So, here is the scenario, and it is the coolest thing.... or not

Just put a set of RV injectors in a customer's 2000. Unit runs fine, except for one little thing

Since the install, the idle is fine, as is the power throughout the rpm band, no problem there. No miss, no pop, no fart, no bark, no problem. The only ticklish issue is the fact that after running at steady rpm for any length of time, when you come back down to idle, the rpm surges approximately 200 rpm, call it a 'bounce' 2 - 5 times before settling back into stock idle rpm.

It will also do this when going from load to no-load condition, such as merely moving off from 1st gear to 2nd gear, then shove the clutch in and let it return to idle.

On stock trucks, quite often a dirty fuel filter will cause this. This truck has a new filter, done at the same time as the injectors, it also has a new ECT, CMP, APPS, VP44, and a GDP GFS392 lift pump system with big lines.

I have run it on a MODIS scanner while driving, attempting to find the source of the problem electronically, and nothing is popping up. Cylinder cut-out test shows all cylinders functioning properly, balance test shows same. Fuel pressure runs a steady 18 psi, with a slight drop to 16.5 under hard throttle, for an instant, then back to 18.

I've been working on diesel related stuff as a heavy equipment technician for the bulk of my life, and I've had my share of fuel/timing/air/electronic problems to contend with, this one has me scratching my nether regions in confusion though. It is not so much a 'problem' as a ' jeez, my brain hurts from all this thinking ' issue.

I am guessing it is something simple, I merely cannot wrap my head around the simple stuff, especially during the busiest time of year. Since there are no driveability complaints, we are going to let it run for a while, and see what happens, and we'll deal with it as time permits.

Truck is a 2000, 2500, 235hp/5speed, stock unit except for lift pump and new injectors. No boost issues, no overboost codes. It is not driven hard, merely as a daily driver.

Any Thoughts?

 

I've seen the bounce a few times and when it does occur it's *always* as the speedo falls below 10 mph so it must be ecm related. I've got a hot pump so things are a bit different for me, but maybe that observation helps?

 

Ok, this one occurs at any given speed, once the clutch is disengaged and the rpm drops to idle.

this particular unit has a stock -027 pump on it as well.

I was beginning to think toward the ECM, but I am not convinced yet, as it only began happening after the injector install. The injectors are the only true "variable" that has changed in this case.

 

How long has it done it? I know the injector size is different, but when I installed my 220 h.p. injectors, it did this for a while, and then just went away. Likewise on my buddy's with oversized lines and connector tubes. I wouldn't worry with it unless it gets worse. Just my .02.

 

This is funny, i was just going to post a thread on this, 3 weeks ago i also put in RV275's and ever since i've had this "bouce" when i shift gears or as its coming down to an idle, so unplugged the ez, and still does it, loaded the stock SMARTY, and still does it?? Same as above, no other problems at all?? SO guess i'll wait and see what happens....

Capn

 

pind,
It looks like you've done a good job of trying to fix this using your long experience. Let me pose something from the engineering point of view totally out of the box so to speak. I noted that you installed "big lines", injector lines. First of all I would think that all of the lines should be about the same length, no tuning effect like headers but volume effect. So we can assume there is a considerable increase in volume within the tubes. Not gallons of course but say 50 %. It's not hard to calculate...area of the hole times the length of the tube. Compare to the original tubes.

Ok, fluids have some degree of compressibility so at 3-5000 psi whatever the operating pressure is, the volume can vary slightly and even more so in the large lines. So when the motor comes down from speed as with closed throttle the new lines are carring very slightly more volume for a short time. Since it can't backflow to the VP the injector have to bleed it off by the pop off pressure point. So if this is up or down from the original there may be a small amount of residual fuel bleeding off thru the injectors. A small amount may be enough to make the motor gain a few rpm momentarily. Remember we only burn 3 gal per hour at 60mph, 20 mpg and a lot less at idle and even less at coast.

Just a thought.

Also the other guys have said it just went away after a time. I had an idle change too when I installed the new VP. Whether they take time to break in or the computer needs a certain number of starts to reconfigure itself, or there is just a small amount of air in the system, I don't know, but it happens. Possibly one or more of the lines have a low spot in them and a micro amount of air is trapped there. Since it is a stock truck with only injectors and big lines it really doesn't flow the fuel that the hotrod trucks do so it can't get flushed out. Plus as you say it gets driven pretty easy. Same as mine does. Maybe it just needs "a little workout" haha Nothing like going to the health club once in a while.

 

bentwings--I'm guessing the big lines refer to the the fuel line before the VP--but maybe not and if it is indeed bigger injector lines then I'd go back to the stock ones---

I'd start by cleaning or replacing the IAT and MAP sensors---I think that yr truck only has the camshaft sensor--maybe it's starting to go out--not sure if this would affect the idle or not---leaking o-ring on injector or crossover tube--but this usually results in a hard start problem---popoff problem with injectors maybe--were they new or used injectors???---did you double check all the injector hold down bolts???----just kind of tossing things out there to check---since it started with the injector swap I'd be leaning towards the injectors being the culprit----chris

 

Ok, guys, so far, the CMP or cam sensor is new. the big lines are indeed low pressure lines. The Map sensor was done the other day, by the owner, and the IAT is cleaned every oil change, due to the fact that he runs an exhaust brake.

Injectors seated properly, no leaks, no problems, hold down bolts torqued to spec as per ISB service manual. Injectors are brand new. we also replaced the injector feed tubes with the injectors, as a 'matched set' more his thing than mine.

Keep throwing ideas in there, I'll keep checking back.

 

sticky throttle cable??

 

Sorry I made a mistake reading the original post. The lines I was referring to are the individual injector lines. I thought you had installed larger lines here. The larger lift pump lines should be fine.

Ok I think I read it over right this time.

I'm assuming this is the place where you are having the problem:

As the truck comes to a stop and you clutch it, the motor will stay at about 1000 rpm then about at 4-5 mph it drops to the idle speed. 875 I think. This is pretty much normal from what I've seen. On the new VP's that I've been exposed to this doesn't happen quite as clearly for quite a ways maybe 2000 miles or so. My own was even further than that. On the bad pump shortly before it left me stranded, it was a good 250 rpm drop so posibly another indicator of VP failure.

Here is another way out one...your scanner would pick up any alternator or low voltage problem so you can probably rule out bad batteries or charging, but how is the health of the AC. Is the fan clutch cycling properly.???

The fuel pressure is a tad on the high side but lots of guy run even more. Lately there has been talk of cavitation in the lift pump at pressure greater than 15-16 psi and especially if the fuel tank is down to 1/4 or less. Along with this it might be good to check all the fittings on the big line kit.

 

excellent post again, you bent individual you....

Anyway, scanner detects no problems, A/C is good to go, and the low speed thing, not so much

If you are travelling down the highway, say at 55 mph, and shove the clutch in, put the trans in neutral, and let the rpm drop to idle. bounce occurs.

If you are accelerating through the gears, and let off the throttle, let it return to idle, bounce occurs.

If you are parked in neutral, and run the rpm up to say 1500, hold it steady for about 10 seconds, and let it drop to idle, bounce occurs.

There has never been a problem with this particular truck hanging at 1000 rpm until the wheel speed drops, it will happily drop all the way to 750, no problem at all.

Now, as far as the VP possibly being a problem, even though it is new, I am not ruling out that possibility. Not wanting to say that I would enjoy changing yet another one, but what the heck, you can only do so many in a lifetime right.

Keep it coming.

 

I saw the video of the carter pump and the effects of restrictions, but do think this would still be an issue with his walbro pump?

 

Is the idle issue only related to the RV275 sticks? Do you have a fuel leaking out of the adjuster nuts or o-ring on the connector tube? I'm thinking that you put in new o-rings on new connector tubes right? Do you put a light coating of lube. Did you check or look at the connect tube ends? Some come bent or damaged. I bought mine from dodge as I found they where different than cummin's. Put in the original sticks and then prime your VP and injector lines of air. Its only a couple of hours, that if the idle issue really bugs you.

 

does anyone know a part number for the rv 275's?????