Air Temp makes noticeable difference in engine performance?

[wolf]

This is concerning my 1997 land Rover discovery I (non-advanced evap system [i.e., early 1997]) 4.00 liter GEMS engine;

I have noticed this interesting phenomenon a lot lately as we are moving into Spring weather: i.e., at night - its cool out (not freezing - about 40 degrees farenheit) and the engine runs noticeably better (I mean more power (i.e., felt torque out of the hole), better acceleration, better gas mileage, smoother, etc.) than in the day time when it can be warmer (but not a lot warmer right now). Put it this way - its almost like having two different engines - the night-time one is great and a pleasure to drive - the day-time engine is still fun but it feels like its dragging a few grand pianos behind it in comparrison.

What would cause this in the sensor array? MAF? O2's? Intake air temp sensor (I have two of these, one brand new and one old, I have swapped them back and forth with no noticeable effect)? Engine coolant temp? The real stumper for me is that a lot of the sensors are new or relatively new so I am stumped! There are no codes or pending DTC's in the system.

Once the engine is warmed up, according to both my LR instrument display and the DashDaq array I have (it runs right off the ecu) - engine temp is about the same in the day and the night. So the issue seems more related to the air temp the engine is drawing in than the running temp of the engine itself. This made me think MAF but the MAF is in great shape with no codes (it has been cleaned on a regular basis with MAF sensor cleaner as I use the oil-filled K&N air filter).

I have my eye on doing a complete injector replacement with either Ford or Bosch (Mark Adams of Tornado Systems in the UK reccommends Bosch but they also require a different chip [at least, the Bosch ones he suggests]).

anyway - Joey? Disco Mike? any ideas anyone?

Wolf

 

[Disco Mike]

I have never heard of this before, especially if you are not getting any codes. How many miles on the truck, what octane and are your electric fans running?

 

[RDearing]

I would look at OBDII long term fuel trim. even if the fuel trim has not reached its self adaptation limit (setting code) performance can suffer. Most good runners have a long term readings 0-5%. also if your fuel has alot to do with poor performance.
RD

 

[greg409]

In regards to your MAF, when air is denser, (cold or to some extent, humid) it has more ability to absorb/hold heat.

As it passes over the sensor, it will draw more heat off the sensor, lowering it's resistance.

This lowered resistance signals the ECU one of two things, either the rpm (flow) is greater, or that the density or btu potential is greater.

Either way, the ECU knows to maintain the 14.6 to 1 fuel ratio, so it lengthens the pulse time for the injectors.

The result is more horsepower. (sometimes it's noticeable)

That's the theory also behind cold air kits.

In the '60's we would dry-ice the fuel lines and do cold air on our drag cars to help increase the density.

luck,greg

 

[alzerom]

Mine runs better after a rain which is humidity related. Also, mechanics and expert shoppers recommend not to test drive a new car after rain because of the humidity. Accelleration, metal squeaks and interior noises improve. Just a suggestion.

 

[wolf]

In regards to your MAF, when air is denser, (cold or to some extent, humid) it has more ability to absorb/hold heat.

As it passes over the sensor, it will draw more heat off the sensor, lowering it's resistance.

This lowered resistance signals the ECU one of two things, either the rpm (flow) is greater, or that the density or btu potential is greater.

Either way, the ECU knows to maintain the 14.6 to 1 fuel ratio, so it lengthens the pulse time for the injectors.

The result is more horsepower. (sometimes it's noticeable)

That's the theory also behind cold air kits.

In the '60's we would dry-ice the fuel lines and do cold air on our drag cars to help increase the density.

luck,greg

Hey Greg;

I don't think you are too far off the mark here - and that's what has me wanting to fool around with injectors as mine are extremely 'long in the tooth' so to speak. Any of the other sensors that could have been 'marginal' (i.e., old - sluggish but not bad enough to throw a code) in their response to these temp and fueling change requirements have been replaced.

Like I said it is a fascinating phenomenon and I want to hound it down so I will keep you all informed when I have something worthwhile to report.

Wolf

 

[wolf]

I have never heard of this before, especially if you are not getting any codes. How many miles on the truck, what octane and are your electric fans running?

Hi Disco Mike;

I am using Chevron 94 Octane with Lucas Fuel additive (upper cylinder lube); good question on those fans - I will check them out; mileage = just over 140 K miles. Compression is almost too high though - i.e, around 185 psi to 189 psi throughout with #6 cylinder a bit softer owing to exhaust valve sticking. The compression issue had me thinking - well, its awfully high for an engine with that mileage so that most likely is owing to carbon build up in the combustion chamber area. This also had me wondering if the combustion area has been reduced in volume then maybe (just hear me out on this) oxy rich air (i.e., when it is cooler out) will give me better perf than less oxy-rich air that you see in the warmer daytime? Just a wild speculation though. The fact is that this V8 has not seen enough highway/freeway miles - not by a long shot. BTW - the SeaFoam routine has had no noticeable effect on what I suspect is heavy carboning.

Wolf

 

[wolf]

I would look at OBDII long term fuel trim. even if the fuel trim has not reached its self adaptation limit (setting code) performance can suffer. Most good runners have a long term readings 0-5%. also if your fuel has alot to do with poor performance.
RD

I have the gear to do this check so why not? Thanks for the suggestion.

Wolf

 

[greg409]

Wolf, you might enjoy reading about injectors & the extensive research out there, (you may have already), It amazes me how many people throw a set of hi-flow injectors in their engines thinking they'll achieve more horsepower.

That fact is, our lucas rated at 19.2 lbs/hr, are more than sufficient to produce 300hp

My calcs came to 15.6 lbs/hr at a duty cycle of around 80% for our 180hp motors.

Injectors do wear out, although they're more likely to stick, clog, leak from sediment buildup,

As you may already know, our's are hi-impedence (14-18ohm) coils, so you can't use low- impedence(4-9 ohm) injectors.

I installed the fords,19 lbs/hr (70k mi.) which all came from the same car, since it seemed a popular swap, but my lucas were probably just dirty.

I was very rich on startup, rich smelling idle, black exhaust pipe, but I believe the lucas were just dirty ( they also didn't have inlet filters, tho' I dont know if they're suppose to, being single pintle design.)

Luck,greg

 

[wolf]

Wolf, you might enjoy reading about injectors & the extensive research out there, (you may have already), It amazes me how many people throw a set of hi-flow injectors in their engines thinking they'll achieve more horsepower.

That fact is, our lucas rated at 19.2 lbs/hr, are more than sufficient to produce 300hp

My calcs came to 15.6 lbs/hr at a duty cycle of around 80% for our 180hp motors.

Injectors do wear out, although they're more likely to stick, clog, leak from sediment buildup,

As you may already know, our's are hi-impedence (14-18ohm) coils, so you can't use low- impedence(4-9 ohm) injectors.

I installed the fords,19 lbs/hr (70k mi.) which all came from the same car, since it seemed a popular swap, but my lucas were probably just dirty.

I was very rich on startup, rich smelling idle, black exhaust pipe, but I believe the lucas were just dirty ( they also didn't have inlet filters, tho' I dont know if they're suppose to, being single pintle design.)

Luck,greg

Hey Greg;

Pretty much the same story from Mark Adams of Tornado Systems UK - i.e., old Lucas injectors burn awfully rich and, of course, that would be my issue too.

Wolf