Spark Plug Problem or Injectors?Help!

[q45roadwarrior]

After sitting for several days, upon restarting my '01q45t it skips and vibrates for quite a while. (Long enoughto last even a few minutes after temp. gauge shows it'sup to operateing temp.) Any ideas?

Here's the history on this car:

'01 q45T purchased 12/02 @38k miles now has 50k milesuse Mobile One every 3,000 milesMobile One in trans (Flushed @38K)Syn brake fluid @ 38kRadiator flush @ 38kReplaced fuel filter (twice)Lousy Gas mileage from day one....4 cans of 44k since purchasealso had BG injector service @ 48k

after 3 other q45s (the others got 22 to 26 hwy mpg),I cannotunderstand the poor mileage.Maybe the vibration after sitting is a clue. Any help would be appreciated.

Former Yahoo board member

[forecast]

obviously misfiring.

have you done a ECU diagnostic?

only when the cars been sitting for few days? What about just one day? (I'm thinking about a bad coil or power amp that only works right when warm - these will take longer to heat than the coolant)

After a couple miles and getting the rpms up does it normalize?

What sort of driving? Do you get the RPMs up into the high 5000's or 6000's regularly? (I'm thinking of spark plug fouling)

I think the poor gas mileage indicates a spark problem, not a fuel problem. What does the exhuast smell like?

A power balance test will isolate which cylinders are weak.

[Q451990]

Welcome to NICO Road Warrior! Isn't your Q still in warranty? I'd see if you can get them to let you play with a G35 for a few days and let them troubleshoot it. By "lousy gas mileage" what do you mean? I'm with forecast on the power balance being the place to start. Where do you live in SC again? Seems like the low country if I remember correctly, but I don't remember for sure...

Heath

[maxnix]

Perhaps too early for injector failure, but how about water condensation or bad fuel? Has the fuel filter been replaced? Is there pressure on the tank when you release the gas cap?

Try a bottle or three of 100 % ethyl (not methyl) alcohol when you go on a trip.

[Q451990]

Perhaps too early for injector failure...

I wouldn't rule anything out... who knows what the former owner put in the tank - or just a defect from the factory. I once looked at the service records for a 92Q that had all injectors replaced under warranty at something under 10K miles... weird things happen out there in the real world.

Heath

[q45roadwarrior]

yes on the dioganostic,but dosen't show anything while its at the dealers. Maybe I need to let them test it after sitting 4 days or more. No problems when it only sits a day or two. Always premium93 octaine, yes the fuel filter has been changed twice since I've owned the car. I did talk to customer realations and they've agreed to replace the plugs @n/c to me. This one only gets 20 mpg highwy with 38-40 psi in the tires. RPM's rarely over 5000.I tend to baby the car unless I need the power for getting out of some 18 wheelers' way.I hope this posts so everyone can see. I really appreciate the responce from everyone.

[PalmerWMD]

I am curious to see if your plug replacement will cure that.

Also: Does SC use reformulated gas of any kind?expect as much as 1.5 mpg less with some reformulations.

plug fouling does seem indicated, from your driving habits though.

Consider putting in a 100mph run for 5-10 minutes twice per month (I know,. may be hard to do outside of western US:()

Fred...

[DAEDALUS]

Track time is expensive. How about doing freeway speeds in 2nd or 3rd instead?

If the dealership will agree, ask them to number the old plugs so you can have a look at them when you get the car back.

[forecast]

about the RPMs. Actually your not doing you Q any favors by keeping the RPMs low.

Elsewhere I've read recomendations to get over 5000 daily, for 20 sec or more (you can drive for 10 min just below the redline without inflicting any damage)

The problem is plug fouling, the plugs need to get hot enough to burn crud off them that will accumulate at lower RPMs. If they start to get fouled up, the crud will have an insulating effect.

Perhaps if it's just fouled plugs, you still burn it off by warming it with a good drive and then putting in first and driving a mile or so at the high rpm end (5000+).

Any error detected by the ECU is held in memory for 50 starts, so if the dealer says the ECU is clueless, it's clueless.

The fact that it only happens after four days is signifigant. Either something is condensing on the ignition system to short out a coil, or a coil or power transistor is failing but only shows problems when really cold.

[DAEDALUS]

Yep. I'd be surprised due to the mileage, but I had the exact same symptoms due to a bad coil. The insulation was going bad, so the coil was arcing. No error codes, since there was still continuity in the coil, but it kept the plug from firing. Replaced the coil and the problem went away. Looking at the plugs, it was dead obvious which cylinder it was and that arcing was the problem.

[q45roadwarrior]

I think I may not have described my driving habits/style very well.I cover about 10-12 states, constantly driving @ 75-80mph.....sometimes 90 to 100 .(I try to stay away from WOT Starts, probably just my training back on the farm. ( these cars sure are more complicated than anything I've ever driven)

One of the things I tried was WOT from 40 mph to 110mph SEVERAL times. NO smoke- not grey, not black- no smoke at all, and no improvement.The coil problem is a little out of my area of knowledge, but I'll tellthe tech's to check for it. -I'm surprised that maybe a leaking injector wasn't mentioned, but again, I'm not an expert.

Thanks everyone for your help! Especially (Fred and Heath)as I remember you guys from the old board.

[q45roadwarrior]

With the kind of driving I do, which NGK plug should I ask for ?

[Q45tech]

The standard heat range plugs [[6]]. Now if you were holding it at 120 mph in 3rd gear for 20 minutes at a time a colder plug [[7]]might be required.