Author |
Message |
darindeb Samba Member
Joined: February 21, 2016 Posts: 5 Location: United States
|
Posted: Sat Jun 23, 2018 8:58 am Post subject: Type 4 misfire reasons |
|
|
We have a 72 411, that has about 500 miles on shop built motor with hydrallic lifters. Marvin (cars name as its green), has a runability issue. Starts and accelerates well. But while running under steady throttle, wants to cut out, as if missing. Valves have been adjusted and are correct, new injectors and fuel filters clean.
Any suggestions as we are stumped? Really dont want to swap to carbs. But can as we have an extra set.
Any help would be greatly appreciated.
Thanks, Darindeb |
|
Back to top |
|
|
raygreenwood Samba Member
Joined: November 24, 2008 Posts: 21519 Location: Oklahoma City
|
Posted: Sat Jun 23, 2018 10:24 am Post subject: Re: Type 4 misfire reasons |
|
|
darindeb wrote: |
We have a 72 411, that has about 500 miles on shop built motor with hydrallic lifters. Marvin (cars name as its green), has a runability issue. Starts and accelerates well. But while running under steady throttle, wants to cut out, as if missing. Valves have been adjusted and are correct, new injectors and fuel filters clean.
Any suggestions as we are stumped? Really dont want to swap to carbs. But can as we have an extra set.
Any help would be greatly appreciated.
Thanks, Darindeb |
DO NOT ever, ever, ever, ever, ever....use hydraulic lifters with D-jet injection.
D-jet requires a very specific level of valve adjustment....that you will not get with hydraulic lifters. There will always be some idle and very fine fuel injection timing issues because of it. However that is not your problem right now.
Do not replace the injection with carbs. They do not hold a candle to the injection.
What are the specifications your engine was built with?
We need to know exactly what camshaft you used. Currently....there are few if any hydraulic camshafts that I know if that have the correct intake valve timing and lobe spacing for D-jet injection.
Also...what is the compression ratio that was used? Low compression on D-jet runs poorly...because it is hard to tune the fuel mixture correctly. The factory used 8.2:1 compression with domed pistons on all 1.7L with D-jet in the US except California versions and those ran like sh*t. You can run higher upwards to 8.5:1 without any issues.
Also...what valves were used (diameter). Either stock or up to 41mm x 35mm or an absolute max of 42 x 36 on a 1.7L and that last set will require a little tuning.
If everything was perfect at the moment...this could be anything from a vacuum leak in one of many locations....to a loose ground wire on the case centerline....to an improperly adjusted TVS (very commonly creates this exact symptom)....to improper fuel mixture (which is caused by vacuum leaks and improper fuel pressure and MPS adjustment).
Start by posting some pictures and let us wee condition and what is missing and we can help.
Who built the engine and what is their experience with 411 and 412? Bus experience does not necessarily count.
Ray |
|
Back to top |
|
|
Lars S Samba Member
Joined: October 04, 2007 Posts: 785 Location: Sweden
|
Posted: Sat Jun 23, 2018 10:27 pm Post subject: Re: Type 4 misfire reasons |
|
|
Agree with Ray, we should have more spec info to get this right.
Also has the car been running with this symptom all since the rebuild or has this occured lately?
The 1st thing I would look at with the symtoms your car have is the throttle switch (TPS). The car can be run with the TPS electrically disconnected (it will accelerate slower and idle poorly) but if it runs without bucking when unplugged the fault is likely in a worn or dirty TPS.
/Lars S _________________ Porsche 914 -72, Bahia Red daily driver
VW411 2-d -70, White, sold
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold
Husqvarna 118cc, -47, Black, Sold |
|
Back to top |
|
|
raygreenwood Samba Member
Joined: November 24, 2008 Posts: 21519 Location: Oklahoma City
|
Posted: Sun Jun 24, 2018 9:41 am Post subject: Re: Type 4 misfire reasons |
|
|
What Lars said!
To explain a little better about the issues with D-jet and hydraulic lifters.
The problem is not primarily the fact that the lifters are hydraulic. By a certain respect.....keeping effective valve lash down to 0 or near 0 can actually be a positive thing.
The problem is in two areas:
1. The fact that the lifters are hydraulic requires a softer ramp and nose design to the cam lobe to operate. This changes the injection timing in a very subtle way....to our eyes. If it also requires slight changes to ignition timing to compensate.....that right there changes the injection timing slightly.
While these two very slight timing changes have no effect on fuel mixture on the later L-jet system or with carbs......these subtle changes to injection timing affect the vacuum signature.......and D-jet uses this signature to set your main fuel mixture via the MPS.
This can cause slight lean or rich running.....and frequently an alternating cycle of lean to rich at idle and low rpm. That cycle.....changes the vacuum signature even more.....making the lean/rich spikes worse.
This is why cam changes do not have the same effect on L-jet and later injection systems. They do not use vacuum as the load measurement method.
If having hydraulic lifters wers the only factor with the camshaft.....it could be adjusted around with some tweaks to the MPS and the trigger plate.
2. The big problem.....is being able to find a hydraulic type 4 camshaft that has the proper intake valve timing and lobe center. The lobe center is not very hard to find in aftermarket cams. Web cam has several that are in the 106-108° range.
The critical part is finding one with the correct intake valve timing not an excessive amount of lift and duration.
D-jet does not have perfect injection timing. At least two valves are closed when the iniector fires. This alone is a slight idle smoothness issue.......and has some effect on vacuum signature smoothness......but it is carefully distributed to have acceptable enough timing between injection event and intake valve open points at low rpm and idle and still maintain smooth vacuum signature. Above about 1500 rpm.....its all happening so fast that the timing matters less.
But.....cams not optimized for D-jet can have vacuum signature issues all through the range and cause poor adjustability of the MPS and hesitation at shift points.
Cams that are known to work well with D-jet because of the timing are the Webcam #73, the Raby 9550, 9590 and I think the Webcam 124 or 142.....its one or the other on that one. I cannot remember. Its a 914 2.0L grind.
And.....all of those are solid lifter.
The issue....which is why I ask who built the engine....is that too many people who build engines that only have bay window bus experience....have no knowledge in general of D-jet....and consider a 411 or 412 engine to simply be a bus engine with different specs so they use what works well for a bus.
In reality.. .its the other way around. The bus engine us an adaptation of a 411 engine. What works with a bus injection system.....camshaft wise....does not work for a 411/412/914.
Ray |
|
Back to top |
|
|
darindeb Samba Member
Joined: February 21, 2016 Posts: 5 Location: United States
|
Posted: Mon Jun 25, 2018 10:02 pm Post subject: Re: Type 4 misfire reasons |
|
|
This is so much information for me to take in, but l do understand. Will be getting with the shop that built it as well as last owner. Most likely last owner first and then shop.
We have put 400 miles on this motor and he had put 80 on it.
After the valves were adjusted and readjusted, we were able to get Marvin to 70 mph. Thats impressive considering the automatic trans. Its just the constant throttle that gives hiccups. Idles smooth, and accelerates well.
Will be asking these questions to last keeper and mechanic /shop.
Although a question we had has been answered. No to find what lift/duration cam has. If it is one fact one that you mentioned, is it possible to just put in solid lifters?
Thanks to all you knowledgeable Dubbers.
We will get this right,
Darindeb
P.S. we installed air shocks at rear for proper ride height since locating correct ones was not possible. Cant tell, it looks so good. |
|
Back to top |
|
|
dawie Samba Member
Joined: July 27, 2008 Posts: 217 Location: Cape Town, South Africa
|
Posted: Tue Jun 26, 2018 12:07 am Post subject: Re: Type 4 misfire reasons |
|
|
If your hydraulic cam is the bus-type, thats a "lost case". Original hydraulic bus cam is "lazier" than even solid lifter bus cam, because of different timing (in addition to being hydraulic). It has negative overlap at 1mm, and early closing inlet valve. That cam pulls a much higher vacuum at light loads/low rpms, and restricts airflow at higher rpms. Specifically designed to lower hydro-carbon emissions at the expense of reduced torque.
D-jet's control unit is hard-wired to have mixture match longer overlap duration, higher lift, and later inlet valve closing time which is specific to the D-jet cam. |
|
Back to top |
|
|
raygreenwood Samba Member
Joined: November 24, 2008 Posts: 21519 Location: Oklahoma City
|
Posted: Tue Jun 26, 2018 8:40 am Post subject: Re: Type 4 misfire reasons |
|
|
dawie wrote: |
If your hydraulic cam is the bus-type, thats a "lost case". Original hydraulic bus cam is "lazier" than even solid lifter bus cam, because of different timing (in addition to being hydraulic). It has negative overlap at 1mm, and early closing inlet valve. That cam pulls a much higher vacuum at light loads/low rpms, and restricts airflow at higher rpms. Specifically designed to lower hydro-carbon emissions at the expense of reduced torque.
D-jet's control unit is hard-wired to have mixture match longer overlap duration, higher lift, and later inlet valve closing time which is specific to the D-jet cam. |
Very well said. I could noit have explained it better!
For the moment I would suggest carefully adjusting the TVS. That is one of the most direct causes of random misfiring when cruising with the throttle very slightly cracked open but basically stationary. Read through this thread.
https://www.thesamba.com/vw/forum/viewtopic.php?t=683230
Another item that can cause the random misfire is grounds and electrical connections. The connections must be perfect. This does NOT just mean the plugs on the components are tight fitting. The fit of the plug has no relation to the fit of the female connectors inside.
The best way to check this is to get a jewelers screwdriver or pin-out tool and remove each connector one at a time and with a small pair of needle nose pliers....lightly squeeze the rolled sides of each connector so they fit tightly on the male pin.
There are only 23 wires in the system and only 22 of these that need this done.
The other item that commonly causes this issue is the PCV valve. It is in the oil breather chimney under the nipple for the 12mm hose that connects to the center manifold.
It typically either has a cracked seal disc or because of the vacuum signature variation from your cam....is kicking open and closed when not needed causing rich spikes.
Typically a lot of us have gotten this fluctuation out of the PCV valve by removing the internal valve parts and installing a 2-3mm constant flow orifice in the line.
But doing this requires an adjustment of the MPS....so its rather advanced tuning. Ray |
|
Back to top |
|
|
darindeb Samba Member
Joined: February 21, 2016 Posts: 5 Location: United States
|
Posted: Tue Jun 26, 2018 3:30 pm Post subject: Re: Type 4 misfire reasons |
|
|
Thanks Ray and dawie.
Will look more into your advise. And double check all lashes, connections and vacuum lines.
This is a great little car. Just want it to perform without hurting it.
Will keep you posted
Darindeb |
|
Back to top |
|
|
|