My truck has had a random skipping idle with rpms jumping up and down slightly on tach. It skips at any rpm range and very noticeable. I recently upgraded the injection pump because of the computer issues. This didn't help it out at all. I have checked fuel pressure and checked for air in supply to pump. It seemed to have started when i upgraded my injectors to 40hp injectors. I have replaced all seals on injectors and tubes. I did scratch a couple tubes. I did bleed air from every line at head. I don't know if the tubes being scratched would cause this bad of an idle? I can firmly say that from the lift pump to the injection pump is good. Im thinking it is down to connector tubes, injectors or valve guides/seals? I would be surprised if the new injectors would cause this though assuming they were pop tested and have new parts to them. Also the blue smoke is excessive during start up and will last for about 5 minutes before clearing up. It doesn't sound much like a miss (Like loosening line at head), but it doesn't seem to be firing consistently. Could an internal leak in the head (i.e., connector tubes) cause a weird idle? Truck starts great every time. Seems to drive alright. What do you think?

Edited March 27, 20169 yr by Cumminz

Welcome to the forum! 

First off, thank you for having your signature filled out for us  

 

Let's start with the skipping issue. The tach just slightly moving up and down is completely normal. All 24v's have that little bounce to that. Unless you can actually hear the motor going up and down there should be no worries there. Any time you have an issue I would recommend unplugging all aftermarket modules so that we know they aren't causing the issues.

 

The skip / irregular idle is interesting. Where exactly did you scratch the crossover tubes? If it wasn't on either end they "should" be okay, although we will not rule them out. Sometimes the sealing surfaces get deformed from over tightening and it can cause them to leak a bit past the sealing surface of the injector.

Could you describe the exact process you used to install the injectors please?

 

Last, are you sure your grid heater is functioning properly? I get much more smoke (usually white) when the grid heater isn't on. If it's working fine you may need to replace the valve seals. Either way, if the grid heater is working I don't think the blue smoke is going to lead you to your missing issue. How many miles are on the engine? 

Thanks for the reply. You can definitely hear the motor going up and down slightly through the exhaust and it sounds terrible but not like a missing cylinder. My edge comp (although in my sig) I don't even have installed on my truck anymore. I took it all off to replace injection pump and to diagnose this problem. I know i scratched a couple tubes on the threads using the screwdriver method to remove them (but i did replace the o-rings anyway just because I was replacing injectors). The grid heater i know are working because the volt meter goes up and down when they are cycling (which i can also hear them cycling with the volt meter). I have not checked seals for valves. Would i just look if the seals moved up?

Scratching the threaded part doesn't hurt anything. 

When the motor goes up and down are you sure that isn't just the grid heaters cycling?  A video with some sound could really help here.

 

Can you give me a rundown on exactly how you installed the injectors please.

 

I wouldn't worry about the seals until you fix the other issue. It's not really going to hurt anything. There is an article in here on how to replace them though.

Sounds to me the possibility you have an air leak on the suction side of the lift pump. Poss air leak at the fuel tank connection.

 

After you go for a run does the fuel cap have a slight hiss/ sucking sound when loosening the fuel cap slowly? This indicates vacuum in the tank with a venting problem poss compounding an air leak.

 

Me only knows possibilities never absolutes especially with guys like the owner of this site who knows a lot more than me.

I have alldata so i printed out the procedure and did it. If you want the whole rundown youll have to give me sometime to go on alldata again. I might have to make a video but my phones camera doesnt work so ill have to come up with something. Its a rapid random skipping, not the grids. The skipping happens when truck is fully warm too. I only thought the seals if oil was leaking into cylinders. But if that wont affect idle then ill keep searching.

 

jag1, intering you mention the vent issue. One week my tank leaked fuel from what i thought was the rollover valve above tank but it quit and hasnt leaked. Dont know why it started or how it stopped but no suction when i take off cap. when you say suction side do u mean return? If its supply side i checked supply from lift pump to injection pump with clear hose routed up to windshield with no air. 

Try pop testing the injectors?

 

Possibly debris in a crossover tube?

My roll over vent valve did the same thing when I filled the tank. I added my own tank vent.

 

As far as air getting into the fuel I am talking about the section from the tank to the lift pump. Hence the suction side. Also concerned about debri in the tank. But I don't want you to have to go on a work load of possibilities. Do easy stuff first.

I had thought about getting these injectors pop tested. I do suppose i am in denial that they are out of specs considering they are new from industrial injection. But it has crossed my mind. I would love to get this solved so this can help others. Great learning experience. Ill get them pop tested at some point here. Ill also check these crossover tubes for debris and that roll over valve. I was misunderstanding the suction side. How could i check that line? I also haven't messed with anything in the tank. this fass pump was already installed and has been "functioning" so it never crossed my mind to really check it other than pressure to injection pump and air from supply line. If air was getting in through that suction line wouldn't it show up in the supply to the injection pump though? or would those filters just trap the air? I have been draining those filters (fyi new filters). I suppose I have some things to look in to. 

Edited March 27, 20169 yr by Cumminz

If you were having suction issues that should show up via lower fuel pressures. If I'm wrong about this someone please chime in but as far as I know those two things go hand in hand.

 

If you want to see if the tank isn't venting you could always get it warm and have the problem show up and either open the fuel cap or do a bucket test. Either one would tell you if the problem was in the tank or somewhere forward of that.

If the bucket test changes this then you might have a suction line issue.

That's what I was thinkin too Mike. If that were the case it's either suction or vent problems right?

Edited March 28, 20169 yr by notlimah

I have sent you the wrong thinking by hoping it is something simple. If air is getting in via the suction side of the LP it would show up in the clear tubing fuel line.

 

If you had a venting problem the engine would smooth out as soon as you opened the fuel cap.

 

Another thought is to park the front end uphill so engine is higher than the tank. Park overnight that way and see if you are getting tank drain back, loosing prime, letting in air from bad injector seals. Sometimes they wont leak fuel but will let in smaller air molecules.

 

I keep wanting it to be the inexpensive things anyhow

 

Other thoughts are bad overflow valve or bad sensor somewhere.

 

Make sure PCM ground, all other grounds and batteries have good clean tight connections.

Edited March 28, 20169 yr by JAG1

My driveway does have a slant to it. and I have played with directions with the truck. No difference really. If there was drain-back im sure the truck would have a hard start if it was facing up but starts up instantly no issues (unlike the neighbors 12 valve...different story). Overflow valve was replaced with the midwest injection pump. Upgraded to timbos apps sensor. Ill have to check iat and map. If they had issues wouldnt they throw codes though? Ill check pcm grounds. Batteries are still in great condition and have checked connections. I need a video...bare with me guys. great input. I have also checked for alternator noise. Again lots of blue smoke even with high idle until really warmed up and real bad sounding idle. My truck even sounds weird when i let off the pedal cruising down the road...

I also am not sure if this is relevant but i keep getting p0500 and p1693. I think i have cleared those codes like 5 times but keeps coming back. I am not spinning tires and my speedo does work correctly. Just fyi

Could it be a camshaft position sensor on the fritz or going bad? Just spit balling here, but sounds like you've covered all the typical things and it checks out good so it's like what else ya know!?

 

As far as your codes, mine will show those regularly with the same things as you. What's weird though is when checking codes prior to starting with the hypertech tuner deal, it would show those codes. When checking with my OBDlink mx or with Tyler's Smarty, no codes would show. So it may be just the scan tool your using but I tend to trust the OBDlink and Smarty more then the hypertech.

Yeah those codes... IDK. The Camshaft Position Sensor was replaced since i was replacing the injection pump. Well i was using the truck almost all day today. Noticed the rearview mirror shaking pretty bad. I pulled over and had a 3/4 wrench and cracked open 4 high pressure lines at the head and no change. I am hard-pressed this is not an "air-in-the-lines" kind of situation. I mean the thing sounds rough enough i don't even want to drive it. But its not as bad as like a diesel misfire (which is awful sounding). You guys (as well as myself) are kind of convincing me this is an injector (or connector tube) issue. I wish I had my old injectors to swap out to test it because i think it might be these new injectors giving me this MASSIVE headache. Thanks for all your input guys. Ill try to keep this updated. It might be a little bit before i can get MORE injectors/connector tubes.

Edited March 29, 20169 yr by Cumminz

So if you cracked open 4 injectors when it was running and the engine made no change that definitely sounds like air in the system somewhere. Now trying to isolate the problem is a bit tougher. Could start with a bucket test to rule out the tank being the issue. If the problems still there then the problem is from the lift pump forward. 

Did this start when you changed those injectors? Are they brand new not rebuilt/ reconditioned?

 

Both my Cummins one with 425,000 miles and the other with 87,000 miles blow blue smoke till warmed up. It's normal unless it is excessive.

Edited March 29, 20169 yr by JAG1

When i cracked the 4 lines open it did change the sound just not a change in the way it is idling/running. The mirror was still shaking. This happened AROUND the time i changed the injectors. They are industrial injections 40 hp ones. I bought them as slightly better upgrade for my truck and to hopefully smooth out the idle. Turns out mine are doing the opposite. It could be the haze is from the injectors dribbling too. Mine seems to smoke way worse than the neighbors 12 valve. The haze does go away when its warmed up so thats a good sign.

Can air in the return line cause a hard start AND rough idle? 

Air in the return can cause hard start but should not cause a rough idle. Air in the supply side will cause a rough idle.