Guys,

Would a bent valve always show up on a compression test or leak down test? That is, is there any chance that it could seat properly for the test, but not seat properly during engine operation?

Still chasing my idle misfire problem...

 

Never seen that. Either it leaks, or it doesnt.

 

Theoretically possible, but not likely. They tend to beat the valve guides up when bent and just get worse as it goes.

The occasional one will still seal(usually after its beat itself into the head), I've only seen this a few times, so I would have to go with 99-1 it will show up if its bent valve or possible seat issue..

Another fairly easy way to test it wouold be too pull the valve cover and put a screwdriver thru the spring and see if u can raise the valve any further. Would at least let u know if everything is sealing. Just use the scewdriver like a lever and see if u can bring the valve up any....

I really hope u figure something out on this, I'm getting curious too

good luck
Jeremy

 

I had sent the heads back to AFR a year or two ago (been so long, I can't remember!) for them to inspect them. Someone recently mentioned the possibility of a bent valve, so it got me to thinking how thorough an inspection AFR performed. I posted this on the 2nd gen site www.nastyz28.com and have pretty much received the same "it's literally impossible" response.

The other day, I pulled the MiniRam off thinking the manifold might be defective and intending to ship it back to TPIS for inspection. But, for the life of me I can't see anything wrong with it. No holes, porosity, warped flanges, etc. With the gaskets still on the heads, I can see that there's uniform contact pressure along the entire length of the gaskets. Far as I can tell, this manifold is fine.

With the bent valve idea planted in my head, I started debating whether to pull the passenger side head off (again). But it sounds like it'd be another wild goose chase at best since the #2 cylinder shows up fine (even stronger than some of the other cylinders) when I performed the leak down and compression tests).

 

You've completely ruled out the ignition and injectors?

 

Ohhhhhh yeah!

A long time ago.


It's all been replaced during the search for the problem.

 

Did u do what said and tried pulling up on the valvespring?

later
Jeremy

 

Not yet. I'll have to give that a try...

 

Why do you suspect the #2 cylinder?

 

My diagnostics have pinpointed that cylinder as the culprit.

The ol' pull-one-injector-plug-off-at-a-time-and-see-what-happens. Kevin91Z and DynoDon were extraoridarily helpful several weeks ago in helping me confirm the #2 cylinder as the problem using a wideband O2 sensor. Now, it's just a matter of figuring out the root cause. The symptom is a very lean-running cylinder at idle speed- causing the passenger side cylinder bank to register an 18 to 19:1 air fuel ratio on the wideband.

 

OKay, if I undersatnd correctly, you disable the injector from feedng fuel to that cylinder, and there is no difference in operation?

Means (to me) problem is related to fueling the cylinder.

But you mention lean A/F ratio to the whole bank, so I may be confused again as to why you're dialing in on #2?

I realize you have probalby posted your issues before, so how about posting a link to the thread and maybe we can figure out what's up.

 

BTW, if you had a poorly seating valve, the fuel mixture exiting that chamber would be rich...unburnt fuel...so I'd wonder why it would be indicating a lean mixture?

 

I'm guessing that by now you've already removed the injectors and sent them in for flow matching. Even new sets can be off. Aftermarkets are terrible about this.

If you haven't already had the injectors dialed in, Check with Rich at http://www.cruzinperformance.com/ and he can relate some of his experiences with injector "sets" and how they are matched.

 

Exactly.


If the #2 cylinder is reading lean, wouldn't that show up as lean on the entire bank of the O2 sensor is in the collector?

 

I've swapped injectors around from one cylinder to another aw well as tried out a completely different set and swapping those injectors around too.

I'm 99.99999999999999999999999999% certain it's not the injectors.

 

I read a story once about injectors grounding out on... *gasp* get this... an Edelbrock TPI manifold. (My daily pick on Edelbrock).
Anyway, the injectors were touching metal on the manifold and causing problems (so I heard). Maybe check that on your miniram? See if that injector is shorting. Sounds hokey to me, but stranger things have happened.

Might also want to inspect that wiring. Doesnt matter if its OEM or Painless or the like, the ones I have seen do the same thing, they run back to around where the distributor is and group themselves into 2 wires back to the ecm. Make sure the wires themselves arent shorted/frayed/touching. And dont unwind them

 

You know, I can put my finger on my injectors and feel them cycling at idle, can you get to them under the MR? Can you get a noid light under it?

Also, depending on how much the ECM can compensate on PW, it will increase the PW on all injectors to try and maintain AF ratio, so may not show as lean condition.


You may be having a problem with ignition on the hole also. #2 shuold be an easy one to put in a cheap spark checker, compare the spark to another cylinder. I borrowed an inductive spark checker once that displayed the volts, they cost about a hundred bucks, but sure are sweet to use.

 

Along the same lines, here's something for you.

A bad cam lobe, SEVERELY bent pushrod (not sure if thats even possible) or broken rocker/stud can cause a problem on individual cylinders.

You're missing some of the symptoms I was, but when a valve doesn't open, compression test will reveal NOTHING, as compression stays good, the cylinder just isn't doing any work.

I broke an intake valve stud. I could hear it with the engine running (just a bit) but pulling the injector clip made no difference in how it ran, so I knew which cylinder it was. Had to drive it after the stud broke, before I could pull the injector plug, and eventually set a rich O2 code. Also started smoking the longer I drove. (dual exhaust, again proved which bank was the problem)

In *my* case, since the intake valve was "dead" the injector kept firing, which filled the runner, which eventually fed the other cylinders extra fuel, which set the rich O2 code. The smoking was due to extreme suction caused by no intake valve opening, which was pulling in oil past the rings. All of this was verified when I took the top end of the engine apart.

Thats more of an example of cause and effect. Until it happened and I tore the engine down, I never would have imagined what was actually going on. I'd think with good compression but still no power from that cylinder, ignition totally ruled out, you've definitely got a valvetrain issue, but not with valve seating.

 

I had thought about all of that a couple of years ago, which prompted me to chanege the cam and lifters.

Well, I gave this a shot today, but nothing unusual observed. Couldn't bring the valve or valve spring up at all. I even measured the height against the neighboring springs and they were all the same.

 

Actually the O2 will not read the fuel. It will pick up the oxygen and see it as lean