91 Q45 Misfiring

[CastorTroy777]

Hey,

Just bought a 91 Q45 today from an auction, first glance everything looks ok, but after the bidding was done and i bought the car, we finally got to actually look at it and put gas in it because it was allmost out of gas and was sputtering a bit. Gas seemed to make it run fine, so i paid and drove it out of there, then not long after i pulled out i noticed a lack of power and sputtering up to about 50km/h then it feels great. Lots of clean power. So we came to the conclusion that it was misfiring, and maybe only running on 7 cylinders. It has 224000km on the car and is in otherwise good condition. except a few minor things im not too worried about. Any Ideas or suggestions are very very welcome, need some help.

Thanks Again

[metaverse3]

Fuel injectors.. Smoothing out at high RPM and bogging down at low rpm.. That would be my diagnosis...

[squeefoo]

Try a fuel filter first, then clean out the throttle body.

INFO. at: http://www.q45.orgThey put a lot of work into all this info and it has all the basics to get it running right.

[CastorTroy777]

Cool,

Thanks guys, I'll keep this updated to my progress, the car is at the garage, because i got fed up yesterday with my backyard mechanic sayin my cylinder head was cracked or my head gasket is blown. Which the "real" mechanics think is total BS. Not overheating or blowing excessive smoke from exaust. What u guys think?

Thanks,Ronnie

[Q_SHIP]

Before you do injectors, try a can of BG 44k. I was about to do injectors and tried that stuff. It smoothed right out and saved me some money.

[maxnix]

No one thinks it may have jumped timing? Better do the chain guide check before you even start it again.

[CastorTroy777]

hello,

Trying not to sound like a bone head here but how do i do that?

[Q_SHIP]

I highly doubt it has jumped timing considering it runs, and it runs strong at higher speeds. I have had my issues with these cars injectors and I would be willing to bet that it is the injectors.

[DAEDALUS]

If not an injector then suspect a coil/plug.

[CastorTroy777]

Hey,

Well i'm 96% sure we have located the problem, and its inside the head, a valve, thats what the mechanic said $280 later, well spent though got a tune up out of the deal and computer analysis. i can get a used motor for $750, he says it will run for a long time like that but now that i have felt the power of the Q i need her runnin top notch. My first Q, unbelievable cars, never knew that they were that nice in and out and fast as hell. VERY IMPRESSED!!!

So he says its cheaper and faster to replace the motor then to replace the cylinder head. i believe him, but if hes wrong i wouldnt mind knowing.

Thanks for all the help guys, Ronnie

[DAEDALUS]

He's right about the swap being cheaper and better than a rebuilt head, but I would like to know more about his diagnosis and how he came to his conclusion. A 5 minute vacuum measurement might provide the confirmation I'd need before committing that kind of money. What did he do for the "tune up"?

[CastorTroy777]

Hey.

As far as i know they ran the diagnostic first, that said that there were misfires in a cylinder or two, then they replaced the plugs, cleaned the fuel injectors, cleaned out the intake i think he said. then they put the dioelectric grease or what ever its called around and cleaned up around the head to look for leakage. which there was none.

Far as i know that is it.

And i replaced the fuel filter when i got home.

[DAEDALUS]

If he replaced the plugs then that's not a bad deal for $280. The "diagnostic" says that there's a misfire, which I assume means that 1 or 2 plugs isn't firing. Confirm this first with him. Assuming this is the case, a bad valve can't cause a plug to not fire. A consistent single-cylinder spark plug misfire can be due to bad plugs, bad coils, bad harness, bad ignitor, bad ECU, or bad voltage. Plugs are new (are they OEM?). Of the other candidates, the coils fail most often.

May I assume since he was replacing the plugs that he went ahead and did a compression check?

[CastorTroy777]

oyea forgot to tell u this, he started the car for me and unplugged #8 injector, still ran the same, (idled poorly).

He said he ran the aircare test on it, which is a test used in BC, toxic emmisions...etc.. like california said it owuld have failed the test but if i took it through and unplugged the #8 injector i would pass no problem,

and i forget the plugs i used they were not OEM, but were of good quality, had 4 contact points on each plug. forget the name brand, black box

and no compression test, i asked him, he said that it most likely wouldnt show anything, but hed be hapy to take my $$$ to do it.

[DAEDALUS]

Sounds like he used Bosch. They simply don't work well in Nissans. Many stories on here about premature failures, some of which damaged the engine.So the HC values dropped when he unplugged the injector, meaning it was providing gas that wasn't igniting. Still doesn't indicate to me that it's a bad valve and not a bad coil. Used coils are relatively cheap to replace, used heads aren't. Again, do a vacuum check...if the needle's solid then I'd try replacing the coil first. The risk is low--cost of a used part and installation.

[Q45tech]

More DAMAGE is done by untrained [mechanics] on Nissan Q45 than almost any other thing except owner abuse.

Certified Infiniti techs ONLY that work on a few examples PER DAY of your year series model [90-93 or 94-95 or 96 or 1997-2001].

A used engine for $750 is a time bomb without replacing chain guides and $1500 worth of EXTRA R&R ------not counting swap labor...........his not knowing or telling you this shows some problems in his education!!!!!!!

[CastorTroy777]

They are NGK Platniums, thats what i just found out. Hope these are acceptable.

G-Power Platinum BKR5EGP 7090 0.044

[DAEDALUS]

Those have beveled grounds, not 4-points. They cost 1/3 as much as OEM spec, hope they don't last 1/3 as long!

http://www.ngk.com/results_cross.asp?pid=bkr5egp

[maxnix]

I highly doubt it has jumped timing considering it runs, and it runs strong at higher speeds. I have had my issues with these cars injectors and I would be willing to bet that it is the injectors.

A one tooth jump on the intake cam would have exactly that effect.

Remember, the "running strong" opinion is from someone who has most likely never experienced a properly tuned stock VH45DE, which are truly amazing engines when all's up to snuff.

[DAEDALUS]

But then there would be 4 cylinders out of whack, not just 1. A single cylinder cannot be out of time because of a valvetrain problem.

[gniknave]

I still don't understand how that guy came up with that diagnostic answer.

I can't begin to tell you how correct Q45tech is about untrained mechanics on Q45's. On this car you almost always have to research (this site and Q45.org) to find the cause of similar problems others have had on the same car. IMO, unless you're taking it to an Infiniti or Nissan dealer, or a shop like T3 that see's Q45's constantly, you're almost always wasting your money.

For a misfire I would have started cheap and then gone up the ladder.

- Run a can of BG44k through the system- Do a wiggle test on the igniter pack wires, CAS (Crank angle sensor) connector, MAF connector...- Fuel pump humming?- Replace the fuel filter- NGK PFR68-11 plugs installed? Put em in.- Ohm the injectors

That would have been my process.

In 10 months of owning my Q, I've gotten to the point where I trust no one but myself and the dealer to diagnose anything on my Q.

My advice to you and any potential Q owner is to get to know the car inside and out, and get to know it's known problems before you go taking it to independent mechanics to have it worked on.

[DAEDALUS]

Assuming it is indeed a single cylinder miss, the cause won't be the MAF, fuel pump or fuel filter. Determine if the problem is a "some" or "all" problem, then you can begin the process of elimination.

[maxnix]

Assuming it is indeed a single cylinder miss, the cause won't be the MAF, fuel pump or fuel filter. Determine if the problem is a "some" or "all" problem, then you can begin the process of elimination.

Correct! I thought it was an "all" problem because of the low vs. high rpm behavior.

[Q451990]

It's very possible that the #8 injector is sticking open, causing flooding and your emissions problems. Don't throw out this engine yet! Get a power balance test done with Nissan Consult and let us know what they find. It's very likely a bad injector. What did the plug from that cylinder look like when he removed it?

Heath

[DAEDALUS]

If the HCs drop when the injector's unplugged then it's not stuck open.

[Q45tech]

"#8 injector is sticking open" ?

very very very very rare failure mode [never seen one] as the entire rail would fill the cylinder in a minute........370cc/minute injector in a 561cc cylinder......... and hydrolock.

Failure to flow [enough] correctly is 100,000 times more likely. Lean idle misfire.

[Q451990]

Sorry, that's what I meant... I know my injector failures always fouled out the corresponding spark plug with black soot....

Heath

[CastorTroy777]

HEY!

I think u guys nailed it! My plug was BLACK! And i am experiancing all of the symptoms of the lean idle misfire. as described in this....

"The injectors need to be cleaned, if an engine is experiencing any of the classic symptoms of dirty injectors, such as lean misfire, rough idle, hesitation and stumbling on light acceleration, a loss of power, and higher hydrocarbon (HC) and carbon monoxide (CO) emissions.

Lean misfire may also trigger a misfire code and turn on the Check Engine light on 1996 and newer vehicles with OBD II systems. The code often will be a P0300 random misfire code, or you may find one or more misfire codes for individual cylinders, depending on which injectors are most affected."

So now what do i do about this? Proper procedure?... bg44K? new plugs...again? (OEM).

Just tell me and consider it done.

Thanks Soooooo Much Guys!!!!!Ronnie

[CastorTroy777]

Hey!

just got the BG TDC Kit today, allready filled her up and put in the BG44K, took off the air intake boot and sprayed the throttle valve half a can in while off half while on. took her for a spin around the block as directed, now i have the can of fuel injector system cleaner that i cant seem to use myself. I believe i need some sort of apparatus to connect it to the vehicle. Maybe i should have a tech do that?

Will this make a difference just using 2 of 3 of the kit? And should i be replacing the plugs again? Someone let me know please before i just did this for nothing.

Thanks,Ronnie

[Q451990]

No need to replace the plug again until you fix the injector on that cylinder. After the repair, just clean that one plug... I've used an old tootbrush and gasoline. After it's sparking again it'll burn off the rest of the residue.

Heath