Cold Plugs or Hot Plugs??

[oldmako]

My '99 has developed an intermittent miss when operating under WOT and at high engine rpm/load. It starts easily and idles smoothly. During normal city driving it runs flawlessly, but when I stomp it on the highway and really let it eat (above 90) it starts to miss. Not terrible, but it's there and it did not do this before. Obviously there is a loss of power and acceleration. Sucks it does.

It has 125K and I have no record of the plugs having ever been changed so that's where I'm going to start. The manual recommends the colder range if the car is used on the highway. 95% of my driving is at 65-80mph, so I am leaning toward the colder plug. Before I drop 80 bucks, I thought that I'd solicit the advice of the motorheads on the board. PFR6 or PFR5??

I have inspected the MAF and it looks clean. It has a new air filter, and the intake is clean up to the throttle body. I found the TB to be surprisingly clean but I have not gotten deeper than the opening, although I will when I do the plugs. I will also check the injectors. My mileage has been fair, with most tanks yielding 19-20...but occasionally 21-23. I wonder if perhaps there is a cause for the difference in mileage? (Other than my Emmo foot) I ran BG through the fuel system in december.

When I do the plugs I will also try to clean and lube (dilectric) each coil connector along with any other connector I can persuade apart.

I've got plenty of beer and 18 gig on the ipod. There's some Makers Mark for emergencies and my neighbors are used to hearing me cuss in the parking lot. Anything else I ought to do while I'm under the hood??

[qship96]

Based on your location,and driving pattern,I would stick with the normal heat range plug-but be sure to use the NGK OEM plug ONLY,NO SUBSTITUTES!!!!!!!

The miss problem could be due to old worn plugs, or possible coilpack issue beginning.When was fuel filter replaced last?

Is check engine light on? I so, pull codes

[oldmako]

I have a fuel filter ready to install. No idea how old the current on is. Probably ancient.

No CEL

NGK fo' sho' my man!

Why not the cooler ones?

Almost forgot....Anti-seize on dem plug threads??? Dielectric on the plug connectors?? (never had a coil car so I have NO freakin idea what's going on in there)


Modified by oldmako at 9:52 PM 3/3/2008

[maxnix]

You could use the cooler 6 heat range ones in the summer, but you won't want to install the hotter 5 ones for the winter. 6 is only for Texas, AZ and south Florida.

Take my advice, get all gaskets and clean the whole intake and replace the valve cover gaskets while you are at it. Even the lower intake gaskets.

You will find much contamination and a blocked EGR tube in the plenum. Once you are done, you won't want to return for a very long time. Do it all now.

[StarPD]

I have a fuel filter ready to install. No idea how old the current on is. Probably ancient.

No CEL

NGK fo' sho' my man!

Why not the cooler ones?

Almost forgot....Anti-seize on dem plug threads??? Dielectric on the plug connectors?? (never had a coil car so I have NO freakin idea what's going on in there)

Modified by oldmako at 9:52 PM 3/3/2008

If you want to be anal about it, and why not since you're going to do the job, might as well do it right, here's a few suggestions. These are from "the old days", when serious car enthusiasts did all their own work, and knew that "the devil is in the details".

First of all, get yourself a correct thread chasing tap Make sure it's well greased to pick up the debris you'll be remooving from the plug hole threads. VERY carefully (remember, those threads are aluminum)clean the threads in each spark plug hole. Make sure the plugs are gapped correctly, don't trust the factory. Use anti-seize SPARINGLY. Install finger tight, then use a known good calibrated click stop micrometer torque wrench to snug the plugs. DO NOT OVERTIGHTEN! Stripping threads in an aluminum head is something you don't even want to contemplate. DO use dielectric grease on coil connections.

Oh, and while the plugs are out, might as well do a compression check. There is a right way and a wrong way, so learn how to do it correctly. Make sure there's no juice to the coils, make sure no fuel can get to the injectors (pull fuel pump fuse and run engine dry before beginning the entire process), and block the throttle wide open). If you can get the right test equipment (rental or borrowing?), do a cylinder leakdown test while you're at it. Maybe Dennis (Q45 tech) can tell you how to do it if you ask him nice.

If this doesn't cure your high-speed miss, do the rest of the usual diagnostics: Test the coils, ohm the injectors, check fuel pressure, replace the fuel filter and air filter. If the problem still persists, have the dealer do a Consult and check timing, etc., if only to eliminate other possibilities.

Now, please be sure to report back when you've finally isolated and fixed your problem. Other members here need to know what you've found so they can diagnose their own similar problems. Remember, we're all here to help each other.

Good luck.

[oldmako]

George, Maxnix and qship96

Many thanks for the information gents. I've got the day off and I can get the plugs locally but not the gaskets, so I'll start with them. I'll also clean as much of the intake, and as many connectors as I can. The forecast is for rain this afternoon so I may not finish.

I've owned it since Dec and have put about 6000 on it. This week is the first time that I've noticed the misfire. Perhaps its just lousy gas from my last trip. The engine has run silky smooth the rest of the time, and has pulled strongly right up to the shift points under WOT. I've never owned a V8 that shifts at 6600....which is pretty cool in and of itself. It sounds great winding up even though it's the red headed, hair-lipped, effete, emasculated, limp-wristed, bidet using, lisping bastard stepchild of the 4.5 engine. The earlier cars must be NICE. "Horsepower good, ugh!"

I realize that I have an old car, with fairly high mileage and a marginal maintenance history. In that regard I have no problem doing this work, and doing the little things which will allow the car to regain some of it's former glory. The suspension rehab paid huge dividends, and I suspect this work will as well. I picked this car up for 4500 bucks and it looks damn near new, so I am willing to drop some coin on it.

This buds for you, but the next 4 are mine,Off to skin my knuckles!

[maxnix]

Check Joe for the plugs. He has smoking deals sometimes.

If not, http://www.sparkplugs.com

Be patient and thorough.

[oldmako]

I got the plugs across the street at autozone for less than 10 bucks a pop. I was anxious to get started. I'm halfway done and hit a snag.

I have run the search, and I have gone through the owners man and the FSM.....and I cannot find a torque value for the plugs anywhere!!

I called my local stealership and was on hold for 15 mins before I got disconnected.

Any help from the motorheads??

ps. These F-n connectors make child proof caps at old folks homes look like childs play. I think some evil bastard glued mine together during assembly. Kind of like Brian Bosworth at the GM plant.

On a positive note....the pax side plugs were quite worn, so I am going to take that as encouragement before I dive into 1-3-5-7

[96Qowner]

FarFetched says 14-22 ft/lbs, Brian says 18 ft/lbs.

Should be on the NGK box?

zerothread?id=119914

[maxnix]

I choose the middle. It is in the FSM and on the box.

[StarPD]

FarFetched says 14-22 ft/lbs, Brian says 18 ft/lbs.

Should be on the NGK box?

zerothread?id=119914

Torque specs are not commonly on spark plug boxes. Plug manufacturer has no way of knowing what head material and type it will be installed in.

Depending on bore size and threaded depth of the hole, 22 ft-lbs is pretty stiff for a small plug in a cast aluminum head. Absent specs to the contrary, I'd suggest 15-18 ft lbs as a max. That should be adequate to seat the plug against the head for proper heat transfer.

For my credentials, I happen to be the World Champeen of thread stripping and bolt shearing.

[oldmako]

The box only said another half a turn or so.....so I used the TQ wrench and did the best I could. Some were tough due to the angle and the extension so I did them by hand.....a hand job if you will.

I'm pleased to report that the car is now in one piece...one well running piece in fact. The old plugs were very uniform in appearance, and very uniformly worn. The difference in the old electrode and the new was significant. I was unsuccessful in posting a pic so you'll just have to use your imagination. Instead of a pin, each one was more like a small pyramid....and probably almost as old. No evidence of oil or uneven burning. They were all the same approx color and texture.

I cleaned each coil connector (both male and female ends) and applied dielectric grease to the connector pins and the plugs themselves. The connectors were very clean internally, with no evidence of corrosion, miasma or smeg.

The new plugs made a significant improvement. The car 'catches' much sooner now when starting. It used to take 3 to 4 "ree-tee-tee-tees". Half that now. More like "ree'-tee-zoom". How's that for technical jargon?Low end torque has improved dramatically. When easing away from a stop the car pulls better and smoother. It also pulls mo' 'betta under heavy acceleration and at speed. I do still have a slight mis around 90+ at WOT. Perhaps one half to one quarter of what I had, but not perf yet. At any other speed and throttle setting the car runs like a chainsaw. I did not have time to change the fuel filter. That's next.

Likewise I did not have time to dig into the intake beyond the throttle body. I cleaned the MAF and all plumbing and connectors just up to the TB. It was all spotless. Another surprise.

I used the 3/8" fuel hose trick to thread each plug with a light coat of AS compound. I then backed each out, inspected for crud, recoated and reinstalled. Not a chance that any are in crooked.

The plenum job awaits. I did not have the gaskets or energy to delve into that today.

Overall, not as bad a job as I initially thought. I spent about 3.5 hours and that included the torque search, yakking with my hot neighbor, and schleppin to Advance for some Dielectric grease, one cigar and two Buds. I took Maxnix's advice and worked slowly and deliberately. Coupla' times my tongue was in the wrong spot and that really slowed me down, but in the end I got 'er done.

I do believe that these were the original plugs. The connectors had to be removed and then moved aside to allow access to several of the coil screws. The wires were tie-wrapped to the valve covers and prevented me from reaching the screws, so I guess that nobody ever went after them before.

Thanks again for the info.