fishbiting IP fuel metering questions and observations

[Hubert]

Take a look at this ..... I took a part a DS 5521 IP that was having fishbiting problems. I have for some time thought fishbiting was a fuel metering problem. I found the fuel solenoid plunger had some gualling or fretting on the shaft. I think this causes poor performance of fuel solenoid fuel metering action which showed up as fishbiting.

So this is how I think it works correct me if I am wrong. The timing chain turns the IP. It pumps via plungers that are driven by a camring. The clock position relation sets the timing of the (possible) injection pump fuel pulse. The stepper motor varies cam ring time position according to engine temp and timing corrections per PCM control. This sets the possible begining of the injection event.

BUT .... Thats all for naught on a DS IP as the fuel solenoid actually controls the fuel injection pulse from the IP towards the injectors which are in turn dumb spring mechanisms and when pressure is correct they "pop" and the fuel squirts into the cylinder.

I don't have it all figured but something like this....

So The IP pumps fuel. The fuel solenoid either allows the fuel to recuirculate internal to the IP by opening an internal relief path or it closes the relief path and fuel pressure rises and the injectors are the escape path. So closure time of the fuel solenoid controls the fuel metering and timing of the injection event. But its driven by the camring time position so its not totally independant.

Ignore the scratches on the plunger I might have done that mis handling parts and pieces while finish taking IP apart. The only other thing that looked worn on internals to the naked eye was the wave spring in the IP and I thought that it had excessive scuffs-gualling and wondered why. And how that would affect things That wear apparently comes from camring timing adjustments from stepper motor.

[CedarGrove]

I'm proud to say that this is the pump out of my formerly fishbiting truck. Let the autopsy begin!

Lewis

[Hubert]

I had always wanted to get my hands on IP to take apart and see some stuff.

I don't claim to be a good IP coroner. I definately couldn't put it back together but never intended to so and was a little sloppy. I have no bench testing equipment other than a homeowner's DMM and basic tools. I do have some experience with machining and surface metrology but not the super finishing stuff under 4 microinch Ra. I was basically looking for visible wear and as a learning experience.

It looks like the fuel solenoid was pulling the plunger a little crooked. There was uneven wear on the plunger 180 degrees apart on opposite ends. Fretting is probably not the best descriptor for this it more scuffing wear less than gualling . Where the magnet of the solenoid pulls the plunger head did show some differences in fretting or bruising from contact one side was a little more worn than other but not bad and don't know how it compares to normal. I'll assume the PCM measures solenoid closure time via current draw on the solenoid as I don't see any other mechanism for measuring of open/closed. And further figure since the electronic part was "OK" then no codes were set but wear did cause a performance deterioration in fuel metering the OBD system doesn't pick up.

And maybe thats more it as the plunger hammers away over time it wears and then the seat and seal is not as good. Or the solenoid plunger wears doesn't move as easily and opens slower??? Add fuel lubricity issues, slop of timing chain, and injector wear along with other age then precise fuel metering suffers.

[CedarGrove]

Would high pop injectors play into this somewhere? I did throw some in when I installed the Reviva rebuild. Anyone?

[Hubert]

I was hoping someone might comment before I ramble too much more. How many miles were on the IP before the fresh hi pops? Yeah, I have read reports of issues with marine injectors that were not stock specs matched with a stock truck IP problems with idle quality.

POP pressure and orifice size does have an appreciable effect on the dynamics of the injection spray. The timing, spray pattern, and penetration rate (and flame front speed) into the precombustion chamber. Would the mismatch cause fishbite but not other issues like rough idle or difference in start up and warm up, I don't think so.

Kinda disappointed no one has commented. I guess its asking a bit much to really diagnose the IP on visual inspection from pics and not precise measurements though. I mean there are some really tight tolerances and special setups there the eyeball can't measure. BUT sometimes mating and wear patterns are also hard to quantify especially with fine finishes and these tight tolerances and thus sometimes visual is an ok indicator.

The pump "plungers" were worn too and maybe its also just clearance issues of the fuel distributor and the thing that holds the plungers and spins. Could very well be an older IP is having a hard time maintaining consistent pumping pressure once the injectors open and the fuel actually surges a bit through the injectors and not a nice precisely metered consistent spray. Lewis mentioned he had the pump bench tested but that may only time the injection and measure volume etc and not pick up on quality of or consistency of injection pulse. Still more .... underhood temps and fuel quality would also add variables a bench test might not measure accurately to real world (also real world variable loading of engine and harmonics of rotating engine dynamics again etc etc).

[Robyn]

The fuel solenoid run by the PMD dithers at a high rate and meters fuel to the plungers based on what the ECM calls for.
The mechanical plungers do the actual hard work of building pressure and forcing the fuel through the injectors.

The solenoid is subject to a fairly low pressure atmosphere of fuel.

Dirty fuel, water and low lubricity (ULSD) can and does lead to solenoid issues and will cause all sorts of nasty crap to happen.

If the solenoid hicups every so often the engine will also hicup.

A PMD thats hinky can also do this but usually the engine will just shut off with a bad PMD.
A PMD can also cause a runaway condition too that will get very interesting.
I have seen two do this and it can be a real eye opener for sure

Usually the engine screams at governor limit and the black smoke rolls out in copious quantities then the engine shuts off, Plop.

Some times they will restart and sometimes not.

Best

Robyn

[Hubert]

Ahh that makes more sense that the metering is done before pressurization of fuel. But according to most fishbite tales no OBD codes are stored. So theoretically fuel solenoid electronically measures ok. At least the closure time long or short codes are not set.

[Robyn]

Is there a particular fuel level in the tank that will see this "fishbite" occur??

If it happens with the tank level below 1/3 I would suspect air entering the system through the tank suction screen bypass valve.

Usually if the solenoid is giving issue there will be a response time error and resultant code set.

Is the fishbite more at cruising speeds with light throttle or under a more hard pull??

Have you tried swapping the PMD yet.

Unless its a Blatant issue that sets a hard code I always suspect the PMD as a possible culprit on driveability issues.

Let us know.

Robyn

[Hubert]

Here is the original post.

http://www.thedieselpageforums.com/t...ad.php?t=31954


But this is not just specific to this thread. I am also trying to understand the dynamics.

In the above post there had been some history of P1216 = fuel solenoid response time short
so that lends suspicion about health of the fuel solenoid.

A new FSD did not solve fishbite but a new IP seems to have solved it. It appears to me that probably/MAYBE the worn fuel solenoid plunger and different fuel qualities were a big player for this case.

But I don't believe code was present for all the fishbiting and many don't have the code but do have drivibility decline.

[TAG]

Im pretty sure the metering takes place after pressurization. Its my understanding the plungers pump full all the time & the fuel solenoid opens to dump the fuel that is not needed back into the rotor area. If the solenoid doesnt get a pulse from the fsd it dumps all the fuel thats in the plungers, if solenoid armature should stick in the on (extended) position, the engine runs away until the pcm regulates it with the fuel shutoff solenoid.

[JohnC]

TAG is correct. The fuel Solenoid dumps fuel from the pumping chamber after the injector has delivered the desired amount of fuel, hence it has to be able to withstand the injector pop pressure.

If the solenoid won't close no fuel is delivered. If it won't open the full load of 80+ mm2 is delivered.

Here's something i don't get though - if it won't open no fuel should be allowed into the pumping chamber on the next stroke...

Also, there is no mechanical governor. If the fuel solenoid sticks the engine will not be governed. This is why the health of the fuel shutoff solenoid can be so important...

[Hubert]

Thanks, it makes sense after but wasn't sure the solenoid could overcome fuel pressure but maybe its a differential pressure more than full force.

JohnC I thought there was an internal mechanism to transfer fuel to the rotor/plungers and that was the big deal with feeding the beast mod where better fuel delivery to the IP helps injection pump fuel delivery output consistency (at higher fuel rates).

I guess any fuel the solenoid dumps back to the rotor/plunger area instead of injecting to cylinders would keep lift pump fuel from coming in and that fuel would return to tank. I think return break back to tank pressure is about what 15 ish psi. Such that if fuel solenoid wasn't opening (stuck or FSD shorted out ) the IP would just pump out its max output depeding on fuel delivery from LP, internal housing pressure fill rate, and the fuel shutoff solenoid being open. PCM would shut fuel off with shut off solenoid if it sensed a runaway fuel metering solenoid runaway.

So either way I am still thinking in this case fuel solenoid plunger wear and fuel metering is still a plausable cause of fishbite maybe due to a surging affect of fuel metering and engine dynamics. But the closure time of fuel solenoid was not sensed bad enough for an OBD code.

[Hubert]

Differential pressure meaning difference in IP pressure and injector pop pressure.

Just read it again in another post that the IP has an internal transfer pump. I think that fills the plunger/rotor/ring area. I didn't catch or notice another pump mechanism inside the IP explicitly (could have easily missed it) but figure its really this dumping and/or constant pumping action of the plungers matched with a check valve at certain rotation of rotor (much less than pop pressure rotation) for return to plunger area/or return to tank flow that actually pumps fuel from tank (when LP bad) and flows fuel through the IP that's not injected.

In which case JohnC only way for an IP to runaway would be for a working LP to exsist (and shutoff solenoid to be open) is this kind of what you mean if the 100% of fuel is injected plungers wouldn't fill again on next stroke because the "transfer pump" wouldn't be pumping if 100% of fuel is injected.

That would definately point to why the feeding the beast mod helps at high fuel rates it actually insures this transfer pump pressure is satifactory to fill plungers.

[JohnC]

The info I have is a little unclear. It seems to imply that the solenoid has to open in order for the fuel to make its way into the pumping chamber, but the diagram can be interpreted to say that there is an alternate way in.

The solenoid has to withstand the pressure differential between the pumping chamber and the spill chamber, on the order of 1700 psi. Of course, the area is small so the force in lbs is relatively small, too. It looks like it may be a balanced valve design, too, so the effective force is very small.

[Robyn]

I want to correct an error I made.
As John C mentioned, the fuel solenoid controls the dump or cutoff of the fuel delivery session in the DS4

A DB2 on the other hand has the fuel controled by the delivery valve (Throttle) instead and works in a different way.

The mode of operation is the reason that the operation of the fuel solenoid is so critical and why the response times are so important.

Spent a couple hours the other day at the Pump shop and got the complete rundown on how the DS4 works and got some hands on during a rebuild process and then watched the test run on the machine.

Very interesting indeed.

One thing for sure is if the solenoid sticks closed the engine will run away unless the power to the shut off of is turned off. (PCM can I believe do this if RPM gets too great)

So basically the shut off solenoid is a fail safe and not the primary engine shut down device

Robyn

[Hubert]

Yeah, seems I have read similar a couple of times. For the fuel shut off solenoid I THINK 12v comes from a shared node switched via key switch and the PCM supplies ground (if normal RPM operation sensed).???

I looked again and don't see a "transfer pump" but don't exactly know what to look for. Is it maybe forward of the cam ring along the main shaft? I haven't been able to get that part apart yet. I could invision a little gear pump but don't think thats likely after taking it this far apart.

I would have enjoyed the pump lesson you got Robyn. What do you think the most common misconception is about the IP? I think there are some real neat little simple mechanism working there. Check valves, balanced valves, and timed porting galore. I had kinda forgotten about the centrifugal force trying to sling the plungers outward combined with camring pushing them back inward; in and of itself that would make a little recipricating pump. Its just a little harder to figure out since the liquid isn't really compressible.