Intermittent Engine Load?

Hello folks,

I've got a 2012 4cyl Reg Cab with the 5pd that just turned 5000 miles. It's spent most of it's time empty hauling my fat ass back and forth to school on the freeway (I'm actually squeezing almost 30mpg out of it). During these long stretches on the freeway I've noticed that randomly the truck will act like it's had a sudden load turned on. It feels a lot like the A\C Compressor kicking in, I've got to add more throttle to maintain speed. It seems completely random other than the coolant must be up to temperature. Sometimes it doesn't do it at all, sometime it does it 4-5 times in 30 miles. It lasts anywhere from 20 seconds to a few minutes and shuts off noticeably.

I know the A\C can kick on anytime the selector is set to defrost but it does it regardless of the climate control settings. It does it with the fan to off, the temp at 9 O'Clock (not on max A\C), and the vents on dashboard so I don't think it's the A\C.

It's also not the cooling fan, I've had that removed for the last 3000 miles. An aside did you know the heater core is big enough to remove all net heat production when sitting at idle? I found that out during an unexpected warm spell and unexpected traffic jam. One of these days I'm putting in an electric fan.

Anyone felt anything like this in their machine? The two theories I've come up with are it's load on the alternator from the smog pump or the ECU is doing something to the F\A mixture for emissions and isn't masking it very well. Theories? Thoughts? Wild ass guesses?

Matt

 

I'll give this one more bump and then assume no one else has felt this. In that case I highly doubt the dealer is going to be able to track it down, guess I'll just live with it.

 

You removed your cooling fan and maintain temperature by running your heater when it gets hot?

My truck doesn't do what you describe.

/slash not \backslash

 

I keep meaning to put an electric fan in but things keep getting in the way and this works just fine for now.

 

Could it be that the engine is running hot due to lack of a fan, and the ECM backs the timing down to compensate? The factory gauge might not move right away when it starts to heat up.

 

I don't think so. At freeway speeds, anything above about 15mph actually, there is more than enough airflow to carry away excess engine heat. Normally the water pump just circulates water in the block and the stuff in the radiator is at or near ambient temperature. When the engine heats up the coolant in the block sufficiently the thermostat allows a small amount water from the radiator to circulate til the temperature goes back down. It actually wanders a few degrees all day long but you stock coolant gauge isn't sensitive (at all) enough to measure this though. With no air flow over the radiator (i.e. sitting idling) I can idle for 2-3 minutes before the radiator comes up to temperature and the gauge starts to rise. However if I haven't been moving above 10-15mph for a bit the gauge starts rising much quicker as the coolant in the radiator hasn't been able to cool down.

I had that happen when stuck in traffic the during a warm spell a month or two ago. It would cool off if I was moving faster than 10mph but start warming again within 10-20 seconds depending on how long I'd been moving. I remembered the heater core before I'd broached 250F and with the fan on hi and the windows open that's more than enough to do the job. These trucks have a big heater core! Besides it did it before I took the fan out (I originally took it out to see if the fan clutch was malfunctioning).

And Worth: Dude 33MPG? You got your dog pushing or something? I only just recently broke 30MPG and that's doing 55 with some minor driving with load (we've got a lot of long rolling hills around here).

 

Maybe it's the VVT-i adjusting valve timing to optimize power/efficiency under the driving conditions. I usually feel the switchover around 45-55 mph depending on the engine load and rpm's.

A Google search should help if you're interested in how VVT-i works.

 

Now that's an interesting theory. My speed is constantly varying between 50-65 depending on whether I'm going up or down a hill. I hadn't thought of that before. It might be confused and hunts between cam timings sometimes because the programmers who did the cam logic expected me to be running at a constant speed a little faster. I believe it happens more often when I'm fighting a strong headwind too. I've driven it so rarely at a constant 60-65 it's hard to tell. I think it might be experiment time. Thanks!