Difficult Wam Starts - Warm up Regulator? - PeachParts Mercedes-Benz Forum

Mervyn · #1 09-11-2002, 02:51 AM

I've gone thru all posts on the "warm up regulator" but somehow I still need someone to address my problem.

Mine is a Euro 1983 W126 (280SEL) - M110 engine. I've been having difficult warm starts lately. Takes a couple of seconds of cranking and flooring the accelrator to get the car starting. My mechanic suggested the problem to be the warm up regulator, but before I spend that $$ on it, I thought I'd better check it in this forum first. The regulator is not cheap.

Another symtom which I thought could be attributed to the regulator is that the car, when started, goes to very high RPM for about 30 secs to a minute, before finally dropping to normal idle speed. The same happens when I shift from "D" to "P", even when after driving for some time.

Could anyone tell me what is really at fault? I've checked and my car does not have the infamous OVP relay, so I've ruled that out.

I've got new Idle control valve, cap and rotors, plugs, fuel filter etc........or could the cause be the fuel pressure regulator?

Any advice is appreciated, thanks!

#2 09-11-2002, 06:01 AM

Disclaimer - coming from some CIS experience, no direct MB knowledge.
Sounds more like an extra air valve problem than WUR. Even if WUR went very rich or very lean, revs would not go very high. For peace of mind, put a gauge in between distributor head and WUR, check cold and hot pressures. Hot should be ~50-60% of system pressure, cold around 20psi or less.
Check that you have 12V to the WUR, extra air valve, thermotime switch when hot. If the extra air valve opened while hot you would have a high idle all the time. Sure the throttle is not sticking open?

HTH
jp

stevebfl · #3 09-11-2002, 08:20 AM

As jp said, engine speed is a air flow problem not a fuel quantity issue.

Forget the term warm-up regulator. Use the term control pressure regulator and you will stay out of trouble here. It keeps one from assigning functions by leaving the interpretation out of the name. In your symptoms the car is already "warmed-up" and the control pressure regulator has the smallest affect on a warm car.

My initial reaction was a vapor lock condition caused by the loss of residual fuel pressure. The condition of high idle speed changes that concept. With that thrown in I think you have a variable vacuum leak. Large enough to impede lean restarts, high enough to raise the rpms. One part that the euro car has that can cause this is a decel dump valve. It is a black plastic valve bigger than a golf ball and hooked to two large rubber pipes and a small vacuum line. It is below, outside and to the front of the airfilter. During throttle closed decel the vacuum line causes the valve to open and large volumes of air dilute the mixture.

Mervyn · #4 09-12-2002, 11:44 AM

"As jp said, engine speed is a air flow problem not a fuel quantity issue."

Thanks JP and Steve, for drumming that into my head. Why didnt I think of that? I'd always thot the high idle is due to fuel delivery problems.

But what I couldnt figure out is how, when there is a vacuum leak, leads to the warm start problem? Steve, could you explain what is meant by "Large enough to impede lean restarts, high enough to raise the rpms. " Why I ask is because the warm start problem occurs only about 2 weeks ago, while I've been having the high idle for 2 years already ever since I bought over the car.

Took down some figures today:
Start from cold - Idle at 1300RPM (lasts for approx. 2mins before dropping to 600RPM)
With engine warm, "D" engaged to "P" - idle raises again to 1300RPM even after driving for about 30 mins. Drops to 600 again when "D" is engaged.
Warm starts - idle rises immediately to 1300RPM despite warm engine, and stays for about 30 secs before dropping to 600

Sometimes it gets rather embarassing to have a loud running engine in a stationary car, especially late at night in a quiet neighbourhood, or in an enclosed carpark.

JP: the throttle isnt open all the time, and besides, the high idle only comes on when the car is started or when engaged in "D"

Steve: I'll go check the decel dump valve tomorrow. WHat other vacuum items should I check? If it really is a vacuum leak, why is it affecting only the warm starts and idle, and not the central locking and/or other vacuum controlled functions? Is this going to be a trial-and-error method of slowly replacing vacuum lines and valves?

Pls advise, thanks again!

#5 09-14-2002, 02:31 AM

What are you gear changes like? There is usually a vacuum connection to a modulator in the box, and if that line is damaged/broken, or the modulator in the box is leaking, you have an air leak. This should cause some hard shifts, so you should have noticed it. The way it starts running high then slows down may point to a softened/cracked hose that leaks briefly, then shuts as it is distorted by vacuum. Maybe the extra air valve is misbehaving? Any other strange things happening?
jp

Mervyn · #6 09-14-2002, 07:27 AM

Hi JP, thanks for your input. My gear changes are a tad rough at times, and it has been so since I bought the car 2 years ago. I would say the occasional harsh shifting is not yet to the extent to requiring a tranny overhaul. I've already replaced my ATF, fliter, and vacuum modulator in the past year.

I like what you'd suggested - "a softened/cracked hose that leaks briefly, then shuts as it is distorted by vacuum" - it is similar to Steve's suggestion that it might likely be a variable vacuum leak. Fuel delivery seems alriight, the pump is buzzing, the fuel filter is new.......I agree its more likely a vacuum problem.

In fact, I just got back from the mechanic's shop for my regular servicing, and my mech also thinks its a air valve problem rather than fuel related. But because I'm running late, so I shall come back another day to let him have a thorough check on the vacuum lines and valves.

Steve, I've located the black decel dump valve, but how do I check if its leaking or not?

kennysin · #7 01-23-2003, 09:46 AM

Hi Mervyn

Great to have got in touch. I have the same problem as your w126, and my mechanic located the valve and found if faulty. However, on replacing the valve, a new problem arose. Every time the valve engaged (vacuum controlled by a solenoid switch activated by microprocessor) extra air creates a very lean mixture and the engine stalls. My workshop is unable to explain the phenomenon, and I have had to put the faulty valve back.

Some thoughts:

1. If the vacuum leak is from this source, plugging the vacuum line should improve the warm start and idle status.

2. There should be no adverse impact from this action since the valve does not work anyway.

3. It is greatly puzzling why replacing a faulty valve should create a new problem.

4. There must be a coexisting fault somewhere else to have produced this domino effect.

I'll keep you updated of further developments!

Kenny

Mervyn · #8 01-24-2003, 07:20 AM

Yo Kenny, welcome to the club!

For the benefit of others who has not been following this thread, I am still living with the abovementioned problems.

Here's my thoughts:

1. Kenny, perhaps u might want to re-adjust your lean air/fuel ratio via the screw located beside the engine body. It might be that your mixture was adjusted to compensate for the faulty valve and so tho it might work previously, it is actually low on air and thus your new valve makes it even leaner to the extent that it stalls. Just a layman's thot on this.

2. You might want to try the new valve on my car and see if the same thing happens. Might yield more leads that way.

Awaiting good news from u, cheers!

Regards

stevebfl · #9 01-24-2003, 07:45 AM

I lost track here a bit as I really have never read the theory of operation of the valve. I have neutered every one that got in my way; making the car run good. They were designed only to take the fuel away in decel. Basically it bypasses the airflow meter.

No US model used any such devise so I have never seen a wiring diagram. Its vacuum controlled, with the vacuum coming from an electricallyt controlled switch over valve. I don't know who does the control but it should only open when in decel. Decel is defined as closed throttle, high rpms. From the engines stand point there is never a time for this valve. So bypassing it is an appropriate test mechanism. If the car exhibits the same problem with it blocked then its not part of the problem.

kennysin · #10 01-24-2003, 08:37 AM

Hi Mervyn,

Thanks for the suggestion. I am pleased to announce that I have solved the problem.

My workshop finally installed the new decel dump valve, solving the vacuum leak. However, as Steve mentioned, the valve had to be neutered. The electronic switch is activated by a push-rod mechanism behind the injector system, and by moving the switch out of reach (a distance of a few mm), this prevented activation. Other possible solutions is to disable the power supply, or just unplug the vacuum line from the valve and stopper it.

The warm start is now perfect. The idle speed at D and P are now within normal limits (600-700, smooth idle). However, the auto trans is still a bit harsh, but none the worse.

Steve - thanks for the pointer to the offending valve. Although the warm start was fixed, we had no clue as to the function of the valve, and at one point my workshop guy was wandering around all the workshops in the locality with the part in his hand seeking a "guru" with an answer!

After that, I tracked down an exMB technician (he started in 1985, at the time of the switchover from the M110 to M103) and showed him the valve. He confirms that he had no clue as to its function, but was a common cause of hot start difficulties even then. The fix, when he was in MB, was to block the valve(!), and he opined that I need not have obtained a new replacement!!

Mervyn - I hope this helps your car.

Thanks for the assist guys

Kenny

Mervyn · #11 01-25-2003, 06:48 AM

Congrats Kenny, its always nice to hear good news!

I'll definitely give it a try, and thanks also to Steve and JP for their patience and valuable insight. Will let everyone know if I succeed as well!

Cheers...

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