How I fixed my VP44
11-29-2015, 12:47 PM
#1
How I fixed my VP44
My truck finally died one very hot day last summer. After 250,000 miles on the original pump. I'm hardheaded about throwing money away on what I consider a bad investment (rebuilt pump). So I tore mine apart and of course other than a cracked diaphram, mechanically the pump was in good shape considering its age. The FCU on top was bad and I found out trying to get another one was not going to be easy. All the shops say they replace all electronics but don't ever have any in their trash cans and your core is no good if the wires are cut or the FCU has been opened even though its "going in the trash" anyways. Since I know electronics and programing I decided to build one. After a couple tries and burnt up fuel solenoids my truck would start and run most of the time but was unstable. I needed it going to tow a trailer so I put the scratch built controller on hold and decided to take a second look at the FCU now that I know what all it does. The main FET for the fuel solenoid was fried and one of the leads got hot enough to pop off the FET. I saw some Youtube videos about fixing it but didn't like the mounting method and the thermal transfer characteristics. So I mounted my new FET driver and clamp circuit on a separate board with a heatsink. It gets pretty warm so I changed to a larger heatsink. It has been running great for three months now.
If you are expirenced with building electronic circuits and your pump is bad and you have nothing to loose execpt your core here are some pictures.
IMPORTANT this will not fix a dead pedal thats a communication problem nor will it fix a p0216. The FCU senses the solenoid current and drive waveforms so the wires need to be large enough and short or else the pump will trigger codes like p0951, p0952 and starting with low battery voltage on cold days could be difficult. Pics and schematic PDF Attached.
If you are expirenced with building electronic circuits and your pump is bad and you have nothing to loose execpt your core here are some pictures.
IMPORTANT this will not fix a dead pedal thats a communication problem nor will it fix a p0216. The FCU senses the solenoid current and drive waveforms so the wires need to be large enough and short or else the pump will trigger codes like p0951, p0952 and starting with low battery voltage on cold days could be difficult. Pics and schematic PDF Attached.
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Marine (09-05-2023)
11-29-2015, 02:28 PM
#3
Registered User
You sir Junkdude get the brownie award..... 
The only problem I understand about messing with the PSG and/or replacing it by itself is that the PSG and VP timing must be synced which supposedly requires the Bosch bench. So much so is this that the shaft key is specific to the calibrations of that VP its found on.
But nonetheless, I completely commend someone with the guts and knowledge to even attempt this.
Let me just throw another idea some people have tried too. Since the PSG running hot is a big concern, leading to the dreaded heat cycles, trying to relocate the PSG off and away of the VP was an idea. But that led to outside interference through the ribbon. Too bad that cant be solved.....
Also, I understand the PSG transducer and/or the solder connections to the transducer burn up. I'm no electrical engineer so.....
The only problem I understand about messing with the PSG and/or replacing it by itself is that the PSG and VP timing must be synced which supposedly requires the Bosch bench. So much so is this that the shaft key is specific to the calibrations of that VP its found on.
But nonetheless, I completely commend someone with the guts and knowledge to even attempt this.
Let me just throw another idea some people have tried too. Since the PSG running hot is a big concern, leading to the dreaded heat cycles, trying to relocate the PSG off and away of the VP was an idea. But that led to outside interference through the ribbon. Too bad that cant be solved.....
Also, I understand the PSG transducer and/or the solder connections to the transducer burn up. I'm no electrical engineer so.....
11-30-2015, 04:12 PM
#4
I think the shaft key is used to zero out manufacturing and machining variations.
I also think putting a used PSG on a pump will work but may have a slight change in
things like cylinder balance and timing. It will probably run ok may have a change in fuel mileage.
I have heard that a new PSG is not programmed. The program has to be downloaded
from Bosch and then run on the bench.
There is a lot of bad information and myths about these pumps. I get the feeling that rebuilders are even kept in the dark about the details of the test bench.
I also think putting a used PSG on a pump will work but may have a slight change in
things like cylinder balance and timing. It will probably run ok may have a change in fuel mileage.
I have heard that a new PSG is not programmed. The program has to be downloaded
from Bosch and then run on the bench.
There is a lot of bad information and myths about these pumps. I get the feeling that rebuilders are even kept in the dark about the details of the test bench.
11-30-2015, 09:49 PM
#5
Administrator
That's impressive. This electronics technician tips his hat to ya! 
When you had yours open, did you see any evidence of tin whiskers? It's often told that they used lead free solder, but I'm not sure when most of the industry changed over.
When you had yours open, did you see any evidence of tin whiskers? It's often told that they used lead free solder, but I'm not sure when most of the industry changed over.
11-30-2015, 10:15 PM
#6
Registered User
I too understood that, as you stated, the new PSG's aren't programmed. Therefore if you bought a separate PSG and just installed it without the Bosch bench then the PSG will not be calibrated to the timing and fueling parameters for that application. Obviously the engine will still run but that must mean that there are some rudimentary functions. Matter of fact, we all know a VP will still allow the engine run by hot wiring pin 7. But since you remove all other variable inputs by doing so, the engine will only idle.
That said, I dont know if the shaft key zeros the manufacturing and machining variations as much as it zeros the timing which the PSG is calibrated too. This potentially being the reason why if the key accidentally slips its position and gets partially smashed while torquing down the timing gear nut then the inaccurate timing of the shaft will result in a slight miss at idle, slight loss in power, and drop in fuel mileage. That would tell me its not so much the specialty of the key per say but rather "that" particular key used which could vary minor amounts sitting next to the rest of the keys in the bin.
That said, I dont know if the shaft key zeros the manufacturing and machining variations as much as it zeros the timing which the PSG is calibrated too. This potentially being the reason why if the key accidentally slips its position and gets partially smashed while torquing down the timing gear nut then the inaccurate timing of the shaft will result in a slight miss at idle, slight loss in power, and drop in fuel mileage. That would tell me its not so much the specialty of the key per say but rather "that" particular key used which could vary minor amounts sitting next to the rest of the keys in the bin.
12-02-2015, 09:43 PM
#7
There is actually very little solder used in the PSG. It is mostly un packaged intergrated circuit dies mounted to a ceramic board and a couple of higher power devices glued to the aluminum base. The ICs are connected by ball welding bond wires and the other componets are connected with aluminum bond wires that are wedge welded. Read more here https://en.wikipedia.org/wiki/Wire_bonding
I think the key works like setting timing on a P7100 its just an offset between TDC and pump posistion. The VP has a cam ring that moves about the pump shaft like the breaker point base plate in a distribitor connected to a vacum advance. The timing piston moves the ring based on vane pump presure which increases with speed. Like the VE pumps. The posiston sensor is mounted to the cam ring and senses teeth on a wheel mounted on the pump shaft. There are missing teeth, the missing teeth are NOT TDC of a cylinder. Half way between (9 of 18 teeth for a six cylinder) is where the pump plungers start to inject. The ECM provides a ref. pulse 6 times per revolution to the VP on connector pin 8. The ECM derives the ref signal from the CMP or CKP (depends on year) in the engine. The PSG measures the time difference of the signal edges from the ref. pulse and posistion sensor to determine the cam ring posistion reletive to the pump shaft. The key is used set the static offset between pump shaft and crankshaft. The CAN bus from the ECM tells the PSG the desired timing advance. The PSG varies the duty cycle of the Timing Control Valve which leaks some of the preasure away from the timing piston. The PSG will try to make its measured timing offset equal to the commanded value from the ECM if it can't then it throws P0216. The vane pump regulator, piston springs and orifices are set up so that a malfunction or error in the timing commands or control of the TCV will keep the timing in a kind of safe zone.
In other words if you ask for 30 deg of advace at idle its not possible because there wont be enough fuel presure from the vane pump to move the piston that far.
I think the key works like setting timing on a P7100 its just an offset between TDC and pump posistion. The VP has a cam ring that moves about the pump shaft like the breaker point base plate in a distribitor connected to a vacum advance. The timing piston moves the ring based on vane pump presure which increases with speed. Like the VE pumps. The posiston sensor is mounted to the cam ring and senses teeth on a wheel mounted on the pump shaft. There are missing teeth, the missing teeth are NOT TDC of a cylinder. Half way between (9 of 18 teeth for a six cylinder) is where the pump plungers start to inject. The ECM provides a ref. pulse 6 times per revolution to the VP on connector pin 8. The ECM derives the ref signal from the CMP or CKP (depends on year) in the engine. The PSG measures the time difference of the signal edges from the ref. pulse and posistion sensor to determine the cam ring posistion reletive to the pump shaft. The key is used set the static offset between pump shaft and crankshaft. The CAN bus from the ECM tells the PSG the desired timing advance. The PSG varies the duty cycle of the Timing Control Valve which leaks some of the preasure away from the timing piston. The PSG will try to make its measured timing offset equal to the commanded value from the ECM if it can't then it throws P0216. The vane pump regulator, piston springs and orifices are set up so that a malfunction or error in the timing commands or control of the TCV will keep the timing in a kind of safe zone.
In other words if you ask for 30 deg of advace at idle its not possible because there wont be enough fuel presure from the vane pump to move the piston that far.
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12-02-2015, 09:54 PM
#8
Registered User
Very interesting and explains a few unknowns I dont think I've heard anyone ever touch on. But question..... With what you said about the solder, why are some of the European PSG suppliers referencing the transducer wiring and related solder as one of the main problems? Even actually showing pictures of burnt connections. I "believe" that I even remember seeing someone try to replace the transducer alone but I couldn't tell you what the results were.
12-02-2015, 10:39 PM
#9
The angle / posistion / transducer seems to have different names. It is small and has a thin ribbon cable. It has to be very flexible. Looks like a printer head cable. It tears if the PSG is yanked away from the pump without removing the screws in the sensor body.I found this out the hard way. It does not come with a new PSG. The old cable
which is thin mylar or plastic has to be soldered by hand to the new PSG. Using the wrong soldering iron or tools or junk solder and inexperence will yield poor results. It is possible to replace the PSG with the pump still on the truck. The wires on the back have to be cut though.
I do agree though that lead free solder and no clean flux are difficult to use for manual soldering. It does work for controlled process systems with some tinkering.
Better stock up on some good old 60/40 rosin core 0.32" while its still available.
which is thin mylar or plastic has to be soldered by hand to the new PSG. Using the wrong soldering iron or tools or junk solder and inexperence will yield poor results. It is possible to replace the PSG with the pump still on the truck. The wires on the back have to be cut though.
I do agree though that lead free solder and no clean flux are difficult to use for manual soldering. It does work for controlled process systems with some tinkering.
Better stock up on some good old 60/40 rosin core 0.32" while its still available.
12-04-2015, 09:16 PM
#11
I should have taken more pictures before the epoxy went on. Here is a close up of a broken PSG I used for practice to see if it would take solder.
The yellow wire goes where the solder blob is.
The yellow wire goes where the solder blob is.
12-04-2015, 09:37 PM
#12
That said, I dont know if the shaft key zeros the manufacturing and machining variations as much as it zeros the timing which the PSG is calibrated too. This potentially being the reason why if the key accidentally slips its position and gets partially smashed while torquing down the timing gear nut then the inaccurate timing of the shaft will result in a slight miss at idle, slight loss in power, and drop in fuel mileage. That would tell me its not so much the specialty of the key per say but rather "that" particular key used which could vary minor amounts sitting next to the rest of the keys in the bin.
edge.
I wonder if the timimg reference pulses from ECM to PSG could be "fooled"
to produce a timing change and just how much before a code gets thrown
12-05-2015, 08:46 AM
#14
Administrator
I could never wrap my mind around why the shaft key plays such a big role in these pumps.
I mean, these almost look like a standard Woodruff key. These keys are used in all sorts of things, lawnmowers, outboard motors (flywheel locator), machine tools. In my outboards (Evinrude/Johnson) the key locates the flywheel onto a specific spot on the crankshaft. The flywheel contains the magnets which charge the ignition coils to fire the plugs. I can change the key and it will not impact the ignition timing.
The RPMs are much different between the outboards and the VP44. My outboards turn 5500-6000 RPM at WOT. The VP44 only turns ~1600 RPM at WOT (½ crankshaft speed). What is different between VP44 shaft keys? Thickness? Height?
I learn much from these threads too. Years ago I had run across a white paper on the VP44 which detailed some of its operation, but I don't know where I saw it, and I didn't save it either.
I mean, these almost look like a standard Woodruff key. These keys are used in all sorts of things, lawnmowers, outboard motors (flywheel locator), machine tools. In my outboards (Evinrude/Johnson) the key locates the flywheel onto a specific spot on the crankshaft. The flywheel contains the magnets which charge the ignition coils to fire the plugs. I can change the key and it will not impact the ignition timing.
The RPMs are much different between the outboards and the VP44. My outboards turn 5500-6000 RPM at WOT. The VP44 only turns ~1600 RPM at WOT (½ crankshaft speed). What is different between VP44 shaft keys? Thickness? Height?
I learn much from these threads too. Years ago I had run across a white paper on the VP44 which detailed some of its operation, but I don't know where I saw it, and I didn't save it either.
12-05-2015, 02:05 PM
#15
I learn a bit aso but, some of this information in this thread is a bit over my head!
Great thread though!!!
Great thread though!!!