Still have bucking 92 UrS4

[Draky]

My 92 UrS4 gave me some bucking this morning while driving. I had thought it had gone away because I put a new grand wire on the head (where the 2.0T coils are grounded) and it hasn't happened since October till now.

Conditions this morning:
About 25 degrees out and dry.
Driving at 70mph, pushed the accelerator more than half way to pass a truck and I got a buck after about a second of accelerating. I backed off the accelerator and it didn't do it stopped. I did a second test, same conditions and verified same problem. No headlights and I turned off the heater for the second pull to verify it wasn't a power problem. I've verified 13.8-13.9volts at the battery while idle.

I'm thinking it's either fuel or possibly mechanical? What do you guys think it could be?

[bradyzq]

Try reading the codes.

[gabriel.b]

Engine is shot put an o7k in it

[Draky]

I've never had any codes when I tried to read it in the past so I doubt I do now. I'll try again..

[loxxrider]

My 92 UrS4 gave me some bucking this morning while driving. I had thought it had gone away because I put a new grand wire on the head (where the 2.0T coils are grounded) and it hasn't happened since October till now.

Conditions this morning:
About 25 degrees out and dry.
Driving at 70mph, pushed the accelerator more than half way to pass a truck and I got a buck after about a second of accelerating. I backed off the accelerator and it didn't do it stopped. I did a second test, same conditions and verified same problem. No headlights and I turned off the heater for the second pull to verify it wasn't a power problem. I've verified 13.8-13.9volts at the battery while idle.

I'm thinking it's either fuel or possibly mechanical? What do you guys think it could be?

Is this occurring at full boost? It could be overboost fuel cut. Is it just a single large buck or a stuttering/hesitation?

[Draky]

Good question, this is not full boost. I'll put "bar" on the trip computer and watch it but there's normally quite a bit more to go in my car than what it was giving at the time.

And the bucking happens, violently, until I let up on the accelerator. A full buck is about a full second long as well. So I can get just 1 buck or I can get quite a few. I normally don't let it happen more than twice. I've let it happen up to 5 bucks but it's so violent I'm afraid to let it go more than I have to.

[PRY4SNO]

Almost sounds like a fuel pump, but that's just a guess.

[Aktapod]

My 200 behaved the exact same way when my vacuum lines had disintegrated to nothing. 4th or 5th gear under partial load bucked so violently it felt like the car was trying to throw you off.

I dunno if there were any codes, but boost leaks would be the first thing I would check.

[Draky]

My 200 behaved the exact same way when my vacuum lines had disintegrated to nothing. 4th or 5th gear under partial load bucked so violently it felt like the car was trying to throw you off.

I dunno if there were any codes, but boost leaks would be the first thing I would check.

That sounds almost exactly what my car is doing. The lines look good so I have no idea what to replace. Guess I just should replace everything.

[Mentosman42]

I am having a similar problem with the S6, you can hear boost build but the engine will buck a bit and then hit overboost fuel cut. This really only happens in 4th and 5th gear. Once the weather breaks and I am able to drive the URQ I am going to pull the wastegate apart. I almost feel like the shaft/seal is worn and the N75 isnt able to pressurize the bottom port of the wastegate making the engine "overboost"(ecu is trying to limit boost but isnt able to so it cuts fuel).

Honestly not sure how plausible this is but I know my plugs are good(I spent the $$$$ on platins) and I am not misfiring and I have pressure tested the entire intake tract/pcv systems aswell as checked the wastegate diaphragm.

[Draky]

I was thinking of doing something like this: http://www.amazon.com/Vibrant-2691-Anod ... B0018033OQ an auto vacuum manifold. This way when/if I convert to vacuum brakes and get rid of the bomb I will have a source.

Anyone use one of those and have a brand they would recommend or a reason I shouldn't?

[DE80q]

I have one of the vibrant ones, and a 42draft as well. The 42draft is the one I installed on the bandit and it works great! The vibrant will be going in my friends 1.8t B4.

[DE80q]

This is the newer design of the one I'm running.
http://www.42draftdesigns.com/6-port-vacuum-manifold/

[Draky]

This is the newer design of the one I'm running.
http://www.42draftdesigns.com/6-port-vacuum-manifold/

That was the one I was looking for... I imagine it would be but 4 ports should be just fine, correct?

[DE80q]

Should be fine. Mine goes from the intake manifold, to the brake booster. I think I have 3 small vacuum line coming off of it.

[vt10vt]

I am having a similar problem with the S6, you can hear boost build but the engine will buck a bit and then hit overboost fuel cut. This really only happens in 4th and 5th gear. Once the weather breaks and I am able to drive the URQ I am going to pull the wastegate apart. I almost feel like the shaft/seal is worn and the N75 isnt able to pressurize the bottom port of the wastegate making the engine "overboost"(ecu is trying to limit boost but isnt able to so it cuts fuel).

Honestly not sure how plausible this is but I know my plugs are good(I spent the $$$$ on platins) and I am not misfiring and I have pressure tested the entire intake tract/pcv systems aswell as checked the wastegate diaphragm.

Do you not just have a boost gauge you can throw in it and see what it's doing or do you not know what boost level fuel cut is at in your chip?

To you and the OP, if you're thinking overboost, pull the lower WG line, blow in it, if it holds as much pressure as you can put on it, the diaphragm is fine. Bypass the N75 with a straight fitting and test. That way you're at spring pressure, if it goes away, overboost/fuel cut. If not, it's a misfire. IMHO they don't feel at all alike though.

[Draky]

I'm sure it's not overboost with mine. I also have a forged DV on there that I clean and lube every few months with my oil change.

I know what fuel cut feels like, this isn't it.

I know what missing feels like, this isn't it.

I'm pretty sure this is a boost leak after thinking about it and suggestions from here and others.

[bradyzq]

How about those codes?

What does the tach needle do when this happens?

Describe what you mean by a buck. Does a one second buck mean no power at all for a second?

[loxxrider]

I'm sure it's not overboost with mine. I also have a forged DV on there that I clean and lube every few months with my oil change.

I know what fuel cut feels like, this isn't it.

I know what missing feels like, this isn't it.

I'm pretty sure this is a boost leak after thinking about it and suggestions from here and others.

Doesn't really matter how clean your dv is. That has no bearing on overboosting or not.

[chaloux]

You can't be sure until you test it. People hate testing for boost leaks for some reason. Like they'd rather do anything than cobble together a test plug.

Boost gauge or test the pipes and also pull the codes. There's really no need to sit here guessing.

Unplug the n75 (no need to bypass it). My guess is that your problem will go away with less boost.

[vt10vt]

You can't be sure until you test it. People hate testing for boost leaks for some reason. Like they'd rather do anything than cobble together a test plug.

I'm guilty of having an aversion to pressure testing... don't know why but I hate doing it lol

[Draky]

How about those codes?

What does the tach needle do when this happens?

Describe what you mean by a buck. Does a one second buck mean no power at all for a second?

No codes when I've had it checked. I wasn't able to check it over the past week due to a crazy work schedule.

The tach needle does nothing, like the engine doesn't even feel what's happening to it. And it's not like we're too high in the RPM's either. This happened last when I was in 5th gear and put my pedal almost to the floor at 70MPH. The RPM was at 3500 when it happened, I was maybe doing 74MPH. Also, the "bar" display in the trip computer doesn't show anything either. The time I was looking for it I saw the "bar" display 1.8. I've had it up to 2.3 before and since that time. I didn't see where it was the last time it happened.

For bucking, it feels like you're going from accelerating to no power at all. It literally, probably, could pull you out of your seat if the seat belt wasn't on.

But it doesn't happen all the time. I drove an hour from Park, CO to Colorado Springs this weekend and back. Cruising around 80MPH up hills and down, no problems. I'm thinking vacuum because I don't think anything else makes sense.

[Rabbitracer43]

It kind of sounds like an ignition miss, at 70 mph in 5 th gear you would be loading the engine pretty good and at that point a weak coil could show its face.

[loxxrider]

It does sound exactly like an ignition miss except for the severity of the buck.

[Rabbitracer43]

I've scene some pretty bad bucking with a bad ignition system, and that is exactly the load on an engine where it would happen