BLM’s peg to 160, in closed loop on lightly moded 305, HELP!
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Joined: Aug 2001
Posts: 2,136
Likes: 2
From: Costal Alabama
Car: 1989 Iroc-Z
Engine: 350, ZZ4 equivalent
Transmission: Pro-Built Road Race 700R4
Axle/Gears: 3.23 Dana 44
BLM’s peg to 160, in closed loop on lightly moded 305, HELP!
My brother’s car has been problematic for about a year now. It has been sitting for quite some time because we can not figure out how to fix it. It is a 92 Z28 with a 305 TPI lightly moded; ported heads, shorty headers, G92 dual cats, and some other little things.
When you start it up it runs fine, idles smooth, drives fine. But once it heats up and goes into closed loop it runs horrible. The BLM’s peg to 160 the exhaust starts popping, the idle becomes very rough.
Here is what we have tried to fix it:
- Replaced injectors
- Replaced O2
- Started with a fresh copy of a factory bin
- Checked timing, set to 6 degrees advance
- Checked wires, plugs, coil, cap and rotor
- Checked fuel pressure, holds 42 PSI
Anyone have any ideas what could be causing this?
When you start it up it runs fine, idles smooth, drives fine. But once it heats up and goes into closed loop it runs horrible. The BLM’s peg to 160 the exhaust starts popping, the idle becomes very rough.
Here is what we have tried to fix it:
- Replaced injectors
- Replaced O2
- Started with a fresh copy of a factory bin
- Checked timing, set to 6 degrees advance
- Checked wires, plugs, coil, cap and rotor
- Checked fuel pressure, holds 42 PSI
Anyone have any ideas what could be causing this?
Last edited by 89 Iroc Z; Jul 29, 2003 at 07:39 PM.
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Joined: May 2002
Posts: 510
Likes: 5
From: Santiago, CHILE
Car: 1986 Pontiac Firebird Trans Am
Engine: 305 Tuned Port Injection
Transmission: The famous 700R4
Axle/Gears: No idea
- Vacuum leak?
- Air leak in intake runners?. Causes could be: cracked intake manifold, cracked int. manif. gasket, bad intake man./head ports matching, then the mixture will be AIR/FUEL + AIR = lean.
- Air leak in intake runners?. Causes could be: cracked intake manifold, cracked int. manif. gasket, bad intake man./head ports matching, then the mixture will be AIR/FUEL + AIR = lean.
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From: Chasing Electrons
Car: check
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Transmission: check
Re: BLM’s peg to 160, in closed loop on lightly moded 305, HELP!
Originally posted by 89 Iroc Z
When you start it up it runs fine, idles smooth, drives fine. But once it heats up and goes into closed loop it runs horrible. The BLM’s peg to 160 the exhaust starts popping, the idle becomes very rough.
Here is what we have tried to fix it:
- Replaced injectors
- Replaced O2
- Started with a fresh copy of a factory bin
- Checked timing, set to 6 degrees advance
- Checked wires, plugs, coil, cap and rotor
- Checked fuel pressure, holds 42 PSI
Anyone have any ideas what could be causing this?
When you start it up it runs fine, idles smooth, drives fine. But once it heats up and goes into closed loop it runs horrible. The BLM’s peg to 160 the exhaust starts popping, the idle becomes very rough.
Here is what we have tried to fix it:
- Replaced injectors
- Replaced O2
- Started with a fresh copy of a factory bin
- Checked timing, set to 6 degrees advance
- Checked wires, plugs, coil, cap and rotor
- Checked fuel pressure, holds 42 PSI
Anyone have any ideas what could be causing this?
RBob.
Thread Starter
Supreme Member
Joined: Aug 2001
Posts: 2,136
Likes: 2
From: Costal Alabama
Car: 1989 Iroc-Z
Engine: 350, ZZ4 equivalent
Transmission: Pro-Built Road Race 700R4
Axle/Gears: 3.23 Dana 44
Today I unhooked the smog line to the driver side header and put a plug on it. Now the BLM’s are at 113 on a stock chip at idle!! I replaced the smog check valve on the header with one I know works off my Camaro and the BLM’s went to 158, that’s a 45 BLM difference between smog hooked up and unhooked. So it’s has to be something wrong with smog, but what??
This also raises another important question, how much does a fully functional smog system affect O2 readings (I know not as much as my brother’s car)? Has anyone noticed a few BLM’s of difference with it on compared to off?
This also raises another important question, how much does a fully functional smog system affect O2 readings (I know not as much as my brother’s car)? Has anyone noticed a few BLM’s of difference with it on compared to off?
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From: Chasing Electrons
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Originally posted by 89 Iroc Z
This also raises another important question, how much does a fully functional smog system affect O2 readings (I know not as much as my brother’s car)? Has anyone noticed a few BLM’s of difference with it on compared to off?
This also raises another important question, how much does a fully functional smog system affect O2 readings (I know not as much as my brother’s car)? Has anyone noticed a few BLM’s of difference with it on compared to off?
It actually sounds like there is still somehting wrong with the system.
On a '92 TPI the air will only go to the exhaust ports during cold engine operation. With a warm engine the air then goes to the cat-con.
The air will be diverted (dumped) during: rich operation (RE), ECM trouble code set, deceleration, during high RPM operation.
RBob.
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