TheSamba.com :: View topic - alrighty experts... need help! Losing power

Tue Aug 26, 2008 12:44 am

alrighty. I have no idea where to start on this one, because I just checked the usual suspects.

first off, this is a highly intermittent problem, and seems to happen randomly for no reason at all. sometimes its right at warm up, sometimes not until well after a jaunt on the freeway.

anyways this started two days ago when I eliminated an air leak. at high RPM, in any gear, at totally random times, the car will start sputtering, jerking wildly, or just immediately losing power (as if the fuel was suddenly cut off to a trickle, or all the advances were locked up or something)

and then, for no apparent reason at all, BAM it comes back and acts like nothing just happened!

i pulled the spark plugs, and all 4 looked perfect. light tan/brown and no oil or gas or black soot. so mixture seems fine.

checked timing, and its spot on 0tdc, using a file as a guide to make sure.

no air leaks at all, and the idle is set at 850 rpm.

it SOUNDS to me, at least, like there might be a miss or something, becuase at idle, at random times, the idle sort of wavers. not really surging or hunting, the change is only about 25-50 rpm in either direction.

valves were just adjusted and checked, they're fine.

My fuel pressure gauge is broken, so I don't know whats up with that, and I only replaced the fuel filter a thousand or so miles ago, but It COULD be that, except I dont know why then it seems so randomly intermittent (for example, last night it didnt do it at all despite driving over 100miles)

i thought maybe grounds or injector plugs or maybe the power relays/connections were to blame, but all seem tight and wiggling them seems to have no noticeable affect. fuses look fine from visual inspection.

specs for those who dont remember:

71 1600 DP D jet FI squareback

pertronix ign

alternator conv.

other than that no mods that i can think of, rest of the engine is pretty much bone stock.

thoughts? Ideas? anything I should be looking for?

Tue Aug 26, 2008 12:52 am

I get the same problem with my car, also FI and stock. Sometimes I can drive 50 miles without missing a beat, and other times I don't make it 2 miles to school before experiencing the jerky sputtering/misfiring issue. I don't have a fuel pressure gauge either but it doesn't really seem like I am running too rich.. no vacuum leaks either.

Tue Aug 26, 2008 1:00 am

sounds like vacuum to me (but I'm no expert :) )

Tue Aug 26, 2008 3:20 am

from what I remember of my FI experience, sounds like a vacuum leak to me as well...

Tue Aug 26, 2008 6:43 am

put points back in, see if the problem stops...

Tue Aug 26, 2008 6:46 am

Mine was doing the same thing. I found a real sloppy ground connection on the left FI ground! I squeezed/pried on it for 1/2 hour until I got the perfect grip! I also found a broken phenolic spacer! Seems to run 100% better? :wink:

Tue Aug 26, 2008 8:13 am

That is a symptom of a throttle switch going bad. The wiper that goes across the contacts is worn, and making 2 of the contacts at a time, instead of just one as it was designed.
My 73 does the same thing occasionally, but not as violently. I have been watching for a NOS switch.
Your D switch should not be that hard to find.

Tue Aug 26, 2008 4:21 pm

Joe, I have a Bosch 0280120040. Is this the one you need?

Tue Aug 26, 2008 4:50 pm

My car had been doing that, until I found that the distributor clamp stud had pulled out from the case, causing poor grounding for the ignition.

Tue Aug 26, 2008 7:36 pm

rosevillain wrote: My car had been doing that, until I found that the distributor clamp stud had pulled out from the case, causing poor grounding for the ignition.

ding ding ding ding! we have a winner!

after pulling my hair out I went to twist the distributor, see if it was coming loose, and the whole stud just fell out! :shock:

I dont think it was the grounding per se, but I think the distributor was rising up and unseating, and then at lower RPM catching again. anyway, once I tightened it the problem sort of/kind of went away.

by sort of kind of, I had ONE instance of it happening again and since then nothing, but I haven't driven that far.

However, it still isn't running perfect. there seems to be a miss at idle and at very high RPM (points or elec. ignition doesn't make a difference) and I haven't found any vacuum leaks despite pulling off the runners and checking near the heads.

Russ, I'll check the TVS anyway, see what kind of shape its in. I'm having this strange issue that if I barely give it any gas, essentially in 1st or 2nd in parking lots, and just hold it steady (about 1000-1500rpm) it starts to surge cyclically, but not buck or stutter hard, just sort of surge a little in very even cycles, as if one cylinder was firing harder than the others. is that a sign of the TVS going out?

anyways, right now the original stud is back in but I don't trust it at all, the hole in the case is pretty well stripped. I went out and bought a replacement stud that was supposed to be slightly bigger but it was far too large for putting into the hole without a reamer and a tap. does anyone know of the best way to repair this stud and keep it from coming out again?

also, my fuel mileage has taken a complete nose dive, the last 80 miles used up a full half tank of gas. i cant tell if its from the bad running issues or something else. when I last pulled the plugs (before i left on this trip im on) they were a perfect mixture but I have yet to pull them again. tires are the proper pressure and whatnot.

anyway, to recap, your thoughts would be much appreciated on:

distributor clamp stud repair

miss at idle/high rpm

surging at steady (but low) throttle in low gears

awful mileage

Tue Aug 26, 2008 7:47 pm

Do you have a lot of play in the throttle shaft in the IAD? A rare but potential source of air leaks. At idle, it the shaft trapped by the closed throttle plate, and will be steady (since you compensate with the idle air bypass adjustment). But above idle, it might be free to shift and change the amount of the air leaking past, screwing with your mixture and rpm.

Tue Aug 26, 2008 8:36 pm

KTPhil wrote: Do you have a lot of play in the throttle shaft in the IAD? A rare but potential source of air leaks. At idle, it the shaft trapped by the closed throttle plate, and will be steady (since you compensate with the idle air bypass adjustment). But above idle, it might be free to shift and change the amount of the air leaking past, screwing with your mixture and rpm.

I had this problem a long time ago with a different intake box, but this one is in great shape, with very little, if any, leaking past

Tue Aug 26, 2008 8:40 pm

Surging, miss, lumpy idle all sound like richness, typically from air leaks. But you of all people know how to check for air leaks, so I'm puzzled...

I'd recommend a helicoil for the stud. A larger stud might require you to enlarge the clamp hole, which would then be loose should you revert to a standard stud.

Yes, I'm a stock nazi I suppose!

Tue Aug 26, 2008 9:27 pm

KTPhil wrote: Surging, miss, lumpy idle all sound like richness, typically from air leaks. But you of all people know how to check for air leaks, so I'm puzzled...

I'd recommend a helicoil for the stud. A larger stud might require you to enlarge the clamp hole, which would then be loose should you revert to a standard stud.

Yes, I'm a stock nazi I suppose!

see thats the kicker, it ACTS as if its running rich, and I keep checking for leaks and then when I dont find any i say "ill pull the spark plugs, and then I'll know!" but all 4 always look text book perfect, light tan and clean. not wet. its the damndest thing. ](*,) :-k

I have a theory here, that I'll run by you guys. I recently turned my inner MAP adjustment 1/4 turn richer because of some (perhaps perceived) heat issues I was having. the mixture on the plugs became SLIGHTLY browner, but not all that different from before. Should I change it back and see how it responds?

i say perhaps perceived, because i felt that it was hot, but maybe it was just me over-reacting. I dont have any temperature gauges but I just picked up some cylinder head and oil pressure gauges that I intend to hook up, as well as an oil temp gauge. I might as well ask now, what are typical/acceptable/ ideal temps for cylinder heads and oil? (and what pressure should it be)? I haven't had the chance to gauge ambient engine bay and tin heat from T3 to T3, i only know mine and the engine in my ghia. in the ghia, the tins are cool to the touch even after freeway runs, but on the square they're too hot to touch. I know everyone says that t3 engines dont run any hotter, but the engine bay certainly feels much warmer than that of a T1. Am i just feeling the excess heat coming off the ISP exhaust or am I having a heat issue?

Tue Aug 26, 2008 10:18 pm

I cannot touch my intake or tins on the square after running on the freeway and my engine hasn't crapped on itself yet. In all of my other cars, the tins are much cooler.

Tue Aug 26, 2008 10:23 pm

Heli-coil to repair the stud.
As for T-3 engine temps, remember that the T-3 engine does not have air being pulled through the einge compartment like the T-1 engine does.
All of our air is pulled in through the intake boot, and goes through the fan and is exhausted under the car. There is not the air movement through the engine compartment like a bug. The engine tin will "feel" warmer.

You can put gages on your engine, but it will make you paranoid.
Sometimes, ignorance is actually better. I do not worry about engine temps on my VW's. And I have never had one fail to get me home.

Tue Aug 26, 2008 10:30 pm

Russ Wolfe wrote: Heli-coil to repair the stud.
As for T-3 engine temps, remember that the T-3 engine does not have air being pulled through the einge compartment like the T-1 engine does.
All of our air is pulled in through the intake boot, and goes through the fan and is exhausted under the car. There is not the air movement through the engine compartment like a bug. The engine tin will "feel" warmer.

You can put gages on your engine, but it will make you paranoid.
Sometimes, ignorance is actually better. I do not worry about engine temps on my VW's. And I have never had one fail to get me home.

I'm already paranoid but thats sage advice there my friend. I think I'll add the gauges, simply because I have them and I feel like it, but I'll try not to let it get to me.

so its ok that the tins, intake runners, all that stuff gets too hot to touch after a freeway or lots of stop and go traffic run? i've tried the dipstick test but thats always too hot to hold for more than 1 or 2 seconds. I just dont want to overheat the bugger.

Wed Aug 27, 2008 8:28 am

Like Russ said, on a T3 the engine bay will feel hotter because there is no convective cooling from air circulation. Furthermore, on a T3 you have that nice shiny heat reflector just a few inches from the hot block and tin, making the surface of the engine even hotter. But it's what's inside that matters, and will be no hotter than a Bug.

Wed Aug 27, 2008 9:41 am

KTPhil wrote: Like Russ said, on a T3 the engine bay will feel hotter because there is no convective cooling from air circulation. Furthermore, on a T3 you have that nice shiny heat reflector just a few inches from the hot block and tin, making the surface of the engine even hotter. But it's what's inside that matters, and will be no hotter than a Bug.

Phil, I'm gonna have your and russ's comments put on a magnet and put on my air cleaner :lol:

alrighty, well i don't have any tools with me (forgot my spark plug removal socket) so for now it'll stay at the mixture its at. when i get home tomoro ill snap some photos and then compare those plugs with the slightly leaner mix I used to have it at and see how it performs, and see what you guys think.

Wed Aug 27, 2008 10:19 am

DON'T do the gauges; you'll just drive yourself nuts with paranoia and wind up selling the damn car.