1995 Q45t running rough & bucking - SOLVED!

[GseaQ]

Hi folks,

Well, I have a 1995 Q45t we bought about 3 years ago from a NICO moderator. That was the worst car-buying experience of our lives, so couldn't stomach posting or visiting much after that. Rightly or wrongly, I had regarded moderators as honourable and trustworthy. In retrospect, this is the internet and nobody should be truly trusted until they have actually earned that trust. I learned a very hard lesson. I used to be here, and the old Yahoo Group before that, almost daily and tried to help anybody I could with what I had learned. Anyway, maybe I've burned some bridges, but c'est la vie, we got burned bad, too. I hope some of you will still offer some helpful advice.

The car was pretty screwed when we got it, so I did quite a bit of work on it to make it right - actually, better than right. Here's a list - new aluminum radiator (original COPPER one had the bottom dented upward 2 full inches above the damaged crossmember), new knock sensors, new under plenum hoses, 1 new injector and all new injector seals, resealed valve covers, new fan blade, replaced leaky steering rack with the good, quicker ratio one from my 1992 Q45, replaced transmission (felt like it was slipping) with the 1992 one (perfect condition and shorter 1st & 2nd gears), put in the 1993 TCU that was controlling the 1992 trans, replaced howling 4.08(?) diff with the original that was supposed to come with the car but I had to get shipped from AZ, replaced both front and one rear caliper with new, replaced upper links and replaced 2 window regulators followed by a third one several months later. I think there is more that I haven't thought of. It came with a JWT ECU, Eibach springs and Tokico blues. With that ECU and the 1992 transmission 1993 TCU combo I just leave it in Drive - no need to ever manually shift. It kicks down to 1st up to 30 mph (was 25 with OEM set-up) and shifts into 2nd gear automatically at 7100 RPM, into 3rd at about 6800. You get the idea, she's a rocket! Still pulling at those rev's, too.

About a year and a half ago the MAF went wonky on it. On really hot days the engine would suddenly violently start to buck when leaving a stop sign, for example. Never really happened when just cruising, it always seemed to be triggered by starting normally from a stop. It seems the MAF's on the '95-'96 cars are different from the '90-'94 (some '94's are apparently the same as '95-'96). Mine has an oval plug whereas the older cars have a rectangular plug. I could not find one used, so I re-soldered the 3 terminals (well, warmed up the existing solder) at the connector and it was fixed - never bucked again.

Until now, but this time it's different, so I don't know if it is the MAF at fault. She starts smooth when cold, and runs smooth for a few minutes when driving until warmed up. Then it developes a rough idle and, worse, when cruising easily with zero load in the 1300-1800 RPM range (RPM depends on the speed and the lack of load on the engine) it will start to buck violently. If I ease off or accelerate it will stop. It is also very rough and missing when accelerating normally from a stop, but not bucking. I haven't used it much since this started, been using the bike as much as possible for the commute. Cruising on the freeway at over 55-60 mph and it is fine. It does have a "spitting", irregular miss at full throttle so I don't do that.

I have plugged in the Consult cable and NDS and get code 55 (nothing's wrong). It has never given me a check engine light (light works when key on, engine off). I did a quasi power balance test and thought I had a miss on #3, so I swapped #3 & #5 coils. The miss was I think, my imagination. Several re-tests show pretty equal results when shutting off the cylinders one at a time. If anything, #3,4 & 8 seem to show slightly less RPM loss, but not really noticeably different.

I must say, when this happened the car had been running like a top. In fact, the previous tank of gas had given me 26 mpg instead of the usual 24 mpg (imperial gallons). I was driving through town and all was well. At one intersection, it was as perfect as always, I stopped at the red light to turn right and as soon as I started to move it was like a switch turned on or off - instant miss and rough running.

I have re-soldered the MAF terminals again with a stronger soldering iron and added a touch of new solder to them - no change. I didn't think it would be the TPS because of the varying RPM's involved and I really don't think it is always the same throttle position, but I could be wrong. I will change the plugs, but I'm sure that's not it as no one cylinder is at fault. They were also just put in 25,000-30,000 miles ago when I did all the other work. I did run a can of Techron through it at double strength.

All thoughts are welcome.

Thanks,
Glenn

[Infinitiguy19]

Never thought I would see you back here but have you done a BG fuel injector flush? I plan on doing one of those these days to resolve my ever so slight idle issue.

[goody90q45]

It sounds like the fuel pump and/or the FPCU is going south. Any humming from the trunk? How's the FPCU connector look? Any burning?

[GseaQ]

Never thought I would see you back here but have you done a BG fuel injector flush? I plan on doing one of those these days to resolve my ever so slight idle issue.

Yeah, I know. I used to really enjoy it here. No, I haven't done the actual BG flush, yet. The can of Techron Concentrate didn't improve anything, though. I still think it was something sudden and distinctive - a single event with a component - rather than dirty injectors which would likely develop over time. Still, maybe I will do that just to rule it out. Another thing, I make sure not to use any ethanol. Chevron and Shell both use it now.

[Q451990]

Good to see you here again! I agree that it seems fuel pressure related. Might be worth checking it, or just replaing your fuel pump control unit with a working one and see what happens...

If that checks out OK, and you feel sure it's not a MAF problem - maybe look toward the crank angle sensor? I've heard those can go bad - but I've never had it happen, so I don't know the actual symptoms.

Heath

[GseaQ]

Good to see you here again! I agree that it seems fuel pressure related. Might be worth checking it, or just replaing your fuel pump control unit with a working one and see what happens...

If that checks out OK, and you feel sure it's not a MAF problem - maybe look toward the crank angle sensor? I've heard those can go bad - but I've never had it happen, so I don't know the actual symptoms.

Heath

Hi Heath, thanks for the welcome back. Actually, it feels more like a sudden component failure than fuel pressure, to be honest. Having said that, it seems to have gotten worse. It used to be smooth at cold start up and be OK for a few minutes. Now it's rough at idle and take off, as well as full throttle high revs the single time I tried it. However at a steady highway cruise - above the easy load 40-50 mph - she's smooth(er). At least there's no roughness to be felt.

Goody, hi, I don't know how I missed your reply before. Anyway guys, the fuel pump is not noisy. The symptoms seem to happen in more than one zone of the FPCU. I will look at the contacts for signs of heat damage, though. I do have a spare that I can swap in.

Hello again Infinitiguy. Thanks for your input on the VH45DET site as well.

Cheers,
Glenn

[GseaQ]

Well folks,

I just did a quick check. The values for the MAF should be approx. 0.2 with key on/engine off and 1.0-1.4 at warm idle. Mine is 0.11-0.13 KO/EO and 1.1 at idle. They are low but in spec I'd say, although they are both just a hair over half the spec. Does anybody know how low is a fail?

Turning off #3, 4 or 8 has less effect than turning off any of the others. I now realize that I can hear the fuel pump. I have to have a look at the FPCU in a bit.

Cheers,
Glenn

[Q451990]

I seem to remember Q45Tech saying that these numbers are very critical - but I really don't know. The warm idle number is going to have everything to do with how many RPMs you're running at idle. I would bet the .4 difference corresponds with the +/- 50 in the base idle spec.

There's a thread in the Q45 forum, where a new member says he had incredible results cleaning his chassis grounds after chasing a knock sensor problem for a while... Might be another thing to check.

Have you ohmed your injectors lately?

Heath

[GseaQ]

I seem to remember Q45Tech saying that these numbers are very critical - but I really don't know. The warm idle number is going to have everything to do with how many RPMs you're running at idle. I would bet the .4 difference corresponds with the +/- 50 in the base idle spec.

There's a thread in the Q45 forum, where a new member says he had incredible results cleaning his chassis grounds after chasing a knock sensor problem for a while... Might be another thing to check.

Have you ohmed your injectors lately?

Heath

Hi Heath,

The idle hasn't changed - 630-650. I had set my AAC to 25% which seemed to be the best result. Tonight it shows 29%, but the idle speed has not changed. The grounds are a valid point - they should be checked every 15 years whether they need it or not, but never are.

I'm still suspicious about the low MAF numbers, but still have to check the FPCU - especially now that I noticed I can hear the fuel pump with a half tank of gas. The noise is not intrusive or even noticeable until I listened for it. Now I can hear it without trying, but not sure if I should change it on spec. I guess if there is any sign of heat damage on the FPCU plug I will change it right away along with the FPCU.

The fact that I keep finding the #3,4 & 8 cylinders having a little less impact when shut off means I should indeed ohm the injectors. I think I've been subconsciously avoiding that.

I work the next 4 days (14 hrs per) so the next chance to do anything will be Sunday.

Thanks,
Glenn

[GseaQ]

I seem to remember Q45Tech saying that these numbers are very critical - but I really don't know. The warm idle number is going to have everything to do with how many RPMs you're running at idle. I would bet the .4 difference corresponds with the +/- 50 in the base idle spec.

There's a thread in the Q45 forum, where a new member says he had incredible results cleaning his chassis grounds after chasing a knock sensor problem for a while... Might be another thing to check.

Have you ohmed your injectors lately?

Heath

Hi Heath,

The idle hasn't changed - 630-650. I had set my AAC to 25% which seemed to be the best result. Tonight it shows 29%, but the idle speed has not changed. The grounds are a valid point - they should be checked every 15 years whether they need it or not, but never are.

I'm still suspicious about the low MAF numbers, but still have to check the FPCU - especially now that I noticed I can hear the fuel pump with a half tank of gas. The noise is not intrusive or even noticeable until I listened for it. Now I can hear it without trying, but not sure if I should change it on spec. I guess if there is any sign of heat damage on the FPCU plug I will change it right away along with the FPCU.

The fact that I keep finding the #3,4 & 8 cylinders having a little less impact when shut off means I should indeed ohm the injectors. I think I've been subconsciously avoiding that.

I work the next 4 days (14 hrs per) so the next chance to do anything will be Sunday.

Thanks,
Glenn

Well, 1st of all, there has been a change in the symptoms. In neutral or park the idle is 630-650, which in retrospect is down a bit from the 650-675 I set it at a couple of years ago. In gear at a stop sign it sort of floats between 300-450 by the tach (the same reference I always use - it matches the NDS display) to the point of almost stalling. Slipping it into neutral brings the idle back to "normal".

I did a little testing today and can only call it inconclusive. I checked the plug at the FPCU and it and the connector look perfect. I plugged in my spare FPCU - just hung in place with a jumper from the mounting bracket to ground. No change in symptoms.

Then I unplugged it and jumpered the ground to run the full 12 volts to the fuel pump. While at what I think is the middle speed I can hear the fuel pump if I listen for it at the current fuel level - 1/4 tank. Jumpered to 12 volts and max speed it is quite noticeable. The idle goes back up to the previously set 650-675 with no load. However, it is still rough and misses when leaving a stop at the lower revs - no change. It still idles at 300-450 when in gear at a stop. No change.

Oddly, I don't think I ever heard the fuel pump running at the full 12 volts before. The sound is quite noticeable. Turning the key on with the FPCU plugged in seems to run the pump at the medium speed (only judging by the sound - I think I can hear middle and max speed, but not low speed, but I have nothing to base this thought on).

Then I ohmed the injectors and Knock Sensors. With the key off no injector readings. With the key on #2 is 14.2, #5 & 8 are 14.3, #3, 4 & 6 are 14.4, #7 is 14.5 & #1 is 14.6. Six or seven of them are the Deatch ones and the other one or two are new I installed after buying the car 3.5 years ago. I never consciously bought ethanol laced fuel but may have this year before I noticed the Chevron and Shell are now 5-10% ethanol. While seemingly borderline readings, the fact that they are all so close with 1 or 2 of them being newer than the others makes me think they are probably OK.

The knock sensors are both 812 ohms with the key on or off. Again out of spec, but somehow I don't think they would cause the symptoms I have. I think I will change the fuel filter as it is overdue. Then I will do the spark plugs even though they only have about 45,000 kms on them. They're supposed to be good for double that.

Lastly, I am going to get a replacement MAF because I don't like the low readings I saw when I checked last week. This may actually get done before some of the other stuff.

BTW, still have code 55 - nothing's wrong. Nothing's wrong, my a**!

Does any of this ring any bells?

Cheers,
Glenn

[GseaQ]

Well, I guess it's time to re-group and re-organize my thoughts. I put in the new-to-me MAF today. The result was absolutely no change in the symptoms. I've already bypassed the FPCU and jumpered the pump to ground which honestly made no difference. Oh well, new spark plugs can't hurt, but I can't get past the fact that this originally happened in a split second, indicating something failed, not wore out or got dirty with gradually worsening performance. I haven't checked the accuracy of my meter with a 10 ohm resister, yet, but the values were basically equal on all injectors. Also, how likely is it that the knock sensors would both fail and read 812 ohms each? They were both new 3.5 years and 40-50,000 kms ago. The knock sensors went on my old Q and the symptom was a lack of power, but still ran smooth with no missing.

Well, I'll keep you all posted.

Cheers,
Glenn

[Q451990]

It almost seems like your AAC valve isn't working for the RPMs to go that low. I would try unplugging the electrical connector to the AAC valve and then check everything again.

I don't think knock sensors would have anything to do with idle issues. The injectors sound fine... like you said, with them all grouped together it seems that they're OK.

Heath

[GseaQ]

Hi Heath,

I'm pretty sure I'll need to check the AAC valve and no doubt do a TB fogger-cleaning. BUT, the idle isn't the problem, it's a symptom as far as I can tell. Something is causing the missing, rough running and bucking. You know, I've noticed something else, when I start it cold it is smooth for the first few minutes idling AND driving. Then it gets rough.

The parts store didn't have the NGK plugs, but rather Bosch Platinum 4 electrode ones. I was going to put them in tomorrow. Any thoughts on these?

Thanks,
Glenn

[Q451990]

You really want to avoid the Bosch plugs! T3 has seen multiple instances of electrodes falling off of those plugs! At one point they were actually installing the standard Bosch Platinum plugs, and actually went back and replaced them in customer's cars with the factory specified plug at no charge due to issues.

Heath

[GseaQ]

Thanks Heath. I thought I remembered something about that. Back they go in favour of something old-fashioned.

Glenn

[GseaQ]

Well folks, here's the mystery and I don't like it one bit. The car is running like a million bucks and there is no reason for it.

I drove it to work today - 50 miles. After work I started it and it seemed to be running even worse - rough idle, surging, bucking at no load cruise under 1750 RPM.

Then at some point on the trip home it started running like new again. I thought when I turned it off to refuel it would bugger up when restarted, but still smooth as silk.

Then I punched it at 25 mph. Absolutely screamed to 7200 RPM and shifted hard into second and kept climbing - never missed a beat. Kicked it down at 50 mph, same thing - smooth power all the way up to the shift to 3rd at 7000 RPM.

So, now I can't trust it. I didn't fix it so it will break again. There's nothing I can do until it does - not that I really wish it to. Maybe I should take off the IACV for a look. Maybe it was dirty and stuck, then tonight came unstuck?

F*&#%@g intermittent problems. The starter went dead a couple of years ago intermittently. The minute we wired in an auxiliary start button to troubleshoot Ignition switch or starter it never happened again. I still have a brand new starter in a box waiting to be used. Anybody want to buy it?

So, any more ideas out there?

Cheers,
Glenn

[GseaQ]

Well, that didn't last long. It was running like a million bucks last night. This morning it's back to it's old rough ways. I must say, though, the symptoms are not as severe this time around. I will continue with troubleshooting/cleaning the IACV.

On the bright side, I feel OK with the fuel pump, now, given how well it ran last night. Also, I had been thinking of a possible vacuum leak/cracked hose, but I doubt it would repair itself for an hour after a month and then fail again.

[goody90q45]

Could the wires in the MAF pigtail be shorting out? Are the wires stiff? Brittle? Any corrosion?

[GseaQ]

Could the wires in the MAF pigtail be shorting out? Are the wires stiff? Brittle? Any corrosion?

Hi Mike,

I don't think that's it. I looked the contacts & wires over pretty good when I put the replacement MAF on a few days ago and all looked good. The wires don't seem brittle at all, but I will take off the ground and clean/re-do it just in case. When I had the MAF problem before the tach would drop when the engine cut out/stumbled. I also got the MAF code back then, too, but no codes this time.

We will find it (or I'll part it out...)

Thanks,
Glenn

[GseaQ]

Well, here's an update. Today I took off the IACV, took it apart and cleaned it. It was kind of dirty, but not as bad as I expected. Before doing that, however, I unplugged it with the car running. Immediately the idle dropped way down - maybe to 400 or so. I blipped the throttle and when the idled dropped instantly it stalled. I plugged it back in and the idle went back to normal, so that tells me the thing is functioning.

The verdict - no change after the cleaning.

One distinct symptom is that it runs perfectly smooth when started cold until it warms up. Then it starts running rough. Rough at idle, rough and stumbling when accelerating. If I shut it off for 15 minutes it starts and runs perfectly smooth for a minute or two, then gets rough as usual.

Next is the fuel filter just because it's overdue. Anybody have more thoughts on this?

Thanks,
Glenn

[Q451990]

The whole temperature thing leads me to believe it's an electronic component.

Let me mull it for a while... nothing comes to mind at the moment.

Heath

[GseaQ]

The whole temperature thing leads me to believe it's an electronic component.

Let me mull it for a while... nothing comes to mind at the moment.

Heath

That's what it seemed like from the beginning, Heath. It was running perfectly, then suddenly when turning right from a red light it stumbled and ran rough - something instantly failed. But, never a code. I looked at the vacuum hoses that I could see and they all look and feel fine. They were all replaced along with fuel and coolant hoses when I got the car 3.5 years ago. I checked the operation of the EGR valve and it was fine. Could an O2 sensor do this?

Thanks,
Glenn

[Q451990]

I don't think an O2 sensor would cause it - but I've never experienced a failure. I would think that woud trigger a code or MIL.

Have you tried to run your consult/data scan setup in real time to watch for something to change when it goes from good cold driving to bad hot driving? Maybe have someone else drive while you watch it?

Heath

[GseaQ]

I don't think an O2 sensor would cause it - but I've never experienced a failure. I would think that woud trigger a code or MIL.

Have you tried to run your consult/data scan setup in real time to watch for something to change when it goes from good cold driving to bad hot driving? Maybe have someone else drive while you watch it?

Heath

I have run it with the NDS dashboard on the screen, but hard to see more than a wavering idle or O2 sensor indicators. I'll have to take it for a drive with a passenger to drive or watch. I do know the car tach doesn't even waver when it is happening.

This morning I did and uncomfortable thing by accelerating hard before it was warm. I never even put it in gear until it's warm. Anyway, it was still idling silky smooth at about 1200 RPM and stayed silky smooth and as strong as ever all the way up the range. Seconds later it was warm enough to be running roughly again.

When running like that it will surge as it accelerates and actually make a coughing/spitting noise at high revs. I don't run it that way normally. In fact, I try not to run it at all. Lately I've even noticed an occasional pop/backfire when accelerating at - say - 1/4-1/2 throttle and low speed. It's almost like fuel injector symptoms, but no code and they all ohmed equal within a few tenths of an ohm, albeit a few tenths over 14 ohms. I still have to check my meter calibration, but I doubt if all injectors would fail at the same time.

Next days off it's the fuel filter and at least the left bank spark plugs because I still have that side uncovered.

Thanks,
Glenn

[Q451990]

Have you checked the fuel pressure? A very senior Infiniti tech. once suggested that my backfiring problem could be a bad FPCU - or timing chain guides - which unfortunately turned out to be the problem.

I know you tried a known good FPCU, but I wonder if the pump itself could be failing? Maybe it's something failing with the pump as it warms up... I've never done the Q45Tech tape-a-gauge-onto-the-windshield test, but it might be worth your while.

Heath

[GseaQ]

I know you tried a known good FPCU, but I wonder if the pump itself could be failing? Maybe it's something failing with the pump as it warms up... I've never done the Q45Tech tape-a-gauge-onto-the-windshield test, but it might be worth your while. Have you checked the fuel pressure? A very senior Infiniti tech. once suggested that my backfiring problem could be a bad FPCU - or timing chain guides - which unfortunately turned out to be the problem. Heath

No, I haven't actually checked the fuel pressure. However, I did bypass the FPCU and drive it with the pump at the max speed. That didn't fix it, but fuel pressure gets added to the list.

[GseaQ]

Well, the new fuel filter didn't fix it (I knew it wouldn't). No time to do the plugs last weekend, hopefully this weekend. It's actually running worse than ever today. The symptoms of missing and bucking are worse and now at higher revs and speed. It even feels rougher now when cold. I don't really drive it anymore. That's why there are long gaps between updates.

Anybody ever have injectors fail when warm? They're all pretty equal resistance-wise, but the symptoms remind me of injector failure. What are the odds that they would all meter equally, but one or more or all would fail at once?

Glenn

[Q451990]

The injectors will typically read differenty when warm, but still read off while cold if there's a problem. So you might read 200 ohms hot and 150 cold, but I don't think you'd get a normal cold reading and then have them go out when warm.

Heath

[Ace2cool]

So just to be sure, you have done a power balance test, where you unplug spark plugs one at a time and see which ones change/don't change the idle, correct?

Second question: What happens when you go WOT? I had a very similar problem with my old SVX, and it turned out that the upper plenum bolts were finger-tight. It was letting air in once it was warm, but not when it was cold. I kicked myself when I finally found it. I'd double check to make sure you don't have any vacuum leaks or broken gaskets on mating surfaces of the plenum/TB.

[GseaQ]

So just to be sure, you have done a power balance test, where you unplug spark plugs one at a time and see which ones change/don't change the idle, correct?

Second question: What happens when you go WOT? I had a very similar problem with my old SVX, and it turned out that the upper plenum bolts were finger-tight. It was letting air in once it was warm, but not when it was cold. I kicked myself when I finally found it. I'd double check to make sure you don't have any vacuum leaks or broken gaskets on mating surfaces of the plenum/TB.

Yes, I have done the power balance test at a no load idle - several times, but as of yesterday, she is running worse (same symptoms with increased severity), so maybe another PB test may now be more conclusive. The previous tests produced the same results - #3, 4 & 6 showed less RPM drop than the others, those 3 were about equal while the other 5 were equal to each other with very pronounced idle drop when any of them were shut off.

I discounted the air/vacuum leak for 2 reasons - 1) symptoms only appeared when the engine had warmed up (until a few days ago, but I think I have to have another go at cleaning the IACV) and, 2) twice now the symptoms have mysteriously disappeared and the engine ran normally (smooth and strong) for an extended period - say an hour or more.

At WOT the symptoms are the same, but worse in severity - the missing becomes surging and spitting/popping.

For the whole time until very recently the symptoms seem most noticeable under 1800 RPM and at WOT. The midrange at 1/2 to 3/4 throttle seemed strong and smooth. Now it is still better there, but less so than before.

I still have to look at the plugs and check injector resistance when hot.