Can't figure this one out..
#1
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And I hope this is an ok place to post this.
Short story - I'm a tech at an independent Honda/Japanese specialist. We do work on domestic, but it is less advertised. I pretty much do all the diagnosing and this one has me atm.
Car was grabbed by a car lot, one that we trust and doesn't sell junk, and they said it has been to others that have done compression tests, etc.
It is absolutely not any specific dead cylinder(s). It only gives a random 300 code, idles like a cam, but gets no better when revved. It has 11-13" of vacuum that fluctuates back and forth quickly.
At idle, the front O2's stay pegged rich. Off idle, steady rpm, they stay pegged lean. O2's and harness is clean. Only other thing I've done is pull the rail and flipped it over to check injector spray.
The last detail... the car is a pristinely clean 2002, 29k miles, of the Firebird variety, with a slushbox. There is nothing to suggest any bad vibes about this car. Though, I am leaning to cam timing, it's just such a pain in the *** to check. Sorry guys, I am spoiled by the 4 cylinders.
Any ideas? thoughts? experience?
Short story - I'm a tech at an independent Honda/Japanese specialist. We do work on domestic, but it is less advertised. I pretty much do all the diagnosing and this one has me atm.
Car was grabbed by a car lot, one that we trust and doesn't sell junk, and they said it has been to others that have done compression tests, etc.
It is absolutely not any specific dead cylinder(s). It only gives a random 300 code, idles like a cam, but gets no better when revved. It has 11-13" of vacuum that fluctuates back and forth quickly.
At idle, the front O2's stay pegged rich. Off idle, steady rpm, they stay pegged lean. O2's and harness is clean. Only other thing I've done is pull the rail and flipped it over to check injector spray.
The last detail... the car is a pristinely clean 2002, 29k miles, of the Firebird variety, with a slushbox. There is nothing to suggest any bad vibes about this car. Though, I am leaning to cam timing, it's just such a pain in the *** to check. Sorry guys, I am spoiled by the 4 cylinders.
Any ideas? thoughts? experience?
Last edited by niqht; 10-06-2011 at 05:32 PM.
#5
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Given the rich at idle, it runs worse as it warms up. Gets to be a pain fighting the stalling. You can smell the cat.
MAF shows ~8grams at idle. up to 150 with a punch of the gas. I have used an air blower to get the MAF reading higher and I can watch the O2 voltage come up, but that was difficult to maintain and I didn't notice a difference in smoothness.
MAP agrees with vacuum gauge. There is practically no where on this motor to leak vacuum to. Even so, it should improve with higher rpm.
MAF shows ~8grams at idle. up to 150 with a punch of the gas. I have used an air blower to get the MAF reading higher and I can watch the O2 voltage come up, but that was difficult to maintain and I didn't notice a difference in smoothness.
MAP agrees with vacuum gauge. There is practically no where on this motor to leak vacuum to. Even so, it should improve with higher rpm.
#7
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ok, it has a broke valve spring. Something I've never seen before, but apparently it isn't stock. It does have titanium retainers and straight springs with green paint marks. Ordered an OEM dealer spring and it has the tapered top.
Do I have the wrong part from the dealer or is this an aftermarket spring kit?
Do I have the wrong part from the dealer or is this an aftermarket spring kit?
Last edited by niqht; 10-11-2011 at 10:37 AM.
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#10
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I could maybe get a pic but there isn't much to it.
We used to have a bore scope but it vanished. I doubt I could get it in that plug hole anyway.
It didn't drop a valve, it just wasn't closing. I don't know what kinda clearances domestics run. In Honda land it would have hit the piston, but here I never heard any noise.
We used to have a bore scope but it vanished. I doubt I could get it in that plug hole anyway.
It didn't drop a valve, it just wasn't closing. I don't know what kinda clearances domestics run. In Honda land it would have hit the piston, but here I never heard any noise.
#11
TECH Senior Member
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ok, it has a broke valve spring. Something I've never seen before, but apparently it isn't stock. It does have titanium retainers and straight springs with green paint marks. Ordered an OEM dealer spring and it has the tapered top.
Do I have the wrong part from the dealer or is this an aftermarket spring kit?
Do I have the wrong part from the dealer or is this an aftermarket spring kit?
If you post a pic of the broken spring, someone can identify it and you can get a like replacement.
The fluctuating vac gauge is a sign of a problem with a valve.
#13
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I'm with you, but it isn't my call. I may not know domestics, but I know performance. They got a square spring from a head shop we use, the ti retainer doesn't fit snug in the spring and the retainer is scored. Only a matter of time before it splits in half.
In other news, it is running much better with consistent 18" vacuum, but still dead on number 8. Valve has to have been tweaked...
Doing a leak down when it cools down again.
In other news, it is running much better with consistent 18" vacuum, but still dead on number 8. Valve has to have been tweaked...
Doing a leak down when it cools down again.
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#15
TECH Senior Member
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I'm with you, but it isn't my call. I may not know domestics, but I know performance. They got a square spring from a head shop we use, the ti retainer doesn't fit snug in the spring and the retainer is scored. Only a matter of time before it splits in half.
In other news, it is running much better with consistent 18" vacuum, but still dead on number 8. Valve has to have been tweaked...
Doing a leak down when it cools down again.
In other news, it is running much better with consistent 18" vacuum, but still dead on number 8. Valve has to have been tweaked...
Doing a leak down when it cools down again.
If your shop doesn't do the job right, you will end up breaking the customer's engine, and he will hold your shop responsible for it... you would be better off to farm this out to an LS1 speed shop.
#16
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Had a workshop that was good on Gen 1 engines rebuild my LS1 & it ended up being a very bad mistake, still ended up costing me & them a lot of $$$$$ to get it rebuilt again 1800km later.