Car too weak to redline in 1st, but idles fine. Wtf?

[Ryann]

Nice! I can think of at least ONE cat option.:D

[Earendil]

Ding ding ding! Clogged cat is this weeks winning answer! I pulled the O2 sensor and it ran MUCH better. Naturally not perfect, but the vacuum pressure showed a solid reading at idle with it out, and it kept some amount of vacuum through a much wider range of throttle positions. It could also make it to redline! Now to figure out cat options, and perhaps why it failed prematurely in the first place...
So in the end, my few clues were misleading. The driver at the time that the exhaust blew out said there was a loss of power. Also, that it was a relatively new cat also didn't mean anything. At least I know of a bunch of very solid components in the car!

Thanks everyone for your help!

[Ryann]

Idk, dude. The symptoms and gauge reading point to an obstructed exhaust. Maybe it's a POS Chinese cat who's guts dislodged and turned sideways?

[Earendil]

It's totally the exhaust.

See scenario 14:
http://www.secondchancegarage.com/public/186.cfm

I suppose so... I looked under the car and the cat looks new, though it's smaller than mine. Everything under there is new. The PO said he spent $1400 replacing it all, and it looks like it. Just seems odd...

[Ryann]

It's totally the exhaust.

See scenario 14:

http://www.secondchancegarage.com/public/186.cfm

[Earendil]

Pull the o2 sensor! The open hole should let out enough exhaust pressure to make a difference if you've got a plugged up exhaust.

And that sir shall be my next test.
New voltage regulator in, and the car is holding steady at a more sane 14.1v. However this had no noticeable effect in the engine. I attached the vacuum gauge and got a wavering reading from 11-14 on intervals of about 2 seconds, so not likely a per cylinder issue, right?


So that's low, when my own E30 idles at 16. If I add a little throttle it'll start to climb to about 17hg around 2000rpm, but at 3000rpm and my foot near the floor, the vacuum went to zero and stayed there.

I'll have better test tonight, when all the traffic on the roads clears out a bit. I can't for example tell you if the pressure was responding to the throttle position, or the RPM.

Looking more like a plugged cat all the time, aye?

I think we can rule out injectors now.

If pulling the O2 sensor does nothing, I'll make jlevie happy and go get a smoke test. I'm not going to advise my friend do that though until I'm relatively sure that's the issue.

[Ryann]

Pull the o2 sensor! The open hole should let out enough exhaust pressure to make a difference if you've got a plugged up exhaust.

[Earendil]

I missed the part where it did this all at once. A worn cam can happen quickly if there are oiling problems or valves out of adjustment, but not all at once.

Following HPDE's logic, worn cams wouls reduce air movement by not allowing the valves to open properly. A broken cam would make noise.

A bad cat could certainly cause what you're seeing. If the regulator doesn't fix it you need to disconnect the exhaust from the manifold and drive it.

Agreed. I still may be looking at a two part problem though. Assuming the PO wasn't lying to me, and the CAT isn't old, then something must have caused the CAT to fail at such a young age, yes? I'll try and take a look under the car when I see it next, see if I can determine how "new" the CAT is. Those things are usually so beat to shit and dirty after a few miles that it's hard to tell :(
Hopefully I'll see a quick disconnect point as well. Daytime highers are being weird and actually reaching up into the low 40's, and we haven't had any snow yet. This time last year we had a couple feet... This should make me more likely to actually spend some time outside the car wrenching :)

[603Racing]

I missed the part where it did this all at once. A worn cam can happen quickly if there are oiling problems or valves out of adjustment, but not all at once.

Following HPDE's logic, worn cams wouls reduce air movement by not allowing the valves to open properly. A broken cam would make noise.

A bad cat could certainly cause what you're seeing. If the regulator doesn't fix it you need to disconnect the exhaust from the manifold and drive it.

[Earendil]

I have not dismissed the Cat idea, but I have focused on other things do first because the ENTIRE exhaust system is only 2-3 years old. Also, when the exhaust blew out, the driver said it lost even more power. Now if it were a blocked cat, wouldn't blowing a hole pre-cat only help it? Lastly, the hole pre-cat was mostly assisted by a missing bolt, and 2 incorrect ones (small, non-locking). I like to think my engineering prows are not completely off to check for a vacuum leak (easy) before checking the cat (difficult).

So first things first, get the car running at the right voltage, and then we'll see about moving the car to a location where we can run the engine at high RPM without the cat and muffler. It's currently sitting at my friends work, and it wouldn't be good for business to do it there :)

[hpde30]

just thinking out loud here, but I wouldn't be surprised if your pre-cat exhaust issues were a result of excess back pressure due to the cat being clogged.

[hpde30]

ITS YOUR CAT!

ive seen it mentioned half a dozen times but you keep dismising it. you say you're an engineer, so look at this problem like one. the engine is just an o2pump, it lets air in and it lets it out. in the process of doing that it uses the air to burn fuel. fuel makes the power! If you aren't making power then you aren't burning fuel or getting air in/out of the motor.

You said you switched intakes/maf ect and there was no change, so it sounds like the motor is getting enough o2. You said it drives and idles fine at anything other than WOT, which sounds like you're getting enough fuel. All signs point to exhaust not being able to get out. Its also one of the few things you haven't checked/confirmed.

I know you said its hard to take the exhaust apart, but I think you're going to have to bite the bullet and get it done if you want to fix the car.

[Earendil]

My thoughts would be the cam, which really can't be checked unless it's removed and mic'd.

Yeah, I don't have the tools to check it, or the motivation to remove another cam. I did that once on my car, which was fine for the educational experience. Out of curiosity, what would happen with the cams? Would they become less than straight, causing increased/decreased travel on some valves?

And the cat, which is the easiest. Just remove the cat section of the exhaust and take it for a ride, carefully.

Sadly, the exhaust manifold to header connection lost one of the 6 bolts, and popped loose at about the same time. In an attempt to get the car back to a place where I could test the engine, I slapped some liquid exhaust gasket shit from NAPA on it, added a nut, and sealed it back up. The patch was only meant to hold until I could get a proper gasket in there. But I fear that just "popping it off" is going to require sanding some of that junk off before applying more or adding an OEM gasket.

Also, the last time I ran my personal car with the header off, my car was loud as @#$%. Like scary loud. I can't imagine actually driving it with it sounding like that? I don't think there is an unwelded connection between the exhaust manifold and the cat, but I'll double check.

The injectors, which would also have to be removed. But I would see if you could ohm them out while on the car.

If you would like a set of injectors let me know I have a stock set I'll let go dirt cheap to help your cause, and I also have a set of 19lbs if your friend is interested.
Good luck with your hunting....

Yeah, I'll see if I can't ohm check the injectors. I think this should be possible without removing the intake. Awful kind of you to offer the OEM injectors. PM coming.

[EthirtyIS]

My thoughts would be the cam, which really can't be checked unless it's removed and mic'd.
The injectors, which would also have to be removed. But I would see if you could ohm them out while on the car.
And the cat, which is the easiest. Just remove the cat section of the exhaust and take it for a ride, carefully.
If you would like a set of injectors let me know I have a stock set I'll let go dirt cheap to help your cause, and I also have a set of 19lbs if your friend is interested.
Good luck with your hunting....

[kojack]

Had a car that had the same sort of problems after the cat fell apart and clogged itself. I'd try popping the exhaust tubing off the headers starting it and seeing if that clears things up.