Next question -- #4 plug overheating, others look good
11-09-2006, 10:34 PM
#1
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Next question -- #4 plug overheating, others look good
Per my other thread, I just dropped off the 951 this week for a preventative rod bearing replacement, installation of new SFR headers to replace my cracking originals, and a timing belt. I figured that this would be a fine time to have the HG done as well -- I'm still on the original at 132k miles and doing about 15 track days a year now. The car has been running like a top, with no evidence of HG problems, perfect oil pressure, normal temps, no drop in power, etc. The car is entirely stock except for the basic Guru chips, a 3 bar FPR, and a reliaboost set to 14psi instead of the allowed 15psi for safety.
My wrench did a leakdown before removing the head to make sure the rings are OK and check for any issues. Cylinders 1-3 were good, number 4 had a leakdown of about 15%. This surprised me, as the car is running perfectly and I did a compression test 20k miles ago and got a perfect 145psi across all 4 cylinders. He also told me that plugs 1-3 looked perfect, while #4 had a burnt electrode. This really surprised me, as I replaced the plugs 6 months ago (after 2 years of service) and the 4 that came out looked like new. I also had the injectors cleaned at this time, and all 4 were perfect before and after cleaning according to the report. I'm really ****.
Unfortunately, I didn't get the story as to whether it was the valves or HG causing the mediocre leakdown. However, I was told that the HG looked good when it came out.
Now, for a few of questions:
1. Does an overheating NGK BPR7ES (one range colder than stock) necessarily indicate a lean condition, or could it just be caused by an ailing HG causing cooling problems in that cylinder?
2. Other than a leaking intake manifold gasket (possible) or inadequate fuel delivery to #4 (i.e., due to a bad injector, which is unlikely since they were just serviced and were perfect), what could cause a lean condition in a single cylinder? Is it possible that leaky valves are responsible?
3. I guess, more to the point, do I need to worry about this, or will the fresh HG and valve job take care of this?
My wrench suggested that I might want to back off the boost a bit, but I don't think that's the issue since I'm running less than the chips allow and my plugs looked textbook perfect 6 months ago after 2 years with this setup. FWIW, my narrowband Autometer A/F gauge certainly suggests that the car is running as it always has on full boost (one or two LEDs into the rich zone).
My wrench did a leakdown before removing the head to make sure the rings are OK and check for any issues. Cylinders 1-3 were good, number 4 had a leakdown of about 15%. This surprised me, as the car is running perfectly and I did a compression test 20k miles ago and got a perfect 145psi across all 4 cylinders. He also told me that plugs 1-3 looked perfect, while #4 had a burnt electrode. This really surprised me, as I replaced the plugs 6 months ago (after 2 years of service) and the 4 that came out looked like new. I also had the injectors cleaned at this time, and all 4 were perfect before and after cleaning according to the report. I'm really ****.
Unfortunately, I didn't get the story as to whether it was the valves or HG causing the mediocre leakdown. However, I was told that the HG looked good when it came out.
Now, for a few of questions:
1. Does an overheating NGK BPR7ES (one range colder than stock) necessarily indicate a lean condition, or could it just be caused by an ailing HG causing cooling problems in that cylinder?
2. Other than a leaking intake manifold gasket (possible) or inadequate fuel delivery to #4 (i.e., due to a bad injector, which is unlikely since they were just serviced and were perfect), what could cause a lean condition in a single cylinder? Is it possible that leaky valves are responsible?
3. I guess, more to the point, do I need to worry about this, or will the fresh HG and valve job take care of this?
My wrench suggested that I might want to back off the boost a bit, but I don't think that's the issue since I'm running less than the chips allow and my plugs looked textbook perfect 6 months ago after 2 years with this setup. FWIW, my narrowband Autometer A/F gauge certainly suggests that the car is running as it always has on full boost (one or two LEDs into the rich zone).
Last edited by KLR; 11-09-2006 at 11:43 PM.
11-11-2006, 12:31 PM
#2
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Bump.
Seriously -- should I be worried that I'm running lean in the #4 cylinder or just assume that this was a cooling issue that will be addressed by the new HG and valve job?
Seriously -- should I be worried that I'm running lean in the #4 cylinder or just assume that this was a cooling issue that will be addressed by the new HG and valve job?
11-11-2006, 12:42 PM
#3
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If your leak down number(s) are up then the damage has already started. Might not be too severe but there is something wrong more than the just plug issue. If you are really running lean you may have started to burn a valve causing a bad seal on the exhaust valve. It could be all sorts of things –get your shop to look a little closer. When doing a leak down test you usually can hear where the air is leaking from – that will tell you a lot.
11-11-2006, 02:44 PM
#5
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Perry's problem was going the other way -- his #4 plug wasn't getting hot enough (i.e., was looking a bit fouled).
Chris -- The head is already off and at the machine shop, so I suppose we'll find out soon enough if it needs anything besides typical R&R. I guess my question at this point is, "do I need to worry about diagnosing an issue, or should I just plan to monitor my plugs after getting the car back?" The car is basically stock, runs modest boost for the modest aftermarket chips and 3-bar FPR, and the injectors were recently balanced. I know that cylinder #4 typically runs hotter than the others. Could this plug be showing signs of running too hot for reasons that will be addressed with the new HG and head rebuild, or do I need to worry that I have another problem?
Chris -- The head is already off and at the machine shop, so I suppose we'll find out soon enough if it needs anything besides typical R&R. I guess my question at this point is, "do I need to worry about diagnosing an issue, or should I just plan to monitor my plugs after getting the car back?" The car is basically stock, runs modest boost for the modest aftermarket chips and 3-bar FPR, and the injectors were recently balanced. I know that cylinder #4 typically runs hotter than the others. Could this plug be showing signs of running too hot for reasons that will be addressed with the new HG and head rebuild, or do I need to worry that I have another problem?
