Bucking B4 - acceleration problems!

[natescape]

OK, my Passat gained a new problem today (whhhhhhheeeeeeeeeeeeeeeeeeeee). When I accelerate at rates greater than granny speed, the car bucks. We're talking potentially VIOLENT bucking if I push it too hard. This happens in all gears, but is really noticeable in 2nd.

The car cruises fine. If I drive like a granny, it's fine. It's not the engine mount, as that was recently replaced and I know what that feels like.

Ideas? It DOES have a CEL (and has had one for a while) related to a faulty fuel temp sensor. I just got that part and plan to replace it soon.

[ December 19, 2002, 13:15: Message edited by: natescape ]

 

[lrpavlo]

Mine wasn't super consistent but progressively got worse till I changed the N75. Perfect fix!

 

[natescape]

This was sudden and severe. The car almost suddenly started doing it, and the effect is severe.

 

[natescape]

There doesn't seem to be any extra smoke.

 

[dieseldorf]

I didn't notice any smoke, either. It behaves as if someone was turning the fuel on and off - - very abruptly.

 

[Boundless]

If you were to accelerate slowly, can you get the RPM/power up without bucking?

If you were to slowly wind out in first gear, how high in RPM can you go before it bucks?

I'm trying to differentiate if this is an acceleration or peak power issue, or a combo.

Just because it's so simple, check the wire on the fuel cut-off solenoid. Make sure it's okay.

Have you done anything to the engine lately?

Any other symptoms?

 

[MITBeta]

Are you getting sufficient fuel flow?

 

[TDIMeister]

Check the fuel filter, especially the plastic tee-connector hose.

 

[natescape]

I'll try winding out 1st (and 2nd) when I drive home this evening. But it seemed that I could get going pretty good without bucking IF I accelerated slowly.

Haven't done anything to the engine recently.

Phil, I know where you're going. It's not a fuel filter issue. I am actually running about b5 right now (waiting for an order of bio). And both Tom and I agreed it's not fuel filter or gelled bio related.

 

[Nitejav]

I had this once with my audi 5000. It turned out to be the clutch springs. (assuming your driving stick) Clutch was fine but one of the springs broke, and then another spring broke and it started bucking very heavily, especially in lower gears. If you can cruise in second with no bucking, punch the gas, and the bucking starts it may be your clutch.

The clutch in the 5000 made it 200,000 miles (original no less) and had plenty of meat on it, it was the springs that broke due to age and wear.

See part number 2. The springs are those four little things in the drawing that go around the center shaft. Those break you could get some really nasty bucking in your car.

To give you an idea of how bad the bucking was, it was like I was getting hit from behind or I was hitting something myself. Slam go forward, Slam go forward, it was a pretty nasty ride.

[ December 19, 2002, 15:17: Message edited by: Nitejav ]

 

[natescape]

I just got the clutch replaced, oh, 6 months ago.

Well, it's not speed or RPM related... I revved the car way up in 2nd and 3rd with no issues if I didn't accelerate quickly.

Also, there's a definite exhaust rattle from the front, say a couple of feet from under the go pedal.

 

[natescape]

dp

[ December 19, 2002, 15:46: Message edited by: natescape ]

 

[dieseldorf]

I drove nate's car this afternoon and this condition is severe to the point the exhaust system is banging against the bottom of the car. It's alsmost as if the engine is turning on and off when more than 1/2 throttle is used. This in not minor surging. This is severe. It is almost dangerous to pull out in traffic since the power may go away entirely without warning.

 

[Boundless]

A simple misfire shouldn't be all to violent.

What ever you do... do not make it buck anymore.

Does the car make any smoke with these bucking events?

 

[christi]

My wife's Audi 80 TDI did something similarish when one of the injector leak off pipes (small bore rubber pipes daisy chained between injectors) split.

At low power it was fine, but any demand for serious power resulted in a misfire.

After a while we got CEL (3rd injector) and after a couple more days it killed the 3rd injector entirely.

In the end I needed 5$ worth of pipe and a new (used) 3rd injector.

I'm not quite sure if this sounds the same, but it might be worth looking for holes / splits in those leak off pipes.

 

[natescape]

Well, the car barely bucks at high speeds or high gears. The bucking diminishes once I'm past 2nd gear, so I think it's torque related.

And the exhaust is definitely rattling in front. When idling at a light, I played with the throttle a bit and at about 925-950 RPM, it was rattling. When it does the bucking, you can really hear the exhaust banging in front.

The only quasi cool thing is that if I'm driving at night, I can make the whole front end bounce like I'm a rap star or something.

 

[Boundless]

nate,

Did this bucking start shortly after refueling?

Perhaps check the water separator?

 

[dieseldorf]

nate, did all this occur when you switched back to rude crude? or was it occuring when using BD?

..perhaps the car is rebelling.

 

[natescape]

No. I had refueled on Wednesday at a Mobil on Route 1 in Foxboro that's heavily used by trucks. I then drove home, drove back to work on Thursday, and it started when I got near work. I had gone a good 125 miles before it started.

<head position="hanging in shame">
This is my second or third consecutive tank of dino, so I don't think it has anything to do with the fuel or my car rebelling.
</head>

[ December 20, 2002, 07:08: Message edited by: natescape ]

 

[Boundless]

Call in an Exorcist!

 

[MITBeta]

Call in an Exorcist!

<font size="2" face="Verdana, Helvetica, sans-serif">Yes... last night I was thinking, perhaps a priest is in order...

 

[Cabok]

quote:
It DOES have a CEL (and has had one for a while) related to a faulty fuel temp sensor. I just got that part and plan to replace it soon.
-------------------------------------------

The fuel temp sensor will tell the ECU how much timing advance the fuel pump should have. If you have a bad signal, and the timing is off, you may have a nasty problem.

 

[Boundless]

Nate,

I'll guess that the bucking is a result of the whacked out engine mount.

This explains why you can get revs up gently, but hard acceleration caused problems. The torque of a hard accel can now move your engine around like it's not supposed to be moved. That might cause wierd geometries for the CV joints. They objected.

I expect that once the engine is securely fastened, this problem will be over.

Hope it all works out for you.

Happy Holidays

 

[natescape]

Well, MITBeta fixed the fuel temp sensor, and the check engine light is gone.

But, the engine mount is SCREWED up. It's out of its spot in the frame, and is at least a couple of inches high. The screw to the tranny was off to the side (but not unscrewed... just "out"), and the thing that it screws to was chipped. We took a photo with Phil's digital camera that I'm waiting to post. He can either post it here or email it to me and I'll post it.

Now, the question is, can this be the CAUSE of the bucking, or is it just an effect? The engine is still bucking, although less since we tightened the screw. But it still ain't properly mounted.

 

[tdipoet]

is this the same engine mount that was repaired before, in the garage of tom?

 

[MITBeta]

Yes. Same engine mount...

 

[natescape]

Same mount.

I'm hoping Boundless is right and just restoring the mount will take care of it. But I fear that the chip on the tranny manifold (if that's what it's called ...Phil, could you post the photo) may require additional work.

 

[dieseldorf]

nate, did the engine mount bolt break again?

 

[tdipoet]

yeah phil, post the pics.

i can't believe we're all up this early on a sunday. sick, sick, sick.

 

[MITBeta]

Okay, here we go:

Nate's engine mount/transmission connection:

Nate took this picture, so don't blame the messenger. Right in the middle of the picture you can see where the transmission/flywheel mount has been chipped. The engine mount itself appears to have jumped out of its receiver on the frame and landed skewed so that it's tilted towards the driver's side of the car.

How is the mount held into the receiver?

The bolt that you see in the picture was unscrewed quite a bit, so I tightened it up, lest Nate drop his engine on the ground on the way home from my place...

[ December 22, 2002, 07:01: Message edited by: MITBeta ]