1998 Dodge Dakota 5.2L V8 Cylinder Misfire and Spark Knock

[gnelson49]

I am having an issue with my 1998 Dodge Dakota 5. 2L V8 Manual transmission.   Once it is warm, at lower RPM's (1200-2000) the truck is very sluggish and tends to ping or knock (sounds like a spark knock).   This has been getting worse over the past month or so.   Just this past weekend while driving up a hill at 55-60 MPH in 5th gear in cruise it threw a P0307 indicating Cylinder #7 misfire.   I could feel it!  The other thing I have noticed once warm is when I am out of gear and the truck is trying to go to idle, the tach bounces several times before settling at 550 RPM.   This low idle also causes my oil pressure to drop (<40 psi) and my voltmeter shows discharge (drops quickly below 12V with lights on) and my lights dim significantly at night.   When it is cold it idles around 600-650 RPMS and I have good oil pressure (50+psi) and voltage (14V).   I have replaced the throttle position sensor and checked the harness and it seemed to help for a few days but the problem came back and is much worse.   I have been reading a lot online and noticed several TSBs for my truck regarding rough idle, sag/hesitation and spark knock.  It references TSB #180500, and there are subsequent additions 180500A-G or so.   I haven't bought a subscription to ALLDATA yet, but I wanted some advice to see if that TSB would be helpful and if you have any thoughts.  I am thinking a bad coil or rotor?? I checked the plug wires and plug gap and they are ok, any thoughts??   

[Transman]

You haven't said how many miles are on your vehicle, how old and what brand are the plugs & wires? These vehicles are sensitive to brand so do yourself a favor and replace with OEM only. The nice thing about your code is that it tells you which cylinder is causing grief. Do a Compression test and make sure the engine is sound.
If you are capable, move the injector to another hole and see if the miss moves, swap the spark plug to a different hole and see where the miss moves to. The coil can affect just one cylinder but unless it is coil over then a bad coil will usually affect more than one. Post back your results and more info, Transman

[gnelson49]

Thanks for the quick reply.   I can answer a few of your questions.   The truck has 96,000 miles, the wires are OEM.   I am unsure whether the plugs are or not, I can't recall.   I also don't know the age of the wires and plugs, they look pretty new but I just bought the truck in November with 94,000 miles and it was fine at that time.   I tested the resistance in the wires and they were around 400 Ohms per inch or about 4800 Ohms per foot which seems pretty low.   One thing I have also noticed recently is my truck takes on a strong static charge.   Every time I get out regardless of how short or long a distance I drove I get a sharp spark when I touch the door or any part of the metal framework.   I am going to reinspect the plug wires for a possible electrical leak, and also swap the plugs as you suggested.   I am not sure if I can do the injector, but I'll let you know.  I'll also give the info on the plugs!

[Transman]

FWIW, These vehicles, as with most of the newer vehicles, are very sensitive to spark plug brand. Try to stick with OEM plugs only. Stay as far away from autolite as possible, some guys still swear by them but everytime we get one in with a misfire it seems the customer has just put autolites in and replacing them with OEM solves the problem.
The wires seem about right. The static might be from really dry cold air, not sure where you are, but might be a good idea to make sure your grounds are good and the battery is clean/corrosion free. Post back, Transman

[gnelson49]

Ok, so I replaced the spark plugs with OEM plugs.   The plugs were OEM that were in the truck, but wow they were bad! The gap was close to 0. 1 in.  Considering it should be . 04 in.  that was a serious problem.  Not to mention the threads were rusted up and the plugs were in poor condition overall.   The replacements have made a huge difference.   There is no more sluggishness when under load, no misfires or codes thrown, and the tach seems to be steadier.   I do still have my oil pressure drop when it is warmed up and idling, if I just barely tap the accelerator it climbs back up, so it appears the idle is a little low.   The charging system is sound now, no dimming of the lights anymore.   I wasn't able to swap the injectors or do a compression test, those are a bit beyond my abilities, and more than I can do just working outside at the moment.   The static seems to have subsided as well, part of that can probably be attributed to the weather.   I live in Boise, ID and we have a pretty arid climate, low humidity.   I know the idle is controlled by the computer, is there anything I can do to bump it up a notch or something else I might be missing??

[Transman]

Did you clean the throttle body when you replaced the plugs? The PCV Valve?
Don't try to raise the idle to get your oil pressure up, you might have low oil pressure and that should be checked with a gauge to verify. You only need 8 psi to make the engine happy although you want more. So even if it does drop to 8 psi at idle, as long as it raises when the rpm raises, I don't think you have anything to worry about.
This engine had problems with "charcoal" like pellets developing inside the oil pan which would clog the pump inlet screen and I have seen this on vehicles where the owner was religious about 3k oil changes and used premium oil. The only sure way to deal with this problem is remove the oil pan and physically clean them out. I have seen nothing on the market that dissolves them. You might want to live with the oil pressure problem for awhile.
I think your static as well as the other problems can easily be attributed to the bad spark plugs and I'm glad you got that handled. Transman

[ironhead]

Does this truck use any oil?  They are famous for bad intake manifold lower cover gaskets. That gasket is under the intake so when it fails, you end up with a vacuum leak inside the engine. This usually causes Misfire, oil consumption, knocking/preignition, and every other symptom of a vacuum leak.
Guy

[gnelson49]

Yes it does use oil.   I went through about 1 quart over 2,000 miles.   I agree with you on the gasket, it appears I have some leaking underneath the manifold.    Some of the symptoms have come back, the tach still bounces, and the RPM's have dropped to where the electrical system discharges at warm idle again.    I haven't researched how difficult the gasket is to replace, can you give me an idea of what it takes to replace it and what I might expect to pay if I took it to a mechanic to be replaced?? I don't have a garage right now so I am a fair weather mechanic until summer :)

I am going to clean the throttle body and PCV valve next and continue from there. . .

[ironhead]

You need to remove the intake manifold, then flip it over and you will see a large flat cover on the bottom with a bunch of small bolts all the way around it. Just remove that cover and you will probably see the gasket broken at one of the rear corners. It looks intimidating, but it really isn`t that bad a job. To verify that this is your problem, remove the PCV valve from the drivers side valve cover and plug the hole in the valve cover and the end of the valve. Then pull the breather hose from the passenger side valve cover off of the air cleaner. Start the engine and hold your thumb over the end of the breather hose for about 30 seconds. If you build any vacuum in that hose, you have a confirmed internal vacuum leak. Time to pull the manifold.
Let us know what you find.
Guy

[Paul]

Based on whats been described you have,had two problems going on,the spark plugs and the issue Mr.Ironhead talked about,those gaskets are a fairly common failure.

[gnelson49]

So I pulled the breather hose from the air cleaner and removed the hose between the PCV valve and the intake manifold and I ran the engine for 30 seconds and I didn't get a vacuum, I got a lot of air pressure build up in the breather hose.   When I removed my finger from the end it blew out a lot of air, so does that eliminate the intake manifold gasket as a problem??

Also, how do I get the PCV valve out of the valve cover, it has a rubber grommet around where it goes into the valve cover and based on the information I have you are supposed to turn it CCV about 90 degrees or until the end points down and it should pull out. .  but I can't get it out so I can see if the pistle is good and clean it. .

I am going to also perform the TSB 18-48-98 procedure regarding the spark plug wires to see if that helps.   I am back to a pretty strong spark knock and some hesitation at low idle, voltage drop and oil pressure drop at idle as I previously described.   Any other thoughts???

[Transman]

Have you done a fuel pressure test on this vehicle? I have seen fuel pumps with low pressure cause the same symptoms. A quick test with a fuel pressure tester will eliminate this as a potential cause. Transman

[gnelson49]

I'll have to round up a pressure gauge to do check my fuel pressure.   I did the plug wire re-routing following TSB 18-48-98 and it is still running rough.   I am going to clean the throttle body, try and clean/check the PCV valve and then pull the plugs and clean them and see if that helps. .  the plugs may be fouled since it has still been acting up. . 

I am hoping I can knock this problem out soon. .  it is a bummer deal :( 

[gnelson49]

Well here is where I am at so far:

I have replaced the distributor cap, rotor, plugs and wires, PCV, TPS and re-routed the wires as per the TSB for spark knock, pulled and cleaned the entire throttle body and checked the intake manifold vacuum.    I haven't been able to check for fuel pressure, although after replacing all of the above items the truck runs noticeably better.    The distributor had a lot of corrosion and the rotor was worn, I think that had a lot to do with it.    Cleaning the throttle body and IAC motor probably made a difference too.    

I still am concerned about my truck when it is warm, only once the truck is warmed up all of the way, the voltage drops at idle along with the oil pressure.    This just doesn't seem right to me?? But if I just tap the accelerator a little bit or under normal driving they jump right back up.    Is this normal?? I have never owned a vehicle where the voltage drops only at idle?? Could the computer be bad? I have no codes to report, and performance is improved although I think it still may be a bit degraded.    I pulled the plugs last weekend, about a month or so since they were replaced and they were clean and the gap was still .  040, so I don't think they are fouling or having any other issues there.  . 

Could it be a bad sending unit causing the pressure drop on the guage.   It drops to probably around 25 psi on the guage at idle and up to 70-75 psi under load.  Would this affect the voltage guage, maybe a short in the sending unit?

Is there something else I am missing? Have you heard of one of these trucks doing this??

[Transman]

Have you had the Battery/Charging system checked recently? Check belt tension. I don't think it is an issue as the engine warms the computer will bring the idle down as far as it can. You will see the oil pressure drop. this is normal. The battery voltage can drop for the same reason if you have lots of accessories on as you have more voltage going out than the alternator can put back at idle but if this were mine I would get that battery checked. Post back, Transman
P.S. You didn't say if the spark knock is gone