My 1994 Q45 runs like a dream 99.9% of the time. It will develop a bucking/jerking the other .01%. Feels like fuel starvation, but if I put the car in neutral the engine revs great. If I'm on the highway I can kick it and it will accelerate like a rocket and keep running. If I'm driving in traffic it will die and I just put it in neutral and restart it and keep driving. I may have to restart it 3-4 times and then it goes away and runs great until the next "episode." This might happen once or twice a day, sometimes nothing happens. I tried cleaning the MAF. Pep-Boys recently replaced all the belts and then the power steering belt shredded and they replaced the power steering idler pulley, said it was binding. I was thinking that might be the problem, but it happened again yesterday. I took it back to Pep-Boys and they looked for codes and found nothing. This seems to happen after the car is warmed up and particularly after it is warmed-up and then turned off and sits awhile. ANYBODY GOT ANY IDEAS? I'm thinking of taking it to Infiniti, but if there's no codes, what are they gonna do?

My guess is that it's a failing fuel pump and controller. The pumps tend to get noisy at about 80K and should be replaced when noisy. If it goes too long, the fuel pump controller will overheat and you'll have to replace it as well. Try searching (if the search works now) for "Fuel Pump" "Fuel Pump Contoller" "FPCU" etc.

You might still take it to the dealer for diagnosis... there's more to repairing a car than checking codes... Pep Boys typically isn't the best service option for a car as complex as the Q45 (hell any car in my mind) but they do serve a purpose as a good source for oil, cleaning supplies, and a few parts...

Good luck!

Heath

It was only intermittant at high (95+F) ambient temperatures - but I'm sure they have many different failure modes.

Heath

Discover the power of the button!

If it gets too strange the ecu relies more on the TPS voltage to try to maintain engine running.........shifting back and forth from high weighted MAF to high weighted TPS can be some of bucking.

So many 94-96 are now failing intermittently after 10 years that we usually just change them and wait and see if the problem disappears.........95% of the time it does go away...........but this is after we have checked Consult and fuel pressure under load and done the usual other diagnosis steps.

Junkyard/ebay units are likely to be bad or go bad as well.........just age!

Are you seeing more problems with with the 94-96 units vs. the 90-93? I seem to remember you saying that MAF failures on the 90-93 were relativey rare, although there have been lots of problems with the connector.

Heath

Were they able to re-create the problem? They should be able to monitor it while bucking with Consult and get more of an idea what's going on. If they could substitute a known good MAF for the diagnostics, I'd try that next. The issue showing up after a warm soak points to something electrical to me - but these things are definately frustrating.

Heath

I had an injector problem that showed up only under these circumstances... one injector would bleed down and cause a slight flooding issue making the car hard to start. If it sat overnight the car started fine - I guess the gas leaked down into the oil past the rings after sitting long enough.

Heath

With a little careful shopping they should be cheap. and the install appears fairly simple ( tho I admit never having done it so I am obviously ready to be corrected if need be)

Fred..

You could buy one from our sponsors for 25% off list and install it yourself.

I got Wes's 94 TCU. The death at startup and bucking went away for the entire weekend.

Then we replaced my deep fried Bosch plugs with his NGK Platinums which only had 9k on them. The idle went from lumpy to smoothtastic.

Then the bucking problem came back about 75 miles from Wes's house. And it got progressively worse as my 300 mile journey home came to an end, and then suddenly went away.

Timing is fine, I'm at a loss for ideas. I sent my old burned fuel pump control module to a friend for soldering and adding the bypass wire (see Tangalora's post). We'll see if that helps. The fuel pump is only a year or so old.

Battery cables are new. Alternator checks out fine. Next item will be battery replacement and cleaning KS ground (need to flip through the manual to figure out what that is).

-Jesda

I also have two cars, so it is not as pressing. One thing I did find that eliminated it was shorting the ground to the fuel pump itself. The issue with that is obviously you are burning your pump up, so keep the tank fuel to cool the pump.

Does anyone know the resistive values the fuel pump modulator gives to the fuel pump for varying rpms? You should be able to wire a POT on there and set a value that will not send as much current to the pump, at least until you fix it.

I will post back when I finally locate the issue. It was not the FPM and my MAF is clean, no water issues with fuel either. Sometime this week I will tear into it again and post back. Since it is intermittent, I don't really know what the dealer can do. Except maybe throw parts at it ... I can do that ... and a lot cheaper!

Just for kicks and giggles, looking in the FSM under "Surging" in the EF/EC, the only thing it points to is o2 sensors and the EGR valve... And I forgot to give you my o2 sensors...

Trust me on this one. Go out and buy a can of throttle body cleaner and throughly clean it. Make sure you completely open the WOT plate and clean as far as you can go. It mays fix it.

I highly doubted that the dealer can fix your problem the first time you bring your car in. It probably take them 3 or 4 times before they fix your problem.

I'm also considering a fuel injector cleaning. Tell me if this theory has any validity:
As I'm cruising, excess fuel is being dumped in by dirty injectors, causing it to buck because its running too rich.
Though I once had it happen while passing (on Sunday coming home from Indy). It started bucking, so I gunned it, and it had a hell of a time accelerating as it was bucking. Typically, a romp on the gas made it go away for a while.

So I'm pondering a pressurized injector cleaning.

*sigh*

Nissan fuel systems are such worthless trash. If there's anything where GM > Nissan, its making injectors and pumps that can handle the sulfur-loaded crap we pump into our tanks.

-Jesda

I gave my old fried fuel pump relay to a friend to solder two bypass wires to see if we could get it working again. Just for the heck of it, I'll see if it resolves my bucking problem. My old fuel pump relay/module has no noticeable burn marks on it from overheating, however.

I'll update in a couple days.

-Jesda

Well, the ground wire to the pump from the FPC wiring harness stopped working last night. Shudder Studder ...

It seems there are two or three separate problems being defined in this thread by various posters, so I will define mine in the hopes it may help another poster at some time. I am heading to the dealer, they have one good mechanic there and I let them know the car will stay there until he can look at it.

The history:

My car had no problems except the fuel pump was buzzing. I replaced it with a OEM new one, fuel filter at the same time. Three weeks later, the car would randomly sputter and want to die. At mid pump output, the pump is three stages, a one second pause would occur in the car. When I stopped, low pump output time, it would stall. Putting the car in neutral and revving the engine would stop it from stalling. Then it would go away. I could drive it for miles and no problem.

Grounding the fuel pump resolved it. After ISO-Heet in the tank, cleaning the MAF, and re-soldering the connections, it appeared to work. Next day, at it again. I replaced the FPC with a salvaged unit, worked for a few days and then at it again.

I can run the car 70-80 mph on cruise control and it works fine on the highway for 400 miles. When I slow to go through a town, you might make it without it sputtering, but even if it did it usually sputters when you first re-engage the cruise to 70-80 again. Zoom Zoom, then sput sput for two seconds ... then clean ... for another hundred miles before you have to slow down.

I have really been trying to save up some cash for a multi-stage paint job, the bumper's paint is flaking and I have a ding on the hood. But this car is starting to eat $$$. And I haven't had to do the chain guides yet ...

seems I need to get a third car before I worry about paint ....

My battery is loose, no hold-down. I've been meaning to get a replacement hold-down. The battery slides a little sideways but doesn't travel too much. Think that could have anything to do with it?

Thanks

Dan

I'm an engineer ... I got clips. It is viable the connection was not making, I didn't care. I just connected back to the FPC and she ran the three miles home.

Inifinity gave me a new G35 to ride while they play ... they still haven't found what is going on. I told the mechanic already, don't throw parts at my car trying to fix it... and me pay for it.

Sweet pic by the way, you are the man! You have helped me more than a few times ....

will holler back tommorrow ... hopefully they will have it done then.

The fuel pump relay mod was inspired by "Tangalora", whose amazingly well documented posts made it possible. My friend did all the work; I plugged it in today and so far it works perfectly! I'm leaving it in for a week to see if the bucking comes back.

Here's close-ups in case anyone wants to do the same:
http://www.spilky.com/bo/stf/fuelpump/

Just wanna ask how much will it be purchasing those sensor (new and/or used)?? And how hard will be the installation of the knock sensors??

I only know how to replace the MAF but not the knocks.......sorry for these newbie Qs...