Cold--lotsa power. Crisp acceleration.
After 20 min on the freeway -- not so fast anymore. Idle a little rough also. Like a little shake at idle on the throttle foot. Also doesn't seem to really wanna go.
New: fuel pump/reg; mass flow sensor, plugs, dealer 90k service.
Dealer and private tech -- no joy.
Normal temps, no diagnostics.
94 Q45 90K.
Diagnostic puzzleQ45 '94
Based on temp gauge, perfectly normal, just below 1/2 travel. Ditto based on look, feel, and smell, i.e. no hints of hot.
Your thoughts are that ECU retards timing if eng is hot? How hot? Is the sensor the same as the sensor that drives the temp gauge?
When the car is fully warmed up there is a definite sag in acceleration at tip in. Not a stall or misfire, just a sag.
Your thoughts are that ECU retards timing if eng is hot? How hot? Is the sensor the same as the sensor that drives the temp gauge?
When the car is fully warmed up there is a definite sag in acceleration at tip in. Not a stall or misfire, just a sag.
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Q45tech
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1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
The interior temp gauge runs off a seperate sensor and is grossly inaccurate and time damped to not show variations when centered at 3 o'clock.
195F as seen by ecu coolant temp sensor is the point of first reduction.
Generally a Q with a 4-6 year old radiator or a 3-4 year old thermostat and any dirt or trash between the condenser and rad will not be operating at the optimum temperature of 176F at cruise.
The AC control head also signals ecu that the AC is on [part of the WOT AC cutoff bidirectional line] this primes the ECU for Summer action. Generally running the AC raises the coolant by 6-10F [182-186F] so if anything is not perfect you can get to 195F.
Requires a Consult and usually more smarts than the average technican to get you out of the acceleration sag.I love to fix problems no one else in the country can.....unfortunately I only do so with the understanding of Carte Blanc........I say you change this or that and you agree in advance even if you have to take a third house mortgage.
Need to graph the ignition advance vs load and make sure that you don't exceed 15 BTDC at idle as the knock sensors can be to sensitive. You need to graph coolant temp vs ambient at cruise then pull off and log the minutes/seconds per 1F degree rise do you have 2,3,4,5 minutes before critical temp is reached!
After all the engine didn't do it new so things are not as new and need to be returned to as new!
195F as seen by ecu coolant temp sensor is the point of first reduction.
Generally a Q with a 4-6 year old radiator or a 3-4 year old thermostat and any dirt or trash between the condenser and rad will not be operating at the optimum temperature of 176F at cruise.
The AC control head also signals ecu that the AC is on [part of the WOT AC cutoff bidirectional line] this primes the ECU for Summer action. Generally running the AC raises the coolant by 6-10F [182-186F] so if anything is not perfect you can get to 195F.
Requires a Consult and usually more smarts than the average technican to get you out of the acceleration sag.I love to fix problems no one else in the country can.....unfortunately I only do so with the understanding of Carte Blanc........I say you change this or that and you agree in advance even if you have to take a third house mortgage.
Need to graph the ignition advance vs load and make sure that you don't exceed 15 BTDC at idle as the knock sensors can be to sensitive. You need to graph coolant temp vs ambient at cruise then pull off and log the minutes/seconds per 1F degree rise do you have 2,3,4,5 minutes before critical temp is reached!
After all the engine didn't do it new so things are not as new and need to be returned to as new!
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Q45tech
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1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Also think in terms of the change over to Summer fuels [volatility changes] even though the octane still says 91 or 93 the blend can be different as something like 8F increase in ambient ingested air may require more octane ........one more point in the motor octane test.
Since I use premium all year round I am always surprised when the knocks/rattles start in June as the temps get above 80F.
Usually points out the need to clean the combustion chambers and valves to restore the 10.2 compression from the 11-11.5 the build up of crud causes.
Without a Consult graph you don't notice that the 28 degrees WOT 6600 rpm suddenly is down to 22-24 because the engine has knocked and gotten retarded.
The typical dealer tech [of yore] took the easy way out [instead of getting the customer to pay for a complete clean] he just retarded the timing to 11-12-13 degrees, the knock goes away and so does the power. But the problem is still their eventually it comes back.........worse as the reduced advance promotes build up in combustion chambers.
It takes a few hours of PAID detailed testing to arrive at what's happening from the customer comments of a power loss in Summer.
The problem is convincing the owner that they need a cooling system replacement just to drop the temp 5F.
Important to double check the cooling temp sensor's ACCURACY and how the ecu translates this to the exact temp reading.Usually easier to just replace than to spend an hour testing the old one..............but the sensor tolerance is a few degrees and every degree counts when you are running up against the 194.9999 F WALL
Can you imagine putting the sensor in water and raising the temp to 195F with a calibrated thermometer measuring the resistance to the accurate OHM then reverse engineering a graph to trim the sensor reading.
Nice to know how the coolant behaves in a WOT acceleration.Consider driving in Summer heat and pulling into a rest area, turn the car off and 10-15 minutes later the coolant is thru the roof, then accelerate in the ramp merging with a lot less power than you came in with..................just like the brake pads are hotter when you leave than they were when you came to a stop and turned the car off..........the brake fluid could be boiling as you accelerate to merge.
Since I use premium all year round I am always surprised when the knocks/rattles start in June as the temps get above 80F.
Usually points out the need to clean the combustion chambers and valves to restore the 10.2 compression from the 11-11.5 the build up of crud causes.
Without a Consult graph you don't notice that the 28 degrees WOT 6600 rpm suddenly is down to 22-24 because the engine has knocked and gotten retarded.
The typical dealer tech [of yore] took the easy way out [instead of getting the customer to pay for a complete clean] he just retarded the timing to 11-12-13 degrees, the knock goes away and so does the power. But the problem is still their eventually it comes back.........worse as the reduced advance promotes build up in combustion chambers.
It takes a few hours of PAID detailed testing to arrive at what's happening from the customer comments of a power loss in Summer.
The problem is convincing the owner that they need a cooling system replacement just to drop the temp 5F.
Important to double check the cooling temp sensor's ACCURACY and how the ecu translates this to the exact temp reading.Usually easier to just replace than to spend an hour testing the old one..............but the sensor tolerance is a few degrees and every degree counts when you are running up against the 194.9999 F WALL
Can you imagine putting the sensor in water and raising the temp to 195F with a calibrated thermometer measuring the resistance to the accurate OHM then reverse engineering a graph to trim the sensor reading.
Nice to know how the coolant behaves in a WOT acceleration.Consider driving in Summer heat and pulling into a rest area, turn the car off and 10-15 minutes later the coolant is thru the roof, then accelerate in the ramp merging with a lot less power than you came in with..................just like the brake pads are hotter when you leave than they were when you came to a stop and turned the car off..........the brake fluid could be boiling as you accelerate to merge.
Kinda illustrates the importance of going with a thinner coolant mix in summer.The raised heat capacity of a 70% water (distilled) mix ,is higher, so the heads can dump in more btu's, for a given rise in degrees in the coolant leaving the heads.
This can really help with heat spikes, due to acceleration of engine stops.
Fred...
PS: BTW our coolant recomendation for Q in summer is 70% distilled (or deionized) water+ 1 bottle redline wetter water, rest antifreeze (the old style pure <not> the pre mixed 50/50).
This can really help with heat spikes, due to acceleration of engine stops.
Fred...
PS: BTW our coolant recomendation for Q in summer is 70% distilled (or deionized) water+ 1 bottle redline wetter water, rest antifreeze (the old style pure <not> the pre mixed 50/50).
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Q45tech
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But remember the coolant temp sensor will read higher as more heat was absorbed from the heads with RRWW.........kind of a Catch 22 unless you understand the fix.Just make sure that the sensor is accurately reading the real or desired temperature to the ecu. Desired does not have to be real as long as you don't drop below 176F but it is a very fine line in trimming the sensor.
Which is better a 5F drop in head temperature or a 3F hotter coolant reading.............does the ecu have to accurately read the temperature............what would happpen if the ecu read 194F when it was in truth it was 199F..................all depends on the exact blend of gasoline and the ambient air temperature.
Afterall a 2% accuracy is 4F at 200F.
Which is better a 5F drop in head temperature or a 3F hotter coolant reading.............does the ecu have to accurately read the temperature............what would happpen if the ecu read 194F when it was in truth it was 199F..................all depends on the exact blend of gasoline and the ambient air temperature.
Afterall a 2% accuracy is 4F at 200F.
Yes, but the higher heat capacity of the thinner coolant will allow the coolant to absorb more btu's <per degree> of coolant temp rise.Which of the two factors, wins out in our favorite coolant mix, the RWW or the thiness?I am unsure, but I have a feeling the extra heat capacity has it.:ofaceEven if the RWW improves the heat pickup (which I am unconvinced, if that is really a significant effect, I like to use the RWW for it reducing water pump cavitation)Q45tech wrote:But remember the coolant temp sensor will read higher as more heat was absorbed from the heads with RRWW.........kind of a Catch 22 unless you understand the fix.
Fred...
heat transfer:
We could solve that problem or at least give a good approximation if I had the following data:
-Surface area of heads in contact with coolant.-Heat capacity and specific heat transfer constants for the aluminum heads (are they pure aluminum?)-Heat capacity of mix with will be a weigfhed average of water and AF ( neglegting the RWW as insignificant contribution)-Speed of teh flow of coolant past the head as well as thickness and lenght oif all coolant galleries.-surface area of rad.-pick a representaive speed at which air travels over radiator-time it takes for coolant to see radiator fins when coming from heads.- and...
Hmm this is getting more than I thought, I better stop before it keeps me from going to bed and I really need to go there..
Fred..:sleep
We could solve that problem or at least give a good approximation if I had the following data:
-Surface area of heads in contact with coolant.-Heat capacity and specific heat transfer constants for the aluminum heads (are they pure aluminum?)-Heat capacity of mix with will be a weigfhed average of water and AF ( neglegting the RWW as insignificant contribution)-Speed of teh flow of coolant past the head as well as thickness and lenght oif all coolant galleries.-surface area of rad.-pick a representaive speed at which air travels over radiator-time it takes for coolant to see radiator fins when coming from heads.- and...
Hmm this is getting more than I thought, I better stop before it keeps me from going to bed and I really need to go there..
Fred..:sleep
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Take my word for it water's temperature goes up as it absorbs more heat.
Your missing the point the ecu was calibrated assuming 50/50 mix, if you use RRWW and 20/80 you need to recalibrate the ecu coolant vs timing curves [hard] or recalibrate the coolant temp sensor [easy].
Another important thing to adjust or at least find out is the EXACT temperature at which the thermoswitches activate the auxillary condenser fan...............the goal being to minimize the excursions beyond 195F [as read by the ecu] while keeping 176F as the coldest coolant --- WITHOUT the knock sensors activating a retard.
This is where something like the MDM-100 comes in allowing real time coolant temp reporting.
Think summer/winter switch where a 0-10>15>20-30 ohm resistor [each car will have a different value] is added in series with sensor or shorted out [in winter]. At 176F the sensor will read 300-330 ohms.............the resistance drops as the temperature increases. Therefore a very small extra series resistance will lower the temperature the ecu sees.So you measure the resistance at 212F and graph the change down to 176F and you trim the sensor for a 4-5F error vs real.Or you get a 40 [?] ohm potentiometer and play around till you find the sweet spot.I was beating around the bush hopeing someone would come up with the solution.
Your missing the point the ecu was calibrated assuming 50/50 mix, if you use RRWW and 20/80 you need to recalibrate the ecu coolant vs timing curves [hard] or recalibrate the coolant temp sensor [easy].
Another important thing to adjust or at least find out is the EXACT temperature at which the thermoswitches activate the auxillary condenser fan...............the goal being to minimize the excursions beyond 195F [as read by the ecu] while keeping 176F as the coldest coolant --- WITHOUT the knock sensors activating a retard.
This is where something like the MDM-100 comes in allowing real time coolant temp reporting.
Think summer/winter switch where a 0-10>15>20-30 ohm resistor [each car will have a different value] is added in series with sensor or shorted out [in winter]. At 176F the sensor will read 300-330 ohms.............the resistance drops as the temperature increases. Therefore a very small extra series resistance will lower the temperature the ecu sees.So you measure the resistance at 212F and graph the change down to 176F and you trim the sensor for a 4-5F error vs real.Or you get a 40 [?] ohm potentiometer and play around till you find the sweet spot.I was beating around the bush hopeing someone would come up with the solution.
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Jeff Williams
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maxnix
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Electric Fan
The stock fan is activated by a viscous clutch. Might check this thread:http://www.nissaninfiniticlub....c+fanJeff Williams wrote:Along these lines, I was wondering, if I was to replace the stock radiator fan, bolted to the engine, and install an electric fan, with a thermostat set at 195 degrees, would I cause more trouble, than the extra HP is worth?