Hey... I need some help here. I'm having a split blms issue.


The passenger side is reading really lean and is dumping more fuel then the driver's side. If that makes sense. A friend put a scope on the car and said the pluse width on the passenger side is twice as wide or long (can't remember if he said wide or long) as the driver's side. He said it looks like the passenger side is getting unmetered O2 from a leak or something.

We pressurized the intake with smoke at 7psi and we couldn't see any leaks.

I installed a new o2 on the passenger side and there was NO change.

I'm going to remove the cat and maybe the header itself and pump smoke into it to see if there is a crack before the 02 in the collector.

Don't see any header gaskets leaks.. Using Earls header gaskets.

We also disconnected the PCV system from the intake. No change.

Fuel pressure is 38 at idle and over 40 with gas applied. Could it be possible for one side of the rail to get less pressure then other other?

Please give me thoughts, suggestions, anything. I'm pulling my hair here.

engine:
GM 847 cam
LPE LT4 cnced heads
LPE LT4 intake
Forged 383
ASM TB 58mm
stock maf with 1000cfm housing
EM long tubes
3" true dual exhaust.
xpipe

Edit:
I installed the engine NOV 2006 and at idle there was a 10% or less of a split at idle then while driving they were even or 2 to 3% difference. Now the driver's side is at a -10 or around zero while the passenger side slow goes up to 50% and stays there.

I'm using autotap to get the %s... I can e-mail anyone the autotap logs if that would help.

 

No personal experience here, but I've seen many threads over the years about split BLMS on LT1s with large cams.

You might search over on camaroz28.com in the LT1 and computer sections.

Here's one suggestion:
http://web.camaross.com/forums/showp...2&postcount=18

 

If it was OK before and now isn't then it's not the "split blm" issue involving the throttle body.
It is possible to have an intake manifold leak to the rocker valley also, though you should show signs of sucking oil into the combustion chambers also. How do the plugs look on that side?

 

Typically with larger camshafts you will have split fuel trims at idle. Especially with an unmodified ASM throttle body. Have you checked the idle air passage on that TB? As you know the LTx intake manifolds uses a dedicated idle air passage system that is casted into these intake manifolds. Using some aftermarket TBs and especially the ASM brand, their idle air passage allows idle air to enter the main plenum through the throttle bores.
Go here and click on the "LT1/LT4 link then click on the "improve your idle" link:

http://members.***.net/chipsbyal/page/index.html

In that website it describes in detail how to repair a ASM TB to correct this condition.

You should not see +50% fuel trims on one bank and have it negative on the other. There is something wrong if you see it split in that manner. Most of the time if its that drastic, its indicative of a air leak in the exhaust system or you have a intermitent misfire causing unburned o2 into the exhaust stream. Just always remember that these sensors only react to one thing and that is OXYGEN. The more complete the burn is in the combustion chamber the less o2 that you will have in the exhaust stream, the more o2 or in the exhaust the leaner the PCM will think it is and will skew the fuel trims accordingly.

 

THANK YOU ALL!! I closed the TB blades and the split went down to less then 10% at idle and 4% or less at 1000-3000rpms and it's almost dead on all time above 3000rpm.

I opened the blades recently, not fully understanding the affects, to improve the idle.

There is a lot of good information on the camaross.com website.

My idle is off but I'm going to do the ASM mod in the link tjwong posted. Since I don’t have any way to make the little piece of metal to prevent the IAC air from entering the intake plenum. I’m going to use the small bushing you can buy a lowes that a few people have used to fix this issue. There is a post on camaross.com about it.

Thanks again guys!!!!!

 

Good to hear.