High RPM hesitation

[carolsdavid]

My car sputters and hesitates as it rev's over 3800 rpm's. It had the symptons last week at much lower rpm's. After a quick inspection, I found the valve covers leaking. No problem. Replaced those, as well as the COP boots for the cylinders floating in oil. At the same time, I replaced all spark plugs for the first time in 145'000 miles. What a great car. Let's see the foreign brands run that good for that long!!!!!!!! I don't think they can, but I digress. Anyways, the initial problem is repaired, but now it bucks, sputters and hesitates as they are climbing over 3800 rpm's. I removed the COP's again to look for any signs, but found none so far. I have an OPD II, but no codes. Are there any test for the COP's?

[shorod]

If you have a scan tool that can access the component parameters, you should be able to monitor the misfires on individual cylinders, even if they are not high enough to set the check engine light.

Make sure that in the process of changing the gaskets and plugs you got any vacuum lines correctly installed and that the air intake tube is properly installed (no lips folded over). You may also want to replace the fuel filter and put a bottle of fuel injector cleaner in the fuel tank.

Did you replace the coils, or just the rubber boots for the coils?

-Rod

[carolsdavid]

Vaccum lines look good. I just replaced the boots, not the coils. I will replace the filter next. Any brand of injector cleaner?

[shorod]

As for the injector cleaner, I think they are all pretty much the same. I've never noticed a significant difference between any of them, but then again I use a bottle at every oil change, so the fuel system is probably pretty clean already.

There is a chance that one or more of the coils is weak due to previous misfires, and replacing the boot on the coil would not solve such an issue. I don't really know how likely that is. I know transformers (which is essentially what an ignition coil is) can degrade if run at max load for a long time, but the duty cycle of an ignition coil is pretty low.

At this point if the filter and injector cleaner don't fix the issue, it's probably time to find a shop with the appropriate scan tool to monitor misfires real-time and see if it can at least be narrowed down to a specific cylinder.

-Rod