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Heated O2 install ... engine mising like crazy, what did I do wrong?

and I , didn't say it was going to fix the problem either... ;) just that, that was why you run a heated unit with headers, so you can run it down at the collector...

he really needs some data collection...
 
Like you said, only getting data from two cylinders...data collection isn't going to tell you much if the problem is elsewhere. Or one of those two cylinders.

O2 is almost certainly seeing a problem (open vs. closed loop issue), need to ensure both cylinders are working properly before spending time and money relocating the O2 sensor. Wouldn't be a terrible idea to move it, just don't think it's necessary at this point.

As I read the post, this happened AFTER a heated O2 install only? The original should have been getting plenty warm, if it was working properly.
 
Update:

I have not been able to find a shop that will weld in a bung for a reasonable price ($250 doesn't work for me) so I figured in the meanwhile I would put back my stock O2 sensor. I wanted to do that so I could take it to a shop and get the emissions test and get my tags (they are expired now) so at the very least I could drive my truck again.

After putting the original sensor in (actually a new one) I have the exact same problem. Once the truck warms up, the engine starts missing like crazy. And of course it runs really rich too (like it did before).

So the symptoms are:

COLD - first 5 minutes or so:
  • Runs very rich - clouds of gasoline are obvious
  • A little rough at idle
  • Drives smooth
HOT - and this comes on very suddenly - literally one minute everything is smooth, then suddenly something "turned off":
  • Runs very rich, I can't roll down the window.
  • Misses like crazy, with a constant miss and then other cylinders periodically missing. It feels like at least 1-2 cylinders are not firing at all, and then another 2-4 are missing.
Of slight importance is to know that I did NOT cut the O2 wire on the truck when I installed the new heated O2 sensor - rather I cut the wire off my old sensor, then connected the new sensor wire to the old sensor wire+plug, so I didn't modify the wire harness on the truck. I hope I didn't damage it, but I was very careful not to yank it so I think not?

I've ordered an ALDL cable, and once that gets here I'm going to see if the ECM can tell me anything.

I have recently replaced most of the engine electronics, such as the MAP, TPS, ignition module, EGR, and some other bits. It has a new cap and rotor, wires, and plugs. Also new are the FPR and injectors.

If anyone has some suggestions on what might be causing this please let me know.
 
I don't think your O2 is the main cause of your issues.. "missing" is not a symptom whatsoever of a wonky O2...


is your CEL working? what codes are you getting? sounds like a bad injector to me.....
 
Ryoken's right, faulty O2 sensors generally don't cause such problems, they just usually mean your truck won't run efficiently as it's supposed to.

Since you've replaced most of the electronics, just do your due diligence and make sure everything is installed properly, timing set correctly, etc. Check the valvetrain. Wiped cam lobes or broken valve springs can cause misfires.
 
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Yep, concur. The "turned off" you are describing is most likely once the engine is warm enough, it goes closed loop (starts using the O2 sensor) and it's trying to compensate for whatever problem you have. Up until recently I had "open" exhaust on the truck, and my open loop tune wasn't real precise. It ran ok, but it made a lot of noise until it went closed loop, which quieted it way down. Very easy to "hear" the open/closed loop transition in that case.

I'd be guessing fuel injector as well, I suppose a bad fuel pressure regulator could cause it, if pressure is too high. Injectors can be tested partially by you, not sure what the spec is (in ohms) for good TBI injectors, I know its ~15 for the TPI ones, and I assume TBI your vintage is the same, but should be easy enough to search and find.

You can find mild steel O2 bungs for pretty cheap (or get the proper size jam nut, I think it's M18x1.5) and just weld it in yourself. I'd do that vs. paying someone $250. I think all of us are on board that it's not an O2 sensor issue however. Placement nor heated/unheated is going to matter for this.
 
Thanks guys, once the ALDL cable gets here I'll run some tests. Right now there are no error codes at the terminal, so hopefully the ODBI data can help. After that I will have to test the injectors, FPR, coil, and whatever else I can think of.

Fortunately I have the service manuals, but they all say to test with the ODBI port first, so I am going to have to trust that - and you guys.
 
keep in mind, GM ASSumes that everything is hunky dorey with the fuel system... they carried that thought WELL past TBI mills too..

you can generally tell how an injector is spraying by watching the consistency and atomization of the pattern... watching it with a timing light strobe helps you see it better...

doubtful you have an "overfueling" issue due to a regulator... it takes a TON of pressure to have a TBI injector overfuel.... I run 14 psi from a 45 psi pump without issue.. 99% of the time, they are underfueling and barely running decent with a factory setup... most factory setups are in the single digit psi range...

but if you have a pintle hanging up, it couldvery well be dripping, pouring fuel in.. which is what I suspect you have going on...
 
Interesting. I'll pull out my timing light tomorrow and try to get some video of it, and I'll post it up.

That reminds me of a funny story with one of my other Blazers (not the current one with problems).

So, I had this other Blazer, and I put in some new injectors. Unfortunately, at the time I did not realize I missed one of the o-rings that seat the injector into the housing. That meant that when the fuel system was turned on, fuel literally pumped into the throttle body like a garden hose. I of course, didn't know this when I went to start my truck. It kinda ran for a second, and then wouldn't run anymore. So I let it sit for a few seconds, then tried again.

Click ... and a hummmm, but the engine would not turn over.

That's weird, right? So for whatever reason, I decided to take off the air filter housing and see what was going on. Much to my aghast, I notice the fuel just running down the throttle body. I scurry and turn off the ignition.

I realize I have hydro-locked the engine ... with GASOLINE.

Brilliant, I know.

So, I take out the spark plugs, and disconnect the coil, and proceed to turn it over.

Well, a few CUPS of gasoline go flying out of the engine bay, and then immediately there is a big explosion (of course) and now my truck is on fire!

Being the clever guy I am, I keep my fire extinguisher nearby. And by nearby, I mean inside the house, upstairs, on the far side of the kitchen, on top of the fridge. So off I run, pushing my wife out of the way, and scurry back to the truck to put it out.

Luckily, only one vacuum line melted, and required surgery. Everything else was intact, just covered with white crap.

And since I know you have to prove stupid things on the internet ... here are pics of the aftermath.

A little white smoke from the fire extinguisher:

GwakmFq.jpg


667eF4c.jpg


The engine bay:

njkmCo3.jpg



And a few cups of gasoline that made it all the way out the exhaust pipe!

lhaeGDf.jpg


Yup, this is who you are helping. A certified moron. I appreciate all the help!
 
Did you say you used a wire tap on the sensor wire? Those things are plain evil and I'd replace it if that's what it was.

I'm not sure what the deal is with soldering the sensor wire, but I soldered mine and did the same with my Honda without trouble.
 
The problem with the sensor wire is this: Oxygen sensors need a reference to compare the amount of oxygen in the exhaust to. On the sensors used on those year trucks, it got the tiny amount of outside air it needed from the sensor wire.
The air actually wicked down the sensor wire between the inside wire and the insulation.
Splicing the wire did not automatically stop the process. But, in insulating the connection, you often sealed the connection so well that it could not get any air.

I understand the reason they did it that way was because the earlier sensors had a screened hole in the body that would soon get clogged with road dirt and stuff and kill the action of the unit. So they started using the wire.

As for your problem, unless I am mistaken, and I'm sure someone will jump in here if I am, you could take out the sensor, plug the hole, cut the sensor off and throw it in the river. The truck would still run OK.
Not great, and not with the best economy, but a heck of a lot better than its running now.

By that, I mean how it runs cold. Your last post on its running said that it runs really rich when cold. And gets worse when the engine warms up. We need to try to figure out why its running so rich cold.
Having it get worse is a clue, but not the main problem.

Its kinda sounding like an injector problem like your flaming one. If its running rich, either the computer is telling it to, or the computer cannot stop it.

That engine has a temp sensor for the computer. I have seen some weird things happen when the temp sensor sends the computer the wrong data. If its telling the computer its minus 25 degrees outside, the computer is going to run rich to compensate.
Don't think it has an air temp sensor, if so I would suspect it.
How about a MAF or MAP? They can really screw things up if bad.
 
Ok, long time no update, but I got the ALDL cable and got it to work and it tells me I have a bad pickup coil. So, I'm going to replace that, and maybe the distributor if it's loose, and go from there.

The only reason why I didn't solder the O2 sensor wire is because the type of wire doesn't seem to take to the solder. I gave up after a while, which is why I used the tap. Seeing as how the stock sensor didn't work either, I think it was just a fluke that I was playing with the O2 sensor at the same time as the pickup coil going bad.
 
Jessie James said:
Ok, long time no update, but I got the ALDL cable and got it to work and it tells me I have a bad pickup coil. So, I'm going to replace that, and maybe the distributor if it's loose, and go from there.

The only reason why I didn't solder the O2 sensor wire is because the type of wire doesn't seem to take to the solder. I gave up after a while, which is why I used the tap. Seeing as how the stock sensor didn't work either, I think it was just a fluke that I was playing with the O2 sensor at the same time as the pickup coil going bad.
Click to expand...

Yes, you may just want to look at a complete replacement distributor. Once you add the pickup coil, module, cap and rotor, you are likely near the cost of a new distributor. Plus whatever wear your distributor and shaft already have in the "hard parts", if that's something that is taken into account when the rebuild is accomplished.
 
I'm not an expert , just a stoodent.

You said you wired the O2 sensor into the 12v fuel pump relay? ...12volts?
Could it be attached to the 5 volt ref?

From what I understand the HO2s runs on a 5v reference signal not 12v.
It's range should operate between .5 to 4.5 volts.



The heater part of the Ho2s has power. This should be 4 wires, 12v heater power and ground, and the sensor 5v signal and separate ground.
I may be wrong.

If the reference signal gets too much voltage it signals to the PCM that there is a lean condition, high voltage = high O2 levels in the exhaust.
The computer reacts to bad input & everything gets weird in the closed loop.



Jessie James said:
So I have a 91 K5, TBI, CA truck that has the emissions pump removed, and headers installed. The O2 sensor was not upgraded with the headers, so it always ran way too rich.

I bought a heated O2 sensor (can't remember which one, but it was the same as someone else here bought) and installed it carefully. No silicon got on the sensor. I wired up to 12v+ on the fuel pump relay. I used an OEM style quick-disconnect connector, and a wire tap to connect the O2 sensor signal wire to the harness sensor wire (not soldered).

When I first started my truck, it immediately started up, unlike previously where it would take 3-5 seconds, so that was good. It idles absolutely perfectly. And for the first 5 minutes of driving, it's absolutely perfect.

However ... once it gets warmed up the engine starts missing like crazy. It has to be missing on 4 or more cylinders. I am pretty sure it's running too lean because the smell coming out of the exhaust is a scorched burning smell.

What did I do wrong? Is there a specific heated O2 sensor I should be using? Have to reset the ECM?

Any help would be greatly appreciated.
Click to expand...
 
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