Multiple Misfires

[jalbin]

1997 Dodge Ram 1500 5.9L V8 Magnum

Just fixed an opening in the valve cover (aftermarket covers had four openings, one being unnecessary) and did an oil flush. Now getting multiple misfire code, had an o2 sensor voltage code that hasn't returned, and its been reading C3 4 and 5 misfires. The catalyst system is now reading incomplete when it wasn't before. Where should I begin looking for the source of the misfires? I'm praying for just a vacuum leak, but my gauge is a being a little funny after dropping it. Hoping I'm not gonna need a new cat or o2 sensors. Any advice is helpful. Thank you.

 

[jalbin]

Update

Immediately after posting, I just found a broken vac line to the cruise control. Could this leak be causing so many misfires?

 

[dudeman2009]

First off, no a vacuum leak on these trucks won't do much at all, unless its in the plenum which i'll get into later.

Secondly, what do you mean an oil flush? You mean an oil change, or did you do something more?

As for the misfire, check all your plugs and wires. The plugs shouldn't be cracked or bent. If there is a lot of buildup on them, its probably time to replace them. If you do, only replace them with Copper plugs, don't let anyone upsell you to platinum or iridium, its only going to cause a misfire. Wires, make sure they are not overlapping, if they must overlap make sure its as close to 90 degrees as possible. Twisting around each other or running alongside each other can cause misfires in wires with thin or old insulation.

Check the cap and rotor, no cracks and not a lot of buildup, if there is, replace them.

Ohm test the coil. There is a two pin connector on the bottom. Between those two pins you should read about 1 ohm. Then between the tower and one of the pins it should read from 12K-15K ohms.

If none of those seem to be an issue, do you burn oil? get poor gas mileage, sub 13mpg highway? You might have a plenum leak, usually cylinders 7 and 8 go first, but its possible for it to cause other cylinders to have issues as well.

 

[jalbin]

By oil flush I mean I added a motor flush to the oil before draining it, added regular clean oil and drained again, and then added high mileage oil. I did this because when I bought it, the valve cover on drivers side was open with a magical "fourth hole".

The plugs and wires are all brand new. I'll go through and check all of them again. 2 and 4 have some fresh oil on them, but I'm looking for that leak now. I'll get back to you with the ohm readings. I don't think I'm burning oil, and I can't say much for the gas mileage as I just bought it and have only used about a quarter tank (for about 60 miles city) so far. I'm going to use a magnet to check if the plenum is OEM or replaced (oem is magnetic, aftermarket is aluminum). The PCV valve grommet appears to have seen better days, so I'm planning to replace that as well, but the PCV valve itself seems to be fine.

Thanks, and I'll get back to you.

 

[dapepper9]

I would suggest plenum and a tuneup with oem or equivalent ngk plugs, new wires and verify they're not crossing (they "talk" to each other otherwise) and if your 02 code is for the front aka upstream, replace it.

 

[jalbin]

So the plug wires all run alongside each other and are ziptied at a few points, but they are all new with good insulation. The coil read just like you said, 1.3 ohms at the pins and 13.7K from the pin to the tower. The plenum is magnetic, so I'm assuming it is factory. The PCV valve grommet is chewed up as I said. Not open or anything, but not pretty.

 

[jalbin]

I would suggest plenum and a tuneup with oem or equivalent ngk plugs, new wires and verify they're not crossing (they "talk" to each other otherwise) and if your 02 code is for the front aka upstream, replace it.

Plugs are all brand new with brand new wires. The O2 sensor code only came up once before I changed the oil and fixed a vacuum leak, but has not returned since.

 

[dudeman2009]

I'd go with the plenum then. Its possible that it was fixed before and they just used a proper gasket with the steel pan. Which is completely fine, but you won't know until you pull it to check.

Thats where i'd start, i'd also un-ziptie those plug wires and route them with a little space between each other. Unless you get really thick insulated wires, there can be enough capacitive coupling to get even a weak spark on nearby wires.

 

[jalbin]

So I've done most of what you've suggested, but I haven't checked out the plenum yet, as it would be a days work for me, and this is my only running vehicle right now. Are there any simple ways to try to confirm a diagnosis of a plenum leak? Also, I'm not sure if this is related or another issue, but the oil pressure is fine when first driving, but after I get going a while, the oil pressure drops to the lower end of the "within normal limits" area and sometimes triggers the oil pressure light. The oil levels are fine and there's a brand new Mopar oil filter installed. At idle without brakes and when backing up slowly, it kinda hops like a rough idle (I'm assuming from the misfires)? Any other suggestions/alternative diagnostics or things to check out?

Also, could plugging that "fourth hole" with a breather cap have been a mistake/should I have just found a way to cap it?

 

[dudeman2009]

I wouldn't worry about that 4th hole. The whole crankcase is kept under some vacuum and it pulls air from the intake air filter. Anything that will stop animals or large debris from entering is fine.

As for the plenum, there is no sure way to tell other than taking it apart. Some guys say you can check it by checking the MAP sensor, unless there is a hole in your pan, you won't notice anything. Another way to check is to take a borescope and look around the edges of the pan for a thin black strip sticking out, but you will only be able to see it if its a large leak already.

 

[jalbin]

Am I okay with just replacing the gasket? The fix for it is like $250 here. About how long of a job is it? I've never cracked open an intake before. Furthest I've gotten is swapping a throttle body on a Blazer.

 

[dudeman2009]

yeah, if you get a felpro gasket its completely fine to just replace that. You'll need an intake gasket set for re-assembly, as well as new intake bolts, I wouldn't try to reuse those.

For first timers giver yourself 4 hours to get it all done. You'll have to unbolt the throttle body and move it to the side, then you can either disconnect the fuel line (after relieving pressure with the schrader valve) or you can leave it connected and just pay attention to how much pressure you put on the connection.

The procedure is as follows. Remove the air cleaner assembly and vacuum or blow off all the garbage that builds up around the valve covers. Remove the radiator cap and either remove the lower radiator hose or open the drain **** on the bottom driverside of the radiator.

You'll want to do an oil change afterwards as well.

Once the throttle body is removed start unplugging the electrical connectors from the injectors. You might break a couple of the lock pins, but its ok.

At this point spray down the front four intake bolts with something to break up rust. The problem is dirt that gets into the holes and packs in between the bolt and the intake, they don't get stuck in the head often. Before you go to remove each of the bolts, heat them with a torch and quench them with water or WD-40. I do that three times and i've yet to have one snap on me after doing that. Otherwise i've broken 2 in the same spot.

Once you get all the bolts out, the intake mightnot come off easily, you just need to pry on it a little bit with a long screwdriver or crowbar to get it to pop up. After the intake is off, get a rag or something to stick under the intake mating surface on the heads so you can catch most of the oil gasket and rust as you scrape it off.

On the intake, the bottom is lined with bolts that holds the plenum pan on, these usually don't get stuck. You'll have to scrape that gasket off too.

Now is the time to spray cleaning solution into the intake valves on the heads.

Once you get the plenum gasket installed torque to spec. Then place the intake gaskets and reverse the removal procedure for install making sure to follow the instructions for torquing the intake bolts.

 

[jalbin]

Awesome, thank you! I'll try to get back to ya as soon as I get around to it.

 

[Shadow_Death]

I haven't been around here long enough to get a feel for what people think about Hughes Engines but....

Hughes Engines Plenum Plate 129.99

Hughes Engine Plenum Plate kit with felpro gaskets 159.99

I recommend the second one. It will cost more but those felpro gaskets were nice.

I did this to my truck about a month ago. It took me about 6-8 hours total but that was with trips to the parts store and lunch involved. Not to mention I wasn't in that much of a hurry as it was a nice Saturday until Texas happened and it started to rain.

 

[Yeret]

Be warned, the factory intake manifold mounting bolts break VERY easily. It's a common issue for those who do the job and I myself broke TWO of the buggers, one in each head.

This ultimately led to a very long, ridiculous saga involving me, my truck, hours and hours on IA-80, my now-ex mechanic and a bunch of people who really, REALLY didn't need to get involved with things.

Anyway, nuke those SOBs with penetrating oil well before you start the job. Don't be ginger. Once you get them out, throw them in a fire and buy new ones and follow the torque spec to the letter (we're talking inch/lbs here). All I can say is plan for the worst and be ready for busted bolt extraction. This is not a job you want to do on the Sunday before work.

 

[Shadow_Death]

Anyway, nuke those SOBs with penetrating oil well before you start the job. Don't be ginger. Once you get them out, throw them in a fire and buy new ones and follow the torque spec to the letter (we're talking inch/lbs here). All I can say is plan for the worst and be ready for busted bolt extraction. This is not a job you want to do on the Sunday before work.

Man I must have really lucked out. Whoever did mine the first time had them slightly above hand tightened. Talk about annoying.. but hey.. they were easy to get out.

 

[jalbin]

Update

I have not yet replaced the plenum gasket, but now my misfires are counting (with the random multiple misfire code) cylinders 2 3 4 and 5. I haven't had another O2 sensor code yet, but it still runs and drives fine, just very bouncy rolling in idle (and reverse). The idle is not as rough in park. Could it be a fuel delivery issue? Sorry, I've been doing more research than repair so far. What about TPS or IAC? I know the plenum is a very common issue with this engine, but I just have this gut feeling that isn't it. I've heard that you usually see the misfires in the 7 or 8 cylinders first, but I've yet to see a code for either.

 

[dudeman2009]

By bouncing when rolling in drive or reverse, if I have it right, you're feeling the truck jerk back and forth as if something is rubber banding back and forth slightly?

Thats what mine is doing, it runs pretty smooth at idle (you cn barely tell its running if you feel the valve covers is so smooth). In my case, the fuel sync is off, I replaced the whole distributor on my brand used engine as the housing was cracked. I got it pretty close to TDC on the distributor, but its off by a few degrees.

Is it possible that you or someone else might've moved that distributor a bit? If its far enough off, it could cause random misfire. Unfortunately, i'm not sure how you'd go about checking if its in sync or if its even possible without a DRBIII scantool.

 

[jalbin]

I couldn't tell you if the distributor has been moved. It is very possible, as I bought it from someone off of OfferUp. As for the bouncing, it is as if the whole front end is bouncing up and down a little bit. Like if someone were to be pressing up and down on the front bumper. It doesnt occur at a stop or if I'm actually driving, just when I let it roll forward or backward. Isn't the timing automatic? I don't know much about that stuff.

 

[dudeman2009]

The timing is computer controlled but the cam pickup is in the distributor. On install the computer doesn't know where TDC is. So you have to put the engine at TDC and set the sync to 0 so the PCM knows its now at top dead center according to the reading its currently getting from the cam sensor.