Author Topic: Slow starting problem  (Read 161 times)

irvine

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Slow starting problem
« on: 02 June 2019, 03:00 AM »
Hey everyone, I’ve a a recent problem that I need to fix before I get stuck.
If the car is left overnight or for a long period it’s hard to start.
It cranks but is hesitant to start. The battery has 12v and keeps it no problem (only a year old) so that rules out the alternator. As I’ve also replaced the voltage regulator.

Is there a way to test the starter motor??

Only things I’ve yet to replace are the coil, starter and alternator.

Thanks Neil.

daantjie

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Re: Slow starting problem
« Reply #1 on: 02 June 2019, 06:50 AM »
Maybe check fuel delivery. Sounds to me like classic fuel accumulator issue.
Daniel
1977 450 SEL 6.9 - Astralsilber

s class

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Re: Slow starting problem
« Reply #2 on: 02 June 2019, 10:32 AM »
Unlikely.  Fuel accumulator problems are evident after 30 to 60 mins cool down.  Not an issue after an overnight full cool down.

'76 6.9 Euro, '78 6.9 AMG, '80 280SE, '74 350SE, '82 500SEL euro full hydro, '83 500SEL euro full hydro , '81 500SL

revilla

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Re: Slow starting problem
« Reply #3 on: 02 June 2019, 01:02 PM »
Hi Neil,
There are 2 big branches: fuel and spark.
Do you have spark coming out of the coil?
If yes, do you have spark at plugs? check all 6. If yes to both, you can focus on fuel.
When you experience the engine start problem, put your lever in ‘D’. Then turn the key as if you are trying to start the engine. This won’t engage the starter but it will engage the fuel pump, thus pressurizing the system. Stop after 10/20 seconds. Go back to ‘P’ quick. Try a normal start. Any difference?
I don’t think it’s your accumulator as once system under pressure a failing accumulator will take a while to let the pressure down.
I’m assuming your engine cranks (right?) so let the starter alone for now.
My guess is a leaking injectior(s), one or several out of seven. If you floor the throttle and the engine starts better it means your system was flooded (leaking injector).  Flooring the pedal puts tons of air in thus flushing the excess of fuel.
Give these simple tests a try and let us know so we can rule things out before nailing the root cause.
It’s too early in the process but later you can also check timing and mixture as both can cause the symptoms you described.

Cheers
Robert
W116 1977 280SEL & 1979 280SE

irvine

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Re: Slow starting problem
« Reply #4 on: 02 June 2019, 11:23 PM »
A leaking injector does sound close.
Injector 3 had a slight leak and possibly failed seal.
I’m about to order a seal kit for the injectors and refurb the fuel system while I’m at it.

I’ll get the kit ordered ASAP and see what happens.

You guys are legends 👍
Thanks.

revilla

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Re: Slow starting problem
« Reply #5 on: 03 June 2019, 02:43 AM »
Good move Neil.

As you are refurbishing the fuel system that should include your WUR.  I can assure you that once all pressures (system P, control P and static P) are in spec, tuned mixture, working thermo-time switch, cold start injector, operational AAV, good accumulator, good check valve at the pump, new filter, tuned pressure regulator at the FD  and no air leaks the engine will start in 1 millisecond cold and hot guaranteed  :)

It takes a bit of patience but the results are rewarding.

Good luck

Robert

 
Robert
W116 1977 280SEL & 1979 280SE

TJ 450

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Re: Slow starting problem
« Reply #6 on: 03 June 2019, 09:37 PM »
What you could do is send the WUR and fuel distributor away for refurb and calibration depending on whether you have a backup vehicle. K-Jet Colin in Qld has everything to get them A1. The injector seals are a good start though, it it would be worth changing or cleaning the strainer in the fuel tank if you’re really keen.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394

TJ 450

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Re: Slow starting problem
« Reply #7 on: 03 June 2019, 09:38 PM »
Also, if the cold start valve is malfunctioning the car will be difficult to start in cold weather.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394