By on May 18, 2011

TTAC reader sportsuburbanGT writes:

Hi Sajeev,

Have a couple of questions: I have a 72 Dodge Dart that I am performing a 318 to 340 swap.  It’s taken longer than I planned (lack of time), I backed the car in the garage 2 years ago and now I am planning on firing it up in this April.  The question is the gas: I had about a half tank when I backed it in, and I put some Stabil in the tank, but I took the cap off to try a new cap and the tank smelled really awful.  I replaced the fuel filter, but should I drain the tank and refill with fresh gas, put some fresh gas in the tank to mix up what is in there, or pull the tank have it boiled out and refill.  I was driving the car up until March 2009, and I put that last half tank in there in March 2009.  I am in Long Island, NY so we have that crap gas till April.

My second question is on my (daily driver) 2005 Dodge Magnum RT, with 87k on it.  I replaced the O2 sensors (all 4) as preventative maintenance and now I keep getting a p0152 code.  It’s the code for the upstream right side O2 sensor.  I installed new Bosch sensors, but I received the first CEL right after I started it up after the new sensors were installed.  I replaced the right upstream with a new unit (Bosch), no code on start up.  The CEL came back after 4 days and 300 miles, stayed on for a day then went off for a day and came back this Sat and is still there.  I disconnected the neg. battery before I performed this work.  I replaced the sensors as preventative maintenance; I was under the impression they last for about 100k.  I also have the Mopar Performance long tube headers with a Borla exhaust on the car, they have been there since about 15k.  Is the Magnum eating O2 sensors, or are these Bosch sensors no good?

Great write ups, I have really enjoyed reading them, thanks in advance for any help.

Sajeev answers:

I like your tastes in cars, this brand loyalty proves why some (Detroit) brands need not stray far from what made them so popular in the first place. Not that we all need Dodge Darts in lieu of a Toyota Prius, but that’s not the point…

The Dart: I really can’t decide between 100% fresh gas or diluted with fresh gas. It also depends on if you plan on a carburetor rebuild/upgrade in the future. I think it’s less work to buy a several fuel filters and replace as needed, carefully (low RPMs, please!) driving the car until the old stuff burns off.  But that’s because I absolutely loathe messing with gas tanks.  And, once again, you might need to re-jet the carb to compensate for the extra cubes, so who cares if you get junk from old fuel in there?

The Magnum: if the wiring does not look frayed/melted, get a new sensor, it should be warrantied at your parts store.  I have Kooks headers on my ’95 Mark VIII and I love my “non-factory” Bosch O2 sensors for a Ford truck. These have been very good to me for over 5 years and 40,000 miles. But others have complained on the forums, for reasons I can’t logically understand. But then again, I only have one sensor per exhaust bank.

sportsuburbanGT answers:

Thanks for the pointers.  I will replace the O2, I hope three times is a charm.  The wiring is mint, it is nit hitting or rubbing anything. I will also go for the fresh gas in the Dart a little of the summer blend 93 should do the trick.

That Mark sounds sweet.

Sajeev concludes:

Oops, I mis-read your comment.  If that’s your third O2 sensor, I’d look much, MUCH closer at the wiring harness.  It’s amazing what little contact it takes to melt those wires against a set of long tube headers, especially if you doubt the skill of the installation.  If the wiring checks and there’s no other trouble codes, consider the OEM-branded replacement sensor. I can’t imagine any other problem creeping up so quickly after installation of your first set of Bosch sensors.

And yes, its modifications like yours (ours?) make my Mark so much fun to drive, so difficult to sell in the face of more modern, far superior iron. I’m sure you know the feeling. Good luck to you.

Send your queries to [email protected]. Spare no details and ask for a speedy resolution if you’re in a hurry.

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23 Comments on “Piston Slap: The Gassy Dart, the Bosch-eating Magnum...”

  • avatar

    Hmmm, I wonder if that’s what killed the wiring harness on my Mystique. I’ve finally given up and have decided to put the car up for sale, hoping that someone that has a wrecked Contour or Mystique might want it and could swatch out parts out. It’s too nice a car to scrap.

    So I guess what can be taken from this is that we have to always check the wires!

    • 0 avatar

      Ah the common/mistake as we referred to them back in the day. The vehicle that was always less than the sum of it’s parts. When running right very pleasant to drive especially in SVT form. Unfortunately that car was bean counted to death in North America. Recalls on that load before they left the plant in ’94 (fuel tank replacement oh what a joy that was). ’95 to ’97 had a wonderful extended warranty program for the engine compartment wiring harness (seems the Mexican supplier used a grade of insulation that was unable to withstand the engine compartment temperatures . . . go figure). Raise your hand if you could beat the paltry labor time for a V6 auto with ABS . . . what no hands? The car coulda been a contender, but Jack Nasser was on his crusade of buying up JLR, Aston and Volvo in his quest to be the #1 automaker in the world. Imagine all those billions in SUV profits put into a proper Taurus back then, along with some world class Lincolns. Thank God for Mullaley, but for me I now work for the commuter rail. Ford dealers lost a significant number of senior master techs (myself included) and replaced them with kids out of trade school most of which I wouldn’t trust to fix a sandwich never mind my car.

  • avatar

    Don’t know what’s wrong with the guy’s car but that’s a great photo of the engine call-out on the hood of a ’69 Dart GTS or Swinger 340.

  • avatar

    I’ve heard from several people that Chrysler products don’t seem to like Bosch O2 sensors for some reason. The OEM sensors were manufactured by NGK, so if you can find those in the aftermarket, I’d go with them. After all, if NGK was the OEM supplier, all the software development and testing was performed around the way they operate and respond.

  • avatar

    Since the plan was to do this in April and it’s already May this might be a little late. Never the less, drain the tank, check to see what it looks like i.e., is it just bad gas or is it rust and other junk that got in there a long time ago. If you haven’t fired the 340 up yet running bad gas or the potential for getting gunk in the carb at the outset can make getting the engine running and tuned right a real pain and take a lot longer. Dropping a tank is no fun, but dropping a tank after you filled the carb full of rust, varnish and dirt is worse. I do agree with the post on your Magnum, change to a different sensor and check that harness! Good luck!

  • avatar
    Educator(of teachers)Dan

    Whatever happens, I like his taste in cars too. Big thumbs up.

  • avatar

    Just asking…but instead of throwing parts at your 02 problem, why dont you diagnose it???
    Not that hard! Just find the sensor wire and backprobe the ECU, watch the voltage.You should see a .1 to .9VDC constant change while hot.
    A code for 02 doesnt necessarily mean the part itself is defective–the 02 is a camera on the system, and if that bank is running too lean or too rich, you WILL get an 02 code.
    The days of “Get a code, get a part” are long gone.

    • 0 avatar

      While true, if the system threw a code immediately upon replacement of the O2 sensors (and was 100% perfect beforehand) either the sensor or its harness is the problem.

      Lucky me, I was right this time too.

  • avatar
    M 1

    Burn the old gas. The “old gas” fear-thing is blown way the hell out of proportion. I’ve owned almost 60 cars in my time, and many of them have sat undriven for long periods. Old gas just doesn’t matter. Almost any car will burn it just fine.

    And if it doesn’t, it really isn’t the end of the world.

    Turn the key and see what happens, and stop being such a puss.

    • 0 avatar
      Educator(of teachers)Dan

      I’ve never said this to M1, but… +1

      Every October my father parks his 1967 Mustang convertible. He puts nothing in the tank to stablize the gas. Every April or May (depending on the weather) he fires it up and the orginal 289V8 burns it just fine. Now he does try to put it away with only a few gallons in the tank, but still he just fills it back up when the spring comes. I do the same thing with my scooter, no problems.

      • 0 avatar

        Dan, it would be better if he filled the tank up completely before parking the car for the off-season. Condensation in the gas tank contributes to the tank rusting from the inside, and fouling-up the gas. In my family, we have parked our summer cars in the garage for 6 months at a time since the mid 80’s, and the only fuel system prep has been to completely fill the tank. Just within the past 2 years have I started using Stabil out of concern for the ethanol in the fuel. I also started filling my cars with high octane before storing, even if they don’t require it, since high octane gas supposedly contains less or no ethanol.

    • 0 avatar

      M1, I am with you for the most part on gas less than 2 years old.

      I would get a gas container and fill it up with premium to dilute the new and old gas.
      Change the fuel filter so that later you will understand how much sediment accurs from the gas tank. An old filter may already be partially clogged.
      Then see if it will fire up. If it runs, I would take the advice to drive it easy for the first tank of gas. You don’t want to stand on it and have it mis-fire or ping.
      After 500 miles I would change the fuel filter again and see how much sediment pours out. Then you can decide if a few more filter changes are in order or a complete tank clean-out.

      On the Magnum sensor.. You did not have a problem before the sensor changes. The sensors are the only thing that has changed. I would get some OEM sensors and start over if they are not too expensive. That will give you a clean base for any further troubleshooting.

    • 0 avatar

      Climate might play a role in this. In Charlottesville Virginia, for example, there is so much hunidity in the air that it turns tanked gasoline into flame retardent in a matter of months. One time when I was visiting my folks I took on the task of starting their chipper shredder. After making sure it had a spark, I discovered that the gasoline had turned into fowl water. It wouldn’t burn with a match. I bought some fresh gas and the engine was fine. It is possible that a newish car with today’s evaporative emissions controls would stand a chance of preserving the quality of gas in its tank. The 1972 Dart is not that sort of car though. I had a 1971 Scamp that needed to have its tank cut open, de-rusted, and painted around 1985. I’m glad this story had a happy ending, but results may vary.

    • 0 avatar

      I agree on the gas. I park my lawnmower each December, and start it up in April with the same gas. I don’t drain it or anything. No problems after 20+ years of this routine.

  • avatar

    I wound up replacing the O2 Sensors with the OEM Mopar units and the CEL went away. I then got a CEL for the left side O2 Sensors, replaced those with the Mopar units and that code went away. The wiring was in great shape, zip tied away from the headers. The Magnum just did not like the Bosch sensors. I’m sticking with the Mopar sensors going forward.

    I added 5 gals of premium to the tank of the Dart and it runs very well. I should have added that I had the motor tuned and broken in on a dyno, and I have a new carb on there. The 340 turned my little Dart into an animal!

    • 0 avatar

      Awesome on both counts. That brought a huge smile to my face, so thank you.

      • 0 avatar

        I’ve always been part of the “if it ain’t broke don’t fix it” crowd. My ’99 Continental with original factory O2 sensors returned consistent 25 MPG right up to 170,000 (4.6 32 valve INTECH V8 btw). Watching their response on a scan tool verified they were up to snuff. But alas the AX4N has finally given up it’s forward clutch and is now in need of an overhaul. Although I’ll be dropping the cat assy to remove the tranny, the original O2’s are staying right where they are. Now if only there was a conversion available to allow me to swap in the new 6 speed auto . . .

  • avatar

    On the old gas, back 20 years ago I would say to dilute it and burn it. I had a number of old non-driving but still-running cars (including a 1941 Chevy parked on the side of the house that I started up every few months) that I had the same tank of gas in for literally years and they always started up on it. Back then I didn’t even know that there was such a thing as fuel stabilizer (which I now use religiously in my lawn mower and 2-cycle gas).

    But with “new(er)” gas, I have had gas go bad in my lawn mower twice during the summer (the few months of sometimes-hot weather kills back the grass so the lawn mower stays parked), and it was definitely the gas each time. I first disassembled and cleaned out the carb (after testing that I had spark, and verifying that the engine would run on a shot of starting fluid), but after replacing with fresh gas, it ran fine.

    So they have definitely changed the formulation of gas over the past X years – my own sniffer tells me that they are putting more highly-volatile solvents into it, and I suspect that these solvents are vaporizing away first leaving the heaver, less-flammable components behind. If you don’t want to drop the tank but want to get the old gas out, they make this really cool siphon hose that you simply shake to get the siphon started (no mouthfulls of sour gas, blech), google “super siphon.”

    I’ve also read recently that these highly-volatile solvents in the gas can actually pass through the plastic portable fuel containers (what about plastic fuel tanks on cars?) that are the norm these days (where can you even buy a steel one besides an imported Jerry can, and even those are getting hard to find), and that you should use a tightly-sealed steel container to keep gas fresh for a long time. Well the CO2 leaks right through the plastic on a 2-liter bottle over time too, so I think that theory may have some validity.

    On the O2 sensor, nothing against Bosch sensors, I ran one on my ’88 Buick just fine, but I have heard several stories on the Honda forums of Hondas not liking the Bosch sensors either, so I tend go go OEM on these parts (especially on OBD-II cars which are VERY finicky about the O2 readings).

    • 0 avatar

      I had a similar thing with my mower last summer. Tried running gas in it that had sat in a plastic container over the previous winter. The mower engine ran, but poorly. Replaced the old stuff with fresh gas and it ran fine.

      Though my much abused extra car, a 1994 Pontiac Grand Prix, was parked for 6+ months two seperate times with mechanical problems before I had time to fix it, and never had issues with sitting gas.

  • avatar

    I’ve heard (you know… from “guys”) that it’s advised to replace the cat at the same time as the O2 sensor(s). To some extent this makes sense to me. If the cat has lost some material or become caked with soot and can’t burn off some of the pollution then the computer MIGHT think that one of the O2 sensors is off because to it, there’s no way the difference in signal from the two sensors can happen. Remember what an OBD-II code tells you. It’s not a diagnosis, it’s a code. You have to do some research to see what could be causing a p0152 code BESIDES just a bad O2 sensor.

  • avatar

    If you haven’t done so already, check the emissions warranty on your Magnum, although it may only be up to 80,000 miles.

    If it’s out of warranty, it may be worth making a call to Chrysler customer relations; there may be a hidden warranty on your vehicle…or who knows? The rep you speak with may decide that you’re close enough to 80,000 miles to justify a “special adjustment.” Stranger things have happened when it comes to warranty claims. In any event, it’s worth a shot.

  • avatar

    I bought a Contour that had sat for 2 years with a 1/2 tank of gas. I had wondered if it would start after I charged the battery back up, considering the ancient gas.

    It started right up, and stank to high heaven thanks to the stale gas, put fresh gas in it and it did just fine, stopped smelling after the 3rd tank.

  • avatar

    Replacing O2 sensors as preventative maintenance doesn’t make sense to me. I’ve seen them go 200k+ miles with no fuel economy or operating issues.

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