1993 Q45 engine runs better when ambient temperature is above 70*F

[Infinitiguy19]

Hey I know I have made a ton of topics on my 1993 Q45 with a stumble at idle. But since temperatures have warmed up here in New England my Q45 runs a little better than in cold conditions.

Does this in any way help narrow down what the possible cause of the stumble at idle or when at a stop in gear?

I highly doubt this may be the cause but I have an exhaust leak that I will have repaired next week, Do you think that will fix EVERYTHING?

Like I said the engine would idle like a Lexus, In that you wouldn't even know its on and you wouldn't even feel the car running.

Also I believe the idle changes with temperature changes, But again I am going by the dashboard tachometer not a laptop Consult. I feel like getting a net book and having that just for the Q.

All posts are appreciated as always.

[Q451990]

All electrical parts that have intermittant problems are subject to being temperature sensitive. You might try a can of "freeze spray" available at electronics supply houses if you want to test something specifically.

The only other thought that I have is if the car isn't warming up enough to go into closed loop (bad thermostat seal) unless the ambient temperature warms up enough to approach the limits of the cooling system.

Heath

[Infinitiguy19]

All electrical parts that have intermittant problems are subject to being temperature sensitive. You might try a can of "freeze spray" available at electronics supply houses if you want to test something specifically.

I can try it on the MAF, TPS and Alternator and see what that yeilds. But those are know good at least the MAF for sure.

The only other thought that I have is if the car isn't warming up enough to go into closed loop (bad thermostat seal) unless the ambient temperature warms up enough to approach the limits of the cooling system.

Heath

If there is a temprature that the engine needs to reach to go into closed loop would it be 176*F+?

I know thats it goes above that on a bad day, I have seen 196*F on a 100*F day. I am sure glad I have a external trans cooler.

[Q45tech]

When the coolant temp sensor tells ecu that it is above 195.5 -199.9F weird things start to happen because it goes into summer overheat protection.

[Infinitiguy19]

Right you have said it many times: "The ECU decreases timing by one degrees for every degree over 196*F"

I think you also said that it forces the engine to run richer in order to protect the cats.

I can tell you I have never seen the engine get above 196*F with the laptop Consult plugged in, even then it was OK.

But the temperature can cause the warmed idle RPM's to go from 638-725. And that was recorded at .3 of a second interval. But that was before we got higher temperatures here. I will plug in the laptop consult and see what changed with the higher summer temperatures.

Do these sensor's ever get dirty or corroded enough to affect its job?

If so would it be ideal to replace the coolant temperature sensor(s*) and oil pressure sensors?

*TCS has an extra sensor for the coolant.

[Q45tech]

Obviously you misread: it is 1 DEGREE FOR EVERY 5Fto a maximum of 5 degrees total of retard below the normal amount if coolant gets to 220F.

Until I replaced my radiator with a larger [15%] coolant capacity unit fillled with 75% water in summer,I had to trick ecu into thinking coolant was a few degrees cooler to avoid the weirdness whenever I would stop at a redlight in Summer heat.

Now I can idle [in drive ac on] for 6-9 minutes before the software starts puking.

Many need to data long coolant temp vs time vs rpm vs ignition advance then graph..............to visualize from were the idiosyncrasies start.

[lino]

Until I replaced my radiator with a larger [15%] coolant capacity unit ...

What brand/model radiator did you get?

[maxnix]

What brand/model radiator did you get?

Custom Griffin

http://www.griffinrad.com

Used in NASCAR a lot!

[Infinitiguy19]

Obviously you misread: it is 1 DEGREE FOR EVERY 5Fto a maximum of 5 degrees total of retard below the normal amount if coolant gets to 220F.

Damn I thought I was right, there will come a day though.

And just an update I check the alternator and it bad because it can't put out the minimal required voltage at idle. With a full load (All the accesories on) at idle it maintaind ~12.7 volts.

So I will replace the alternator with a rebuilt 1991 Q45 one (The rebuilder has been in buisness for 20 years and has tons of custormers). replace all belts and replace all belt pulley bearings with the ones I got from Keith (Texas Oil).

And fix the stupid exhaust leak. And after all that this b**** better be quiet.

[Epod]

Please keep us posted on whether the alternator helps your stumbling issue.

[SleepinTXQ45]

Obviously you misread: it is 1 DEGREE FOR EVERY 5Fto a maximum of 5 degrees total of retard below the normal amount if coolant gets to 220F.

Until I replaced my radiator with a larger [15%] coolant capacity unit fillled with 75% water in summer,I had to trick ecu into thinking coolant was a few degrees cooler to avoid the weirdness whenever I would stop at a redlight in Summer heat.

Now I can idle [in drive ac on] for 6-9 minutes before the software starts puking.

Many need to data long coolant temp vs time vs rpm vs ignition advance then graph..............to visualize from were the idiosyncrasies start.

wow, right on, even if my car sits in the sun all day & start it up, its somewhat find till the stop & go traffic of S.A. comes along & it wants do do crazy things. die out & ping like a SOB

i finally get home & put my probes in it & .... ofcourse no problems crazy ..... only when it gets really hot from sitting in traffic for a hour or so....ahhh

[maxnix]

wow, right on, even if my car sits in the sun all day & start it up, its somewhat find till the stop & go traffic of S.A. comes along & it wants do do crazy things. die out & ping like a SOB

So what is the condition of your cooling system and what have you done to maintain it? Pretty marginal if compromised in the least.

[elwesso]

seems weird that the car would run better when its hot, most Q owners report exactly the opposite...

what is your typical driving cycle?

[Q45tech]

Occurred to me that many old Q have old thermostats which take a long time to warm up prolonging the misery until well after what most are use to. Some may never warm up unless hot outside.

Important we have accurate coolant temp day vs ambient vs time since starting [minutes seconds].

[bgerner12]

Probably a long-shot but are you running cold plugs?

Also, with every other car I've owned I've found they run worse withplatinum plugs. Seems Infinity calls for platinums in this car but I'mwondering if that's more for the prolonged replacement interval thanfor performance.

[Infinitiguy19]

I am running the OEM hot plugs (PFR5G-11) and I recently changed them 3-4 months ago if that.

Important we have accurate coolant temp day vs ambient vs time since starting [minutes seconds].

I always let mine warm up for 5 min in the summer or until it reaches the middle (Yes I know the coolant temp gauge is not accurate) and I let it warm up in the winter of course.

But I will get you the ambient temp VS coolant temp VS time tomorrow to see if it makes a difference.

Would you be able to tell how old (Good) the thermostat is with above comparison?

[goody90q45]

Doesn't your consult program monitor engine temp? On a summer morning it should warm up to about 179* within 4-5 minutes. IIRC the temp gauge in the speedo cluster points to 3 oclock at about 160* and does not rise any further as the engine warms to operating temperature. If it's taking much longer the thermostat is failed open and depending on driving conditions you may not get to 179*.

[bgerner12]

If you do find a solution for this issue, please let me know as mine runs considerably better whenit's warmer out also. It's especially noticeable when the throttle is just off idle - the rpms jumparound like the ecu is confused.

I'd also be interested in learning if replacing the alternator has any effect. My expectation isthat it won't.

[Q451990]

Would you be able to tell how old (Good) the thermostat is with above comparison?

Only if you knew the warm-up time at a certain ambient temperature with a known good (new) one.

Heath

[Q45tech]

Without counting the exact number and time of injector openings?Say 1000 rpms average [4,000 squirts] x 5 minutes 20k squirts roughly 0.125 gallons of gasoline creating about 15,000 BTU of heat.

10 quarts of coolant [5 of which is inside thermostat part of system] so 10 lbs of water/coolant.

You now have every thing you need to calculate except the ratios of heat out exhaust, and specific heat of aluminum. and mass of engine..

~~ about 17F rise starting at 77F per minute

[Infinitiguy19]

If you do find a solution for this issue, please let me know as mine runs considerably better whenit's warmer out also. It's especially noticeable when the throttle is just off idle - the rpms jumparound like the ecu is confused.

I'd also be interested in learning if replacing the alternator has any effect. My expectation isthat it won't.

Weird thing is the idle just got way better on mine, not perfect but better than before. WHich leads me to belive driving it hard and doing 2nd gear 70MPH runs must have helped because those were the last thing I did.

OK from what I have learned from Q45techs posts (I would't have read them if it wasn't for Brian AKA Maxnix because he kinda convinced me into reading them). Its usually:

clogged injectors--BG flush costs $100--ISO-HEET and Redline S1 help

Bad or dirty MAF --Test MAF voltage with multimeter or Nissan consult or equivilent--See this: http://www.q45.org/maf.html

possibly TPS sensor--Check TPS voltage in the service manual

And dirty intake path--requires a plenum job to do a complete one, But most can just clean the throttle body, AAC valve and EGR valve.

No doubt I missed some but thats should get you started.

Thanks to the rest of you for the help.

[Infinitiguy19]

Well today after puting in a bottle of ISO-Heet and cleaning the MAF with non chlorinated brake parts cleaner~Electrical parts cleaner, The car ran a tiny little bit better. I then remmbered what Kiven22 (Sorry if I got your name wrong) well he said that if your un-connect the MAF sensor plug the car will still run at idle. I did that for the second time and the check engine light came one (MAF code duh) and the car would'nt rev above 2000 RPMs...Cool.

So I will BG flush the injectors and see what happens.

This link also helped me alot: zerothread/40749
Modified by Paul Wall at 6:51 PM 9/7/2009

[Infinitiguy19]

Yet another update (I feel like Berner AKA Unknown007):

I hooked up the laptop Consult to my car yet again and I got 2 codes: MAF sensor and CAS.

I of couse got the MAF sensor code because I unplugged it to see if there was a change (no).

But the CAS code has me stumped and suprised.

But also in the active test part of the OBD scan tech. I turned on the VVT solinoids on at idle and i could hear what sounded like valve clatter. Metal to metal would be closer I guess.

But I know the VVT solinoids don't normally operate at idle. But I could only the drivers side made that kind of noise, I really did'nt get anything out of the passenger side one. But I am unsure if it was working or not.

So is the above normal?

[Infinitiguy19]

OK I did a few tests today:

I noticed the car will idle with out a MAF sensor at warm idle on the 1994 Q45 ECU (California). The car will NOT idle with a 1993 Q45 ECU (Federal) with the MAF sensor unplugged.

Is the 1993 Q45 ECU defective?

I could not connect to it when the car is running, but I can connect to it when the engine is off and the key is at ACC.

It also said the MAF voltage was 0.8 when the key was in ACC. While the 1994 Q45 ECU said it was .20-.22 volts.

Also I think the 1994 Q45 ECU (California) does a better job at maintaining idle.

Does the 1994 Q45 ECU have far different maps than the 1993 Q45 ECU?

Or is it because one is California and one is Federal? ------------------------------------------------------------------------------------------------

I also did another test in the FSM that said if you disconnect the connector going to the AAC valve the idle will drop. that did NOT happen in my case and the AAC valve Ohm's at about 10 Ohm's. And I can see on my laptop Consult that the AAC valve does move (But I assume its just the ECU commanding it to do so). I also cleaned the AAC valve as best as I could but it was still black in the end after TWO brake parts cleaner bottles. ------------------------------------------------------------------------------------------------

I also checked for intake leaks and there were none. I pinched the blow by hose and the idle dropped a little. The idle would go up if there was a leak.

I also checked for a vacuum leak by disconnecting and plugging the carbon canister purge line hose. And the idle stayed the same after a short drive. ------------------------------------------------------------------------------------------------

I also cleaned up the Injector, Knock Sensor, MAF connectors as well as one ground I found. ------------------------------------------------------------------------------------------------

So a little maintenance history recap:

Under plenum work done in 2005: Injectors, Harness and rails along with all the hoses replace, Although I do have some extras in a box which I am confused about. This was also done a trusted shop by the previous owner so I doubt they cleaned the intake and EGR.

Redline S1 every 3000 Mile oil change

93 Octane (According to the premium gas stations) I go to: Shell, Irving (My favorite), Hess and Cumberland farms.

Power steering pump replaced 200X

Spark plugs replaced a couple of months ago

MAF was re-soldered and cleaned

No fuel pump noise, But I never tested the fuel pressure. But I did the grounding test and there was not any noticeable difference (Thanks Mike).

All electrical connections cleaned (MAF, Injector harness, CAS, Knock Sensor, AAC valve, ECU, TCU.

But I do think the O2 sensor need to be replaced since they some what sluggish. ------------------------------------------------------------------------------------------------

So my symptoms:

Not going above 6775 RPMs

Doesn't start on the first turn over (battery was replaced and connections were cleaned).

Kind of bad idle when first starting up and after warmup.

Idle is worst when EGR stops functioning at 1500-1600 RPMs (according to OBD Scan Tech Nissan) (it shakes the worst at that RPM range).

------------------------------------------------------------------------------------------------My theory:

Could it be a bad EGR valve?

Plugged Injectors?

Fuel Pump?
Modified by Paul Wall at 2:37 PM 9/15/2009

[bgerner12]

Have you tried monitoring the ignition timing to see if it's correct at idleand advancing with rpm?

Since the purpose of the EGR system is to lower combustion temp it wouldseem that if it's not working right, perhaps the ECU is detecting this andretarding the ignition to prevent pinging? That might also be consistentwith running better when it's cooler outside. The cooler intake air wouldlikely allow the ECU to advance the timing a bit. Just a wag on my part.

The EGR port in the intake manifold on my wife's Jag was plugged up solidlast year. It ran a lot better after I cleaned it out.

[Infinitiguy19]

Important we have accurate coolant temp day vs ambient vs time since starting [minutes seconds].

Time: 12:53:52.807 Coolant temperature: 72* F

Time: 01:05:40.261 Coolant temperature: 178* F

Ambient Temperature: ~80

Have you tried monitoring the ignition timing to see if it's correct at idle and advancing with rpm?

Since the purpose of the EGR system is to lower combustion temp it would seem that if it's not working right, perhaps the ECU is detecting this and retarding the ignition to prevent pinging? That might also be consistent with running better when it's cooler outside. The cooler intake air would likely allow the ECU to advance the timing a bit. Just a wag on my part.

The EGR port in the intake manifold on my wife's Jag was plugged up solid last year. It ran a lot better after I cleaned it out.

I never did look at the EGR port on the plenum when I cleaned the EGR, I will take it off and see.

When I said the underplenum work was done at a shop. I assume they never cleaned the intake, EGR and AAC valve. I could and hope I am wrong though.

I am not sure on the timing but I can tell you OBD Scan Tech Nissan reports 45* at warmed idle

RPM: 600-650 Coolant Temperature: 185 TPS:.44 MAF: 1.20-1.24 AAC: 10 LH O2 sensor: 0.69-0.3 LH Injector: 2.0--2.17 Battery: 13.76-13.84 Duty Cycle LH: 1 O2 sensor RH: 0.03-0.09 Duty Cycle RH: 0 RH Injector: Forgot to record

Sometimes it idles at: 738-750

Coolant Temperature: 185 TPS:.44 MAF: 1.23-1.25 AAC: 10 LH O2 sensor: 0.65-0.84 LH Injector: 2.0--2.08 Battery: 13.76-13.84 Duty Cycle LH: 1 O2 sensor RH: 0.15-0.77 Duty Cycle RH: 1 RH Injector: 2.1-2.9

I have a ton of Consult logs but Google Docs and Windows Live documents don't allow me to post.

I can how ever email them or host them in a rar file for anyone who wished to review them.

[mtzgr777]

That's almost the complete opposite of mine. I'm not going to go into the specifics like Paul has, but my Q seems to run A LOT better in the cooler weather with the ambient temp between 40*F and 60*F. Strange.

[Infinitiguy19]

I'm not going to go into the specifics like Paul has

Sometimes to solve a problem you need spesifics.

Tech I could really use you help right now, I appreciate all the help you have given me so far but something tell me that you know the answer as usual.

A couple more tests:

Replaced TCS relays because 1 or more were bad (1991 Q45 part car FTMFW).

Grounded fuel pump and the car ran rich (Thanks to OBD scan tech) (Mike or anyone interested call me up or email me and I will show you how to unleash the power of OBD Scan tech Nissan) But no improvement well not much any way.

Tested the O2 sensors with the method above and they show lean and rich on either bank and do alternate So thats good.

Does the EGR system have to do anything with the car starting?

I plan to test for injector leaks.

I also think I am ready to move up to big biy work and clean the plenum and Throttle Body.

[bgerner12]

Just throwing out ideas and I'm not as familiar with the Q45 as I am withmy other cars (yet) but does the Q have an intake air temp sensor and ifyes, are you getting any readings off that with your diag tool?

Since the problem seems temperature related and results in the oppositebehavior of what would be normal (normal = runs better when coolambient), perhaps some temp sensor is telling the ECU that the ambientis warmer than it really is. If true, that should result in harder starting thecooler it is out (rich mixture for cold start not kicking in). I could see wherethat might confuse the ECU in that the sensor would always be telling it touse settings that would be correct for warmer ambient temps.

[Infinitiguy19]

There is'nt an intake temprature sensor on the G50 Q45 that I am aware of. But I do know that the ECU goes by the signal from the HVAC control unit, When you turn the A/C on the ECU thinks that its cold out.

And I am sorry I think I should change the title to this topic because its pretty random I think. There is definatly a differnce between the 1994 and 1993 Q45 ECU though.

I'm going to go out on a limp and say "weak starter" because it does'nt start up right away, but I am just throwing ideas out there.

If you would'nt mind I can meet up with you and see what you think?

I will even bring my Consult to make it worth you while.