Plugged Cat ?

[AL91GTR]

Sorry if this is an obvious post, but I've looked around and not found the info I'm looking for:

My car starts great, runs smooth and has good boost, etc... But, The last couple of times after driving for about 20-30 minutes of varied highway and city it suddenly starts to misfire, run rough and otherwise run like ass. This happened again yesterday so I ran the codes within about 15 min of getting home and got a 55 so all seems to be okay there. When it was running rough, I pulled over to listen from outside and could smell rich, stinky exhaust. I got inside and revved it expecting to see some dark smoke from the tailpipe but there was nothing at all visible.

I was sorting through some paperwork and found the previous owner had installed a $59 cat converter about 1.5 years ago to get it through an e-test ... think this pos could be starting to cause issues? I'm going to put a test pipe on it and see if this solves the issues before buying a decent high-flow cat.

Anything else obvious that could be looked at? I was going to double check grounding on the ignitor, cas, etc... just to eliminate anthing obvious too.

Since last fall I've put new NGK plugs in (0.8 gap), new coil pack harness, HKS hardpipe kit, general tune up and clean up some connectors, etc... I only put in Sunoco (Petro) 94 octane gas and have triple checked all vacuum and turbo plumbing and all seems to be good.

Thanks for any help!

[Micho]

I had a similar issue on the highway as well, replaced both the coilpack harness and new splitfires solved the job....I think.

[DarkCaporaL]

My money's on a good ol' missfire (check plugs, coilpacks).

Plugged cat would be more noticeable. Like trying to accelerate with the brakes on. Car would also likely completely stall as well since it would be choking itself.

[AL91GTR]

Thanks guys, I was first thinking the same thing but would it really take that long (30 min +/-) for a misfire to start happening? I put new plugs in this spring (NGK 7's) and a new coilpack harness. It's Likely my coils are pooched since they are originals (22 yrs old, 125k, hmmm yeah). if anything you would think a misfire would happen at full boost not just cruising around.

Think NGK 7's are too cold for an everyday plug? Stock internals with HKS dumps, dp, catback, intakes, boost at 1.0 bar, Mine's ECU, just basic bolt-ons

Time for some new coils ... and maybe remove or vent the harness/coil cover to let some air in there.

[Daryl @ RightDrive]

Not sure if I would trust a $59 cat...try that first and see what happens
As for venting the plug cover, it won't have much benefit if you are just street driving the car.

[Skym]

Fully blocked cat = cat overheat light on dash lighting up if cat over heat light sensor is screwed into cat. Leaks in exhaust can be checked by temporarily (few seconds) blocking tip of exhaust while engine is idling to listen for leak or see soot on flange area, etc.

Coilpacks should be changed at 100,000km (routine maintenance) for street use. Or way less if a trackday car or drag car (can be after each run).

When coilpacks fail they crack under mounting bracket (hottest area) and leak charge onto mounting bracket which creates grey marks under mounting bracket on both sides of coilpack. Also get black tip on sparkplug which has the weakest spark (what happened on my car). Main causes of coilpack failure is incorrect sparkplug gap, heat range or just age related.

Cheap (temporary) fix some use is to dip them in resin to fill the cracks on both sides of coilpack.

[Terrh]

Plugged cat will usually make your car sound/feel like it's running fine, but be gutless when you hit the gas pedal.

Since you're compliaining about a misfire I'd suspect coils/ignitor first.

The coils can fail without any visible signs of damage - the only proper way to test them is check the resistance.

The resistance should be under 1 ohm, under 1.3 is probably okay, and anything above 2 is likely bad or getting there. Brand new ones test at 0.7. Any that test out of range or in the hundreds are definitely no good already. And you may want to test them "hot" to be sure problem ones show up.

You test between two of the pins on the harness side, but I don't remember which two off hand. I think between E and - but just hook your multimeter up and see which pair of pins gives you a sensible reading.

[Skym]

Good advice ^^^^.

Some mechanics or auto electricians have a coilpack testing machine that measures voltage into and out of coilpack and heats coilpack up (had my cars coilpacks tested that way and 2x coilpacks had weak spark / output). It's common for 2x coilpacks to fail and the rest are ok.

[AL91GTR]

Thanks for the help guys. I tested all coils last night and they all showed exactly the same at 1.2 Ohms so figure they are on the way out. Nothing visible but obviously they are getting tired. I did actually find on the 5th plug back that the 'E' terminal on the coil was bent and i don't think it was even plugged in properly so this would seem to me to be the cause.

Checked/verified gap for all plugs is at .8 and added new grounds from the coil mounting bar (aluminum bar thing) to the firewall and another from the ignitor ground point to the firewall just for good measure. The plug with the bad coil connection was obviously sooty so I think this was definately the issue.

Hopefully will get a season out of these coils ... wife needs a new fence/bbq/vacation instead of my new coils hahaha

On a side note, I noticed that 3 of the coils had # 042 on the bottom and 3 had the # 055 on the bottom ?? All had the same Nissan part No.