Multiple Random Misfire fixed, but not

[tnwoodsman]

I have a 2002 dodge ram 1500 SLT 5.9L with roughly 153,000 miles.
A couple weeks ago went to start my truck and it wouldn't start, but would turnover. Done some digging and spark plugs were in bad shape so I got NGK spark plugs and put in it and it started right up. I drove it that evening and on my way back it started misfiring and I got a DTC P0300 (multiple random cylinder misfire) so I replaced plug wires, coil pack, cam and crank sensors, distributor cap and rotor button. This did absolutely nothing. When you first started it up, it idled fine, but when It started to warm up it would misfire every minute or so and then when you would go to accelerate from stop light it would hesitate. So I took it to the dealer last week and they kept it 2 days and determined it was spark plugs. They said in older dodges your suppose to use copper spark plugs (Champion) and NGK plugs contain iridium and that this was causing plugs to overheat and misfire. So they changed plugs and took $370 from me (bunch of BS). 2 days later it began to miss again, but now it only misses after you get to 40 mph or higher and it has a rough idle. The longer you sit at a stop sign or light the worse the idle gets and it still hesitates when accelerating. However, now I don't have misfire code, but large evap leak P0455 and Catalyst System Efficiency Below Threshold (bank 1). The evap leak has been on my truck before and I never could find a leak and it eventually went away. So I changed evap canister purge solenoid and am now thinking it could be catalytic converter, but I don't have a rattle or sulfur smell. Or it could be O2 sensor(s). Has anyone ever come across anything like this before? If it causes anymore aggravation I might find a cliff and send it over the edge.

 

[MADDOG]

It's true about copper vs. alloy metal plugs in the HEMI but I've never heard of them causing issues in the LA family of engines. Sure, FCA recommends copper replacements but I didn't think the 5.9L was picky about it.

Seems you had or still have other issues that are causing some stutter and hesitation. Those evap system hoses and cannisters are problematic. When you changed out the cannister did you check the vent hoses for cracks?

 

[tnwoodsman]

To be honest I didn't realize the difference between plugs until the dealer told me that and I started reading up on them. Yeah I checked all of the hoses on the 2 canisters in front of the fuel tank and then when I replace the purge solenoid I checked all the vacuum lines on the truck again. I had previously checked them when it first started, because my initial thought was vacuum leak causing lean misfire, but I have yet to find a cracked hose. We tried spraying starting fluid on all vaccum hoses while letting the truck idle, because if there is a crack or place in the hose the idle should increase. I also cleaned the throttle body and carburetor (it was pretty bad) but didn't make a big difference. I mean it could be a number of things wrong, I was just trying to do as much as I could without taking it back to the dealer.

 

[dudeman2009]

There could be a couple things going on. Yes the Magnums are picky about the heat range of plugs you use. But a Copper plug is a copper plug, if that is the heatrange specified, thats what it should be. The NGKs you bought, as long as they were copper, were fine. Why the dealer said otherwise is beyond me.

But if they put the copper ones back in, then we can rule that out. With everything else you've done, you've covered quite a bit. But have you or the previous owner ever had the plenum repaired? If not, that would be the very next thing I do. As you are describing nearly exactly what that problem causes.

 

[tnwoodsman]

No I have never repaired the plenum gasket, not sure about previous owner. After reading up on it, it does sound like it could be a contender, but looks like a pain in the butt to change. Could you check this by doing pressure test to check for leaks? I've yet to have a pressure test done. I was thinking Throttle position sensor or idle air control valve too, but they would probably throw a code.

 

[dudeman2009]

There is no way to test the plenum other than taking it off. Its really not that hard. About 8 hours for a first timer. TPS isn't super likely to cause this issue, usually it will only cause lack of acceleration and poor idle issues from the start. An easy way to test that is just to look at the TPS value with a scantool. It should ne 17-18% idle, and near 72-78%ish floored. I don't remember exact right now. But really the TPS won't cause and misfire or pinging. The IAC won't cause this issue either, it only ever affects the truck when you are at idle RPM, then if it is a problem, you usually high idle or stall. Or it will hunt, but it wont misfire or ping.

 

[tnwoodsman]

Does anyone know about how much torque is needed for plenum gasket bolts?

 

[tnwoodsman]

Disregard torque question, I found specs on another thread.

 

[tnwoodsman]

Well I changed the plenum gasket, intake runner gaskets, throttle body gasket, radiator thermostat and gasket, cleaned the fuel injectors and changed O rings, and changed TPS. Changed oil and filter and coolant. IM HAVING THE SAME PROBLEMS THOUGH! Now it misses or stutters or whatever mostly between 40 - 45 mph and still has some hesitation when going to accelerate from a stop once it gets hot, don't seem to be idling as rough so far, but not sure if it will or not. Could it be a PCV valve or what? Getting tired of throwing money at! Thanks for the advice though.

 

[dudeman2009]

How did the gasket look? Was it torn or just missing in some places? Did you ever compression test the cylinders? The plenum leak can kill either cyl7 or 8, or both given time. PCV valve won't cause a miss. Can you get a video. When you replaced the TPS what brand did you use, and did you keep the old one? The TPS won't cause a miss, but it can cause strange problems if you don't use the exact factory replacement. For some reason, all the cheap ones are junk and don't work quite right. Keep the old one, as this one might go out rather quick in the grand scheme if you bought a cheap one from an autozone or something.

 

[tnwoodsman]

Plenum gasket was pretty bad, it was gone in spots. Some of the gaskets looked like the had allowed oil to leak in, I'm assuming that was the intake runner gaskets, but they weren't tore or anything. No, I never did the compression test, but that might be the next thing I do. Yeah I can get a video. Can remember brand of TPS right off the top of my head but I'll look later this evening, but O did get it from O Riley's and I think I still have the old one. So if it can't be PCV valve, IAC, or TPS or anything else I've done so far what's left lol. What your take on clogged cat or bad O2 sensors or CAM Sensor? Btw, my engine light went off after I changed the gaskets, but they was for Catalytic converter and evap system.

 

[dudeman2009]

If its a cat, and its clogged, you probably aren't going to be able to rev above 3krpm, and its going to have trouble getting past 35. Mine is starting to clog and its a real dog to do anything, cat is almost 500 degrees after a long drive xD

If a cylinder has low compression, that very well could cause issues, but if you have fixed the plenum and it was that bad, we really need to see the health of those cylinders. Good news, depending on where you live, its supposed to be above freezing for a little bit tomorrow.

 

[tnwoodsman]

I'll try to get the compression test done tomorrow. Well, it doesn't have a problem with loss of power as far as getting above a certain rpm or mph. Yesterday I got on the interstate and went about a mile and got it up to 70 no problem other than the missing of course. I am thinking about changing CAM sensor tomorrow too. Just wish I would have thought of that while I had everything torn apart since it is inside the Distributor cap. Yeah, I live in northeast Tennessee, so we have been above freezing this past week, but here lately it has been pretty cold, highs in the low teens or twenties.

 

[tnwoodsman]

Hey when you do the compression test do you have to disconnect your injectors? And also do you remove one spark plug at a time and check it or do you remove them all and go down the line that way?

 

[dudeman2009]

You have to disable the fuel system. The easiest way is to pull the fuel pump relay then crank the truck to relieve the pressure on the lines. You can go either way and do them one at a time or pull all the plugs. Some guys will say you need to have the plugs on the rest of the cylinders in so the rpms are accurate, but I have never seen it make a difference. The extra 80rpm you get when all the plugs are out really doesn't matter, the goal is to have consistent rpms for each part of the test. I've also never seen a visible difference from testing with all plugs out or all plugs in on a fully charged and strong battery. Weak batteries will have a hard time cranking over an engine for that long with all the plugs out, let alone in. Make sure you have a charger on the battery that is charging in between tests. Even without meaningful compression its still takes a lot of power to crank over a big V8.

You'll want to do two, three or four tests. Engine cold, engine hot, and optionally, drip a half dozen drops of oil in the plug hole then re-test compression for both or either cold/hot tests.

Record each cylinder and the type of test. Min should be something like 120psi+ at that age with no more than 15-20psi between cylinders in order to be considered an old but acceptable engine.

 

[tnwoodsman]

I completed the compression test today, just when the engine was hot and I got around 130psi across the board, 125-130psi. I will do the test cold tomorrow. I am going to check my fuel pressure tomorrow, may drop the tank and check fuel pump and regulator. Any thoughts?

 

[dudeman2009]

I completed the compression test today, just when the engine was hot and I got around 130psi across the board, 125-130psi. I will do the test cold tomorrow. I am going to check my fuel pressure tomorrow, may drop the tank and check fuel pump and regulator. Any thoughts?

Those pressures look good. I was mistaken, min pressure is 100psi. You can check fuel pressure from the fuel rail in the engine bay. If you can get a scanner that can read live data, you might check to see if the issue starts once the fuel system goes into closed loop mode, seeing as its fine when its cold.

 

[Yeret]

They said in older dodges your suppose to use copper spark plugs (Champion) and NGK plugs contain iridium and that this was causing plugs to overheat and misfire.

They are half right. Our Magnum engines perform optimally with copper plugs and it is well know that they run poorly with platinum or iridium plugs. However, iridium plugs aren't going to overheat in our engines but rather operate too coldly and foul because iridium plugs are meant to be used only on engines with very hot ignition systems and/or very high running cylinder pressures and our Magnum engines have neither. Iridium plugs have a lot of resistance in exchange for exceptional durability but if your ignition is "cold" or has modest cylinder pressure (our engines), they will operate too cold and will eventually foul and misfire.

Catalyst System Efficiency Below Threshold means that the output readings between the upstream and downstream O2 sensors are or are nearly the same. During normal conditions, the upstream O2 sensor will detect more oxygen than the downstream sensor because any unburned oxygen that passes the upstream sensor will be burned off inside the catalytic converter. As such, the downstream sensor should detect pretty much zero oxygen in the exhaust stream at all. In other words, the upstream sensor should detect some oxygen while the downstream sensor should detect none. If the cat is not functioning properly, unburned oxygen will not burn off and will be detected by the downstream sensor. The two sensors will send a similar return voltage to the computer which interprets this as the cat not functioning properly.

Now, this doesn't necessarily mean that the fault is entirely in the catalytic converter. If the O2 sensors become fouled (which is certain if the engine burns oil), they, namely the upstream sensor, might not detect any present oxygen at all due to the "sensing" end being coated with gunk which results in the two sensors sending similar outputs to the computer. Because plenum gasket failure is so common in our trucks and results in excessive oil being burned in the cylinders during combustion, any Magnum engine that has had a leaking plenum for any significant length of time will likely have fouled the O2 sensors.

So, in your case, you may or may not have multiple problems. If you're not too tight on cash, I'd recommend replacing the cat and both O2 sensors. For the cat, consider a universal Magnaflow single in/out with bungs for the O2 sensors. It's a simple swap, other than welding in a 2-1 adapter, is a high-flow design and is a fair bit cheaper than an OEM unit.

 

[tnwoodsman]

It's been a few days since I've been on here, so here's an update. I've not done too much since I checked the compression. I replaced a few vacuum hoses and ordered a magnaflow converter and got both O2 sensors. I hadn't put them on yet though. Today I was thinking about something that happened to my uncle's truck and decided to get an ignition coil. I put the new ignition coil on there and took it for a drive and everything is gone, no miss, no rough idle, no hesitation nothing! I don't know if this is a temporary fix or what but as of right now it's back to normal. Does this make sense? I would have never thought an ignition coil would or could cause all of this?!?!

 

[dudeman2009]

Weak spark can cause an issue yes, but usually it does it all the time when that goes.

Glad to hear you fixed the issue, did you do a tune up?