[mchez]

I've been searching around for a while and haven't found anything quite like my example (yet) so I thought I'd post one.

Scenario: 2011 E90 335i starting after car has recently been run (going from store to store)

Problem: Car has a very weak crank when warm. The starter sounds like it is coughing into life and then the engine turns over. Only twice has it not started on the first try but when it didn't start the first time it started the second.

Cold starts are just fine. Car takes less than a second to go from button pressed to running.

The HPFP was replaced by the dealer when I bought the car just over two years and 30K miles ago and it has always had this problem, but I can tell it is getting worse because the two instances of the car not turning over the first time have happened within the past two weeks. The LPFP has yet to be replaced by me and the car has PPK on it.
I feel as though I should also add that upon low speed maneuvering (backing into a spot mostly) the car will surge and buck. RPMs will oscillate from ~800-1200 and will then return to normal after a few seconds. These could be unrelated, but I figured I'd share.

Any thoughts?

[weehe126]

Sounds like a vacuum leak the gets worse when the engine bay gets hot (plastic gets soft with heat).

[mchez]

Originally Posted by weehe126

Sounds like a vacuum leak the gets worse when the engine bay gets hot (plastic gets soft with heat).

A vacuum leak can cause a weak crank? Novice DIYer here, so any info on why that could be would be extremely helpful.

[vilord]

My N52 does this too... strong crank when cold, and weak crank when hot. Sometimes I wonder if it will start at all, it barely turns the first few turns. Sometimes it *doesn't* turn, but on the second press it'll turn slow and then start.

I replaced my battery yesterday because I was starting to see other battery-is-old problems... I don't know if that will fix it though.

I wonder if the oil that is in it is too heavy... maybe the shop put in 10/40 instead of 5/30, and since the oil hasn't cooled off it is still thick and the starter can't keep up? I dunno... Or maybe my starter is weak.

For you, the surging and bucking sounds like a vacuum leak.

[mchez]

Originally Posted by vilord

My N52 does this too... strong crank when cold, and weak crank when hot. Sometimes I wonder if it will start at all, it barely turns the first few turns. Sometimes it *doesn't* turn, but on the second press it'll turn slow and then start.

I replaced my battery yesterday because I was starting to see other battery-is-old problems... I don't know if that will fix it though.

I wonder if the oil that is in it is too heavy... maybe the shop put in 10/40 instead of 5/30, and since the oil hasn't cooled off it is still thick and the starter can't keep up? I dunno... Or maybe my starter is weak.

For you, the surging and bucking sounds like a vacuum leak.

Vacuum leak causing the surging could be the culprit. I've read that the lines are relatively easy to replace.

I replaced my battery early '18 and it changed nothing about the way the car slow cranked. Oil viscosity is thicker when it's cold, right? So wouldn't it be harder to start when it's cold?

It sounds like you and I have similar starting issues. I'm taking it to the shop on Thursday to get it looked at and will update once I get word as to what it is. I'm hoping for LPFP or starter as it's cheaper than HPFP.

[Antetokounmpo]

Check your engine to frame ground cable. They fray really easily at the bend causing high resistance and very slow crank at times. Had this exact problem on my car and my sisters e90 within the last month.

[vilord]

multigrade oils (10w30, 5w30, 15w50 etc) act different than single grade oils.

0w40 mobil 1 synth for example (which i used to run in my supra) is like water when cold, but is quite thick when warm, and then gets thinner again when very hot. The idea being that it will act like a lightweight oil when cold, to avoid sludging or causing the engine to work too hard to move the oil around, but then when hot it'll act like a thicker oil so it will still lubricate parts.

[vilord]

Originally Posted by Antetokounmpo

Check your engine to frame ground cable. They fray really easily at the bend causing high resistance and very slow crank at times. Had this exact problem on my car and my sisters e90 within the last month.

I had a new ground put in by an independent shop a couple years ago because the old one broke in half and I had to attach jumper cables from the frame to the engine to get it to start at all... I wonder if that replacement is already fraying or if the shop didn't do a good job of cleaning up the attachment points. I think I even have a spare on the shelf.

[Antetokounmpo]

Originally Posted by vilord

I had a new ground put in by an independent shop a couple years ago because the old one broke in half and I had to attach jumper cables from the frame to the engine to get it to start at all... I wonder if that replacement is already fraying or if the shop didn't do a good job of cleaning up the attachment points. I think I even have a spare on the shelf.

Try to ground the engine to the frame again with jumpers like you did. This is how I determined mine was a bad ground.

[mweisdorfer]

Originally Posted by mchez

I've been searching around for a while and haven't found anything quite like my example (yet) so I thought I'd post one.

Scenario: 2011 E90 335i starting after car has recently been run (going from store to store)

Problem: Car has a very weak crank when warm. The starter sounds like it is coughing into life and then the engine turns over. Only twice has it not started on the first try but when it didn't start the first time it started the second.

Cold starts are just fine. Car takes less than a second to go from button pressed to running.

The HPFP was replaced by the dealer when I bought the car just over two years and 30K miles ago and it has always had this problem, but I can tell it is getting worse because the two instances of the car not turning over the first time have happened within the past two weeks. The LPFP has yet to be replaced by me and the car has PPK on it.
I feel as though I should also add that upon low speed maneuvering (backing into a spot mostly) the car will surge and buck. RPMs will oscillate from ~800-1200 and will then return to normal after a few seconds. These could be unrelated, but I figured I'd share.

Any thoughts?

You won't know if your LPFP needs to be replaced unless you check the PSI on it at idol & WOT.

I don't know on an N55 what it should run at. On an N54, it should be at least 72psi & in the 60's at WOT. Mine runs at 82psi at idol 99% of the time.

I did change my LPFP sensor to the updated version before I decided to change my LPFP out. At 167,000 miles, I wanted to make sure I was getting valid Data.

[mchez]

Originally Posted by vilord

multigrade oils (10w30, 5w30, 15w50 etc) act different than single grade oils.

0w40 mobil 1 synth for example (which i used to run in my supra) is like water when cold, but is quite thick when warm, and then gets thinner again when very hot. The idea being that it will act like a lightweight oil when cold, to avoid sludging or causing the engine to work too hard to move the oil around, but then when hot it'll act like a thicker oil so it will still lubricate parts.

Today I learned!

[mchez]

Originally Posted by Antetokounmpo

Check your engine to frame ground cable. They fray really easily at the bend causing high resistance and very slow crank at times. Had this exact problem on my car and my sisters e90 within the last month.

I will definitely look into that. Could a failing frame to ground cable also cause coolant level sensor issues? For the past week my car has been telling me it's low on coolant when it isn't (I check every time I drive it). Issue happened as I was starting the car when it was already warm.

[Antetokounmpo]

Originally Posted by mchez

I will definitely look into that. Could a failing frame to ground cable also cause coolant level sensor issues? For the past week my car has been telling me it's low on coolant when it isn't (I check every time I drive it). Issue happened as I was starting the car when it was already warm.

No it wouldn't

[mchez]

Originally Posted by Antetokounmpo

No it wouldn't

One thing at a time then. I'll take it in to my Indy shop tomorrow and see what they diagnose. Thanks for your help!

[oVeRdOsE.]

Originally Posted by Antetokounmpo

Check your engine to frame ground cable. They fray really easily at the bend causing high resistance and very slow crank at times. Had this exact problem on my car and my sisters e90 within the last month.

+1. By the mean time OP can do a proper grounding kit. even if it doesn't fix the issue, on older car its always a smart idea to do one.

chassis to block, block to alternator, alternator to battery. 8ga wire.
Some people like to ground the throttle body and the starter also, but its up to you.

On those car a ground back to the battery is a bit overkill since its in the trunk, I might go with a 1ft new 8ga : battery to the chassis.

I've also noticed anemic starting on my car, and in fact the passenger side ground was broken. Its been fixed, but I did not complete the grounding kit yet. Soon if I have time, I have all my supplies.

[mchez]

Just to update everyone: I took it to my Indy mechanic and the grounds were all good, the battery was good, but the starter was not. They stress tested it by turning it on and off a few times and after the 3rd or 4th try the car refused to start.

New starter and intake manifold gaskets installed for $600. Starts great now! Now to find the source of the surging...