RockinWs6

A little back ground on what I'm trying to solve. All stock 01 WS6, cold start engine runs smooth for about one min then starts to stumble until the system goes into closed loop. Closed it smooth's out. No codes, no vacuum leaks, fresh plugs and wires, new intake gaskets. The only obvious thing I see is +3 fuel trims on bank 1.

The intake gaskets were changed and the trims stayed the same. +3 bank 1 and 0 bank 2. The car runs ok but has a shaky idle cold and the idle hot is a little unsteady. Only thing I can think of is a injector clogged, I ran fuel injection cleaner through and had professional cleaning done with no change.


One other thing is this has been like this for over 60k miles, Its just starting to irritate me.

I've run into similar trouble before on these LS1 engine's but always found a intake leak or vacuum leak.

Any suggestions?

mrvedit

Swap the injectors between bank 1 and 2. I would also swap the coil packs while you are at it. See if that swaps the fuel trim error. If that doesn't do it, try another set of intake gaskets.
No guarantee of course, by you asked for suggestions.

RockinWs6

Yeah these are things I was thinking about too. I think bank 1 has maybe a partially clogged screen or 2 and bank 2 may have a leaker. I drove it last night and watched the fuel trims closely, under a load above 1200 rpm everything looks right....its just at ide its off.... EFF it not worth worrying about. No codes it runs nice, I'm just a bit of a perfectionist.

RockinWs6

I tightened the 2 rear bolts on intake drivers side a bit more and sure enough it helped. I couldn't find any leaks, but it did help a bunch. So there had to be a leak in that area of the intake. I can't remember for sure but I think when we had the intake off the drivers side had some kind of marks around one of the openings but I figured the gaskets would easily seal them. Does run smooth now, these cars can really test your patients ALOT.

mrvedit

Thanks for the update.
Its a good reminder how critical it is not to have any leaks on the intake manifold, and how hard it can be to find them.

RonSSNova

iTrader: (3)

My Vette has unequal trims too.
I've done all the swapping. Including the O2 sensors themselves.
Idle is fine. Most cruising is fine, but there are areas where they differ.

Now I've got one lazy O2 sensor. Throws a slow response code. They are new GM sensors. Well, three years old. But GM changed the design.

I just live with it. Vette sensors are really hard to replace.

06MonteSS

fuel trims generally are not exactly the same on both banks anyway.. they usually are a little different from each other..

RockinWs6

Well I started with a rough idle cold for about 2 mins until it got into closed loop, then it instantly smoothed out. Then hot it would stumble at idle, ran good but was annoying. I had the plugs and intake gaskets replaced and EVERYTHING was properly tightened with a torque wrench but it still acted funny. Then I found the line from the purge valve barely hanging on BUT it still acted funny.

Finally I tried finding a leak with WD40 but I couldn't find anything SO..... I took socket and long handled ratchet and kinda of felt how tight the intake bolts were related to each other with the engine hot. Those back 2 bolts on the drivers side turned about a 1/4 turn more, the rest felt tight enough. That made the fuel trims very close now and almost no stumbling at idle cold or hot.

I think the manifold has some type of issue back there because I know the new gaskets looked plenty big enough to seal any type of irregularity. But I did see some small marks in that area when we were cleaning up the intake.

I'll tell the weirdest thing about this is the gas mileage really went up since I tightened those bolts and so did the overall throttle response. Stock these engines must be very sensitive to vacuum leaks. Wish I had access to a smoke machine to actually see what's going on. Both sides are negative fuel trims now at idle.

Slowhawk

iTrader: (12)

3% is nothing

RockinWs6

LOL I know but try telling that to a perfectionist? I was squeezing 29mpg out of my 99 TA, this 01 seems to be stuck around 24 but I think now I may be into the 29 territory again. YiPEE

SLO I value your opinion on this, I know you do a bunch of tuning. But dam these things are touchy stock IMO.