Engine bogging/surging (FIXED - Was the CAT)

JohnnyC · Post by **JohnnyC** » Thu Dec 13, 2007 7:41 am

I've noticed my engine has started to 'surge' or 'bog' (whichever way you want to look at it) recently. It isn't too horrible in town, but on the highway it's been doing it a little heavier. Suggestions on what could be the issue?

The effect is kinda like: "VROOOooOOOooOOOooOOOoom" kinda...

What might be causing that?

It isn't throwing a CEL for the problem.

2000 Daewoo Lanos 1.6L

Audacity Racing · Post by **Audacity Racing** » Thu Dec 13, 2007 7:52 am

Check your plugs Johnny

Pir0 · Post by **Pir0** » Thu Dec 13, 2007 5:10 pm

Yeah spark could be a problem or maybe a throttle position sensor? [Think it's called a speed sensor too? not sure]

JohnnyC · Post by **JohnnyC** » Thu Dec 13, 2007 6:12 pm

Replaced the spark plugs... Problem didn't go away. I figured it was a cheap try so I just replaced them. It's been getting progressively worse over the last few days.

Still no CEL at all.... Low end kinda bogs out... then at about 2.5k RPM it doesn't seem to put putting much power to the wheel.

Idles perfectly, no problems there at all. It's only when I'm driving along.

I have a custom air intake (Short Ram with a heat shield between the engine and the intake). It hasn't had any trouble running with that setup since I put it back in, so I don't think it's that. However, due to the short ram, I've become accustomed to the sound it puts out. Normally it's a kind of "Wahh" kind of noise. With the problem happening it's getting more of a gurgled "Wahgh" sound... Generally louder than it was before. Rougher, louder, more grumbly... if that describes it very well.

Ummm... let's see... I have noticed recently that if I start it up and scrape off the ice/etc... there is a distinct smell of exhaust inside the car if I have the heat on when I get inside. It would go away once I start driving, I'm just trying to tell you all anything I can think of that are symptomatic.

I first noticed the problem on monday. When I was driving to school (only a couple miles), I felt a slight amount of bog/loss of power that pulsated a bit... There > gone > there > gone > there > gone. Over the last few days it continued to be an issue only the problem is becoming more exaggerated. Today it felt like it didn't even want to drive up a hill and I had to put the gas to half way down to get it run much at all.

After changing the spark plugs (which were a little dirty, but not too horrid and they all pretty much matched), the problem didn't change AT ALL.

Spark plug wires were just changed this spring. So I highly doubt it's those.

Ummm... I'd be happy to answer any other questions that might help any of you help me diagnose the problem.

In the meanwhile, the Woo will be sitting in the driveway until I can fix the problem.

So... any suggestions, ideas?

Pir0 · Post by **Pir0** » Thu Dec 13, 2007 6:15 pm

I still stick by throttle position sensor or possibly a fuel pressure regulator.

Does it only bog under accel? or does it do it when cruising at a constant speed?

JohnnyC · Post by **JohnnyC** » Thu Dec 13, 2007 6:30 pm

Only bogs out when applying the gas... at idle it's perfect. When I'm rolling along with barely any gas being pressed, it runs smoother, but on the way up to that point it's all herky jerky. In fact, going up hill it was jerking pretty dang hard.

It seems to run alright for the first minute or so, but the problem quickly presents itself. Starts up fine, idle is good. Just driving sucks.

JohnnyC · Post by **JohnnyC** » Thu Dec 13, 2007 7:20 pm

Just went out to see if I could spot anything obvious (first chance in daylight since the problem started that I had a chance to check it over)...

I noticed that there was an awful lot of exhaust coming out of this position:

I also noted that there isn't very much exhaust gas coming out of the tailpipe... I'd say about 1/4 the exhaust is making it to the muffler (also explaining the louder noise)... This also explains the recent smell of exhaust inside the car when it's idling.

I'm guessing that is where the real problem is... a severe exhaust leak in that position causing the engine to lose most of it's back pressure, hence the stuttering and bogging out when the engine is under load.

Thoughts?

If you think I'm right... how much is this going to cost me to fix.

JohnnyC · Post by **JohnnyC** » Thu Dec 13, 2007 7:53 pm

I went around on the web to try and find that part... I only found one place on ebay that sells that setup... for $298 but it comes with a new Catalytic Converter too... which I would prefer not to replace unless I have to.

Audacity Racing · Post by **Audacity Racing** » Thu Dec 13, 2007 7:55 pm

A rip in the flex pipe isn't enough to cause a noticeable change in engine behavior (like a sputtering or surging), but the fix should be less than $100 at a muffler shop

JohnnyC · Post by **JohnnyC** » Thu Dec 13, 2007 8:01 pm

Even if most of the exhaust seems to be coming out of the flex pipe? The back pressure change wouldn't be enough to cause it to want to bog out/stutter etc... ?

You should jump online to help me figure this out.

Audacity Racing · Post by **Audacity Racing** » Thu Dec 13, 2007 8:22 pm

It might bog slightly with a huge rip, but it would get better as the throttle increases. I think you have a slight misfire that's not being picked up by the ECU... tps messed up, iadle air valve gunked up, etc. If the idle air valve can't close all the way, then "unmetered" air enters the engine and it can cause funky side-effects.

That's an easy clean-up with some spray cleaner and a screwdriver. I'd also check for vacuum leaks (just inspect the hoses on the driver's side of the intake manifold) to see if that's another source of unmetered air coming in

daewoomofo · Post by **daewoomofo** » Thu Dec 13, 2007 10:26 pm

has your fuel mileage dropped any? i wonder if it might (big might) be injectors leaking?

JohnnyC · Post by **JohnnyC** » Thu Dec 13, 2007 11:07 pm

I'm unsure about mileage loss... I don't think we're getting poor mileage, but I'm uncertain.

I don't smell any gas around the injectors or anything so at least I know it isn't leaking outside of the injectors. I'll be able to go outside and check for vacuum leaks tomorrow (using incense) and check for gunk inside the throttle body.

If you guys know of any particular tests I should run to try and diagnose the problem, please let me know. I'm really frustrated with this... Christmas was going to be lean already and now it's looking like it's going to be even leaner.

What sort of spray cleaner should I use? I have PB Blaster, WD-40, and some brake cleaner spray. If I need to pick up some other kind, I can do that... but I just need to know.

Once I get it up to speed it will stop jerking quite as much, but trying to go uphill is a chore. It doesn't have any real power (just managed to climb one hill here in town).

Also... does the fact that the problem started lightly (very faint loss of power) on monday and gradually got worse until today (heavy shaking and stuttering, barely drivable) help figure it out at all?

daewoomofo · Post by **daewoomofo** » Thu Dec 13, 2007 11:11 pm

carb or brake cleaner should work fine. if you need a sensor to exahabge with yours to see if you hav a bad one or not, your more than welcome to my parts car, just return it when you get your new one.

JohnnyC · Post by **JohnnyC** » Thu Dec 13, 2007 11:41 pm

I checked for vacuum leaks a few minutes ago (best I could anyway). There wasn't anything that was obviously cracked/sucking air at all. That split down by the flex pipe is bad. I'm going to have to come up with a temporary fix for that until I can get it fixed for real. I'm going to try muffler/exhaust tape and see if that works. I have a couple packages of it around here. If I can cut down the amount it's leaking that would be a step in the right direction and if I manage to completely stop the leak there, then I can eliminate that as part of the problem. I'm not pulling the air intake hose off to check the throttle body until tomorrow.

Are there gaskets around the throttle body? I'm sure it will be a major pain in the ass to clean if I don't take it off there. I don't have replacement gaskets, so if there are gaskets that would need replacing if I removed it, I'll just do the best job cleaning it as I can. Also... with the engine turned off, will turning the throttle allow gas to flood in anyway?