Long cold crank - 560SEL - PeachParts Mercedes-Benz Forum

MikeTangas · #1 11-20-2003, 07:37 PM

This just started during the past week. When cold, sitting for at least 8 hours, the first start takes a good 5-10 second crank before catching. A quick search shows mostly hot start problems, with many suggesting the fuel accummulator or fuel pump relay as the culprit.

On warm/hot starts it catches fast, fast enough you only have to tap the key. It would appear my symptoms are 180* out from everyone else's. Any suggestions on where to start, fuel pump relay or accummulator or cold start valve?

I only have a limited time to sort this out before heading off to the Great White North, where I expect many cold starts.

#2 11-20-2003, 08:06 PM

I had the same problem with my '91 GTi (just sold) and it was the cold start valve. I can thank the Bentley book for some welcome help. My relatively uninformed 2 cents.

Q · #3 11-20-2003, 09:49 PM

Don't forget that there is a fuel line check valve as well as the accumulator that could be the problem.

MikeTangas · #4 11-21-2003, 01:44 AM

I will check the cold start valve for function this weekend. If the CSV checks out I will move to the fuel accumulator. What would be the best test for the fuel accumulator?

I haven't considered the check valve(s) because the problem only exists on full cold starts (8 hours or more parked). I would expect the condition to be present for any start after even a couple hours down.

Time to study on the manual.

william rogers · #5 11-21-2003, 02:23 AM

Mike, My 500 SE dose the same thing but the way I figure it if it never fails to start that 10 seconds of cranking is bringing the oil pressure up.not a bad thing on a cold engine that has been sitting. I always pull the coil wire after an oil change and crank the engine a good bit...........
William Rogers.........

#6 11-21-2003, 09:22 AM

Mike - I would suspect the check valve - logically - it makes sense. If the valve has a slow leak it would take about 8 hours to lose enough pressure to cause the car to crank before firing. I have an old Olds with a V8 and 4 barrel carb on it - the carb has an internal leak that causes the fuel to drain out overnight that causes the car to crank 10 times before starting in the morning -the rest of the day it starts first crank. With the fuel pressure dropping on your car after 8 hours - the check valve seems a good culprit. The accumulator normally acts up when the car is hot and you cannot get enough fuel pressure for it to run properly until you get it to rev a couple of times. I know because mine was bad. Even though it started cold perfectly - it was a nightmare getting it to stay running when first started hot. I would say go for the check valve first.
Morris

mhingram · #7 11-21-2003, 11:12 AM

I am in agreement with moedip, the check valve is the most likely issue. Jump the fuel relay or turn the key to 2 three or four times before cranking it if it starts up fine then you have a slow leak back somewhere the cheapest fix is the check valve.
m

mhingram · #8 11-21-2003, 04:34 PM

the check valve is the cheaper and easier fix if it does not fix it then the accumulator could also be leaking down slowly. If it is the accumulator, it should leak out of the vacuum line into the valve cover not good for the oil but you may see it some gas in the line, Anyway just more stuff to check. Again that is if priming the fuel system fixes the problem if priming does not work then you maybe right it is the cold start system.

MikeTangas · #9 11-21-2003, 05:20 PM

OK, check valves are in the "check it out" mix. Funny, I never thought of them as being the problem because I would expect them to be good or bad, but not a little bad. I'll let the pumps pressurize a couple times before starting after shift, we'll see how it starts then.

Now to check on prices.

MikeTangas · #10 11-21-2003, 08:54 PM

I gave the pumps a couple three cylces to pressurize. Only had a marginal improvement in the start time. Tomorrow, or later tonight I'll try to check the CSV.

mhingram · #11 11-21-2003, 09:15 PM

bummer sorry mike, check your temp sensor while your at it.
m

MikeTangas · #12 11-22-2003, 02:12 AM

Well the car got good and cool, almost 7 hours of sitting after getting home from work (and temp is ~50*F). I pulled the CSV, first thing I noted was that both cap screws were loose, not falling out loose, but not tight. Got the CSV up enough to place in a "vessel" then cranked the engine. Working alone I couldn't see if it was sraying a fine mist or not, engine never started but I cranked a good 20 seconds (probably because of the open hole in the intake), with the expectation that if the valve was functioning there would be fuel in the vessel.

When I went back to the engine the vessel was bone dry. Not even so much as a drop of fuel formed at the injector end.

Now it's looking more like the CSV has gone south for the winter, but I still have to check the temp sensor. Next question is which of the temp sensors drives the CSV?

stevebfl · #13 11-22-2003, 12:10 PM

We have been through this before. If you wish to use archive data to assist diagnosis you MUST understand the underlieing principles.

The whole fuel pressure/ accumulator / leak down affair only affects HOT!! restarts. This is not a problem to cold starting and the accumulator or pressure reserves are only necessary when not running to keep the fuel from boiling. Bag that one!

Cold start injectors whether working or not have never fixed any MB I have ever worked on (I do live in Florida though), with the possible exception of a leaker or two.

I would look to EHA current and see if you are getting ANY first thing and second to see if there is sufficient starting and cold enrichment increases in the current. You shopuld have a combined current while cranking of 50 - 80ma. When it starts the starting enrichment part will go away and you should be left with as much as 20ma cold running enrichment (varies with temp).

stevebfl · #14 11-22-2003, 12:13 PM

BTW, the cold start valve does not operate above somewhere around 50degrees. At the temp it first operates at it will only open for just the briefest time. The time interval increases as the temp drops to a maximum of 12 seconds at -20deg and below.

mhingram · #15 11-22-2003, 12:31 PM

Mike, I believe it is the black four prong on the driver side just behind the csv.
m