Seriously Lean after Intake Swap (LT1)
Thread Starter
Burning Brakes
Joined: Aug 2006
Posts: 878
Likes: 2
From: BC
Seriously Lean after Intake Swap (LT1)
I've just done an LT1 Intake converison and now i'm seeing a seriously lean BLM when logging. The car stumbles on load and mid-heavy throttle.
I've had an ignition problem which seemes to have been cured by replaceing the module in the camaro distributor. At least its not come back yet....
I'm seeing BLM's of 150-160 when loaded up, 128 on idle tickover. Fuel pressure has been adjusted up to nearly 50psi with very little change. I'm also showing 4-6deg of Knock on load.
I'm now stuck at the point at that I don't know if its an ignition problem causing the lean readings, or being so lean that its not stubbling.
Tomorrow I will try and get my Wideband installed to get a better idea of whats going on. I think i'll also burn a chip with LOTS more fuel to see if that makes a difference?
I've never read that people have had to do this much mapping just to get the car running right.
Any advice greatly appreciated!
Heres some history on the car, its a 1985...
Main:
1984 Block with Forged Pistons
1987 128 Alloy Heads
1994 LT1 Intake manifold converted for SBC Gen1 Heads
204/214 @.50 - Summit Cam
Ignition:
1987 Camaro Distributor and Coil Pack
1992 7730 Speed Density ECM
New Rotor
New Leads
Fuel:
1985 Fuel Pump
LT1 Fuel Rails
1992 TPI Fuel Injectors
Adjustable Fuel Pressure Regulator
I've had an ignition problem which seemes to have been cured by replaceing the module in the camaro distributor. At least its not come back yet....
I'm seeing BLM's of 150-160 when loaded up, 128 on idle tickover. Fuel pressure has been adjusted up to nearly 50psi with very little change. I'm also showing 4-6deg of Knock on load.
I'm now stuck at the point at that I don't know if its an ignition problem causing the lean readings, or being so lean that its not stubbling.
Tomorrow I will try and get my Wideband installed to get a better idea of whats going on. I think i'll also burn a chip with LOTS more fuel to see if that makes a difference?
I've never read that people have had to do this much mapping just to get the car running right.
Any advice greatly appreciated!
Heres some history on the car, its a 1985...
Main:
1984 Block with Forged Pistons
1987 128 Alloy Heads
1994 LT1 Intake manifold converted for SBC Gen1 Heads
204/214 @.50 - Summit Cam
Ignition:
1987 Camaro Distributor and Coil Pack
1992 7730 Speed Density ECM
New Rotor
New Leads
Fuel:
1985 Fuel Pump
LT1 Fuel Rails
1992 TPI Fuel Injectors
Adjustable Fuel Pressure Regulator
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
150 is way lean and depending on were the inj. flow rate is set, in proportion to the inj. size being used, I would start by tuning from idle to 1600 (adding fuel) and go from there. (50# for fp is plenty I start w/45lbs.).
Drifting
Joined: May 2004
Posts: 1,747
Likes: 1
From: Port McNicoll Ontario
Thread Starter
Burning Brakes
Joined: Aug 2006
Posts: 878
Likes: 2
From: BC
I know what your saying and I hope that someone will confirm??
The way that I see it is that the MAP sensor is plumbed into the manifold itself so any leaks would be seen at that point? I mean theres nowhere for it to leak AFTER the manifold??
O2 Sensor shows a good switch around 128 at idle so I think thats OK.
The way that I see it is that the MAP sensor is plumbed into the manifold itself so any leaks would be seen at that point? I mean theres nowhere for it to leak AFTER the manifold??
O2 Sensor shows a good switch around 128 at idle so I think thats OK.
Drifting
Joined: May 2004
Posts: 1,747
Likes: 1
From: Port McNicoll Ontario
I know what your saying and I hope that someone will confirm??
The way that I see it is that the MAP sensor is plumbed into the manifold itself so any leaks would be seen at that point? I mean theres nowhere for it to leak AFTER the manifold??
O2 Sensor shows a good switch around 128 at idle so I think thats OK.
The way that I see it is that the MAP sensor is plumbed into the manifold itself so any leaks would be seen at that point? I mean theres nowhere for it to leak AFTER the manifold??
O2 Sensor shows a good switch around 128 at idle so I think thats OK.
It surprises me that no one else has jumped in here with other suggestions.
If the air is not the problem it must be the fuel.
Are you sure the injectors are flowing what they are supposed to?
Have you tried your stock 85 fuel injectors? Have you tested the new injectors?
I don't know if looking at the plugs will tell you anything. Maybe it's only lean in a few of the cylinders. This could help pinpoint where to look.
Come on people, someone must have run into something similar before.
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
crossover point (for cross counts on scan) stock should be at .550. If it has been showing lean for a period of time, and 02 related it will eventually throw a code. You can check for presssure drops while car is under load. Usually any mods on mine (w/sd stradegy) will go rich. Has there been an inj. swap to a smaller inj.?
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Thread Starter
Burning Brakes
Joined: Aug 2006
Posts: 878
Likes: 2
From: BC
The Injectors that I'm using are the exact same ones that I was using when I had the TPI installed and had no problems.
I've not got a hose to run the fuel pressure gauge into the car so thats a bit akward at the moment, but when at standstill the regulator is working as it should...
ECM shows NO codes...
Anyone got a reasonable figure for the MAP sensor at idle?
I've not got a hose to run the fuel pressure gauge into the car so thats a bit akward at the moment, but when at standstill the regulator is working as it should...
ECM shows NO codes...
Anyone got a reasonable figure for the MAP sensor at idle?
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
Safety Car
Joined: May 2006
Posts: 4,290
Likes: 140
From: Salem NH
Not enough AE.
Recently I was told "thousands of guys switch to minirams with no problem". I think thats horsecrap. Everyone I've talked to that went from a LTR to a MINIRAM or singleplane has seen the same thing I saw. Fat idle, lean midrange, so little ae that it runs lean and backfires through the intake.
Increase your AE, make sure your advance is flat after 3k, and you should be fine.
In the stock bins, the advance curve comes back down near the top. Not sure if GM didn't think anyone would run up there or something, but what that does is (retarding under load) is causes your cylinder temp to spike like crazy, which could cause some knock up top under load. Thats why I say dial it in by 3k. I also usually zero out the PE spark adder, and just do all my advance in the main table.
On another note. That motor is nearly identical to one I had built and sold. I was going to use the 113 heads, but ended up selling the motor a few weeks ago. Same block, same cam, same intake I was going to use sorta. (I was gonna miniram it). I'd LOVE to hear how that thing runs. I expected with 9.8:1 compression (where mine was gonna be with the -13cc hyper pistons), some 113 heads, that cam, and a miniram it shoulda been around 345-350 FWHP.
-- Joe
Recently I was told "thousands of guys switch to minirams with no problem". I think thats horsecrap. Everyone I've talked to that went from a LTR to a MINIRAM or singleplane has seen the same thing I saw. Fat idle, lean midrange, so little ae that it runs lean and backfires through the intake.
Increase your AE, make sure your advance is flat after 3k, and you should be fine.
In the stock bins, the advance curve comes back down near the top. Not sure if GM didn't think anyone would run up there or something, but what that does is (retarding under load) is causes your cylinder temp to spike like crazy, which could cause some knock up top under load. Thats why I say dial it in by 3k. I also usually zero out the PE spark adder, and just do all my advance in the main table.
On another note. That motor is nearly identical to one I had built and sold. I was going to use the 113 heads, but ended up selling the motor a few weeks ago. Same block, same cam, same intake I was going to use sorta. (I was gonna miniram it). I'd LOVE to hear how that thing runs. I expected with 9.8:1 compression (where mine was gonna be with the -13cc hyper pistons), some 113 heads, that cam, and a miniram it shoulda been around 345-350 FWHP.
-- Joe
Last edited by anesthes; Feb 2, 2008 at 10:20 AM.
Thread Starter
Burning Brakes
Joined: Aug 2006
Posts: 878
Likes: 2
From: BC
well i managed to drive it for long enough to day that I put some miles on it. Long enough anyway got get an error code out of the ECM...
Code #33 - MAP SENSOR VOLTAGE TO HIGH
Returned back and swaped the MAP Sensor over, went out again and it drove MUCH MUCH better - A little on the lean side with very little Knock counts as well....
Although taking it easy I did do one run upto 5k rpm before I backed off, no knock... it was a strange feeling deciding to back off at those kinda RPM's the TPI would have been telling me a few hundred before thats for sure.
I still need to get a wideband plumbed in and do some tuning with that. At the moment there is a fairly obvious Torque loss, but I am running a completely standard tune where as on the TPI I had lots of Advance on the Spark Tables - so I hope I can get some back!
Code #33 - MAP SENSOR VOLTAGE TO HIGH
Returned back and swaped the MAP Sensor over, went out again and it drove MUCH MUCH better - A little on the lean side with very little Knock counts as well....
Although taking it easy I did do one run upto 5k rpm before I backed off, no knock... it was a strange feeling deciding to back off at those kinda RPM's the TPI would have been telling me a few hundred before thats for sure.
I still need to get a wideband plumbed in and do some tuning with that. At the moment there is a fairly obvious Torque loss, but I am running a completely standard tune where as on the TPI I had lots of Advance on the Spark Tables - so I hope I can get some back!
Race Director
Joined: Aug 2000
Posts: 14,130
Likes: 7
Cruise-In II Veteran
What Throttle Body are you running?
Have you reset the minimum air speed and TPS yet?
You can throw a code 33 and the car will run like garbage if the TB min air speed and TPS isnt adjusted correctly.Just keep this in mind if you havent checked it out.I had a code 33 when using a larger TB like a 58 and 52MM and even a stock TB when the min air speed and tps wasnt properly adjusted.
Have you reset the minimum air speed and TPS yet?
You can throw a code 33 and the car will run like garbage if the TB min air speed and TPS isnt adjusted correctly.Just keep this in mind if you havent checked it out.I had a code 33 when using a larger TB like a 58 and 52MM and even a stock TB when the min air speed and tps wasnt properly adjusted.
Thread Starter
Burning Brakes
Joined: Aug 2006
Posts: 878
Likes: 2
From: BC
I'm using the TPI throttle body and the TPS was setup once all the cables we're atached as they had to be fiddled with somewhat...
I'm pretty confident that it was just the MAP sensor being screwy
I'm pretty confident that it was just the MAP sensor being screwy
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
when using a 727/730 ecm the TPS does not have the parameters on fueling (non adjustable)like the earlier MAF based cars, and min. air should not have an effect on being extremely lean in other rpm ranges under load.
Pro
Joined: Oct 2004
Posts: 628
Likes: 6
I had the same problem on my 1992 LT-1. It was showing real lean on the drivers bank - it turned out to be an intake leak sucking oil and air into cylinders 5 and 7. The overall effect was too much air getting to the O2 sensor (and extra oil consumption). The problem turned out to be that the people who had installed my intake had doubled up on the gaskets to avoid the front and rear of the intake touching the block; on my boosted engine it blew a path through the gaskets.
One milled intake later and all is good again....
Just my .02 - possible gasket problem?
(and just to completely mess with your head, the overall effect was that the engine ran RICH despite the 'lean' BLMs because of the false O2 readings).
One milled intake later and all is good again....
Just my .02 - possible gasket problem?
(and just to completely mess with your head, the overall effect was that the engine ran RICH despite the 'lean' BLMs because of the false O2 readings).