Low Boost, Boost Leaks and No Resolve
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Low Boost, Boost Leaks and Now a Burnt Valve?
The car has been running 10:1 AFR, knock sum jumps up around 5k rpm, boost is down, and power is down. Far different from the 11:1 AFR, no knock sum, 19-20psi, and power everywhere.
When I initially started looking at my problem, my boost pressure was probably peaking around 1.1-1.3 kg/cm2.
I pressure tested the intake system and couldn't get the pressure above 10psi due to using a leakdown regulator. Air was dumping out at the throttle body faster than the regulator would flow. I ordered the Works high pressure seals, tore the throttle body apart, replaced the seals without issue, and got the whole thing back together about two weeks later. Out with the datalogger and boost was up to 1.2-1.3 kg/cm2 and the knock sum is still going crazy; really no different.
I pressure tested the intake system again. At 12psi, I could audibly hear the bypass valve bleeding air. At around 19-20psi, the valve just fully dumped. Another order, another week. While under the car, I bumped the lower intercooler pipe and it leaked. I tightened it up some and it appeared to stop.
The new bypass valve is now installed. As luck would have it, the car is now holding solidly at 1.2 kg/cm2. I'll be re-testing the whole intake system again tonight. The car ought to be getting up to 19-20psi, or about 1.4 kg/cm2. The car also feels like it is horribly unhappy and pulling timing, though I haven't logged it with the new bypass valve.
Are there any other things I need to check that I've missed? My snorkel is attached to the radiator support properly. My intake filter is a bit dirty, but not bad (Green panel replacement). Plugs were done less than 5k miles ago, though the car has two track days and quite a few autocrosses. I'll be inspecting and changing them tonight. My car currently has a downpipe and some tuning using the stock control boost system, but it has not been tuned to handle a downpipe. I have the service manual and I'll be checking resistances and operation of the stock boost control solenoid.
-Jon
When I initially started looking at my problem, my boost pressure was probably peaking around 1.1-1.3 kg/cm2.
I pressure tested the intake system and couldn't get the pressure above 10psi due to using a leakdown regulator. Air was dumping out at the throttle body faster than the regulator would flow. I ordered the Works high pressure seals, tore the throttle body apart, replaced the seals without issue, and got the whole thing back together about two weeks later. Out with the datalogger and boost was up to 1.2-1.3 kg/cm2 and the knock sum is still going crazy; really no different.
I pressure tested the intake system again. At 12psi, I could audibly hear the bypass valve bleeding air. At around 19-20psi, the valve just fully dumped. Another order, another week. While under the car, I bumped the lower intercooler pipe and it leaked. I tightened it up some and it appeared to stop.
The new bypass valve is now installed. As luck would have it, the car is now holding solidly at 1.2 kg/cm2. I'll be re-testing the whole intake system again tonight. The car ought to be getting up to 19-20psi, or about 1.4 kg/cm2. The car also feels like it is horribly unhappy and pulling timing, though I haven't logged it with the new bypass valve.
Are there any other things I need to check that I've missed? My snorkel is attached to the radiator support properly. My intake filter is a bit dirty, but not bad (Green panel replacement). Plugs were done less than 5k miles ago, though the car has two track days and quite a few autocrosses. I'll be inspecting and changing them tonight. My car currently has a downpipe and some tuning using the stock control boost system, but it has not been tuned to handle a downpipe. I have the service manual and I'll be checking resistances and operation of the stock boost control solenoid.
-Jon
Last edited by stimpy; Aug 23, 2007 at 10:05 PM.
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The intake system has now been pressure tested up to 25psi with no audible signs of leaking. Another Evo at the shop was leaking at the injectors, so I have all three sets of seals/o-rings when the time comes. They aren't needed right now on my car.
I did a leakdown and compression and the results aren't varying too wildly. It was the first time I did either test so the testing methods could be suspect. The car was at operating temperature. The compression test was the highest number after 5 cranks with the throttle body open. The leakdown test was using the Snap-on tool with 100psi input, oil cap, oil dipstick, and air filter all open and out and the throttle body open. The radiator cap was not open because I don't know how on earth I can pull the radiator cap after the car is up to temp.
Test: 1 2 3 4
Compression: 145 145 147 147
Leakdown: 14% 10% 5% 5%
I pulled the brand-new plugs after about 6 data logging runs. Plug #1 was the least coated, followed by #2. Plug #3 and #4 were a very light cream color; not white, but not golden brown either. The car is pissed as hell to run much over 4 degrees of timing from 4k rpm through 6k rpm where I was stopping. Boost is still settling at between 1.2 and 1.3 kg/cm2 while the datalog shows the car asking for more boost for both requested boost and wastegate dynamics. I'll get the car on the dyno next week to see just what fuel is doing. The boost response does feel improved now, but the car is just not happy running any timing.
-Jon
I did a leakdown and compression and the results aren't varying too wildly. It was the first time I did either test so the testing methods could be suspect. The car was at operating temperature. The compression test was the highest number after 5 cranks with the throttle body open. The leakdown test was using the Snap-on tool with 100psi input, oil cap, oil dipstick, and air filter all open and out and the throttle body open. The radiator cap was not open because I don't know how on earth I can pull the radiator cap after the car is up to temp.
Test: 1 2 3 4
Compression: 145 145 147 147
Leakdown: 14% 10% 5% 5%
I pulled the brand-new plugs after about 6 data logging runs. Plug #1 was the least coated, followed by #2. Plug #3 and #4 were a very light cream color; not white, but not golden brown either. The car is pissed as hell to run much over 4 degrees of timing from 4k rpm through 6k rpm where I was stopping. Boost is still settling at between 1.2 and 1.3 kg/cm2 while the datalog shows the car asking for more boost for both requested boost and wastegate dynamics. I'll get the car on the dyno next week to see just what fuel is doing. The boost response does feel improved now, but the car is just not happy running any timing.
-Jon
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I redid the leakdown test last night, this time immediately after getting the car up to temp. As the plugs came out, just about all were coated evenly with a light cream color. The heat difference was quite evident on the plug, so there appears to be spark and a flame front.
The test results this time, under supervision of somebody who knows how to do the leakdown, were:
1 2 3 4
8% 10% 3% 8%
Number 2 was leaking, as best we could tell, most audibly out out of the dipstick.
While waiting for the car to come up to operating temperature, I did hear an odd clicking/rattling coming from the head. Using a screwdriver/stethescope, the sound is concentrated near number 1's intake side. The sound persists when spinning the motor up to about 2-3k, but it is not audible anywhere else but leaning into the engine bay.
We put the car on the dyno once again and the results were abysmal. The knocksum was climbing to about 7 or 8 at 3000 rpm, dropping down to 4 knocksum and running 1 degree of timing at peak torque, knocksum going as low as 1 at 4700 rpm and immediately followed by up to 11 at 5000 with 2 degrees of timing (shown in the R-500 knock sensor as a decent spike), 16 knocksum at 6000 with 4 degrees of timing, saw things were not good and finally stopped the pull showing as high as 28 knocksum with 4 degrees of timing at 6500 rpm. Power and torque were strong up until the knocksum forced a decrease in timing.
Right now the running theory is a seriously bad tank of gas. I'll be burning off this tank and trying some 100 octane to see if the knock disappears.
-Jon
The test results this time, under supervision of somebody who knows how to do the leakdown, were:
1 2 3 4
8% 10% 3% 8%
Number 2 was leaking, as best we could tell, most audibly out out of the dipstick.
While waiting for the car to come up to operating temperature, I did hear an odd clicking/rattling coming from the head. Using a screwdriver/stethescope, the sound is concentrated near number 1's intake side. The sound persists when spinning the motor up to about 2-3k, but it is not audible anywhere else but leaning into the engine bay.
We put the car on the dyno once again and the results were abysmal. The knocksum was climbing to about 7 or 8 at 3000 rpm, dropping down to 4 knocksum and running 1 degree of timing at peak torque, knocksum going as low as 1 at 4700 rpm and immediately followed by up to 11 at 5000 with 2 degrees of timing (shown in the R-500 knock sensor as a decent spike), 16 knocksum at 6000 with 4 degrees of timing, saw things were not good and finally stopped the pull showing as high as 28 knocksum with 4 degrees of timing at 6500 rpm. Power and torque were strong up until the knocksum forced a decrease in timing.
Right now the running theory is a seriously bad tank of gas. I'll be burning off this tank and trying some 100 octane to see if the knock disappears.
Code:
"Time Stamp" "Ignition Timing" "Knock Sum" "Load Fuel" "Load Timing" "RPM" "R-Series-AFR" 21:20:54.17 17 0 99 83 2172 13.72 21:20:54.38 17 0 99 83 2172 13.92 21:20:54.58 17 0 99 83 2172 14.11 21:20:54.78 16 0 111 96 2246 14.19 21:20:54.98 16 0 111 96 2246 14.07 21:20:55.19 16 0 116 100 2324 13.88 21:20:55.39 16 0 116 100 2324 13.52 21:20:55.59 16 0 116 100 2324 13.37 21:20:55.80 16 0 121 103 2406 13.17 21:20:56.00 16 0 121 103 2406 13.09 21:20:56.20 16 0 121 103 2406 13.05 21:20:56.41 16 0 123 107 2492 13.05 21:20:56.61 16 0 123 107 2492 13.09 21:20:56.81 16 0 123 107 2492 13.05 21:20:57.02 15 0 126 110 2586 13.17 21:20:57.22 15 0 126 110 2586 13.09 21:20:57.42 15 0 126 110 2586 12.94 21:20:57.63 16 0 132 113 2699 13.01 21:20:57.83 16 0 132 113 2699 13.05 21:20:58.03 16 0 132 113 2699 12.86 21:20:58.23 16 0 137 117 2809 12.94 21:20:58.44 16 0 137 117 2809 12.7 21:20:58.64 16 0 137 117 2809 12.62 21:20:58.84 11 7 145 124 2918 12.5 21:20:59.05 11 7 145 124 2918 12.5 21:20:59.25 11 7 145 124 2918 12.35 21:20:59.45 7 7 157 135 3043 12.07 21:20:59.66 7 7 157 135 3043 11.88 21:20:59.86 7 7 157 135 3043 11.68 21:21:00.06 4 6 175 149 3176 11.68 21:21:00.27 4 6 175 149 3176 11.52 21:21:00.47 4 6 175 149 3176 11.52 21:21:00.67 2 5 198 167 3316 11.45 21:21:00.88 2 5 198 167 3316 11.29 21:21:01.08 2 5 198 167 3316 11.21 21:21:01.28 2 5 222 188 3480 11.33 21:21:01.48 2 5 222 188 3480 11.45 21:21:01.69 1 4 235 197 3656 11.25 21:21:01.89 1 4 235 197 3656 11.37 21:21:02.09 1 4 235 197 3656 11.09 21:21:02.30 3 3 238 201 3836 11.17 21:21:02.50 3 3 238 201 3836 11.21 21:21:02.70 3 3 238 201 3836 11.05 21:21:02.91 3 2 244 208 4035 10.98 21:21:03.11 3 2 244 208 4035 10.98 21:21:03.31 3 2 244 208 4035 11.02 21:21:03.52 3 2 236 199 4195 10.98 21:21:03.72 3 2 236 199 4195 10.94 21:21:03.92 3 2 236 199 4195 10.94 21:21:04.13 5 1 235 198 4375 11.05 21:21:04.33 5 1 235 198 4375 11.09 21:21:04.53 5 1 235 198 4375 10.98 21:21:04.73 5 2 233 195 4555 11.09 21:21:04.94 5 2 233 195 4555 11.05 21:21:05.14 5 2 233 195 4555 10.98 21:21:05.34 5 1 235 196 4746 11.02 21:21:05.55 5 1 235 196 4746 10.98 21:21:05.75 5 1 235 196 4746 10.9 21:21:05.95 2 11 240 199 4918 10.94 21:21:06.16 2 11 240 199 4918 10.98 21:21:06.36 2 11 240 199 4918 10.94 21:21:06.56 2 10 239 198 5070 10.9 21:21:06.77 2 10 239 198 5070 11.02 21:21:06.97 3 9 240 198 5215 10.86 21:21:07.17 3 9 240 198 5215 10.82 21:21:07.38 3 9 240 198 5215 10.82 21:21:07.58 4 8 245 201 5387 10.82 21:21:07.78 4 8 245 201 5387 10.9 21:21:07.98 4 8 245 201 5387 10.98 21:21:08.19 4 8 240 197 5555 10.9 21:21:08.39 4 8 240 197 5555 10.9 21:21:08.59 4 8 240 197 5555 10.86 21:21:08.80 4 10 240 195 5699 10.9 21:21:09.00 4 10 240 195 5699 10.78 21:21:09.20 4 10 240 195 5699 10.74 21:21:09.41 4 10 241 196 5836 10.7 21:21:09.61 4 10 241 196 5836 10.74 21:21:09.81 4 10 241 196 5836 10.78 21:21:10.02 5 9 240 194 5992 10.78 21:21:10.22 5 9 240 194 5992 10.54 21:21:10.42 5 9 240 194 5992 10.62 21:21:10.63 4 16 245 199 6121 10.58 21:21:10.83 4 16 245 199 6121 10.66 21:21:11.03 4 16 245 199 6121 10.62 21:21:11.23 5 15 236 192 6254 10.58 21:21:11.44 5 15 236 192 6254 10.62 21:21:11.64 5 15 236 192 6254 10.66 21:21:11.84 5 20 242 194 6367 10.62 21:21:12.05 5 20 242 194 6367 10.54 21:21:12.25 4 28 234 189 6449 10.47 21:21:12.45 4 28 234 189 6449 10.47 21:21:12.66 4 28 234 189 6449 10.47 21:21:12.86 29 27 232 188 6199 10.43 21:21:13.78 28 0 15 13 5359 10.82 21:21:13.88 28 0 15 13 5359 10.86 21:21:14.08 23 0 13 11 4414 10.9 21:21:14.28 23 0 13 11 4414 10.98 21:21:14.48 23 0 13 11 4414 11.09 21:21:14.69 37 0 14 12 4367 11.17
Check your headgasket, you could have a tiny crack in it. I supect this because of all the knock and the changed AFR's you are getting. Also all the knock would pull timing making the car slower. Also the fact that you do track days which puts alot of heat and strain on the car. Have you noticed any coolant loss or when your car heats up pushing coolant out the overflow. What about smoke coming out the exhaust.
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I originally suspected a mechanical issue, found boost leak after boost leak, and gained nothing. The leakdown results are questionable, but not out of the question for a car that has 7 track days, countless autocrosses, a lot of dyno time, and almost 27k miles. I don't have a water temp gauge, but I've monitored oil temps closely every time I've gone out and saw over 125C once. Always buffered with 3-5 gallons of 100 octane.
Coolant is down slightly from where it was filled up back in January. I'm not aware of any black or white smoke coming out of the tailpipe. The overflow rises just as suspected, moving from full cold to full hot, but not excessively.
With regard to the fueling, seriously retarded timing will cause the AFR to go rich. It would be hard to draw a conclusion upon fueling alone.
I know the reduced timing is making the car slower. On the dyno last night, as soon as the knocksum went up, timing went down, and power went down. There is a pretty strong correlation. Boost is now in line with what was originally seen when tuned, it just drops when timing drops.
I'm less concerned with the power output at the moment and more concerned with the inability to run any timing. A knocksum of 8 at 3000 rpm? The car shouldn't even be sensitive to knock in that area. Oddly, peak torque, where a car is most prone to knock, shows a relatively low knocksum. The knocksum is also increasing proportionately with rpm. The knock sensor is showing increasing engine noise as the rpms rise, but only one real spike, corresponding to the jump in knocksum found at around 5000 rpm.
-Jon
Coolant is down slightly from where it was filled up back in January. I'm not aware of any black or white smoke coming out of the tailpipe. The overflow rises just as suspected, moving from full cold to full hot, but not excessively.
With regard to the fueling, seriously retarded timing will cause the AFR to go rich. It would be hard to draw a conclusion upon fueling alone.
I know the reduced timing is making the car slower. On the dyno last night, as soon as the knocksum went up, timing went down, and power went down. There is a pretty strong correlation. Boost is now in line with what was originally seen when tuned, it just drops when timing drops.
I'm less concerned with the power output at the moment and more concerned with the inability to run any timing. A knocksum of 8 at 3000 rpm? The car shouldn't even be sensitive to knock in that area. Oddly, peak torque, where a car is most prone to knock, shows a relatively low knocksum. The knocksum is also increasing proportionately with rpm. The knock sensor is showing increasing engine noise as the rpms rise, but only one real spike, corresponding to the jump in knocksum found at around 5000 rpm.
-Jon
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I can't pinpoint an exact time when the behavior showed up. I'm trying to clean up all obvious mechanical issues then I'll be resorting to a known mechanical state.
The downpipe is a test piece that had the cross bars spaced out. I haven't seen any evidence of it rubbing. There is also a prototype heatshield that was installed at some point this year. On my list of really oddball things to try, removing the downpipe and heatshield will be one of them.
-Jon
The downpipe is a test piece that had the cross bars spaced out. I haven't seen any evidence of it rubbing. There is also a prototype heatshield that was installed at some point this year. On my list of really oddball things to try, removing the downpipe and heatshield will be one of them.
-Jon
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I pulled the test downpipe and found evidence of rubbing against the transfer case. I also removed the exhaust manifold heatshield, which should have been fine. The knocksum showing at 3000rpm is no longer there, the timing is slightly improved, but still gets severely worse as rpm increases. I get out of it at about 6k rpm with 10 knocksum.
We increased fuel and pulled timing with no real results. As rpms rise, it requires less and less timing, respectively. We stopped running the car after realizing that the car wanted 5 deg of timing from 4k-6k rpm.
I'll be checking injectors, coils, and some race gas to see if anything changes. Then I'll move on to cleaning the lash adjusters. Finally, I may just pull the head and inspect the valves, headgasket, and pistons.
One of the Subarus here at the shop is running fine with a cylinder showing 12% leakdown so I'm rather spooked that my car won't run with leakdown numbers close to that.
-Jon
We increased fuel and pulled timing with no real results. As rpms rise, it requires less and less timing, respectively. We stopped running the car after realizing that the car wanted 5 deg of timing from 4k-6k rpm.
I'll be checking injectors, coils, and some race gas to see if anything changes. Then I'll move on to cleaning the lash adjusters. Finally, I may just pull the head and inspect the valves, headgasket, and pistons.
One of the Subarus here at the shop is running fine with a cylinder showing 12% leakdown so I'm rather spooked that my car won't run with leakdown numbers close to that.
-Jon
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I tested the resistance on the injectors, coils, and wires and they all checked out. The continuity test listed in the service manual didn't work on the two coils I tried, one was from my car and one was not. I discounted it thinking I was just doing it wrong.
With the gas tank nearly empty, I mixed in about 3 gallons of Sunoco GT100 and went for some datalogging runs. The knocksum was reduced once again, but was not gone. Furthermore, the knocksum still continued to climb above about 5500rpm. Partial throttle is still running clean all the way through the rpm range. It was improved, but that car ought to be able to run more than 7 deg of timing above 5500rpm with race gas.
Today I brought the car up to temp and did yet another leakdown. This time I wasn't looking for numbers, the numbers were already showing some leakage, but to see if I could pinpoint leaking from something other than just the dipstick.
Immediately I noticed that there was a faint hissing coming from the dipstick, the oil fill cap, and all cylinders. To the uneducated ear, the leaking appears to be coming from everywhere. After a bunch of discussion with my boss, who has built his fair share of engines, I got some more direction on how to properly identify what the leakdown was telling me.
Any motor is going to leak, that is just the way they are. As I moved across all the cylinders, even the good ones at 3% were sounding the same at the throttle body and the dipstick.
The first one we were discussing was cylinder number two. The hissing was everywhere, but with the spark plug boots in the other open cylinders, there was a much LOUDER hiss in cylinder number four. What I've heard in the past is that a headgasket is at fault when there is leaking going from one cylinder to the other. According to my boss, my circumstance where the air is skipping adjacent cylinders is probably valves.
I disconnected the upper intercooler hose to really listen. Again, there was a faint hissing sound at the throttle body that changed slightly when the throttle body was opened. We moved through the good cylinders only to note that the same sounds were present while showing only 3% leakdown.
On cylinder one, it was obvious: opening the throttle plate went from a slight air moving through a pipe sound to a loud hissing almost as if the pressure at the tester was changing. After prodding around a little more, cylinder two was concluded to be leaking out of the exhaust valve where cylinder one was leaking out of the intake valve.
I have two things that can be done next:
1) Pull the valve cover and inspect for any odd wear across the cam lobes, hoping for a sticky, collapsed, or pumped hydraulic lash adjuster and possibly cleaning them if suspect.
2) Pull the entire head to visually inspect the valves for signs of inconsistent burn or wear. When something is wrong, there will be some component that looks very different from the other components and it just narrows the search. If there is still nothing obvious, just rebuild the head by pulling all the valves and checking for trueness on a valve grinder and checking springs with a spring compressor.
I'll be trying option 1 first, tomorrow.
-Jon
With the gas tank nearly empty, I mixed in about 3 gallons of Sunoco GT100 and went for some datalogging runs. The knocksum was reduced once again, but was not gone. Furthermore, the knocksum still continued to climb above about 5500rpm. Partial throttle is still running clean all the way through the rpm range. It was improved, but that car ought to be able to run more than 7 deg of timing above 5500rpm with race gas.
Today I brought the car up to temp and did yet another leakdown. This time I wasn't looking for numbers, the numbers were already showing some leakage, but to see if I could pinpoint leaking from something other than just the dipstick.
Immediately I noticed that there was a faint hissing coming from the dipstick, the oil fill cap, and all cylinders. To the uneducated ear, the leaking appears to be coming from everywhere. After a bunch of discussion with my boss, who has built his fair share of engines, I got some more direction on how to properly identify what the leakdown was telling me.
Any motor is going to leak, that is just the way they are. As I moved across all the cylinders, even the good ones at 3% were sounding the same at the throttle body and the dipstick.
The first one we were discussing was cylinder number two. The hissing was everywhere, but with the spark plug boots in the other open cylinders, there was a much LOUDER hiss in cylinder number four. What I've heard in the past is that a headgasket is at fault when there is leaking going from one cylinder to the other. According to my boss, my circumstance where the air is skipping adjacent cylinders is probably valves.
I disconnected the upper intercooler hose to really listen. Again, there was a faint hissing sound at the throttle body that changed slightly when the throttle body was opened. We moved through the good cylinders only to note that the same sounds were present while showing only 3% leakdown.
On cylinder one, it was obvious: opening the throttle plate went from a slight air moving through a pipe sound to a loud hissing almost as if the pressure at the tester was changing. After prodding around a little more, cylinder two was concluded to be leaking out of the exhaust valve where cylinder one was leaking out of the intake valve.
I have two things that can be done next:
1) Pull the valve cover and inspect for any odd wear across the cam lobes, hoping for a sticky, collapsed, or pumped hydraulic lash adjuster and possibly cleaning them if suspect.
2) Pull the entire head to visually inspect the valves for signs of inconsistent burn or wear. When something is wrong, there will be some component that looks very different from the other components and it just narrows the search. If there is still nothing obvious, just rebuild the head by pulling all the valves and checking for trueness on a valve grinder and checking springs with a spring compressor.
I'll be trying option 1 first, tomorrow.
-Jon
I've been following this thread, but haven't posted in it as I don't have a whole lot to contribute here...
I'm curious as to what physical symptoms your seeing (not empirical - meaning, not the numbers, the actual feeling of the car). Is it a gradual loss of power, does it pull normally but just not as strong, does it stutter/sputter?
Also, I'm not an expert by any means, but if your headgasket was cracked (even just a tiny bit) wouldn't you see SOME kind of oil backing up into your coolant system?
P.S. good luck and let us know what you find!
I'm curious as to what physical symptoms your seeing (not empirical - meaning, not the numbers, the actual feeling of the car). Is it a gradual loss of power, does it pull normally but just not as strong, does it stutter/sputter?
Also, I'm not an expert by any means, but if your headgasket was cracked (even just a tiny bit) wouldn't you see SOME kind of oil backing up into your coolant system?
P.S. good luck and let us know what you find!
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The physical symptoms included, originally, a decrease in both maximum boost pressure as well as boost response. The air/fuel ratios were also off compared to when the car was originally tuned. When run on the dyno with boost leaks, the onset of boost was lagging behind where it should have been.
After resolving all boost leaks, the car would pull timing under conditions that were previously knock free. This can be identified by either feeling the car accelerate (any jerks while accelerating are usually a sign of pulled timing) or by datalogging knocksum, found in a number of Evo data loggers. All this was reinforced by my most recent tests on the dyno where the car would equal the power of the original tune up until about 4500-5000rpm, where torque started to plummet as the knocksum skyrocketed.
I'm not that experienced with headgasket problems, but typically a headgasket is associated with a white smoke in the exhaust, indicating burning coolant; coolant in the oil; bubbles in the coolant when doing a leakdown; strong fluctuations in the coolant levels, indicating burning off or pressurizing of the coolant; and often times overheating issues.
-Jon
After resolving all boost leaks, the car would pull timing under conditions that were previously knock free. This can be identified by either feeling the car accelerate (any jerks while accelerating are usually a sign of pulled timing) or by datalogging knocksum, found in a number of Evo data loggers. All this was reinforced by my most recent tests on the dyno where the car would equal the power of the original tune up until about 4500-5000rpm, where torque started to plummet as the knocksum skyrocketed.
I'm not that experienced with headgasket problems, but typically a headgasket is associated with a white smoke in the exhaust, indicating burning coolant; coolant in the oil; bubbles in the coolant when doing a leakdown; strong fluctuations in the coolant levels, indicating burning off or pressurizing of the coolant; and often times overheating issues.
-Jon
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The leakdown results remained consistent after removing the cams so the problem was isolated to within the head.
During the initial disassembly of the head, we have found one burnt and bent valve, located on the exhaust side of cylinder number 1. All valve seats appear to be strong and the valve guides are not excessively worn. The exhaust valves on cylinder number 2 have the greatest amount of pitting. There is an off chance that the pitting spans the entire seat width and is causing some leakdown. It may also be possible that there was some carbon sitting between the valve and the seat, that has since been cleaned up.
All valves are going to the machine shop tomorrow for cutting and I will know, then, if there are any other bad valves. We will also be looking at the lifters and testing the rates on all of the valve springs.
All in all, the bottom and top-end appear to be pretty healthy (other that the owned valve, of course). I have only speculations on the valve, at this point.
There are a couple running theories, none of which have been substantiated yet. [*] There may have been excessive EGTs generated by the boost leaks that burnt the valve. Also with the boost leaks, the fuel would have swung rich and created carbon deposits that may have caused the pitting found on the other valves. [*] It also could have been overrevved in the 4500 miles the previous owner had it or the dealership or alignment shop overrevved it. An unavoidable necessity when at the mercy of others to do specialized work.[*] Lastly, it may be a bad valve spring that could have prevented the valve from seating properly and transferring the heat away.
-Jon
During the initial disassembly of the head, we have found one burnt and bent valve, located on the exhaust side of cylinder number 1. All valve seats appear to be strong and the valve guides are not excessively worn. The exhaust valves on cylinder number 2 have the greatest amount of pitting. There is an off chance that the pitting spans the entire seat width and is causing some leakdown. It may also be possible that there was some carbon sitting between the valve and the seat, that has since been cleaned up.
All valves are going to the machine shop tomorrow for cutting and I will know, then, if there are any other bad valves. We will also be looking at the lifters and testing the rates on all of the valve springs.
All in all, the bottom and top-end appear to be pretty healthy (other that the owned valve, of course). I have only speculations on the valve, at this point.
There are a couple running theories, none of which have been substantiated yet. [*] There may have been excessive EGTs generated by the boost leaks that burnt the valve. Also with the boost leaks, the fuel would have swung rich and created carbon deposits that may have caused the pitting found on the other valves. [*] It also could have been overrevved in the 4500 miles the previous owner had it or the dealership or alignment shop overrevved it. An unavoidable necessity when at the mercy of others to do specialized work.[*] Lastly, it may be a bad valve spring that could have prevented the valve from seating properly and transferring the heat away.
-Jon
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