Low RPM stumble problem found!

[Sean 94z28]

I'll give some major key clues and we'll see who can guess what it was.

94 LT1, 6spd, SLP CAI-Shorties-2 on the left, Random cat, centerforce DF, SLP lightweight flywheel. 168,000 miles

4 second cranking to start when warm
Stumble below 2k in closed and open loop (bad stumble when in 6th)
New Opti, plugs, wires, fuel pump, fuel filter, egr, pcv
158 Long term fuel trim on passenger side.
Swapping sides with the injectors didn't move the 158 to the other bank.
Cleaned extremely dirty and oil saturated Throttle Body w/ new gaskets
Fuel pressure in spec and steady w/ clean injectors
You can assume all replaced parts were good.

I got more good clues, or I'll just tell you if I'm being a dork about it.

Sean (happy to know why!!!)

[wolfdogs]

bad muffler bearings?

[shadyphi]

No gas in the gas tank? lol

[Sean 94z28]

bad muffler bearings?

I was to the point where I was going to change those.
Problem was driving crazy. Or technically not driving me.

My problem started out as the typical broken exhaust manifold bolt. Got the shorties because there's no clearence to remove it, and the SLPs use a different bolt

Problem still exsisted after the install

Sean

[Sean 94z28]

I guess that wasn't fun eh? We'll just in case somebody ever searches for this problem, here is the answer.

Head gasket blown to an adjacent head bolt. Compression loss into the valve cover area.

I have decided to send the heads to Lloyd and then run the stock cam for now. 1.6 rockers and some tuning too.

I'll pull the motor next year after we get a house with a bigger garage.

Have a good day!
sean

[Formulaboy95]

hmm.... my list of what I replaced is much longer than that! Even did Intake manifold last week, map sensor too! Didn't get a chance to put the new Fuel Pressure Regulator in yet.

What cyl was it?

[Sean 94z28]

What cyl was it?

8 - compression check would be the best tool to diagnose this problem.

One big key was that it was an open and closed loop problem. I also had tons of oil blow-by in the throttle body and around the filler neck. No water in oil or vice versa.

Sean

[Craig 94 TA GT]

I'm glad you found the problem. I have a similar low end stumble and actually found a similar problem. Only my compression was lost through a loose plug.


However, the stumble still didn't go away for me. The car did run smoother, but still had the stumble that's driving me insane.
But again, I'm glad you're getting yours fixed, as this is one of the worst problems for anyone to diagnose.