What REALLY causes the cold / hot idle lope?

[Dave_WB3FYV]

Does anyone know what REALLY causes the cold / hot idle lope?
My truck was perfect until about 15,000 miles on the clock, and then started surging only when cold. Not enough to even worry about. Now at 26,000 miles, I started noticing it surging even when warmed up AND while driving at slow speeds ABOVE idle to about 1200 rpm (though I could just barely hear it, not feel it). The tach would just barely wiggle at idle, all other gauges normal. The truck had the TCM/ECM updates done several months ago for another reason, so that wasn't going to be the fix. I haven't heard of a reputable GM service center near Homestead Florida that I could take it in to get the injection pump / injectors checked out, and always being the kind of guy that tries to solve my own problems - I dumped in half a bottle of the generic diesel fuel treatment that the local auto parts store sells (couldn't find Stanadyne locally). It was labeled as a 'conditioner', supposed to raise the cetane by 4 points, and contained no alcohol. By the time I had used a quarter of that tank of fuel, the lope was dramatically reduced . Now the truck only lopes when first started, and then only until the voltmeter swings up to normal after the intake heater switches off - not more than a few seconds. I dumped in the other half-bottle for the next tankful, figuring it couldn't hurt, and that's where I am now. Not using the Juice, everything else stock, 1000 miles on the fuel filter, fuel obtained from the same station for the last 3 months - no change until now and it still surged with different fuel suppliers. They don't blend for winter down here...

What's going on here? The fix can't be that simple.

Has anyone else noticed the surge going away after using an additive?
:confused: :confused: :confused:

[SoMnDMAX]

Wow, does this sound familiar!!!! Welcome to my world.

You explained exactly what my truck does to a "T", even the part pertaining to the additive and how it affects the lope(I use FPPF though).

The fix: the "RPCV" also know as the Rail Pressure Control Valve, also know as the Fuel Pressure Regulator, needs to be replaced. Replacement of the regulator is supposed to fix the problem. I see conflicting reports on the exact fix- some say the regulator itself gets replaced, and some say the whole injection pump gets replaced, since the regulator is part of the pump.

My dealer has a pump on order, and hopefully it'll be in this week.

Your dealer can reference Preliminary Information Bulletin # PI0037 for more info. The bulletin is accessible thru the GM Techline service website which is available to dealers only.

Just for the record, when was your truck built? The sticker in the frame below the drivers door has the date, or you could look on the top of the drivers side valvecover on the engine. My truck was built 11-14-00, and the engine was built 10-00. I've got 29,500 miles on mine, and trust me- the lope gets worse, especially in the cold- even to the point that treating the fuel no longer covers up the problem....

[ 12-05-2002: Message edited by: SoMnDMAX ]</p>

[woundedbear]

Dave_WB3FYV,

Man, do I wish I knew the answer to your question on what causes the cold lope!

In regards to your last question, my answer is no. I first noticed my cold lope with less than 1K before I used an additive. When I started to use a FPPF Total Power/8+ Cetane Improver cocktail in every fill-up, my cold lope was still present.

I am a little paranoid that there may be an injector/pump problem, but don't know what other syptoms to be looking for. I can say that I definately have smoke during hard acceleration, when other members of the forum say that they cannot create smoke even when mashing their accelerator from a stand still. :confused:

I have no fuel in my oil, and get good mileage. I, too, am not one to rush into the dealer until I have substantiated a problem. But @ 25K, I want to make sure the problem is taken care of, or at least look at, prior to me reaching 36K.

Has anyone that has had an injector/pump replaced experienced a cold lope that was eliminated?

I have reservations on bringing my issue up to my dealer because to date, I think that I am the only Duramax they have ever sold. Can anyone recommend a reputable Duramax dealer with qualified technicians in the Milwaukee area?

[DMG]

Dave, my 02 did the same thing at approximately 5,500 miles and my dealer replaced the fuel pump and that was the end of the problem and the only thing that the truck has ever been in for service. Now have 15,000 on the clock.

Dave N8EUX

[ 12-05-2002: Message edited by: DMG ]</p>

[Jayhawker]

My 2001 started developing this problem at least 8 months ago, at first barely noticable and recently began getting progressively worse. Became especially bad while idling through parking lots or loafing down streets having 25 mph zones.

Dealer said it was a bad fuel pressure regulator that was causing "fuel pressure spikes". The entire injection pump assembly had to be replaced, comletely curing the problem.

[SDWA]

I have to agree that the injection pump is indeed the cause of the lope, hot or cold. I drive an early 2001 work truck that started developing the lope (hot or cold, bad enough that if you -just- let off the brakes, the truck would surge with the lope) at around 25,000 and it got worse on the way to 30,000. The injection pump was replaced at 31,000 and the lope was gone.

Take it in, get that pump replaced!

Scott

[ 12-05-2002: Message edited by: SDWA ]</p>

[Jon L.]

Have 01 with 41k miles just replaced injector pump, the pump was leeking profusely. I have bd 90hp edge box chip. I am wondering if the chip had something to do with this. I also experienced some loping at idle, prior to the pump going out. I am a little edgy about putting the chip back in. I have not felt any loping since the new pump but its only been a couple of days.

[Dave_WB3FYV]

SoMnDMAX
Thanks, at least now I know I'm not crazy! Thought I was hearing things at first since it went away so easily. Wonder what the additive does? It almost has to be a lubrication issue, it should take a fairly strong solvent to quickly 'clean' a dirty injector/pump/regulator that has been sticking for so long in that enviroment. That would also kinda explain why it gets better when hot, the clearances would open up at higher temperature.
That's why I went with the cheap stuff, I figured everyone else would be using the high-priced-spread, and I was looking for a comparrison. Seems like anything will do (though I'm not brave enough to try Marvel Mystery Oil!).

How long did the additive remain effective?

Thanks for the bulliten numbers, I'll try to find an accomodating dealer around here, the closest ones get the "I'm not taking MY truck there" report when I ask the guys here at work. Maybe it'll hold together until I get back to Texas... Had a good dealer when I was in New York, wish I would have taken it in when it first acted up.

Found a thread about Recommended Dealers, http://www.thedieselpage.com/dealers.htm, old from July and only has one in Florida... Phooey!

Guess I'll run out this tankful, then run a few without additives to get it to lope again before I try to convince a dealer I have a problem. As it is, it won't lope now except when cold.

My truck was built May 2001, I'll have to check the engine build date tonite.
I still get great mileage, best 24 - worst 12 towing 13,000lbs at 80mph thru the mountains.
Also, no fuel in the oil. Can get it to puff a little smoke, but only under extreme acceleration, unless I strap on the Juice L4 !!!

Do you think we should start a database of build dates and locations so the problem can be pinpointed and a recall issued before somebody else has a problem while far from home? If the fix involves replacing expensive parts this needs to be done before we bump up against the end-of-warranty.
Especially parts that have to be ordered...

I look forward to hearing how yours gets fixed. If it's perfect afterwards, like Jayhawker, SDWA and and DMG, then I'm heading to a dealer NOW and would suggest Woundedbear do the same!

Jon L.
I'm now wondering if this is the root of my Juice problem??? I don't think I had the lope before the Juice, but it never acted right for me and I bet I haven't had it on for more than a hundred miles. I loaned it to my boss, it acted up for him too and he doesn't have the lope, but his is a low mileage 2002. Don't know if the Juice causes it or just makes it more obvious, other reports indicate the Juice will smooth out a lopey idle. I'll hold off getting the 4.61 Juice update to see if the pump replacement will allow me to use the current 4.3.

This is gonna be fun...

Thanks to all for the quick replies! :D
Additional comments appreciated!

[D-max Man]

If the lope is only there when cold then a software upgrade should fix the problem.

If it lopes when warmed up, the RPCV is most likely the cause. Even a small amount of water could cause enough rust on the valve sleeve to cause it to stick.

These sleeves have been changed over to stainless steel now but many 01' models were built before the design change.

At first the entire pump had to be changed but I believe the RPCV's are now available separately and can be serviced without removing the pump.

[DMAXDiva]

My '02 lopes when cold only, but it is VERY noticeable. Haven't seen any tach spikes while loping either. I run Stanadyne every tankful, but that has never made any difference. Hot Juice hasn't seemed to matter one way or the other (but it sure has put a silly smile on my face! :D ), and this truck has never been in for updates (17500 miles now). Wish I could find a decent DMAX tech around here; I don't trust her with just ANYONE! ;)

[hoot]

Mine lopes slightly when cold. 40,000 miles.

Built Feb 01.

I won't mind getting a brand new pump.

[ 12-05-2002: Message edited by: hoot ]</p>

[Jimamatic]

I have the lope too. Very noticable when cold,
and even worse in drive at idle. Apply light brake
pressure and it will surge forwawrd. It even does
it when warm on occasion, but not as bad. Mine is
a 2001 built in July with only 11200 miles. I called the dealer today and scheduled an appointment for the 11th. These engines should idle smooth with no additives. To date I've had no other major problems except for the one piece driveline install. BTW, the lope has gotten worse since new.

Jim

[SoMnDMAX]

Dave, though treating the fuel wouldn't make 100% of the idle lope dissappear, 80% would be gone. The lope mellowed out enough so that you wouldn't get bumped at a stoplight. Typically, the lope would come back after 1-2 untreated tanks of fuel. The additive adds lubricity to the fuel, reducing the tendency for the regulator to stick.

Jon L, the Edge box does not alter fuel pressure. I HIGHLY DOUBT it was the cause of your pump failure. The pump most likely flat out failed. Add Juice, and enjoy!!

The software update fixed most of my cold idle lope, but after a while it came back. No doubt because of a bad RPCV. If your truck lopes when cold, have the reflash done. It'll help.

Dmax Man, from the info I was given (my dealer), GM is replacing pumps again, not just the RPCV. Now, whether we can take this as gospel or not, I don't know. The last indication I had from my dealer was that the whole IP is getting replaced. I'll know more tomorrow.


FYI- the injection pump is covered under the 5 year/100,000 mile warranty. Those approaching or past 36K- don't sweat it. Other than paying a deductible ($50 I think), you'll incurr no costs. The pump is about $850, plus 8-10 hours install time. :eek:

Matt

[D-max Man]

It might take 8-10 hours if the tech has never changed one before but I can change the pump in about 4 hours.

[ 12-06-2002: Message edited by: D-max Man ]</p>

[Dave_WB3FYV]

Matt,
It's good know the pump is covered under the long warranty. I was hoping that was the case, makes it worth the price of admission!
This looks like a problem with the early trucks, anybody with a late '02 or '03 with a lope?

DMAXDiva and DMG,
Are your trucks Early '02 build dates?

D-max Man
I had all the updates done before the lope, maybe that's why it isn't so bad now. Wonder how much life there is left in this pump...
Too bad you're so far north, I'd be calling you to get this thing fixed, and I'll bet the Diva wouldn't mind you putting your hands on her (truck I mean!) tongue.gif
It really is hard to find a good tech. Most of my past experiences result in the wrench-jerker fixing what was originally broke, then tearing up 2 more things so I have to go Back!

Can anyone recommend a competent service tech in south Florida?

[hoot]

Dmax man,

Four hours? As many pumps as you've changed I would have thought you could do better than that. :D :D

[DMAXDiva]

Dave:

My truck was built 02/02. Yeah, I agree about the dearth of good techs...maybe I'll just pack up the cat and head on out to Wyotech and learn how to fix her myself! :D

You know, the scariest thing about that is I've been known to do off-the-wall things like that in the past; besides, I'm just fascinated with the machinations of these beasts! ;)

[DMG]

Dave, mine was an early build, one of the first 02's that my dealer got. I don't know if it is fact or fiction but I was advised that they use two different pump suppliers and that there is a considerable difference in price and that I had the miss fortune of getting one of the cheap ones. All three pumps that they had changed at that point in time were the cheap ones.

Dave N8EUX

[ 12-06-2002: Message edited by: DMG ]</p>

[D-max Man]

Bosh is the only supplier of pumps for the D-Max 6600

[woundedbear]

My truck was an early 02MY vehicle, built October 11, 2001.

From the posts, it sounds like the pump is the root cause of the cold lope...thanks to everyone that replied. I, like the majority here, only wish I already knew of a competent tech in the area to introduce myself to.

[Dakota]

My '02 with 10K miles was built 8/01 and definitely has lopy idle but only while cold. If I recall, a reprogram was out last year that may take care of the cold idle problem so I plan to finally have that done first. Since it seems to idle smooth when warmed up, maybe the pump is still okay on this one?

[dieseldealer]

D-MAXMAN, Any idea about a truck that sits for a couple of days, then cranks over and starts and then dies and will not restart? Any help would be greatly appreciated._

[thechevyhdman]

My truck did lope, pretty bad at idle too. It loped enough to see the rpms spike at a rythmic pace. It was fixed with a software upgrade, My truck has a build date of 8-15-01. The software upgrade definitely fixed it. Today it was about 8 degrees out when I started it you can hear it lope a tiny, tiny bit for the first minute after startup but thats it. In question to the upgrade what exactly does the upgrade change? It seemed like it could be fixed by just raising up the rpm's by a hair. My stealer told me it took him a whole afternoon to fix my lope seems like BS but who knows.

[hoot]

I think they raised the rpms slightly. I don't think they can do anything with the valve on the pump with the computer.

[Jimamatic]

Well, My truck is at the dealer getting a new
injection pump for the lopey idle problem. They
said it should be ready by midday tomorrow. I
hope it solves the problem. Sounds like those
who've had this done fixed the lope. I'll keep
you all posted on the outcome...

Jim

[D-max Man]

dieseldealer,

Sounds like you have a small leak in the fuel line between the fuel tank and the fuel pump causing it to loose its prime.

[tmorris]

I had the same problems...esp when cold but seemed to get worse. I took it in several times before the 36K warranty expired as numerous people had I'd the problem as the fuel pump.

Mine finally triggered the check eng lite and it ended up being the fuel pump. Most dealers seem to "know" of the problem, but won't fix it until it triggers the lite.

Once I got mine fixed...problem totally went away.

Hope that helps.

Terry

[hoot]

tmorris,

I believe we are good to 5 years and 100,000 miles on the pump. Hopefully they'll do like they did with the 6.5 and extend the warranty. I can't believe they have injection pump issues after the 6.5 fiasco.

[Black Dog]

Took mine in yesterday for the hot idle lope. Never tripped a code. New pump on order, should be here next week. The tech just called the support line, and they had him take a snapshot of the fuel pressure and compare to one that is available on-line. When he called back, they said order a pump.

[SoMnDMAX]

Still no pump for me. The dealer has had the order cancelled twice by GM. Now, as of Monday GM finally accepted the order and the pump SHOULD be here today, barring another cancellation or back order condition.

I have an easier time getting parts for my CBX (motorcycle), and it's been out of production for 21 years!!! How ef'n ridiculous!!! :mad: :mad:

At least my truck still runs. When my fuel pressure sender failed the first summer I owned the truck, it sat in the shop waiting for parts for just about two weeks. GM cancelled the parts order twice, and in order to get the sender, a call had to be placed to the regional rep - by the parts man- to finally get the function block. The truck almost stayed there permanently.
_______________________________________________

On Edit-

Woo Hoo!!! The pump is here!!! Monday, 8:00 AM my truck is going in to get fixed!! Finally.... smile.gif

[ 12-13-2002: Message edited by: SoMnDMAX ]</p>

[Jimamatic]

Just got my truck back today. Got the new injection pump for lopey idle. The tech said
the cold lope was greater than 100 rpm, limit
is 50 rpm. According to the service writter,
the guy that worked on my rig has over 20 yrs
experience in the business. Seems to have done
a good job. Hav'nt started my truck cold yet,
but I can tell it runs much better than before.
Idles much smoother now and does'nt surge at
all in D when stopped. The dealership had the
pump in stock and did not give me any guff about
repair under warranty. I've got a pretty good
relationship with them, maybe that helped.
Good luck to those waiting for the fix....

Jim
-----------------
K2500hd 4x4 c/c s/b d/a finally drives like a
40k rig....

[Black Dog]

Mine is now fixed also. They ordered the pump last Thursday, it was in on Monday. They said the pumps were on back order, but they got one from another dealer. Took the tech a day and a half to swap out the pump. I only drove it two miles back here to work from the dealership so far, but the idle surge seems to be gone. They rented me an '03 1/2 ton 4WD Chevy to use last night, and boy am I glad to have my truck back. The '03 1/2 ton seems like a low rider in comparison to my truck. It also had an airbag warning light that would not turn off, a wind noise from the driver's door weatherstrip that would drive you nuts in short order, and a rattle from the rear passenger area. The '03 also had P rated Goodyear tires that completely sucked for handling and had NO traction on wet roads. I can't complain about the 5.3 though.

[afp]

I have a very minor lope when cold. I talked to the DMax guy at the local Chevy house, andasked how much lope was needed before they's replace the pump. He said it was up to me. I'll take it in whan I get a break in my schedule.

Blaine

[SoMnDMAX]

My pump came in last Friday, the truck went into the shop on Monday, and was finished Wednesday afternoon. They had some trouble getting the gaskets necessary to reassemble the engine.

All is well, runs like a top!!! No lope, no slow speed roughness, and did I mention it runs better?

I'm a happy camper again!! :D

'99 Ford Ranger loaner... Kind of a tight fit for someone 6' 6" and 315 lbs.... :eek:

[ 12-21-2002: Message edited by: SoMnDMAX ]</p>

[6.6L&94ImpalaSS]

Do any of you guy's with the lope also have blue smoke from the tail pipe?

When my lopes (not all the time - hot or cold), I get an aweful lot of blue smoke pouring out the tailpipe.

I am in a battle with my dealer to fix my issues, but my lope comes and goes, so it is tough to get to the dealer when it is doing it so they don't think im nuts.

Mike

[mackin]

I tend to believe Blue smoke is caused by poor fuel or injectors (not that that will make you feel better).....I'd try running a additive and see if it subsides.....I wouldn't mention this to you know who as a attempted resolve.....So far (very early on) I'm getting good results from Total Power....

How big is your mail box (email)????I got a mpeg 8.4 mb of my blue smoke,idle no load, rpm increasing.....Got DSL??? This was at a fuel filter change 3/4 thousand miles ago....I'll be doing it again after a FEW tanks of Total Power+,to compare.....

MAC

Mind you I have the Lop.....Yes cold and minor hot, but better now with additive especially cold....What is in that stuff???? :eek:

[6.6L&94ImpalaSS]

I do use an additive (Stanadyne Performance Formula Conditioner), fuel filter changed every 3000 miles and I get my fuel from reputable stations. The blue smoke ONLY occurs during the lope.

Mike

[MNBowTie]

6.6L&94ImpalaSS,

Sounds like I have the same blue smoke issue you

[armalite]

Anyone else get their pump replaced? Anyone find out what GM has determined to be the real cause of the lopey idle? My fuel pump is getting replaced and I can't wait to have my truck back especially with a nice smooth idle.

[Livin2DMax]

6.6L,

Mine "loped" when cold from the get go. Local dealers basically gave me the "normal for a diesel" diagnosis until finally it started smoking one day (around 3000mi)....lots of blue smoke. They couldn't ignore it then...took a look and found a bad injector. My truck is now at 12000mi and purrs like it should no matter what the temp.

[6.6L&94ImpalaSS]

Livin2DMax,

I have had the Tech II hooked up when it was lopeing and blue smoke coming out the tailpipe. We found the injector pulse width hi on some injectors, but it would change from one to another. Also, the rpm's would bounce 200 rpm. In any case the tech said it was out of spec and I had a problem. So I set up an appointment a week later and the truck, believe it or not was running fine and they could not duplicate the problems. Charged me $135 (two hours of looking it over)and said have a nice day.

I have been compiling data from the post here and I gave the information to the service manager. I told them it does not do it all the time, but here is my problems and gave him a stack of posts to read. I then told him to call me when they get the approval to fix it, or I will try to drive it in when it starts to act up again.

It has been fun for me.

Mike

[armalite]

Just got my truck back last night. New Injector pump installed. Idles great and runs great so far...

[D-max Man]

armalite,

What causes the lopey idle is RUST. The RPCV solonid sleeve would rust if water got ito the system and cause it to stick on the eairly models. GM switched over to a stainless steel sleeve and eliminated the problem but all trucks with the old design have the potential forthis problem if enough water gets into the fuel system.

[woundedbear]

D-max Man,

Do you know the build date in which the stainless sleeve was first used?

[D-max Man]

I don't know exactly but I believe it was near the end of the 2001 model year.

[armalite]

D-max,

I am hoping the new pump will address the problem of anything non-stainless steel. The dealership did reference Preliminary Information Bulletin # PI0037 on my work order.

[mackin]

The "partial" software reflash that was flashed or loaded in my truck last week, was the lopey idle fix....Does seem to quiet it down, but not eliminate entirely....May just be the pump after all,since it lopes about the same HOT....Not ready for a dealer trip,yet....Well I'm hoping I'm late 01,May....Considering July is normal cut off....

MAC ;)

[ 01-07-2003: Message edited by: mackin ]</p>

[D-max Man]

The reflash is only for a cold lope. If it lopes when hot, the RPCV is most likley the problem.

[hoot]

My truck has a slight lope when cold that has almost gone away since I started using FPPF additive.

Will that RPCV valve eventually go bad because of a design issue or was it a mechanical/assy issue?

In other words.... will all 2001 pumps eventually get replaced?

[D-max Man]

Hoot,
As long as the sleeve doesn

[MountainMax]

D-max Man; It's good to see you on the board. I haven't seen you post in awile. Very few if any of the newer members know who you are and what you did for us early members (01 owners) when no one knew what was wrong or how to fix it. I see in this case you have'nt lost the touch. It can't be said enough.... but THANKS for all you've done for us.

[D-max Man]

MountainMax,
Thanks for the kind words.
I have been very busy latley. In the last 6 months I got married, sold one house and bought another, moved, changed jobs, spent 3 weekends in Columbus, Ohio at the AQHA Wolrd Congress (D-Max specialist for GMC) & still had to run my own business.

Other than that things have been a bit slow. :D

I will help when I can but I don't have direct acess to all the latest developments on the D-Max anymore. (I do still have contacts though).

For the sake of the newbe's:
http://www.thedieselpage.com/duramax/powrtour.htm
I am the big guy next to the truck.

[hoot]

################################################## ###
Hoot,
As long as the sleeve doesn

[6.6L&94ImpalaSS]

D-max man,

Can the rust and sticking cause blue smoke to occur when the lope is present or is this an injector issue.

I ask, because with 65,000 miles on the truck I need to get all my warranty issues taken care of soon.

Mike

[mackin]

Rust ..... :confused:

What type of STEEL are they made off???? If stainless anyone know the alloy???

Got one to send ,I'll tell you exactly what it is ???


MAC ;)

Edited for not proof reading,I meant valve sleeve,not inj cup........ :rolleyes:

[ 01-08-2003: Message edited by: mackin ]</p>

[D-max Man]

Mac,

We are talking about the Rail Pressure Control Valve (RPCV). They do use stainless now but many 2001's were built before they changed to it.

6.6L&94ImpalaSS,

I don't know about the smoking issue but it causes a jearky response(sawtooth wave pattern for you tech'y types) that is mostly noticable at lower speeds.

[ 01-08-2003: Message edited by: D-max Man ]</p>

[mackin]

D-max Man

OK so what was the original material, if you know or can say? I'm just :confused: on the RUST.... How much water could be in the fuel to saturate it enough to form pits and rust in the valve that quickly, and not show a constant water in fuel warning......I could see if it were to sit for extended periods of time,possibly.....

I could see if it were made out of a Magnetic Iron,worse than a low grade carbon...That stuff if you breath on a dry (no oil) spot it would RUST overnite....Hope they didn't make the sleeve out of that,that's refrigerator washer dryer outer skins.....I'm sure they didn't ,just an example....

I'm not doubting you,at all,I'd just like to know what they used.......So I can hope I don't have it,or get in line for a new pump......

MAC smile.gif

[D-max Man]

Mac,
I don't know what material was used on the early ones but the tolerances are so tight that it doesn