Problem!

[Nate's Alero]

Originally Posted by [ion] C2

Another JBO member said he ran his car without the strap without any issues. Cliff says the ICM is grounded through the harness, don't need the one on the cover.

Some guy on JBO suggested:

To which I responded:

And then he says:

And I say:


And then I tried it. It's very odd... I only disconnected the O2 for a short while and let it idle, but it seemed to run perfect... I'm not sure what this guy knows about this but it doesn't make much sense.

ECM relearn?

[[ion] C2]

I replaced the soldered connections with posi-lock connected ones, as they should be, and the issue still occurs.

Then I checked, it does run rough still with the O2 disconnected at the harness. I couldn't really tell last night but tonight I confirmed it definitely still occurs even with the O2 physically disconnected.

I am fairly sure that my 4th injector is leaking (vacuum leak) where it goes into the head (I can hear something like a hiss when running from that area and when I sprayed WD-40 around the o-ring it hissed loudly and the WD-40 disappeared and the idle may have changed (It was running rough to begin with, hard to say).

May have caused my hunting/dying at 600 RPM issue back when I put them on in the first place 3 weeks ago that I "fixed" by raising the idle RPM to 750. Pulling the rail tomorrow and ensuring it's sealed. It has to be it. Nothing else fits, besides if the header isn't sealed.

I don't get why it would happen right after a header install, unless the vibrations from cutting the pipes and air wrenching on and off the nuts did something, Oh and pushing against the lines and such when trying to make room to get it in/out.

[guiguilandry]

sometimes when the rubber seals is dryed because of high mileage it can crack if you change one seals than change them all and put a little silicone grease when putting the injectors back it will help

[[ion] C2]

Nah they're basically new injectors and o-rings from a Cobalt SS/SC.

Pulled the rail and ensured the injectors are seated properly. No difference.

WTF. I'm going to do a compression test, hoping it's terrible (new engine goes in next week).

[[ion] C2]

Updated Summary

Problem
Engine shakes and apparently misfires at idle after header installation.

Overview
header --> downpipe --> flexpipe --> cat --> magnaflow --> piping --> dynomax --> outlets
(New components being the header, downpipe, and flexpipe)

Header
The header is a Pacesetter, JET-HOT coated, made for the Cavalier with EGR. I used a new 2000+ non-EGR gasket for my 2000 LD9 in the Alero, which is supposed to block the EGR tube on the fourth exhaust runner.

During the problem
- RPMs don't fluctuate much at all
- Occurs in open loop as well as closed, regardless of AFR at idle (not O2 related)
- Exhaust sounds like it's getting little bursts of energy every second or so, it thumps like misfiring
- Zero DTCs

What I tried so far
- new spark plugs
- new coil pack housing
- new spark plug boots/springs
- sprayed WD-40 to check for vacuum leaks, none noticed
- ran a wire from the ICM bottom (between the ICM and IDI cover) to an IDI cover bolt to test if I needed the ground strap I removed 15 minutes before header install by swapping engine covers
- pulled fuel rail and reinstalled, ensuring the injectors were seated properly

Possible causes
- nuts may not be tight making the header not seal against the gasket and head
- head gasket (odd that it’d finally go the moment a header is installed)
- FPR or fuel pump (48 PSI at idle as it should be…)
- injector could be locked open?


I'm going to check for vacuum leaks again tomorrow. It fits the symptoms... and it's what misslindseysue's been saying all along. The only one we messed with was the brake booster.

Originally Posted by Symptoms of Vacuum Leaks - Yahoo! Answers

At idle likely engine will run rough ... for automatics more noticable in drive or reverse with foot on the brake... shudders at traffic lights etc.

on gently opening of throttle response will be more sluggish than normal and may be so slight almost undetectable to untranined individuals (mechanics or technicians)...

under full throttle it wouldn't affect things much unless a really bad one like a EGR valve stuck open or a Power Brake vaccum booster diapham bad...(these are very big leaks and the extremes)

[DOHC_tuner]

replace your idle sensor and check your positive crankcase ventilation hoses and breather if you have one

[[ion] C2]

ya my PCV hoses and baffle are good, they don't affect idle either, only oil

my "idle sensor?" my IAC valve works properly if that's what you mean, i can check it in HPTuners, and idle stays constant, it's just rough, misfiring, vacuum leak is likely the cause.

[DOHC_tuner]

Yeah the idle air control valve. So all you did was install the header? Why not try and uninstall it and replace the stock exhaust manifold? It could be just that the header has the EGR port.

Do you see or feel anything on the front of the head where the EGR would go?

[[ion] C2]

Others have used the 2000+ gasket with an EGR header without issue. If I remember correctly, so are you. Using a 2000 gasket, the EGR tube on the runner is blocked off.

And lol I doubt Midas has the stocker, and it'll cost to have them put that sucker back on. If I do anything it'll be to cut off the EGR tube and weld the hole in the runner.

Everyone says it's not that, and others have used my same setup with success.

[DOHC_tuner]

Nope I got the header without EGR.

Others who have tried it....are they cavaliers or Aleros?

[[ion] C2]

Cavaliers, but it's the same engine. The only difference is the side the O2 bung is on.

[[ion] C2]

Well, checked the nuts on the header, they're all definitely tight.

Checked for vacuum leaks again, everything looks perfect... sprayed carb cleaner all over the place and no change..

I've been looking all over this engine for something we must have changed... I can't find anything out of the ordinary or think of anything we touched but the brake booster line, pulled out my oil dipstick, took off the strut tower bar.

Still have yet to do a compression test, but the new engine goes in tomorrow if all goes well.. Speed Industry should be able to figure it out if it still exists after they do the swap.

[DOHC_tuner]

Well now I have a problem...I got a random misfire now.

[[ion] C2]

wewt for misfires without any reasonable cause

[DOHC_tuner]

well i effed up and hook up the PCV hose to a vacuum hose....I wasnt thinking obviously!

It suck oil all INSIDE the intake manifold and the cylinder walls. I disassembled everything...cleaned it up, new plugs, and now it misfires.

I effED UP!!!!!!!!

[[ion] C2]

I'm thinking it quite possibly could be the IAC. This one came with my 62mm TB, used. I could go throw on my old one from my other throttle body. Or first just remove this one and see how nasty it is.

[[ion] C2]

It's not TPS or IAC, both function perfectly. This doesn't seem to affect anything but idle.. just tested WOT and logged in HPTuners to confirm: thing pulls hard as hell, everything looks good. My cruising is perfect, my part throttle seems like it's always been.

Just idle. Seems when it thumps and seems like it misfires there's a spike to lean real quick. Dunno...

Checked FPR again, 'tis perfect. Don't get it.

[01OldsAleroGt]

well im still thinking it may be the EGR... but who knows... DO A COMP TEST DAMNIT !

[[ion] C2]

Detailed Summary
Ignore everything else.

This doesn't seem to affect anything but idle.. just tested WOT and logged in HPTuners to confirm: thing pulls hard, everything looks good. My cruising is perfect, my part throttle seems like it's always been.

Just idle. Seems when it thumps and may misfire there's a spike to lean real quick.

So.

What causes a rough idle (apparent misfire) but:
- runs fine otherwise as far as I can tell
- displays no codes
- no apparent vacuum leaks
- FPR, IAC, TPS are fine
- header nuts are tight, no exhaust leaks
- not O2 related
- kitty is nice and clear
- installed new spark plugs/coil pack housing/boots/springs
- ran a wire from the ICM bottom (between the ICM and IDI cover) to an IDI cover bolt to test if I needed the ground strap I removed 15 minutes before header install by swapping engine covers
- pulled fuel rail and reinstalled, ensuring the injectors were seated properly
- fuel pressure at idle is 48 psi

header --> downpipe --> flexpipe --> cat --> magnaflow --> piping --> dynomax --> outlets

All we did during the header install was:
1. unbolt stock downpipe
2. cut off pipe after cat just before magnaflow
3. removed strut bar, heat shield, coolant bracket, then stock manifold and gasket
4. installed header, had to remove oil dipstick and move the brake booster hose out of the way
5. tightened nuts, reinstalled dipstick and booster line and bracket
6. realized o2 bung location left zero room, so we plugged it with a threaded plug
7. welded o2 bungs (upstream & wideband) on the downpipe
8. bolted downpipe to header
9. welded flexpipe to downpipe
10. cut cat off of old piping, welded it to flexpipe and magnaflow
11. welded bung after cat for rear o2
12. reinstalled all o2 sensors

[Nate's Alero]

umm issues? TAKE HEADER OFF ANDSEE WTF IS ThT MAKES A DIFF