I've Got Those Check Engine Light Blues

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Buccaneer Bob

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Hi Guys,

Pardon the long story, but I'm not sure what all is relevant, so here goes.

I've got a 98 Dodge Ram 1500 5.2/318 2WD with 241,*** miles on it.

About six weeks ago, my truck started running really sluggish, and at first I suspected the transmission. (It was taking a dump whenever I tried to go into overdrive, so "transmission" was what I was thinking at the time.)

I took it to a transmission guy who "serviced" it, replaced a seal, etc., and one of the things he told me when I went to pick it back up was that he disconnected the muffler to drop the transmission so he could replace that seal.

After that, he did a test drive with the muffler disconnected, and my truck ran about a thousand times better with the muffler off, so he thought part of my trouble was a clogged catalytic converter.

I then took my truck to a muffler guy, and he replaced the catalytic converter with a Walker universal model.

I drove away and made it about 10 minutes before the "Check Engine" light came on.

I headed back to the muffler guy, he checked things out and said that my problem was something else, not the new catalytic converter.

I will say that the truck does run a thousand times better with the new catalytic converter, so at least my transmission guy saved me a lot of trouble with that deal.

Well anyway, then I took my truck to a regular mechanic, he checked the trouble codes, told me that I had a "lean mix" situation, and he gave me a long list of possible problems.

So far, he has replaced the spark plugs, distributor cap and rotor, and the MAP sensor. He also cleaned the IAC solenoid, checked the spark plug cables with a timing light, did a fuel pressure test, and did a "smoke test" on the intake system to check for vacuum leaks.

And still no joy. He clears the codes and 10 minutes after I start her up, my "Check Engine" light comes back on.

Worth noting is the fact that I never had the "Check Engine" light come on until AFTER I replaced the catalytic converter. It's weird that it didn't come on, actually, considering how poorly my truck was running at the time.

But maybe the clogged catalytic converter was masking the problem? And what if the problem actually caused the catalytic converter to clog up? Those are two questions I would love answers to.

But anyway, onward. I decided to take my truck over to Autozone, and their equipment says:

Troubleshooting P0300
OEM Brand: Domestic

Definition
* Cylinder misfire detected - random cylinders

Explanation
* The powertrain control module monitors the crankshaft speed and has detected a misfire condition

Probable cause
* Ignition system fault - spark plug(s), ignition wires, coil
* Vacuum leak
* Injector fault
* high or low fuel pressure

So as near as I can tell, the only possibilities left are 1) a bad ignition coil; 2) a bad fuel injector; 3) a bad sensor (O2 sensor? Crank sensor? etc.) or 4) something that we already tested but we need to test again.

Or what am I missing here?

Any advice y'all can give me would be greatly appreciated. I like to keep 'em running as long as I can, but this Dodge Ram of mine is really starting to eat my bacon.
 

Yeret

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Does the engine use oil? The intake plenum gasket is pretty much guaranteed to fail at some point on our engines and when it does, oil gets drawn into the cylinders and will cause all kinds of problems, including random cylinder misfires (due to fouled plugs), plugged catalytic converter (due to burning oil), spark knock, weak power, stuttering in overdrive.

I dealt with that P0300 ******* for ages until I finally got my intake gasket replaced as well as misfire codes for specific cylinders. And the issue trashed two catalytic converters before it was resolved.
 
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Buccaneer Bob

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You know, there for a few years, I was getting a bit of blue smoke if I spent more than 10 minutes idling.

But oddly enough, I haven't seen even a smidgen of blue smoke in about five years.

However, it might well be that this is what clogged my last catalytic converter, and I haven't had enough time to see the blue smoke coming through the new catalytic converter since I started right off dealing with the "Check Engine" light situation.

I will definitely have to check that out.

Thanks so much.
 

David H

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Years ago, my misfires were caused by bad plug wires. I see those were not replaced. There is also a TSB which reroutes the wires. This needs to be done.

X2 on the plenum gasket. If it's blown you'll be using at least a quart of oil between 3000 mile oil changes.
 
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Buccaneer Bob

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Thanks so much for the input, David H.

Yeah, the spark plug cables could certainly be causing trouble. We sortof tested them with a timing light, but that doesn't tell us about the cable-to-plug connection or how strong the spark is.

And that plenum deal is definitely on the horizon.

So nobody thinks it might be a weak coil? I've always heard that either they work or they don't, but I've been reading that sometimes they can be working but throwing a weak spark.

And nobody thinks it might be a bad O2 sensor or something like that?
 

Yeret

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A blown plenum is going to cause the engine to burn well more than a quart every 3,000 miles. When mine was blown, I was using a quart every 200 miles. It got so bad that every time I started the engine, a huge cloud of blue smoke would burp from the exhaust. Was pretty embarrassing actually. One quart of oil loss every 3,000 miles is actually pretty normal for a high-mileage engine and won't cause any real issues. I've had a few vehicles that used oil at such a rate and never had running issues.

If you want, you can pretty easily test the coil if you have a multimeter. Pluck out the coil, set your meter to "resistance" and place the probes on the two tabs in the connector end. You should read as close to one ohm as possible. Then keep one probe on one of the tabs and place the other probe on the terminal. You should read somewhere between 6,000 and 9,000 ohms. If either reading is outside the range, replace the coil.

If you have a scanner with a live data function, the O2 sensors can also be monitored. The engine has to be at operating temperature and in "closed loop" mode to do it. It's been quite a while since I've done this so I'm not sure what the ideal range is but I do know that the upstream sensor should have a rapidly fluctuating reading within a small range while the downstream sensor should be fairly stagnant. This difference indicates that the catalytic converter is functioning correctly. In regards to fuel/air mixture, the upstream sensor is the important one. If it is faulty, the ECU will either add too much or too little fuel, usually too much, and this could result in misfiring but mainly this will cause a reduction in performance and excessive fuel consumption.
 
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Buccaneer Bob

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Thanks for the info, Yeret.

As near as I can tell, my truck really isn't burning much oil right now. Back about 10 years ago it was, but I'm really not seeing any blue smoke right now.

I've got a crazy theory that the oil might have baked into the spaces in the plenum gasket and sealed them, but I'm not going to get my hopes up on that.

I just know that I haven't been using very much oil here lately.

That said, the test for the coil sounds promising. It's raining right now, but I'm going to check it in the morning and see how it reads.

And I really do need to find somebody with one of those live scanners. I've been reading about them, and one of those scanners would tell me which cylinders I'm supposedly missing on, how the sensors are reading, and everything.

I wonder if they have one of those at Autozone. I know they've got the code reader types, but I wonder if they have one of those live scanner deals.
 

David H

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If you're not using a noticable amount of oil then I wouldn't sweat the plenum just yet. I was using a quart every 3k when my cat plugged up. Replaced the cat and did the plenum shortly after resulting in no more oil loss. I had no other running issues at that time however.
Your cat may have failed all on it's own. Tough to tell but watch your oil consumption closely. If you're blowing oil into the exhaust you may be buying another cat.

IMO the missing is more likely ignition related. Let us know how that coil checks out. Either way, I would be adding some quality plug wires to my shopping list.

Also, where are you at? Someone may be close buy that has a scanner.
 
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Buccaneer Bob

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Hi David H,

Thanks so much for the followups, and sorry I haven't been able to follow up on my end. Between work and rain, I just haven't been able to catch a break.

My current list of things to do is:
* Test ignition coil with multimeter - primary resistance of .95-1.2 ohms and secondary resistance of 11,300-15,300 ohms
* Test ignition cables with multimeter - not more than 8,000 ohms per linear foot of cable length
* If possible, swap front and rear O2 sensors and see what happens.

Basically, I'm trying to do everything that I can do for free right now.

My wife is so pissed about how much money I've spent on the truck, here lately, that I'm not even in the Doghouse right now. I'm in the Outhouse wishing I was in the Doghouse again.

So anyway, once the rain clears up, I'm going to get after it, and once I see what I come up with on the free testing, I'll report back.
 

David H

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Good plan and good luck.

Keep in mind that good resistance checks on plug wires does not mean the wire housing has not broken down due to time, heat, chafe or all of these. A very common malfunction of these wires is arcing (causing misfires) because the insulation is old and ineffective. Often times you can hear this happening or even see it in a dark shop.
 
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Buccaneer Bob

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Okay, I finally caught a break in the weather today. The ignition coil tested pretty well. The primary read 1.3 ohms, a smidgen over 1.2 ohms, but I'm thinking it's really not that far off.

But the ignition cables were waaayyy off. The first cable I checked read either 7,000 ohms or 31,000 ohms, depending on how I wiggled it. The second cable measured 80,000 ohms!!!

I triple checked, and yeah, 80,000 ohms. That's 30,000 ohms over Dodge's maximum spec of 50,000 ohms. So I just stopped right there. If two out of two cables are bad, that's good enough for me.

So I ran it by Momma, and she gave me the go-ahead to buy a new set of ignition cables. I'll hopefully have them in tomorrow, and once they're in, I'll let y'all know how it worked out.
 
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Buccaneer Bob

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Okay, I got busy before it got dark, replaced the ignition cables, went for a test drive, and my "Check Engine" light came on after 10 minutes.

But rather than getting discouraged, I went to Autozone to see what kind of code I was getting, and I no longer have P0300 "Random Misfires".

Now I am getting P0132 "High voltage in H02S11 (Heated oxygen sensor - bank 1 sensor 1)".

So I really, really want to believe that I am down to just a bad oxygen sensor at this stage of the game, but I don't dare get my hopes up because I have been wrong before.

Given that I have already gone through our meager savings replacing a clogged catalytic converter, servicing the transmission, going back and forth between various mechanics, etc., Momma says that I have to wait a week or two to buy a new oxygen sensor.

However, I think I'm going to crawl up underneath the next afternoon I can catch a break and monkey around with the sensors to see what happens.

Since my muffler guy had to swap the sensor over from the old catalytic converter to the new one, there is a chance that he pulled a wire out or something along those lines.

So I will really inspect the wiring closely, repair anything out of the ordinary, unplug and replug the connectors, clean off the tip of the sensor, etc., to see if I can get it working properly.

Barring that, another possibility might be to swap the front and rear sensors to see if that makes a difference.

I will keep y'all posted.
 

dapepper9

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If you want, you can pretty easily test the coil if you have a multimeter. Pluck out the coil, set your meter to "resistance" and place the probes on the two tabs in the connector end. You should read as close to one ohm as possible. Then keep one probe on one of the tabs and place the other probe on the terminal. You should read somewhere between 6,000 and 9,000 ohms. If either reading is outside the range, replace the coil.

11,000-15,000

As for the OP, wire routing has been mentioned but pretty well skipped over in discussion. Good thing to verify or you'll be chasing your own tail for a while if it's this simple
http://dodgeram.info/tsb/1998/18-48-98/18-48-98-v8.htm
Thicker wires have also been shown to reduce/eliminate crossfire
 

dapepper9

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Also, can't swap front and rear 02 sensors as they have different functions. Front very directly affects air/fuel ratio whereas downstream only monitors the converters efficiency. Hell i don't even run a downstream, that's where my wideband for my a/f gauge got put.
 

David H

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Sounds like progress. I believe when it comes to O2 sensors the advice is to use oem parts. Thinking oem for these trucks is NTK. Someone here knows for sure. I do know you can spend $70 per sensor but a little shopping around will get you the same part for $30.
I buy from these guys more often than not... 1998 DODGE RAM 1500 PICKUP 5.2L V8 Oxygen (O2) Sensor | RockAuto
 

Gr8bawana

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Rock Auto has NKT O2 sensors for $32.79 which is a pretty darn good deal. I have yet to be disappointed with anything I have ordered from them.
 
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Buccaneer Bob

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Hi Guys,

Momma gave me the go ahead to replace the oxygen sensor yesterday, so I went to Autozone, and they showed two different models, one with a 12" lead and one with an 18" lead.

I was getting the P0132 code (High voltage in H02S11 (Heated oxygen sensor - bank 1 sensor 1)), and bank 1, sensor 1 is the front oxygen sensor, the one with the 18" lead.

If dapepper9 is correct about the sensors not being reversible, I think I managed to get the correct model to replace the sensor I had that was going bad.

So far, I have driven 70 minutes -- some city and some highway miles -- without the check engine light coming on, so it's looking pretty good. Obviously I need more time to know for sure, but I am starting to get cautiously optimistic. Before this, I rarely went more that 10 minutes before my "Check Engine" light came on.

One thing I am noticing is that my engine is no longer "rattlesnaking". It's running as smooth as silk after replacing the oxygen sensor, so that's definitely feeding my optimism.

Another observation I wanted to mention -- for anyone searching this forum for a P0300 trouble code (random misfires) -- is to start with the obvious culprits: spark plugs, spark plug wires, distributor cap and rotor, intake leaks, etc.

But if, after you've done all the obvious stuff, you are still getting the P0300 code, start looking real hard at your oxygen sensors.

Because what I found out with my truck is that: 1) the oxygen sensor goes bad and thinks there is a "lean mixture" scenario; 2) the powertrain control module (PCM) tells the fuel injectors to start dumping more gasoline into the cylinders to enrich the mixture; 3) that overabundance of gasoline starts the motor misfiring (cylinders alternating between firing overly hard and not firing at all); 4) those misfires trigger the PCM to go from a P0132 code (bad sensor) to a P0300 code (random misfires).

At least that is what I found. I lucked out one time and had my "Check Engine" light come on right in front of Autozone, and that is the one time that they gave me a P0132 code. But if I had to drive 20 or 30 minutes to get to Autozone, their testers would see a P0300 code at that point.

So anyway, if you're somebody searching this forum for a P0300 code and you find this, fix the obvious culprits first. But if you're still getting a P0300 code, look real hard at your oxygen sensors, because a P0300 code CAN be caused by a bad oxygen sensor, as well, as I illustrated above.

I will post another followup in a week or so, after I've had more time to run my truck and ensure that the problem is solved, but I wanted to do a quick followup about where I am so far, for all of you great guys who have helped so far.

Thanks so much, and I'll be in touch.
 
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Buccaneer Bob

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Okay, guys, I said I'd follow up, so here goes.

It's been a week, I have logged about a dozen hours of drive time, both city and highway miles, and not even a flicker of the "Check Engine" light, so I guess I got it fixed.

Thanks so much to everybody who helped!

Cheers,
Buccaneer Bob
 

Gr8bawana

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Glad to hear you got it fixed.
 
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