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Discussion Starter · #1 ·
I would like to investigate what BALLSS said about the clogged cat that caused 'his front side O2 see more exhaust and read high' in the 'Odd Symptoms...' post by Pocket Sized Jesus.

I have a problem with my '94 Caprice 4.3L V-8 (157K miles w/single exhaust) that sounds very similar to the 'Odd Symptoms...' post a month or so ago. The exhaust always has a high HC (hydrocarbon) smell and fuel economy is very poor. Also, idle gets very erratic (chuggles). When I first start the car the left O2 stays roughly around 450 mV and the right O2 stays roughly around 825 mV; it stays in Open Loop (of course) for a short time until it warms up. I think the 825 mV reading indicates a rich condition (correct??).

Once it goes into Closed Loop (at idle), the left O2 stays around the 450mV level, but the right one fluctuates ALOT... goes down to about 20 mV and up to around 875 mV... it keeps cycling up and down. After a bit of this cycling, the idle starts to stumble pretty bad and then goes to Open Loop (apparently, the ECM makes the decision because it is running so poorly). Then, after about a minute or so of Open Loop, it tries Closed Loop again... and the cycle keeps repeating. I checked the car as I am driving at ~40 MPH and it was in Closed Loop and the right O2 was doing the wild swings there too.

So, back to the clogged Cat. This spring, I had a lot of trouble with the Accel Optispark cap and rotor I installed about two years ago. After a fair amount of backfiring and spitting, I zeroed in on the Opti and could actually see it arching on the front. I put on a new Dephi cap & rotor and that problem was solved. Perhaps the backfiring caused the Cat to break up and somewhat clog??? I have noticed this rich condition ever since replacing the opti this Spring. However, it may have existed prior to the 'Opti Episode'.

At this point I have done the following to resolve my current problem:
- New AC/Delco (the good ones) O2 sensors this Spring; when I installed the Delphi Opti.
- Verified no exhaust manifold leaks by feeling and listening and using a thin piece of paper; however, I still need to try the 'listen with a piece of hose' method.
- changed PCV valve
- replaced vacuum line at right front of throttle body (because this is the one that generally breaks down)
- cleaned air filter
- Verified coil connections clean and OK (coil was replaced a couple years ago)
- New Delphi plug wires and Autolite platinum plugs
- Replaced rubber grommet on right valve cover (I just had new ones)
- New air filter
- Tried propane all around intake manifold, and no idle changes (I was a little nervous about this)
- Using stethescope, I am fairly sure all fuel injectors are firing; kind of hard to get on them.

It now looks like I have to get serious. My next thing is to drop the exhaust system (from the rear of both Cats) and see if the right cat is flowing about the same as the left; trying to determine if the right one is clogged. If it is, then it sounds like (per BALLSS input) it could be causing the right O2 to be high (~850 mV) during initial Open Loop... and likely be the source of the problem. Does this sound right???

I think I am really stuck on the right O2 sensor readings and think it means something specific the right side of the engine. Any agreement here??

Any help would be appreciated.

Kevin.
 

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kevin

when I was chasing a 0152 code that would pop up every now and then (bank 2 sensor 1=front 02) I did all the usual checks. swaped 02's from side to side to see if problem migrated to other side. check injectors, exhaust leaks, fuel pressure. My scan software showed the RS 02 pegged 700-800 range all the time.

with 105k on the stock CATS I decided to swap them...bingo. I just measured again and mv go all over the place from 1xx to 8xx constantly, which is what I understand they should do.

my tuner suggested I check my CATS and he was right (ED Wright). what appears to have been going on is the right side CAT was clogged enough to hold exhaust back some so the front 02 saw "rich".. you can have a muffler shop cut into the CAT carefully and check out the honeycomb and if it is OK he can quickly patch it up if they are ok. maybe put hand over each exhaust pipe and try and feel if there is any difference.

for me anyway new CATS solved, and still do, the problem.

high FP can cause rich also.
 

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Kevin, are you getting a p0152 code? Is this a stock PCM tune? Yes, the 825 indicates a rich condition.
 

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What a wild coincidence that I should look at this thread. My 95 Impala (210K) has been having similar problems with what sounds and feels like it's missing or just running very rough.

I datalogged it this morning, and noticed a similar condition: left side stays mostly very high (800+) while the RS stays mostly below 50 or 60. Of course, the values will fluctuate, but for the most part one side is very high and the other is consistently low.

Cats, huh? I'll see what I can further diagnose this weekend.

Anyone have any other good suggestions?
 

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I went back and looked at a thread I had made back in the spring about emissions testing failure. Sure enough, my car was failing emissions when sniffing the left side, but passed like a new car when the inspector re-tested using the right tailpipe. So, this issue has been around for a while longer than I had thought.

Cat clogged. I wonder????????
 

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Discussion Starter · #6 ·
I will post an update... thanks for all of the interest and input.

No codes are being set, and the PCM has the stock calibration.

I dropped the exhaust system (cats back). I started the engine and both sides seemed to be expelling exhaust at about the same amount. However, much to my surprise, the driver side cat was 'totally empty'; all of th catalyst ceramic honeycomb was gone. I then reasoned that possibly the right one was somewhat plugged or maybe just it having intact honeycomb - while the left one was empty - could be causing the problem. I also figured the right one was about to breakup (on its own) soon. So... it took a while, but I was able to 'empty' the right cat. Crow bar, tire iron, long prybar and a powerful canister vacuum cleaner... and about 2-3 hours.

I reset the PCM and checked the O2 readings; no change... basically no help. I have added this and a few more things to the end of my list below.

One weird thing that I hesitate to add is that while I had the car up (after emptying the right cat), I was running the engine and monitoring the O2 readings. The car ran out of gas (I had just siphoened some out) and as it died, the right O2 went to about 4 mV consistently while the left one stayed somewhere between 200 to 300. Kind of made me think that possibly a right fuel injector was staying open too long and caused the right side to lose fuel first??? That is why I decided the next step was to check the fuel rail pressure. Not sure that this really means anything...

At this point I have done the following to resolve my current problem:
- New AC/Delco (the good ones) O2 sensors this Spring; when I installed the Delphi Opti.
- Verified no exhaust manifold leaks by feeling and listening and using a thin piece of paper; however, I still need to try the 'listen with a piece of hose' method.
- changed PCV valve
- replaced vacuum line at right front of throttle body (because this is the one that generally breaks down)
- cleaned air filter
- Verified coil connections clean and OK (coil was replaced a couple years ago)
- New Delphi plug wires and Autolite platinum plugs
- Replaced rubber grommet on right valve cover (I just had new ones)
- New air filter
- Tried propane all around intake manifold, and no idle changes (I was a little nervous about this)
- Using stethescope, I am fairly sure all fuel injectors are firing; kind of hard to get on them.
- Emptied right cat to 'match' left cat. Reset PCM and same problem (with exhaust system open after cats).
- Blew compressed air through 'single' exhaust system from cats back to be reasonably sure it isn't clogged. Air flows freely and doesn't build up any pressure, so I think it is OK.
- Checked fuel rail pressure and at 35 PSI while running. Goes to 41 PSI upon engine shut down and holds at ~40 PSI for about 45 minutes.
 

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so the DS CAT was empty and now you gutted the PS CAT. Well I guess they are now just pipes and would not be a cause of possible restriction...although their function as CATS is now void.

moving on you could pull plugs and see if anyone, passenger side, is richer than the other. if so check injector associated with that cyl. but even if it 'sounded" the same as others might be hanging open. cruzinperformance.com will clean/rebuild them for $8 each and send a flow chart before/after.

really check for exhaust leaks...and confirm the rear exhaust manifold bolts are not broken or lose.
 

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I would also check the EGR valve too if you haven't already.

It can cause some weird symptoms if it starts barely sticking open, since it draws exhaust from the RH side before the O2.
 

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Discussion Starter · #9 ·
Well, I was still planning to more thoroughly check for an exhaust manifold leak; I just didn't put a high enough priority on it.

Before getting BALLSS's reply last night (thank you), I had to pull the throttle body to get the lower screw out of the IAC... in order to get it out and ensure the passages to it were clean. I ended up cleaning the throttle body fairly well. The passages to the IAC were clean. I put in new screws that mount the IAC. And, no help.

Today, I decided to look for any missing bolts in the right exhaust manifold (per BALLSS's reply)... and... bingo! The furthest one back was broken off. I listened closely while running, but still couldn't hear any puffing. I did notice very slight whiffs of exhaust smell. Now, it was time to try the 'listen through a hose' technique; new one on me. The hose method really worked well, and I did hear a 'put, put, put...' in the vicinity of the broken bolt; I made sure the hose wasn't touching anything, so I am confident there is a leak.

Now, on to fixing it. About two years ago I had a broken bolt in the left exhaust manifold and managed to get the broken bolt out with an 'easy-out'. Hopefully I will be successful with this rear-most broken bolt on the right side. I am not sure if I will be able to drill straight into the center of the broken off bolt; there may not be enough room for the head of my 'right angle' elelctric drill.

I really still don't understand how the leak would cause the O2 sensor to read rich during Open Loop, but I will fix the leak and hope it takes care of the problem. And, I will follow up with another post in a couple days or so.

Thanks...
 

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Discussion Starter · #10 ·
I have fixed the right exhaust manifold leak.

I will spare you 'all' of the gory details, but the 'easy out' broke off in the furthest back broken stud; my back is OK, and a Dremel tool with aluminum oxide stones is wonderful. Somehow - through a ton of time and patience... and craftsmanship - I drilled and tapped the hole to 1/2" coarse thread (original is 3/8"). And, straight in too; however, it took a while before I realized the mirror was messing me up (backwards viewing). Fortunately, it turned out well... or else it would have been either headers (on a 4.3 V-8 (totally unnecessary)) or replace the head.

This did fix the exhaust manifold leak (which needed to be done), but, NO... it didn't fix the 'problem'.

I had not tried swapping the O2 sensors because 1. they were new AC/Delco and 2. the threads in the right cat tube were somewhat messed up (didn't know if I could turn another one in). But, the next alternatives were getting tougher; EGR tube wasn't leaking, rebuild fuel injectors??, replace intake manifold gasket??, etc.

So, I went for the O2 sensor 'position swap'. And... the 'problem' followed the O2 sensor! Problem solved. Now, I just need to get another new O2 sensor.

I will do a final post, once replaced, to confirm problem is fixed.

Thanks,
Kevin.
 

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Discussion Starter · #11 ·
Car is now running like new!

After seeing the problem follow the O2 sensor, I purchased a new AC/Delco at the local parts store. I installed it, and car ran better, but not right. Also, the left (brand new) and right O2 sensors provided much different readings. I then began to wonder if the original two sensors were even the correct type. The stamped numbers were very light; one was AFS 141 and the other was AFS 138. When I bought them via eBay, they were specified as being AFS 75, but apparently I never checked the number on the case. I didn't know there were a variety of these AC/Delco O2 sensors that all looked identical (except for the small number stamped on the outer case). I checked the brand new one (currently in left position) and it was AFS 75.

So, I went and bought another AFS 75 from the local parts store (AC/Delco is currently transitioning to a new style, so I made sure I got another of the older style (GM# 25312184) (slots in sensor area instead of small holes). After installing it, both sides provided similar readings. I test drove car and ran great. It even seemed fairly fast; especially for a 4.3.

eBay Buyer Protection won't help me because it has been longer than 45 days (~6 months)... and eBay vendor will not reply to my emails. So, from now on NO MORE OXYGEN SENSORS FROM EBAY! I will continue to buy other stuff, but not O2 sensors. There are just too many that think they can make substitutions... and everything will be OK [NOT].

Thanks for everyone's help with this,
Kevin.
 
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