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Engine Specific Info and Questions => IDI Engine => Topic started by: fspGTD on May 06, 2004, 11:51:09 am
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I've driven just a day from them, so have just gotten a feel for how they are... initial reactions are, at cold idle the vibrations are fairly bad. Usually the vibrations are just kinda bad, but now with the heavy duty sides it's worse. But then as the engine warms up it gets better. There is just a little more vibrations at hot idle than there used to be. Also, under power when driving I can feel a little more vibrations being transmitted into the chassis (makes the rear view mirror shake more at certain RPMs.) For these reasons, maybe the A1 poly side inserts aren't all that streetable for a VW Diesel. I am hoping I will be able to live with them however. I might try removing the driver's side motor mount insert (leaving only the passenger side poly insert in place), and seeing how that works. Also, there may be extra vibrations coming in through the new front mount... the new replacement mount seems fatter than the old one, and is definitely tighter fitting than the old one, fitting tightly into the mounting cup where the old one fit loosely in the cup. That could be partly responsible as well. Feeling the vibrations of the engine-side mounts at idle, there are a LOT of idle vibrations at that front mount bracket. Edit: the new front mount also isn't genuine VW part. I might try a genuine VW front mount, since it's easy to change and they are cheap anyway.
Anyway, the biggest bummer is after installing the new mounts, I still have some clunks/popping noises over on the passenger's side from engine accel/decel or brakes or something (possibly something in the front suspension?) I will check out the alignment of my boost tubes and exhaust, check for any loose suspension fasteners! Gotta fix the clunk/popping noises! :(
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OK... drove the car some more. The idle vibrations seem to depend largely on... what do you know, alternator current draw! Weird, huh? It seems like the current draw only drops the idle RPMs by a very tiny amount (not enough to really even register noticeably on the tach) but it makes a big difference in the idle vibrations. Without much current draw, the vibrations are downright perfectly fine and streetable. :D I should try tightening my alternator belt some more and see if that makes a difference - it's on there quite loose and I've noticed that it whips around a lot at idle. I ordered a new locking alternator adjust nut that I need to get on there too, as it has a tendency to loosen with the nut I am using right now.
By the way, I weighed my car at the local dump, and it's weight loaded with me, fuel level 2 clicks above red (about 1/3 tank) and on its heavy street tires was 1990 lbs. So without me, but still on street tires and with the same amount of fuel, it weighs 1840 lbs. And with a minimum of fuel, lightweight racing tires, it weights.... ? (think it will make it under 1800 lbs? 8) )
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i figure my car is at 1800Ibs, no fuel, no driver... or just above that.
i'm going to weigh it at a truck weighing station on the highway when i see one that is shut down for the day (they still leave the scales turned on though ;)).
no airbox, no washer bottle, no AC, no kneebar, no headliner, no sunroof liner, no interior behind the driver, no spare tire, no stereo or components, stock brakes/rims.
1800Ibs sans fuel/driver you think? i think it will be about 1825Ibs.
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regarding the shakey idle/alternator draw...
would an idle stabilizer valve or adjustable voltage regulator help at all? on the G60 i took off the ISV because i axed the AC and didn't feel i needed it anymore... but i added an adjustable voltage regulator (transpo unit). the transpo regulator gets rid of the battery light without blipping the throttle... and its supposed to adjust to provide max power... cant really report on much other than that it stopped the battery light from staying on.. and they are supposed to keep the G60 setups happy (lack of power from the alt really hurts performance in G60s).
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A Mercedes I'm messing with has a dial on the dash that allows the idle to be adjusted from the drivers seat.
Works great for getting rid of that extra vibration at cold idle.
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that would be similar to our ignition advance (or 'choke' as my friends say) on our vw diesel cars wouldn't it?
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Have you guys seen a factory VW '86 on diesel cold-start mechanism? It actually has some extra linkage on the pump that kicks up the idle RPM. There are 2 stages depending on how much you have the cold start knob pulled out. On earlier model the cold start knob only advances the timing, doesn't adjust the governor input shaft.
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By the way, my lightweight denso alternator always kicks on immediately after starting. I learned that there is a circuit that is lacking in the bosch that is present in the denso that allows this it required a switched +12v connection be made, which I just routed from the injector pump stop solenoid. It's a great feature!
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By the way itchy - you've got a 50 lb weight advantage over my car since you've got a 2-door and I've got a 4-door. Since I've got what I've got, I'm going all out to see how light I can make it anyway, though. That is probably my last big single chunk of weight I could lose, but it would be major work swapping the chassis, so I have been putting that one off (maybe permanently putting it off.) I'm betting that I'll be able to compensate in other areas (namely, DIESEL POWER! ;) )
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Hmm, I found a knob to the lower left of the steering wheel on my Quantum the other day, and wondered what it did. I'll have to try it out tonight to see if it's a high-idle knob. Thanks guys!
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VW racer, that is the coldstart knob. I don't know what year your car is but if it doesn't have all the extra stuff attached to the end of that cable where it meets the injection pump, it will only advance the injection pump timing during idle, not increase the idle speed.
They started using it to up the idle as early as '86 eh?
I've been waiting on this report about the poly mounts. I always assumed it would cause too much vibration.
fspGTD is your engine balanced especially well? Does it normally run smoother than most turbo diesels?
If cold idle is the only problem, we can deal with that.
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Don't slap that poly into your A1 diesel daily driver just yet... the idle vibes are worsened after the install of the poly-inserted side mounts. I was careful in aligning them, the exhaust system, etc. I have a popping noise when I accel/decel sometimes that is my top priority. I was hoping to solve it with the new mounts, but there was no help. I am wondering CV joints possibly? Doesn't seem to worsen when turning tight radius, the noise commonly happens just coasting forward, in fact. None of the CV boots are torn, but both halfshafts are cheap high mileage rebuilds, partly why I am suspecting them.
I also found one spot where the exhaust system downpipe could come into contact with a pressure hardline on the the power steering pump. There is only about 1 finger thickness of clearance, could hit under heavy accel. I'm not confident that's really what my popping problem is though, since it happens with conditions other than hard accel.
I have a couple things to try to reduce the idle vibrations, namely removing the passenger mount poly insert, and finding a different brand with looser fit (Imaybe an OEM from the dealer) of front mount. Either way since I have a 4-puck solid center racing clutch, which has kind of a chattery character that I think is really hard on mounts, combined with traction of the race slicks and limited slip (i tcommonly burns both front tires when launching) I will probably find some way to live with the passenge side poly insert. I'll report back as to whether I can make it work for what I think would be reasonable for a daily driver... preliminary report is (subjectively of course) the poly side mounts are maybe about "1/2 as bad" as a techtonics front mount.
I have a totally bone-stock (non-balanced) bottom end. It is not compression balanced nor weight balanced. It's what most would typically get for a daily-driver, non-performance application. In fact, I've measured the piston projection and it varies quite a bit from cylinder to cylinder. It could definitely be built a lot smoother I am sure. Still, it's not that bad, and I've also got an ultra-light flywheel. The flywheel and pressure plate are highly precision balanced.
Any ideas on the popping noise... I guess if I could try and diagnose the noise with the front end up on jackstands and the driveline moving... could be a good way to go if I could get the noise to reproduce in that setup.
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They started using it to up the idle as early as '86 eh?
I'm not sure if it was that early, but I recall a friend's '85 or '86 Jetta 1.6lTD did have the idle-RPM bump in the coldstart feature in it.
The '85 Jetta TD that dad just bought doesn't have it. So it could have even been late '85, maybe it was '86.
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My Quantum is an '85, and it has the cold start knob. Works, too! :)
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All VW Diesels have a cold start knob... do you mean that your cold start advance is connected to an idle-RPM increase linkage at the injection pump? You've got it if the position of the injection pump input shaft rotates at all depending on whether the cold start knob is pulled or not. It's a cool feature IMO, even though it adds some complixity and might make access to the glow plugs a little more difficult...
Another feature on the later pumps that is lacking on the earlier ones is an adjustment for "residual pressure" (which I still do not understand really. Anyone want to take a whack at explaining that one to me? ;) )
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My 86 TD has the two stage cold-start, with the timing advance, and the second setting for idle increase.
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I have a popping noise when I accel/decel sometimes that is my top priority. I was hoping to solve it with the new mounts, but there was no help. I am wondering CV joints possibly? Doesn't seem to worsen when turning tight radius, the noise commonly happens just coasting forward, in fact. None of the CV boots are torn, but both halfshafts are cheap high mileage rebuilds, partly why I am suspecting them.
I also found one spot where the exhaust system downpipe could come into contact with a pressure hardline on the the power steering pump. There is only about 1 finger thickness of clearance, could hit under heavy accel. I'm not confident that's really what my popping problem is though, since it happens with conditions other than hard accel.
I think I found this popping noise I was baffled on earlier (as noted above...) it indeed looks like one of the spring-clamps from the downpipe flex joints was hitting under acceleration, on one of the power steering rack hardlines, and this was obvious as there was a divot in the poor hardline from where it was getting hit. (This was easy to spot with the head and the turbo/downpipe removed.)
To fix, I just bent the power steering rack hardline down a little bit (using a tube bender so as to not kink) and was able to gain about 3/8" additional clearance underneath the spring clamp. That should be enough to do the trick, because I determined that if the downpipe were to move down that far under acceleration, the downpipe itself would interfere with the front swaybar before the spring clamp made contact with the hardline.
It's good to figure out these little niggling sort of details... :D
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from what i understand of my 1.9s pump the governer idle spring (normally located on the end of the governer spring assembly) is moved to a seperate lever on the outside of the pump making it another seperate adjustment where that linkage from the cold start would tighten the spring and bump up the idle.
The residual pressure adjustment you were talking about i believe is the old idle adjustment and what ive found is that this adjustment can be lowered so that the revs will drop off when the accelerator is released under increased fueling, on the older pumps this meant the idle dropped as well but it seems with this setup that the idle can remain at a higher rpm and the residual would allow it to drop below the idle fueling level until the governor balances with the idle spring helping to reduce the rpm runaway effect.
Hard to explain and im not sure if i have the right idea or not but this is what ive found. At the fueling levels i have my car at, my idle sits at 950 rpm and the revs drop like a rock when i let off.
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Another feature on the later pumps that is lacking on the earlier ones is an adjustment for "residual pressure" (which I still do not understand really. Anyone want to take a whack at explaining that one to me? ;) )
Not residual pressure, but residual volume. This is not a feature, but the sole function of the "previous" idle adjust on the newer pumps with idle boost.
The cold start nob has two detents on the later pumps. The first detent is an idle boost - a few hundred rpm. The second detent is an additional idle boost - maybe 30 rpm, and the cold start advance function.
The idle on these pumps is adjusted by means of a screw that effects the default rest position of the idle linkage on the side of the pump. The governor arm rest position stop screw is used to adjust residual pump volume, and should only be adjusted if symptoms of high residual volume (surging, unadjustable high idle) or low volume (bucking, long cranking times) are noted.
The idle mechanism on the later style pump is more complex and prone to sticking with age, which results in erratic idle.
Drew
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So the residual volume adjustment of the later pumps is just part of a more complicated adjustment for the idle stop position of the throttle input shaft lever? It doesn't do anything else like adjust something directly inside the pump dealing with the governor characteristic, etc? (A picture of this adjustment/mechanism would be great!) Thanks for the clarification, guys.