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Discussion Starter · #1 · (Edited)
I joined this forum a year ago after one year of most enjoyable driving my 03 3.9 V6 extended cab. It seems there are a couple of things that always come up when asking about 3.9 engines. One is the need to swap to a V8 for added power. The other seems to be trying to clear a random miss . I have a couple of threads with 3000 views which I'm pleased with then I realize Yamaha racer has 48,000 views on P303. Due to supply issues my 3.9 V6 build may be held up till Dec. I have kept notes as to codes, parts replaced and MPG of every tank of gas. Most posts read the same Got this code and nothing seems to correct it. Same list of parts same issues. Lets drill down on this issue and come up with a repair that works. Having bought and worked on a core 3.9 V6 engine I now better understand the mechanics. My current focus is getting the current engine in the truck to run right. I began my search for a replacement PCM yesterday no luck yet. I did speak with a company that reconditions PCMs. If I find one send it in and they will fix it. I'd send mine in but need the truck. Once I have one checked and repaired I'll send mine in. I'll go over my notes and see what I can put together in the way of, I have tried and the results. Steve
 

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Discussion Starter · #2 ·
A few months ago I had every reason to believe I'd have my new project engine completed by now. The engine in my truck has a couple of issues that kept me from doing more than min required. Someone jacked the truck under the oil pan. If that's not enough it appears a timing cover was replaced and where the cover meets the pan roughly what appears to be two tubes of silicone have not fully stopped the leak. I have an extra pan but changing in frame does not appear reasonable. While some books mention timing chain under some of the codes I don't buy that. My plan is to renew the cooling system, remove clean reseal intake and clean TB. I'll have to get a few things. My new engine has reused block, crank, head castings, intake and valve & timing cover. Every thing else is new. I'll get started soon. Steve
 

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Discussion Starter · #3 ·
I'm not much different from anyone else. I have a wife, son, daughter, dog, cat and a few fish. Since I have been thinking of chasing running issues the truck has been on good behavior and the house has presented issue after issue. A truck you can park and jump in something else. Having the fridge and whole house AC go out at the same time was a hoot. I'm now a fridge repair man. While my younger brother and I designed and installed the AC in my home built in 1910 little brother has passed and I no longer can carry my end of a 4 ton air handler to the third floor or remove the old one. All good on the home front and the truck is back at it. I am so over this bad running condition I even looked at another Dakota this week. It turned out to be a 2000, 2wd, auto, 4.7 V8 club cab Sport. I was given a phone number at first and the fellow selling had no idea what it was. He first told me it was 2003 (that's my year) with a 318 V8. A quick check with my friend the Mature Marine and we knew something was funny. At first I was excited thinking of asking Ralph how to convert a V8 to a 6 cyl. Once I saw the truck I was really unhappy. It has not been well cared for and has the clear coat cancer. It does have options, electric windows, cruise, sliding rear window the big rear end with 4.10 but drums. Interior is much better than in my truck and seems to have been a non smoker. The frame is very clean and the under side little or no rust. Why is it people bump something just ahead of the right rear wheel? Other wise the body is nice and mostly bumper cover in the front needs attention as well as all over paint job. I walked away but now have a new plan. Steve
 

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Discussion Starter · #4 ·
The new plan is rethink this whole truck thing. I bought the truck because it was cheap transportation and I could get the AC working. I really like the Gen 2 shape. I also like the extra secure space the extra cab provides. It is likely a truck in this weight range would be better off with a V8. It's to late I have already spent V8 money on a V6. I'm currently leaning toward making in frame repairs and once it runs like it should sell it to someone needing a basic truck. I'll be on the hunt for a much nicer truck to house my new 3.9 V6. I tend to buy the next before I let one go. Steve
 

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Discussion Starter · #5 ·
OK, I have just about had enough. Coming form a long line of we don't accept no very well. In spite of spending money on parts, machine work and lots of my time my new 3.9 V6 won't be complete until additional parts become available. Current expected delivery date maybe December this year. The truck was giving me about a good week and several bad days. I have a family of four drivers. Last week we had 4 cars and the truck on the road. Due to ongoing running issues with the truck we now have 5 cars and the truck. When three are approaching 200,000 miles a spare or two is good. The new replacement is two years old and under 20,000. I'll be buying another in the near future for the wife. Following that the hunt for a really nice 03 3.9 V6 club cab rwd manual 5 speed. low miles just plain nice.
While none of the above is important, I now feel free to park the truck for awhile and begin sorting the running issues.
1st. When it runs right I'm very pleased with it's empty performance 14/16 mpg town 19/20 highway.
2nd. When it runs bad max 6/7 mpg. Can not maintain idle stalls at stops, and a vacuum gauge shows zero vacuum.
3rd. I have yet to have the time to figure where the vacuum is going. Or the size of a leak that would do this.
4th. Black smoke and constant pumping the gas pedal is only way to get moving.
The list of codes goes on 300, 303, 172, 171, 121, and 305 recently. I had wanted to do a complete direct engine exchange but the bast laid plans. I feel I must resolve this problem with the current engine. Steve
 

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P0303 indicates cylinder 3; P0305 indicates cylinder 5; P0300 says "Gots mor'n one boss".

P0171/P0172 means the system is running too lean or rich (yah, go figure.)

Didn't you do the plenum already? I'd first be checking that AND all vacuum lines.

Then check EGR - if there's a bad EGR leak, it could cause it to run excessively lean at times.

I'd also check the intake manifold / head gasket pair to make sure they (especially the 1/3/5 one!) isn't leaking at times.

Since it's OBDII, I'd also seriously consider data logging several items - MAP readings, TPS, EGR demand, O2 etc while driving - a ELM327 Bluetooth OBDII adapter and Torque Pro (to get its wider datalogging capabilities - don't sweat, the program is under $10!) to see what the ECU THINKS is going on.

Time to break out the late 20th Century tech on it; the ECU will tell you if you but ask it why it thinks it's doing what it's doing.

And then we can apply logic to why it thinks that, and work on the problem!

RwP
 

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Discussion Starter · #7 ·
OK, Ralph I really am ready to step off into the dark side. It appears there are as many ELM327 adapters as people wanting one. I'd like to get the correct stuff right off. You didn't reply to the 121 code ( poor performance to high intake temp ). It looks like I'll end up doing what I should have done to begin with. Pull the engine, strip, hone, clean, cam bearings, freeze plugs, valve job, timing kit, rings, bearings, gaskets and water pump. I'll surface the flywheel and add a new clutch. Steve
 

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OK, Ralph I really am ready to step off into the dark side. It appears there are as many ELM327 adapters as people wanting one. I'd like to get the correct stuff right off. You didn't reply to the 121 code ( poor performance to high intake temp ). It looks like I'll end up doing what I should have done to begin with. Pull the engine, strip, hone, clean, cam bearings, freeze plugs, valve job, timing kit, rings, bearings, gaskets and water pump. I'll surface the flywheel and add a new clutch. Steve
Sorry, was so busy with the others I forgot the P0121.

That's not a temp code .. .it's a throttle position code.

P0121 DODGE: Code Meaning, Causes, Symptoms, & Tech Notes (engine-codes.com)

That can easily be a bad ground causing the voltage back from the TPS to be too high; a bad connection causing the voltage to never go high enough; or just a bad connection. Or a bad TPS for that matter; I'd be probing it with a multimeter and seeing what my TPS is actually doing.

(Hint: There isn't a code 121; there' a code P0121 and maybe another letter with the 0121 - but OBDII codes are four digit, not three. And the letter? Yah, it makes a difference.)

You're right about that; ELM327 is like saying "Sealed Power ring set". It's the actual chip used within. But here, you realize that the cheapest crap is cheap crap, right? Find one that has decent reviews and grab it.

RwP
 

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Discussion Starter · #9 · (Edited)
Some days I have more trouble with computers than others. I'd really like to get the correct electronics for testing first time out. Could you take a look at the Autel MK 808 OB2? I'd like to get it all in one package. If this is not what I'm looking for inform me. Thanks Steve
 

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Discussion Starter · #10 ·
I edited my last post and have yet to get a reply. Not surprised but will continue to look for info here. Or I could start a new thread. I have looked at systems in the $3000 range and hope something a little less could work for me. Thanks Steve
 
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