zimbo

iTrader: (4)

I'm experiencing something very strange. Here are the symptoms:

- When I turn on the car, the A/F ratio at idle (as measured on the driver's side) starts out at the regular 14.7 or so and gradually decreases over the next 20-30 seconds to the very low 11s. As this is happening, there is an accompanying drop in RPMs and the vacuum level gradually decreases from -22Hg to around -18Hg.

- Shortly after the A/F reaches the low 11s, the engine will bump up the RPMs and the A/F ratio will jump back up to 15.0 or so and the whole process will repeat.

- Driving around town, the car is richer than it used to be when I'm not at WOT. Under full boost at WOT, A/F is unchanged.

- I'm getting a SES light with two codes: multiple cylinder misfire and driver side bank too rich.

- The plugs on the driver side are dark--not caked but they definitely show signs of running rich; the plugs on the passenger side are squeaky clean.

- I do NOT see white smoke trailing the car. Sometimes the exhaust drips a bit of water if I idle for long periods of time--but I have always chalked that up to the humidity of the air in North Carolina.

Here's what I've checked:

- I've replaced the plenum gaskets and have checked and double checked for air leaks.

- I've swapped the front driver- and passenger-side O2 sensors (i.e. the OEM engine A/F sensors), yet the driver side continues to run rich

- I've done a compression test: all cylinders are in the 180 range

- I've done a leakdown test: all cylinders are at 5% except cylinders 1 and 3 which are at 10-15%.

- Oil level does not show signs of burn; nor does it smell funny

- Coolant level does not show signs of fluid loss (although this hasn't been happening long enough perhaps)

One hypothesis proposed by my tuner is that I have a small head gasket leak on the passenger side which allows just enough water in to "steam clean" the plugs and increase the A/F. To compensate, the car adds more fuel which causes the driver side to run rich.

That's as good an explanation as any, but I guess I was thinking that in order for a gasket leak to affect idle it would have to be more obvious (i.e. leakdown results).

Any ideas? I've at least temporarily ruled out the MAF or an E-Manage wiring problem if only because of the disparity between the driver and passenger side banks.

--Steve

Sharif@Forged

iTrader: (92)

Can you read your MAF voltage? Make sure it's in range. Somewhere around 1volt at idle..maybe a bit less.

Second, if you had any type of head gasket issue, you would see white smoke for the water burnining in the combustion chamber.

Your symptoms really point to a vaccum leak...but sounds like you checked everything out. I would continue focusing on sources of vaccum leaks...PVC valves, plenum, worn lines..etc. When I had a vaccum leak in my plenum, my car did the exact same thing you described.

zimbo

iTrader: (4)

Can you think of any vacuum leak that would cause one side to run richer than the other? That's the puzzler and the only thing that makes me think it's not a vacuum leak.

OTOH, I just rechecked the coolant level and it's not any lower than it was a week ago. If it were a gasket leak big enough to cause idle problems it sure seems like I would see less water in the radiator!!

--Steve

Sharif@Forged

iTrader: (92)

yes...if the vaccum leak is on one side of the plenum, than one bank could run richer/leaner than the other. Plus, when stuff like this happens, it sometimes takes a bit of time for the ECU to trigger the error on the other bank.

Hope this helps you find the source of the problem.

G3po

iTrader: (8)

You could also get a vacuum leak on the lower plenum, which would be more "side" specific than the top plenum. Id you replaced both disregard this comment.

zimbo

iTrader: (4)

I have not yet replaced the lower plenum gasket--just the upper one. I have a lower gasket on order and will try that ASAP.

--Steve

Sharif@Forged

iTrader: (92)

also, you probablyi already know this...but dont overtighten those bolts and nuts. The heads/manifolds are AL, and they will break very easily if overtightened...maybe 20ft/lbs or so. Don't ask me how I know this...dooooaa!

G3po

iTrader: (8)

The plenum TQ specs are in the manual.
Note when TQing small bolts 24lbs and down, make sure you use
a small inch-pound TQ wrench. The bigger ft-pound wrenches , though they may be graded down to 20ft-lbs, are "very" inaccurate a the low end settings. Another don't ask me how I know this, dooooa!

King Tut

iTrader: (1)

I know bout needing a small inch-pound TQ wrench too, dooooa! When it says 7 ft/lbs and you figure you just won't go all the way on your 20 ft/lbs TQ wrench, SSSNNNAAAPPP.

Sharif@Forged

iTrader: (92)

i dont feel bad...sounds like I wasnt the only one.

zimbo

iTrader: (4)

Any other ideas? I STILL have not figured this out. I've replaced the upper and lower manifold (from another engine); I've replaced both gaskets with new ones; I've tried disconnecting all vacuum lines that come out of the front left "hole" in the plenum, using the stock plenum vacuum cap instead. Are there other vacuum lines or tubing to check?

I still have the issue. I don't see smoke or steam; my coolant level is not dropping; the car still pulls hard under boost.

--Steve

booger

iTrader: (6)

there is a vacuum line on the throttle body .Thats where I run my boost gauge off of . Have you done a comp test yet ? And or a leak down test ?

G3po

iTrader: (8)

Have your O2 sensors checked.

zimbo

iTrader: (4)

I've done both. See above.

One thing I haven't done is remove the entire intake manifold. I've removed the upper and lower pieces of the plenum (aka manifold collectors). I know that there are two gaskets under there--one for each side. I'll try that next.

--Steve

Sharif@Forged

iTrader: (92)

Zimbo...do you have crawford plenum?

If so...I am willing to bet $1 that those four bolts in the lower manifold that plug the stock manifold mounting bolts....have backed out...and you have an vaccum leak there. The dead ringer is that you mentioned you are loosing vaccum as this happens.

Take your plenum off, and double check those bolts. Use blue loctite so they dont back out.

A small headgasket leak doesnt cause a vaccum leak, and since your compression check came up fine...I highly doubt its a head gasket.

Let us know what you find.

zimbo

iTrader: (4)

I have the Crawford plenum and suspected it might be the culprit--but as I mentioned I completely replaced the upper and lower plenum pieces with the stock ones from the engine I bought to build up. It made no difference.

--Steve

Sharif@Forged

iTrader: (92)

very weird. Steve...you definately have a vaccuum leak...no question about it. I just dont know where??? Wish I could be of more help!

zimbo

iTrader: (4)

Dammit! I have replaced the entire lower manifold (that the injectors plug into) along with the gaskets beneath it. I was pretty sure that was the culprit (see my first post for symptoms). But that's not it. Now I'm tempted to buy new O2 sensors.

I'm running out of things to try. I'm offering a $75 PayPal reward to anyone who can solve my problem!!!

--Steve

spazpilot

iTrader: (2)

check and make sure you are getting proper voltage to the injectors on the bank running rich. also make sure one of the injectors are not stuck open. swap injectors to the other side see if it follows the problem. One other thing is to also check the valve cover for leaks. I heard greddy had problems at one point with the valve cover, though I have not run into this problem yet. start swapping from one side to another till it follows and if it does not I would agree on a small head gasket leak but you would see it on a leak down test.. It just has to be something stupid. only last thing is that the little black box to get an rpm may have failed and is no longer reading three of the injectors resulting in a rich condition. then then it would be strange for three to go bad on the same side. also swap the coils maybe something happen in destroy or crippling the coils on that side. hope this helps.