Proper way to start 92 7.3 IDI Motor

[icanfixall]

The best way of testing the fast idle solenoid is to jumper it from the battery. A lot of times the solenoid works but its not adjusted properly. A 1/4 inch socket will make any neded adjustments. I have also found that mine will sometimes require an adjustment to the bracket when I change out the pumps. The mounting bolt holes in the bracket have a slightly larger hole in them than the bolts are. So you can loosen the bracket and move it forwards or backwards on the pump.

 

[RANOVRU]

As mentioned its a solenoid that when activated pushes a plunger against the throttle blade to increase the RPMs.

Warm..

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Cold...

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There is a plug on the back of the solenoid as you can see in this pic. I would imagine you could start troubleshooting there if it doesnt seem to be working.

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[icanfixall]

Those are some great pictures of whats being discussd here. Nothing like actually seeing what we are refering to.. thanks...

 

[RANOVRU]

Those are some great pictures of whats being discussd here. Nothing like actually seeing what we are refering to.. thanks...

No problem.

I love photography and taking pictures. And its a nice asset if youre a auto freak. Ive learned so much from all over the net on different forums from helpful people that it only seems right to help when I can, even though Im a novice to the diesel seen.

If Im familliar with the subject I have no problem going out to the truck to snap a few shots. I actually enjoy it.

 

[gdhillon]

Feathering the throttle while cranking doesn't help it start? Mine has difficulty in cold so I usually father it to give her some help, I thought holding throttle open when starting can risk flooding?

 

[SkipBurney]

Feathering the throttle while cranking doesn't help it start? Mine has difficulty in cold so I usually father it to give her some help, I thought holding throttle open when starting can risk flooding?

Thats what I thought too if I hold the throttle down while it`s cranking it is just pumping a lot of raw fuel into the cylinder and thats the last thing I need

 

[DragRag]

Flood a diesel? Never happened to me before. Is that even possible? Some how I kind of doubt it, some onechimein and tell me I'm wrong if it is.

 

[icanfixall]

Nope... Can't really flood a diesel like you can a gasser. About all that can happen to a diesel is hydrolock it from water or coolant in the cylinders. We only have about 42 thousands clearance between the piston tops and the cylinder head. Actually the gasket makes up the clearance and without it the pistons will hit big time .... Because they raise up as much as 31 thousands out of the cylinders....

 

[G. Mann]

The term "Flooding a diesel" gives kind of the wrong mental picture. In order for a diesel engine to start it needs to raise the temperature of the compression chamber to the flash point of diesel fuel in the air/fuel charge that is there.

The desired way to do that is with the high compression ratio of the engine. Many things can influence "if and how" that happens.
1. Cranking speed. Slow cranking speed doesn't squeeze the air molecules together enough to heat them up. Low batteries, cold oil, loose clearances in a worn engine, are a few factors.
2. Air / Fuel mix. If more fuel is introduced into the mix, the "wetter" mixture takes a higher temperature to reach the flash point of the fuel. Ideal Stochiometric Ratio for starting is pretty lean when compared to gasoline engines.
3. Use of Ether [AKA death gas for diesels] simply introduces a material that has a lower flash point temperature than cold diesel droplets which by it's ignition, raises the ambient temp of the combustion chamber so that the next charge of diesel droplet mist will be ignited. Hot air from a hair dryer or heat gun will have the same effect, as does engine preheat.
4. Fast idle is intended to just bump up the idle speed so you don't have to set with your foot on the throttle to "warm up the engine" as a convenience item. By rotating faster [slightly] the compression raises combustion temp of the compressed air which fires off the fuel.. etc etc etc..

So, pumping more raw fuel into the engine on startup cranking does not raise your chances of starting.. presuming fuel is being supplied as designed. [no air leaks and a tight fuel system, properly working injection pump and nozzles].

 

[OLDBULL8]

My 92 F450, 7.3, has a non functioning fast idle. What exactly tells it to activate?

Is it tied to engine temp sensor? How and where?

Is there a test to see if the fast idle solenoid works by it's self?

How do you troubleshoot it?

Thanks...

G Mann wrote:

The term "Flooding a diesel" gives kind of the wrong mental picture. In order for a diesel engine to start it needs to raise the temperature of the compression chamber to the flash point of diesel fuel in the air/fuel charge that is there.

The desired way to do that is with the high compression ratio of the engine. Many things can influence "if and how" that happens.
1. Cranking speed. Slow cranking speed doesn't squeeze the air molecules together enough to heat them up. Low batteries, cold oil, loose clearances in a worn engine, are a few factors.
2. Air / Fuel mix. If more fuel is introduced into the mix, the "wetter" mixture takes a higher temperature to reach the flash point of the fuel. Ideal Stochiometric Ratio for starting is pretty lean when compared to gasoline engines.
3. Use of Ether [AKA death gas for diesels] simply introduces a material that has a lower flash point temperature than cold diesel droplets which by it's ignition, raises the ambient temp of the combustion chamber so that the next charge of diesel droplet mist will be ignited. Hot air from a hair dryer or heat gun will have the same effect, as does engine preheat.
4. Fast idle is intended to just bump up the idle speed so you don't have to set with your foot on the throttle to "warm up the engine" as a convenience item. By rotating faster [slightly] the compression raises combustion temp of the compressed air which fires off the fuel.. etc etc etc..

So, pumping more raw fuel into the engine on startup cranking does not raise your chances of starting.. presuming fuel is being supplied as designed. [no air leaks and a tight fuel system, properly working injection pump and nozzles

Quite a writeup.

 

[gdhillon]

So, in theory if your high idle doesn't work you can just sit in the truck with the go pedal down?
And giving her mire throttle won't add just more fuel but more fuel air mixture?

 

[Wyreth]

So, in theory if your high idle doesn't work you can just sit in the truck with the go pedal down?
And giving her mire throttle won't add just more fuel but more fuel air mixture?

The high idle is really only for after the engine is started. The faster the engine spins, the easier it is for the cylinders to fire. When your engine is cold that's important.

The throttle just ads fuel. As far as air goes, a diesel is always WOT. Giving her more throttle just richens the mix. As G. Mann posted, that makes it a little harder to ignite.

Now granted I am a Vegan, so I don't really understand what this whole "cold start" thing is, but the only time I ever opened the throttle while cranking was when I was having air intrusion problems and couldn't get fuel TO the IP on start.

 

[gdhillon]

Hmm interesting

 

[gdhillon]

The term "Flooding a diesel" gives kind of the wrong mental picture. In order for a diesel engine to start it needs to raise the temperature of the compression chamber to the flash point of diesel fuel in the air/fuel charge that is there.

The desired way to do that is with the high compression ratio of the engine. Many things can influence "if and how" that happens.
1. Cranking speed. Slow cranking speed doesn't squeeze the air molecules together enough to heat them up. Low batteries, cold oil, loose clearances in a worn engine, are a few factors.
2. Air / Fuel mix. If more fuel is introduced into the mix, the "wetter" mixture takes a higher temperature to reach the flash point of the fuel. Ideal Stochiometric Ratio for starting is pretty lean when compared to gasoline engines.
3. Use of Ether [AKA death gas for diesels] simply introduces a material that has a lower flash point temperature than cold diesel droplets which by it's ignition, raises the ambient temp of the combustion chamber so that the next charge of diesel droplet mist will be ignited. Hot air from a hair dryer or heat gun will have the same effect, as does engine preheat.
4. Fast idle is intended to just bump up the idle speed so you don't have to set with your foot on the throttle to "warm up the engine" as a convenience item. By rotating faster [slightly] the compression raises combustion temp of the compressed air which fires off the fuel.. etc etc etc..

So, pumping more raw fuel into the engine on startup cranking does not raise your chances of starting.. presuming fuel is being supplied as designed. [no air leaks and a tight fuel system, properly working injection pump and nozzles].[/QUOTE

Pointing a hair dryer into intake will help with starting then]?

 

[Wyreth]

Pointing a hair dryer into intake will help with starting then?

Yes, in fact, somewhere there is a video of a member doing exactly that.
(I'd try and find it, but the search on this forum doth sucketh)