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Discussion Starter #1
Still looking around at various things, there is an array you can alter to remove the effect of the P1093 2000rpm rev limiter that can cause you a lot of grief.

I wouldn't suggest this as a "fix" for the problem, but it can improve the safety of a truck that is prone to P1093's.

It is under:

Calibration>Fuel Injection>Quantity>Engine Protection 2,3,4.

This would help you out if you were waiting to get shimmed, but perhaps would be a replacement for the shim entirely.

Since neither of our trucks 1093's, I cannot test it, but logically it makes sense, as the table mimics the behavior you feel when driving with a 1093.

You would adjust the values to max all the way up to stop the effect.
 

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We've already discussed this and played with it a bit. It is not a replacement for the shim entirely because you are still blowing off the valve and dropping fuel rail pressure until the pressure is low enough for the valve to seat again.
 

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You can eliminate the 1093 all together and not jeopardize the integrity of limp modes engine protection when it is needed during another type of failure.

If you go into engine diagnostics>DTC processing enablers and DTC MIL illumination, you can simply disable the ability for the code to even process and effect your normal engine operation.

Brandon R.
 

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All you will do in that case is elimate the MIL from being set or a code from being set. You will still get the 2000rpm limit.
 

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Doesn't the processing enable/disable function keep that code from being reported to the ecm? So stopping it from being reported would keep it out of limp mode wouldn't it?

Brandon R.
 

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Doesn't the processing enable/disable function keep that code from being reported to the ecm. So stopping it from being reported would keep it out of limp mode wouldn't it?

Brandon R.
I'd have to agree with you.
 

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Discussion Starter #7
I'd think you'd want to know if you're dumping rail pressure.

If you kill the diagnostic, you won't know if a stuck valve is causing your truck to run like crap.

P1093's can also be dirty fuel filter.
 

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The way I understand it is that if you stop it from reporting you are doing just that and nothing else. It still will go into protection mode. This has also been the experience of someone who tested just that.
 

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Ahh I see. Well in that case I'll take your word for it.
 

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When the valve pops, you loose rail psi and power....1093 code or not...you will not have any power(lay down). It is still unsafe. The best thing to do is have the MIL come on when a 1093 code is set. This warns you that there has been a problem and the truck will not go over 2000 rpm. Anytime my MIL comes on now, I assume that the truck will not go over 2000 rpm. I have tuned out the 1093 by making my tune better. My new TCM has eliminated my 1093 troubles on shifts completely. My valve is not shimmed.
 

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Why not change {B0732} so that when you DO set a P1093, you can get more than 2000 rpm out of it...? That way, it'll set a code, and a MIL, but you won't get caught with your pants down if you're in the process of passing someone when you throw a 1093. :eek:

{B0732} Limp Home Fuel Limit
When the ECM is in limp home mode, this is the maximum amount of fuel that can be injected.
Limp mode is generally entered once certain fault codes are set or engine sensors are faulty.
 

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Here's a screenshot for those too lazy to look it up :cool:
 

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I'm not sure if what I said has sunk in yet, so I'll say it again. The rail psi dumps......there is no power. The rail psi dumps....there is no power. Your pants are down....there is no power!! If you pop the valve, the rail psi dumps...you loose all your power and you are screwed. You can set the 1093 to run at 8000 rpm if you want. With no rail psi, you will have a hard time getting there. Also, with the loss of power comes some very interesting feed back from the TCM and ECM...they see your throttle input and expect the output to match....it don't because the frpsi is too low to make any kind of power. Crazy downshifts happen along with some codes , etc.....not a good idea! The ONLY way to fix this is to prevent the valve from popping by tuning or shimming.
 

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Bobo, there is nothing wrong with raising the B0732 "Limp home fuel limit" .. I did manage to set a P1093 the other day when my filters were due to be changed (and running a huge tune).

Since I changed my limp home fuel to fuel up to 2500 rpm's I could maintain a decent highway speed after popping the relief valve. True, you won't have anything near full power, but you will have enough to keep you from causing a traffic jam trying to get off the road.


Your TCM solved the 1093's huh?

You're not fooling me any.... How are your 1093's getting better with a different TCM cal?

Does it make your heated seats warmer too? I bet you're getting 10 mpg more from this TCM too?

Heck, where can we get one??

There are only a few TCM's that work on our trucks, and they've all been tried. Having a buddy at the distributor load a medium duty cal on your TCM is nothing new.
 

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I hate to bust up the topic a little but why do the LB7's don't throw 1093's when the rail pressures drop off due to big tunes?
 

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IIRC the LB7 fuel rail and PRV are of a different design.
 

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Also, the nature of the LLY torque curve is much less linear than that of the LB7. The LLY comes on much harder than the LB7 does, thereby causing a greater fuel pressure demand in a shorter amount of time.

Harness boxes are especially bad about this because they are increasing pusle width, generally without increasing pressure.

Since you are using more volume with a fixed displacement pump, naturally the pressure is going to drop. The ECM sees this drop, but doesn't see the increased pulse width at the injector since the boxes are virtually transparent to the ECM.

So the ECM, trying to keep things on the level commands a higher fuel pressure to get closer to it's desired number for the conditions. It doesn't know why the fuel pressure is low, but it is, so it fixes it.

When you let off the throttle there is an abundance of fuel pressure and not much demand any more, but it has to go somewhere, so it acts on the FPRV (Fuel Pressure Relief Valve) and there's your P1093.

Clear as mud?
 

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Since I changed my limp home fuel to fuel up to 2500 rpm's I could maintain a decent highway speed after popping the relief valve. True, you won't have anything near full power, but you will have enough to keep you from causing a traffic jam trying to get off the road.
That's :exactly: what I thought. Thanks for proving it, Brayden.
 

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I'm not sure if what I said has sunk in yet, so I'll say it again. The rail psi dumps......there is no power. The rail psi dumps....there is no power. Your pants are down....there is no power!! If you pop the valve, the rail psi dumps...you loose all your power and you are screwed. You can set the 1093 to run at 8000 rpm if you want. With no rail psi, you will have a hard time getting there. Also, with the loss of power comes some very interesting feed back from the TCM and ECM...they see your throttle input and expect the output to match....it don't because the frpsi is too low to make any kind of power. Crazy downshifts happen along with some codes , etc.....not a good idea! The ONLY way to fix this is to prevent the valve from popping by tuning or shimming.
I realize that when you initially pop the valve that there is no pressure. My point is that when you pedal it, the pressure demand goes down, and the valve re-seats, you could get more than the 2000 rpm out of it that ECM would otherwise govern you to until you cycle the key.

Why don't you let that "sink in". ;)
 
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