94 Q cutting out when I accelerate

[cmccort]

Where should I start? The car seems to bog out when I put the accelerator all the way to the floor. Also I notice the A/C blows warm air as if the compressor is shutting off when I reach high RPM's.

Any ideas?

Thanks

[qship96]

compressor cuts out at full throttle to boost acceleration,by design

[cmccort]

Thanks, that what I was thinking just did not know for sure.

[goody90q45]

How many miles on your Q? Ever replaced the fuel pump or fuel pump control unit (FPCU)? Sounds suspicously like a fuel delivery problem.

[cmccort]

Just got it, it has 138,000 on it. How can I determine if that is the problem?

Thanks

[goody90q45]

Unplug the FPCU. The connector is shown in the pic. Run a ground wire from the pin with the alligator clip on it in the pic (the ground) to an unpainted spot on the body. Best to use a pair of alligator clips connected with the same size wire as the connector wire. This will force the fuel pump to run on high speed only and if it solves the acceleration problem it points to a bad FPCU.

When you replaced the fuel pump did you replace the FPCU also? If not, did you notice if the insulation on the rear deck over the two FPCU bolts has been removed? This is a good indicator as to whether the FPCU has ever been replaced. Let us know what you find.

[cmccort]

Thanks Mike,

I just got it so I do not know if the FSPU or the Pump have ever been replaced? Is the FSPU near the gas tank? I will try what you said.

Thanks

[goody90q45]

The FPCU is in the background in the pic, a silver ribbed unit, mounted on the underside of the rear deck above the gas tank. Follow the wires from the fuel pump. If you have to remove the sticky black insulation to get to the two bolts it's never been changed. Access the two bolts from the topside of the deck after removing the rear parcel deck trim. Oh, and you've got to take the back seat out first. Go to the Tech Help section of Q45.org for step-by-step instructions.

[maxnix]

I just got it so I do not know if the FSPU or the Pump have ever been replaced? Is the FSPU near the gas tank? I will try what you said.

You test the fuel pressure after the filter under a variety of rpm.

you need to replace all filters and fluids as a start. Then you need to get the FSM and TSB and study them at least once through to start. Then you need to read all the previous sposts by Q45tech and TexasOil.

Then you will be able to better assess the symptoms your are observing and establish a rehabilitaion plan.

AZHitman has a good shop in Phoenix area. European Motors, or something close.

[96Qowner]

Just got it, it has 138,000 on it. How can I determine if that is the problem?Thanks

Q45 fuel pumps don't tend to last much longer than that. They get a little corroded and start to draw more current. This causes the FPCU to overheat and it will often intermittently melt/solidify weak solder connections and cause fuel delivery failure that will correct itself when the connection re-solidifies.

You should replace your fuel pump if you can't determine that it's been replaced already. Even if the FPCU is still alright, it will start to fail if the pump continues to draw too much current.

If you spend a little time searching, you'll find a lot of information about the fuel pump and FPCU in old threads, including detailed instructions for dealing with them. Be sure to select "post bodies" and both archived and recent posts. Look in Q45 Forum and Infiniti Online Mechanic and also check Infiniti General.

[cmccort]

Where can I get an FSM & TSB? I am assuming these are some sort of manual?

Thanks

[maxnix]

Where can I get an FSM & TSB? I am assuming these are some sort of manual?

You need to really dig in to the posts and learn the less than perfect search function.

Free manual at http://www.phatg20.net You will need winrar to uncompress the file.

FSM and TSB and other goodies are available at

http://www.nissan-techinfo.com/infiniti/ for a one day subscription.

[96Qowner]

Re: the fuel pump - I forgot to ask: Do you hear any noise from the trunk? Loud humming/buzzing? If it's stone-quiet, then you don't have a problem with your pump. If it's noisy, you should look into the fuel pump/FPCU.

But I suspect we've gone off-track. There are a lot of other things to check out. It could be as simple as a dirty MAF, or a dirty intake path. If you haven't already, put in some puttering time under the hood. Pull the MAF and CAS connectors and clean and grease 'em. Spray down the MAF itself with cleaner (instructions at Q45.org). Wiggle connectors with the engine running to see if they're solid. You should locate some BG44K, put it in the tank and take the car for a nice highway run.

Etc.

I know when I first got mine, acceleration improved dramatically when I cleaned my MAF.

[cmccort]

I need some advice. I believe I have determined the problem. After replacing the MAF I noticed the fuel pump was making noise. The reason I did not notice it sooned is that I thought it was the antenna going up and down, it was not. So I have pulled everything apart and the FPCU has not been replaced. I took it apart and it looks like new, none of the joints have been melted it looks like new. Is there a way to determine whether or not it needs to be replaced?

Thanks

[96Qowner]

Dennis will tell you that T3 used to chase all sorts of problems that ended up being a bad FPCU. The only way to be sure is to hook up a pressure gauge and read fuel pressure as the FPCU switches pump speeds. But that won't necessarily show what happens when it gets hot.

The pump has three speeds. If the FPCU can't switch to the highest speed, you'd have bogging at full throttle.

But the symptoms ring a bell with me - just can't remember the solution. If I remember correctly, a bad CAS connector will cause problems at high rpms, for instance. I know I remember hearing about these same symptoms - maybe someone will pipe up.

Found this old thread:

zerothread?id=73334

Knock sensors, maybe?

[cmccort]

Where is the CAS located? I can't seem to find it in my FSM? It could be the KS I do hear what appears to be spark knock when I am driving the car.

Thanks