Help,

I have a wind blowing from my valve cover when the PCV hose is removed and the engine is idling. The books (Chilton's, Hayne's, Factory Sevice Manual) all say there should be slight suction.

I think that my rebuilt cylinder head failed on my freshly rebuilt 2.5 L 4cylinder engine.

It has about 250 miles on it and the idle wanders noticeably. You can smell an oil odor outside the car after is has been driven. It is also losing oil at the rate of 1/2 QT per 500 miles, but there are no signs of leaks and the exhaust is clean (no smoke, no residue on back of car).

The engine shop said they installed stainless steel valve guides on the exhaust side. So, do I have a crack or did they lie? I am betting that there is a crack between the exhaust ports and the space under the valve cover.

Why? There is no wind coming out of the dipstick when idling.

My conclusion:
It's blowing by, but not in the crankcase.

Proposed solution:
Replace cylinder head.

Does this sound right? What do you think?

Was your motor a total rebuilt or just the head? U state that you are losing oil @1/2 qt per 500 miles but you only have 250 miles on the motor? I would venture to say that your rings have not seated yet, were you told to break-in the motor if it was a total rebuild?

Was the head checked for cracks(magnafluxed)? You should have "wind" coming from the PCV valve hole and a suction on the end of the PCV when you put a finger over the hole.

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Advanced Dealer in the Great Material Continuum . . .
Non Fiero Website: http://tractorsport.com
You can't race a dyno . . .

That was where I was confused too. You should have 'wind' coming from the hole when the pcv is removed. That is how the thing works. The wind pushes the little ball up inside the pcv valve.

And a freshly rebuilt motor will smell like oil and all sorts of things until it is broken in.

I'm not saying you don't have a problem because I don't know, but a lot of the things you are describing could be normal. The 1/2 quart of oil is not good though. But you should have some evidence of it somewhere, either in smoke from the exhaust, drips, or even a clogged pcv if it is that much. Have you checked your coolant to make sure there is no oil seeping in there somehow. Somewhere there should be a trace if 1/2 quart of oil disappeared within 250 miles.

Maybe you just checked the oil before you started the car and the filter hadn't filled up yet... it could happen...

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Tennessee Fiero Owners

Thanks for the responses.

The engine blows air from both the vent and the PCV valve. It's very hot air that comes out fast, like it's from a heat gun.

And on the oil thing . . .

I have added a 1/2 quart to the second oil change. The first oil change was only in the engine for the first 1/2 hour of break in (2000 rpm for 30 minutes). Then, I replaced the filter and changed the oil.

I have topped it off twice since then, a total of 700 cc have been added after 250 miles of driving and a total of two hours of idling while diagnosis the lousy idle. However, the oil level is slightly higher than at first (was at 1/2 of the range, now at 3/4). So, I estimated about 1/2 a quart in 500 miles of driving. Maybe it's a little more, or a little less. It is hard to say with so few miles on it.

The idle is rough with periodic dips. The exhaust is clean but it sounds like a big truck (way too throaty for an Iron Duke, sounds sick). In drive, the engine struggles to idle.

There's way too much air coming out of the valve cover to be normal. And, there's no air pressure coming out of the dipstick. If the rings were leaky, then there would be blow by in the crankcase.

The crankcase vent allows the engine to ingest small amounts of air as temperature changes. The PCV valve allows air out to prevent accumulation of cylinder air that has slipped past the rings into the crankcase.

So, if there's no positive pressure in the crankcase and there is huge positive pressure in the valve cover there must be a leak into the valve cover. Since compression is 150 to 155 psi in all four cylinders, the leak must not involve the cylinders themselves. This leaves one other source of hot air: the exhuast port.

A crack from the exhuast port to the valve cover explains what I have observed.

The head was magnafluxed before the machine work was done. I insisted. Then, stainless steel valve guides were inserted into the part of the cylinder head that seperates the exhuast from the valve cover. They were in fact pressed into position. So, it is plausible that the insertion of the guides is the cause of a major crack.

Regardless, the engine is impossible to tune. The idle dips to the verge of stalling periodically in drive. In park, the idle is better, but still dips with the same period. Every sensor is new (and has been swapped with a known good used one to be certain). Two different ECMs have been tried. Two different distributors, TBIs, TPSs, MAPs, Alternator, plugs, and so on. All of it had no effect.

I have followed all of the diagnostics in the service manual and the electronics all check out as good. There are no codes on the computer and fuel pressure is a lovely 12 psi. The cat is new and the vacuum increases with RPM (a clogged exhuast is indicated by a decrease in intake vacuum with increasing RPM).

The books say that you should feel slight suction at the PCV vent hole with the filter removed. You do not. Instead you feel significant positive pressure. Remove the PCV valve too and there is still lots of positive pressure. Go turn on a hair dryer on high and you can experience the same thing first hand (no pun intended).

My plan is to pull the head and take it back to the machinist. I started this thread to see if my diagnosis was right before I took it apart.

DOH! I should read before I post

[This message has been edited by 84Bill (edited 06-14-2001).]

I don't see where pressing in SS valve guides will crack a head? Its not that much of a press fit, unless they totally screwed that up at the machineshop. Your idle problem might be a valve (ext) that isn't seating correctly. Also check the valve stem to guide clearance maybe a problem there, might be way to loose?

My 2.5 motor has the same oil/idle problems . . . but it has 155,000 miles on it so its bound to have problems. I just add oil till I can rebuild another engine and live with the idle problem. I just drop it in "N" when I stop and pull into "D" when I want to go. Never have to worry bout my wife wanting to drive my car since she doesn't want to have to deal with this

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Advanced Dealer in the Great Material Continuum . . .
Non Fiero Website: http://tractorsport.com
You can't race a dyno . . .

If the hose attached to your PCV valve is hooked up to the right nipple on the throttle body, there's no way you should have anything blowing out of it. There absolutely should be a very noticeable vacuum. Sounds impossible. This would severely affect your idle too. Where does the hose go?

When the vacuum hose is attached from the TBI to the PCV port (exactly as instructed on the decklid sticker), the hot wind blows out of the crankcase vent hole. The crankcase filter slows it down a bit, but not much.

On the other hand, there's no wind from the dipstick.

The problem has perplexed many. It's not impossible, as I can make it happen just by starting my Fiero.

It has been suggested that I do the following:

1. Compression leak down test
2. Dynamic compression (engine running on three cylinders, compression tester on forth cylinder)
3. Remove valve cover, apply pressure to each cylinder from a compressor and search for leaks.
4. See if the blowby still occurs when the engine is cold (cracks may open fully only when the engine is hot)

I'll post again when these steps are completed.

In the meantime, I am searching for a new casting cylinder head on the assumption that the rebuilt one I have is cracked.

We shall see . . .

Well, if there's actual "wind" comming from the valve cover, would it be possible to redirect that wind to the rear? The duke needs all the help it can get. If you have enough wear, it could act as a J.A.T.O. assist. And if someone's following you, the accumulated oil that is carried in that wind might be enough to reduce tire adhesion and make 'em spin out, like on Batman. Or was that speed racer or get smart?

[This message has been edited by EdsB52 (edited 06-15-2001).]

Tested the compression and rechecked the PCV system. There is vacuum after all, so blow by does not seem to be the cause of my idling problem after all.

Compression is
still 150 psig in all four cylinder with closed throttle and 160 in all four with WOT.
Dynamic compression was about 60 psig peak in all four cylinders

The spark plugs in #1 and #3 have some carbon build up at and are very tan in color otherwise. The other two sprak plugs look light tan with very little build up, if any.

So, now it looks like the idle problem is an ignition problem, or the camshaft failed. The engine missfires at all rpm, not just idle. And, the vacuum varies from 15 to 20" at idle. The problem seems to be getting worse.

I am grateful for all the advice. But, it seems like it is time to start a new post with a better statement of the symptoms.