Early morning engine bucking or lurching solved!

Dieselworld

Veteran Member
Joined
Mar 8, 1999
Location
Atlanta, GA USA
After having the dreaded stumble or bucking on the first run of the day for the Tdi, I noticed that running cetane boost cured the problem. I have run 3 tanks of cetane boost from Amsoil and have not had one instance of the engine bucking in the morning. Nothing else has changed except that variable. Evidently the bucking is similar to a gasoline engine misfiring or running a to "rich" mixture. Since the engine is cold as well as the fuel the thermal efficiency should be at its lowest. The low cetane in the USA must agrivate this condition and give us the dreaded bucking. I can only deduce that increased cetane helps the fuel to burn quicker in a low thermal state. While this may not be the total "scientific" explanation to why this seems to cure the problem, on a cause and effect relationship it is working and continues to work.

If anybody else is having this problem give it a try and see if it helps you.

Chow
 

Ric Woodruff

BANNED, Ric went to Coventry.
Joined
Feb 19, 1999
Congradulations Russell! You found a reason to actually justify using a cetane booster.

Also, it is funny that you mention the problem today because just this morning, I experienced the very same thing. It has not happened for probably 6 months, and may not happen for another 6 months.

If the problem is really due to low cetane, one would think that a particular tank of fuel would be especially pesky until you fill up again. Do keep us informed. This is an especially interesting observation.

I had a 4 cylinder 1981 Ford Fairmont that had a "Feedback Fuel System" (computer controlled?) that behaved the same way. It did not matter if the engine was hot or cold. Being in an accelerate or decelerate mode, it ran well, but under steady state conditions, it tended to buck like the TDI occasionally does. This leads me to believe that under certain conditions the ECU goes into an unstable feedback mode.

I have never seen the problem when the engine was warm. Different engine parts heat up at different rates. I believe that the problem is related to that fact.
 

jaydhall

Veteran Member
Joined
Apr 2, 1999
Location
Aurora Colorado
TDI
2012 Passat SE, 1999 NB, 1999.5 Jetta GLS, 2004 Jetta
Russell,

I have been thinking about the amsoil stuff. It seems pretty good. How much is the ctane booster? I am thinking of becoming a 'dealer' and getting a price break.

Mickey,
Now this is not the kind of dealer you spoke about in the other thread. So, don't be telling the Police to look out for a Siver Jetta TDI! (I do not fit the profile...)
 

Dieselworld

Veteran Member
Joined
Mar 8, 1999
Location
Atlanta, GA USA
jaydhall,
I believe the cetane boost is about $4-$5 per can and will treat between 100-200 gallons of fuel. I use 2oz per tank full. If you will give me your address I will send you the form you need to sign up as a dealer and send to Amsoil. If you can email me direct or want to phone me thats fine.
(770) 435-7970 ext. 4567
 

Farmboy

Veteran Member
Joined
Jul 29, 1999
Location
Bloomington (Minneapolis), MN, USA
TDI
'15 Golf SE TDI 6spd 109k miles; '00 A4 NB 5spd 216k; '96 B4 Passat Sedan 220k
The previous thread on lurching kind of surprised me, as I hadn't 'noticed' it myself, but I filed it away in the back of my mind. After reading through another thread or two discussing glow plugs and pre-heat I stopped paying attention to my light and started the car right up and drove off as soon as I felt I could trust that the oil pressure was up. Even when the temp is in the 70F/24C range, with a cold car at light throttle I experience mild lurching.

It's nearly always there, but I notice it much less when I take the time to let the preheat run it's course and let ther car run for a minute or five before rolling. Early on in life with much less refined vehicles I had learned that certain throttle positions with a cold engine were to be avoided, depending on the situation.

A person could develop a response to floor it when the lurching starts... but that will help shorten your engine life. Instead I developed an automatic response to shift up through the gears letting the engine stay basically at idle until I achieved the speed I wanted for the short term or until the car was warm enough to drive normally.

Also, I learned to 'feather' the accelerator when necessary - a skill that has saved me when one of my el cheapo cars has wanted to die in front of approaching traffic.

I also learned that if I don't 'tripod' my right foot against the tunnel, feedback through my foot can make the lurching much, much worse.

Does any of this make sense?

Of course, as I am learning more about the potential of my car I am getting more interested in using Cetane booster anyhow, but the above is my 'Plugger' response to the problem for the near term.

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98 Jetta TDI 5spd - 2200 miles/mo

[This message has been edited by Farmboy (edited August 05, 1999).]
 

Jimmy

Veteran Member
Joined
Feb 24, 1999
Location
Canada
I hate to raise the Glow Plug issue, you may want to take a peek at some new info:
http://www.vw-industrieverkauf.de/englisch/kommunikation/pdf/tdi-technik-eng.pdf

Page 26 mentions the "afterglow" phase. If it is correct, the glow plugs are turned on for a short while whenever the engine is started, and swithced off above 2500 rpms. One surmises "afterglowing" also ceases when a coolant temp comes up a bit.

Now the ECU controls the turning on an off of the Glow plugs, and can sense if one fails. If it were fooled that your temp was above a certain value (bad coolant temp sensor perhaps?), you may not be getting any "afterglow".

It may be useful to tap a LED into the glow plug power circuit after the relay. The spot to so do would be a heavy red & white wire, form either terminal 6 or 4 of the Glow plug relay (#180). I had a look at schematic of that area at a dealer as I planned to do the same some time.
 
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mickey

Guest
For that matter, just revving your car above 2500 rpms right after starting it will shut off the glow plugs.

I wish I understood all this "bucking and kicking" stuff. Where do you people live that you even need glow plugs in the middle of the summer, anyway? Antarctica? I've never waited for the glow plug cycle if the overnight temperature stayed above 40 degrees F. or so, and I've never experienced any problems. Certainly the car doesn't run quite as smooth when it's cold as it does after warming up, but it's a diesel engine not an electric motor. If it's a nice, warm summer morning and your car is actually "bucking and kicking" and not just running slightly rough then you have a mechanical or electronic problem of some sort.

-mickey
 

Paul

Veteran Member
Joined
Mar 6, 1999
Location
LaGrangeville, NY, USA
98 Jetta TDI, ~26K miles, a little over a year old -

I never had any "bucking" or engine stumble of any kind, through summer or winter, ever !
In fact, compared to my 91 Jetta IDI, the smoothness at startup was really amazing to me. I always get in, hit the key, wait for the light to go out, start and drive away immediately. No cetane boost, stock everything,and I fill at a Citgo that has a diesel pump that says "40 cetane minimum" (yuck !!) Could be something wrong with your car ?
 

Lug_Nut

TDIClub Enthusiast, Pre-Forum Veteran Member
Joined
Jun 20, 1998
Location
Sterling, Massachusetts. USA
TDI
idi: 1988 Bolens DGT1700H, the other oil burner: 1967 Saab Sonett II two stroke
The glow plugs remain on even after the dash indicator goes out. They will go off at engine speeds above 2500 rpm, but come back on when the speed drops below that point. They will be in this mode until the coolant is above 140 degrees F, or as near to that point as I can guess from the temperature gauge. I wait for my glow plug indicator to go off before starting the engine, it just gives me time to ensure that the other idiot lights are operational. Still living with the buck.

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Jonathan Bartlett
 

Warsaw Falcon

Veteran Member
Joined
Apr 16, 1999
Location
Brandenburg
I knew there had to be other buckers and kickers out there! I have been living with this annoyance for 8 months; the dealer claims it's "normal for diesels", to which I reply HOGWASH. This is my 5th VW diesel, and the first ever to have this problem. I'll try the cetane booster, as well as monitor the glowplug cycling. Keep the input coming! I wonder how many of us would put up with this problem if we were driving a Neon!
 
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SkyPup

Guest
DI DIESEL GLOW PLUG OPERATION:
ALL TDI ENGINES INCLUDING 96-97 PASSAT, 97-98 A3 TDI JETTAS, 98-99
A4 NB TDI, 99 A4 JETTA TDI, 99 A4 GOLF TDI
VW ENGINE CODES - AHU, ALH

Due to the high efficiency of the TDI engine, the additional heat that the glow plugs provide is not needed until temperatures drop to approximately 48 degrees F. (9 degrees C.). This function is known as preglow. In addition to preglowing, the glow plugs will continue to operate after the engine is started. This is known as afterglowing and is used to reduce engine noise, improve idle quality and reduce hydrocarbon emissions. The afterglow function is enabled after every start, both hot or cold until the specified time has expired or the engine speed exceeds 2,500 rpm. The glow plug system is controlled by the Engine Control Module (ECM) and the Engine Coolant Temperature (ECT) sensor. The period of the preglow depends on the temperature of the engine coolant as determined by the ECT. A dash mounted indicator light signals the driver that preglowing is operating. Preglowing is not linked to operation of the drivers s door as in some earlier Volkswagen diesel systems.

ALL PREVIOUS NONTDI VW DIESEL ENGINES:
VW ENGINE CODES - ACC, AAZ

The glow plug system is controlled by the automatic glow plug time control module and the glow plug relay. The system is activated by the drivers s door switch. Once the door is opened and then closed, the pre-glow is initiated. The length of time that the system operates is controlled by an engine temperature sensor. Above certain temperature, the system does not operate.
 
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SkyPup

Guest
I have two TDI's and have never had any bucking problems as described. The afterglow setup is to keep the combustion chamber hot enough to support compression ignition since whilst the engine is realatively cold on start-up, the heat generated first goes into the cool cylinder walls instead of into providing heat of combustion, it also improves emissions condsiderably too.
I would tend to believe that this bucking could be attributable to clogged or malfunctioning injectors as the ECU reroutes fuel immediately to the other cylinders to makeup for a loss in a cylinder. In fact, disconnect one of the injectors totally and NO CHANGE in idle or operation is detectable! The ECU can support a 25% loss in power and correct for it internally.
Both my TDI's, when I start up first thing in the morning, I idle in 1st, 2nd, and 3rd the two mile ride I have to my front gate, thereby allowing the engine to slowly warm up. During this time, winter, spring or summer, there has never been any bucking or stalling whatsoever, so that indicates that indeed this situation is problematic and not normal. Once I have idled out the driveway and passed the gate, I run the engine normally. Even idling in any gear below 4th, never have experienced any difficulty.
Hope that helps somewhat
 

Dieselworld

Veteran Member
Joined
Mar 8, 1999
Location
Atlanta, GA USA
I think the real issue here is a thermal one. A "cold" diesel engine, at whatever temperature is at a small disadvantage in terms of combustion. The inherant nature of using physics to burn a substance introduced into super compressed air (around 1800 degrees) will rise as more heat can be kept inside the combustion chamber. At 0 degrees or 100 degrees outside temperature, the engine needs some room to get the combustion temp to a level where the fuel burns without much fuss. Heat flows to a cold source, so until the cylinder walls and surrounding metal surfaces are at or near combustion temp, the engine will be at a thermal disadvantage. Fuel quality and cetane levels can assist this thermal problem by being easier to burn. Remember cetane increases the fuels susciptible to burning, octane in gas slows down the rate at which fuel will burn.

So those of you who do not experience this bucking might have fuel with better cetane rating or possibly better compression etc. Many factors probably contribute to this lurching and sinse every engine is not exactly the same as the next one, this could be a compound result. It might be that a few psi difference in an engine that bucks and one that does not could make the difference. If the compression ratio for one car measured is 18.5 and another is 19.2 there will be a sight increase in the temperature at the maximum compression stroke. Say 1800 degrees compared to 1897 degrees.(just relation example) This might be enough to allow the combustion process to go almost unnoticed.

The bottom line is if all systems check out ok, that bucking, while not normal is probaly more fuel cured than anything else. VW telling people that this is normal is a COP OUT period!

Chow
 

dparnell

Top Post Dawg
Joined
Mar 14, 1999
Location
Herron Island, WA
TDI
2003 Jetta Wagon
Someone asked if Dr Diesel raises cetane---it really doesn't. Most rough running of diesels on start up is due to low ambient temperature which make the oil thicker when using a single wt oil. When the engine warms up this goes away. If you are already using a multigrade 5w-something, then I don't know---I run into this problem with diesels using a straight 30wt.

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Plastic19

Active member
Joined
Feb 20, 1999
Location
Grayslake, IL USA
My .02 on the bucking.

A month or so ago my dealer replaced my ECU. Before the change I did not experience the bucking problem. With the new ECU I have the problem. Although, to me it is not really that annoying. As long as I don't accelerate to hard in first gear it is hardly noticeable. The bucking usually stops after I shift into second gear.

Does anyone with an after market chip experience the bucking?
 
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mickey

Guest
Good question. Maybe EVERYONE should get a Wetterauer chip!

I never had the problem before or after "the chip".

-mickey
 

Jimmy

Veteran Member
Joined
Feb 24, 1999
Location
Canada
Well here is another thought. Those of you with "bucking engines": Have you disconnected the battery? Did you take it to the dealer afterwards and have them set the ECU back to "basic settings" ? I read several of the TSB's, and it is repeated in each one where the battery has been disconnected, that this must be done. It is silly, but one of the important settings is "throttle adaptation". Take a peek at the following:
http://tech.vw.com/pdf/01-98-14.pdf

This is for the Beetle, but I think it applies to the Jetta & Golf as well. I guess the question must be posed: Did anyone ever disconnect their battery and then notice any difference in performace?
 

dparnell

Top Post Dawg
Joined
Mar 14, 1999
Location
Herron Island, WA
TDI
2003 Jetta Wagon
I had chinese food last night---the fortune cookie read:
The chip and power box are underated by those who don't have them and appreciated by those who do.

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[This message has been edited by dparnell (edited August 07, 1999).]
 

Ric Woodruff

BANNED, Ric went to Coventry.
Joined
Feb 19, 1999
I disconnected my battery (and removed it) a few weeks ago in order to remove the intercooler input duct, in order to look inside to see how clean it is.

The performance was exactly the same afterwards and the infrequent bucking is still about the same.
 
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mickey

Guest
"Overrated and overpriced"? Spoken like somebody who wishes he could afford one. I DO have a Wetterauer chip, and there is nothing you can do to get that big a power boost and seamless operation for anywhere near the price. They would be cheap at twice the price.

-mickey

p.s. What was I saying about a possible "Vortex Invasion"? They're heeeeerrrre!
 

Bry

Well-known member
Joined
Jun 30, 1999
Location
Atlanta, Georgia, USA
As far as my engine is concerned, I don't think the cetane rating has anything to do with the bucking/lurching. It seems to be fickle, coming and going when it likes, without rhyme nor reason. All I've managed to deduce is that it isn't temperature related (I live in Florida, and it did it to me just the other day), nor does the fuel seem to be a factor. In my instance its gone after no more than a block or so of travel. Maybe the ECU is trying to apply a defective "map" or something?!?

Also, is there anyone who has Wetted their TDI and has the lurch? Could be an extra selling point for Der Chippen.

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96 Passat TDI (sedan)
 

dzajano

Active member
Joined
Mar 13, 1999
Location
Phoenix, MD, USA
I haven't had any bucking at all in A4 w/ 14,500 miles. Did have problem with glow plug light blinking intermittently. First trip to the dealer fixed it - for one week. When it came back I let it go until it occurred all the time. Also noted that cruise control did not function intermittently when glow plug lamp blinked. This time it appears to be fixed for good - at least I haven't seen the glow plug light flash except when I start the car in the morning. What did the dealer do? Replaced the parking brake warning light switch and "repaired wiring at the brakes". Go figure.
 

Fritz

Veteran Member
Joined
Jun 30, 1999
Location
Marietta, Georgia USA
If the dealer is correct who said that the "bucking" is normal for the TDI, I'm glad my
99TDI is "abnormal."

I have never experienced any of the mentioned
bucking.

Don't think I'll have my car "fixed" either.
Hehe

Fritz
 

lundgrji

Active member
Joined
Mar 3, 1999
Location
Minnesota, USA
My 98 NB TDI bucks or surges for the first block while lightly accelerating in first gear up a slight grade out of my neighborhood. It happens at any ambient temp. after an overnight cold soak. It goes away after shifting into second. Perhaps this condition only occurs under certain conditions; i.e. light load, first gear, ect... and those who do not experience it have a different traffic/road situation. Some info. that would be useful to know includes:

How long does engine idle after starting and pulling out of driveway, or into traffic, ect...

How aggressively must you accelerate the first minute of operation; do you pull directly onto a highway or putter through residential roads immediately after starting?

Is the car garaged? Just a wild guess, but if the garage temp is significanly different than outside air temp. there could be some effect on engine operation since on start-up the sensors tell the computer one thing, but then experience a totally different temp. a moment later. Just a guess.

I'm going to do some experimenting with my NB to see if changing my routine for the first minute of engine operation affects the bucking. I have been turning the key immediately when above 40 F, letting it idle for 5 seconds then idle out of the driveway in first gear(I always back it into the garage). When I turn onto the residential road after 40 feet of idling across the driveway I lightly accelerate, and that's when it bucks or surges.
 

Peter Cheuk

Gasser :P
Joined
Aug 31, 1998
Location
Daly City, Calif., USA
TDI
'06 Jetta GLI
I only experienced the cold bucking/lurching after installing the Hopa module and tuning it for power. This went away pretty much altogether after restricting the EGR. Now, it's back but not as severe as it used to be (must be the electronics 'learning' that the EGR doesn't flow as good as it used to). Now, I get a mild lurch after every cold start. Doesn't matter if I start in the morning (neither parked in a warm garage with cold outside air, or parked outside overnight) or at the end of the day (parked outside). As long as the motor's cold, it lurches.
 

josh_w

New member
Joined
Aug 13, 1999
Location
Columbus, OH, USA
BUY YOUR FUEL SOMEWHERE ELSE!!

My now x-wife insisted on putting BP crap fuel in our new Jetta because the station was close to work for her. Then she would whine about how crappy VWs were when it sputtered and stalled on her way to work in the mornings. I begged her to stop getting fuel at BP because of what I'd read on various VW mailing lists. She continued, and eventually had to have the 2-month-old car TOWED to the dealership one morning when it stalled at a stoplight. They told her to stop buying crappy fuel, to buy from Marathon or Shell. She listened to them, and after a tankfull, the problem went away.

It seams that the additives some companies put in their fuel can be a problem, as can water that gets into their tanks. On cool mornings, something must be condensing somewhere, leaving you with just air or water vapor hitting your spark instead of fuel. This would explain whay adding the booster would help.

I've also found that my '83 GTI runs and idles better on high-test,even though it has a low-compression engine, and VW says it should be fine on 87 octane. The same proved true for a friend of mine who's 89 GLI got to where it couldn't even lurch out of the driveway in the morning. It ran fine in the afternoon, and I had him fill-up with Premium - no more problems.

was that long-winded enough.
 

Lug_Nut

TDIClub Enthusiast, Pre-Forum Veteran Member
Joined
Jun 20, 1998
Location
Sterling, Massachusetts. USA
TDI
idi: 1988 Bolens DGT1700H, the other oil burner: 1967 Saab Sonett II two stroke
The "Bucking" on my 1996 Passat has existed at least for 80,000 miles now. I have found that constant low load engine speeds (no or very light acceleration), just over idle (about 1200 rpm), with a relatively cold (under 100 F.) coolant temp will create this phenomenon. I simply have avoided it by accelerating harder, or running the engine slightly faster or slower or, on rare occasions, waiting for the coolant temp to rise more. I have been doing this for so long that I do not even think of the reason why. I also do not recall experiencing this phenomenon prior to the ECU and injectorectomy performed around 20,000 miles due to excessive smoking.

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Jonathan Bartlett
 
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mickey

Guest
Jeez, Josh! I'd be miffed if my wife filled my Bug with crud, but divorce seems a little extreme!


-mickey
 
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