328, difficult to start when hot

Maybe the cold start valve still injecting gas?

 

I'm no expert but I had a similar problem. I had a mechanic come to have a look and what he did was remove the cold start injector and put his hand over the hole to see if it injected (into a bottle) while starting hot. The fix was simply unplugging the injector which made cold start hard until I could pick up a new thermotime valve (located next to the oil filter). Now, 1 year later, I'm having a similar issue but this time I need to hit the gas pedal a bit to get it started and I'm told to focus on the Warm up regulator. I would say that an easy try is to simply run it until warm then unplug the injector as see if it behaves differently. Hope this helps.

 

Your fuel system is supposed to retain pressure after you shut the engine off. This prevents vapor lock among other things. My guess is that you have an internal leak in your fuel system perhaps at the fuel accumulator.

I had a 1980 CIS Mercedes years ago. The system was a close look alike to 328 system. The MB did exactly what yours is doing. If you drove the car and shut if off and let it sit for a few minutes it would not start. But if you attempted to restart it immediately, it would start just fine because it did not have time to lose its pressure. A cold start always worked fine.

One way you can tell is with the engine just shut off, there should be some resistance to pressing down on the disk in your fuel distributor. The disk is the circular plate whose position tells the computer how much air is coming into the engine. Let 10 minutes go by and press again. If the resistance is gone, you have a leak in your fuel system.

 

These are my hot start notes as I too am beginning to have this problem. I have yet to do anything about it though.

These are often times a copy paste of someones remarks and perhaps I have not referenced the original poster in my notes.


http://www.ferrarichat.com/forum/showthread.php?t=292644
http://www.ferrarichat.com/forum/showthread.php?t=250491
http://www.ferrarichat.com/forum/showthread.php?t=163628
http://www.ferrarichat.com/forum/showthread.php?t=162517
http://www.ferrarichat.com/forum/showthread.php?t=141506
http://www.ferrarichat.com/forum/showthread.php?t=307094
http://www.ferrarichat.com/forum/showthread.php?t=317051

fuel accumulator
check valve
fuel pump
thermoswitch
thermo-time switch
injectors
cold start injector
WUR
replace the two O ring seals in the fuel pressure regulator located on the airbox side of the fuel distributor

tests:
disconnect cold start injector

When you have the hot restart problem (i.e., starter cranks over OK but engine never fires):
1. Unplug the safety switch on the airflow meter and turn the key "on" (Pos II) -- confirm that you can hear the
2. If the fuel pump does run, turn the key to Pos III (start) and see if it will start.
If you fail test 1 -- electrical problem with fuel pump/fuse block stuff.
If you pass test 1 but not test 2 -- put a timing light on it to confirm/deny the presence of ignition.
If you pass both test 1 and test 2 -- most likely the check valve on the fuel pump (outlet) or accumulator is kap

check accumulator for leaking gas


Hope this helps,
Aaron

 

great post Aaron

 

The calibrated index finger is a most interesting approach and so easy as to be a mandatory second test. First test being removing the cold start injector electrical connector which LowRider proposed at the first indication of no-start when warm. This proves the thermo-time switch to be good or bad. And if you simply choose to throw parts at the problem, change both the accumulator AND thermo-time switch. Me?, I took the analytic route and bought a pressure tester (about $100) to analyze the system. In the end it wasn't pressure related...it was the thermo-time switch. Haven't used the tester since.

FYI The purpose of the WUR (warm up regulator) is to increase fuel pressure to the fuel distributor as the engine warms up, improving economy and performance by leaning the mixture. WURs don't often fail but can be tested with a pressure tester. The common WUR failure is the internal electrical heater, the WUR still eventually functions but much more slowly as the engine warms.

The pressure tester if the best way to prove efficacy of the accumulator. The related check valve is an anti-backflow valve at the fuel pump and doesn't fail as often as accumulators but should be replaced when changing the fuel pump. Best discussion of these components are in the 1983 Mondial QV Workshop Manual Section D.
GL