sluggish acceleration

[randyboy]

1999 q45t w/ very slow acceleration after engine warms up. on cold starts car would accelerate fine. knock sensors have been changed. MAF? CATALYTIC CONVERTER? INJECTORS? I NEED SOME HELP FELLAS!

[maxnix]

We need a detailed maintenance history and current operating specifications.

[randyboy]

200k miles 2nd hand great interior and exterior when it warms up, then acceleration is slow

[paranoidjack]

200k miles 2nd hand great interior and exterior when it warms up, then acceleration is slow

that enough for you Brian? Hehe...

[maxnix]

Got it nailed! Needs a polish and wax and a JDM speedometer.

Please don't tell us you have done nothing for the car since you have owned it?

[randyboy]

BOTH KNOCK SENSORS WERE CHANGED OIL , FUEL FILTER, AIR FILTER, COOLANT FLUSH, ALL BELTS WERE ALSO CHANGED. GENUINE SPARK PLUGS ARE NEXT. POLISH AND WAX AND JDM CLUSTER DONE! YOU GUYS GOT ANY EDUCATED GUESSES!

[maxnix]

BG44K? Fuel filter?

Replace the plugs with NGK as specified by FSM and get back to us. You may well want to have VC gaskets and Nissan RTV on hand with EGR, TB and IAC gaskets also.

Presume an OBD II scan produces no codes?
Modified by maxnix at 6:37 AM 9/19/2008

[gammer_ghn]

The car doesn't have a problem you just think its slow. trust me this is a freeway car. 0-60 is horrible but 60-120 is another story! Be safe if you attempt anything like that. Check your motor and transmission mounts since a lot of power is lost when you have old or weak mounts.

Edit: Your shift point is higher when you select gear. For example if your car is in 2nd gear on the shift gear you can actual go all the way to red line and your 2nd gear speed is 90mph i think ill check tomorrow

[Scotte123]

Hi Randyboy,

I had/have some similar problems. The guys here helped out A LOT! So give them a chance. Newbies post the same questions over and over again and that gets very tiresome (beleive me, I used to live in a resort town and after you've heard the same thing over and over a gain you can get a little rude).

The more detailed on the maintenance and repairs done the more accurate and detailed the anwers will be. (The pro's here should make up a form to fill out before they will answer..LOL).

My '94 was inherited at 120k miles and had all prior service done by the dealer on schedule. After I received the car the maintenance was done locally. Performance started slipping very imperceptibly, until about November of last year. The crew here diagnosed multiple system failures; the fuel pump, and the knock sensors (KS). I tried to fix the pump and KS myself (bad mistake unless you have a lot of time to do the work). My local guy put it together and found some other issues when it had to be smogged. So now it has new KS, FP, CATS, Pre CATs, EGR, fuel filter, air filter, O2. It runs well but not perfect. Gas mileage is about 20 on the highway and 16 around town.

It accerates OK up to 4000 RPM then it TAKES OFF like it used to. It's FAST over 4000 but sluggish until then. I'm wondering if the FPCU needs replacing or if the timing might be retarded until 4000 rpm. Any thoughts anyone?

Sorry to be so long winded.

[qship96]

Normal powerband for this engine as peak torque occurs at 4000 rpm unlike alot of mostly domestic pushrod v8 that peak at 2000+/- rpm-just a function of a 32 valve dohc to make power in mid and upper band at the expense of low end power

[dusred]

You could be low on Fuel pressure.

Check fuel pressure and report back.

[Scotte123]

Great advice. I am not quite sure how to go about it though. Does the pressure need to be tested under load? Is there a kit with all the fittings necessary to test fuel pressure?

[elwesso]

Id check the ECU codes first just to make sure... See if anything is stored.. Could be a lot of things, but first thing on any Q IMO is to check fuel pressure, then go from there...

[dusred]

Great advice. I am not quite sure how to go about it though. Does the pressure need to be tested under load? Is there a kit with all the fittings necessary to test fuel pressure?

If you aren't mechanically inclined you can take it to a shop and have them do it for you.

I would change the filter first just to make sure that's not holding back fuel pressure.

Just test it right past the fuel filter cut the tubing, splice a tee in there then hook a manual fuel pressure gauge on there (an air pressure gauge works fine).

The pressure should be around 65PSI if I remember right.

[Q45tech]

More inaccurate info:

35 psi at idle and cruise [steady speed no acceleration]43.4 psi under WOT acceleration.

[Infinitiguy19]

More inaccurate info:

35 psi at idle and cruise [steady speed no acceleration]43.4 psi under WOT acceleration.

I am sorry but in the FSM it says that at idle the fuel pressure is 34 PSI.

I am sure it was a typo or a mistake we all make them.

[mtzgr777]

Did Randyboy or Scotte123 ever find out what the problem was? I ask because I'm having the same EXACT issue as Randyboy.

[Q45tech]

Everyone knows idle and wot precise pressure depends on the precise atmospheric pressure inside the plenum where the regulator receives it's sample.

Actually at 1,000 feet AMSL the pressure will be 1.5 psi below the number in FSM depending on uncorrected barometer [not the corrected number they report on tv].

Most gauage are not corrected for altitude and barometric pressure so they read relative not ABSOLUTE PSI.

Everyone knows that weight is not precise and constant everywhere around the Earth. THe exact froce of gravity varies with the underlying mass. http://apod.nasa.gov/apod/ap030723.html There is an almost +- 0.75% variation.

[maxnix]

Does the pressure need to be tested under load?

Yes, just T off after the new fuel filter.

Did you replace all hoses and gaskets under the plenum and the KS harness? Did he put it back OEM new clean, or 140K miles dirty?

[gammer_ghn]

More inaccurate info:

35 psi at idle and cruise [steady speed no acceleration]43.4 psi under WOT acceleration.

I am sorry but in the FSM it says that at idle the fuel pressure is 34 PSI.

I am sure it was a typo or a mistake we all make them.

Everyone knows idle and wot precise pressure depends on the precise atmospheric pressure inside the plenum where the regulator receives it's sample.

Actually at 1,000 feet AMSL the pressure will be 1.5 psi below the number in FSM depending on uncorrected barometer [not the corrected number they report on tv].

Most gauage are not corrected for altitude and barometric pressure so they read relative not ABSOLUTE PSI.

Everyone knows that weight is not precise and constant everywhere around the Earth. THe exact froce of gravity varies with the underlying mass. http://apod.nasa.gov/apod/ap030723.html There is an almost +- 0.75% variation.

Damn i have not laughed so hard for so long!