Rough Running 1999 Q45

[turbozkid]

ok i just purchased a 1999 Q45 and this is what iam having problems with:

1999 Infiniti Q45has an engine miss at idle sometimesThe problem is most pronounced after the car has been run for 10 or 20 miles and then parked for about an hour (I presume the heat builds/soaks the engine). After re-start the "missing" is most pronounced for a few minutes but will continue to miss at idle (stop lights) and is 'jerky' under very light load.

no check engine light is on. if it were i would be able to figure it out but the fact that its not toughing a cell is odd to me.

i heard the the coil packs tend to go bad but so do the injectors.] i dont want to just start replacing stuff with out knowing what it is for sure cause these parts are not cheap

could it be just a bad/ dirty maf??? idk i need some help please

[Romeo5k]

My first guess would be injectors. And thats without getting technical.I suggest before getting technical, running a can of BG44k in half a tank of SUPREME gas! See if that helps any. If it does, Play close attn to it, If it doesnt, get ready to get technical. Its time to Ohm your injectors. All that is somewhere if you use the search field. But before u start like i stated , do simple stuff first.

[rkeats]

Replace the coils!! I had the exact same thing in my 99Q45t. I finally gave up and got all 8 of them(coils), took me about an hour to replace them all and I am not a mechanic. It has been pointed out many times on this forum that the coils are the answer to the idle miss. It has been sweet running now for over a year. Now on to the rear shocks/struts!!

[turbozkid]

My first guess would be injectors. And thats without getting technical.I suggest before getting technical, running a can of BG44k in half a tank of SUPREME gas! See if that helps any. If it does, Play close attn to it, If it doesnt, get ready to get technical. Its time to Ohm your injectors. All that is somewhere if you use the search field. But before u start like i stated , do simple stuff first.

ok well iam not afraid to get technical. i have lots of experience workin on cars. but to test the resistance in the injectors dose the plenum have to be removed or can i reach them with out doin so???

NEVER MIND I FOUND IT
Modified by turbozkid at 1:57 PM 1/19/2010

[turbozkid]

Replace the coils!! I had the exact same thing in my 99Q45t. I finally gave up and got all 8 of them(coils), took me about an hour to replace them all and I am not a mechanic. It has been pointed out many times on this forum that the coils are the answer to the idle miss. It has been sweet running now for over a year. Now on to the rear shocks/struts!!

so your car did not throw a check engine light either ??? cause i was thinkin if it was a miss fire from a coil it would "catch" it and i would be able to pin point it.

witch kind of makes me believe its an injector problem. still not sure tho

[bullittandy]

Its coils, coils, coils. I swear to God.

[turbozkid]

ok so today it finally throw a cell it came back as 2 different knock sensor codes and an evap code.

witch leads me to believe its 1 or 2 bad injectors that's makin the car run lean and the knock sensor is pickin it up.

but i still need to test the ohms of each injector to confirm.

will update with results..........

[bullittandy]

You'll see.

Its the coils.

[paranoidjack]

You'll see.

Its the coils.

Lol - I read that in the voice of the little poltergeist girl.

[turbozkid]

You'll see.

Its the coils.

lol iam not doubting you. by the looks of it you have far more experience with these cars then i do.

but how often do the knock sensors go on these cars??

i just want to rule out every other possibility

[Q45tech]

Knock sensors fail on every Nissan ever built as they are made of plastic which cracks under temperature extremes [hot summer shut offs] with hood closed EXCEEDS oem KS specs for a few minutes which adds up after years.

They usually last 8-10 years except in Death Valley, Lake Havasu City, Ariz avg July 111F . or Cloncurry, Queensland peaking at 123F.

KS are a part of the historical overheat indication to tell technicians that owner abused vehicle if they melt vs just crack.

I have personally seen over 25 melted KS just on Q45 alone. We use to love it because that means a owner gets to buy a new engine or junk the vehicle to us.

[oldmako]

How much of an overheat does it take to melt one? I would think that the engine would seize beforehand or at least shut down.

[maxnix]

You also have to think of heat soak after shut down when temperatures peak.

[bullittandy]

Feel free to replace the K/S as they are a wear item. they fail either early (100K) or late (150K).

It is unlikely that the injectors are the issue as they appear solid on 97+ cars. Earlier cars had trouble but 97+ cars have coil problems and 96 and earlier cars have injector problems.

there does not seem to be any rhyme or reason as to why the computer does not trip the SES when a coil fails. i bet there is some computer code issue (similar to Windows problems) that does not trip the SES on 97+ cars.

I wish that someone with a ton of engineering degrees would explain how an engine code does not get tripped on these cars but alas. . .