99 Q45 running problem

[Q_SHIP]

My Y33 is having a problem. The car idles great but once i give it any gas at all, it stumbles. It's almost as if the car is running on 6 cylinders. It does this in park and when driving. My SES light was also flashing. When I read the codes, it came back with "multiable cylinder random misfires detected". Any ideas? I chacked the plugs and all seemed normal. I know my description is a little vague but thats what I have to go with. Thanks guys.

EDIT: the car has brand new Knock sensors and MAF sensor as well.

[maxnix]

Try a better more complete diagnosis. Maybe a power balance test.

[elwesso]

Fuel pressure. Check it!!! Sounds like a fuel pump failure...

Does it get better if you WOT it?

(BTW, dont cross post!)

[Q_SHIP]

UUMM, Not really. I have a steady miss pretty much all across the board. It almost feels like Knock sensors again but im not getting that code. Plus I just replaced them and the harness.

[elwesso]

Well definitely check your fuel pressure....

You dont need a lot of fuel pressure to make the car idle but even a litlte bit of extra power needed after you get off idle and the pump may not catch up....

When you turn the car on (and the pump primes) you should see about 40PSI, and about 34psi at idle..... Take it up to WOT and you should still see about 40PSI (actually more like 43)

[Q_SHIP]

I'll have to have my mechanic check it on monday. I don't have the tools to do it. Thanks for a place to start.

[elwesso]

just go buy a fuel pressure gauge....... its like $10 plus a few$ in fittings to T it in after the fuel filter

[Q_SHIP]

This car is strange. I drove the car through the weekend after I cleared the codes. Friday and saturday, the car ran like crap but still got no SES light. Sunday comes, car runs PERFECT. I changed nothing. Same gas even. Car runs perfect now. Oh and now my SES light is on.

[maxnix]

Oh and now my SES light is on.

And the code is?

[Q_SHIP]

Same as always, Bank 2 sensor 2 O2 sensor.

[texasoil]

A multi-cylinder misfire code indicates something that is common to several cylinders--like a crank angle sensor, low voltage, low fuel pressure, bad MAF signal,etc. Unlikely to be multiple ignition coil failure at same time or multiple injector failure. Could be bad connection between ECU and engine wiring.

[maxnix]

Same as always, Bank 2 sensor 2 O2 sensor.

Great. Then repair that first (might check the duty cycle of others to see if they shouldbe replaced also) and we will proceed. Must eliminate known defects first.

[elwesso]

we know thats the problem, nad indeed it is a problem, but it didnt cause this problem....

those 2nd o2 sensors are for the treehuggers....

[Q_SHIP]

HAHA

I never remembered an o2 sensor to make a car run like this.

[elwesso]

HAHA

I never remembered an o2 sensor to make a car run like this.

It wont!!! thats why i said the rear o2 sensors are just for the tree huggers.

[maxnix]

It wont!!! thats why i said the rear o2 sensors are just for the tree huggers.

They're not. They provide the trim information for the OBD II.

The deal is, multiple problems can mask and hide other problems. Fix it and proceed, or keep urinating into the wind. It's your shoes.

[elwesso]

i agree with you brian... you ALWAYS need to fix what you KNOW is wrong, every time all the time no questions asked...

however, all the secondary o2 sensors do is monitor the catalytic converter.... any of the TRIMMING is done by the primary o2 sensors.

[renkema]

The dealer told me I had the multiple cylinder failure code and that I needed to replace ALL the coils and the 2 knock sensors ($3,500). I called another infiniti dealer's parts department and the guy read me the usage of coils and they were all 1s and 2s, no eights. He said that they should be able to identify the culprit coil. Reading your post, I'm wondering if it is the coils at all. Is it correct that they cannot determine electronically which coil is bad or is that BS? Thanks for the help.

[maxnix]

however, all the secondary o2 sensors do is monitor the catalytic converter.... any of the TRIMMING is done by the primary o2 sensors.

Maybe you are right, but I was told (and I can't read wiring diagrams that well), that their values were looped back via the ECU to validate the primary O2 sensors. Hence they did have a trimming function of sorts.

But maybe not. If not, I wonder what happens to that data in the ECU?