P0303 and Coolant

The problem actually turned out to be a weak valve spring in an older GC that hung open if it ran over 3,500 rpm. Referring to this as 'overrevving' was a misnomer; as you mentioned, PCM's won't let you run the engine beyond OEM-spec redline. It took a LONG time to figure this one out though.

Do we know why this is? I just put in iridium/platinum plugs in to my Sienna and got a couple more MPG over the original plugs. It is coming up to the time where I will be replacing the plugs on my 2002 TJ. Do we really just go with the standard old Champion coppers? Almost seems cave-man-like today.... . Tomes

The conventional wisdom is that the heat range isn't quite right. The only thing that iridium/platinum buys you in that case, is a set of plugs that don't burn quite right, leading to loss of mileage and perhaps other problems, but doing so for a long, long time.

Earle

cave-man-like

What defines a _good_ code scanner? This is primary on my list this year. I was thinking of the $65-85 one that pretty much reads and clears the codes (the one at Autozone, an Actron model). Do I, as someone who can fix/replace the simple stuff like brakes but is baffled by carb guts, need the more advanced frills? Tomes

In my opinion, no you do not need any more frills than you get for $65 to $85. Actron seems to offer 4 models, with the two you are looking at as the mid-priced units. Of the two, I'd go with the higher end unit, but I'm hard pressed to tell you why.

I think a code reader is an important addition to your tool chest. I know it would be a handy addition to mine.

I've not heard (documented) bad things about the Bosch (Single) Platinum plugs which is what I used in my 4 liter XJ and now my WJ and in Mark's 4.7 but then their technology is over 20 years old now.

I've heard a lot about of negative stuff about the new high tech plugs (+2,

+4, iridium, Splitfire) including Dave St Louis (Service Manager at Belleville Dodge/Chrysler/Jeep.

A fair number of Jeepers dislike the platinums of any type although I don't know if that is partially guilt by association with the new high tech offerings.

There is a big difference between a code SCANNER and a code READER.

The $79 cheapies you see at Pep Boys are readers. If all you want to do is retrieve numeric codes and reset the MIL, this is fine.

For another $100-150 more, a code SCANNER will give you information about idle speed, IAT temp, real-time TPS voltage, O2 voltate readings, fuel trim percentages (long and short term), exact coolant temp at the sensor, RPM variations, cylinder power balances, and my favorite: the ever-popular rediness check, which tests every input/output sensor to make sure everything is in-spec before visting the smog-check testing center.

You can spend more if you need transmission diagnostics and other esoteric information. I don't need all of that stuff, but the O2 sensor data is valuable to me: I can look at each sensor's performance and tell if there's a pending problem, or if one has failed, know EXACTLY which one at a glance without having to look anything up in a manual.

I settled on an Actron 9145 code scanner for about $180 on sale. This is more than most shadetree mechanics will ever need. I've easily recouped that cost in the last few years by reading my own codes, resetting the 'crank sensor out of spec' when I unplug it to prime the engine after an oil/filter change, and the one infamous time when I removed/cleaned the EGR valve and had a serious out-of-spec idle problem afterwards. (It actually said the EGR valve gasket was leaking - how the computer knew that is a mystery to me.)

Either way, a code scanner/reader is a very good investment.

Incidentally, if all you want is codes, newer Chrysler and Jeep products will display this on the odometer display by pressing the odometer reset button while turning the key to the RUN position --no need to buy a seperate code reader if this will suffice.

I once met a guy who was so fanatical about spark plug performance, he would actually shim each one (indexing) so that the open end of the electrodes faced the intake valve on each cylinder. He swore that he gained 10+ hp. from this. I think he's been out in the sun too long.

I've tried every kind of spark plug ever made on a variety of vehicles. I've never seen any differenc in either performance or service life between any of them.

My preference: Champion Coppers which retail for about $1.39 each, the choice of Cavemen everywhere.

Mongo like Chamipon but like Autolite a bit better. Think Autolite heavier like large club, work good.

My belief is that putting in fresh plugs every 4-5k is a cheap way of keeping an eye on the engine for any odd combustion.

Earle go Chevrolet dealer one time with exact plug specification from '85 Cavalier Owner's Manual that say AC plugs. First cave man Earle talk to say "Chevrolet never use AC plugs". Second cave man say "That car use Champion", try to give Earle plugs with completely different design. Earle take Owner's Manual to Autozone, get right plugs, AC, just like come in car from factory. You cave mans see Earle in TV?

Earle

Didn't Buick buy AC in ... something like 1908?

go on ebay and watch wht you come up with

Tomes wrote:

OK, thanks so far to you and Jeff, much appreciated, and I welcome others' opinions on this as well. Looking at their website I am guessing I was looking at the 9125, but I need to go back and look again. It was the lowest end model that was there.

So, Outa, if I do get (ask Santa for) the 9145, the added benefits will allow me to go through all the stuff and find things that are impending. It also sounds like I will be in the garage every spare minute (is this a good or a bad thing...) with the toy, I mean tool. this could be good for only for my 2002 TJ (77K miles), but for the aging 98 Sienna (187K miles).

I am all interested in this now because for the first time I went to the Autozone and had them read the codes on the CEL-lit Sienna and I had a list of cylinder malfunctions that I fixed with new wires and those Bosch Platinum Ir Fusion (they were on sale) plugs (it is not easy to get at those rear plugs....). Saved a lot of cash by not having to bring it in. Now with the Sienna at the point where more stuff will be popping up, your post below is telling me that hunting through all that other stuff would be prudent and likely save me more money by heading things off. Sooner or later this applies to the TJ too.

Am I looking at this right or am I being too optimistic in my limited abilities? Tomes