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I have a 1999 ML430 and tonight suddenly it wouldn't go over…

Customer Question
I have a 1999...

I have a 1999 ML430 and tonight suddenly it wouldn't go over 35mph and the engine started to shake. Its not the transmission fluid, or any of the other fluids. What could be the problem?

Mechanic's Assistant: When was the last time your transmission fluid was checked? Changed?

I don't know when it was last changed The level was checked 5-6 months ago and to be on the safe side I added some transmission fluid tonight per the suggestion of someone that knows cars. It did not help the issue at all. Would the spark plugs or the cable to the spark plugs cause an issue like this?

Mechanic's Assistant: Are you fixing your ML430 yourself? What have you tried so far?

All I have tried was adding transmission fluid I have not done anything else. I've just been researching the issue on the internet I dont' want to do anything in case I damage it further

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

No that's it - the car has been running fine and every week I check the coolant and the oil.

Submitted: 10 days ago.Category: Mercedes
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Answered in 1 hour by:
7/11/2018
Mercedes Mechanic: Matt, Engineer replied 10 days ago
Matt
Matt, Engineer
Category: Mercedes
Satisfied Customers: 23,314
Experience: Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Hello and welcome to Just Answer

This sounds like a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.
1st thing to try is to remove the fuel filler cap and then flick the ignition on whilst listening for the brief ‘buzz’ of the pump
If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,
Ideally measure the pressure at the injector rail (should usually be around 3Bar / 45psi +) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

You can also get this issue with contaminated fuel , if there’s water or dirt in the tank then either the petrol floats on top of the water or the filter sock on the pump is choked up – so if the other things check out then I’d consider pulling out the fuel pump and cleaning the filter sock

And one other thing to try is to loosen off the fuel filler cap, as there’s a 1 way valve built into the cap to let air into the tank and so prevent too great a vacuum from being created as the fuel leaves the tank to the engine
If this helps then replace the cap with a new item

you don't mention any 'check engine' or other fault lights but if you do have one illuminated then this typically means one or more of the sensors has failed or has a faulty connection.

The fault can be something quite simple and nothing that’s going to stop the car to something quite major that will reduce engine power and possibly stop the engine

The ECU senses this and may put the car into 'limp home' mode which typically limits the revs and the amount of power available. Usually the car is safe to drive for a short distance as the mode is intended is intended to get you home without incurring any engine damage

The quickest route to repair is to have the car plugged into a diagnostic machine which will read off the fault code stored in the ECU (providing the light is still on at this point) and indicate which sensor has failed or whether the fault is more serious.

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Mercedes Mechanic: Matt, Engineer replied 10 days ago

My goal is to give you the best advice that I can and I hope that I've helped today. Please remember to rate my service by selecting from the 5 stars at the top of the screen before you leave. If you need more help, use the reply box to let me know.
If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

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Customer reply replied 9 days ago
I’ve had the problem diagnosed is the spark plugs - I have to replace 12 of them - how much can i expect to pay to have a mechanic do this?
Mercedes Mechanic: Matt, Engineer replied 9 days ago

OK

I think you mean replace all 8 plugs not 12? as this the M113 V8 engine so 8 cylinders.

unless you have a V12 in there? but an ML430 should be the 4.3 ltr V8 engine

you can go for genuine Merc plugs at $20 apiece or fit NGK plugs at $12 for the same result

so either $160 or $100 for plugs depending on what you would prefer

and then an hours labour to change them all

so if you use an independent their labour charge is usually about $80-100 / hour where a dealer rate is about $200 / hour at least

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Customer reply replied 9 days ago
Matt my ML430 has # 2,3,4,5,6,7 misfiring and that car has 2 spark plugs each which is 12 - this is what was diagnosed - I have purchased the spark plugs and just need them installed and just wanted an idea of what that would cost to have done.
Mercedes Mechanic: Matt, Engineer replied 9 days ago

OK thanks for letting me know

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