Erratic rail pressure

J

JasonCzerak

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Aug 10, 2006
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At speed no cruise control):
[ame="http://www.youtube.com/watch?v=OMB5YxA7EhE"]http://www.youtube.com/watch?v=OMB5YxA7EhE[/ame]

At speed with Cruise control (sorry for the jumpiness):
[ame="http://www.youtube.com/watch?v=9BGaE1ztPlc"]http://www.youtube.com/watch?v=9BGaE1ztPlc[/ame]

Idle:
[ame="http://www.youtube.com/watch?v=MG1fft-ElNY"]http://www.youtube.com/watch?v=MG1fft-ElNY[/ame]

So, this just started today. I had the truck with out batteries for several hours, that's about it. I've been running the normal TNT (latest version) since I loaned out my smarty a few weeks ago. It's been fine and I think the normal TNT runs better, cleaner then the old TNT/R (circa 2008 version).

Software #3 TM 1 (stock) Rail 1 (stock) or 2 (mild) timing 3. MP8 removed.

There's a surge with the cruise set to 60 or 70. hills, or no small hills (or slight inclines on the road, hills to me). I can't get it surge such that I feel it jerk when I use my foot, but the rail gauge is + or - 10,000PSI!!! at times!!! With the cruise set, it's jerky

Part to full throttle it seems it's a little jumpiness in the guage, 2000psi-ish, but the truck pulls very well considering the pump I have on it vs injector size. WOT pressure the gauge pegs 25,000. Makes 50psi.

I put my rail cap block in there. No change. put the RV back in.

SOME of my symptoms are in Rich's IAT/MAP replacement solution in this thread: OK...lets fix my truck....please! - Competition Diesel.Com - Bringing The BEST Together

The rail gauge seems to read high, but I certainly can get above 15,000.

FCA will be replaced with the entire pump this coming Saturday.

No codes.

When using my PLX odb-ii box and any of the iphone apps that use it, the boost is about 5 psi off the auto meter gauge. In fact it shows a vacuum at idle of about .5psi.
 
Have you tried unhooking the gauge and harness from the rail pressure sensor? Sometimes my guage will read a little low and this always corrects the issue.
 
Mine does some thing similar nothing at a idle but while cruisin.I took my pressure box off and not as bad but still does it some.
 
Spooler said:
Have you tried unhooking the gauge and harness from the rail pressure sensor? Sometimes my guage will read a little low and this always corrects the issue.
Click to expand...

You must be thinking of the diProcol gauges, they'd get all messed up.. the IsPro ones never read high or get out of sync. I have not tried with it unplugged tho. certainly worth a try.

EDIT:
I'm going to give Cummins NPower a call tomorrow to see if they have a MAP/IAT and swap it out for good measure. If that fails I'll resort to the leak back test to see if the injectors are toast.. They shouldn't be, they were rebuilt and never had a pump that could come close to abusing them yet.

Speaking of injectors, the "smokey starts".. Ever since the day I posted that it's gotten better and better again. this afternoon, idled perfectly with out any hesitation, normal haze. Trucks been off 2 days-ish.
 
WUnderwood said:
does the throttle feel jumpy with the erratic rail pressure?
Click to expand...

you mean is the truck accelerating and decelerating with the gauge's erratic movements? Yes with the cruise, no with my foot.

I can hear the tone in the injectors change that seems to be in sync with the rail gauge's movements. It sounds like someone is playing with the MP8 knob. So, yeah. if your cruising at 17,000psi, crank it from 0-100% and back and forth. your do not necessary go faster but your do hear it rattle more. So I unplugged that, no change.
 
I had this problem two weeks ago before the truck got stuck at WOT. Changed the rail pressure sensor and both FCA's with no change (stuck at max RP). Hopefully yours does not get stuck at max RP as well, because I have still not found a fix for it.
 
So, calling around to find partnumber locally. 3971106 for the iat/map -- $80 part from cummins. No one has it, day out.

Dodge does $230. LOL. Right.

Still erratic, idle was smooth at startup for the 10 minutes I idled and made calls this morning, then it got wacky

Is the map supposed to show a vacuum?
 
So, jeff talked me into the fca

Stock software still has the cruise surge and symptoms.
 
mine does this but thats with my music turned up, also mine did that when right before my pump blew. but that was my fault i let the check ball fall out of the pump.
 
rajkalkat said:
mine does this but thats with my music turned up, also mine did that when right before my pump blew. but that was my fault i let the check ball fall out of the pump.
Click to expand...

No music. But yeah, mine would with the music up too.

I wonder.... could these new batteries be causing this?

What is the correct running and idling voltage that should be seen?
 
Seems kinda odd..if you watch your boost gauge, it makes zero movement. When I am playing with my MP-8 like you describe I see a corresponding move with my boost gauge.

If the gauge moves but the truck doesnt "Surge"...then id call it a gauge issue and not a hard part...
 
2007 5.9 said:
Seems kinda odd..if you watch your boost gauge, it makes zero movement. When I am playing with my MP-8 like you describe I see a corresponding move with my boost gauge.

If the gauge moves but the truck doesnt "Surge"...then id call it a gauge issue and not a hard part...
Click to expand...

I have corresponding injector rattle with the gauge. Also cruise at 60-70 surges slightly, you can feel it.

Tried a stock 100,000 mile + FCA. Exact same symptoms. Stock software too

I'll be unplugging the rail gauge to see if the cruise control smooths out now.

Plus, my boost gauge isn't pictured in the video, that's water pressure.
 
And yes sometimes my rp gauge freaks out and kinda does the same thing but not as violent as yours does.

Unplugging gauge should take care of it...
 
i think he has the water psi for his water injection if i remember right. I hope you get it figured out jason, good luck.
 
SuperiorRam said:
Has your idle rp always in that range?
Click to expand...

Nope.

2007 5.9 said:
Water pressure??? That's a new one...can I ask why??
Click to expand...

Why not? :) I have a huge thread detailing my water system install and customization. I have a pressure sensor in between the shutoff valve and the pump to ensure my jet size isn't "too big" for what's expected to be WOT water pressure and to monitor where the progressive pressures are at with the progressive controller, also to ensure I have water flowing.. It can be shutdown in a way where there's pressure in the system. infact boost can push into the pump, but not the other way around. that's why there's about 50psi of water pressure when it's in fact off. Holds that pressure for days on end.

2007 5.9 said:
And yes sometimes my rp gauge freaks out and kinda does the same thing but not as violent as yours does.

Unplugging gauge should take care of it...
Click to expand...

Do you have a diprocol gauge? If so, that's your problem.

But I do have some good news.

SOLVED!!!!

And I have Michael@ISSPRO to thank for taking a random call from me! Thank you!

So, changing out the batteries was the the cause of the problem. Had I not done that I wouldn't of missed the ECU ground wire!!! Holly crap that was a bone head move.

This came to be when I unplugged the rail gauge. I had a crank but no start. Every relay was clicking if I key-forward-nostart. 2059 I believe was the code that was set.

So I plug the rail gauge in and it start. About all you can think at that point is.... W T F M F F F F F F F W T F?

So drove home, called Mike and he explained to me how some of these magical ECU things work and while he was saying ground my eye caught the wire I tucked outa the way to get the battery out on the drivers side. Mike tells me I should be fine, but I could of seriously fried the ECU. I did drive maybe 75 miles today in this condition.

Essentially the motor only ran because the rail gauge allowed the ECU to ground though it's ground wire. normally the gauge will use the signal it gets from the gauge (green wire) and ground that voltage back to the black wire for the sensor signal.

Un real.. the rail pressure is back down like 5000 psi at cruise and it's steady as it should be.

Close this out after everyone is done calling me an idiot. :)
 
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