What Does this Mean - #4CYL at 25% - Do I Need a Valve Job?
#1
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What Does this Mean - #4CYL at 25% - Do I Need a Valve Job?
OK - the saga continues:
BACKGROUND: 8 weeks ago my 98, 3.4 v6 4x4 started to run rough when warm and at an idle. Plus, my gas mileage has gone WAY down & at one point the check engine light even came on.
REPAIRS TO DATE: So, in an effort to remedy this I have run the codes and done/replaced the following: tune-up (plugs & wires), intake manifold gasket, 02 sensor, coolant thermostat, cleaned MAF, done complete intake leak & vacuum leak test (no leaks).
RESULT OF ABOVE: Though the check engine light has not come on again, I still have the rough idle and lousy gas mileage.
SO in a last ditch effort, I (gasp) took it to the dealership and paid them for diagnostics and this is what they came back with "test-drove vehicle w/a scan tool, all sensor values were within spec, leak tested each CYL & found CYL #1,2,3,5,6 at 10%, found #4CYL at 25%."
QUESTION: What does that mean to you - the dealership says it means a $3000.00 valve job! Any thoughts.
My next step is to clean the IAC.
BACKGROUND: 8 weeks ago my 98, 3.4 v6 4x4 started to run rough when warm and at an idle. Plus, my gas mileage has gone WAY down & at one point the check engine light even came on.
REPAIRS TO DATE: So, in an effort to remedy this I have run the codes and done/replaced the following: tune-up (plugs & wires), intake manifold gasket, 02 sensor, coolant thermostat, cleaned MAF, done complete intake leak & vacuum leak test (no leaks).
RESULT OF ABOVE: Though the check engine light has not come on again, I still have the rough idle and lousy gas mileage.
SO in a last ditch effort, I (gasp) took it to the dealership and paid them for diagnostics and this is what they came back with "test-drove vehicle w/a scan tool, all sensor values were within spec, leak tested each CYL & found CYL #1,2,3,5,6 at 10%, found #4CYL at 25%."
QUESTION: What does that mean to you - the dealership says it means a $3000.00 valve job! Any thoughts.
My next step is to clean the IAC.
#3
usually anything over 20 and a delership will want to pull the head. when you say rough do you mean a little vibration or was it misfiring?
Last edited by alexe; 03-09-2007 at 08:07 PM.
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No, no misfiring - just a rough idle. Rough enough that coffee in a cup in the dash cupholder sloshes around and the kids in the back seat says it feels like an earthquake.
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Not sure what kind of vacuum leak test was performed but a vacuum gauge will usually fluctuate when you have leaky valve(s). The 25% down cylinder is a problem and should be addressed whether it be leaky valves or bad rings.
At $3k for a valve job, I would be tempted to shop for a junkyard motor. Tearing into your motor and doing just the valves might be a bit of a waste depending on the condition of your rings and bearings.
At $3k for a valve job, I would be tempted to shop for a junkyard motor. Tearing into your motor and doing just the valves might be a bit of a waste depending on the condition of your rings and bearings.
#7
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It is a leakdown test (positive pressure not vacuum).
I agree that 25% might be worth looking into on #4 but I have a tough time saying that your extremely rough idle is all because of that. I am very curious what CEL came on briefly but I guess unless it comes back, who knows. Have you also done a resistance test on the injectors? If not you might want to try that as well. Make sure you spray the MAF with brake cleaner because I found that the electrical contact cleaner wasn't getting the job done.
I agree that 25% might be worth looking into on #4 but I have a tough time saying that your extremely rough idle is all because of that. I am very curious what CEL came on briefly but I guess unless it comes back, who knows. Have you also done a resistance test on the injectors? If not you might want to try that as well. Make sure you spray the MAF with brake cleaner because I found that the electrical contact cleaner wasn't getting the job done.
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#9
i would also try doing a wet compression test. that will indicate whether its your valves or your rings. a wet compression test is just pouring a small amount of oil in the cylinder after testing, then retest, if your compression goes up, its rings, if it stays the same its valves. i mean a small amount, no more then a capfull of oil.
oh and check your motor mounts, shaking that bad without a misfire sounds like a busted mount
oh and check your motor mounts, shaking that bad without a misfire sounds like a busted mount
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