95 Q45 engines stumbles after hot soak

[GseaQ]

Hi guys,

It's been a while. a new problem developed a couple of weeks ago. After sitting in the sun on a 85 degree day for several hours - maybe even the first trip of the day - she started right up as normal. I drove a few blocks - air on, of course - and after making a left turn, the engine suddenly quit, tach to zero and just as suddenly came back to life and the stumbled like that a few times and all was well again. It was like it starved for fuel, but it was too quick to be that. More like the ignition was being turned off and on quickly.

A few days later it happened again. I can't remember if I was turning left or not, but the heat situation was the same. I had been fiddling with the IAC adjustment after getting the car. When I picked it up, it was idling at about 1200 or so. After I took the engine apart for the fuel injector, O-rings and knock sensors, I discovered the vacuum hose to the FPR was cracked wide open. That was the cause of the high and somewhat erratic idle. Since then I've been trying to fine tune the IAC to balance throttle response off idle with ease of starting (not having to crank for 3-4 seconds). I ended up with the screw at 2 turns. My 92 Q45 was always set at 1.5 turns and started instantly and had immediate off idle throttle response. So, in light of all this, I turned the IAC screw back in 1/4 turn. It started quicker and had better throttle response. There was no more stumbling until today - DAMN, I thought it was fixed!

Today, the car was fine until it sat in the sun at ambient air temp of about 85 degrees for an hour and a half. I started it up, the air went to max, I sat there for a minute for a phone call then put it in gear. Nothing! It had stalled without me even noticing. I re-started and drove away. I notice it was idling low - 500-550 instead of the usual 650-700. After a left turn a minute later it started bucking again with the tach going to zero and back to normal several times. At the next light I moved to the side and revved it in neutral a few times to 5000 or so - just short, quick revs. The first couple were stumbling a bit, then it seemed OK. After that it was fine again.

Any ideas? BTW, there has never been a check engine light since I've had it - about 6 months, now.

Thanks,Glenn

[goody90q45]

Sounds like either a bad MAF or connection, or, fuel pump control unit. Since you haven't got a CEL I'm guessing the FPCU. How's the fuel pump sound?

Do the simple stuff first- Unplug the FPCU connector (in the background in the pic) and look for burning/melting/scorching at the connection. You can also use an alligator clip jumper wire, taking the FPCU out of the loop, and ground the fuel pump next time the symptoms come back.

[Q45tech]

Summer blend gasoline vs winter blend and ambient air temperature.

I always end up with 2 slightly different IAC air bypass settings and fine tune in May and November.............primarily because of AC load in ATL.

Easy to see with a Consult [for accurate idle rpm] and IAC duty cycle.

I've never discussed this before since most don't have easy access to Consult.

Modern designs [ OBD2] have a IAT [which Q does not] to alert ECU to air temperature changes and make fine adjustments.

A good plenum and TB clean and check for other air leaks in hoses will probably make yours better.

Measure fuel pressure and check FPCU.

Q45 [90-95] [90-93 almost NEVER] rarely throw MIL light since most systems kinda work.

[GseaQ]

Thanks Goody and Dennis,

I'm sure the MAF connection was tight when I had it apart for the work in Jan or Feb, but I will check again. I think we also cleaned the MAF then, but that might have been on the 92.

I do have a spare good FPCU that I can swap in when I inspect the original one.

I had IOS send a new pump to the previous owner to install before he shipped the car out to me. He said the pump was noisy and offered to install a new one if I sent him one. I haven't heard any pump noise since I've had the car.

When the plenum and fuel rails were off in Jan or Feb, we cleaned the TB and plenum runners as far as we could reach. Maybe a BG throttle body service wouldn't hurt now though.

While I don't have a consult, I do have a BlazT USB cable which I tried to use unsuccessfully on my old laptop with the ECUTalk program. I have a Nissan Data Scan CD that came with the cable, so I just have to pay the activation fee and I can use that (IF I can figure out how!). Failing that, my friend has a pretty new computer scanner that he uses on any make/model car that comes into his shop. We've had it on mine before to check codes and do power balance tests and stuff. So, Dennis, using NDS or my friend's diagnostic computer, what should I be looking for as a duty cycle % (I've seen both 10% & 15% here) and is there anything else to look for. I guess base timing should be confirmed at 15* BTDC before anything else?

Thanks guys,Glenn
Modified by GseaQ at 1:10 PM 7/3/2008

[Q45tech]

10-15% is correct, as each individual engine will have its own sweet spot.Really the exact number depends on how much air is flowing under TB plate and thru IAC manual bypass screw.

10-15% extra air than the above two flow.

Hot shake is common when fuel gets above 100F and may almost boil or boil in fuwl rails after shut off and the rails don't cool down until a few minutes of circulation and forward motion.

[Q45denver]

Might be worth it to wrap the fuel rails and metal fuel lines with insulation. Probably a lot easier with the plenum off.

[GseaQ]

Thanks Dennis & Q45denver. I'll check everything over the next few days. The 80* weather is now 60* and wet! No problem with the engine's operation today. For sure the next time the plenum is off the fuel rails will be insulated.

Glenn

[jimbyjimb]

As a side note make sure to really check that MAF connector. I inspected mine several times by pulling, visually, cleaning and had similar problems and got no CEL. Turns out the ground was loose and would occasionally un-ground the MAF. I found it by accident when I was changing my CAS. I accidentally bumped the connector and the ground just fell out. The connector ends have weak crimps. Upon re-installation I reccomend soldering the wire to the end as well as crimping. Good luck and I hope you "Git 'er done"!

[GseaQ]

Thanks Jim,

It happened again today, but with slightly different factors. It was only 70*, but quite humid. I started the car for the first time today and it stalled immediately. I restarted and it idled normally for 10-15 seconds and suddenly quit and re-caught instantly, but this time the Check Engine Light came on for a second and went out again. I didn't see the light before, but if it was only on for a second maybe I missed it with the sun glare on that end of the instrument panel.

I did check the MAF connector and wires afterwards today. It's tight and won't even really wiggle when I try. I also tugged on all the wires coming out of the connector, but the engine did not falter. There is a bigger green wire (4th wire) from the connector to a plenum bolt that looks like a modified ground, but, no matter, it is also solid.

Maybe tomorrow I'll swap FPCU's. I'm pretty confident of the hoses. The iffy vacuum ones were replaced in Jan or Feb.

I have to get either ECUTalk or NDS set up so I can see if there's a code to go with the CEL.

[GseaQ]

I did check the MAF connector and wires afterwards today. It's tight and won't even really wiggle when I try. I also tugged on all the wires coming out of the connector, but the engine did not falter. There is a bigger green wire (4th wire) from the connector to a plenum bolt that looks like a modified ground, but, no matter, it is also solid.

I have to get either ECUTalk or NDS set up so I can see if there's a code to go with the CEL.

Well, first a correction. The green wire is not from the MAF connector, but from the harness with the other 3 wires going to the MAF connector. It does ground to a plenum bolt, though.

I got Nissan Data Scan set up today and when I started the car after sitting for about 3 hours, it stumbled and stalled while showing the CEL. I restarted the engine being careful not to turn the key OFF before doing so. When I plugged in NDS I got a code 12 "airflow meter circuit" I think it said.

I cleared the code and wiggled, pulled and twisted the MAF sensor plug and nothing happened. The engine stayed smooth and no new code. I even tried tapping on top of the MAf and still nothing happened.

One more thing, I tried to figure out the IAC valve adjustment with NDS. There were 2 "gauges" on the NDS screen for "Duty Cycle" and "AAC Valve". The Duty Cycle reading was 1.32-1.40 and the AAC Valve was 8. Also, the timing display showed 45. Is it 30 that we have to subtract to get the true number? Do I need to make an adjustment to the IAC Valve?

Any thoughts as to what to look at next? All suggestions appreciated.

Thanks guys,Glenn

[96Qowner]

Electronic component failure is starting to show up across brands, due to years of vibration and hot/cold cycles. Solder joints begin to deteriorate. A few NICO Q45 owners have taken the cover off their MAFs to get to the circuit board and found bad connections. I'm betting that's your problem. You can either swap in another new/used one, or take yours apart and resolder the joints - not very difficult.

Repairing MAF

Fixed MAF in spare time

[qship96]

Electronic failure due to vibration/shock is accelerated when one modifies their car with large wheels/low profile tires, stiffer springs/poly bushings, stiffer dampers.....just one of the untold degrations most "improvements" create in the quest for looks

[GseaQ]

96Qowner,

Thanks for the super links and info. I'll have a look, but I suspect replacing the MAF is the route I'll have to go. The Q is our only car and is driven daily. We can't really have too much down time if we can help it.

qship96,

You are absolutely right. Improvements for performance invariably stress other components and have an unknown cost over the long term. Still, for many the risk of such cost is tolerable for the increase in performance.

So, the question to you all, does anyone have a good serviceable MAF they can sell me?

Thanks guys,Glenn

[3Q Jay]

One more thing, I tried to figure out the IAC valve adjustment with NDS. There were 2 "gauges" on the NDS screen for "Duty Cycle" and "AAC Valve". The Duty Cycle reading was 1.32-1.40 and the AAC Valve was 8. Also, the timing display showed 45. Is it 30 that we have to subtract to get the true number? Do I need to make an adjustment to the IAC Valve?

Glenn

duty cycle is for injector. AAC is what you want to adjust. i like it at 15% hot idle no A/C min electrical load. you have to race engine no load 2-3x and then let it resettle to idle.timing is not true. you need to read it with a light. then you can offset 45 to whatever true is, and read timing advance as rpm varies.might check the classifieds for a MAF. i have a working spare early style (fits the 3-pin 1995s, but not the 4-pin late 95-96).

[GseaQ]

Thanks 3Q Jay. I'll give the IAC another go. When adjusting with the NDS plugged in, do I unplug the IAC or leave it plugged in for the adjustment? The funny thing is that the more I back out the IAC screw, the longer it cranks before starting - still only a couple of seconds, but not just 1 rotation like the '92 was. It was at 1 3/4 turns with the reading of 8. The '92 was always at 1 1/2 turns and started instantly and had great tip-in from idle.

I emailed a guy who has one in our NICO classifieds from a '94 with TCS. I haven't heard back yet. Mine must be an early '95 because there are only 3 wires coming out of the plug.

Thanks again,Glenn

[96Qowner]

Most of us have had good luck locating a yard through car-part.com:

http://car-part.com/

It's under Air Flow Meter. I see several for pre 11/94, and a few (mostly unpriced) for post 11/94. 95 and 96 are the same MAF and plug.

[GseaQ]

Thanks a lot 96Qowner. I didn't realize the '95 MAF was the same as the '96. At least mine should be with a build date of 5/95. I expect the MAF stayed the same after the JDM engine swap.

Glenn

[3Q Jay]

if you have NDS going, then adjust with AAC mated (under ECU control).turning the screw IN (clockwise) will increase ECU duty cycle--since you are causing less 'fixed' bypass air, the ECU must open the bypass air more to compensate.

[GseaQ]

if you have NDS going, then adjust with AAC mated (under ECU control).turning the screw IN (clockwise) will increase ECU duty cycle--since you are causing less 'fixed' bypass air, the ECU must open the bypass air more to compensate.

Thanks 3Q Jay. So, if I understand, leave the AAC plugged in, and turn the screw IN (clockwise) to raise the % from 8 up to, say 12 or so.

[3Q Jay]

yes

[GseaQ]

Don't know where this post came from...

[GseaQ]

Well, that didn't go well. I plugged in NDS, shifted to neutral, AC and all other loads OFF, did a couple of quick revs to about 4000, held steady at 2000 for about a minute (this was interupted by the MAF fault induced misses), then let idle stabilize to a AAC reading of 8. I adjusted the screw IN a total of 3/4 of a turn, 1/4 at a time with the revving, holding and stabilizing between each increment. Still showed 8%.

I did clear the code 12 a couple of times. After going through this process a few times, turning the screw in and out, and even driving around the block and letting it stabilize, it finished up at 25%. This is at 1 1/2 turns out from seated. I know it's too high, but it was earlier at 8% for 1 1/2 turns.

The temp stayed at 86-88*C the whole time. I did not take any readings or make any adjustments with the AC cooling fan running. I don't think it ever came on (I visually checked repeatedly when adjusting). The idle is stable at 650-675. The timing is wavering from 45-48, which I believe is really 15-18.

I wonder if the MAF fault is making an accurate AAC adjustment impossible. I have a replacement MAF on the way and will try all this again after replacement.

Oh yeah, I didn't see the point in changing the FPCU after confirming the MAF code 12 with each stumbling occurance.

Am I on the right track?

Thanks,Glenn

[3Q Jay]

one of the reasons i suggested 15% aac is that at 10 and below it seems to 'freeze'. when you turn on the a/c and compressor engages--does the aac duty cycle jump up to maintain target rpm?one quick way to make sure you are under ecu control is to unplug the aac while idling--the revs should drop about 50 or so (crude check). then when you plug in the aac--they will shoot up to about 1200 and then float back down as ecu regains control.

yes, get your maf going. also--what is the tps reading? exactly 0.44V at hot idle?

[GseaQ]

Yes 3Q Jay, I'm sure the aac jumps up when the AC is on, but I will check for that specifically tomorrow. Idon't think the AC was on anytime I had the NDS plugged in. I know when I put it in gear it jumps up from 8 to 20-25. Same thing every time the MAF causes a stumble and the engine comes back to life.

If I unplug the aac the rpm does drop by about 50 - barely perceptible. BUT, it does not go up at all when plugged back in - I suppose it may go up 50.

I haven't checked the TPS voltage, but will.

Thanks for all your help.

Glenn

[GseaQ]

Well, we've encountered a delay. I bought a MAF off a fellow NICO member who said it would fit 94-96 and that it came off a 95. Turns out it has the same 3 prong connector my 92 had, not the 4 prong rounded end connector that fits my 95 (built 5/95) and the 96's.

So, I still need to find a MAF. I don't think there's any point in continuing troubleshooting until that thing is replaced.

Glenn

[96Qowner]

Bummer! His musta been an early '95?

[GseaQ]

No, his was a 94. He bought it but didn't need it. It came off a 95, but he told me it fit 94-96. I guess it did come off an early 95.

[Q45tech]

The ACcompressor is too coarse as it draws 3-5 HP at startup, why not try the power steering or better yet headlights on/off as a 10% change vs a 25% change for ac.

[GseaQ]

Thanks Dennis. I will try that with the headlights. I just think I should wait until I get a replacement MAF in place before trying to set up the right aac %.

Glenn

[GseaQ]

Hi guys,

Well, yesterday I took the top off the MAF and heated up the solder on the connector pins and also where those pin diodes(?) connect to the PCB. I didn't add any solder thinking just heating what's there with the soldering iron might close any gaps that may have developed. If that fails, I'll add a bit of solder to them. The PCB looked perfectly clean with no indication of heat damage. I need some hot weather now to see if the MAF fault is fixed or not, but that may be a week away.

Then I went after the AAC setup again. It was at 8 and I wanted 10-15. That's a pretty finicky adjustment. With a 1/4 turn it would go from 8 up to 24. I finally found a sweet spot between maybe 9 and 18 where if I turned the screw just a hair I could settle it at 13. This was in Park with lights, AC, radio and AC fan OFF. I realized after the book says to have the trans in Neutral so I hope Park is OK.

Turning on the AC sent the number up to 24-25.

The TPS was 0.40 at idle according to the NDS display. Is this acceptable or is the TPS toast for not reading 0.44 at idle? What, if anything will cause a TPS code?

Thanks,Glenn
Modified by GseaQ at 10:03 AM 8/22/2008