Cat & Mouse

[onZedge]

Long post, but I hope my experience helps a fellow Pelicanite in the future: The other day, I left for work, and as started up the street, but my '87 924S would not accelerate over about 3000 RPM.

Checking my records, I found I had not done a major tune-up in a while, so I performed the needed maintenance on one system at a time to identify the culprit:

Fuel: Since my fuel pump had started making noise, I replaced (7-year old) fuel pump, (original) tank strainer, (4-year old) fuel filter, and performed fuel pressure tests. Static, idle, and residual pressures checked out OK.
No change in RPM limit.

Air: Intake had about 1/2 cup of pine nuts in it. I had recently waged battle against mice that were getting into my basement pantry (I think I won - for now). Cleaned out pine nuts, replaced (4-year old) air filter, temporarily installed a spare new MAF sensor (I have NA Tune), and inspected the intake hoses.
No change in RPM limit. Hmm.

Ignition: Replaced (all 4-year old) plugs, wires, cap, rotor, and inspected wiring for mouse damage. Plugs were most definitely worn out, and no rodent damage found.
No change in RPM limit. OK, WTH?

Then I remembered reading a few PP posts about a clogged catalytic converter causing similar issues, so I pulled the (12-year old) aftermarket cat, and sure enough, I could see a chunk of the matrix blocking about 75% of the outlet pipe with the outlet pipe pointing down. I presume that as I accelerated, there was enough exhaust flow velocity to push that chunk of matrix up against the cat outlet pipe opening.

With a length of random 3/4" copper pipe I had laying around, I "converted" the cat into a resonator. I can now fully appreciate the benefit of the LR NA-Tune MAF conversion, along with the 4* cam offset key.

I suspect what happened in my case was: clogged strainer > cavitating fuel pump > low fuel flow > lean (hot) mixture = cat damage.

One thing I had stopped doing several years ago, was adding a 12oz container of Techron fuel system cleaner to the fuel tank every oil change, so I'm going back to making that a standard part of oil changes. Might be why the strainer was clogged.

[onZedge]

CAT:




MOUSE:

[Monkey Wrench]

the pine nuts were evidence that you needed a new cat ;-)

[wwdwgs]

If your post mentioned the mice, I thought that it was abut a cat, not a CAT....