This is starting to chap my ass (low vac at idle/decel)

[psychlow]

Well, here's my story.

If I drive around town normally, or drive downhill, the car runs OK at part throttle. If I snap the throttle open quickly, the car just sits there for a second and accelerates VERY slowly. If I spool the turbo very slowly at part throttle, it accelerates FASTER than if I go WOT quickly.

My stock boost/vac gauge (I know, I know, but it shows MAF readings) never gets to the -7 mark on the meter, even on hard deceleration.

So, I vacuum tested my car today. Here's what happened:

At idle I pull a whopping 10-12inHg, (the needle is very steady). As soon as I open the throttle at all, it goes right to 0. I didn't try the 'clogged cat' test to see if the vac is low at higher RPM, because I didn't know about doing that until researching later today.

So, here's where I am. I know I had only one very minor boost leak coming from my t/b elbow. I put some RTV in there (haven't pressure tested it again, yet) but I put an open propane hose next to it and the idle didn't change a bit.

So what are my possible causes? I know of these:
- Clogged cat (likely, I get a weird hollow leaking noise from under the car)
- Stuck open EGR
- Incorrect ignition timing
- Incorrect valve timing (compression is a little low, could be this)
- Damaged valves, valve guides, worn piston rings

Anything else anyone can think of? Any opinions?

Sorry this post is so long, and thanks.

PS - Please keep in mind that I'm at over 5,000 feet of elevation, so normal vacuum for me is in the 13-17inHg range. I can also quickly peg my vacuum gauge to over 10PSI (it's mechanical limit) when I rev in neutral.

 

[ProjectTwin]

Installed: SBR-B16G, 2G exhaust mani, and a massive boost leak.

Might be a longshot but did you actually ever fix that boost leak?

 

[psychlow]

Yeah, what I'm hearing is actually coming from under/behind the car. I thought that sound was a boost leak, but after pressure testing it the only leak I had was one that took it about 30 seconds to leak down from 10 PSI after I removed the air source, and I've since put RTV in where the leak was (haven't pressure tested it yet again, though).

It's exhibiting the exact same symptoms before and after I attempted the small leak fix, though.

 

[painmaster]

Sounds like you need to datalog. Can you find somebody in your area to help you out? If you could see all your sensor readings you would probably be able to tell whats going on.

Check your TPS.

 

[psychlow]

Good points. This might be helpful also:

One, my O2 sensor isn't hooked up, but I also get crappy vac readings when the engine is first started too, so that probably won't be a huge part of my problems.

I have a logger, but I just haven't gotten a chance to get it on. When I went to first testdrive this car, I tried to run a log to see what was going on, but I ended up breaking one of the connectors on my cable when I tried to put it on.

Out of curiosity, do you think a bad TPS would cause bad vac at idle? I don't have any problems like surging, the idle holds pretty steady at 800 RPMS once the car warms up.

 

[painmaster]

Your right, I dont think the TPS would cause your bad idle. The ECU uses the idle switch to know when its supposed to be idling. I was thinking more about when you stomp the gas but the car doesnt respond, this could be caused by a faulty TPS.

Huh, your O2 isn't connected?? I dont know what the car would do without an O2. The ECU might be in some kind of limp home mode. Re-connect the O2 and see what happens.

After re-reading your posts it seems there are two issues, is this correct?
1) Bad cold idle (low vac), but its steady.
2) Bad full throtle acceleration.

When did these problems start?

 

[psychlow]

As long as I've owned the car, this problem has been present. I don't believe the O2 sensor has been properly hooked up as long as I've owned the car either, but I can't confirm that.

Originally, the old exhaust manifold I had was cracked almost all the way around cylinder #4's runner, so I thought it was exhaust air leaking around that. Then I changed the turbo and the exhaust manifold, and got the same air leak sound, turbo gauge readings, and acceleration results, just a slightly faster than before, so I thought it was a boost leak or a bad MAF in conjunction with another problem. My pressure testing seems to have destroyed those theories, though, as the only leak I found was a VERY slow leak.

I pulled my plugs today (actually replaced them, the idiot PO had Platinum plugs in there) and put NGK 6's in. On the old plugs, I have slight carbon build up on the threads that are inside the head, indicating a slight rich condition (probably from my O2 sensor being disconnected).

 

[painmaster]

I would start with what I knew was wrong, and that is the lack of an O2 sensor. The O2 should correct idle problems, and maybe some of your other issues. Once you know the O2 is working you can move on to the next problem, whatever that may turn out to be.

Oh ya, and get that datalogger working!

 

[psychlow]

Check. The only issue I have is the fact that I'm gonna have to do a whole bunch of soldering to get the sensor back on. The PO broke the O2 sensor wiring to the female plug, so I have to patch it all up.

I guess I'll try checking vacuum with the oxygen sensor out completely to see if a plugged cat might be my problem, too.

 

[psychlow]

OK, got my logger working (yay).

TPS is 9.7% at closed throttle and smoothly increases as I apply throttle, so everything looks good there.

Fuel trims are all 100%, which was surprising considering the O2 sensor's not installed.

I'll get some logs with MAF Hz soon.

 

[painmaster]

I believe what you are seeing is because you dont have an o2. I think the car is setting fuel trims in the neutral position, becuase it doesn't know what the mixture is really at. If you put an O2 back on the car then the trims will most likely adjust to where the mixture really is.

Anybody have first hand knowledge if this is the case? I've never driven around without an O2 sensor.

Isn't your check engine light on? What other engine codes do you see?

 

[nc_99_99]

My O2 isn't heated right now and I get close to the same symptoms when the car is cold. When I first start her up and I get a rich idle it bogs down and I get 12-14 inHg. Then once the sensor is warm I get 18-20. Put in an O2!

 

[Tallen]

Chack and make sure you didnt skip a tooth!

 

[psychlow]

Matt, yeah, that's one of the things I'm concerned about as well. I'm wondering if the belt was off a tooth or two when it was last replaced.

Nc_99_99, thanks a billion for that info. I'll definitely give that one a go.

I couldn't remember how to do the engine code scan last night with MMCD - have to look up how to do that again. I think you have to press one of the Palm's buttons while you're in the software, but I couldn't remember what to press.

I don't currently have a CEL, which surprised the hell out of me, too. The check engine light comes on in KOEO mode, so the indicator light itself is functional.

I think at this point, the ECU doesn't even know the O2 sensor isn't there. It's just keeps waiting for the sensor to warm up and start registering, and since that never happens, I'm wondering if it never goes into closed loop mode.

Regardless, the oxygen sensor still doesn't explain the shitty WOT performance, though. When you go WOT it goes open loop and injects fuel based on MAF data and hard-coded fuel maps.

 

[97gstnick]

your all wrong, its the blow off valve. i dont know if im the first one to coin this phrase, but your 'blow off valve is floating'. creating a vacuum. mine does that all the time with the right amount of pedal pressure in a certain gear

 

[psychlow]

If that was the case, wouldn't my leak tester show this when I pressurize the system?

I'll try capping off the BOV line to see if that improves my vac, though...

 

[painmaster]

I doubt its the blowoff valve. Stick with the O2 for now, we know you need that!

 

[Damn 2nd Gear]

why havent you did the 02 yet?

 

[psychlow]

Because the female connector (that goes to the ECU) is all screwed up... I have to do some western union soldering (not the money transfer, a type of wire-soldering) inside the engine bay, which is really hard to do with the limited space in there. I'm going to have to take off a few hoses to get to it, and with work and all I just really haven't had time.

As an update, though, I did buy an O2 sensor socket and removed the old sensor. I was going to start her up and test vac with the sensor out, but the battery was dead and I didn't have time to jump her. I started soldering the new O2 sensor on today, though - I should hopefully have it back together and tested by tomorrow, if all goes as planned.

 

[psychlow]

OK, got everything soldered after about a half-roll of solder, a BUNCH of wiring, about 40 zipties and a lot of electrical tape (stupid RadioShack was out of heatshrink tubing).

O2 is working great, much to my surprise considering it registered right when I plugged it in the first time, no hassles. Woot.

What does everyone else get on 1G MAFs at idle? I'm running high 50's-low 60's Hz or so at about 875RPM. My O2 fuel trim was in the 60% range at idle.

Also, whenever I step on the gas quickly, I get 43 counts of knock.

Any ideas? I think my next step will be to check my base timing.