My lb7 has within the last week or so developed a cough during hard acceleration. It feels like it has completly missed an entire stroke and then comes back even stronger. Like a stutter step almost. It can do it hard enough that the rear tires will bark on smooth pavment. It will do this cough above 2300 rpm with atleast 40% throttle.

Here is the tricky part. The rail pressure doesn't drop according to EFI. I first though fuel filter but then looked closer at the rail pressures and I am acctually about 200psi higher than desired when it happens???? I can see that MAF is effected during this and my buddy said he heard a cough comming from the passenger side. All of my hoses are tight... WHAT GIVES???????

Frame 153 showes one miss well. Latter in the log it will show several misses before i release the throttle

allergy's

That is what i thought. maybe the summer air??? I need to tow 8klbs this comming up weekend so i should probably figure this out...

Have you cleaned your MAF sensor? Maybe its on the induction side rather than the fuel side. Did show a P0089 and P0101 codes, thats why I ask about the MAF sensor. I doubt it means anything, but the problem area seems to show a drop in timing and commanded fuel, I dont know enough about the tuning but may be worth sending off to Nick to take a look at. Thats my stab in the dark

I saw that code and I cleaned a couple of times but the code won't go away. I am running a little too much pressure on my lift pump but I don't have a gauge to adjust it properly yet. I think that is where the code is comming from

super pro... how does the p0089 code relate to MAF?

I don't see anything too suspicious in the log file. There doesn't appear to be any defuel related to the codes mentioned. If you want to give me a call, I can probably help troubleshoot it a lot easier over the phone.

Nick

try the tap test, start logging info on the MAF and take a Small screwdriver and tap on the maf, if it changes the readings when you tap on it, replace it.

She is in the shop right now getting new injectors. I found 3 possibly 4 bad balance rates. If that doesn't fix the skipping then I will try the tap trick and replace filters again. Wish me luck

Ok bad news. The new injectors did not fix the problem. I have tried the Tap trick on the maf and logged anything between 43g/s to 46g/s. I don't know what the tolerance is but it was not effected by the tapping. What else can I try?

Here is an update. I talked with nick @ duramax tuner and he looked at my log files and he thinks that it is something with transmission. I did check fluid and everything so that is not the case. I tried calling suncoast and they are not open. Neither is Inglewood tranny. Does anyone have any experience with any of this?

Here is a tranny log

I have noticed that my skipping problem goes away whenever I do a full reflash on the computer. However, the problem only goes away during the first key cycle. If I turn the motor off and then back on my problem is back. Anyone ever seen this or know which direction to point me?

FWIW
I was going to work one day and really put my foot in it, just as I did some nut cut into my lane and back out almost as quickly. I got out of the pedal and right back in, just as I did she went Kack, Kack, Kack,... hard. It was as if the engine was cutting off and back on at WOT! A real jolt!

When I posted it, Eric said he had experienced the same thing, he suggested a grounding issue. I replaced a couple of the engine grounding washers and problem SOLVED.

D

Can you tell me where these grounds are

mine did this shortly after i got it and i had to get a new ecm. i doubt that this is your problem. have you tried changing the tune. or have you changed the tune lately. i wouldnt rule out tranny issues but i am leaning more torwards a fueling issue. i would think if it was some type of tranny issue and it was slipping then the you would have some type of rpm gain during it. dont the lb7's have some type of junction boxes that the lift pump feeds in to. perhaps this is going out

I have tried several tunes. It does it even on the stock tune. Does anyone know where all of the grounds are located? I would like to check those out. How do you test an ecm.

I got your PM.. I'll let you know if I can find anything in them.

Brayden

Thanks a bunch.

I have tried several tunes. It does it even on the stock tune. Does anyone know where all of the grounds are located? I would like to check those out. How do you test an ecm.

There are some grounds on the frame under the driver door and the main straps under the hood on the firewall. Those are all I know of.

Here is another log. I put it into 3rd and held it while it was skipping so that maybe it would be easier to see a problem. Look inbetween Frame 1300 and 1480. That entire span is where I am having the problem. It isn't a constant skip. It more sounds like a DaDaDaDaaaaaDaDaDaaaaaaaaaaDaDaaaaaaaaDaDa. Where each of the D's are where it feels like it is missing. Above that RMP it seems to smoth out but then I shift and it will reach that RPM range again and will start doing it.

OK so I decided to run some balance rates on my truck again. Thinking they would be good since the dealer replaced them all last week I didn't think thay would be this bad. Anyway, I found that all of my injectors are out of tolerance. The closest one to tolerance is 4.98mm3 and the worst one is -7mm3 in drive and only 3 were in tolerance in park. Am I crazy? Should I go to the dealer and get him to replace them all again? What should I tell him? (i told him the first time that my buddy has a tech II and said my injectors were bad)

I need to tow on tuesday. Should I run some diesel Kleen thruogh it and hope for the best???

Come on guys I know you read this thing on sundays

i have no idea buddy

It has now classified itself into an intermitten problem. This morning it was smooth as silk. I didn't have my logger so I couldn't log it. Today after work problem is back. That tells me that it could be something electrical. I don't think that it is rough enough to say that it is an injector connector problem that i should do an ice pick fix on. I thought those were on the LBZ anyways. I have a fuel test port on the front of the motor as i am sure everyone has. Has there ever been any issues with those? When My lift pump was running high pressure i noticed that it was bubbling a little. (one bubble every second or so) now I have the pressure on my lift pump down to around 6.5psi and when in park the pressure never changes across the rpm range of course there is no load but im not laying under it during a power brake.

Any Ideas from that??? maybe air getting into it from somewhere? Where could I look to find it and how do I find it???

If you are drawing air it would have to be on the vaccum side of things, so before your pump. I would think that the air wouldn't be jerking the truck around as hard though when it happened as there would likely be some fuel with it, so you'd be more of a soft combustion rather than a miss.

I need to tow on tuesday. Should I run some diesel Kleen thruogh it and hope for the best???

try getting some sea foam and remove the fuel filter and dump out the diesel and fill it up with the sea foam. if there anything in there that will get it out.

Did you ever do the fuel filter? I saw that you posted that you initially suspected it, but then went on to other theories. I just got a scIV and thought that it wasn't leaning after resetting taps. I changed the fuel filter and it started shifting smoothly. It felt as though it was skipping too. And there was even a little bit of water in the bottom of the filter. If you are already pretty low, try running the rest of the tank out and fill up and change the filter.

might want to pull your bed and check out your fuel sending unit for cracks or a loose hose if thats the case think of it as trying to drink pop through a straw that has a hole in the side of it ..

Ok guys On my way to Georgia the truck ran great. 10 min before i got to where i needed to be she fell flat on her face. I towed it to the dealership and they changed out my Crank shaft reluctor wheel. I looked at the old part and it looks like two of the three bolts that hold it on had sheared off. It has been a couple of weeks since the part was replaced and no stuttering or hessitation.