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Valve issue? Hesitation from idle.
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kamolzt
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PostPosted: Mon May 10, 2021 9:57 pm    Post subject: Valve issue? Hesitation from idle. Reply with quote

Long time reader. Novice poster.

Hitting a wall with troubleshooting a hesitation issue with my 85 1.9L engine.

This is a GW 2.2L rebuild that is ~10 yrs and 100K on it.

I have an increasingly consistent hesitation off idle.

Engine sounds reasonable smooth at Idle and while my gas mileage isn't great seems to have decent power.

Replaced in the last 2-3 yrs:
- Rebuilt injectors
- Rebuilt ECU
- Rebuilt AFM

Recent - GW new throttle body

To me it sounds like there is consistent valve train noise even after warm up.

I did a manifold vacuum test and observed a consistent bouncing from ~8-10 in. hg. at idle. Bouncing at idle seems to indicate worn valves/ leaky valves. https://www.ih8mud.com/tech/vacuum.php

I would like to know if anyone has any guidance on next steps here. I don't really want to rebuild the engine if i don't have to. would new valves/cleaning up seats be the next step? Is it possible that i have a rounded over lobe(s) on a camshaft? Is that common with these? (seemingly not based on my search results)

I tried to measure valve lift to assess cam integrity, but got some pretty variable results and was struggling to get a dial indicator wedged in to get an accurate measurement. Also uncertain how the hydraulic lifters behave in a more static environment.

I have not done a leakdown test, yet.

Any guidance would be appreciated.

Video that is 10x longer than it needs to be. vacuum bounce is illustrated almost immediately. Major hesitation issue is towards the end like 1:40.

https://vimeo.com/547811324
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bobbyblack Premium Member
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PostPosted: Tue May 11, 2021 6:18 am    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

Thinking on this...

Question; You did a GW 2.2. Did you also change things like the coolant system to the newer style? Fill us in on what you did, or had done, maybe more thoughts will come to us as you get us a few more details.

Also, you mentioned that you've got the GW Throttle Body. This almost certainly has the single TPS, which is different from the original 1.9 engine's two. How did you deal with that issue? Has the hesitation been happening since the TB got changed? Could be as simple as an issue with the two systems not cooperating with one another.

-bobby
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MarkWard
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PostPosted: Tue May 11, 2021 7:35 am    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

Where did you check the vacuum?
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kamolzt
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PostPosted: Tue May 11, 2021 7:46 am    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

Sorry for the confusion, it is still a digijet 1.9 engine that is bored out to 2.2. Did Not do a digifant swap.

Hesitation has been happening in some form or another for a couple years. Initial attempt was to put the rebuilt injectors in it. A solution that comes up often if you search this forum for hesitation.

I have been focused on the electrical side of things. I have had it in a shop where they tried other known working ECU and AFM.

The hesitation seems to be changing/getting worse with what is now a low level backfire some of the time can be heard at the end of the video that i posted above.

Hesitation was happening previous to GW throttle body swap I thought the excessive wear on my original TB might be causing issues with air fuel mixture as there was a LOT of slop and daylight showing through the original. I followed their instructions and it is now just a 2 wire connector vs the two wires spliced into 4 connectors for the two switch setup.

Vacuum was checked tee'd off at the fuel pressure regulator. I can try again closer to the TB and see if the results are the same.

Thanks.
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MarkWard
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PostPosted: Tue May 11, 2021 8:10 am    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

The pressure regulator supply should be adequate but for testing, I'd connect the hose directly to the gauge bypassing the regulator.

You should also see what your fuel pressure is doing. Also, a hesitation is often a lean condition as the throttle plate is cracked open. The ECU needs to know precisely when that happens.

You can partially restrict the fuel return after the regulator and if drivability improves, you've narrowed it to a lean condition and will know where to start.

Your vacuum numbers seem low forgetting the pulsing.
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PostPosted: Tue May 11, 2021 8:16 am    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

So, if i am guessing correctly you might be expressing concern about the Idle Air Valve. Have you had it off, and cleaned it out good? Made sure the wire harness to it has all good connections, etc? You can take that out of the mix, from what I have read by some well trusted folks here... Even if only for a short time to just do tests, at least block it off, and/or read up on how it is supposed to function. Another friend of mine who doesn't post, but phones me, has a similar issue and has been carrying around a few IAC's for his 1.9 setup. The IACircuit board and connectors can get crusty, inside and out.
Here's a link you might have a read on about that..
https://www.thesamba.com/vw/forum/viewtopic.php?t=566331

I entirely agree about slop in the TB, I had similar issues where I couldn't adjust out enough and so I also replaced my TB, but not to the GW version. Anyway, its possible the adjustment needs to be checked to be sure that is in spec.

More; Vacuum is one interesting part, but leaks are the usual culprit. Hard to check without a smoke box. Although they are easy enough to build for a few $'s, there are plenty of folks on ebay that will build one for you at a reasonably low cost.
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Wildthings
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PostPosted: Tue May 11, 2021 10:13 am    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

If the valves are making noise, I would start by adding a quart of Marvel Mystery Oil to your engine oil. Then after it has been in for at least 100 miles I would go through and adjust the valves being very sure that you locate the point of zero lash accurately. The feel can vary greatly from valve to valve and may be very subtle on some (or all) of them. You want to use your fingers to turn the screw to find the point of contact, verses using a screwdriver.

I have always used two turns of preload and believe that if you use less than a turn you are limiting the ability of the lifters to self adjust as the miles add up and wear occurs.

You should also check that the ends of you valve stems are flat and that your adjusting screws aren't beat to heck.

For future oil changes use synthetic oil, as a synthetic will keep the insides of your engine, including your lifters, cleaner.

Your ignition timing should be 28° BTDC @3800+ rpm, hoses off and plugged. You also want your DIS bypassed when setting the timing.


Last edited by Wildthings on Tue May 11, 2021 10:51 am; edited 1 time in total
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PostPosted: Tue May 11, 2021 10:23 am    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

Possibly a leaky retard diaphragm in the vacuum advance on the distributor. Run into this time and time again. Even a rebuilt distributor could have a nice freshly painted leaky vac canister.
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Wildthings
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PostPosted: Tue May 11, 2021 10:49 am    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

simd0ggie wrote:
Possibly a leaky retard diaphragm in the vacuum advance on the distributor. Run into this time and time again. Even a rebuilt distributor could have a nice freshly painted leaky vac canister.


Which is one of the reasons your should always time a Digijet at full mechanical advance verses by the book. When timing by the book every piece of the distributor needs to work like it did when the van left the factory, but now decades later having such a distributor is pretty much a fuzzy memory.

Note that the DIS needs to be bypassed when setting the timing even when doing it at full mechanical advance, as a failing DIS can effect the timing off at any rpm, not just at idle.
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PostPosted: Tue May 11, 2021 4:58 pm    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

One vacuum leak that does not get a lot of press here is the case of the damaged diaphragm in the breather tower. This source of vacuum leaks gets more pronounced over the years as an engine develops more and more blow-by.

https://www.gowesty.com/product/mechanical/20266/breather-tower-?v=
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PostPosted: Tue May 11, 2021 5:13 pm    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

Howesight wrote:
One vacuum leak that does not get a lot of press here is the case of the damaged diaphragm in the breather tower. This source of vacuum leaks gets more pronounced over the years as an engine develops more and more blow-by.

https://www.gowesty.com/product/mechanical/20266/breather-tower-?v=


Yes, but from what I've read it has minimal effect.

My biggest gripe about the vent tower diaphragm failure is the oil mess from the tiny vent hole!

I sealed that tiny hole.
My vent tower is shot but my 2.1 runs like a top!

Dave
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PostPosted: Tue May 11, 2021 5:28 pm    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

I hear the valves. Hesitation off idle seems like a throttle position switch adjustment issue to me. What does the switch look like on a GW Digifant throttle body? Maybe separate issues?
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PostPosted: Tue May 11, 2021 7:47 pm    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

djkeev wrote:

Yes, but from what I've read it has minimal effect.

My biggest gripe about the vent tower diaphragm failure is the oil mess from the tiny vent hole!

I sealed that tiny hole.
My vent tower is shot but my 2.1 runs like a top!

Dave


I bought a new breather tower from my 83 1/2 years ago as the diaphragm in the old one was totally shot. Installing the new one had no noticeable effect on how the engine ran. The vent hole is tiny and the only vacuum it sees is that created by the air cleaner element, so almost nil. As you experience the breather typically doesn't even see any vacuum, but sees crankcase pressure.
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Steve M.
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PostPosted: Wed May 12, 2021 4:31 am    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

"Consistant valve train noise"
Just out of curiousity have you checked or readjusted the preload on the rocker arms adjusting screws?
I know the hyraulic tappets are self adjusting, but it is a good idea to check and adjust the prepreload because nothing lasts forever.

What does this valve noise sound like that has got you mentioning it?
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kamolzt
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PostPosted: Mon May 17, 2021 9:14 pm    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

MarkWard wrote:
The pressure regulator supply should be adequate but for testing, I'd connect the hose directly to the gauge bypassing the regulator.

You should also see what your fuel pressure is doing. Also, a hesitation is often a lean condition as the throttle plate is cracked open. The ECU needs to know precisely when that happens.

You can partially restrict the fuel return after the regulator and if drivability improves, you've narrowed it to a lean condition and will know where to start.

Your vacuum numbers seem low forgetting the pulsing.


Tested vacuum at the different places and did not affect reading in any meaningful way. I have somewhat recently tested the fuel pressure and the fuel pressure regulator seems to be behaving normally. Key from this comment and the following is overall vacuum pressure and timing.

Wildthings wrote:
If the valves are making noise, I would start by adding a quart of Marvel Mystery Oil to your engine oil. Then after it has been in for at least 100 miles I would go through and adjust the valves being very sure that you locate the point of zero lash accurately. The feel can vary greatly from valve to valve and may be very subtle on some (or all) of them. You want to use your fingers to turn the screw to find the point of contact, verses using a screwdriver.

I have always used two turns of preload and believe that if you use less than a turn you are limiting the ability of the lifters to self adjust as the miles add up and wear occurs.

You should also check that the ends of you valve stems are flat and that your adjusting screws aren't beat to heck.

For future oil changes use synthetic oil, as a synthetic will keep the insides of your engine, including your lifters, cleaner.

Your ignition timing should be 28° BTDC @3800+ rpm, hoses off and plugged. You also want your DIS bypassed when setting the timing.


I bought a timing light and set it based on this method with the distributor plugged off on the one side with vacuum gauge connected to the manifold side. With a minimal advance to the timing I have my manifold vacuum now bouncing between 13-15 in Hg so closer to a normal range based on what i have seen. The hesitation is significantly reduced.

Yesterday I put in a new distributor that I bought a while ago since they were NLA and while i have not test driven it yet, I was not able to replicate the hesitation at all with a warm engine in the driveway.

The timing advance also seems to have quieted the valve "clacking", however I plan to do a valve adjustment check this week. I don't know how to better describe the valve noise than clacking (like if you're driving down the highway with a window down you can hear the valve noise bounce off the concrete median)

I intend to take this on a 5K+ mile road trip leaving in the next week or so and have a lot of other prep work going on to get ready for that.

Thank you Mark and Wildthings for the pointed advice.

The breather tower situation is not one i intend to tackle right now. I agree with what Wildthings posted my understanding is the diaphragm acts like a PCV valve.


Last edited by kamolzt on Mon May 17, 2021 9:57 pm; edited 3 times in total
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PostPosted: Mon May 17, 2021 9:22 pm    Post subject: Re: Valve issue? Hesitation from idle. Reply with quote

Yellow Rabbit wrote:
I hear the valves. Hesitation off idle seems like a throttle position switch adjustment issue to me. What does the switch look like on a GW Digifant throttle body? Maybe separate issues?


Their new throttle body has it all built in and you cannot see it. You can listen to it click when you actuate from close and when it hits WOT. The only adjustments are the idle position and idle air control as on the stock throttle body.
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