dllhg

Just in the last couple days I started having these issues. Car has always started quickly before. Did it maybe once or twice before but today it did it every single time I restarted the car. Turn key and starter sounds strong /fast but it doesn't fire. Had to turn all the way off and start over. When it does start I have a rough idle for a while before it settles down. It almost reminds me of a old carbed car that gets flooded or something.

Actually the last week or two I have been having a really rough idle on start up for maybe a minute then all is good.

Another strange thing that has happened three times so far. Going up steep hill in turns really slowly like 5-10 MPH the car suddenly has no power like the gas isnt pushed down. Push down 50% and nothing. then goes back to normal.

Also noticed a much stronger exhaust smell inn the cabin than before. First I thought it was an exhaust leak or something. Now Im wondering if there is a fuel issue.

Have good fuel pressure. Plugs ? MAF sensor ? Fuel pump ?

Any ideas ?

09_BSM_Z51

internet diagnosis is telling me fuel pump. Hate to say it because it's a nightmare to deal with in these cars. Your gonna have to take it to a shop to be sure though. Fingers crossed it's something easy and I'm wrong.

Dano523

Start with swapping the fuel pump relay in the engine fuse box with another one of the 8866 relays that is not being used that much instead. This will to weed out if the problem is just the fuel pump relay in the engine fuse box itself going south alone.

Also, have you pulled codes to see what has been stored? Hence not just a full out trouble code, but what was stored in a mode 6 scan that may not have tripped enough times before becoming a full trouble code instead.

schpenxel

He said fuel pressure is good?

Joe_G

Any codes?

AORoads

Maybe try the inexpensive stuff first: push on all the plug wires to make sure one hasn't suddenly come slightly/completely disconnected. It has happened at least a few times on here in just the last year. Codes, if there any, would also be a good source of info.

timd38

So, are you saying relays can deteriorate and still work?

Thanks!

Joe_G

They infrequently go bad, but I've never seen one partially work. They either work or not, they are simple electromechanical switch that has been tried and true for a very long time.

BUT I certainly haven't seen it all, I get surprised all the time with stuff I've never seen.

timd38

Same experience here. That is why I asked.

Thanks!

dllhg

Thanks,

No I havent had any codes pop up. I have HP tuner would that work on stored codes even if they dont trigger the light ?

Fuel pump cant be worse than my E55. $1200+ for pumps plus labor ..

Could pump be issue even though I have good pressure ? It reads pretty solid 50 PSI soon as key goes on.


Cold start fires right up every time. Leaving it off for a few minutes it is fine. When it sits for a decent amount of time then start up it does this. That being said, today I stopped it for about 1 hour and it was just fine. Rough idling too on start ups for a few weeks now for maybe 30 seconds. when I go WOT the power is all there and fuel pressure seems solid.

Joe_G

Yes HP tuners will get stored codes.
I don't think this is fuel pressure related. It's pretty common for cammed and tuned cars to do this. The change in weather could have caused it to come up now. If you add say 5% more starting airflow it should fix it. There is a table in Hp tuners for starting airflow. Or you could give it a little gas with your foot which is doing the same thing.

timd38

Are you running E85? We got bought by a big oil company and got an education about E85 and I won't use any E85 out of pump. The quality is very inconsistent and could be the issue.

schpenxel

You have to drop the fuel tank to get to the fuel pump in these. GM's method involves dropping the transmission/rear cradle/torque tube to get access.. so I suspect it is actually worse than on the BMW (labor wise). It's not really necessary to pull the driveline, but it's a tight squeeze with it in. New pump/fuel level sensor is ~$250 so it's at least better parts wise.

If you have solid and consistent fuel pressure I don't think that's your problem though

Dano523

Yep, motor needs air, spark, and fuel.

So if you can weed out the fuel as not being the problem, the next on the list is spark. Hence could be a problem with the crank or cam sensors or there wiring instead when the car get hot.

The cam shaft sensor is not too bad to get to since it on the front of the motor to the right of the HB to check it to make sure it still plugged in/ the lock tab on it has not broken off and allowing the wiring harness to back out of it when the motor gets hot.



While the crank shaft sensor it a real bear to get at since it hidden down on the side of the starter isntead.
Back one on the left, and yes that is the top of the starter in the second photo.

dllhg

Not getting email notifications ...

Okay will check for stored codes. Weather is back to 75 degrees right now. It didnt do this before. also cold start or if it sits a decent amount of time is fine. Still worth changing those tables you think ?

hoping some obvious code pops up.


Spark plug seems like it would be as bad or worse when cold. I will check a couple anyway just to see. Occasionally now It gets a little rough while at a light.

dllhg

So cam sensor can be seen without getting under car ? Will take a look at that too.

Oh and to top things off the upgraded radiator has sprung a tiny leak on plastic tank. tried JB welding it but it didnt hold

dllhg

Problem has persisted. Map was fine. Swapped MAFF sensor to rule that out.

What I now notice is if I restart within 5-10 minutes it will start back up. If I wait like an hour it starts up. Cold it starts right up. Its in the 15-40 minute range it wont start first time. If I dont let it crank for a long time and shut it off right away it will fire right up on second try. If I let it crank too much it wont restart. Takes many attempts then.

FYI Fuel pressure seems to be 40+ When first trying to start. Usually its 55-58 when colder. After driving a bit it drops to about 50.

Car runs good most of the time . At low speeds and stop signs it starts idling rough. Hit the gas and it smooths right out. Giving any decent amount of gas or WOT it always seem to be fine.

Seems like something is overheating when I let it crank too much. Would a fuel pump overheat when cranking car like that ? Coils ? Relay ? Well I actually swapped the relay too.
__________________

Joe_G

Did you add some starting airflow with HP Tuners?

This problem can be tricky and seems to happen with non-stock fuel injectors. My car starts perfectly all the time (bear in mind it's never below 50 here when I drive the car) but my buddy's 05, we tried many many times to fix a slow warm start problem and never got it right. I suspect it was due to his non-stock injectors and some table not being changed for a warm start, but he just learned to step on the gas a little on a warm start which worked ever time.

schpenxel

The "all of a sudden" part is what baffles me about it

Mine had this issue recently too.. if it sat for a few hours it would start just fine, cold it would start fine in any temperature. Let it sit for 15-30 minutes and it would turn over a lot longer than normal then barely start and slowly work it's way up from 200-300 RPM's up to idle speed. Fortunately I barely ever restart in the 15-30 minute timeframe so it's nothing I really have noticed much, but I did want to try to make it better.

What I did was decreased the cranking VE, increased idle startup airflow and smoothed out the cranking timing table. For some reason it had a few weird cells that were like -10 while everything else around them were positive and were in the temp range I'd see when re-starting after 15-30 minutes

No idea if any of that will help on yours, but that is what did it on mine. It hasn't done it since I made those changes

Joe_G

^^^ Great post Schpenxel.

I suspect the all of a sudden may be due to weather changes as he first posted about this in November. Seems he recently got the car last summer I"m guessing?

Don't know where he is but even here in Miami our weather changes a little then.