1.9L engine miss at 2800 rpm?

[84Westy48]

Hello Samba Fourm,

Recently my 84 Westy 1.9L gas engine has started to miss at exactly 2800 rpm. Prior and after 2800 rpm it runs fine.

Any ideas as to where I should start trouble shooting?

Thank you,
John

[0to60in6min]

seems like a worn spot on the AFM's carbon track to me...

[hdenter]

Is that just at idle, or while driving? Does it do it in any gear at that RPM?

Hans
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'79 triple white convertible bug
'84 sunroof vanagon
'85 weekender

[Ahwahnee]

A simple thing you might try is cleaning the AFM track. I use some spray contact cleaner from Radio Shack but I think it is just alcohol and a light lubricant.

You can watch the AFM arm/contact as you rev to see if the action is smooth. You can also test the voltage output to look for any 'drop-outs'. It cannot be reliably tested with just your usual ohmmeter.

[84Westy48]

Great place to start troubleshooting. Will let you know.
Thank you,
John

[0to60in6min]

if it is a worn spot on the carbon track you could move the whole plate a bit (a fraction) so the contact point will be on a new track.

[Ahwahnee]

The track can also be changed by slightly modifying the bend in the arm -- tricky and possibly risky but it did improve mine.

Before:


Link


After:


Link

[84Westy48]

Here is a picture of 34 years of grime. Not to bad really. Have not had a chance to take on a substantial test drive yet but it seems to have made a difference.

Thanks again for your posts,
John

[/img]

[84Westy48]

The cleaning of the AFM was not enough to eliminate the miss at 2800 rpm. Decided to take your advise and adjust the location of the arm on the shaft. I lowered the arm as much as possible which moved the contact points slightly further north. Seems to be tracking on a slightly different location and the engine miss is not longer present.

Thanks again for the info.

John

[djkeev]

Pop your distributor cap, look at your rotor.

Is it one piece or do your have an RPM limiting rotor installed?

Dave
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[84Westy48]

Hi Dave,

One piece rotor.

[84Westy48]

I am still having the problem. So far I have done a general tune up. Plugs, wires, cap and, rotor. Also replaced the AFM and the wire harness that connects to the AFM.

I have cleaned the ground wires on the block and plan to clean the wires below the coil next.

GoWesty mentioned the throttle position sensors might be the issue. What do you guys think?

What should I investigate next?

[84Westy48]

Would like to update my process of eliminating the miss I am getting at 2800 rpm during acceleration and when at a constant speed on the freeway.

This is what I have done so far:

Replaced AFM with a remanufactured GoWesty part.
Replaced plug harness at the AFM.
Replaced boot between AFM and TB.
Tune up consisting of plugs, wires, cap and rotor and timing.
Replaced distributor with new Bosch.
Replaced coil.
Cleaned ground connections. Engine block to frame.
Cleaned computer harness.
Replaced vacuum lines.
Inspected both micro switches on TB. Both make clicking sound just off idle and at wide open throttle.

The tough part is I use the van while working in the Bay Area so I don’t have a lot of time to drop it off at a reputable shop. Most of the work I have done is replacing parts in the attempt to repair the issue. In the next year I plan on upgrading to a 2.1 from GoWesty so I don’t mind replacing some of the parts that will go on the new engine. The engine has over 250,000 miles and until recently it has ran great. I would still like to fix this issue.

I was thinking of replacing the throttle body next which I would do when putting in the new engine anyway. Do you guys know if I can upgrade to the TB with only one micro switch?

Thanks for your help.

[shagginwagon83]

I think you can. I have a two switch and I believe on Gowestys ad it recommends you buying another product?

[Wildthings]

Try bypassing your digital idle stabilizer. If you haven't done so I would also recommend dumping some FI cleaner into your tank. This can sometimes solve persistent problems in minutes.

[calo1956]

Be it far for me to be a expert in this problems, as i have had more than my fair share, but in all the tune up parts you mentioned, you didn't mention the condenser. I don't know if it would make a difference, but i would try that as well....
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[TomInAlaska]

In the interest of not creating more threads on the same topic...

Since I've been driving my van a little more lately, I can't help but notice a hard miss at about ~2800 rpm. It runs great below and above, but every single time the engine is at ~2800 rpm and at partial or full throttle (accelerating or cruising) it bucks and misses. I can easily accelerate through the miss and continue accelerating until I upshift and then have the same miss at the same rpm in the next gear. Happens in all four gears (presumably in reverse, too, but I haven't tried!) and when cold or warmed up to operating temp.

As far as what all is new/serviced up to now that may be related: new plugs, wires, cap, rotor, checked and cleaned the Hall effect sensor with aerosol electronic cleaner and straightened the slightly bent reluctor wheel, cleaned injectors, all new fuel lines (ALL of them), new fuel pump and filter, checked all the vacuum lines I can find, cleaned all the electrical connectors and ground I can find (I'll do another round of ground cleaning later today), checked the AFM and found the carbon track looked brand new and that someone had installed an anti-vanagon syndrome capacitor inside the AFM housing so that's cool, checked the temp sensors' wiring and replace a small section of the temp1 wire that was cracked and frayed inside the plastic sheath, and replaced the alternator wiring harness with one from gowesty. I've also checked and set the timing and all the voltages/ohms at the ECU plug. I haven't checked the actual fuel pressure or adjusted the valves yet. I also have some slight exhaust leaks at the heads that I'm going to address this weekend with a new gasket set (probably hollow out the cat, too if it isn't already). And I don't actually have am idle stabilizer so that is definitely bypassed!

Given my issue (and the OP's) occurs at a very specific rpm, I have to assume its something in the ignition or maybe in the ECU. Pretty much the only things I haven't changed on my van are the distributor, coil, and ECU all of which look like original equipment. I think I read on a post somewhere on here that someone had a similar issue and a new coil cleared it up, so that's my the next part I'm going to throw at the problem unless anyone has any other ideas?
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'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=

[Howesight]

The symptoms sound like a misadjusted or failing throttle switch. The Digijet ECU is programmed to cut fuel when the engine has a trailing-throttle condition, like going down a steep hill with foot off the accelerator. This is done by cutting the signal to all 4 injectors. This saves fuel that otherwise would be wasted, and reduces exhaust emissions. As the vehicle slows and engine rpm's drop, the ECU causes the "fuel cut" condition to stop and allows the injectors to inject fuel again. This is to prevent stalling.

All of this is dependent upon the ECU receiving the correct input from the throttle switches. The correct signal depends on adjustment of the throttle switches, and upon the wiring working as designed, as opposed to intermittent connection(s).

All this is somewhat complicated by the fact that the WBX throttle body is poorly designed and as a result, wears the throttle shaft quite a bit in normal operation. The worn throttle shaft contributes to uneven and intermittent operation of the throttle switches.

There are no other features in the Digijet system that are programmed to occur at a specified rpm, except for small increments in spark timing which would not cause the described symptoms. Similarly, there is nothing in the AFM that would or could pinpoint exactly 2,800 rpm. This is almost certainly a problem with deceleration fuel cut, and the solution will be finding why the signal from the switch circuit to the ECU is not consistent or not properly adjusted. For some reason, in your case, the ECU must be receiving a signal that the throttle idle switch is, even if intermittently, in the closed throttle position. This could occur with a failing switch (they do get dirt and oxidation on the contacts) or other parts of the wiring in that circuit.

See pages 70 to 74 in the Digijet Pro-Training manual, especially page 71.

Here in the Samba FAQ section, I found this link to the Digijet Pro-Training manual:

http://loam.org/vw/Vanagon/VanagonProTraining/FuelSystems/
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'86 Syncro Westy SVX

[TomInAlaska]

[TomInAlaska]

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?
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'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=