q45 bucking/jerking DESPERATE!

[logisoft]

Here's the deal.

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?

[Q451990]

Do you hear a humming noise from behind the back seat, especially when the gas gauge shows 1/2 or less? How many miles on your car? When was the fuel pump replaced last?

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

[reliant]

Had exact same issues on 94 q45. Its the MAF. Took dealer 6 weeks to repair after I told them this was suspect. It did not show up on any tests they did.

[Jesda]

http://www.q45.org/maf.html

[Q451990]

My MAF failure put the car in "fail safe" mode. I would pull off from an intersection with almost no power, then the RPMs would jump to 2K and run, then drop back down...

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

Heath

[maxnix]

I took it back to Pep-Boys and they looked for codes and found nothing.

Did they have a Consult, or did they pull the ECU? Either way, I'll bet the reason they found nothing is they neither know how nor where to look for the codes.

[Q45tech]

There is no double check on the MAF voltage as long as it provides about 1.0-1.5 volts at start it is deemed ok..........drop outs weird high and low voltages are just tracked by injectors as if they are real and correct.

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!

[Q451990]

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

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

[logisoft]

Well, I took it to Infiniti and they found no codes. They suspected the MAF and "tightened the pins" in the connector as an initial attempt. They said sometimes this works. Why didn't they replace the connector? $110 and no improvement. I guess the MAF is next. It seems to only happen or most likely to happen after I drive the car warm and let it sit for awhile and restart it. Then it starts bucking within a block or two and goes away within 5 minutes.

[Q451990]

Well, I took it to Infiniti and they found no codes. They suspected the MAF and "tightened the pins" in the connector as an initial attempt. They said sometimes this works. Why didn't they replace the connector? $110 and no improvement. I guess the MAF is next. It seems to only happen or most likely to happen after I drive the car warm and let it sit for awhile and restart it. Then it starts bucking within a block or two and goes away within 5 minutes.

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

[Jesda]

Curiosity strikes!Why would a problem that occurs after a warm soak possibly lead to something electrical?

[Q45tech]

Side comment we currently have a 95 MAF shorted internally and it melted the entire wiring harness all the way back to ecu including the main ecu connector.

[Rex Rich]

I have a 91Q and it dies intermittently could happen anytime when warm no hum no ruff running either just shuts off? I gotta fix it too. Plz let no what you come up with?

[logisoft]

There's no re-creating the problem. This happens very infrequently. I don't get the "warm soak" comments. I've got a call into Infiniti and see what more they recommend. Remind me again of the benefit of all this technology?

[Q451990]

Warm Soak is basically when you drive the car to normal operating temperature, turn it off (e.g. go into a strore for 30 minutes) and then return and start it up again. My thought is that the temperatures under the hood just after you turn the car off are higher than while driving with the absence of the fans and air flow... so an electronic sensor or device that's heat sensitive could show a problem then that wouldn't show up at other times. Just a theory...

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

[logisoft]

I bet with winter coming it wouldn't happen again till Spring. Well, Infiniti says an MAF and connector is $585 installed. That's what they recommend. What happens if they guessed wrong? Should I go their way or find a used one and take my chances?

[PalmerWMD]

I'd look for a used one.

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..

[Q45tech]

You can always try a used one but it could have a similar or different problem? We usually give the customer a week to decide whether he wants to pay [or return for a swap back to his old one] but we have special relationships with most of them and we have tried other things first. We just hold their credit card number/check and don't charge them TILL the time period is up.

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

[DAEDALUS]

10 minute job. If you decide to get a new one order it from Joe; either way, do it yourself. Such an intermittent thing, seems unlikely to be the sensor itself, but anything is possible. You can also call Joe for a quote on the connector I think.

[elwesso]

if you need a new MAF (or good working used one) email me, I will set you up...... Its not from my Q but from a friend who has an extra Q maf.....

[logisoft]

Uh, whose Joe?

[logisoft]

Actually, that would be, "Who is Joe?"

[DAEDALUS]

Joe is the parts managaer at http://www.everythinginfiniti.com.<-------------------- sponsor

[Jesda]

Im having the same problem with bucking and jerking.

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

[SurfinGator]

I'm living this too ... check the tech forum under fuel pump replacement. Some good info there ... but I still haven't been able to fix it. It is intermittent and I have too many other items to deal with at work.

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!

[VA99Q45]

If you haven't, definitely clean the throttle body. Tape a tooth brush to a long stick that help you clean deep inside the throttle body. I think 70% of idle problem relates to a dirty throttle body.

[Jesda]

I'm sick of guessing (and sick of bucking). I'll save up for a dealer diagnosis. This is crap.

[elwesso]

I *highly* doubt the dealer will sucessfully be able to accurately diagnose and fix this problem..

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...

[VA99Q45]

Jesda,

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.

[Jesda]

I already did that. Also cleaned MAF, MAF connector, TPS connector, CAS connector, new plugs, 94 TCU, ran BG44k... the plugs and TCU made the largest difference. My old fuel pump control unit should be ready to go in a week. I had a friend solder two wires Tangalora-style based on his photo and description.

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