# Popping/cackling on decel



## vwgroundpilot (Mar 7, 2004)

I have an '86 GTI 1.8 8v, RD engine code, CIS-E. Running a European G-grind hydro cam, TT adjustable cam sprocket set to +/- 0 degrees, opened up airbox with K&N filter, later Mk2 dual-outlet manifold and downpipe, TT 2.25" cat-back exhaust, cat test pipe (with o2 bung fitted), and Spintech muffler.

When I'm at cruise and lift off the throttle, I get a popping and cackling sound. Almost like unburned fuel is getting dumped into the exhaust. Any suggestions? I'm going to be checking the timing and testing the idle switch on the throttle tomorrow... if the idle switch needs replaced, where can I get a replacement? The only ones I found were for later cars at Germanautoparts.com (88-on 8V and 16V) and NGP Racing (16V only).

Thanks!


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## WaterWheels (Aug 14, 2005)

With a free flowing exhaust, or less restricted than the factory one, getting some popping when you lift off the gas is totally normal. It should be more pronounced going down hills or when driving faster and then going into a "coast" situation (called over-run in most manuals). So unless it sounds like something is "wrong" and not just the normal rumble and popping don't worry. You might be able to tone it down some by adjusting the timing and mixture if they are off, but it will never go away completely.

Just for your information, GTi's with RD engines should have G grind hydraulic cams (no European deal) and a dual (4-2-1) exhaust setup from the factory. If by open air box you mean holes drilled into it (Swiss cheesed) then keep it to yourself as it is really a waste of time and a good air filter box. Many people will dump on you for doing it unless you just want to hear that sucking air sound. The KN filter has also proven to be no improvement except you don't have to buy another filter for a long long time. Try setting the cam gear to -2 or -4 degrees, this seems to work well on most 8v engines if you like to drive in the higher RPM range. If not then try +2 degrees which should help a little in the "round town" type of driving (short stop and go, parking lots, quick trips to the 7 Eleven, etc.


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## vwgroundpilot (Mar 7, 2004)

Thanks for the info on the exhaust crackling and cam timing. I'll try advancing it a little (+2 deg, perhaps), drive it for a week, then retard it to -2 deg and drive it for another week. I'm a fairly low-key driver, don't really use the upper rev range except when merging into high-speed traffic... but my commute is mostly highway, so the motor is spinning at 3k almost all the way to work. I'll experiment a bit to see what feels best.

About that airbox... I cut the airbox when I was still a dumb kid... I've owned this car since I was 16 (28 now). I've been thinking about making a trip to the wrecking yard to get an uncut box, actually. Had a bit of a wake-up call when I saw several blog posts about unmolested Mk2s going for upwards of $10k... I think I'm going to slowly start restoring mine. Mk2s are turning into the Austin Minis of my generation. Anyway, I added the cut airbox info to this thread because reduced intake restriction may be affecting the driveability (whether positive or negative). FYI... I recall noticing an improvement in throttle responsiveness, but not really any gain in power (bear in mind, this is from my "butt dyno" nearly 12 years ago). Additionally, I'm going back to a good paper filter after doing more research on the actual pressure differential and filtering capabilities of different filter media. Only hope I haven't already damaged the engine with dust ingestion.

On the engine code info... my engine is clearly stamped with RD... was sold/titled/VIN'd as a 1986, but it was a late '85 production car. It came stock with the single-outlet manifold and downpipe, and according to Mr. Bentley, that's what it was supposed to have (I'd scan the page and post it, but the Bentley manual is at home, and I'm on lunch at work).

I don't know for sure what the deal was with the cam... again, dumb kid teenager when I bought it, didn't know what I was doing, I was told it was the euro G-grind hydro cam. No way to verify the actual specs. However, I mic'd the cam lobes on the new one and my old one, and I can tell you for sure that the one I put in had higher lift than the one I pulled out. There was no way for me to measure duration with what I had in the garage.


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## A1peopleS2wagons (Dec 2, 2010)

I love the cackle,mine is very suttle.
I am all stock,punched out cat.,with a glass pack.


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## WaterWheels (Aug 14, 2005)

vwgroundpilot said:


> ... was sold/titled/VIN'd as a 1986, but it was a late '85 production car. It came stock with the single-outlet manifold and downpipe, and according to Mr. Bentley, that's what it was supposed to have . . . However, I mic'd the cam lobes on the new one and my old one, and I can tell you for sure that the one I put in had higher lift than the one I pulled out.


Could be possible I'm sure that as a cross-over model it could have come with odd parts installed. I will look in ETKA later and see if there was an exhaust and cam difference in the early ones. Could be like the injection system, early CIS-e was a bit different from the later systems.


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## WaterWheels (Aug 14, 2005)

In North America the dual manifold and downpipe on 8v engines seems to have started when the RD was dropped and the PF came into being, so yes you would have had the single clamp-on system. In Europe, where I happen to be, the dual system started on the Golf/Jetta II from the beginning. The GTi engine was first the EV code which had the dual manifold and down pipe. The cam from the beginning for the RD engine was the hydraulic G grind (code). Maybe someone had swapped in a different one before selling you the car? Do you know any of the markings from them or remember the lift measurments at all?


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## vwturbofox (Jul 31, 2010)

My car pops on decel and backfires after in boost when i let off real fast. so dont worry your car is fine


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## ps2375 (Aug 13, 2003)

My 80' Rabbit ( and all my CIS injected VW's) have had the "snap-crackle-pop", as I call it. And when I switched my Rabbit over to MS, it still had it. Until I leaned out the low kPa bins that the engine would be in during Overrun, but it still does it while it is in Warm-up enrichment in the mornings. It is all totally normal, and some day I may "re-tune" to get it back.


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## A1peopleS2wagons (Dec 2, 2010)

ps2375 said:


> My 80' Rabbit ( and all my CIS injected VW's) have had the "snap-crackle-pop", as I call it. And when I switched my Rabbit over to MS, it still had it. Until I leaned out the low kPa bins that the engine would be in during Overrun, but it still does it while it is in Warm-up enrichment in the mornings. It is all totally normal, and some day I may "re-tune" to get it back.


Nice I like to "snap,crackle,pop!".
When I down shift and pass some one.
Especially when I want to be noticed.
"Hey look I am in a Scirocco!"


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## vwgroundpilot (Mar 7, 2004)

> The cam from the beginning for the RD engine was the hydraulic G grind (code). Maybe someone had swapped in a different one before selling you the car? Do you know any of the markings from them or remember the lift measurments at all?


I don't remember the values, because I made the measurements when I installed it, which was probably 10 years ago (1-2 years after I bought the car). However... I still have the original cam, so I could hit it with the mic and take pics of any markings.

As far as NA vs European spec cars... yeah, the US-spec cars were watered down because of a) emissions regs, and b) American mfr's are cheap. :banghead: My VIN starts with 1, meaning it was a US-built car. It wouldn't surprise me in the least if it didn't have correct European-spec GTI parts in it.


Back to the cackling/popping decel... turns out my idle switch had disintegrated (specifically, the little rubber button in the middle). Of course, it's buried under the throttle body so I couldn't tell until I yanked the whole assembly this last weekend. I pulled an intact switch assembly off the spare cylinder head/intake/TB assembly I have sitting in the garage... tested the switches, they worked, so I installed those. Now it briefly pops/crackles when shifting (as all performance cars should), but does not continuously cackle when I'm coasting downhill above 2000 rpm. Brief cackle/pop when I let off the gas, then a zero-fuel THRUMMMMM, which is as it should be (the CIS-E is supposed to cut off the fuel when the idle switch is engaged at engine speeds above ~1600 RPM... it's just a big air pump in that state). I still love starting out from inside the bridge toll booths around here... 1st-2nd at the right RPM, and it gives me a nice *POP* between gears.


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## Glegor (Mar 31, 2008)

my gas VWs always cackle going down hills, unless they got stock pipes on them. then there just silent.. my 86 golf does not cackle down hill yet, but i think it will soon enough. Flowmaster 40 series sounds nice on VW 4 bangers.. :thumbup:

i think some of it has to do with bad injector o-rings also..


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## vwgroundpilot (Mar 7, 2004)

Yeah, I just replaced all the injector seals (and the plastic seats) about 2 months ago... the old ones were totally dried out and split. I'm sure the massive vacuum leak wasn't helping anything.


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## WaterWheels (Aug 14, 2005)

vwgroundpilot said:


> ... I still have the original cam, so I could hit it with the mic and take pics of any markings. . . As far as NA vs European spec cars... yeah, the US-spec cars were watered down because of a) emissions regs, and b) American mfr's are cheap. . . Now it briefly pops/crackles when shifting, but does not continuously cackle when I'm coasting downhill above 2000 rpm. . . (the CIS-E is supposed to cut off the fuel when the idle switch is engaged at engine speeds above ~1600 RPM... it's just a big air pump in that state).


Pictures, posting the markings you find or better yet both would help identify the cam that was in it before you swapped them. Would be interseting to see what turns up.

North American models are not really down-graded as it seems lots of people think. Yes, they were equipped with emission systems to get them to comply with the EPA standards for the states they were sold in, but the basic parts are the same as the European models. Bumpers, side lights, EGR systems, CAT much sooner even fuel injection itself were all to meet the EPA stuff. Carburetors and no CAT was the "norm" in Europe until late 80's early 90's. Only the GTI or like models were equipped with fuel injection for the most part. But the basic internal engine parts are the same and the quality is the same too (early Mexico parts were not so well made but that changed). 

Bad idle switch could cause the long rumble but as you state, it is still there, has to be. Yes, CIS-e, even some CIS basic systems, cut off fuel during over-run situations just as (not the same way) EFI systems do.


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## vwgroundpilot (Mar 7, 2004)

Measurements:
Outermost dimension at cam lobe peak: 44.20mm (1.7402")
Outermost dimension at lobe minimum: 34.05mm (1.3406")
Cam Lift is therefore: 10.15mm (0.3996")


Markings stamped into the gaps between cylinder cam lobe pairs:

(First gap) 026

(Second gap) GERMANY WZ0

(Third gap) 6743

(Fourth gap) VW/Audi logo

No measurements on the new cam... no time to unbolt the valve cover. P/N on the box it came in is the following: 049 109 101 GH. Eurospec lists that cam as having 11.2mm of lift (0.4409"), which is quite a bit more than what came out of the car.


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## WaterWheels (Aug 14, 2005)

The current camshaft I believe, speculation on my part, is not a "European GTi camshaft" as they came with the same ones as US models except maybe in the early A1 models. What I think it is is an old VW Motorsport camshaft. I used to be able to look through the part numbers for VWMS listings when I played with 16v engines, but it is no longer on the Internet. The VWMS program used many of the Volkswagen parts numbers and changed them, often in the suffix, like in this case (G vs. GH). The data for that camshaft is about the exact same as the old Hör 270° camshaft (now Autotech Sport 270° camshaft) and might have been produced by them when Volkswagen raced A2 vehicles. In any case it should be a good all around camshaft with good power in the 2500-5500RPM range and a good idle.

The cam you removed is still a question mark of sorts. It is very close to the RD engine camshaft, could be you are a little off with the measurement and/or wear, but does not have 100% the correct markings for one. At this point I am guessing it is from a HT code engine, but that is just a guess as I never had an HT code engine to look into.


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## Glegor (Mar 31, 2008)

WaterWheels said:


> The current camshaft I believe, speculation on my part, is not a "European GTi camshaft" as they came with the same ones as US models except maybe in the early A1 models. What I think it is is an old VW Motorsport camshaft. I used to be able to look through the part numbers for VWMS listings when I played with 16v engines, but it is no longer on the Internet. The VWMS program used many of the Volkswagen parts numbers and changed them, often in the suffix, like in this case (G vs. GH). The data for that camshaft is about the exact same as the old Hör 270° camshaft (now Autotech Sport 270° camshaft) and might have been produced by them when Volkswagen raced A2 vehicles. In any case it should be a good all around camshaft with good power in the 2500-5500RPM range and a good idle.
> 
> The cam you removed is still a question mark of sorts. It is very close to the RD engine camshaft, could be you are a little off with the measurement and/or wear, but does not have 100% the correct markings for one. *At this point I am guessing it is from a HT code engine*, but that is just a guess as I never had an HT code engine to look into.


in the 3rd space, the HT cam has 5322, instead of 6743, other than that, same.


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## vwgroundpilot (Mar 7, 2004)

Good info. As stated previously, I bought/installed the new one when I was still a teenager (read: dumb kid), and had no idea what I was doing. All I knew then was I wanted "a hotter cam". :facepalm: The guy at the parts store told me it was "a G-grind cam", and stated something to the effect of it being European spec. Being an ignorant kid, I bought it based on that description.

Today, I know a lot more about this engine and what I want it to do, and what parts will get me there. I would have sought out a cam like the Autotech Sport 270 Hydro cam... so if this one is similar, I'm lucky in that I don't need to add a cam to my "to buy list".

With the TT adjustable cam sprocket set to +/- 0 degrees, this cam definitely lives happily in the 3000-5000 range. It _just_ starts coming to life around 2500, and power starts tapering off over 5000. Honestly, I haven't ever run it up to 6k, so I can't speak to how it feels at that engine speed. When I'm passing quickly on a 2-lane highway or "enjoying" a freeway onramp, I shift at just over 5k. Idle characteristics are civilized. Slight lope when it comes off the warm-up circuit, nothing obnoxious or excessive.

On the old cam measurements, it's possible the measurements are a bit off. I ran the caliper across the peak of the cam until I found the highest point, and that's the peak value I used. Ran the caliper around the base circle until I found the minimum, and recorded that value. Measured the intake and exhaust lobes for the #1 cyl, no others. Identical measurements for intake and exhaust. Note that this cam could have been showing signs of wear... I pulled it somewhere between 110k and 120k miles. No guarantees on the accuracy of the caliper... it's one of the ~$30 ones off Amazon, made in China. (I couldn't justify quadrupling the price to get a German or Japanese caliper that I might use once or twice a year and only need 1/10th of a mm accuracy at best)


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## A1peopleS2wagons (Dec 2, 2010)

A1peopleS2wagons said:


> Nice I like to "snap,crackle,pop!".
> When I down shift and pass some one.
> Especially when I want to be noticed.
> "Hey look I am in a Scirocco!"


I noticed its like's to do it at 2,700 rpm to like 3,200 rpm just depends on if I am speeding up/shifting or slowing down.
I was running pig rich,the more I unrichened it the more suttle it got ,but its still there.
I have a question?
GermanAutoParts has a gti grind cam shaft for 123 dollars.I want to get one.Is that the 270 degree.
I like the power range from 2,500 to 5,500.I dont think the J/H likes more than 5k.
I want to port out the 2nd intake I have,and find a 9-24 80 mm air flapper deal.
Now that I know the CIS can be richened,and actualy I under stand more how it functions.
I build up a j/h with a hydrolic head.


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## A1peopleS2wagons (Dec 2, 2010)

vwgroundpilot said:


> Good info. As stated previously, I bought/installed the new one when I was still a teenager (read: dumb kid), and had no idea what I was doing. All I knew then was I wanted "a hotter cam". :facepalm: The guy at the parts store told me it was "a G-grind cam", and stated something to the effect of it being European spec. Being an ignorant kid, I bought it based on that description.
> 
> Today, I know a lot more about this engine and what I want it to do, and what parts will get me there. I would have sought out a cam like the Autotech Sport 270 Hydro cam... so if this one is similar, I'm lucky in that I don't need to add a cam to my "to buy list".
> 
> ...


 Did I get the right link?
http://www.autotechwarehouse.com/Auto_Tech_Warehouse.php


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## Glegor (Mar 31, 2008)

A1peopleS2wagons said:


> I noticed its like's to do it at 2,700 rpm to like 3,200 rpm just depends on if I am speeding up/shifting or slowing down.
> I was running pig rich,the more I unrichened it the more suttle it got ,but its still there.
> I have a question?
> GermanAutoParts has a gti grind cam shaft for 123 dollars.I want to get one.Is that the 270 degree.
> ...


a stock GTI cam is far from a 270*

i took the stock G grind cam out of my gti, and upgraded to a Neuspeed 268*, and oh man, there was a world of improvement.. with that neuspeed 268*, it would pull right till the 6250 rev limiter..

it was a night and day improvement when i put a different cam in my GTI..


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## vwgroundpilot (Mar 7, 2004)

A1peopleS2wagons said:


> Did I get the right link?
> http://www.autotechwarehouse.com/Auto_Tech_Warehouse.php


A swing and a miss...

Here's the Autotech we're referring to:
http://www.autotech.com/

Here's their page on camshafts for Mk2 8-valve motors:
http://www.autotech.com/category/camshafts.html?fromcat=golf-gti-rabbit-mkii-8v

I'd love to see some back-to-back dyno pulls on the same motor, same cam timing, with the Autotech Sport 270 vs the Neuspeed 268.

Honestly, the lift and duration are only part of the equation... the ramp profile makes a difference in engine behaviour as well, but that's not really defined in the specs you see listed for each cam. You can have two cams with the same numbers but different ramp profiles, and they'll behave differently.

Designing a camshaft is kinda like voodoo. You don't really know how it'll behave until you try it out. CFD processes still don't have combustion mechanics fully nailed down, and until then, there is no way to simulate/calculate what a given cam profile is going to do.


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## Glegor (Mar 31, 2008)

heres the specs of the neuspeed:

.438 Lift
268° Duration
113° Lobe Center
Intake Timing:
Open 21° Before TDC
Close 67° After BDC
Exhaust Timing:
Open 67° Before BDC
Close 21° After TDC
The above timing is checked at .004 lifter rise.

RPM good to 6500 RPM. Mid range to high end cam.

and heres the specs for the Autotech..

Lift: 0.449". Duration: 270° at 0.1mm check, 112° lobe center. The 270 cam is designed for dual valve spring hydraulic lifter 8V Vws.

HOLY CRAP!! neuspeed is proud of their products.. almost 3 bills for a cam shaft!

based on price alone, i would NOT get the Neuspeed cam, only reason i have one: it was free...

another thing, your car is probably going to develop a "buck" at idle.. i know i HATED driving my GTI in traffic jams, and low speed traffic.. if you gave it any amount of throttle, it wouldnt buck..


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## vwgroundpilot (Mar 7, 2004)

Glegor said:


> heres the specs of the neuspeed:
> 
> another thing, your car is probably going to develop a "buck" at idle.. i know i HATED driving my GTI in traffic jams, and low speed traffic.. if you gave it any amount of throttle, it wouldnt buck..


Yeah... mine is just the OEM+ cam, but it still sucks to drive in stop-and-go traffic. It wants you to have the throttle ON or OFF. None of this puttering at idle crap. Even when I'm trying to cruise at 50 (like when I'm waiting for a clearing to pass a truck on the backroads), the load is light enough that it doesn't like it. It wants me to be going at least 55... at speeds north of that, there's enough drag that I can keep the throttle open far enough doesn't do the on/off throttle surging. Anything below that, and the throttle is open so slightly that it does this on/off surging. Almost like the Ducati 900SS I had... that thing did not like low-throttle cruising either. It wanted to be accelerating (under load) or decelerating. Didn't like cruising at low speeds.


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## A1peopleS2wagons (Dec 2, 2010)

> A swing and a miss...


Strike one.....I thought the site I got was B.S.
Thank you for the link.
Book Marked.


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## Glegor (Mar 31, 2008)

vwgroundpilot said:


> Yeah... mine is just the OEM+ cam, but it still sucks to drive in stop-and-go traffic. It wants you to have the throttle ON or OFF. None of this puttering at idle crap. Even when I'm trying to cruise at 50 (like when I'm waiting for a clearing to pass a truck on the backroads), the load is light enough that it doesn't like it. It wants me to be going at least 55... at speeds north of that, there's enough drag that I can keep the throttle open far enough doesn't do the on/off throttle surging. Anything below that, and the throttle is open so slightly that it does this on/off surging. Almost like the Ducati 900SS I had... that thing did not like low-throttle cruising either. It wanted to be accelerating (under load) or decelerating. Didn't like cruising at low speeds.


mine never did that.. i would say that the part throttle issue was probably a vacuum leak..

my vacuum leaks went from "not bad" with the stock cam, to "HOLY CRAP, TIME TO FIX THOSE VACUUM LEAKS!" with the neuspeed cam i installed..


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