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So I finally have to ask this. My Pathy has been running rich for along time now. I can smell it. I'm not showing any codes. There is a miss/stumble when it's cold. It's hardly even there once it's warmed up. What could be causing this that wouldn't show a code? Checked my plugs and they're burning clean. I don't think the miss is in the ignition. I could be wrong though. The only thing I can think of is maybe a vacuum leak someplace that I can't find.

 

What do you guys think?

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I'm curious to see the answer/thoughts on this one. I kinda have a similar situation and somewhat suspect the 02 sensor but have not changed it out to see if it helps.

 

I could see how a vacuum leak after the MAF could cause it to be rich. It would lean out the mixture which the 02 sensor would read as too lean and then tell the injectors to give more gas. Maybe.

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We have a heated O2 sensor, so it doesn't work until it and the exhaust gasses are hot. It will always smell rich before then. You could have a minor fuel/vapor leak instead?

 

Checked my plugs and they're burning clean

This tells me there is no issue when everything is warmed up. Plugs don't lie, I've been reading them for 30 years and they have never steered me wrong.

 

You could still have a vacuum leak though, check with a flammable aerosol, I prefer WD-40 but Aquanet will work just as well... :D

 

B

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If you're running rich, your gas mileage should be really horrible, worse than ours normally is, I mean something like 13 or 14, round there. You're an Old Timer here so I would have to assume you already know the laundry list of numerous issues it could be / need to be checked out and or replaced i.e. Wires, Dizzy cap and rotor, PCV mass airflow sensor, your coil or ignition control module may be failing.

 

I had a similar problem a little while back where sometimes my truck would intermittently start running horribly or die when I came to a stop or slow to turn, and it would run rich and idle rough, black smoke come out the exhaust, but once I gave it a little gas it would pick right up and run fine. Finally got it resolved (after replacing everything I just mentioned) by having my local Kwik Car do a Gumout 3 stage fuel system treatment with a bottle in the tank, an IV drip thing for about 15 minutes (into one of the vacuum lines I think) and throttle body cleanout. After that it's been running great with no more issues. Service cost me like 80 bucks.

 

I never checked my ecu for codes so I don't know if I was getting one or not. Since you're not getting a code, your ecu doesn't know something is wrong somehow..I don't know.

Edited by gv280z
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gv280z: Yeah I've replaced, cleaned or check basically everything you listed.

 

Here is some other helpful info. While driving across the country I noticed that when you punch it on the interstate it blows out a small plume of black smoke. when the trans would kick down and let the engine rev really high. I suspected this was going on before this trip but I was always driving and the smoke is not enough to really notice out the rear view mirror.

 

Fuel millage has always been bad 13 - 14 mpg. While driving across the country I was getting around 21mpg but we were also driving 55 - 60 mph due to that bring the top speed on my bread truck while completely over loaded.

 

I think I'm going to take it in to have it smoke tested for vacuum leaks. Depending on how much they want to charge me for the test. Never done that before so I have no idea what it should cost.

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Have you replaced the Coolant Temp Sensor before? CHTS/CTS are notorious for causing misses/stumbles when cold but fine when warmed up on a crap ton of Nissans. They don't always throw codes either.

 

Dirty MAF/corroded connections. Bad O2 sensor.

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The black smoke when you punch it is un burned fuel. When you did that, did it ever actually accelerate or just act as if it had no power. That would involve I guess a vacuum advanced ignition on the distributor (I don't know how our advance timing works, vacuum or centrifugal) but when you punch it, the timing should advance to continue burning the fuel air mixture at the optimal time which would be just a few degrees before top dead center. If the timing advance isn't working then you would have a bunch of fuel dumped in the cylinder and the engine wouldn't know what to do with it, therefore you get black smoke.

 

Anyway regardless of that, given everything that you've done and still no resolution and no codes from the ECU makes me just think that you have a generally bad ECU and it's diagnostic circuits are dead, along with whatever else that is supposed to be controlling the performance of the engine.

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The black smoke when you punch it is un burned fuel. When you did that, did it ever actually accelerate or just act as if it had no power. That would involve I guess a vacuum advanced ignition on the distributor (I don't know how our advance timing works, vacuum or centrifugal) but when you punch it, the timing should advance to continue burning the fuel air mixture at the optimal time which would be just a few degrees before top dead center. If the timing advance isn't working then you would have a bunch of fuel dumped in the cylinder and the engine wouldn't know what to do with it, therefore you get black smoke.

 

Anyway regardless of that, given everything that you've done and still no resolution and no codes from the ECU makes me just think that you have a generally bad ECU and it's diagnostic circuits are dead, along with whatever else that is supposed to be controlling the performance of the engine.

 

When I punch it and the smoke comes out it runs just fine. It kicks down and takes off as it should. Not hesitation that I'm noticing. I know what you're talking about I've experienced this in my old carbureted hot rods that I owned in the past. As for the ECU. I have two of them. This was going on with the factory one and when I switched it nothing changed. I changed it for a completely different reason but I can safely say it was going on before with the other ECU. The temp switch is a little over a year old. Sure that doesn't mean it's not bad. Maybe after I get it smoke tested and fix any vacuum leaks it may have I'll address the switch again if the problem is still there. Won't hurt to have a spare and they are that expensive.

 

Oh and one more thing. Our trucks are meant to have a high idle when cold. Sometimes after driving for sometime it's still doing that. When I go to stop at the light I can feel it, like I'm still hitting the gas while trying to brake. This will eventually stop too. But keep in mind the smoke happened cold or hot.

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Just change all the vacuum lines. I did them one at a time so none got mixed up and eliminated that as an issue. Didn't take very long and the hose cost like 2 dollars.

 

Stock timing is 15degrees BTDC.

 

Sent from my BlackBerry 9670 using Tapatalk

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So the high idle lasts longer? That sounds like the coolant temp sensor to me... it thinks it's too cold so it's staying in open loop warm up mode.

 

I haven't heard of one laying black smoke, though. Maybe it thinks it's really really cold!

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I don't know anything about the temp sensor which is an automatic choke I guess? But what yall are saying about it, it sounds like it fits to me, that would want to enrichen the fuel for a cold start and if it's faulty and staying open or active or whatever it does, it would be continually enriching the fuel because it never gets the "Okay, we're all good down here, you can take a break!" signal

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The temp sensor is for the ECU (there is another for the temp gauge), but if it was running rich the whole time, the plugs would show it. :shrug:

 

I agree, start with the vacuum lines to get them out of the way, and check the EGR valve function. It could be sticking or clogged.

 

B

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  • 3 weeks later...

Ok so I still haven't smoked the engine for vacuum leaks (I will soon enough) but I did fix some of the problems. While driving it the other day I started to hear a whining noise when the engine RPM went up. Started to really worry that things were taking a turn for the worse with my 235,000 mile engine. Got home and started pulling belts hoping it was something simple. It was. It ended out being ether the AC pump or the brand new idler pulley. Ether way I no longer live in AZ so I don't need that crap anyway. While I was working on it I decided to check the timing just to insure it was right before I sent it off to be smoked. The timing was off, quite a bit actually. Have no idea how it got that way. I set it correctly about 6 months ago. Oh well ether way it's correct now and really changed the way it was running dramatically. The engine runs really smooth now. I no longer have high idle issues and it's not missing/stumbling anymore.

 

However there is still some smoke. Not as much but there is some. hmmm....

 

Anyway I'm just updating everyone on the progress. Don't want to leave another "I have a problem" thread without a solution or a conclusion.

 

I need to ether start building a fuel injected 350 and matching drive train to stuff in her or find another VG30 to start rebuilding while I get every last little bit of use out of the engine I currently have. Wish I didn't have to sell my supercharged GM V6 before I left. Ether way I need to find something to start building to replace this engine once it's ready to go. I'd like a little more power and much better fuel mileage.

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  • 3 months later...

Just change all the vacuum lines. I did them one at a time so none got mixed up and eliminated that as an issue. Didn't take very long and the hose cost like 2 dollars.

 

Stock timing is 15degrees BTDC.

 

Sent from my BlackBerry 9670 using Tapatalk

 

Out of curiosity do you remember the sizes of the hoses and how much (length) was needed? Where did you purchase your vacuum hose? Thanks :)

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Plugs don't lie, I've been reading them for 30 years and they have never steered me wrong.

 

Is this like how a shaman reads old chicken bones to tell the future?

I just picture this.....shaking them in a rattle and throwing them on the ground and reading them like that while muttering in tounges!

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Checking your oil for any smells of fuel or if its over filled. When my chts went bad it flooded the engine and the fuel made its way past the rings and into the sump. This made it smoke really bad and when i changed my oil it helped allot. I ended up draining 8L i think it was of fuel/oil.

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So I finally have to ask this. My Pathy has been running rich for along time now. I can smell it. I'm not showing any codes. There is a miss/stumble when it's cold. It's hardly even there once it's warmed up. What could be causing this that wouldn't show a code? Checked my plugs and they're burning clean. I don't think the miss is in the ignition. I could be wrong though. The only thing I can think of is maybe a vacuum leak someplace that I can't find.

 

What do you guys think?

 

Based on all the symptoms you give and all the things you have already checked...there is still one thing that has not been mentioned.

 

I had a similar problem and it ended up being the pre cat exhaust piping was corroded (causing it to smell rich and not throwing any codes). Its not easy to check...you really have to get under and follow it up towards the manifold and look for holes.

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Run mode 2 ECU diagnostics. The two lights should blink, synchronized, pretty rapidly at 2,000 rpm with no load. the FSM says more than 5 times in 10 seconds.

 

My own personal experience with this, the original O2 in my 200sx passed the FSM test, but the car never ran right, so I swapped out the O2 for a known good one, and the ECU diagnostic lights turned in to a strobe.

 

This would rule out the O2 which could be keeping the motor just on the edge of keeping the plugs showing that you're running rich.

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Is this like how a shaman reads old chicken bones to tell the future?

I just picture this.....shaking them in a rattle and throwing them on the ground and reading them like that while muttering in tounges!

No, actually I place them on my shrine, build a bonfire, strip naked, put on a goat's head, chant and dance until I have a vision.

 

Wisearse! :lol:

 

B

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That is VERY disturbing Precise....

 

 

 

Back to the thread.....silverton is correct.

The O2 sensor on the WD21 can be bad and not trigger an error code on the ECU.

 

The ECU only registers a fault on the O2 sensor if the singal is outside the established specs.

 

0.5 Volts +/-0.2 is nominal for the 02 sensor signal to the ECM.

As long as the signal the ECU is receiveing from the O2 sensor is within that range the ECU thinks everything is fine.

However they can wear out and 'stick' at say....0.55V and read that constantly, so the ECU will not flash a check engine light and will accept the input...... and make the truck run like pooo

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Ok so here is where things stand right now with the pathy. I've been driving it as it was after my last update. Smoking issues seems to have gone away. Idle issues is still some what there but not nearly as bad. Ether way winter is starting to finally kick in over here in Syracuse. I just picked up a 2000 Saab 9-5 wagon so I could park my pathy for the winter and take care of some much needed issues. That and add a few cool up grades. If the money is there I may even do a SAS. IF THE MONEY IS THERE... Me and my other half our finally planning for our wedding and we need a pretty penny for it. So we'll see how it all plays out. I think I may do a full custom interior from front to back and maybe cage her before the SAS.

 

The trans will be coming out and maybe even the engine too. Lots planned and she's earned it. Even my other half agrees with me on the repairs and upgrades. She's come to really like the Pathy and appreciate the fun and experiences she's brought us as a family. That always helps when it comes to spending money like that lol.

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