Car running way rich....at times

[V10SpeedLuvr]

About a year ago, my gas mileage started getting really funky. It'd be anywhere from 12-22 on the highway (normal 6th gear, 70-80mph type driving). Replaced one upstream oxygen sensor and that got it to a steady 18mpg. Replaced the 2nd one and that got it to a steady 22mpg. After a couple months, its doing the same thing. On my recent trip to FL, my gas mileage was 18-ish mpg on the way down there. Before leaving, I filled up. When I stopped on the way home and topped off, I had gotten 22mpg on that tank. When I filled up again after I got home, it was only 15mpg.

Took it to Dodge yesterday and they put the scan tool on it and said all oxygen sensors are switching and short term fuel trim looks good. They said what concerns them is my injectors were "jumping all over the place". Tony Armour has already cleaned and flow checked them, and said they were fine, so I don't believe the problem is with the injectors themselves.

I have Borla Headers, Moroso Spiralflow mufflers in place of the OEM cats and no rear muffler.

I am running one OEM oxygen sensor and one oxygen sensor from DC Performance b/c they have extended leads and the ********* on my LH header is further down and an OEM sensor won't reach.

The tech at Dodge said with me being catless, the rear oxygen sensors (both OEM) are confusing the PCM and it is sending all sorts of crazy signals to the injectors. He recommended rear o2 sensor simulators, or high flow cats. Never had a check engine light.

Does this sound right or anyone else have any suggestions?

 

[dave6666]

I thought the rear O2's were NOT used for tuning?

 

[Dom426h]

How do you know she is running rich? Are you simply assuming that because of your gas mileage?

Took it to Dodge yesterday and they put the scan tool on it and said all oxygen sensors are switching and short term fuel trim looks good. They said what concerns them is my injectors were "jumping all over the place".

Interesting

The tech at Dodge said with me being catless, the rear oxygen sensors (both OEM) are confusing the PCM and it is sending all sorts of crazy signals to the injectors. He recommended rear o2 sensor simulators, or high flow cats. Never had a check engine light.

That sounds like Bullsh!t to me. The Front/Upstream sensors are what the PCM uses to determine how much fuel to spit. Not the rears. The Drone is giving you a generic anti-catless response.

What size are your spiralflows? Do you have a 3" Borla header going into the stock 2.25-2.5" system?

 

[EllowViper]

I think you are on the right line of logic Chad. I was recently messing with some generic universal "cheapo" 02 sensors and the engine just dumped fuel. I ended up putting in my old sensors and it started to run fine. I am running rear sims by the way. Not sure what to say on what sensors to use up front. I have to think the PCM is expecting a certain calibration based on OEM or specific manufacturer signal output vs. AFR. I'm thinking all sensor outputs are not the same based on a given AFR....maybe theoretical, but not as delivered by the specific sensor/manufacturer.

 

[Russ M]

Lets start with what year car you are talking about and what mods it has.

Pictures suggest gen 3 or IV profile suggest gen 1

 

[V10SpeedLuvr]

How do you know she is running rich? Are you simply assuming that because of your gass mileage?

Yes. Plus you can stand behind it at idle and get a headache off the gas fumes.

That sounds like Bullsh!t to me. The Front/Upstream sensors are what the PCM uses to determine how much fuel to spit. Not the rears. The Drone is giving you a generic anti-catless response.

Thats what I thought and even mentioned it to the tech but he said I was wrong.

What size are your spiralflows? Do you have a 3" Borla header going into the stock 2.25-2.5" system?

I believe so. I know it is still the factory sized exhaust pipe. Only the headers and mufflers have been added from the OEM setup.

I think you are on the right line of logic Chad. I was recently messing with some generic universal "cheapo" 02 sensors and the engine just dumped fuel. I ended up putting in my old sensors and it started to run fine. I am running rear sims by the way. Not sure what to say on what sensors to use up front. I have to think the PCM is expecting a certain calibration based on OEM or specific manufacturer signal output vs. AFR. I'm thinking all sensor outputs are not the same based on a given AFR....maybe theoretical, but not as delivered by the specific sensor/manufacturer.

If I need to replace the DC Performance sensor with an OEM one, thats not a problem. I just preferred the DC ones since they'd be no splicing/soldering involved to lengthen the wires.

Lets start with what year car you are talking about and what mods it has.

Pictures suggest gen 3 or IV profile suggest gen 1

Car is a 96' RT/10 (Gen 1 engine). Mods: Borla Headers, Moroso Spiral Flow mufflers in place of OEM cats, no rear muffler.

 

[Phun70]

Check your fuel pressure. I have a sneaking suspicion that the fuel pressure regulator has malfunctioned and the fuel pressure is somewhere north of 90 psi, when it should be about half that. When that occurs, you will dump more fuel than the computer can pull away with injector pulse width attenuation. If this is indeed the case, you will need to replace the fuel pump to correct the situation. Funny though that the tech said fuel trims were ok. That wouldn't make sense if it was running pig rich as you say.

 

[hou99gts]

Your car is too excited after all the ******'s girls that have been in it, and it can't control its fuel anymore.....

(sorry for the thread hijack, I couldn't resist)

 

[V10SpeedLuvr]

Check your fuel pressure. I have a sneaking suspicion that the fuel pressure regulator has malfunctioned and the fuel pressure is somewhere north of 90 psi, when it should be about half that. When that occurs, you will dump more fuel than the computer can pull away with injector pulse width attenuation. If this is indeed the case, you will need to replace the fuel pump to correct the situation. Funny though that the tech said fuel trims were ok. That wouldn't make sense if it was running pig rich as you say.

Thanks, I'll give it a try. When this 1st occured like a year ago, my fuel trims were all screwed up. I think it was a steady 13. Back then they said it was the left bank running so rich. Right bank was fine. Yesterday, the tech said the trims were right around 5.

 

[Mopar Boy]

Might also consider Herb question if you cant seem to solve it after this thread.

 

[-FROG-]

Most cars without cats will give you a headache, not nessecarily from it running rich. My GTS and friends Z06 give me a headach after cruising around a bit. Neither of us have cats. Both cars run fine.

 

[99 R/T 10]

Thinking it's a bad O2 sensor. They can be bad out of the box. You can get a bosch from autozone, #13100 I think.

 

[EllowViper]

Get your 02 sensor extensions here...that way you don't have to piss around with location.

Chrysler / Dodge / Jeep - Specializing in automotive interconnect and wiring systems

 

[Black Moon]

About a year ago, my gas mileage started getting really funky. It'd be anywhere from 12-22 on the highway (normal 6th gear, 70-80mph type driving). Replaced one upstream oxygen sensor and that got it to a steady 18mpg. Replaced the 2nd one and that got it to a steady 22mpg. After a couple months, its doing the same thing. On my recent trip to FL, my gas mileage was 18-ish mpg on the way down there. Before leaving, I filled up. When I stopped on the way home and topped off, I had gotten 22mpg on that tank. When I filled up again after I got home, it was only 15mpg.

Took it to Dodge yesterday and they put the scan tool on it and said all oxygen sensors are switching and short term fuel trim looks good. They said what concerns them is my injectors were "jumping all over the place". Tony Armour has already cleaned and flow checked them, and said they were fine, so I don't believe the problem is with the injectors themselves.

I have Borla Headers, Moroso Spiralflow mufflers in place of the OEM cats and no rear muffler.

I am running one OEM oxygen sensor and one oxygen sensor from DC Performance b/c they have extended leads and the ********* on my LH header is further down and an OEM sensor won't reach.

The tech at Dodge said with me being catless, the rear oxygen sensors (both OEM) are confusing the PCM and it is sending all sorts of crazy signals to the injectors. He recommended rear o2 sensor simulators, or high flow cats. Never had a check engine light.

Does this sound right or anyone else have any suggestions?

Turn off the rear sensors completely. If you've done a tune on it that would have been done. Any tuning software?

 

[V10SpeedLuvr]

Turn off the rear sensors completely. If you've done a tune on it that would have been done. Any tuning software?

I don't have any tuning software and car has never been tuned before.

 

[Black Moon]

I don't have any tuning software and car has never been tuned before.

Time for an SCT. Well worth the money and will eliminate all the O2 issues.

 

[Jack B]

A few items to add:

1. The rear O2's do nothing but check on the operation of the cat.

2. If you were running rich your LTFT wold be out of range and you would set a code.

3. The 1996 PCM does not care if you have removed the cat.

4. The STFT does not tell you too much unless you can turn off the LTFT.

5. As was stated, a catless car automatically has that odor that says I am rich and this has nothing to do with the a/f.

6. A bad plug or wire could cause excess fuel to exit the exhaust, therefore, giving the rich smell. However, this would not show up at the O2's, they only look at the oxygen level. You could dump fuel on the O2 and it would not register. A bad plug or wire will actually show lean.

 

[uvbnbit]

Unless I missed it, where are your upstream O2's located? In the collector or in the 5 and 6 header tubes? I ran rich (exhaust, not monetarily speaking ) for 3 yrs. Moved the O2's to the collector and helped big time.

 

[bluesrt]

cell the car

 

[V10SpeedLuvr]

A few items to add:

1. The rear O2's do nothing but check on the operation of the cat.

2. If you were running rich your LTFT wold be out of range and you would set a code.

3. The 1996 PCM does not care if you have removed the cat.

4. The STFT does not tell you too much unless you can turn off the LTFT.

5. As was stated, a catless car automatically has that odor that says I am rich and this has nothing to do with the a/f.

6. A bad plug or wire could cause excess fuel to exit the exhaust, therefore, giving the rich smell. However, this would not show up at the O2's, they only look at the oxygen level. You could dump fuel on the O2 and it would not register. A bad plug or wire will actually show lean.

Thanks Jack. The LTFT was around 9. The tech said that was nothing to worry about and would change when he revved the car. STFT was 5. I'll check the plugs and wires to see what they look like. They are both fairly new (<5k miles on them)

Unless I missed it, where are your upstream O2's located? In the collector or in the 5 and 6 header tubes? I ran rich (exhaust, not monetarily speaking ) for 3 yrs. Moved the O2's to the collector and helped big time.

The O2's are in the collector.

I am kinda hoping its the fuel pump regulator as mentioned earlier. I've been having a intermittent prob with the rollover valve sticking (can't get gas in car at times) and have noticed my fuel gauge floats a lot more than it used to do. If I could fix all 3 probs with 1 new part, I'm all for it. Even if it is a PITA to do.

cell the car

I'd be lying if I said that hadn't crossed my mind several times. I've had a fun 4 years with the car. Bad part is, I've owned it 5. Owning a Dodge paperweight just isn't much fun.

 

[Phun70]

Check that fuel pressure!

 

[V10SpeedLuvr]

Check that fuel pressure!

Just got done. Key on (car not running): 50psi

Car running: 50psi

Revving car a little bit: 50-52psi

Service manual says it should be 55, so I may be a little low (depending on how accurate gauge is), but definitely not high. Ofcourse with this being an intermittent problem, getting a good reading now is entirely possible and it still be messed up.

Anyone wanna buy the car? I'm tired of this.

 

[speedracervr4]

10k chad? I'll pick it up..LOL. My guess would be a bad 02 sensor, but seems like you've already ruled that out...hope you find the issue.

 

[Phun70]

I'd like to know what the o2 sensors are doing. I'd also like to see the fuel pressure when it's acting up. Mine did the exact same thing and after I replaced the pump all was good.

 

[V10SpeedLuvr]

When this started happening a year ago, I had a compression test and vacuum test done. 1 of the cylinders (#2 I think) was down a little from the others, but all were over 100. IIRC, most were in the 130 range. #2 was 115.

Just for a quick comparison, I pulled 3 of the plugs (I'm estimating about 5k on the plugs and wires). #1 is obviously sootier than the others.

Cylinder 1:

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Cylinder 3:

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Cylinder 5:

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[Jack B]

Quotet:
"When this started happening a year ago, I had a compression test and vacuum test done. 1 of the cylinders (#2 I think) was down a little from the others, but all were over 100. IIRC, most were in the 130 range. #2 was 115."

That is way off, unless the tech did something wrong. My guess is that most stock compression vipers are going to run 150-175 psi. The plugs do not look bad. You should redo the compression test with a warm car, throttle open and a little wd40 in the chamber. If you are still in the 115- 130 range you have a problem. Also, crank the engine the same number of revolutions for each cylinder.

Make sure you do not have a code when the car feels rich. In some cases if the pcm senses the engine running lean it will set a code and enrich the mixture, therefore, run rich. A misfire could cause this to happen.

It probably would not hurt to keep a scanner plugged in and when the condition crops up, start recording. That would find the problem for sure, it is hard to hide from hard data. If you record the following, LTFT, STFT, MAP, RPM and throttle position you will find what is happening, next, would be to find the cause.

 

[uvbnbit]

Have you checked the A/F with a WBO or tail pipe sniffer?

 

[Phun70]

good suggestions. Those plugs don't look as sooty as I would expect if it's running super rich. Follow Jacks thoughts and let us know what u find.

 

[EllowViper]

Is the mileage worse before or after eating at *******? I know for a fact I get worse mileage after eating at *******. Your actual mileage may vary however...

 

[V10SpeedLuvr]

That is way off, unless the tech did something wrong. My guess is that most stock compression vipers are going to run 150-175 psi.

I maybe wrong, I'm trying to remember the #'s from a while back. I'll check into redoing it, to get more up-to-date results

Make sure you do not have a code when the car feels rich. In some cases if the pcm senses the engine running lean it will set a code and enrich the mixture, therefore, run rich. A misfire could cause this to happen.

A while back, when I replaced the plugs, the #1 spark plug's gap was closed up and I drove the car for approximately 10 miles before noticing it wasn't driving right, went home, pulled all plugs and found the closed up plug. (we're thinking that was installer error and not a internal mechanic issue) Is it possible that could have anything to do with this? 2 compression tests were done after this and #1 cylinder showed normal compression (in same range as all other cylinders).

It probably would not hurt to keep a scanner plugged in and when the condition crops up, start recording. That would find the problem for sure, it is hard to hide from hard data. If you record the following, LTFT, STFT, MAP, RPM and throttle position you will find what is happening, next, would be to find the cause.

I know the handheld scanner I have doesn't record any live data, so I'll have to try to find one to borrow or buy a new one.

Have you checked the A/F with a WBO or tail pipe sniffer?

No, but I'm trying to find a place that can. The dyno place I use is in Atlanta and at this point, I'm not keen on driving it that far.

good suggestions. Those plugs don't look as sooty as I would expect if it's running super rich. Follow Jacks thoughts and let us know what u find.

Will do. Thanks for all the help everyone!

Is the mileage worse before or after eating at *******? I know for a fact I get worse mileage after eating at *******. Your actual mileage may vary however...

With it acting stupid, I've been punishing it by not taking it to *******. That doesn't mean I'm not going....just the car isn't