7.3 very slow when cold

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Nov 20, 2014 | 07:13 AM

#16

BoKnowsDiesel

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Joined: May 2014

Posts: 243

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From: Central Ohio

Right, but they are still going to raise the fuel trim when the engine is cold, to try and get it to normal operating temperature.

Nov 20, 2014 | 07:23 AM

#17

jroehl

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Joined: Apr 2004

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From: Lafayette, IN

Quote:

Originally Posted by Nothing Special

Rich / lean mixture isn't at all the same in a diesel as a gas engine. Gassers need the mixture to be prety close to stoichiometric (perfect mix to burn all the fuel using all the oxygen). So gassers adjust power by throttling the amount of air that goes in and then putting the right amount of fuel in to use all the air. If a gassers computer wanted to limit power it would do it by limiting how far the throttle was opened.

You've got that backwards. In a gasser, the "gas" pedal is wired to the throttle body, which controls the amount of airflow. A sensor on that tells the computer the position of the throttle, then the computer checks the oxygen sensors and determines how much gas to throw at the engine, changing that amount by changing how long it opens the injectors. The computer doesn't control the throttle at all, except for at idle through the Idle Air Control (in Fords, anyway). Once you're driving, your foot controls the throttle.

Jason

Nov 20, 2014 | 11:49 AM

#18

Nothing Special

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Joined: Feb 2013

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From: Roseville, MN

Quote:

Originally Posted by BoKnowsDiesel

Right, but they are still going to raise the fuel trim when the engine is cold, to try and get it to normal operating temperature.

That may be. I'm not at all familiar with diesels with catalytic converters. But this is a '95 so it doesn't have a cat. And as you said in your first post, that is going to be very different.

Quote:

Originally Posted by jroehl

You are misunderstanding me. Yes, the throttle controls power in a gas engine, and it does it by controlling air flow. That's what I said.

But no, the "gas" pedal doesn't connect to the throttle, at least on computer controlled gas engines where the computer can significantly limit the engines power output. For the computer to be able to limit a gas engine's power output it has to control the air flow (remember, that's how a gas engines power output is controlled). So newer gas engines are drive-by-wire, where the "gas" pedal is just connected to a variable resistor that sends an electrical signal to the computer which takes that into consideration as it decides how much to open the throttle, which it does using a stepper motor or some other sort of actuator.

Our vintage of trucks don't have this of course, they actually have throttle cables (one of the reasons I no longer own a Super Duty). But the computers can't significantly limit power output during warmup on them either.

Nov 23, 2014 | 09:24 PM

#19

Dutter 2

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Joined: Sep 2013

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wow i missed alot being gone, and all very good inputs that make sense. Now as far as my computer tryn to get my truck to warm up quicker i dont see that. This thing takes a good 5 miles to even pick up the temp needle and its not a cable throttle it works off of a switch. Now my glow plugs were hooked up manually by a button so that they are only used to start. Should i hook that up back to OEM ? cus i know there suppose to stay on running. The truck had this when i got it. And sure ill try putting some more fuel cleaner in it.

Nov 24, 2014 | 11:55 AM

#20

Nothing Special

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Joined: Feb 2013

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From: Roseville, MN

Quote:

Originally Posted by Dutter 2

I doubt the glow plugs make much difference once the engine is running. It might be a good idea to return the wiring to stock, but I don't think it will affect your warm-up time at all.