Might be worth checking if you're totally stumped.

 

That rules out the thermo-time switch which was my problem causing flooding which is a common warm start problem. Guess you could remove the injector, plugging the hole to see if it made a difference, but if it were not turning off and was dripping gas, flooding the car, I would expect you to notice other performance issues from the rich mixture.

Next step is pressure gauge on the distributor. Mine cost about $100. If you do this, be sure to replace the copper crush washer when you remove the gauge. And my mechanic lent me his Bosch book on CIS. Believe your system is Lambda injection so make sure your book covers that iteration.

 

Do you smell fuel while cranking? Is fuel the issue at all? Crank for a few seconds when hot, then pull a spark plug and see if there is gas on it. You might have an ignition issue. Doesn't seem likely but you have replaced the two items that cause 99% of hot start issues in K-jet cars (accumulator and check valve).

 

Very interesting post.

Not to hijack the Mondial thread, but I am having exactly this problem with my 86 930 Turbo SE. My symptoms are:

1. Car starts perfectly when cold and runs perfectly once started
2. If car left for 5 minutes or less will hot start no problem
3. If car left for more than 5 minutes, bloody difficult to start. Lots of cranking required, catches on less than 6 cylinders and takes 15 seconds to smooth out

I bought a trailer queen concours polished extraordinaire that had only 7,000kms since new and had very little use during last 10 years. Car has had huge money spent on it on an ongoing basis but not used. I am now remedying that situation with 1,000 kms during last week including school bus duty.

We have noticed that there is a fuel issue as the plugs are not burning evenly. Compression is perfect in all cylinders. We are thinking that since the car has sat a lot the fuel injection system has dirt, dried rubber parts, etc and will rebuild replace.

I drove the 930 Turbo SE and my 288 GTO on the same day earlier this week. For the life of me I cannot understand why the 2 cars are valued so differently now. They are both fantastic cars - the Porsche is certainly not 1/10th the car.

 

With a set of fuel pressure gauges, or gauge (to verify that the system is losing pressure through bleed-back when the key is switched off)...and following this gents tried and true advice, indeed 99% of all hot start issues will be resolved.

Often, fuel can actually be seen leaking from the "drain" hose on the accumulator.




David

 

If the car does run for 1 second every time, but when warm, only continues to run some of the time ...
I'm not familiar with the Mondial, only 308. While built differently, I'm assuming they use the same circuitry.

When the ignition key changes from 'start' to 'run', the fuel pump gets it's voltage from a different circuit. If the fuel pump voltage is dropping out causing the engine to stop after using the gas stored in the accumulator pressure (the aforementioned 1 second). If this is true so far, one needs to troubleshoot components (relays and connections) involved in this 'start' to 'run' changeover.

Stopping here for you to verify my assumptions and understanding. If this does seem to fit the situation, I can post some electrical circuits which might help solve this mystery or at least, identify the culprits involved. But if my understanding is off base, I don't want to waste bandwidth and your time diverting the search from pressure to electrical.

 

Incidentally, good price on a accumulator for 308/328 here ($133):

http://www.autohausaz.com/search/product.aspx?sid=wklgun2jw1yanh55u4fusfir&partnumber=0438170004


Just in case anyone needs to replace theirs.