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Can someone tell me what pressure I should be seeing on the high side during crank?
Its below freezing right now, I'm seeing in the low 130 bar (less than 2000 psi) range and the car will not start. I'm wondering if my pressure regulator could be faulty. It's been having starting issues for a while now that I cannot solve.
I found an article that says I should be seeing 270 bar while cranking, last test showed around 134 bar. Seems like I have a pressure issue. maybe leaky injector or regulator problem, I guess?
Are you sure the battery is good? When it started to get cold last year, I had issues where everything seemed normal, except the cranking speed was off a little. It wouldn't start, but it fired off as soon as you put a jump on it.
new battery earlier this year. doesn't have any issues cranking. slower when the oil is cold but doesn't seem abnormal. On the charger tonight since I attempted several starts while looking at the live data. Fuel rail pressure seems very low. New in tank pump but I'm going to borrow a pressure gauge and verify low side pressure tomorrow if I can.
FYI. first start attempt this morning, no luck. pulled an air cleaner and sprayed some brake cleaner in the intake, after a longish crank time, it started. I'm thinking this is further confirmation that fuel pressure is an issue? going to warm it up and look at cranking pressure again with the scanner.
Normal rail pressure for start is close to 5000 psi, so sounds like you have some problems.
When it started? Can you read low fuel pressure?
If low pressure is OK, injector leak test might be next.
Pressure regulating valve is another item.
Old Diesel mechanic's trick: add a quart of 2-stroke oil to the fuel tank. If starting improves the injection pump is suspect (in this case, the high pressure pump). It raises the viscosity of the fuel.
Be careful spraying anything flammable into the intake of an engine with working glow plugs.
Do you have any documentation from Mercedes that shows necessary starting fuel pressure? 5000 psi seems high, it idles nicely at 260 bar which is about 3700 psi and I've never seen anything close to 5000 when cranking or idle. I've seen other figures tossed around for needed pressure to start in articles and the forums but as of yet, no actual documentation from Mercedes. I was hoping someone here would have it in a manual maybe?
So far, the conclusion is that I cannot read the low pressure with a scanner on this car. would need to T in a gauge. New in tank pump recently (old one was not turning on pretty regularly, new filter, all leaks fixed). New pressure regulator on the way to eliminate is a cause or future cause. Will get into the injectors if i still have an issue after all that I've done.
I found today that my air filters were overly clogged, this spring was super windy here with tons of dust daily, I'm thinking it caused early clogging. I left one off while replacing the camshaft sensor and starting became great! Unfortunately, I did two things at once, replacing the sensor and unrestricting the air. I'm betting on the air since the filters were as bad as I've seen. Maybe it was really throwing off the starting profile? Not sure that explains why it would not start when cold, maybe it was the cam sensor causing that? tomorrow morning's below freezing start will be a good test. If I have time I may put the old sensor back as a test.
fuel pressure readings at idle are unchanged after the filters and sensor, start happens quickly but the pressure looks to below 200 bar when it fires.
interesting trick about the oil, I'll remember that. I spray the cleaner into the intake pipe, engine was off and glow plugs turned off before it ingested it. so, I think I was safe from danger?
The crucial warning about spraying fluids into intake applies to engines, who have GP or other heating elements in the intake manifold.
Not the engines we know here.
I never have seen MB recommendation for pressure, but the question come several times and that is what I measured on my engines.
My engines start on 1st cylinder, so cranking pressure is not easy to catch.
I like HT200, what is clone of AP200 scanner as it shows whole troubleshooting parameters on single page.
It is cheap enough to buy it in situation like that.
Not sure on these cars but is it possible to be dealing with some fuel gelling going on? Not sure how cold it is in your area. Sorry without rereading everything did this start after some of the maintenance you did or was it just after a particularly cold night? Have you disconnected both batteries after changing severly clogged filters?
I have not disconnected the batteries, does the ECU require this? Is that written somewhere? or is that a best practice? Also, I have a thread on the w-164 side talking about my saga with more info if interested, I had compounding issues best I can tell, here I was hoping to get some clarity on required pressures. In any case the car started nicely this morning at an ambient temp of 21 degrees F. Fuel gelling crossed my mind but I've seen no evidence of water and get fuel from various stations, so I bet that is a low probability. Ignition was again around 130 bar of pressure. here is a graph of this morning's start from my youcanic scanner. I have a new pressure regulator on the way, I'll graph starts with that as well and see if there is any difference. I'll be sure and post my findings here.
Thanks for everyone's contributions to the post so far.
Readings for the quantity control valve and pressure control valve. I'm not sure about what units I should be using and what values are good yet, but figured I'd graph for comparison of the new valve. I was thinking that qty and pressure is the same valve on this engine, is that correct? The scanner reads two values though so I'm not sure. I also have no idea if these graphs look normal or not. They are from the same start as the rail pressure graph above.
I've been sent an image form the star system that shows idle rail pressure should be between 292 - 332 bar. That seems to confirm that I have a low-pressure issue at least during idle. Not sure what pressure it is supposed to fire at, since mine seems to fire at much lower pressures than that. Hopefully its not the pump. we'll see.
Are you sure the battery is good? When it started to get cold last year, I had issues where everything seemed normal, except the cranking speed was off a little. It wouldn't start, but it fired off as soon as you put a jump on it.
My cranking RPM is around 160 when warm. Everything I've found states it should be 200 RPM. With a gear driven pump, I'm assuming this could be the cause of lower starting pressure? It sounded like the car was cranking fine, fast even. But the scanner data is telling a different story.
The battery has also had a good charge during this process since it wasn't starting at one point and I felt it was getting low from cranking.
Doesn't explain idle pressure, but still seems like something I need to correct before moving on with my starting issues.
I replaced the starter, and the starting issues have all now been resolved. I'm thinking that the weakened starter was causing reduced heat and pressure during cranking. The car fires up quickly now under various temp conditions. It seems that idle pressure is still low however, it idles fine, but I may replace the regulator sometime soon to see if that changes anything.
12-15-2022, 08:14 PM
