'94 Q45 "bucking bronco"

[metzgerq45]

Just got a Q with 76k miles from an old lady. It is in perfect shape, but it sometimes "bucks" and lurches when driving at a steady 30-40 mph. Acts like the motor shuts-off for a tenth of a second.

It also surges (slightly) at moderate throttle until it gets around 4000 rpm, then it runs great.

I've replaced the air filter, and had the dealer replace one injector (four were done previously). The dealer says they can find nothing wrong with the car. Plugs are original.

Help!!

[elwesso]

Welcome to NICO..

BTW, im located in Anderson.....

I think its probably a faulty MAF, lucky for you i have a spare one that we could toss on your car and see if it fixes it.....!

[Q451990]

Sounds like you found a gem - you should absolutely post some pictures!

I would also check your knock sensors for codes or check the resistance with a VOM. A mild bucking at about 45MPH under light acceleration (4th with t/c locked up) was my EXACT symptom when my harness failed. Very subtle most of the time, but every once in a while I would get a couple of bucks as the t/c unlocked.

If the knock sensors are bad the ECU retards the timing advance to the max (bad fuel map) and the engine has trouble generating enough power under those conditions.

I would also consider a fresh fuel filter, new plugs, and a complete induction cleaning. Most of all, drive it like you stole it for a while... you could just have carbon build-up on the valves due to grandma's ultra conservative driving habits!

I would also immediately exchange all of the fluids (differential, transmission, brake fluid, p/s fluid, coolant) as I suspect with a low mileage vehicle much of this hasn't been done yet.

Welcome to NICO!

Heath

[metzgerq45]

It was at the dealer on Monday, and the only fault code they found was a dead injector. It idles perfectly smooth.

Could a MAF sensor be bad with no fault codes?

[metzgerq45]

BTW: My office looks onto I69 in Fishers!

[metzgerq45]

It's not a transmission issue... it bucks in second at a steady 30 mph on cruise control. I put some Techron in it, and I've drove it to work in second gear today....and it seems better.

[96Qowner]

It was at the dealer on Monday, and the only fault code they found was a dead injector. It idles perfectly smooth.

Could a MAF sensor be bad with no fault codes?

Yes. It's your MAF. Do a search for "bucking". You can find a used one through http://car-part.com for $75 or less - very easy to replace.

[elwesso]

Hardly anything causes a fault code.. The ECU is stupid, its your job to figure out whats wrong! Once you get this figured out, heath is right... You should replace all your fluids because its what your supposed to do!

Anyway, its probably not the KS if it went to the dealer and there was no code.. For sure if the KS go bad they throw a code but not the way with a faulty MAF. hardly ever do MAF fail so bad that they throw a code, they just give crazy voltage readings.

EDIT: BY the way, dreyer and reinbold, especailly on the north side, is probably the most useless infiniti dealer in indiana.

[metzgerq45]

I cleaned the MAF when I installed the new air filter.

A local Q owner has a used MAF, maybe I should try it.

Thanks.

[metzgerq45]

transmission was done at 30k, but I plan to do it again. Can it be done at home? Is Mobil synthetic ok for the transmission?

The radiator was replaced at 60k, so the coolant is decent.

Mobil 1 was installed 3k miles ago.

What's best for the diff?

So, you agree that the MAF is probably the problem??

(Yes, it was at D&R north....)

[Jesda]

MAF MAF MAF MAF.

[elwesso]

So, you agree that the MAF is probably the problem??

(Yes, it was at D&R north....)

It seems like the first and easiest place to start. PLus if you can try one for free...

[metzgerq45]

Sounds good. How do we meet-up to try your MAF?

[Q451990]

If you meet up with Wes, have him show you how to check the resistance on the injectors. If you have a sub-par injector that could easily contribute to your problem. Did the dealer perform a power balance test? If not I would recommend having one done and reporting the results here...

Heath

[CrimsonQ]

Same trouble I had with mine, turned out to be the maf wiring/conector instead. I have a MAF laaying around if anybody wants

[BlackBirdVQ]

I have every new part under the sun in my Q45 and I still get the hesitation on acceleration till around 3K sometimes 4KRPM..... I've just learned to deal with it and don't expect any significant acceleration off the line with it being so sluggish. Wes says its the ECU, and my NICO one will be here tomorrow I hope.

[gniknave]

Metzgerq, Welcome to Nico! Nice to see another Q owner in Indy. My Q did a sort of bucking thing shortly before the transmission went crappo on me. It's currently being rebuilt at B & M Transmissions on S. Meridian in Indianapolis. This guy has done several Q transmission's before. Not to scare you because it could very well be the MAF, but it wouldn't hurt to pay B & M a visit and at least let them road test with you. Make sure to check the Central Meet forum, we have a big meet coming up in Anderson June 3rd.

[gniknave]

EDIT: BY the way, dreyer and reinbold, especailly on the north side, is probably the most useless infiniti dealer in indiana.

Why I work for the South Side...

The techs on the South Side seem to be very knowledgable but there's hardly any Infiniti dealers ANYWHERE in the US that know what the heck to do on a G50 (90-96 Q45). There's a few in California, but G50's are far more common there too. I happen to know for a fact that any mechanic working with Infiniti from 2000-present is likely to have had no training whatsoever on the G50. Half of those are likely to have never worked on one.

[elwesso]

Most of the G50 mechanics have gotten sick of working at dealers by now.

Metzger, fire me an email. Ill give your Q a once over

[sdkhalsa]

Do not forget to check throttle position switch(TPS). Had the same symptoms(similar to bad MAF) with my 94' Q at about 90K. The problem was the TPS. Even though it appeared that speed and throttle movement were not the cause, a failure can be very hard to detect. Q45tech using what I believe was a digital type VOM with data logging function said that he could detect malfuntions that one would be unable to detect with simple VOM. Joe, our favorite parts guy, at Infinity of Scottsdale, told me that the TPS switches regularly go bad by about 100K.

[elwesso]

diagnosed the car today, swapped on the MAF and that wasnt the problem, however the KS are... Dreyer and reinbold is useless, they couldnt even pick up that! Code 34=WIN

Swapped in my ECU and it worked nicely..

car is mint, reminds me of brian's gold car... only a couple of small blemishes.

[elwesso]

ALSO, i forgot to add, some of what he felt was the TC locking up...

[Rex]

... Swapped in my ECU and it worked nicely.. .

Just so we're clear, your NICO ECU ignores the KS's and if he did this versus replacing the knocks he'd have much bigger problems.

[elwesso]

I actually put the ECU on the JWT mode..... Which ignores the KS but is sitll retarded some!

But your definitely right, espeically wiht it getting hot out.

[96Qowner]

Never heard of bad knock sensors causing bucking - dead acceleration, yes, but bucking? It's more likely the MAF connector. Time will tell.

[elwesso]

its definitely the KS! Its hardly noticeable at least when i drove it!