Charleston2012

There have been many write ups and answers to the LT1 split blm issues.
So, if you have definite answers and actual fixes for split blm in regards to vacuum leaks etc.
My particular LT1 has a medium size camshaft, with 230 intake and 236 exhaust on a 114 LSA in a stroker. And I use 42# GM injectors slid Green BOSCH III's.
It has the modified AS&M throttle body to allow the air for idle to be sent through the proper idle circuitry.
The manifold has been port matched to heads.
The heads are ported and polished and I use good header gaskets etc.
I also have converted to heated 3 wire O2 sensors and my O2's are far upstream on thre header collector to not even be affected by a collector leak, if there was one. The wires are a ground, a power source to heat them and the actual sensor wire which has been altered and the sensors are good and tight DENSO sensors.
My manifold has a catch can plumbed into the port for PCV valve and back in to the factory route.
Intake is a 94-96 style with proper fuel rail and EGR and AIR blocked off.
So, where is the vacuum leak causing the split BLMs? They arent little splits, they are 20-30 off, with the left pulling fuel.
I have always had split BLMs in this car. I have had it with different manifold, headers, injectors, throttle bodies, ignitions (Opti to DELTEQ), unheated sensors to heated O2's and the list goes on. So obviously I have missed something to fix the split BLMS. Sorry for so long of a thread.
Now, i am not a novice on this car or engines etc, so if you have dealt with this and have solid answers or avenues to check, please let me know.

Charleston2012

I guess I will answer this to get things started. I took the header out of the driver side. No obvious leak as gaskets had no burn marks or black residue.
So, I put in new gaskets, new plugs, and a new O2 sensor with anti seize on the threads as DENSO says to do.
The Number 7 plug was soaked in fuel. HHHMM.
Checked plug wires, good with ohm meter. Other than that, ???
So, what causes one cylinder to be rich with fuel?

93Rubie

Bad fuel injector, what does it ohm at? Did you have them all flow and spray tested? Injector stuck open or leaking could cause this.

Charleston2012

They are brand new injectors from FIC. I will ohm them later. They are Bosch III's 42 #'s. I am sure it is the same 14-16 ohms. but I need to verify through Jon.

tombrammer

I'll add my 2 cents. I just put a hot cam, 1.6rr's, new valve springs and seals in my 93 vett. I also had my car tuned, it has shown split BLM's at idle and some above (I know only very little about tuning too). I noticed my oil consumption went up drastically after the cam swap, also low vacuum (12-13). I pulled the intake and noticed oil all around the intake ports, both above the gasket and below too. I must have a serious vacuum leak, may be that is the reason for my split BLM's too? I will be watching this thread with interest and hope you can solve this problem. Good luck

Charleston2012

a forum member aboatguy had a intake leak too and it caused this problem.If my injectors and coils (delteq) check out, I will replace th intake manifold gaskets tomorrow.

Charleston2012

I checkd Injectors, lowest was 14.1 OHMs, highest was 14.5 OHMS. Good.
Coil Packs tested sat too.
So, I guess I need to check the manifold. I took the #5 and #7 plug out after diling for 10 minutes and #7 was already showing signs of running richer, at least it was getting dark gray compared to the white of #5. Maybe its oil? Hard to tell, but why one cylinder?

Charleston2012

Okay, Update. I looked at the #7 plug and it is only oil on it. It is not gas. I thought it was at first, but after setting a while on a paper towel, it is just oil soaked. My guess is the intake manifold gasket is ripped or not sealing at that cylinder. And with the oil going to the O2 sensor, it was seeing it as rich and causing the left bank to pull fuel out.

93VettePilot

I have almost the same setup as you. 383, AFR heads, ported intake CC503 cam. I have struggled with split Blms on two different heads and cam LT1 cars. I am of the opinion that the short runner lt1 intake is not very conducive to idleing with a medium size cam due to reversion.

Check to make sure it is firing on all 8 cylinder by pulling the plug wires one at a time. A dead cylinder will cause a bad split.

The reversion with the cam is most likely your culprit. I use an aftermarket computer (accel gen 7)and adjusted the individual fuel trims and sequential injector timing to almost completely alleviate it but it is still noticeable. The front two cylinders and the back two cylinders need more fuel to make it run smooth due to the lt1 intakes poor air distribution.

It would be very unlikely that your intake manifold gasket is leaking. Make sure the connection on your O2 sensors are soldered. The O2 sensors carry a very low voltage and are very susceptable to resistance in the wires. Also bring your idle up to 1000rpm and see if you still have the split blms.

Keep in mind that at idle a 20% split is actually a very small change in fueling due to the small pulse width. If you have a split that size at full thottle throttle it is huge.

STL94LT1

Possible bad valve seal.

Charleston2012

The O2 sensor wiring was soldered, not the sensor itself, but the connectors. Real fun doing this upside down under the car. Then I put heat shrink.
I failed to look at the exhaust valve with the header off to see if it was oil coated.
But when I take the manifold off, I will look at the intake valve. The heads dont have many miles on them and use teflon seals with Mobil one. Not that that is fool proof. Heads were done by CNC inc of Florida, good quality.
The cylinders were all getting sparks, but the oil , I believe , was causing the cylinder to not fire.

STL94LT1

That's where my heads were done. They perform well, but the quality was questionable.

Charleston2012

Only thing I changed was the valve springs when I got the heads. I went from the single 941's to Beehive 918's from PAC Racing.
If they are not good, and I have to remove them, then its AFR and camshaft. I am not screwing around. LOL

Charleston2012

Update: Took manifold off. Dry as a bone on all cylinders.
So, I am getting the valve cover off, to see if I can see anything obvious wrong with the valve stem seal on the exhaust. All intake valve stems were the same. If it isnt the valve stem seal, the only thing it could be is rings.?

Charleston2012

Last update for quite sometime. Was putting manifold back on and one bolt decided to **** to the side. I tried to extract it and it wasnt having anything to do with that. It broke, and even though it is sticking out, vice grips couldnt budge it. Its a drill and extract. I am tired. I am done for some time now. Thanks for all the help. Its a financial, tired of working on this car thing. Its going in lay up, Navy term for, its going to be sitting for sometime.

dizwiz24

[S, etQUOTE=tombrammer;1577554589]I'll add my 2 cents. I just put a hot cam, 1.6rr's, new valve springs and seals in my 93 vett. I also had my car tuned, it has shown split BLM's at idle and some above (I know only very little about tuning too). I noticed my oil consumption went up drastically after the cam swap, also low vacuum (12-13). I pulled the intake and noticed oil all around the intake ports, both above the gasket and below too. I must have a serious vacuum leak, may be that is the reason for my split BLM's too? I will be watching this thread with interest and hope you can solve this problem. Good luck[/QUOTE]

My 93 hotcam (and now supercharged) is like that too.

I even had my old (before sc) injectors leak tested w no issues. I assumed the oil in the intake manifold was due to the supercharger causing a little more blowby then normal.

Incidentally no issues w compression. Compression test is fine.

Left blm is about a 110 and right blm is about 124. I've learned how to tune lately (tunerpro) and am going to try to split the diff to move both sides closer to 128 knowing that I can't get there entirely.

I've already switched to hheated o2. No luck there.

STL94LT1

Don't get discouraged, I'm pretty sure you are close to solving your problem. Unlike some of the others on this site you have been very methodical in resolving the issue.

Charleston2012

Just a little frustrated. I went and got two cobalt bits, and the first one with the extractor didnt work. I am working the second size up and I need a cordless drill as I have been using a power converter from my toyotas lighter and it doesnt have enough uummppphh.
I will probably end up drilling it out and heli coiling it. I have a friends power cordless drill juicing up now. So, tomorrow hopefully I will get the bolts out. I have anew one standing by.
Also, the valve stem seals "looked" okay on the exhaust.
May need to do a compression check. Other than that, I will take the valve stem seal out if compression test is sat, and put a new one in. Simple enough.

Charleston2012

Update: Helicoil is in. Tomorrow I will reinstall manifold. Let it dry a day. Then I will drive to hobby shop and install a couple new teflon valve seals, if doable.

Charleston2012

Update:
Manifold and engine are back together. I am going to let her sit for a day before firing it up.
Then I will take it over to my hobby shop, do a compression test on #7, let it leak down too. See if I can hear anything.
Then I will do a couple more cylinders to verify consistency.
My machine shop here gave me some valve stem seals to try after I take the valve spring off. I will wiggle the exhaust valve too once the spring is off. Not that it is a scientific test, but I will be comparing it to the intake valve.
So, hopefully I will have an answer.
PS, how much are AFR heads?? LOL