Apparently my truck is defueling under load. Here is what is happening;

I can be pulling my trailer up a grade going about 50MPH, boost is at about 25 PSI, fuel pressure is at 15 PSI. Suddenly the boost pressure will drop usually about 10 PSI for about 3-5 seconds and then come right back up to 25 PSI. About a few minutes later it will repeat this.

The other day I was doing some "testing" I didn't have the trailer on the truck. I had my Comp set to 4 x 4 and was going about 100 MPH (on a closed course, and I am a professional driver, don't try this at home). The same thing happened, 15 PSI fuel pressure, 25 PSI boost, boost drops off about 10 PSI for about 3 seconds and then comes right back on.

When this happens the fuel pressure does not drop, the RPMs do not drop. I feel the power drop considerably when it looses boost but it comes right back on when the boost comes back.

The reason I think it is defueling is because the boost drops so suddenly and then bounces back so suddenly.

So,
I know the fuel pressure is excellent and this has happened with two different fuel system setups.

I know the turbo is good and boosts quickly and without any strange situations, the shaft is tight and this situation has happened with two different boost elbows, one plugged completely and one vented as the MFG designed it. The turbo and intercooler boots are all tight and don't appear to leak.

I guess this boils down to electronics, either the Edge Comp, the ECM or the PCM.

Anybody that has not fallen asleep have any ideas?

 

MIne did that before I grounded the comp to the battery instead of the dash. Any codes?

 

No codes on mine. Was yours throwing codes when it was doing that?

 

Not at that time, I have since came down with the 0216 blues but I'm running her till she croaks.

I have read alot of the original comp troubles were a ground issue, also check the wires that go into to comp harness plug I have had one pull out of the harness causing trouble too.

J

 

Bump!

Here is an update. I sent my Comp box back to Edge. They upgraded the software. This weekend I pulled the trailer to the desert. Same problem. It is defueling no doubt. On the pull back up the hill I was at 32 PSI boost, 14 PSI fuel pressure and 1200 degrees EGT. The same exact situation as below with the boost dropping between 10-15 PSI for one to three seconds and then comes back on strong. I noticed the EGTs fall rapidly while this is happening so I know it is defueling. Other than this problem it is running great. I can run her fully loaded up a 6% grade that is 10 miles long at 60 mph!

Any ideas what to check next?

 

Doesnt the edge automatically defuel when the EGT gets up to a certain point?

 

The Edge properly installed and grounded should allow you to fry your engine with way too much fuel if you are not watching the EGT, so I would look to the VP44 as the culprit. More specifically, look for air in the fuel. The infeed line pressure will remain high, but there is enough foam to cause the pump to cavitate and momentarily unload.

Once this happens, you have unquestionably damaged the injection pump and are running on luck. Given the way you say you use the truck I would look to installation of an Air Dog with the dual filters to eliminate the air. Also, if your flexible fuel lines are more than a couple years old, replace them including the two from the tank to the frame lines. And, I suspect you are in line for a rebuilt injection pump. But, fix the fuel supply side to eliminate dissolved air from the fuel before you blow the new one too.

If you input line fuel pressure were momentarily dropping, I would diagnose a stuck bypass valve in the lift pump, but you say the fuel pressure is remaining in the OK range.

 

I believe you are refering to the Edge Attitude chip, which does monitor EGT and you can set it to de-fuel at a certain EGT so you won't have a meltdown.

 

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What RPM are you at when this happens?
A reg comp defuels at 2700 the same way you describe.
Other than your ECM doing the defueling due to a signal (over boost, ect)the Comp is not hiding????

 

The Edge Comp has no way to tell what the EGTs are.

This problem has been going on for two years. Since that time I have changed my fuel system to the Scotty Smartfuel system with a Holley Pump and rubber lines from the tank forward. The symptoms were there before and after the smart fuel system was installed. I don't think it is an air problem. Also, considering how many times it has done this, if it was damaging the VP44, it would be toast by now. It still pulls like a raped ape.

I was considering that it has something to do with either the EGTs or RPMs. We have ruled out the EGTs because the Comp has no way to know what the EGTs are. It really couldn't be the RPMs because it happens at different RPM levels.

Every time I call Edge they just tell me to send the box to them for testing and then I get it back saying it tests fine. I still think it is the Comp. I will see if they can send me a loaner to try.

I don't know what else to try. It runs great and this problem doesn't appear until I am hard into a pull for an extended time.

I wonder if the Comp overrides all the defueling parameters in the ECM. Maybe there is another parameter the ECM is reading and defueling.

Hey Ratsun, Do you know for sure that the Edge defuels at 2700 RPM? That may very well be the problem, I could be at 2700 every time it defuels. I will have to keep an eye on that next time and I will have to make a call to Edge to confirm.

 

What tranny temps are you running? I don't know on the 99 but I think it's possible that the PCM can order the ECM to defuel when tranny temps get too high. What's your water temp?

AlpineRAM

 

I have the DTT tranny and it runs cool, about 180-190 F when I am running the hill. The water temp normally runs about 190 F and it goes up to about 200 F when running the hill.

Everything is normal when this happens, that is what is making it so difficult to diagnose.

I have to find out if the Edge Comp defuels at 2700 RPM, if it does, that may very well be the problem or at least the answer to what I am experiencing.

 

Bump

Here we are still. The desert season is over and I am still having the same problem. It is not a 2700 RPM problem. It happens at different RPMs. Among all the other things that have been changed, I fried the head so the head is new and I have studded it with ARP studs. The only thing that is consistent is that it happens at around 5 minutes or so into a hard pull. The boost drops for a few seconds and then comes right back up to where it was. I can feel the power loss at the drop in boost and then the power comes back strong when the boost returns. The tranny runs cool, 190 degrees consistently (thanks DTT). The coolant runs about 220 consistently according to two gauges. Fuel pressure never drops below 12 PSI (thanks Scotty). This is driving me insane. I am going on three years with this same exact problem and numerous things have been changed or checked during that time. What else can cause a temporary 3-5 second defuel? Could this be a timing retard process causing this?? HELP ME! PLEASE!

 

Stupid question and I know it would be painful, but how about taking the comp out of the equation and testing without it to see if the problem remains. That could at least tell you whether it was the box or not

 

The problem existed before I had the Comp installed. I had an EZ. I think I will disconnect on my next good pull and see what the results are though.