Check Clogged Cats by pulling o2

mjbrox

Well-known member
Jun 30, 2008
1,812
48
Golden CO
Once warm my D1 wont rev past 3k, so I want to confirm that my cats are clogged and was thinking about pulling the o2 sensors. Obviously, this will cause codes, but it should confirm my cats are clogged.

two main questions.

a) is the o2 hole for the exhaust big enough for my test?
b) could this cause other damage.?
 

discostew

Well-known member
Sep 14, 2010
7,706
1,015
Northern Illinois
You could use a vacuum gauge. Make sure your on a manifold vacuum port (as apposed to ported vacuum). Hold the idle up at about 2 grand and the gauge should stay steady. If it fluctuates and and drops its a good indicator that the exhaust is restricted. Then I would split it from the manifold. Problem is when you drop that your going to break one of those studs, if you pull the o2 sensors one of them might be seized in the pipe.

Have you watched the fuel trim while it can't get to 3,000 rpm?
 

mjbrox

Well-known member
Jun 30, 2008
1,812
48
Golden CO
You could use a vacuum gauge. Make sure your on a manifold vacuum port (as apposed to ported vacuum). Hold the idle up at about 2 grand and the gauge should stay steady. If it fluctuates and and drops its a good indicator that the exhaust is restricted. Then I would split it from the manifold. Problem is when you drop that your going to break one of those studs, if you pull the o2 sensors one of them might be seized in the pipe.

Have you watched the fuel trim while it can't get to 3,000 rpm?

I guess watching the fuel trim makes sense. its strarts not reving past 4k, then 3.5k, then 3k Then I cant go up hills
 

jymmiejamz

Well-known member
Dec 5, 2004
6,008
361
35
Los Angeles, Ca
I would take a look at the crank sensor wires. I actually misdiagnosed one years ago with similar symptoms as cats when it was just the insulation of the crank sensor wires had failed. It’s very common and only seems to affect the 6” of wire near the sensor itself.
 

x3chab

New member
Feb 8, 2021
2
0
California
I’m having similar symptoms, and I replaced the CKPS. No change. The reluctor tabs all look good. I did notice that the corrugated tubing around the wires to the CKPS had crumbled off, but I can’t visually detect any issues with the wiring. Should I be able to see an issue, or would I need to test that another way?
 

boxster

Well-known member
Jun 1, 2009
443
88
Fallbrook Ca.
Once warm my D1 wont rev past 3k, so I want to confirm that my cats are clogged and was thinking about pulling the o2 sensors. Obviously, this will cause codes, but it should confirm my cats are clogged.

two main questions.

a) is the o2 hole for the exhaust big enough for my test?
b) could this cause other damage.?
Yes, O2 removed will allow exhaust flow, start up and run, when cats a completely plugged up and plugged cats will do damage.
 

mjbrox

Well-known member
Jun 30, 2008
1,812
48
Golden CO
Had the same problem 97 D1 wouldn’t rev past 2500 turned out to be ECU failed. It lasted 20 yrs.

I ended up having the cats tested and they where clogged. I also have a back up ECU so that wasnt the problem.

Anyway, i got CARB compliant cats from Rock Auto for $500. Since I was worried about the new ones being contaminated i decided to also do my HG. Ill know if this was all worth it in about a week