Misfire on Cylinders 5, 7, 8 (FIXED! Broken Valve Spring)

[Grounded]

I've found 2 people with a similar problem. one had a broken valve spring on #7. The other had a bad ground pcm to head.
Really what you need is someone with a TECHII which is a GM tool and this could more likely be figured out in a matter of minutes

[PAFirefighter11]

Freeze frame information @ idle:

------------------
Fuel Status = 0 byte
Engine Load = 2.353 %
Engine Coolant Temperature = 226.4 °F
Fuel Trim Bank 1 Short Term = -10.938 %
Fuel Trim Bank 1 Long Term = -7.812 %
Fuel Trim Bank 2 Short Term = -14.844 %
Fuel Trim Bank 2 Long Term = -8.594 %
Intake Manifold Pressure = 6.382 psi
Engine RPM = 755.5 rpm
Speed (OBD) = 0 mph
Mass Air Flow Rate = 53.824 cfm
Throttle Position(Manifold) = 0.392 %
End of report.

Per Tom Oates:

[Grounded]

Subject:

97 - 05 Vehicles with 4.8 5.3 5.7 and 6.0 Gen III V8 Engines and Misfires On One Bank






Models:

.



--------------------------------------------------------------------------------

The following diagnosis might be helpful if the vehicle exhibits the described symptoms in the PI.

Condition/Concern:


Check Engine Light with a P0300 due to 2 - 4 cylinders misfiring on the same bank of the engine. DTCs P0171, P0172, P0174 or P0175 may also set for the misfiring bank.

Recommendation/Instructions:


If the published misfire diagnostic does not isolate the cause, perform the following suggestions as necessary:




1.

Perform a fuel injector balance test for all 8 cylinders. If a fuel injector concern exists, it is possible to misfuel an entire bank of the engine, causing multiple cylinders on the same bank to misfire even though the root cause is a single fuel injector.





2.

Inspect O2 sensor connections on the misfiring bank for corrosion or water intrusion. If water intrusion is found on the right bank, it may be due to the AC Evaporator Condensation dripping onto the O2 sensor harness. If this condition is found, reposition and shield the harness to prevent a repeat concern and repair the connections.





3.

Check for excessive exhaust backpressure using the restricted exhaust diagnosis from SI.





4.

Swap the Position 1 O2 sensors side to side to see if the misfires move to the other bank of the engine. If so, replace the O2 sensor.






And get you arm/hand in there get a little bloody and change out the 8th plug. do it when its cold and wrap your hand around the manifold. its ****ty but im sure the intermittent misfire on 8 is more likely a plug.

[Grounded]

Im gonna say to replace the fuel pressure regulator to fix the fuel pressure falling off.
pinch of the return line to see what the pressure does
it would help if you have a tool like the techII that would let you do injector balance

[TNTramair]

i would run a compression test before you throw anything else at it. and if you havent replaced the 8th plug yet...do that while you have it out.
i also think you may have a broken valve spring.

[PAFirefighter11]

Thanks guys. Tomorrow night if I have time I may pull the driver side valve cover to see what is going on and run a compression check if time allows.

Also, re: FPR. I'm hearing mixed reports. Some people are telling me the FPR is on the rail (Including GM Parts), others are saying it's in the tank and the piece on the rail is just a dampner for the pass. side rail to keep pressure the same?

[PAFirefighter11]

So if you're just reading this, #5 and #7 are the misfiring cylinders.

I purchased a compression tester today:


Only had time to do 4 cylinders, but everything checked out fine:


And the plugs ... 1-3-5-7:

[TNTramair]

thats a good start...hopefully the others are in the same condition.

[PAFirefighter11]

I don't know what Mode $06 test results are but here are mine:

Mode $06 report generated by Torque for Android
================================================

Vehicle VIN: Not present
Vehicle Manufacturer: Unknown
Vehicle Calibration ID: Not present

Unit and scaling information are not supplied with the data from the ECU for this type of vehicle. Consulting the manufacturers service book for this information is recommended.

Test report:
------------------
TID:$02 CID:$04
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$10
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$11
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$12
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$20
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$21
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$26
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$30
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$31
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$36
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$40
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$46
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$04 CID:$20
- High sensor Voltage for switch time calculation
Max: 32,766
Test result value: 32,770
FAIL
----
TID:$04 CID:$30
- High sensor Voltage for switch time calculation
Max: 32,766
Test result value: 32,770
FAIL
----
TID:$06 CID:$35
- Lean to Rich sensor switch time(calculated)
Max: 62
Test result value: 19
PASS
----
TID:$06 CID:$41
- Lean to Rich sensor switch time(calculated)
Max: 104
Test result value: 35
PASS
----
TID:$06 CID:$55
- Lean to Rich sensor switch time(calculated)
Max: 67
Test result value: 42
PASS
----
TID:$06 CID:$61
- Lean to Rich sensor switch time(calculated)
Max: 106
Test result value: 50
PASS
----
TID:$07 CID:$0c
- Minimum sensor Voltage for test cycle(calculated)
Max: 0
Test result value: 65,491
FAIL
----
TID:$07 CID:$0d
- Minimum sensor Voltage for test cycle(calculated)
Max: 1
Test result value: 65,491
FAIL
----
TID:$02 CID:$04
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$10
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$11
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$12
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$20
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$21
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$26
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$30
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$31
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$36
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$40
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$02 CID:$46
- Lean to Rich sensor threshold voltage(constant)
Test incomplete or dependant test failed
--
TID:$04 CID:$20
- High sensor Voltage for switch time calculation
Max: 32,766
Test result value: 32,770
FAIL
----
TID:$04 CID:$30
- High sensor Voltage for switch time calculation
Max: 32,766
Test result value: 32,770
FAIL
----
TID:$06 CID:$35
- Lean to Rich sensor switch time(calculated)
Max: 62
Test result value: 19
PASS
----
TID:$06 CID:$41
- Lean to Rich sensor switch time(calculated)
Max: 104
Test result value: 35
PASS
----
TID:$06 CID:$55
- Lean to Rich sensor switch time(calculated)
Max: 67
Test result value: 42
PASS
----
TID:$06 CID:$61
- Lean to Rich sensor switch time(calculated)
Max: 106
Test result value: 50
PASS
----
TID:$07 CID:$0c
- Minimum sensor Voltage for test cycle(calculated)
Max: 0
Test result value: 65,491
FAIL
----
TID:$07 CID:$0d
- Minimum sensor Voltage for test cycle(calculated)
Max: 1
Test result value: 65,491
FAIL
----

End of report.

[PhillyLS1]

I'd bet you money it's the Body Control Module

[PAFirefighter11]

Originally Posted by PhillyLS1

I'd bet you money it's the Body Control Module

When the BCM starts to go bad it usually makes both windows slow or completely stop when going up or down. It also takes out the radio. Why are you thinking it's the BCM?

[FAST of WC]

Originally Posted by PAFirefighter11

Thanks guys. Tomorrow night if I have time I may pull the driver side valve cover to see what is going on and run a compression check if time allows.

Also, re: FPR. I'm hearing mixed reports. Some people are telling me the FPR is on the rail (Including GM Parts), others are saying it's in the tank and the piece on the rail is just a dampner for the pass. side rail to keep pressure the same?

Do a running compression like I suggested.

[elff]

One thing
Can you record a youtube video so we can hear the noise it makes.

I like the suggestion of the timing being off and the possibility of a bent valve or lash adjuster.
You also might have jumped a tooth on the timing chain

Just brainstorming

[PAFirefighter11]

Ignore the voltage. Gauge is off - verified with a multimeter:
November 2012: http://www.youtube.com/watch?v=_n_8yLhQNtU

And for comparison sake - back in April 2012 racing at Cecil:
http://www.youtube.com/watch?v=Gg6cifmbo5U

[TheAlchemist]

Originally Posted by elff

One thing
Can you record a youtube video so we can hear the noise it makes.

I like the suggestion of the timing being off and the possibility of a bent valve or lash adjuster.
You also might have jumped a tooth on the timing chain

Just brainstorming

There are no lash adjusters on these cars, and I've never heard of an ls1 jumping a tooth on a timing chain either. Timing is fine as well.

Originally Posted by PAFirefighter11

Ignore the voltage. Gauge is off - verified with a multimeter:
November 2012: http://www.youtube.com/watch?v=_n_8yLhQNtU

And for comparison sake - back in April 2012 racing at Cecil:
http://www.youtube.com/watch?v=Gg6cifmbo5U

PULL YOUR VALVE COVER RIGHT NOW. I can almost gaurantee a broken valvespring or bent pushrod. It's not that bad of a job to do. Also, have you verified the ground on the back on the driver's side cylinder head?

Lastly, get the car to someone with HPTuners to look at your tune. If you wanna drive up to Doylestown, I'll check it for you. My car sounded like that when I broken a valvespring. A broken valvespring will cause the neighboring cylidners to misfire because of the disturbance it causes around there. With HPtuners, I can actually scan each individual cylinder as it's running and you'll see a huge difference between each cylinder for misfires. So all the cylinders might be tripping the code, but you'll see one cylinder is like 320 misfires per cycyle, while the others are at like 40-50.

[PAFirefighter11]

Originally Posted by TheAlchemist

There are no lash adjusters on these cars, and I've never heard of an ls1 jumping a tooth on a timing chain either. Timing is fine as well.





PULL YOUR VALVE COVER RIGHT NOW. I can almost gaurantee a broken valvespring or bent pushrod. It's not that bad of a job to do. Also, have you verified the ground on the back on the driver's side cylinder head?

Lastly, get the car to someone with HPTuners to look at your tune. If you wanna drive up to Doylestown, I'll check it for you. My car sounded like that when I broken a valvespring. A broken valvespring will cause the neighboring cylidners to misfire because of the disturbance it causes around there. With HPtuners, I can actually scan each individual cylinder as it's running and you'll see a huge difference between each cylinder for misfires. So all the cylinders might be tripping the code, but you'll see one cylinder is like 320 misfires per cycyle, while the others are at like 40-50.

That would ROCK! Thank you! I can get up there today if you're free? lol. I'm not too far from Buckingham Township. If not no worries. PM sent.

[elff]

Alchemist
Thanks for the clarification. Ive got half the engine of the TransAm and have lash adjusters. But i think our line of reasoning is the same for the problem.
I couldnt hear anything for what I was thinking of in the video. I was actually hoping you would put the camera in the engine bay to hear the engine better.

I have HPT as well but just had hip surgery so I cant do a test drive for a while. Im couch/bed ridden for a couple weeks. FAI fixed by FAO surgery for those interested.
Anywho
In the future, PAfighter11, I am right around the corner from your work. If you ever need to tune with HPT, you could borrow mine and just pay for the 2 credits to license your TA vs buying the whole suite

[PAFirefighter11]

Originally Posted by TheAlchemist

PULL YOUR VALVE COVER RIGHT NOW. I can almost gaurantee a broken valvespring or bent pushrod. It's not that bad of a job to do. Also, have you verified the ground on the back on the driver's side cylinder head?

Lastly, get the car to someone with HPTuners to look at your tune. If you wanna drive up to Doylestown, I'll check it for you. My car sounded like that when I broken a valvespring. A broken valvespring will cause the neighboring cylidners to misfire because of the disturbance it causes around there. With HPtuners, I can actually scan each individual cylinder as it's running and you'll see a huge difference between each cylinder for misfires. So all the cylinders might be tripping the code, but you'll see one cylinder is like 320 misfires per cycyle, while the others are at like 40-50.

Thanks so much again for checking out the car! I'll get the driver side valve cover off tomorrow night after work hopefully.

Originally Posted by elff

In the future, PAfighter11, I am right around the corner from your work. If you ever need to tune with HPT, you could borrow mine and just pay for the 2 credits to license your TA vs buying the whole suite

Thanks much for the offer! I may need to tune out the rear o2's eventually as well.

[TheAlchemist]

Not a problem, I was happy to help. Unfortunately, I had another project already going on in the garage or else I would have helped you pull the cover here today.

For the record, he's got misfires only on cylinders 5 and 7, which to me sounded like he has either a broken valve spring or a bent pushrod or valve. Pulling the valve cover will tell a lot.

[PAFirefighter11]

I'll be pulling the valve cover tonight.