98 QX4 missfire issue

[slownlow43]

I'm hoping someone on here can help me. I'm having an issue with my 98 QX4 randomly missing shortly after I start it. This has been happening for the past 2-3 months. The longer I drive it the better it seems to do. Although I just took it on a 2-hour trip and I had the issue the entire time, and it was worse under load.

I've recently replaced the distributor, plugs, and wires with no luck. When I run premium fuel it seems to run a little better for a while. I don't remember the codes, but it's throwing 2 SES codes. One for the infamous knock sensor and another for a faulty gas cap. I replaced the cap, but it didn't clear the code. I have had these codes for about a year now.

Can anyone offer any input?

Also, while I'm thinking of it, has anyone had an issue with their transmission being "indecisive" between drive and overdrive until the transmission warms up?

[smj999smj]

There is no code specifically for a faulty gas cap; likely you have an Evap system leak code, which "could" be caused by a faulty gas cap, along with a number of other reasons (faulty vent control valve, leaking hose or fuel sender "O" seal, to name a couple).

If you are experiencing a misfire when you start it, it would make sense that you have a knock sensor code, as it would sense the misfire.

First. make sure the secondary ignition system is in good shape, especially the distributor cap and ignition wires/spark plugs. If that's okay, it is not uncommon for fuel injectors to stick; there was a TSB on the issue. A professional fuel injection cleaning service is recommended.

[slownlow43]

Thanks for the reply. The distributor I purchased had a lifetime warranty so I exchanged it for a new one. I had a slight bearing squall coming from it anyway. I've only taken it on one short drive, but it seems to have fixed the misfire issue.

While I swapped the distibutors out I left the battery unhooked to clear the codes to see what, if any, codes came up. After the second start I got a CEL with code P1444. A little research has suggested swapping out the charcoal canister as the charcoal may be breaking up and clogging the valve. Have you had any experience with this, and does this sound like a plausible cause for the CEL?

[smj999smj]

Yeah...inside the canister is a foam liner that contains the charcoal. Sometimes they break and tiny pits of charcoal can get sucked all the way up to the intake manifold in some circumstances. This can jam the purge control valve and contaminate everything else on the vacuum line circuit of the Evap system. There was even a TSB on how to clean the system of the debris, when this happens. It's easy to confirm if this has happened to yours. Remove the Evap canister and remove the vent control valve from the canister. Hold the canister so that the "vent control valve" side of the canister is facing down and shake the canister over some newspaper (or anything that will contain a potential mess). If bits of charcoal fall out of the canister, then the foam liner has been compromised and you'll need to replace the canister and used compressed air to completely clean all of the debris out of the system per the TSB procedure.

[slownlow43]

Bringing this one back. Like previously mentioned, I replaced the distributor about 2 weeks ago but have started to get a squeal from it. The prior 2 did the same thing, the last one started to misfire shortly after. A coworker suggested the cam might be loose causing a strain on the distributor bearing. Does that sound like a legitimate possibility?