Nasty freeway surging/bucking

zukgod1

zukgod1

Old fart
Joined
Jul 18, 2006
Messages
1,397
This is happening when I'm traveling at about 75-80, rpms are around 2k, 35-42% throttle. Rail pressure is steady at 18k give or take depending on my foot.

Is driving smooth then starts to buck, if I don't either let off or push the peddle a bit more it will take a drink out if your hand. I mean it gets downright violent!

EFI Live, doesn't matter what tune I'm running its across the board bad even in stock.

Suggestions on where to start the hunt?

Not sure if my Sig will show through tapatalk.

07, 5.9 truck with a 6.7 swap.
200hp from II, Hamilton cam and springs.
62 over a 75 twins. GDP, intake, grid heater delete
FASS supplying fuel at approx 20psi.
Yada yada yada.

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My truck did the same thing. I ran my own tuning. I never did try to log and figure out what the problem was but I think it has something to do with the duration or you need to mess around with the rail pressure PIDs.
On some of my tunes it surged really, really bad and then I'd go back to my old one and try something else.

I bought a tune from Gordon @ Innovative Diesel and the surging went away. I didn't ask him what he changes. But I'd log that area and see if you can find a professional tuner to give you some ideas.

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Thanks for the tips. My tunes are from Phil @ Anarchy.
My truck had been sitting for the last 2 months so I've not had the opportunity to do any fine tuning with them yet. Was hoping to get a dual fuel kit on to supply the 200's at wot. Guess I'll have to drop them a note to see about get the surging taken out.

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I should mention I only had EFI on for a few weeks before it got parked. So no time for much tuning.

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Surging at cruise has often been cause by faulty injectors, it's something to look at. Run a stock tune and see if it happens. Otherwise time to do some retuning and datalogging, no telling what is causing it if its software related.
 
Well I would hope that's not the case. The injector bodies were New from Gillette. Ran for maybe 5000 miles then taken to Industrial for the EDM.

Also in the original post it says, "it doesn't matter what tune I'm running its across the board bad".

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Tune doesn't imply stock, at least not when I think of tune, but I missed the stock part. I saw EFI and tune...

If it happens stock it's more than likely injectors or a sensor. Data log things like boost, IAT, etc...

It could simply be the way the duration tables and cruising interact with the injectors, and it may take tuning to fix it, it could be irregular flow from the nozzles.
 
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Now that I think if it I did get the trail pressure about code twice this last week. It's new as well. In the past that code was linked to the tune.
Honestly this truck is going to be the death of me.

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Rail* can't seem to edit through tapatalk.

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20 psi to the cp3? Little much don't ya think?
 
Gibson said:
20 psi to the cp3? Little much don't ya think?
Click to expand...


I'm guessing on that figure, gauge only goes to 15 and is always pegged. According to Fass it should be at 18.

But honestly why would that matter?



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15 is about max recommended, near 12 is ideal unless it's a modded pump and the mfgr suggests more.
 
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Cummins fca's are more forgiving about high pressure than duramax ones are at least from what I've heard. 18 psi 'should' (a little high maybe) be ok but if you get duels with a duramax top pump then you'd better change something.

I'm running 15-16 psi tho to a lmm cp3 and it's fine but 11-14 psi is ideal. The proper fix would be to swap out the duramax fca for a cummins one.

My injectors were done by II as well. That might be something to consider. I lost one 600 miles from home and II went through them. I haven't noticed surging yet but whether that's tune or injector related idk.

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My truck does the same thing man! It gets on my last nerve!! Now that I think about it mine started doing it when I went from a twin cp3 kit with a dodge top pump to ppe's kit with a dmax top pump..but who knows
 
I really hope it's just the tune.
Thinking I'll load a stock file tomorrow and see what happens. If it stock it still bucks there it's a REALLY high likely hood I'll part the truck.

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