Truck starts harder after being plugged in

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Buddy’s 2002 Toyota Tundra 4.7. He’s using a lower radiator hose heater to help with cold starts this winter. But the truck has been very hard to start after being plugged in. He says it took 45 seconds of on/off cranking to start today. Water temp is just off the cold mark during hard starts. Truck starts fine when not plugged in.

Seems like the heater is doing something counterproductive. Any ideas what is going on? Web seems void of answers on this issue.

Here’s what he’s using: https://north40.com/kats-heaters-lower-r...AiABEgKy7vD_BwE
 
PCM uses the coolant temp sensor to adjust fuel mixture so may be too lean to start normally. Needs a richer mixture to start when cold
 
Dense air with lean fuel. He's bypassing fuel enrichment. He has a warm radiator/Coolant-temp-sensor and a cold engine block.

He'd have more success with a sump heater if his goal is engine protection. Those engines reach operating temperature within a couple of miles.
 
Originally Posted By: jsfalls
PCM uses the coolant temp sensor to adjust fuel mixture so may be too lean to start normally. Needs a richer mixture to start when cold


Bingo. I'd try an oil pan heater, my bet is he will probably eliminate the problem.
 
Originally Posted By: jsfalls
PCM uses the coolant temp sensor to adjust fuel mixture so may be too lean to start normally. Needs a richer mixture to start when cold


Yup
 
Originally Posted By: andyd
How cold is the temp that you feel outside heat is needed to start the truck?
I like to know also -20F might be the temp I'd start looking to plug in. I have started at near -30F on a few vehicles not plugged in overnight slow but ok.
 
I'll pull a Merk and say he got his plug backwards, reversing the polarity, causing the block heater to cool things off.
wink.gif


In all seriousness, the oil pan heater might be a good suggestion. These little "problems" have started to manifest themselves here over the past number of years, too.
 
I had the same problem about 20 years ago with a 1987 Ranger 2.9L EFI. I put in a 1200 or 1500 watt tank heater that hooked to the block using a fitting on the side of the engine block and one of the heater hoses, used convection to heat the block. It worked well, but when it got around zero what would happen is the ECM was reading a higher coolant temperature and using a fuel mixture for a warmer start.

It acted up and started hard.

Never did try to find away around it, but I was going to wire a switch that would bypass the coolant temperature sensor and hook to a resistor that was equal to the resistance of a coolant temperature reading at zero.
 
It makes perfect sense to me. Plug in htr is fooling ECU into thinking the engine is warm. Wabbout a toggle switch to open lead to ECU ? Or an electric thermo time switch Set it for 10 seconds of open before normalizing. Kinda sorta what the earlier 528e s used in the cold start stuff.
 
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