Matt's (mis)adventures with a cammed 3400

[mfuller]

Everyone:

Well, it runs.....sorta.
For anyone who hadn't heard the story, last fall I decided to do a relatively mild build to a 3400, to replace the bolt-on-only 3400 in my 2000 Olds Alero. To say I got a little carried away is an understatement:

3400 block bored .040" over
Sealed Power hyperutectic pistons (and rings)
Balanced rotating assembly
1280 cam grind from the store (Stage 3)
Flowmatched street/strip 3400 heads with SS valves, Comp springs/retainers/locks
Ported upper and lower intake manifolds
S&S headers (ceramic coated) to replace leaky TOG headers

So anyway, it runs, but not very well. I think the FPR might be bad (at least, that the diagnosis of my engine builder). Here's why:
I am seeing very high MAP values at idle (~ 60kPa). This in turn causes my fuel trims to get way outta whack - STFTs eventually level off at +27, and then they naturally start to increase my LTFTs. We pulled the vacuum hose from the top of the FPR (which runs to the MAP sensor), and we can smell fuel. Fuel should not be in the vacuum line. So we'll try that. This same condition happens at cruise too.....and naturally, it bogs real bad off the line since it's drowning in fuel.
We did not notice any misfires or other DTCs, so that promising.
I'll have a video up shortly.
But if anyone has any thoughts on what else might be going on, I'd love to hear them.

[SappySE107]

I think you hit the nail on the head with that one.

[mfuller]

Video for ya'll.....

1280+cam+startup+and+idle%2frev

[Superdave]

you can expect MAP values around 50kpa with that cam, maybe higher depending on your idle RPM. Swap that FPR and see what happens, it should be a beast!

[mfuller]

Well, since I really don't have time to deal with it, I just gave the car to a dealer friend of mine (to fix). Threw a couple codes on the way in this morning too:
P0748
P1133

Maybe there's still an exhaust leak somewhere.

[mfuller]

I think found the problem (and I should have done this a LONG time ago).
Rented a compression tester from AutoZone.
Pulled the plugs - 1, 2, 3 and 4 look fine. 5 is pretty black around the insulator, but the ground strap is clean. 6 is absolutely hosed....the plug is completely black.
Anyway, ran the compression test, starting with cylinders 2, 4 and 6 - they are on the front of the engine and easiest to get to.
Cylinder 2 - 175 PSI
Cylinder 4 - 170 PSI
Cylinder 6 - 15 PSI (!!!!) - I stopped after I saw this one.

Yessiree, Houston, we have a problem. I don't hear any banging when turning the motor over, so I don't think I dropped a valve and nuked the piston. I'm thinking either bad rings or a blown head gasket.
So at best, I was only running on 5 cylinders. But given the state of the #5 plug, I wouldn't be suprised if I was only running on 4. Dammit!!!

Oh....and those codes were due to a melted O2 sensor harness.

[SappySE107]

wow, that sucks!

[mfuller]

Here's what the plugs look like. I'm sure there's no quesion as to what plugs came from where.

[stewartfn18]

damnnnnnnn, that sucks. you didnt do a complete rebuild then? hopefully i wont run into this problem. block was rehoned and i got new piston rings for all the pistons, along with new gaskets and bearings. pretty much a whole new motor, with some goodies. other than the obvious, how did the car run? didnt sound like it was idleing bad or anything.

NVM, i just read your first post. considering you have new pistons and rings, id have to say you prolly blew a head gasket. its really the other other thing that could cause that low of compression.

[mfuller]

Well, I ordered a complete set of new rings and new spark plugs (because I think I've wrecked those NGKs). We'll start tearing the motor back out next weekend. Head gaskets are easy (I think I'll try the graphite ones that GM switched to in 2004), but I'm thinking a combination of the gaskets and rings. It does suck.

[95SleeperAcheiva]

if you haven't tore it down yet....

pull all the plugs.

put about 1-1.5 ounces of oil down the plug hole of #6

take another compression reading.

If the compression stays the same, bad head gasket.

If its suddenly restored or greatly improved, bad rings.

The oil gives a mild seal to bad rings thus sealing them temp for better compression during test. also tends to stay on the rings and such and doesn't blow up to the valves and gasket. This procedure is called a "wet" compression test.

[stewartfn18]

it could also be that you didnt alternate the gaps on the piston rings and thats where youre losing compression. check this road out too.

[sprucegagt]

Got an update on this Matt? I find it really odd that only 5 and 6 are giving you problems.

[3400-95-Modified]

Anyone guess at sticking valves or not? I would do a leak down before tearing the slugs out of the block.

[mfuller]

We have already pulled the motor. I must have had a massive misfire on #1 because the ground strap was touching the electrode (!). Spun the motor over and all of the valves look to be moving normally.
Anyway, at last update, the rear head was pulled off (exposing cylinders 1, 3, and 5). Head gasket looked fine, but we were a bit surprised at how much carbon was built up in the combustion chambers. The other head is coming off today. Kinda scratchin' our heads so far......more later.