GM OBD1 and no O2 codes?

Why would you associate the 02 sensor with what sounds like a misfire and/or clogged cat problem?

1990 MY GMs don't have any code capability WRT misfires.

Because it acts exactly like it did a couple weeks ago when the O2 blew out....

I also thought I read about some shaky Bosch O2 sensors.

Can a vacuum test ID if it is a blocked cat? I have a vacuum gauge, but my experience is more with 'vintage' vehicles.

It does 'miss' at idle and all the way up though.

Mike

Wife's Beretta idled like crap for a long time. Was EGR. Replaced with a junkyard one.

My 2 cents - if it's not tossing a code, you're going to have to go back to basics with regards to diagnostics.

Does it do it hot/cold/both? Does it do it at idle/full throttle/both?

If it was my car, I'd do what I did - head on to a wreckers and start pulling parts. I replaced the IAC and the EGR on the wife's car for 10 bucks and it fixed the problem.

If you pull the front plugs, do they all look the same? Could be a bad coil?

If you know someone with a Tech 1, there is a way to scan them, but I don't have an OBD1 scan tool... so I read through the manual and trusted my gut. Maybe try a junkyard 02 sensor - almost free and if it works then you'll have found your problem.

Ray

btw, which motor? I have the GM shop manual for the Beretta, so if you have a motor which was in the Beretta (2.2 or 3.1) I might be able to give you some useful hints from the manual on what to check.

Ray

The term limp home mode is commonly used for transmission problems. When a transmission is in limp home mode it stays in second gear. Your O2 sensor would not cause this.

Bosch oxygen sensors are total crap. If you feel the problem is still oxygen sensor related replace it with a decent part, but that does not sound like an oxygen sensor problem from here. Since the old one "blew out" I would start by looking for problems with back pressure in the exhaust. Perhaps the cat is clogged.

A bad O2 sensor can set a code but it has to be pretty far out to do so on that car. The computer is more primitive than what you would find on a new car... It doesn't have a before and after the cat O2 sensor and it does not watch for a miss.

Check the plugs and wires again. Just because something is new doesn't mean it is good especially if you are using cheap parts. Have the exhaust checked for back pressure issues. Check fuel filter and fuel pressure.

Steve B.

An 02 blowing out wouldn't cause a misfire though the racket might be easily mistaken for one.

Dan Stern doesn't/didn't like Bosch 02 sensors, I use them because of limited options in this fair Village, don't see chronic failures though.

Yes.

Engine vacuum is engine vacuum no matter how old the engine is. Better would be if your vacuum gauge is a compound gauge that also measures pressure. Use the 18mm adaptor for you compression gauge and install it into the 02 fitting in the manifold, connect the compound vacuum gauge, start the engine and measure back pressure directly. (no, this won't hurt the gauge if you do it reasonably quickly) Anything over 3 PSI is suspect. (note; if there is a Shrader valve in the compression gauge hose/fitting, remove it for the back pressure test)

The old standard; engine vacuum should be higher at 2000 RPM versus idle

-may- show the clogged cat but it is by no means definitive. (be sure the EGR is disabled)

These vehicles were lousy for injector problems, lousy for ignition problems, both of which as you probably know will cause a cat-con to plug.

Another thing you can try is to unplug the alternator while running at idle, if the misfire improves, there's a very good chance that there are shorted injectors.

So how much other rust damage is in there? If the pressure is high enough to blow the O2 sensor out, you must have hell of a blockage in there, even if the pipe is rusty.

Check the exhaust system. I bet there's a lot more rust somewhere else, and I bet it's blocking the muffler or the converter almost completely.

--scott

Yup, guess so.

Both

Both

Good guess! Plug #3 is gas soaked, the other two show normal burn.

It is a 3300 engine with a new O2 by the way.

Thanks Ray.

Mike

O2 sensor will cause all rich or all lean, if you have one plug soaked and others not look elsewhere for your problem. If you've been running with a dead hole for any length of time you may have a clogged cat, which would explain the old O2 blowing out.

nate

On those cats if they are burned out they have a big ball in the cat that rattles around and makes a lot of noise. It can also intermittently plug the output pipe and not show up in a pressure test. Finding plug 3 wet has isolated the problem. How about the rear plugs? I think that blowing the O2 is just a distraction and you need to start with the basics. Many people keep driving for ages with problems showing up and then wonder why it all of a sudden turns into disaster.

Argg, well it seemed like a dead plug, not a coil pack, found that one (#3) with infinity on the ohm meter from the core to the wire clip. Put in new plug, no joy. grrr.

Can a coil pack fail on one leg only?

One plug wire only fails my induction timing light. New plug and old plug the same. That plug is gas soaked so it would seem the injector is working.

I swapped spark plug wires also with the same result, a #3 failure.

The old O2 sensor literally rotted away, it didn't need any back pressure to blow out. LOL!

Cat shouldn't be plugged, the vehicle will still run with power at 120+ kph. It just doesn't like the 'cusp' where the shift points are so it doesn't like OD at 100 kph or even D at 60 kph.

It has an even miss all the way up the throttle band.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:

Found a dead plug which I replaced.

Still no spark to #3 cylinder. All the rest show spark with my induction timing light.

Swapped wires. Same miss.

Plug is gas soaked so injector should be working?

Can a coil pack fail on one leg?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:

It is the 3300 engine.

I found a gas soaked plug that was actually dead according to the ohm meter. Put in new plug, still no spark.

Swapped wires, still no spark.

Plug is gas soaked.

The other leg of the coil pack shows spark.

can one leg of the pack go bad?

Do you maybe have the meter readings to test the coil pack?

I need to get a book for this old thing I guess.

Thanks,

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:

I found a wet spark plug. #3

Changed it, same miss and no spark showing on my induction light.

Swapped wires, same deal.

All the rest of the wires show spark on my timing light.

Coil dead on one leg?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:

Bad coil pack.

Yep, hard for gas to get there if the injector isn't working.

Yes.

I guess the next dumb question from a backyard mechanic who 'really, really' wants to drive 250 km 'tomorrow' on a holiday Monday up here in Canada to get to a cottage for a few weeks vacation with my wife would be can I hot wire the sucker to the other coil HT post and get away with it? LOL!

Then you really WILL blow your muffler off.

--scott

well... not if it is a waste spark ignition system and he connects the wire to the other cylinder in that pair.

Keep in mind that this is assuming a whole lot of stuff about this particular car that I don't know for sure.

nate

It is a 3300 Olds engine with 3 coil packs for 6 cylinders. The HT wires are on one side of each coil pack.

I guess I need two timing lights to see if both fire at once on one of the good coil packs.

Mike