94 Q V8 gas burner 4 cyl. power

[Black stallion]

This is my first time on any forum-ever so any help would be greatly app. I first fell in love with the Qship in 91 when I sat in my aunts Q and everything started moving. I thought My goodness they are making smart cars! Anyway, I was finally able to get one 10 years later. I bought a 94 Q in 2001 with 51000 original miles. It now has 85000 miles only because my work truck broke and I had to drive it daily for a while. Long story short I bought an extended warranty and set out to make it perfect. The local dealer burned bridges with the warranty company (over, over price) to the point they wiggled out of many repairs. Needless to say I ended up doing most of the work my self. Not to mention the incompetent "techs" at the dealer couldn't fix a broken shoelace ("computer say no broke here") I want the experience of 300 horses again. The car idles like a sewing machine builds up rpm's and will eventually hit 130 mph, but can't out accellerate a ford escort. A little help please!

[CrimsonQ]

Nice intro and welcome!

But you seem to have forgotten to post a little more info on your problem!

[Black stallion]

My apologies. Lets start with the strong exhaust smell coming into the cabin with the windows down. A couple guys told me it may be the cat. converter. Knowing this could blow my engine my quick cheap fix-gut it out. Now I have straight pipes all the way to the muffler. Boy did it breath. Still have the smell. A little later I noticed a sporatic loss of power. Sometimes it would leave two rubber streaks sometimes it wouldn't. Now it never accelerates the way it should. I have replaced the plugs air/fuel filters fuel pump/sending unit and carefully cleaned the maf sensor. it idles fine builds rpms normally, but just will not accelerate your soul

[Jeff Williams]

BS (I shortened your name ),

First, welcome to NICO, the BEST forum there is on the Q45. There are a couple threads you can search the archives on a lot of issues. One forum is the Infiniti Online Mechanic, the other is the VH/VK thread. Infiniti General used to have all of us in it, until the Q45 thread was started.

Now, to your problem...

I hope you used NGK plugs, and the correct ones. If not, buy a set, & get them replaced. I used to use Bosch platinums, but the VH45 will burn them up on the highway. It can really hurt your power.

Next, make sure the fuel filter is new and the Air fliter is new. You probably already did this.

Make sure the throttle body is spotless. Use a compelte can of spray cleaner on it. The car will be hard to start afterwards.

Another issue could be the fuel pump going bad. Check the back seat while the engine is running, to see if you hear the angry bee buzz from the fuel tank. It is an easy fix ($300 in parts, about 2 hours tech).

Then, check the codes on the ECU. There are a few threads about this.

The first thing I though of was the knock sensors. If they are reading a failure, you can reset them, then see if the failure comes back (90% chance that is what it is).

When the knock sensors fail, the ECU can limit the timing advance, and KILL the power. The sensors are deep under the plenum (6 to 12 hours tech, $300 to $800 in parts depending on what you replace). You should replace the vacuum lines, fuel lines, and all hoses under the plenum, replace the harness to the knock sensors, and take a hard look at the injectors. Spend some time cleaning the fuel rail and upper and lower intake runners.

I thought my pup cats were plugged on Lola, but when I gutted them, and replaced the exhaust, there was little difference in overall power and performance.

Initial timing can be off.

Check your EGR and IAC valve for proper operation.

If you need a field service manual, shoot me an email with your address, and I will send you one. If you have PayPal, send me a couple bucks for the postage and CD.

[email protected]

Good luck!

I have spent over $6,000 on Lola trying to get her back to original factory condition and improve performance. And all of this does not include labor. It is definitely a love/hate relationship.

[Q45tech]

Find a stopwatch and log a few [locked in 2nd gear WOT accelerations from 50 mph [3500 rpm] to 80 mph [5600 rpm] on a level road ac off] It should take around 6-7 seconds. Give us the average time [to a decimal point] for say 4-5 runs .

Go to track and get a few 1/4 or 1/8 mile timed runs

Without data we cannot function.

[Black stallion]

He shortened my name - what a sense of humor! I did use the ngk platinum ( Used to use bosch as well '84 volvo 242 turbo). Also I failed to mention I had the knock sensors done as well. The computer did read this. There are times when the check engine light will come on for about 3 seconds and go out.

[squeefoo]

Have you cleaned the EGR, or the IAC valve?

My first thought was det sensors too....

Wiggle the MAF connector?

[maxnix]

Along with Q45tech's data request, maintenance history will help us a lot.

For instance, fuel system? FP? Filter? BG44K?

[Jeff Williams]

Has the fuel pump been replaced?

The only time my CEL has gone on, is due to a corroded and loose MAF connection or grime from my old K&N filter getting on the MAF. It usually stumbles when idling right before the CEL.

Have you done a fuel rail flush or power balance? It might be worth the $200 for the dealership to take a look at it.

[Black stallion]

I just want to thank everyone who has responded in my quest to keep and enjoy my Q ship. I did not expect the immediate feedback I have been getting. We have an Acura/Infiniti dealership here and I own an Acura ('91 Legend Leaving rubber everywhere) and am on my second Infiniti (first was a G20 ). It's like I stumbled on to a whole new world of info and I'm trying to take it all in. I don't trust the dealer what-so-ever I won't even give them the thrill of seeing one of my tires touch their lot (my brother was an acura tech and let me in on their dirty little secrets). Needless to say my mechanic buddies(fix anything from Acura to Z) told me every horror story in the book to keep from getting a Q now they just make the sign of the Cross when I come around. Obviously I didn't listen mainly because I also feel I can make anything work-just need a little knowledge-otherwise I would not have bought it. Thanks to you guys I am impowered and making a "Q bible" for my car. Now getting to the point, I haven't cleaned the egr or iac valves; I have changed the fuel pump and sending unit(1.5 hours first time;45 min second time; dealer said 4hrs ) I just found out about BG44K today I use premium gas always and put fuel cleaner in every other fill up; I have never serviced the fuel rail or anything under the plenum except the knock sensors. Q45tech mention 2nd gear WOT (is this while on throttle?) 50 to 80mph. Jeff thanks for the input I do have paypal and would like very much to have a field manual(dealer would not even let me buy one through them

[squeefoo]

WOT = Wide Open Throttle

Pull the EGR off the side off the plenum and you'll see if it's clogged, best way is to take off the throttle body so you don't get the crap inside.

IAC is on the back of the plenum held on 3 (I think) 10mm bolts, and a couple of hoses (the bottom is a pain).

I'm pretty sure there is a write-up on IAC cleaning @: http://www.q45.org on this...

Might be good to check your timing too (easy @ the same www. above) but I'd clean/check these first.

PS: You're welcome.

[maxnix]

Dealer doesn't have FSM as Nissan made all 1994+ manuals available online along with all TSB as downloadable Acrobat files.

You didn't mention fuel filter, nor air filter.

Starnge you didn't replace all under plenum hoses when you did KS and harness! You did use OEM?

[Black stallion]

the q45.org site is temporarily messed up; any other suggestions

[Black stallion]

Fuel and air filters were also changed; I didn't do the ks job a mercedes/diesel mech. buddy of mine did it(it was uder warranty) Had I had this info 2 years ago I would have insisted on everything being replaced I do know some of it was done due to the age and nature of old hoses and brittle plastic

[maxnix]

FSM.

Check the posts in Infiniti Online Mechanic, where this post really should be.

[Black stallion]

I did a few runs in 2nd gear WOT. It took an average of 9-10 seconds to go from 50 - 80mph. I have not been able to get any track times.

[Q45tech]

It took an average of 9-10 seconds to go from 50 - 80mph.

Something is definitely wrong since my 90Q with ecu does it in 5.8 seconds or better depending on temp.

94-95 should take NO MORE THAN 7.0 seconds........6.5 ideal

One starts with fuel pressure measurementsm if no KS codes and power balance is acceptable [no more than 12 rpm variances]

[Black stallion]

Where do I go from here? How do I check fuel pressure and what do I check For. I have new pump and sending unit, new filter; Far as I know, original injectors. I have done MAF, IAC, & EGR cleaning. Car idles like it's not even running, but when you hit the gas there is no thrust.

[Q45tech]

The idle fuel pressure is 34 psi and under acceleration it should go up to 43 psi.

You tape the gauge to windshield so that you can drive and measure simultaneously............better for 2 people one to drive and one to watch as you should check thru the 50-80 or 90 mph.

To check if it is the fuel regulator you just remove it's vacuum control line and the psi should go up to 43 psi at idle.

A quick and dirty test [that doesn't tell you much] is to squeeze shut the return rubber line MOMENTARILY and watch the idle pressure go up to 60-75 psi.

[Black stallion]

What regulates fuel pressure to the injectors? Is it the pump/sending unit or CU (in the trunk). Until I can get my hands on a set of fuel pressure gauges, could it be an injector issue (fine at idle and fall off under acceleration) or is it the fuel pressure to the injectors a prerequisit to diagnostic of the injectors. I'm just lacking knowledge in the area of fuel pressure/regulation

[maxnix]

It is the 3 stage FPCU, fuel pump and fuel pressure regulator.

Get the FSM and read all of Q45tech's posts.
Modified by maxnix at 9:43 AM 9/27/2006

[bullittandy]

My apologies. Lets start with the strong exhaust smell coming into the cabin with the windows down. A couple guys told me it may be the cat. converter. Knowing this could blow my engine my quick cheap fix-gut it out. Now I have straight pipes all the way to the muffler. Boy did it breath. Still have the smell. A little later I noticed a sporatic loss of power. Sometimes it would leave two rubber streaks sometimes it wouldn't. Now it never accelerates the way it should. I have replaced the plugs air/fuel filters fuel pump/sending unit and carefully cleaned the maf sensor. it idles fine builds rpms normally, but just will not accelerate your soul

A fuel smell might be O2 sensors-are the inside of the tailpipes black? If the car was running rich, that kills power and the plugs are probably fouled as a result-also killing power. Just a thought since its a maintainence item anyway.

[Q45tech]

It is somewhat complicated as fuel pressure GAIN is necessary to match the ecu program for accelleration [the ecu expects the psi to be correct and opens the injector in a preprogrammed manner based on MAF, TPS, and RPM signals.

Because the 35 pound [370cc] injectors are so big in potential flow volume [they could flow enough for 450 HP], they are never open more than 60% of there potential time.

Because warm idle requires so little fuel [compared to 300 HP worth] it is a fine line in maintaining pressure. The injectors being the saturated pintle type take longer to go from closed to open [fully]. AT IDLE the injector voltage is not applied long enough for the injector to fully open before it is closed [<1.5 milliseconds] depending on variable parameters .

The fuel pressure regulator function depends on an excess volume in the fuel rail to be sent back to fuel tank................as the is a fuel pulse damper neither of these things fail in my experience!

However to function both have air [vacuum] hoses, the regulator uses plenum vacuum [low pressure] and the damper gets it signal just after the MAF via a port in the big hose. The damper removes a restristion in the fuel feeding the injector rail as the rpms go above 4,000 rpm.........as the individual injectors open closer together.

34psi/44psi= 1.294 take square root = 1.138 or 13.8% more fuel flow in the same time period. This is what the fuel pressure regulator does increase idle cruise flow by ~~14% under WOT acceleration to make sure there is a sufficient excess in fuel to avoid the lean acceleration.

Idle and cruise are maintained near 14.7 AF and acceleration is greater than 12.0 AF and can go as high as 10 parts air to 1 part gasoline.

Excess over 12.0 AF is used to cool the pistons and spark plugs to reduce eliminate detonation.............excess fuel is much better than a lean situation..........the curve of power production vs AF is much better to be too RICH than too lean..............all that happens is the excess fuel blows out the exhaust and cools the cats and makes some minor black smoke.

Over 10 years of business we have changed fuel pumps, fpcu, and injectors.............we have never changed a fuel pressure regulator or fuel damper [we routinely change the vacuum hoses that control these units], we change MAFs but mostly MAF connections.Mostly air leaks from old hoses and cuts from using incorrect tools in previous plenum work.

[Black stallion]

Some of what you said is Greek to me as far as the formulas, but the latter makes a lot of sense. I have had experiences with vacuum hoses that would make the average man an alcoholic. I happen to enjoy the challenge of putting my hands on a piece of machinery and making it work.

The question now is, if you've never changed a regulator what else could be ruled as the culprit.

Since I didn't do the KS job I don't know what the condition of the plenum hoses(personally). The buddy who did it is the type that would check it out and tell me. I either do it myself, get a knowledgeable person to look over my shoulder or get that same person to do it.

I'm not ashamed to say that much of the technical stuff is beyond my expertise, but then only Jesus turned water to wine. I do appreciate the feedback I receive and the time it takes.

I'm just ready to get the Stallion streakin again so I can concentrate on other issues (what?! a supercharged luxury family sedan!)

[Q45tech]

The regulator can only work if the volume pressure exceeds some value.

Inside the regulator is some Japanese air inside a sealed diaphram that only opens the return line valve when the pressure is 34 psi when the vacuum line is applying [18"HG or 8.8 psi]..............as the pressure in the vacuum line increase [the plenum vacuum drops to 2" HG or 14.5 psi] the return valve doesn't open until 43.4 psi.

So 5.0 psi difference in air pressure on the vacuum line changes the fuel pressure by 10 psi.

These common type regulators are called 2:1 rising rate units.

If you could somehow add addition pressure [above ambient] to the so called vacuum line [say with a supercharger] a 6 psi boost would increase fuel pressure from 43.4 to +12 or 55.4 psi.

Hope you can visualize how a 34 psi spring and additional spring like qualities of a pressure diaphram can control fuel psi via reading plenum pressure or lack thereof.

ALL this works great if there is an excess volume of fuel to create a pressure to return to tank.

If you clamp off [closed] the rubber return line the rail pressure will rise until the saftey valve on the fuel pump opens or the pump just cannot get the pressure high enough [~~65-75 psi].

RAIL Fuel injection has been around for 20+ years on most cars so it is not a new concept. Different companies use different psi but in the 90 until returnless regulation came out most used the 34 >43.4 psi standard.

Measure the PSI so we can move on to other diagnostic techniques.

[maxnix]

Since I didn't do the KS job I don't know what the condition of the plenum hoses(personally). The buddy who did it is the type that would check it out and tell me.

Not to impugn your buddy, but if he doesn't have X-ray vision, he probably can't see the deterioration on the inside of the hoses, where structural integrity is lost first. If any of the under plenum hoses are 10 years old, I guarantee they are due to be replaced.

Now, measure the fuel pressure vs. rpm.