the fuel pressure spike has only happened a couple times. all of a sudden the gauge will be reading like 25-26 psi. normally it runs 15-16. i shut the truck off and it was fine when i started it again. what would cause this?


also, when i drive it hard on level 5, it idles really rough right after. it sound kinda like its missing. usually if you rev it up or keep driving it, it'll straighten out. what would be doing that?


thanks

 

couple things to look at, our trucks with bigger sticks and higher settings on boxes on a heavy wot pull when you let off you can what seems to be draining the fuel line and vp, not sure what the technical term is for it. but I know when it has happened to me it either took some time to run and reprime or I had to crack the injectors and prime it again to restart it. I dont know if your exp, this same event. usually if I hit it hard when I go to slow down or stop I keep the rpm's up. when I upgraded from a 95 to the 150 fass this doesnt happen as much as it did.

I would say on the psi reading do you have a isolator before your gauge. in the past I destroyed 2 isolators the diaphram in it popped a hole and slowly would show a higher reading and then it would go back to the norm, I dont know if its possible your getting air in the vp and for those few moments if its possible that it is showing a higher pressure.??? hope this helps

 

i had problems with the pump air locking before. this is different. it will idle like that for a while if you dont drive it or rev it up.

and my fuel pressure gauge is just on the attitude monitor. and its hooked directly onto the airdog

 

undo the wire tap to the pump and see if it changes

 

what does that wire tap affect anyways?

 

words gathered from Marco, creator of the Smarty.
I don't want to rain on anybodys parade but the wire tapping boxes do NOT do their thing the way you're saying here.

Background. The VP meccanical part has been designed by Bosch for two injection strokes. Pre and main injection. To my best knowledge they've never been used except than by the fuelling boxes. The VP electronics have never been implemented for the second injection stroke, thus there's no way to obtain two injection strokes via the ECM

Wire tapping boxes add a second injection impulse after the "main" impulse that was commanded from the ECM has been done.

The signal to the fuel metering valve is straight 12 DC. No digital signals here, only a good Mos-Fet transistor.
The fuel metering valve actually is normally open, to build pressure it has to be held closed. The fuel for the second injection stroke comes from the membrane chamber or pressure reservoir in the VP.....

Marco


and something else found from long ago not sure who posted this.

There is an electronic computer built into the VP44 call the Fuel Pump Control Module, or FPCM. This computer controls the timing and fueling of the VP44.

The FPCM is responsible for carrying out the instructions sent to it by the engine-mounted ECM.

The engine's ECM has fueling limits programmed into it that the FPCM will never exceed-- remember, it's just taking orders.

Every type of add-on box works by manipulating signals, either the signals that the sensors send to the ECM (thereby "tricking" it into producing an outcome it otherwise would not produce), or manipulating the signals AFTER the ECM (sometimes both).

The stock ECM has a number of fueling curves built into it, calibrated to the engine's rating and emissions certifications. Note, these are CURVES-- they gradually increase fueling as more air is added to the engine.

In a stock 24V, the fueling curve "peaks" at 2700rpm. Both above and below this rpm, the ECM is commanding the pump to deliver less than 100% of the fuel that the ECM is allowed to command (within it's programming limitations).

A non-wire tap box like an EZ works by taking this peak value (at 2700 rpm) and making it available at other, lower RPM conditions. So instead of having to rev to 2700rpm to get max fuel, all you have to do with an EZ is achieve 3psi of boost at any rpm lower than 2700. This is why you get such a bottom end enhancement from an EZ. It converts the sloping fueling curve essentially to a flat plateau. So, you get full fuel at 3psi of boost, regardless of RPM

When the ECM is commanding the pump to give 100% fueling, it's only commanding 100% of THE PROGRAMMED FUELING LEVEL. So no matter how hot a box you put in, you CANNOT exceed the fueling level programmed into the stock ECM. Unless...

This is why you have to "tap the wire" to make the big power. When you tap the wire, you are intercepting the ECM's command to the pump and manipulating it before the pump sees it, like a spy intercepting orders in an effort to change a military's actions.

The wire tap boxes DO NOT extend the injection pulse earlier. Remember, they are intercepting a signal-- no signal, no interception!

So, the ECM sends a signal to the pump to give 100%fuel. The fueling box's wire tap intercepts this signal, and ADDS ITS OWN COMMAND. Essentially, the fueling box adds a second injection pulse that's calculated based on the first pulse.

Say you have a TST powermax3, which is a "63%" fueling box. What this means is that it can add a second pulse that contains up to 63% of the fueling of the primary pulse.

In effect, it works almost like the pilot injection on a HPCR truck, only instead of small pilot injection followed by a main pulse, you get the main pulse followed by a smaller (post) injection.

The reason these boxes are known to destroy VP44 has to do with the bypass solenoid (electronic failure) and they dfistribution head (mechanical failure). The mechanical failures are described on Blue Chip's site here: http://www.bluechipdiesel.com

The electrical failures are almost always due to excessive heat caused by the much higher duty cycle of the bypass solenoid within the VP44. This is the solenoid that closes off the internal bypass within the VP44 and forces the fuel into the high pressure section, thereby initiating the injection event. A fueling box MUST increase the duty cycle of this soenoid in order to have it carry out the second injection pulse. The more aggressive the box, the longer it will attempt to hold the bypass solenoid closed, reducing the "rest" time between injection events-- this both generates MORE heat while allowing less cooling time for the existing amount of heat generated-- a double whammy! It's essentially converting cooling time to heating time.

This will show up in EGTs. For two trucks of identical HP level, the wire tap will ALWAYS have a little higher EGT relative to the non-wire tap assuming both have decent injectors. The late secondary injection pulse also explains the massive torque gains that come with many of these boxes-- 350+ lb-ft.

Compare that to the 180lb-ft claimed for a non-tapping EZ.

 

wow thats cool. i dint know you could get multiple injection cycles out of these pumps. does anyone make a good aftermarket pump that lasts better under these conditions?