Engine runs lean after polylocks broke
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Supreme Member
Joined: Feb 2000
Posts: 1,170
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From: Seattle, Washington
Car: '87 IROC-Z/'82 RX7
Engine: SBC 355/1.1L Rotary
Transmission: T56/5 Speed
Axle/Gears: 4.33/3.93
Engine runs lean after polylocks broke
I'm trying to find the source of a lean condition, be it lack of fuel, or extra air.
Drove for 4 weeks as a daily driver. Was perfect. Then:
#5 exhaust poly lock broke
#2 intake polylock broke
Replace the polylocks:
C950 shows I'm 10% lean now at high vacuum areas. (mostly cruise) Idle vacuum is 60kpa in gear so it's not much for vacuum!
Add more fuel, the twitchiness of being lean gets better.
Runs fine under heavy acceleration.
WBo2 shows perfect at WOT, same as when tuned on a dyno.
-Changed plugs
-Replaced Vacuum lines
-Plugged vacuum appliances for test
-Checked fuel Pressure
-Checked plenum gasket
-Checked TB gasket
-Checked IAC
-Gas did not change when the lean condition started
-Tried 3 different tanks of gas, from 3 different stations (Union 76, Shell, Chevron)
-Checked timing
All that I have left is intake manifold gasket. Does that sound resonible? Since if I add fuel it gets better, kind of indicating that the injectors are good? I have not replaced the fuel filter, it's a year old with less than 2000miles.
Anyone have other ideas?
Drove for 4 weeks as a daily driver. Was perfect. Then:
#5 exhaust poly lock broke
#2 intake polylock broke
Replace the polylocks:
C950 shows I'm 10% lean now at high vacuum areas. (mostly cruise) Idle vacuum is 60kpa in gear so it's not much for vacuum!
Add more fuel, the twitchiness of being lean gets better.
Runs fine under heavy acceleration.
WBo2 shows perfect at WOT, same as when tuned on a dyno.
-Changed plugs
-Replaced Vacuum lines
-Plugged vacuum appliances for test
-Checked fuel Pressure
-Checked plenum gasket
-Checked TB gasket
-Checked IAC
-Gas did not change when the lean condition started
-Tried 3 different tanks of gas, from 3 different stations (Union 76, Shell, Chevron)
-Checked timing
All that I have left is intake manifold gasket. Does that sound resonible? Since if I add fuel it gets better, kind of indicating that the injectors are good? I have not replaced the fuel filter, it's a year old with less than 2000miles.
Anyone have other ideas?
Last edited by Twilightoptics; Jan 22, 2006 at 01:59 PM.
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Joined: Feb 2000
Posts: 7,015
Likes: 2
From: Schererville , IN
Car: 91 GTA, 91 Formula, 89 TTA
Engine: all 225+ RWHP
Transmission: all OD
Axle/Gears: Always the good ones
Bent valve(s)?
I would do a leak down test on the affected cylinders.
When the poly locks broke(I have never seen one break yet in person), how much damage was done?
Did the rockers stay in place, wedge anything, etc?
Damaged a spring perhaps?
later
Jeremy
I would do a leak down test on the affected cylinders.
When the poly locks broke(I have never seen one break yet in person), how much damage was done?
Did the rockers stay in place, wedge anything, etc?
Damaged a spring perhaps?
later
Jeremy
Thread Starter
Supreme Member
Joined: Feb 2000
Posts: 1,170
Likes: 0
From: Seattle, Washington
Car: '87 IROC-Z/'82 RX7
Engine: SBC 355/1.1L Rotary
Transmission: T56/5 Speed
Axle/Gears: 4.33/3.93
When the polylocks broke, the rockers just popped off and sat there. Nothing wedged, pushrods were peftectly straight still, etc.
Set the lash with the new locks, cranked the engine over by hand, and everything appeared to move in an orderly fashion.
I had a rockerarm stud break once before with Comp Magnum Rocker Arms, and there was no change (different cylinder though). The Pro Magnum Rollers just popped off.
I replaced my intake gasket last night, got to clean the intake up a bit and reroute some wiring. I was closer inspecting my distributor cap/rotor.... the center post of the cap on the inside, only comes down 1/16". Usually they come down 1/4" and are spring loaded. I think this may be part of my source. A false lean cause by improper burning. My question to that would be, why, when I added more fuel in the tune, did it get better?
Set the lash with the new locks, cranked the engine over by hand, and everything appeared to move in an orderly fashion.
I had a rockerarm stud break once before with Comp Magnum Rocker Arms, and there was no change (different cylinder though). The Pro Magnum Rollers just popped off.
I replaced my intake gasket last night, got to clean the intake up a bit and reroute some wiring. I was closer inspecting my distributor cap/rotor.... the center post of the cap on the inside, only comes down 1/16". Usually they come down 1/4" and are spring loaded. I think this may be part of my source. A false lean cause by improper burning. My question to that would be, why, when I added more fuel in the tune, did it get better?
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