Gotta get to the bottom of this: Ultra sluggish Q45

[elwesso]

Ok, right now Im trying to help 2 people with this problem.....

Ironically, they're both black 94 Qs, maybe they're cursed somehow... We have Andre's Q and Jason Liff's Q, both of which I have driven, and Im doing work on Jason's in a few weeks here......

Anywho, heres the symptoms... We suspected the MAF, and swapped in a known good MAF...

Basically the car feels like its running on 4 cylinders, but the cars idle smoothly and under no load revv just fine..... On Jason's Q the power balance test was perfect, they were all within like 5 RPM or so..... Interestingly enough, with Jason's Q it feels like when you just touch the throttle it feels fine, but when you give it gas it just bogs down, kinda like when the accelerator pump is bad on a carbeurated engine......

On both cars the knock sensors turned out to be bad, and on Jason's Q the o2 sensors are barely hanging in for dear life..

NO CEL's either...

The only other common denominators are is Andre's Q has bosch plugs, and I dont know about Jason's Q but Im going to replace the plugs anyway.....

I can safely say I dont think the KS and O2 sensors are causing the problems.. BOTH of them said when they were describing the problem they both said it feels electronic "like something isnt set right".. And I agree.. In Andre's Q we put in my ECU just for kicks and giggles, and no difference.....

This has me totally lost....

[911/Q45]

Bad knock sensors cause the ECU to dial the timing way back, causing exactly the syptoms you describe.

[maxnix]

Also, I would look at the fuel pressure. Change their filters for them anyway, unless they can verify replacement within last year 8K miles.

[elwesso]

I know what bad KS are like (drove with it for a year) and its not nearly this bad... I mean if you were to drive it you might soil yourself its that bad.....

The bad KS dont make the car this SLOW by any stretch of the imagination.....

We checked the fuel pressure on Andre's Q and its just perfect...

[911/Q45]

Maybe these KS are worse than your's were. If you know they're bad, replace them and you can check for grossly dirty intake, EGR, etc while you're under there.

[maxnix]

We checked the fuel pressure on Andre's Q and its just perfect...

At all three voltages?

[elwesso]

Yes... We had idle fuel pressure, WOT and middle range..... It rises smoothly up to 43-44psi all the way up to WOT.....

[areznik]

Hey guys, I am not in Bloomington yet but miss Q already. Wes, right before I left I replaced all plugs with NGK (I don't remember the part number but its the same as specified in the owners manual). With new plugs it drives much better. After I added BG44k and drove one tank, it made a huge progress. So, before I left I added another can of BG to full tank and drove maybe 50 miles with it. The more I drove the better it gets!! Right now Q is very close to perfect, but not there yet. I think that I had clogged fuel system. Don't know how it can be possible, 'cause I never drive below quarter of the tank and never put in anything but premium. Maybe on my trip to Floriday last spring break I pumped bad gas in there ... . Try that seafoam thing to clean the intake valves, and maybe BG44K too. Let's see what happens.

Andre.

[elwesso]

Oh, so the plugs seemed to help??? When do you get back from "abroad"..?

Where did you get you plugs, infiniti dealer???

I dont think you had a clogged fuel system unless it was after the fuel filter... But its possible..... Would you say that you Q is nearly as fast as mine with JUST BG44k and the new NGKs??

Q45tech, if your looking at this, here is Jason's Q45 power balance test results

Base RPM= 762 RPMCoolant temp" 86*C

1. 50RPM2. 12RPM (have since replaced injector)3. 50RPM4. 50RPM5. 50RPM6. 50RPM7. 50RPM8. 62 RPM

[maxnix]

Once again, power balance done at too low an rpm. Where have all the senior G50 technicians gone?

[jamesmost]

hey hey hey i have a similar problem that sometimes seems to change with barametric pressureaccel at low rpm seems bogged down unless you really get on itthis seems prevalent definitely in first and second gear

[duck3986]

I'm having the same problem as JamesMost with my '98. My sluggishness is at lower rpm and most noticeable in 2nd gear.

I pulled the MAF and cleaned it. I also just replaced the fuel filter.

Thought it was better, but the problem does seem to be affected by weather/barometric pressure. At least it seems to come and go.

If I lay into it and get the rpm above 3000, power comes on strong and it doesn't seem to miss.

I had put in Bosch platinum four tip plugs about 25k miles ago. Made a nice difference when I added them at 65k miles. This weekend I'll be putting in the correct NGK's and will report back.

If that doesn't work my guess is either knock sensors or weak MAF.

Anyone in New Hampshire with a known working MAF want to help me troubleshoot? $400+ is pricey to replace a part if it's not causing the problem.

Don

[jamesmost]

i just removed my bosch 4+ with NGK iridium and did not notice much of a difference

[jamesmost]

how do u clean MAF, my mechanic told me not to f**k with it

[elwesso]

Clean it by spraying brake parts cleaner on it... Nothing further (nothing but the mist touches it)......

Id like to hear what Q45tech has to say about this problem... if there are 2 around me that have this problem SURELY T3 has seen one as well.....

So far it looks like Im going to replce the spark plugs and o2 sensors, and I will try that before I remove the plenum to see if it made any difference...

[jamesmost]

wesu spray break cleaner directly on the element??

[duck3986]

Yes. pulled the MAF out of the car and sprayed cleaner from both sides.

I didn't touch the element with anything.

Don

[90Q45blue]

Sounds like a combination of plugs and knock sensors to me. On my old Q, I noticed no performance difference when replacing my 248,000-mile-old O2 sensors, so I don't think that will help. Be sure you only replace the plugs, check it again, then the O2 sensors, check it again, then the knock sensors, check it again. OR he can spend $100 having Infiniti diagnose the problem I guess.

Nick

[jamesmost]

but wouldn't the car ping if the knock sensors were bad

[90Q45blue]

If the knock sensors were physically broken, yes. When a knock sensor starts to wear however, the ECU retards the timing.

Nick

[elwesso]

When there is no knock sensor signal, the ECU retards the timing 5 degrees or so and richens the mix slightly so theres no chance of pinging.....

Ill just have to talk it over with Jason and see if he wants me to go big or do one thing at a time and stop.....

[Q45tech]

T3 replaces lots of KS, O2, and MAF; spark plugs..........few TPS, CAS, IAC, and coils............almost no ecu/tcu.

Fuel injectors are almost never a problem in Georgia unless the Q came from somewhere else and was exposed.

[elwesso]

I also forgot to add... On andre's Q they replaced the CAS and it didnt do anything.....

[90Q45blue]

When there is no knock sensor signal, the ECU retards the timing 5 degrees or so and richens the mix slightly so theres no chance of pinging.....

Ill just have to talk it over with Jason and see if he wants me to go big or do one thing at a time and stop.....

But if you "go big" you'll never know what caused the problem. Doing things one thing at a time will help you learn the source of the problem. That will prevent you from having to go big on future Q's you might work on that have the same problem.

Nick

[elwesso]

Thats a good point, but Im pretty sure that Jason wants to go big anyway... But its easy enough to button it up before moving to the next job.....

Who knows, maybe we can work out a trade..... He's got a much coveted by Wes Q45a.....

[Q45tech]

CAS [other than connectors] are usually never the problem. Ecu will go into fail safe and rely on 90 degree back up portion of CAS then you know it needs to be replaced. When engine won't rev above 3,000 rpm.

All fully explained in FSM.

[maxnix]

i just removed my bosch 4+ with NGK iridium and did not notice much of a difference

Maybe because the iridium plug is not an OEM plug? OEM are platinum. Main advantage to rid a VH45DE of the Bosch is that when they fail, they can take the whole engine with them.

Up to that point, they are just fine!

What you are also implying is that the Bosch 4+ don't offer any benfit either.

[areznik]

Wes. Yes, BG44K made that much of a difference. I would say (nocking on the wood) that my Q is no weaker than yours or at least thats how I feel it. Do that seafoam thing and pour BG44K. Its inexpensive way to see if the problem disappears. To me it makes sense, because there is no malfunctioning of any unit whatsorever so it is probably something like clogged fuel system or maybe clogged air system. As I said, the more I drove with BG44K the better it ran (hope that it keeps going forever ) ).

I come back on August 25th, but then I start the MBA program on August 29th.

[jamesmost]

the Bosch 4+ offer no advantage except that they offer a steady idle which i never had a problemm and as well the bead that forms is not as hot as a single prong

[texasoil]

badly clogged fuel injectors and deposits in the intake valves will cause very poor performance. As will plugged catalysts.

The stumble on throttle opening and low power exactly fits badly clogged intake valves.