Advanced Cold Start and Hot Start Problems HELP

For the past year my car (1985 308QV USA car) has had a cold start and a hot start issue. I have already replaced the check valve in the fuel pump and the accumulator. I do not drive the car much, but this is becoming a pain for me. Below is some more info regarding these problems.

COLD START
When I start my car the idle is suppose to be about 2,500 rpm until the engine is warm. However, when I start my car cold the idle is at 1,000 rpm's for about 30-60 seconds. After that time the idle goes down to 500 rpm's for about 10 minutes. After 10 minutes when the car is warm, the idle returns to 1,000 rpm.

During the past two weeks I though my Aux Air Valve was bad. I tested the AAV and it checked out OK. Today while in the shop, we noticed that the cold start air valve that is connected inline with the AAV is missing on my car. It appears that someone removed the cold start air valve and bypassed the high idle system. This appears to be the reason why my cold idle RPM is so low.

Does anyone know where this part is suppose to be located in the engine compartment and where the electrical connection is? I show my car at FCA events and I need to keep everything 100% stock. If anyone can take detailed pictures of a USA 308QV engine, I would be very interested in looking at the pictures. I would like to see exactly how this part is piped in and where it is located. Please feel free to email them to me at kdross@msn.com Also, I do not have a cat on my car (it was hollowed out by the previous owner).

HOT START
When my car is at operating temperature, I have a difficult time starting the car. This does not appear to be a heat soak problem (when the car sits for several minutes) because if I shut the car off for a few seconds (or stall at a red light), I have a very hard time starting the car. As I previously stated, I have already replaced the check valve in the fuel pump and the accumulator. Murphy's law was working today and I could not recreate the hot start issue (this is a first!!!) while in the shop. As a result, we could not take any fuel pressure readings.

We were able to read the CO levels, and the car was running rich. The CO level was about 3.5, and we lowered it to 1.3. I wanted it to be at 1.2 or lower, but the engine idle did not sound right at any setting below 1.25-1.30. Would a CO setting of 3.5 cause any of my problems? Is the current setting of 1.3 OK?

My mechanic believes that the emergency fuel shutoff switch on the fuel distributor may be defective and causing my hot start problem. His theory is that these switches go bad (this is apparently a common problem on Mercedes), and when they fail, they do not active the fuel pump. So if my switch is bad, the hot start problem may be related to the switch which is not activating the fuel pump when I go to start the car. I am told that the switch cannot be replaced and that a brand new fuel distributor is required (several thousand dollars). We are planning on jumping the emergency shutoff switch and seeing if this corrects the hot start problem. What are your thoughts on this idea? Any other ideas as to what is causing my hot start problem? We have run out of ideas.

Thanks.
Ken

3.5 CO could definately cause hot start problems...what is the fuel pressure hot & cold?

I would fix the cold start problem first, and see if it crosses over and eliminates the hot start problem as well.

Ken,

To reiterate my previous post concerning CIS problems. If the problem is there today, or not is immaterial to the solution. Focusing on the hot start problem, first.

1) System pressures must be known.
2) Once the hot pressure is known and verified to be in specs, the vehicle is shut off...and the system pressure is monitored. The system should hold pressure, after the slight initial drop, for 20 minutes.
3)If the pressure immediately drops off, the fuel pump check valve and accumulator should be isolated and checked for pressure loss. ("New" doesn't mean functioning properly...)
4)If they test OK, the injectors should be pulled and pop tested. Injector leakage and/or poor spray patterns can cause all sorts of problems with cold and hot starting.
5)The sensor plate height must be spot on for proper hot and cold starting.
6) As to the CO you desire...The correct way to set the CO is to measure the HC on a hot engine. Adjust the HC from high to low. When the lowest HC reading is achieved, the CO level is at its optimum setting.

If you mechanic is familar with MB CIS systems, the problems with your car a truly a no-brainer, as the two systems are identical...

Yourself and others have posted other similar problems with these CIS equipped cars...and the starting point is always system pressures. Why do I stress this point? Simply stated, the CIS system is pressure-based, so you need to know and verify the pressures to accurately diagnose running and starting problems.

HTH...

Regards,
David

Thanks again for the help guys.

David: The CO reading was taken at operating temp. The manual states that the CO setting should be 1.0 with an error of +/- 0.2. It also mentions the HC level should be around 100, but this is for a car with a CAT. My car has a hollow CAT, so should I be concern about the HC level in terms of performance? If I were to adjust the CO level so that the HC level was low, I would have a CO setting of about 3.5. This is where the setting was previously and was probably at that setting for emissions. At this point, I do not care about emissions. At the current setting of about 1.3 for the CO level, the car did not exhibit a hot start problem. Of course the true test will be on a 90 degree day when I am not at the mechanic checking for a problem.

As to the cold start issue, my problem appears to be a missing cold start air valve. Does anyone have any more info on this item? I am particular interested in the location of this part.

Thanks.

Ken,

The HC level is a reflection of the engine's ability for complete combustion...so, the HC level is very important. The lower the HC number, the higher the combustion efficiency is.

So...without cats, you should be able to achieve 180ppm HC, with 1-1.3% CO. Theses are the numbers that I have been able to obtain on numerous non-smog Ferraris, with not too much difficulty.

If I am understanding you correctly, the only way you can achieve low HC is with a CO of 3.5%. If this is true, there are still some problems with the CIS system that need to be addressed.

The CIS system does not know the difference between a 90 degree hot start and a 50 degree hot start...as the hot control pressure are the same.

Sorry, but I am not familiar with the (additional) cold start air valve.

Regards,
David

Ken,

again..3.5% CO is way way off. Yoy shoud have 1,2% CO & 180ppm HC as David stated...if you cannot achieve those numbers then the engine has issues that should be found and corrected. Those issues ARE the reasons your car will not start & run properly.

A test of the fuel system pressures is mandatory in these instances, not optional. There are certian procedures that must be followed to find solutions.

Regards, JRV

I will have pressure readings sometime tomorrow and post the results.

David and JRV. As I stated, when the co reading was at 1.2 or lower, the engine at idle did not sound right. The idle did not sound right until the CO was at 1.20 or higher. In addition, the HC reading was well over 200 (I forget the number, but I would have failed emmisions). Based on what you are telling me, I should be able to have a CO reading of 1.0-1.2 and a HC reading of under 200. Because my car does not currently produce these readings, I still have a problem with my fuel system. Again, I will post my fuel system pressures tomorrow.

>> I should be able to have a CO reading of 1.0-1.2 and a HC reading of under 200. Because my car does not currently produce these readings, I still have a problem ----with my fuel system. <<

Yes Ken you still have most likely several problems working in concert to produce the results of poor starting and poor running. While you may think your engine runs "fine", the 3.5 CO # disagrees with you, and says that the engine is "not running right". There are truly ALOT of factors working together to make an engine run. The fuel system is only one of those factors, but in every easter egg hunt we need to start somewhere in tracking down what the problems are and how to correct them. A good hunt has a good starting point. From there we fill in the blanks with info we need but don't yet have. You filled in one blank so far, CO &amp; HC....those numbers tell us (1- the Fuel Mixture &amp; Combustion effeciency are poor...now we try to find out WHY they are poor...

As the blanks are filled in with info a clearer picture will emerge.

Regards, JRV

Basics. Any mechanic learns in Fuel systems 101, check the 3 fuel pressures, system, cold control and warm control. I believe that your car may have a frequency valve controlling pressures, yes/no? Also remember that the hole through which the mixture is adjusted must be plugged at each test otherwise a leaner reading is obtained. If you can answer some of these questions, I am sure that the esteemed board pros will figure it out.