Author |
Message |
jlrftype7 Samba Member
Joined: July 24, 2018 Posts: 3575 Location: Chicago
|
Posted: Fri Sep 17, 2021 11:09 pm Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
TomInAlaska wrote: |
I just got through troubleshooting the TB switches and found that I'm getting 5v at both sets of connectors, both switches are switching like they should, but they were both out of adjustment (idle wasn't too far off, but the wide-open switch was coming in waaay too soon per the instructions in the above link). I also took the liberty of adding a ground to the AFM body since I saw on another topic that somebody did that and it helped. I haven't driven it yet, but I'm hopeful this will get me closer to a solution.
While I was doing the checking and adjusting, I did notice that the throttle shaft has noticeable radial and axial play and would even sorta catch when fully closed especially when I moved the return spring to the arm it shows it being attached to in the drawings (it was attached to the same arm as the cable and didn't pull quite as much). Anyway, does that mean my TB is worn and should be replaced/upgraded? |
Yeah, they eat themselves up petty well once the wear pattern gets bad enough. Here’s my rebuilt model done by a Samba member
_________________ '68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto |
|
Back to top |
|
|
TomInAlaska Samba Member
Joined: June 02, 2007 Posts: 386 Location: Anchorage, Ak
|
Posted: Sat Sep 18, 2021 7:28 pm Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
An update after yesterday and today's tinkering session: the miss at ~2800 rpm is still there. Today I cleaned up the very corroded socket on the (what I assume is the original) coil, installed a "correct" distributor cap (late style with pins to match the new wire set), changed the terminal on the coil end of that wire to work with the early style coil so everything actually clicks together, and installed a new ground strap from the starter mounting bolt to the body for good measure. There is still a distinct miss / hesitation every time I rev up through 2800-3000 rpms. My next step is going to be to pull the throttle body and see exactly how badly worn it is and try to do something about it if its bad which I suspect is the case.
In my research into the L-Jetronic system, I've found some evidence that in at least some applications, the signal from AFM maxes out at about 3k and then the ECU runs strictly off the internal map. So, if that's the case with our engines, it almost makes sense that a very worn throttle body (and/or vacuum leaks) could cause a very abrupt change in how much fuel the ECU is sending when the revs are passing that changeover point, right? In my mind, if the map in the ECU thinks that the engine is only getting the amount of air that it did from the factory when everything was tight and new but now with all the wear and tear there's actually more air going flowing in than the map anticipates, the ECU will sharply cut the fuel to the ideal factory settings as soon as the signal from the AFM maxes out causing an abrupt miss or hesitation. Or am I grasping at internet straws? _________________ '73 Super Beetle (resto-mod/rally look, 1776)
'84 GL adventure van project (1.9L, 4speed) https://www.thesamba.com/vw/forum/viewtopic.php?t=755844&highlight= |
|
Back to top |
|
|
Wildthings Samba Member
Joined: March 13, 2005 Posts: 50334
|
Posted: Sat Sep 18, 2021 10:27 pm Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
TomInAlaska wrote: |
Or am I grasping at internet straws? |
Unless you have external vacuum leaks all the air entering the throttle body will still have passed through the AFM and have been metered. |
|
Back to top |
|
|
TomInAlaska Samba Member
Joined: June 02, 2007 Posts: 386 Location: Anchorage, Ak
|
Posted: Sat Sep 18, 2021 10:45 pm Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
I guess my question is, will the amount of air flowing through a significantly worn throttle body be different enough at the ~3000 rpm transition point when the ECU starts metering fuel based on its internal fuel map instead of the signal from the AFM (if that’s even a thing that’s happening) to cause an abrupt decrease in the fuel delivery and cause the miss or hesitation that I and at least a few others are seeing?
My first thought is, almost certainly not. But…? _________________ '73 Super Beetle (resto-mod/rally look, 1776)
'84 GL adventure van project (1.9L, 4speed) https://www.thesamba.com/vw/forum/viewtopic.php?t=755844&highlight= |
|
Back to top |
|
|
DanHoug Samba Member
Joined: December 05, 2016 Posts: 4765 Location: Bemidji, MN
|
Posted: Sun Sep 19, 2021 6:04 am Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
Tom- were this mine, i'd want to pin down whether the miss is fuel or spark related. to do that, attach a timing light to the coil lead and either rev the engine stationary if that induces the miss or bring the leads out from the engine cover, tape the timing trigger down so it is always on, and then go for a drive watching the light in the rearview mirror.
if the light goes black or fumbles for flash at 2800, you have an ignition/ECU problem.
the same can be done with a noid light between your injector and harness if the miss occurs while just revving the engine. would have to make an extension harness to watch it while going for a drive or have a helper look at it from the backseat with the engine cover off.
these two tests, 10 minutes in total, will give you a very specific place to start troubleshooting because right now you don't know if the miss is from the spark dropping out, the signal to the fuel injector dropping out, or if those two parameters are good, something entirely different. _________________ -dan
60% of what you find on the internet is wrong, including this post.
'87 Westy & '89 Westy both 2.1 4spd
Past projects can be found at--
www.thefixitworkshop.com |
|
Back to top |
|
|
djkeev Samba Moderator
Joined: September 30, 2007 Posts: 32571 Location: Reading Pennsylvania
|
|
Back to top |
|
|
TomInAlaska Samba Member
Joined: June 02, 2007 Posts: 386 Location: Anchorage, Ak
|
Posted: Sun Sep 19, 2021 10:06 am Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
Dan,
This afternoon I'll definitely put my timing light on and see if there's a spark issue and, if I can put together a tester for the injectors, that too.
Dave,
A replacement Bosch coil should be here later this week. Sadly, I couldn't find one (or even an aftermarket replacement) here in town. _________________ '73 Super Beetle (resto-mod/rally look, 1776)
'84 GL adventure van project (1.9L, 4speed) https://www.thesamba.com/vw/forum/viewtopic.php?t=755844&highlight= |
|
Back to top |
|
|
Wildthings Samba Member
Joined: March 13, 2005 Posts: 50334
|
Posted: Sun Sep 19, 2021 10:44 am Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
If you haven't done so already, try unplugging the wires from the TPS (Throttle Position Switch) |
|
Back to top |
|
|
4Gears4Tires Samba Member
Joined: October 08, 2018 Posts: 3016 Location: MD
|
Posted: Sun Sep 19, 2021 6:06 pm Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
Sounds like the only thing you haven't replaced is the ECU.
I would have originally guessed timing data loss, but you replaced the distributor and that includes the hall sensor. My next guess after the distributor would be the ECU. _________________ '87 Syncro
Ferric Oxyhydroxide Superleggera Edition |
|
Back to top |
|
|
TomInAlaska Samba Member
Joined: June 02, 2007 Posts: 386 Location: Anchorage, Ak
|
Posted: Sun Sep 19, 2021 8:38 pm Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
4Gears4Tires wrote: |
Sounds like the only thing you haven't replaced is the ECU.
I would have originally guessed timing data loss, but you replaced the distributor and that includes the hall sensor. My next guess after the distributor would be the ECU. |
Oh, I actually haven't replaced my distributor (yet!), just cleaned everything on inside as much as I could and checked the Hall unit and timing per the Bentley bible. It's on the list of things to replace, but as far as I can tell, the distributor is good.
Aside, I did pull the ECU and took the aluminum cover off to do a visual check and everything looked ok as far as possible hot spots or broken solder joints so hopefully that's good, too. <fingers crossed>
Oh, and both TPS switches are good and adjusted per the Bentley bible/training manual posted up-thread. <thumbs up> _________________ '73 Super Beetle (resto-mod/rally look, 1776)
'84 GL adventure van project (1.9L, 4speed) https://www.thesamba.com/vw/forum/viewtopic.php?t=755844&highlight= |
|
Back to top |
|
|
djkeev Samba Moderator
Joined: September 30, 2007 Posts: 32571 Location: Reading Pennsylvania
|
|
Back to top |
|
|
4Gears4Tires Samba Member
Joined: October 08, 2018 Posts: 3016 Location: MD
|
Posted: Mon Sep 20, 2021 5:51 am Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
TomInAlaska wrote: |
Oh, I actually haven't replaced my distributor (yet!), just cleaned everything on inside as much as I could and checked the Hall unit and timing per the Bentley bible. It's on the list of things to replace, but as far as I can tell, the distributor is good. |
It's not the actual distributor that I think is the issue. It's the hall sensor included as part of the distributor. The section where the engine harness plug does into.
I've had similar repeatedly specific rpm engine misses (not on a vanagon) and it always ended up being losses of timing data from the sensor, the wheel the sensor reads off, or the ECU. _________________ '87 Syncro
Ferric Oxyhydroxide Superleggera Edition |
|
Back to top |
|
|
Abscate Samba Member
Joined: October 05, 2014 Posts: 22639 Location: NYC/Upstate/ROW
|
Posted: Mon Sep 20, 2021 6:11 am Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
Have you isolated the miss to a cylinder or is it a complete loss of power?
Does she stumble at 2800 or jerk occasionally? _________________ .ssS! |
|
Back to top |
|
|
TomInAlaska Samba Member
Joined: June 02, 2007 Posts: 386 Location: Anchorage, Ak
|
Posted: Mon Sep 20, 2021 11:17 am Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
Dave,
TPSes were verified with a multimeter at the switches and at the ECU plug.
Abscate,
Its a very distinct miss/hesitation/stumble/momentary loss of power at exactly the same rpm or very small range of rpm every time I rev it through ~2800rpm. 100% repeatable and predictable and happens when stationary or driving and under all load and throttle conditions (well, all the throttle conditions that would make the engine rev past 3k anyway)
More information to add to the puzzle: looking at other topics on timing and distributors and misses/hesitations led me to check the wear in my distributor and I found that while it is very tight radially, I have about 5mm of axial/end play. I then put my timing light on and watching the flash as I revved the engine but could not make out any change in the frequency of the flashes during the miss/stumble event. I tested the light on the coil wire and on each cylinder wire for multiple rev cycles. For good measure and since I had the timing light hooked up, I checked the actual timing itself and found it to be a little bit off of the "~35degree all in / Tencentlife method" so I made a fresh mark at 2" CW from the 'U' mark on the second pulley ridge and set the timing there or a touch advanced when all the advance was in. This had the idle timing near the 'U' after I reset the idle speed to about 850rpm using the big screw on the throttle body. The engine seemed to idle smoother and have a little less rpm fluctuations up and down like it had previously and seemed to rev faster and smoother after all these tests and changes just now. However, the miss/hesitation/stumble is STILL there, but it does seem to be improving (might just be my imagination and/or wishful thinking). I'll try to actually drive the van in the next day or so and see how it does. _________________ '73 Super Beetle (resto-mod/rally look, 1776)
'84 GL adventure van project (1.9L, 4speed) https://www.thesamba.com/vw/forum/viewtopic.php?t=755844&highlight= |
|
Back to top |
|
|
Abscate Samba Member
Joined: October 05, 2014 Posts: 22639 Location: NYC/Upstate/ROW
|
Posted: Mon Sep 20, 2021 11:33 am Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
That’s pointing away from fuel delivery and filter issues.
If you are comfortable, crack the top and inspect the AFM TRACK per the post above _________________ .ssS! |
|
Back to top |
|
|
TomInAlaska Samba Member
Joined: June 02, 2007 Posts: 386 Location: Anchorage, Ak
|
Posted: Tue Sep 21, 2021 3:42 pm Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
Abscate wrote: |
That’s pointing away from fuel delivery and filter issues.
If you are comfortable, crack the top and inspect the AFM TRACK per the post above |
There might be a worn spot at the start of the track, but it looks ok to me?
I did try to check it per the Bentley Bible and found 560ohms between the 3 and 4 pin. The ohm reading between 2 and 3 varied but seemed to be very erratic. It started at 532 with the door closed then while slowly moving the door manually (I used a stiff bent wire) my trusty Fluke read "open" for a second, then varied what seemed to me erractically from ~600 ohm up to 2k and bounced around in the 1.2-1.6k range for as far as I could push the door. Shouldn't the resistance vary progressively and consistenty? Is my AFM bad? _________________ '73 Super Beetle (resto-mod/rally look, 1776)
'84 GL adventure van project (1.9L, 4speed) https://www.thesamba.com/vw/forum/viewtopic.php?t=755844&highlight= |
|
Back to top |
|
|
Abscate Samba Member
Joined: October 05, 2014 Posts: 22639 Location: NYC/Upstate/ROW
|
Posted: Tue Sep 21, 2021 4:08 pm Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
Yes, it should be smooth. I also don’t like that cap wiring very much _________________ .ssS! |
|
Back to top |
|
|
TomInAlaska Samba Member
Joined: June 02, 2007 Posts: 386 Location: Anchorage, Ak
|
Posted: Tue Sep 21, 2021 4:23 pm Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
Abscate wrote: |
Yes, it should be smooth. I also don’t like that cap wiring very much |
I didn't like that cap just hanging on there either so I soldered it in place since I had the cover off (for the fourth time ).
I also found a test procedure by Tencentlife on how to check the actual voltage signal with the ignition on and I did that and found that the voltage between pins 2 and 4 seemed to vary smoothly from ~.5v with the door closed to ~4.8v fully open. Does that sound more like it should? Should it be truly at 0v with the door closed or is that .5v ok? _________________ '73 Super Beetle (resto-mod/rally look, 1776)
'84 GL adventure van project (1.9L, 4speed) https://www.thesamba.com/vw/forum/viewtopic.php?t=755844&highlight= |
|
Back to top |
|
|
Abscate Samba Member
Joined: October 05, 2014 Posts: 22639 Location: NYC/Upstate/ROW
|
Posted: Wed Sep 22, 2021 6:58 am Post subject: Re: 1.9L engine miss at 2800 rpm? |
|
|
Waiting on the coil replacement. Ignition wires age, history too? _________________ .ssS! |
|
Back to top |
|
|
TomInAlaska Samba Member
Joined: June 02, 2007 Posts: 386 Location: Anchorage, Ak
|
|
Back to top |
|
|
|