1995 Q45t running rough & bucking - SOLVED!

[GseaQ]

Update - no, not fixed. I've been using the bikes all summer, so haven't moved the Q. I did tinker with her a bit off and on when I had time.

I replaced the fuel filter.

I replaced the spark plugs. They all looked OK for mixture but they were OLD. I didn't put them in as I had thought, so God knows how old they are. One strange thing, though. #6 gap was only 0.6mm instead of 1.1mm. After I ran the new plugs for about 20 kms, I pulled #6 and checked the gap - still at the 1mm as when installed. Weird. BUT, the plug colour was WHITE. Pulled #4 and it was also WHITE. Granted, that's only 20 kms, so I'll check them again tomorrow.

I removed the IAAC valve again and cleaned it with spray intake cleaner and a brush - now like new. I then used a full can of Seafoam Intake Cleaner sprayed into the intake hose behind the MAF. Just before that I took the hose off and used a spray Intake cleaner, rags and elbow grease to get the Throttle Body good and clean.

The result? No change. In fact, it seems worse now than I remember, but that could be my imagination. I had to get it Aircared (smog test) today for licensing. It passed - barely. The numbers seem to indicate it is running lean (just a guess). Here are the numbers from the smog driving cycle tests done December '08 & 149,000 miles followed by today's #'s at 178,000 miles.

Then - Hydrocarbons (HC g/km): Max Allowed - 0.5, my car - 0.0992, Average for this model car - 0.1352
Now - Hydrocarbons (HC g/km): Max Allowed - 0.5, my car - 0.4470, Average for this model car - 0.1419

Then - Carbon Monoxide (CO g/km): Max Allow - 9.32, my car - 1.6233, Average for this model - 2.9640
Now - Carbon Monoxide (CO g/km): Max Allow - 9.32, my car - 5.0413, Average for this model - 4.8305

Then - Oxides of Nitrogen (NOx g/km): Max Allow - 1.24, my car - 0.2354, Average for model - 0.3798
Now - Oxides of Nitrogen (NOx g/km): Max Allow - 1.24, my car - 0.0680, Average for model - 0.2160

As you can see, there is a big difference in the numbers from when the car ran fantastic 3 years ago and running like s*** now.

I'm back to suspecting the fuel pump now. It was supposed to have been replaced by the previous owner before he shipped the car to me (I paid Infiniti of Scotsdale to send one to him), but given how crooked he was, I have no faith it got replaced. If it was replaced, it can't have more than 40,000 miles on it.

Can you guys (Mike, you suspected the fuel pump in the beginning) review this whole thing again, please, and post your thoughts? Do my symptoms fit a failing fuel pump? Is it possible it finally got to the point way back that it just was not supplying enough fuel or pressure? Could the smooth cold running have been (it doesn't even run smooth when cold now) due to the pump running faster when cold (because of the FPCU)? Maybe when warm and loaded by a slight uphill grade at low revs, not enough fuel, nor would there be enough fuel at WOT, thus creating the spitting and lower power. Finally, will a failing fuel pump cause a rough idle, stumble and rough take-off from a stop and bucking under slight low RPM load?

Not knowing if the pump was replaced 40,000 miles ago or not, I'd like some encouragement before buying another one. Time's up, I need to get this sorted out fast now that winter is here.

Thanks,
Glenn

[goody90q45]

Sorry to see that you're still battling this issue. With no ECU codes I'm sticking by my earlier guess of a fuel pump issue. If not the fuel pump then possibly a loose connection at the fuel pump inside the tank. Any other component would throw a code and you've ruled out and/or replaced everything that could have caused this problem. I think it's worth a couple of hours of your time to at least remove the fuel pump and inspect it for any bad connections and to look inside of the tank to see what gunk may be laying on the bottom at the intake filter.

[GseaQ]

Sorry to see that you're still battling this issue. With no ECU codes I'm sticking by my earlier guess of a fuel pump issue. If not the fuel pump then possibly a loose connection at the fuel pump inside the tank. Any other component would throw a code and you've ruled out and/or replaced everything that could have caused this problem. I think it's worth a couple of hours of your time to at least remove the fuel pump and inspect it for any bad connections and to look inside of the tank to see what gunk may be laying on the bottom at the intake filter.

Thanks Mike. That's the encouragement I needed. I'll order one and an o-ring now.

Cheers,
Glenn

[GseaQ]

Well, new fuel pump is in. The core problem of the rough idle, stumbling at take off, and bucking at cruise & slight load (gentle uphill). I just haven't been able to try WOT as it hailed when I test drove it last night. I'll try that today and then jumper the FPCU to finally eliminate that. There is no sign of heat damage on the connector, but just to be sure.

I still have to wonder about a vacuum leak, but can't get past the time it magically cured itself for a whole night. I fiddled with the IACC adjustment last night and thought I could hear a vacuum leak, but couldn't find anything by feeling around the hoses in that area .

I was adjusting the IACC because the idle still seemed a little low. I noticed when I unplugged it that the idle didn't change. With my old Q and this one, too, when I got it, the idle would drop noticably when the IACC got unplugged. I have had it off twice and cleaned it (more thoroughly the second time) so it is VERY clean and the plunger moves freely. I wonder about the solenoid portion of it. Could it have failed? Would that cause these symptoms?

I guess the next real elimination step is an actual injector flush - the kind that plugs right into the fuel rails.

It happened so suddenly and definitively that it just seems like some component failure as opposed to a gradual wear or dirt thing.

Thanks for listening and offering advice.

Glenn

[goody90q45]

Well, new fuel pump is in. The core problem of the rough idle, stumbling at take off, and bucking at cruise & slight load (gentle uphill). I just haven't been able to try WOT as it hailed when I test drove it last night. I'll try that today and then jumper the FPCU to finally eliminate that. There is no sign of heat damage on the connector, but just to be sure.......

Good to see your getting closer to solving the problem. I'm working with an owner in Reno over the phone who had similar issues to yours before the engine wouldn't start. His FPCU connector looked fine but the internals of the FPCU showed damage. It might be worth your time to remove the rear seat, remove the FPCU and open it up. The FPCU damage is pretty obvious in the pic he sent and bypassing the FPCU has solved the problem for now.

....I was adjusting the IACC because the idle still seemed a little low. I noticed when I unplugged it that the idle didn't change. With my old Q and this one, too, when I got it, the idle would drop noticably when the IACC got unplugged...... Could it have failed? Would that cause these symptoms?......

If you determine that the IAC valve is bad I do have one for sale in my part out thread.

parts-for-sale-from-a-94-q-part-out-ca-car-t544053.html

.....I guess the next real elimination step is an actual injector flush - the kind that plugs right into the fuel rails. It happened so suddenly and definitively that it just seems like some component failure as opposed to a gradual wear or dirt thing......Glenn

I thought you have a laptop consult program? You should be able to find a dead or plugged injector by turning off one FI at a time. Have you tried a bottle of Redline or Chevron FI system cleaner in a 1/2 tank of gas before going through the expense of a fuel rail cleaning?

[GseaQ]

Hi Mike,

I think I eliminated the FPCU by bypassing it. Initially it seemed like the idle went up a tad, but then it returned to normal pretty quickly. At full voltage with the new pump the rough idle and stumbling at take off didn't change. The new pump (or possibly adjusting the IACV another 1/2-3/4 turn out) seems to have lessened the spitting at WOT, so I'd say the fuel pump was probably due anyway.

I'm going to test the IACV per the FSM and see what I get. Thank you for the offer. I may need it. I'm finding it hard to determine exactly what year parts fit my engine. A lot of stuff for a '95 doesn't seem to be right so maybe the engine was a '96 JDM? The TPS seems totally different and I see coils listed for 90-95 that won't fit mine.

I do have a Nissan Data Scan program, but my computer crashed and I'm just now getting everything re-installed. Hopefully I get NDS working today or tonight. Through all this though, I've only seen Code 55. Fuel Injectors and MAF should throw a code, but as I am learning the IACV and coils will not. When the MAF went wonky a couple of years ago I did get a code and resoldering the contacts fixed that.

An experienced guy with his own fully equipped shop said yesterday after I described the symptoms that it was probably an ignition problem – a coil or a spark plug boot. From what I can see a coil or IACV problem won’t throw a code, but a fuel injector will. Maybe if the IACV is not it, I’ll get a coil and move it through the cylinders to see if I find a bad one. You have any good coils?

Thanks,
Glenn

[goody90q45]

....Maybe if the IACV is not it, I’ll get a coil and move it through the cylinders to see if I find a bad one. You have any good coils?.....

I do have a partial set of coils for a 90-95 engine but they may not work if you think your engine is a JDM 96. Since I've led you down the wrong path with my guesses so far I'll send you a couple for the price of shipping. Email is msg941atcomcastdotnet.

[GseaQ]

....Maybe if the IACV is not it, I’ll get a coil and move it through the cylinders to see if I find a bad one. You have any good coils?.....

I do have a partial set of coils for a 90-95 engine but they may not work if you think your engine is a JDM 96. Since I've led you down the wrong path with my guesses so far I'll send you a couple for the price of shipping. Email is msg941atcomcastdotnet.

Mike, that's too generous of you. I am trying the generally accepted possibilities. I believe the fuel pump did need to be done.

I have trouble finding time to spend a full day on it at one go, so it's taking me longer to try everything. Yesterday I unplugged the IACV again AFTER the engine was warmed up and the idle was at the 650 I set it at. Still no change. In fact, the engine runs the same whether the IACV is plugged in or not IN THE DRIVEWAY idling and no load revving. I followed the FSM steps for testing the IACV. 1) no idle speed drop when unplugged 2) fuse good [replaced anyway] 3) battery voltage from IACV plug terminal b to ground 4) 10 ohms resistance between the pins on the IACV [I do have to try that again with another multi-meter, though]. Today I'll check continuity between pin 111 on the ECU [ECM?] and the IACV plug terminal a. If that's good and ECU pins are good then why does the IACV not do anything? Rhetorical question. I'll post the results when I get them.

I'll try to post some pictures of my coils versus the ones for my old '92 Q45. The '92 coils are on the left and mine are on the right in the pictures.

Thanks,
Glenn

[goody90q45]

It looks like I have the coils on the left in the pictures with brown plugs. Probable not interchangeable. I replied to your email.

[mattd1979]

Did you try unplugging both o2 sensors? If not, just for kicks, disconnect both of them and see how it does. I know that on 90-93 Qs there will be no code thrown when they are disconnected. My nephew had the same problem you have and it was about a year later that we ended up disconnecting them to see what would happen. It cleared right up.

Matt

[GseaQ]

Hey Matt, thanks for the suggestion! I will try that. I still have to move the coils from the 3 "weak" cylinders (from the power balance test - marginal difference only, though) to strong ones, and maybe do a fuel rail type injector flush just to satisfy myself that the injectors are not restricted. I've also been told it could be a spark plug boot. I have 7 spares, so maybe I'll put them in as well. One thing at a time, though, for troubleshooting purposes.

Cheers,
Glenn

[mattd1979]

Yeah, I'm looking forward to reading what the final cause of the problem was. My car recently started showing the same issues as yours. It started with an intermittent hesitation at cruise from 50 to 70 mph. I didn't notice it at the lower speeds. About two weeks ago my MAF sensor went out. It was funny because the problem didn't show itself until I started the car. The car was fine about 2 hours earlier. I had a back up MAF sensor that I installed and it made it driveable but it would now slightly stumble at idle and when at WOT it would bog. I disconnected both o2 sensors which didn't help. I found that when I disconnect the MAF connector that the engine would suddenly run smooth at idle and have good power up to 2000rpm at the fail safe cut-off. I could even break loose the tires when holding the brakes at part throttle. As soon as I reconnect the MAF, it would go back to stumbling and bogging. I ordered a new MAF and when it arrived, I still had the same symptoms. I put the new MAF on my friends car which is a 1991 Q45 and his car ran fine. I even swapped My ECU into his car which it still ran good. I ended up testing the wiring to the MAF connector which tested good with no shorts or breaks. What I ended up doing in the end is I wired the fuel pump to full speed and noticed that the stumbling went away. I could also power break it. So my nephew and I took it out onto the interstate and noticed that it had great power while cruising but as soon as you put it to the floor and the RPMs climb, it was as if my nephew was easing of the throttle. No bucking or bogging like before. When we got back to the house, I pulled the fuel filter off to check to see if it was clogged, I had a white lid off of a container that I used to catch the fuel. I poured the fuel out the outlet end which should be the filtered side in which a bunch of dirt particles started coming out. I could shake the filter and you would here the element inside bouncing around. I cut it open and found that the element had deteriorated. I believe I changed it about a year ago so it's not like it had been on there for 10 years or so. It was a NAPA Gold fuel filter made in China. So, I believe my injectors are plugging up so I am going to pull the upper plenum and the fuel rail off and try to remove the injectors without breaking them in the process to try and clean off the fine mesh screen on each one. Hopefully this will take care of the problem.

Matt

[GseaQ]

Hey folks,

Well, I tinkered with it again today. I plugged in NDS again and confirmed no fault codes. I did a power balance test again. This time turning off #8 made no difference - well, actually the engine smoothed out a bit. Turning off all others individually and singly made the engine noticeably rougher. I repeated this 3 times with the same result. Then I pulled the coils from #8 & #6 and pulled the #8 spark plug. The plug was nearly white and a bit wet on the side of the electrode. I put it back in and set the #6 coil on it. Then I checked the #6 plug. It was also white - really white - and dry. The white colour bothers me, but there's probably not more than 50 kms on them - probably a lot less, so maybe they are too new for a proper colour check. Anyway, I put the #8 coil on the #6 cylinder and did the power balance test again. Now it is #6 that showed no change when turned off. It does not smooth the engine out at all like #8 did before when this coil was turned off. This time turning off #8 made the engine rougher like turning off the other cylinders does. So, the power balance test result followed the coil from #8 to #6. Can anybody offer a thought as to why turning off #8 before moving the coil actually smoothed the engine out noticeably? Could it simply have to do with the firing order or something - not logical, I know, but what could it be?

I tried testing the resistance of the coil. The FSM says the resistance should be 0.7 ohms. Mine was 0.89. I know my multi-meter is inaccurate at higher readings so not entirely trustworthy. BUT, then I check the resistance of the #6 coil now residing on #8 cylinder and got the same reading 0.89 ohms. Now my FSM has 1994 on the GI page. I know the 1994 coils are different than mine which I am now sure are for a newer than 7/95 and 1996 car. The 1994 coils seem to be that same as the spares I have for the 1992. The plugs on them are different with 5 wires going into the plug from the harness, but still only 3 contacts on the coil. The markings on top of the coil identifying which pin is + or -, etc are different, too. This 1995 also does not have the ignitor boxes on top of the rocker covers like our 1992 had. So, I don't know what pins to check resistance across or even what that resistance is supposed to be. I think I read somewhere that the resistance on a bad coil is usually not out of spec, but then who knows.

I thought I'd swap in one of the spare spark plug boots from a 1992 coil, but they are longer by at least 1/4", so they won't work. I guess I'll try to find a coil and boot.

Glenn

[GseaQ]

Hi folks,

Time for an update. Yesterday I moved the offending coil from #6 (the one that was on #8) across to #5. I wanted to confirm the problem followed the coil before buying a replacement. WELL...it started and idled nice and smooth like it normally always did. I did another power balance test and all was normal. I put in a can of BG 44K to 5 gallons of good Esso 91 or 92 octane (no ethanol) and went for a drive. Silky smooth take-off and normal acceleration with NO bucking under light load top gear. The bad news - still spitting (backfiring, I guess) through the intake at full throttle acceleration at and above 3800 RPM. Actually it will do it at 3800-4000 RPM with 3/4 throttle or more.

Today I bypassed the FPCU again and went for a drive just to eliminate it from the suspect list. The idle today is actually not as smooth as yesterday and I see a blip up on the NDS timing display whenever the miss happens. It still runs and accelerates just as smooth - or just about, at least - as yesterday. The high RPM high load spitting/intake backfiring is still there, but a bit less severe than yesterday (I'm pretty sure). Maybe the double-strength BG 44K is cleaning injectors?

Then I plugged the FPCU back in and went for another drive with the same results, so I am now satisfied the unit is good.

Still, logic says this is still primarily some sort of ignition problem. I'm starting to get to the end of my troubleshooting. I'm still not sure if the IACV is good or not. I followed the steps in the FSM for checking it and it all checks out but makes no difference when unplugging and replugging - so unresolved. The NDS shows it as working properly, though.

I haven't unplugged the O2 sensors, yet. The NDS display shows them working - swinging from 3 to 90. Nor have I taped a fuel pressure gauge to the windshield yet. The TPS voltage ranges from 0.4-4.08 or so. The airflow (MAF) voltage ranges from 1.18-4.33, so I think they are both good.

Here's a picture of today's results.

Cheers,
Glenn

[Q451990]

It's probably a glitch with the software, but it's saying that your EGR solenoid is on... which it shouldn't be at idle. You might check to make sure your EGR is functioning properly. If it's being held open for some reason, I suspect that could do all sorts of thing to your fuel mixture...

Heath

[GseaQ]

It's probably a glitch with the software, but it's saying that your EGR solenoid is on... which it shouldn't be at idle. You might check to make sure your EGR is functioning properly. If it's being held open for some reason, I suspect that could do all sorts of thing to your fuel mixture...

Heath

Hi Heath,

I'm a little lost here now. I thought the EGR was strictly a vacuum/mechanical affair. Do you mean I should take the valve off the manifold and give it a good cleaning (yes, I should as someone mentioned earlier, I believe) or is there more steps I should take? I did - months ago - actually depress the EGR diaphragm from underneath and stalled the engine, which I took to mean it was functioning normally. Perhap not?

Thanks,
Glenn

[black g50]

Hate to bring up old posts...but,is that the way to tell if egr is good.Meaning by pulling up on it and engine chokes?Also have same problems with bucking and backfire.Strange thing is,fuel pump new as well as fpcu,filter,injectors(new),knocks,maf.Temp reading in middle,but engine feels hotter than normal.Mine also feels temp related,can drive for 30min down highway,but on return trip it acts up.I was thinking plugged cat,but can rev good in neutral.Pulled tank and cleaned with new sock.Wiggling maf connector did have some effect on idle,so tightened it up no change.Idle drops disconnecting aic.New coolent sensors,therm,pump,radiator pulled n flushed(no crud on cond).

[Infinitiguy19]

When you pull up on the EGR valve the engine should stall.

What brand parts did you use?

Do you have a accurate Infrared Thermometer and a Nissan Consult or equivalent?

Is the entire intake tract clean?

[black g50]

All parts come from Infiniti dealer in Delaware.Intake is clean and tight.Last night was pretty cold,and she ran great!!!Today back to shuddering and hesitating.NO CODES...Can drive 30miles,then turn around and she leans out.Thought it was cats, back pressure fine........Now,I have noticed when at back of car,when exhaust valves open and feel the turbulence at tips,the idle speed drops with the pulses then recover.Hmmm.

[hk20000]

I have a 1996 with exactly the same symptoms. But since my car is OBD2 compliant I get a bit more insight to the problem I think.

I just had a failed cam angle sensor (code P0340) and I replaced that, but since then the buckling sort of started. Strange I eliminated an engine code but caused another new problem.... Since there is no clear answer to what the problem is I'm just as mystified as you are. My car also buckles and stutter when it's at 1000~1500 rpm range at a lower throttle input (well anything less than WOT) but once it's past that it'll rev smoothly to 6500rpm all day long...

Let's keep each other updated to see if we can find a definite answer.

[black g50]

Does it happen at certain temp?Is it constant or come and go?Mine seems to start acting up soon as the electric fan kicks in.Strange thing is,my water pump started urinating in 100deg heat,yet electric fan never came on.Now I can tell how much driving time I have once fan kicks in.Open hood,and everything is super hot to the touch,including fuel rails.So...Now leaning to temp sensor not reading right sending bad data.

[hk20000]

Right now it only happens at initial start up and about 1 minute from start. The engine can be either cold or optimal operating temp it does not seem to matter.

Sprayed down the MAF with a AF cleaner agent and it seems to have lessened the problem. In the mean time I have to perform a "ceremony" at start up - revving the engine past 3k at least once - before setting off to ensure smooth driving from there onwards.

[Mint Q45A]

Have you completely discarded the possibility that the problem is caused by the MAF sensor? I believe you already looked into that, but it may be worth a second look.
My car did something similar several months ago and after debating what to do I decided to simply open the MAF and re-solder the hot wires, inside. I haven't had a problem since then.
I suggest you use a good magnifier glass to inspect the connections inside the MAF.

[black g50]

OP,did you ever find out what the problem was?Mint,replaced maf no change.Red lined in first for half a mile,temp gauge started going to hot,then came the bucking and one intake backfire.My take off shudder is also back.For some reason it seems to lean out causing engine to run hotter.Only hear pump prime,quiet while driving.At idle I swear I can balance a quarter on plennum.Idle speed 650,600 with headlights on.A while back,my friend said my park idle speed was high and adjusted a screw on throttle body turning speed down,not sure if related.

[Infinitiguy19]

A while back,my friend said my park idle speed was high and adjusted a screw on throttle body turning speed down,not sure if related.

Now you get to ask him for a new throttle body that has been unmolested. Because those screws were not meant to be touched for any reason.

[black g50]

In my Charlie Brown voice..AAARgg!!!

[hk20000]

update: so I tried ripping out the intake parts in an attempt to fix the driver's side valve cover gasket (it's an under plenum job, like seriously wtf Nissan), but I noticed a hose that connected underneath the intake plenum after the TB from the bottom was loose with no clamps. (I can wiggle it in and out of the neck a little bit with fingers)

tightened that up and the bucking is lessened (still bucks once per day or so) but it leads me to believe that it's a very hard to chase vacuum leak somewhere in the system. YMMV...

[Infinitiguy19]

Can you hear a vacuum leak?

What does your vacuum gauge report at idle, Throttle closed?

[black g50]

A while back,my friend said my park idle speed was high and adjusted a screw on throttle body turning speed down,not sure if related.

Now you get to ask him for a new throttle body that has been unmolested. Because those screws were not meant to be touched for any reason.

What are the screws for?Yesterday sprayed throttle clean and changed some gaskets,when I got curious and wanted to know what those screws do.One looks like a rest stop for throttle?

[GseaQ]

Hi folks,

Been a long time. It was indeed an ignition coil. I lost interest and parked the car last fall. Then, a few weeks ago a friend asked how much I wanted for. A friend of his wanted to buy it. I asked how much he might offer and it was enough, so I thought I ought to get it running again.

Well, over winter the battery cried uncle and the starter seized (probably solenoid because a few good smacks with a hammer got it going). So, in went a new battery under Costco warranty and a rebuilt starter I had in the garage. Started up after only a few rotations - incredible! But it was still rough.

I had previously put my 3 suspect coils (from the power balance test) on #3, #5 & #7. I put the new coil on #7 - still rough idle. Then I moved the new coil to #5 and that was IT! Instantly smooth as silk. Went for a little test drive and kicked it down into 1st at 20 mph and she screamed up to 7000 RPM and shifted into 2nd, not a hiccup - perfect!

Yes, with a JWT ECU, a 1992 transmission and a 1993 TCU you get automatic upshifts at 7000 without running out of breath AT ALL. Still pulling. AWESOME. And now she belongs to somebody else.

Thank you for all the suggestions along the way. Clue number 1 for coils on the OBD1 system is NO FAULT CODE. Almost everything else will throw a code.

Regards,
Glenn