occasional coughing/missing

[96Qowner]

I've been experiencing an occasional "cough" from the engine of my 96 Q45. I'm dependant on a Nissan dealer for repairs, so I'd like any feedback I can get from the experts here. It coded for a bad O2 sensor, which was replaced, but it will still "cough", once, at highway speed, as if the fuel supply was interrupted for a second. Now today, in town, it tried to quietly stall twice coming off stop signs and lit up the engine light for another code.

Any ideas before I bring it in again? I bought it used last year and it has 157,000 miles on it, 10,000 of them mine. I've replaced a cam position sensor and the O2 sensor since I've had it. It runs quite smoothly otherwise.

[911/Q45]

Check the fuel filter and pump.

[96Qowner]

Yeah, maybe so. I left here to go home for supper, and it bucked several times, and stalled once. On the way back here it ran fine. I asked the Nissan guys to check the pump, and they said it was allright, but maybe the filter.

Would that cause the code?

[DAEDALUS]

That depends on what code its throwing. Some chain stores will read the code for free if you take it in. Did your tech actually hook up a fuel pressure gauge and drive the car around till it acted up, or did he just confirm the pump is moving fuel?

[96Qowner]

Thanks Daedalus, I don't know, I doubt they were very thorough. It was just one of things I asked them to check. The fuel pump sounded a bit noisy to me.

I'm going to bring it in tomorrow; just wanted an idea of what it might be.

I just got back from a 3500 mile road trip with it, with a bad O2 sensor. Had just a few coughs along the way and I thought that was the problem. Apparantly not.

Thanks again, I'll post the fix when I get it.

[psychic_mechanic]

Did you try cleaning your MAF connectors?

[Jesda]

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

[96Qowner]

I finally took it into the Nissan dealer (I don't drive it daily) and they said it had coded for the O2 sensor they just replaced. Actually, the sensor is ok, but the "heater is bad"?

Make any sense?

They also have full faith in the fuel pump, after checking it better - did a flow test on it, or something.

[Q451990]

Good news then... time to let them try again under the warranty! Not convinced that it'll fix it, but it's worth letting them try since it won't cost you anything...

Heath

[DAEDALUS]

Does the problem only happen when the engine's cold? The heater is integral to the O2 sensor to heat it up faster so it works properly. If the problem also happens when the car is warmed up then I think it's more than just the heater.

http://hostingprod.com/@aa1car...r.htm

[96Qowner]

It's a fairly rare occurance. I took it on a 3000 mile trip with the bad O2 sensor and it "coughed" maybe three times. Just one quick cough and then back to running smoothly. This was warmed up, at highway speeds on slight acceleration.

When I got back to town, it started the bucking. Again, nothing dramatic, happened a couple times, but that DOES seem to have been when the engine was cold.

I bought the car online, used, and have no idea of its repair history. I just want to sort out and repair any little problems, so I can trust it, and also so I can take care of the little things before they become big.

This is a good site. My thanks to all you guys who post for us. We're grateful.

[96Qowner]

It's two weeks later, the O2 sensor was on backorder, still not replaced.

I took it on a 500 mile trip Sunday, and it's now a real problem. It coughed dozens of times on the freeway, even stalling and restarting at speed.

I've seen this symptom described on the board on other threads, including one on Infiniti General right now, so I'll tell you all what I noticed:

The first 200 milles were not a problem; most of it on cruise at 80. At one point, the sun got hot and I turned down the interior temp and boosted the fan to high. Right after that, it coughed several times over a few minutes. Then, as I neared the city, it began to act up. I managed to get to where I was going and turned it off. When I returned 3 hours later, it misbehaved badly in traffic and missed a lot until I got out of freeway congestion and set the cruise. Then it stopped coughing and missing.

Here's the clincher: I pulled over for gas and food. When I got back on the freeway, everything was just fine. No problem all the way back home, another 150 miles.

Fuel pump, yes?

[Jesda]

Please keep us posted! I have the exact same problem and its really pissing me off.Its the kind of vague problem where I'm about ready to dump the car into the Mississippi

Did TCU, plugs, cleaned all electrical contacts, new battery, new neg cable, next is MAF.

-Jesda

[96Qowner]

I haven't fiddled with the MAF yet, and thanks for the earlier link to cleaning instructions.

I'm thinking fuel pump, despite what the Nissan tech said. Here's why, and I hope others will pipe up:

It was not a problem for the first part of the trip. As I approached the city after 200 miles, I broke cruise and began to match traffic speed as it varied. This would have put a little more stress on the pump. The tank was also less than half full by that point.

It was VERY troublesome in traffic. Again, if the pump is weak, this would have stressed it and heated the connections, causing the solder to melt. When I went back to cruise, the load on the pump leveled out, and when I FILLED the tank, the problem went away.

I'll clean the MAF before I do anything with the pump, but I think I just may try to do the pump myself. Sounds easy enough.

[Q45tech]

After reviewing a number of 94-95 and 96 Q, It seems owners must be prepared to replace the fuel pump and FPCU and the MAF at some point past 100,000 miles...........along withe appropriate number of O2 sensors [2 or 4]................think of the $1500 in parts as the timing belt you don't have to change.......[what you would have to spend if you owned an LS400/Audi A8 of the same year at 100-120k].

Certainly not the $3,000 you would have to spend on the 4.3/5.0 liter V8 Mercedes engine at the 100-120k interval for chain replacement.

[Jesda]

96Q:

Sounds like a good theory, but when my pump and pump relay failed, there was no bucking or jerking. It just died instantaneously. Everything behaved normally except for the obnoxious buzzing.

-Jesda

[Q45tech]

That's the way most fail - noise for a few years getting worse and worse, then sudden failure.

But the second case where the first or second pump was replaced [without total failure due to noise] without changing FPCU usually shows the intermittent failure symptoms.

Fooled me twice into spending time looking for something else to blame.

The totally dead part is the easiest to diagnose, the intermittent ones drive you battey.

The bulk of intermittents come from MAF and FPCU neither of which shows a code.

[maxnix]

Just changed my TX 1995 Q45 fuel pump at 63K for that reason. Could have waited, but did not want any strain on FPCU. New pump is quieter.

[96Qowner]

The Nissan dealer has agreed to put in a new fuel pump for $425, so next week I should be able to narrow down the symptoms. If the pump doesn't do it, it's probably the FPCU, in my case. I'll keep track of Jesda's progress with his MAF replacement, on the Infiniti General thread.

Heheh, I printed out 40 pages of NICO posts in the two threads and gave them to the service manager, for the Nissan tech - should help him, I figure, if he reads them.

[96Qowner]

The fuel pump didn't do it.

It runs fine around town, but as soon as I hit the highway, it's undrivable now - worse than ever. A lot of extra pep, though, so the pump was getting weak.

So, I guess a MAF cleaning is next? What's your advice, guys?

[Jesda]

MAF is due for cleaning or replacement. Jeff Williams suggests using brake cleaner instead of electrical cleaner because it doesnt leave a residue. I havent tried it myself, but it works great for him and he's owned many Qs.

[maxnix]

Better look at the FPCU also. Download those posts.

The dealer did replace the fuel filter? Clean tank?

[psychic_mechanic]

On these cars the MAF should be the first thing to check, not the last.

You can clean it yourself for free if you can follow instructions, or have an independant shop do it for a lot less than guessing at other parts (Not that it a bad idea to replace a fuel pump in a nearly 10 year old car anyway)

With it getting progressive;y worse, I would almost bet you it's a slowly degrading MAF signal. After the MAF is cleaned, and aux ground for the MAF added, you should be amazed at the difference.

If that doesn't help, run some BG 44k and ohm all of the injectors.

[Jesda]

What do you mean by adding an aux ground?

[Jberger]

Shhhh, Don't talk so loud, my 91Q overheard you. . .

Jesda, I'm having the same problem according to your description. Today, I think I've narrowed it down to a heat related issue. I never have the problem when the engine is cold, but take an errand run with multiple stops and BAM, it starts bucking, hesitating and will not pull along more than 5-10 MPH even if it's floored. It will clear up for a short time, then re-appear. If I let the car cool off and try it again later, it runs fine, but once it heats up the problem returns. I'm thinking it's the MAF or maybe the FPCU is going bad. . .

[Jberger]

FWIW, Swapped the MAF today and did not see the problem re-appear. Of course, the ambient air temp was much lower than earlier this week, but I think it's safe to say the MAF was the problem.

Hope this helps.

[96Qowner]

Holy Mackerel!!!!

So I finally got around to cleaning the MAF (the Q's not a daily driver) And took it out on the freeway ... sheesh, Q's run a LOT better when the MAF is working right!!! Heheh.

So, as others have pointed out, you want to spray down the MAF with brake cleaner if you ever get bucking/jerking, coughing/missing symptoms. Do that first.

Mph, wow, it just HAULS that 4200 lbs, don' it?

How do the experts feel about MAF cleaning? Is it something a guy would want to add to a regular maintenance regimen?

[Jesda]

Jeff Williams says he does it monthly. I do it whenever I happen to be under the hood and looking for something to do.

Another NICO member who parks in a construction area also cleans his regularly.