Hard start (long crank) on 4.8is

[FourPointEight-is]

I am having some trouble with my X5 starting. Sometimes it’ll crank and crank and crank for over 5 seconds. Then eventually it’ll start up. It’s never failed me yet. Also it seems very sporadic. Sometimes it happens and sometimes it doesn’t. It also runs fine when passing etc (no misfires under full load). Does it both when hot and cold.

Once it does start it splitters and coughs for about 10-15 seconds almost like it’s gonna stall out and the eventually settles in.

I scanned the DME, found fault codes stored for cylinders 4,5,7,8 misfire. Cleared them, went for a drive and came back but found no stored codes.

I viewed the live data for the engine RPM signal when cranking and found that it does give data even during the long crank. It spun up to about 150rpm until it finally “caught”.

The fuel in there is new, I just topped it up last week.

Any ideas?

I’ve heard it can be the fuel filter or the crank position sensor. I don’t just want to throw parts at it without verifying what the fault is though...

[Overboost]

Originally Posted by FourPointEight-is

I am having some trouble with my X5 starting. Sometimes it’ll crank and crank and crank for over 5 seconds. Then eventually it’ll start up. It’s never failed me yet. Also it seems very sporadic. Sometimes it happens and sometimes it doesn’t. It also runs fine when passing etc (no misfires under full load). Does it both when hot and cold.

Once it does start it splitters and coughs for about 10-15 seconds almost like it’s gonna stall out and the eventually settles in.

I scanned the DME, found fault codes stored for cylinders 4,5,7,8 misfire. Cleared them, went for a drive and came back but found no stored codes.

I viewed the live data for the engine RPM signal when cranking and found that it does give data even during the long crank. It spun up to about 150rpm until it finally “caught”.

The fuel in there is new, I just topped it up last week.

Any ideas?

I’ve heard it can be the fuel filter or the crank position sensor. I don’t just want to throw parts at it without verifying what the fault is though...

My suggestion would be to monitor the fuel pressure. It should hold at least 35 PSI pressure over an extended period of time. It sounds like the pressure is bleeding down from a bad fuel filter/pressure regulator or leaking injector(s).

[andrewwynn]

Pressure should be 50 psi. Definitely start with fuel pressure

[Overboost]

Originally Posted by andrewwynn

Pressure should be 50 psi. Definitely start with fuel pressure

Yes sir 50 PSI running, no less than 45 PSI after 15 minutes but at least 35 PSI after sitting overnight or after a few days.

I'm not sure on the 4.8 fuel pump but when the key is turned to position 2 the pump should prime. Maybe the OP can turn the key to position 2 several times before cranking to prime the pump/system to see if it is better. This would give an indication that the fuel pressure is low.

[FourPointEight-is]

Originally Posted by Overboost

Maybe the OP can turn the key to position 2 several times before cranking to prime the pump/system to see if it is better

So I went to try this today. I turned on the key, waited 5 sec, turned it off. Repeated this twice then I went to start the car and the starter went whirr-whirr-click-click-click.

Swapped out the battery with a one from my bench, verified charging system is working OK (shows 13.8-13.9 batt voltage with engine running).



Got to work, parked the up and 2 minutes later someone alerted me my alarm was going off...



Anyway back to the original issue at hand - even with this new battery that's been on the maintainer still cranks forever before starting. No codes stored in the system either (according to my Launch 123). Unfortunately my Launch won't read the fuel rail pressure. Will report back when I manage to get a tool that can do this.

[andrewwynn]

You can use a tire pressure gauge to measure fuel pressure. Just don't use your favorite in case gas affects the seal inside. Also very often when engine turns over slow it's the starter. When a starter fails it will take more and more current. Up to 50% more. The extra current kills the battery voltage and it's got less power so It will crank very slow and long.


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[andrewwynn]

You need to measure for parasitic drain and measure starting current. If you have a peak reading volt meter like a fluke measure the voltage drop from B+under the hood to the cig lighter and multiply by 180. Eg 1.25*180=225A.


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