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Hipo64
Hipo64, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3483
Experience:  Work and diagnose electronics on daily basis.
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My 2009 ml320 blue tec is not starting. It auto cranks 7

Customer Question

My 2009 ml320 blue tec is not starting. It auto cranks for about 7 seconds then stops. I'm getting the p20e8 reluctant pressure too low message. Are these related?
Submitted: 1 year ago.
Category: Mercedes
Expert:  Hipo64 replied 1 year ago.

Hi and welcome to Just Answer! No this code will not cause no start. What is your fuel rail pressure?

Expert:  Hipo64 replied 1 year ago.

Not sure if you have scan tool able to read rail pressure. If pressure does not go up to(###) ###-####psi computer will not open the injectors, Common problem is leaking injector(s) back into return fuel line. Use brake cleaner as starting fluid and spray small amount into intake manifold during cranking time. PLEASE BE CAREFUL USING STARTING FLUID OR BRAKE CLEANER SPRAY CAN- YOU MUST USE SMALL AMOUNTS ONLY IF YOU SPRAY TOO MUCH YOU CAN DAMAGE THE ENGINE, BUT SMAL AMMOUNTS IS SAFE,

if engine starts and stays running, you have injector leak.

please check and let me know, Regards Pavlin!

Customer: replied 1 year ago.
One thing I didn't mention, this is intermittent i.e. it happens only sometimes. I've noticed it tends to happen after I've driven for about 30 minutes first time in the morning, turnew my ML off for about 10 minutes and then tried to start it. This is diesel BTW. I will check the fuel rail pressure the next time this happens. Until that I would like to keep this channel open.
Customer: replied 1 year ago.
Also how do I access intake manifold during cranking time?
Expert:  Hipo64 replied 1 year ago.

Good morning, you can remove the hose between intake manifold and air cooler on the passenger side. Or if you standing in front of the vehicle is to your left. Hose has a clip. You pull up this clip and pull out the hose. It takes couple of minutes.

Customer: replied 1 year ago.
Is it safe to do while the car is cranking? Also did you see my post about the intermittent nature of this problem i.e. it happens only sometimes. I've noticed it tends to happen after I've driven for about 30 minutes first time in the morning, turnew my ML off for about 10 minutes and then tried to start it. This is diesel BTW.
Expert:  Hipo64 replied 1 year ago.

Yes it is safe if you spray just small amount. Yes I know it is diesel. No I have not seen that post. But try this and let me know the result

Expert:  Hipo64 replied 1 year ago.

Yes I will keep this open, you can reply here when you have more information

Expert:  Hipo64 replied 1 year ago.

I may not be able to respond to you right away because I am working in the shop but will keep checking my messages

as often as I can.

Regards Pavlin!

Customer: replied 1 year ago.
I was able to get a reading using a new app on my android phone. When my car is idling it shows 1.28 Atm as the fuel rail pressure. Not sure how this compares to Psi. I will try and get a reading when it doesn't start and keeps cranking.
Customer: replied 1 year ago.
FYI, I changed the units of measure and it shows 130 kPa as the idling fuel rail pressure
Expert:  Hipo64 replied 1 year ago.

Hi, this reading isn't correct. You should see about 3000- 4000 psi on Idle. It vehicle is running pressure is good, it is the scanner I guess. What is the name of it?

Customer: replied 1 year ago.
BAFX Products - Bluetooth OBD2 scan tool - For check engine light & diagnostics - Android ONLY https://www.amazon.com/dp/B005NLQAHS/ref=cm_sw_r_sms_awd_KjSbwbH6ZRK77
Customer: replied 1 year ago.
I'm using OBD car doctor app
Expert:  Hipo64 replied 1 year ago.

okay, this tool should read standard ODD II info, but for some reason is not reading properly, best is to use diagnostic scan tool

again proper idle pressure is 3000 or 4000 or even 5000psi

during cranking pressure should rise very quick from 0 to up to a 1000 psi when engine fires.

Expert:  Hipo64 replied 1 year ago.

if pressure is low during cranking, then you have internal leak from injectors or pressure regulator

but I never have had problem with regulator it is always injectors, when vehicle is hot everything expands causing the issue.

if you can please check with different scanner and get back to me

Greetings

Customer: replied 1 year ago.
I don't think I need to open anything... I can just spray it directly at the intake entry. Here are some pix. Thoughts?
Expert:  Hipo64 replied 1 year ago.

Sure you can go thru filter intake port , I always prefer to go direct. But this is my own preference.

Customer: replied 1 year ago.
it did it again today... I managed to get another program to provide accurate reading of pressure. When cranking it was staying at around 100 psi (typical idling pressure is around 5K psi). Unfortunately I don't have starting fluid or brake cleaner to try what you suggested.
Expert:  Hipo64 replied 1 year ago.

Okay, so we know that we have loss of pressure. Please buy a can of brake cleaner and keep it in the car. Starting fluid has higher detonation and do not like to use on this engine.

Let me know, thanks!

Customer: replied 1 year ago.
What's the long term solution to this?
Expert:  Hipo64 replied 1 year ago.

Must find which injector(s) is(are) leaking and replace them. If fuel return lines are disconnected at the time car is not starting and you crank the engine, observe which injector is leaking through return port. Replace leaking injectors and problem is solved.

Customer: replied 1 year ago.
you don't think this might be problem with the high pressure fuel pump?
Expert:  Hipo64 replied 1 year ago.

No, those pumps are good.

Customer: replied 1 year ago.
I'm confused... if the injector is leaking. Shouldn't I encounter this problem all the time? Why is it intermittent?
Expert:  Hipo64 replied 1 year ago.

Because it expands when hot, you have tested the pressure and confirmed that it is low. Next is to spray into intake when no start. I have seen this many times. I have no chance to work on your vehicle, but symptoms are very similar.