qwiketz

hi guys. I have a few questions pertaining to o2's and cats. I think that I may have melted one or both of my cats a while back when my opti rotor was corroded from the car sitting for several years. The car was misfiring and running very rich. The points on the rotor had corrosion on there which I believe caused some of the poor running. Prior to sitting for a long time, the car had a very accurate tune and ran fine.

My car usually ran with right around 16 inches of vaccuum at idle and I noticed that it's down to about 12.

The car is also running rich.

I'd like to diagnose whether or not it's the cats and am thinking that I could either:
a. take of the exhaust from the long tubes
b. leave a short extension connected to the long tube and disconnect the resonator and the mufflers (I have a 3" b&b system).

My question is, how much length do I need after the long tubes to do my test and have the o2's be able to function with the open exhaust? Do I need just a few inches of tube after the o2's or do I need about a foot (or more)

I probably have about 7-10" for the o2's from the end of the long tube collector. I have probably about 4-6" from the wideband o2 to the end of the header collector.

Finally, my car is going from rich, to really rich as the car heats up and I drive around. Would this be a possible sign that the cats are getting plugged up? O2's start somewhat rich at start up 400's -500's, but creep up to the 800's which is what I normally look for under boost.

Wideband says mid 12's at startup and then into the 11's once the car is warm.

thoughts on any of this?

whalepirot

I submit the low vacuum is telling the ECM of a much wider open throttle, so it is adding fuel to compensate, which is NOT good for either the O2s or the Cats.

You don't say, but is this the '92? (Maybe the red one garaged near ETHS?) Seems I recall the prior owner never go the car to run right, no?

Kevova

Normally restricted cats or exhaust cause a noticeable power loss. Unplug O2 to keep it in open loop. Drop exhaust from headers and drive car. If performance increases an data becomes more normal cat(s) are likely restricted.

Red 91

Make sure coolant temp sensor for ecm is working properly.

qwiketz

Hey Mike, yes, it's me, Russ. I'm in Mission Viejo now and finally getting back to the car. It runs, drives, but is way rich and it's not correct. I drove it from the Lake Forest house down the street to our new house and it did okay but is just down on power and isn't running smooth.

Since I saw you last, I changed the opti, icm, idle air control, plugs, completely drained and flushed the gas and oil, air filter, fuel pump is newer, had the ecm solder joints redone. In other words, about everything other than checking out the exhaust and the coil and plug wires.

I think I have what I need to try to pressure test the exhaust so I'll try to do that this weekend.

The low vacuum may also be from misfires. I'm going to try to swap in some new plug wires and see if that helps as well. I also bought the boot protectors to help them live a better life. While I'm at it, I'll try to visually see how the spark looks. Before I swapped the opti, they were very weak looking. The rotor had some corrosion on the points after sitting for years and having a non-vented opti.

I have a few questions about the coolant temp sensor. It appears to be doing okay based on what I'm seeing in datamaster. It seems like it's acting okay and it's not fluctuating all over the place. That is the one on the water pump right? I heard and researched that the one on the head only operates the gauge? Is that accurate (in other words if that one failed it would only effect my gauge operation)?

thanks all for the help and I'll get wrenching hopefully tonight and make some progress.

qwiketz

Hey Mike. Got my vacuum leak fixed/improved. I'm now seeing 15" at idle which is close to where it should be. I have a faulty one way, check valve feeding my dynaspark, either that or it was user error on the install.

Now to datalog in the morning to see how the health of the car is. Who knows, maybe I don't have as much of a problem as I thought I did. Hopefully I don't jinx myself!!

qwiketz

minor update...

car is still running rich. 12.5-12.8 at turn on and works its way into the 11's.

Checked spark at the plugs and it looks great. Nice and white on the tester.

I used a temp gun and it looks like all the cylinders are running about where they should be. None are drastically off/different.

Plugs are pretty new with idle time only. I pulled 2 of them and they looked okay.

I used the temp gun on the exhaust and at about 5 minutes of idle (maybe not long enough), the temps at the front of the converter were higher than the rear. I am kind of under the impression that based on what I saw on the internet, that the temps post converter should be as hot or hotter than going in. I know that my temp gun isn't going to be the most accurate but I think it's time to either uncork the exhaust before the headers or pressure test it. Or, I can saw off the tubes prior to the converters and see what happens. If I could get some clamps, I could always put it back together.

However, since a number of my theories so far have not been correct, I think I'll likely go the less destructive route and pressure test it since I have the extra bung for the wideband already there. It should be here by the end of the week, so we'll know shortly.