Hello everyone . I have a 92 dakota 3.9 .220k miles on it . I am having a problem with it and CANNOT figure this out . My problem is .... when I start my truck it runs fine ....then after it starts to warm up it starts to backfire, stutter, barely idles runs real rough and starts pushin a ton of excess air through the IAC ( extremely loud hissing ) ... I can push the gas pedal to the floor and it does nothing ( will not rev) ...the only thing I can do to keep it alive is to pump the gas pedal slightly to keep it from dying ...after 5-10 minutes of this ...it clears itself and runs fine . I don't smell a ton of fuel when this occurs . I also noticed yesterday that when it was doing this I put it in gear and it changed the tone of the hissing , I tested this several times . This only happens when the truck initially warms up . I will list all the things I have done in an effort to correct this problem .
New EGR / transducer
New TPS
New IAC
New coolant temp sensor
New thermostat
New distriubtor / pick up coil / cap rotor( indexed)
New battery and cables
New ignition coil
New crank sensor
New throttle body gasket / cleaned throttle body
Fuel pump 2 yrs new
New fuel filter
New oil pressure sensor
New starter
New ignition switch
New muffler ---removed cat ( does have an exhaust leak right after the 02 sensor )
Plugs/ wires are recent

I have fixed 3 splices by the fusebox..2 of which I know are notorious for burnin up on this truck . I continually check for wiring problems vaccum leaks etc . The truck does not throw any codes other than 12 and 55 . I am at my wits end with this . I must have this truck running in an effort to work .But can't even look for work or accept work if I can't be dependable. My money is limited and am near the end of being able to throw parts at it . If anyone has any suggestions or ideas it would be greatly appreciated . Thank you so much!

 

The backfiring sounds like the timing is off, or misplace wires. The Idle problem sounds like the IAC. I know you replaced it, but even new they act up.

I hate to say but you may just have a wire problem to something, may need to completely take out the wire harness and completely uncover and test it.

It also sounds like a vacuum leak. I know you said you checked, but did you check the plenum gasket? These do leak on these engines, and can cause problems.

 

I have not tested the plenum...unsure how to test it . And yes I am suspect of the new IAC aswell. As far as the wiring goes ..it indeed could be a short somewhere. I can see I am going to have to take it to a shop ...this really sucks...I don't trust shops in the first place and with current economic times shops are hungry and will tell you anything to get your money . Sigh I just went out and started my truck ...I didn't have the IAC wiring hooked up to it accidentally ...it ran real rough upon start up ...I realised it wasn't hooked up ...i re hooked it up and now the truck will start but not idle ....wtf?! I think im gonna snap lol Thanks for the response crazy

 

Some people suggest resetting the comp after chaning the iac. Unplug your battery for a half hour or so and see if it helps.

 

I have done that 100 times ...still no effect. Anyways ....It's on a flatbed on it's way to a shop (got a referral from my parents ). I am done tryin to figure this out ...unfortunately I don't have all the proper equipment to diagnose properly . I am saddened by lettin this truck beat me . Very rarely does a vehicle beat me ...this one has . I will let you guys know what the bottom line is as soon as I find out . Maybe it will help someone else one day that struggled with this vehicle like I have . Thanks for responses ...it is appreciated .

 

Hello again everyone .....so ....took my truck to a shop ....they are telling me that my PCM refuses to communicate with any of their diagnostic equipment .. I have a question for you guys ...the PCM that is in the truck is ...Federal emission / High altitude emission . Part #56028742 . New it has a price tag of 250$. I found another PCM federal emission but not high altitude .Part #4741521. For 112$ Will this part work in my truck? I do live at 4000ft. I am unsure how this will effect my truck if I use this part versus the original part. Will it work at all? Will it create problems for me? I don't have to pass emission in this state for veh registration . The shop I was at doesn't know. Dodge dealer didn't know .( lol big surprise) If what the shop says is true ...that they can't communicate with the PCM..it doesn't surprise me that I was unable to get any codes via ignition key cycle . Anyone got a clue? Thanks for your help!

 

As long as the new computer is for the same year, engine, transmission it will work. Good luck, that is an expensive part! If you want to double check take it to most auto part stores, they can check the codes for free.

 

Well Crazy ...the thing is this...the shop tried hooking it up to 3 different diagnostic tools....everytime it came back that they were unable to communicate with the PCM. Since I know I repaired the splices ..one of them to the PCM...and with their diagnosis that the PCM is bad ..and knowing all the parts I have changed ...there really aren't too many parts left to change ... the other thing is ...they aren't trying to sell me the PCM or do the install... so I ask myself...why would they lie or give me false info ? This is the page that I found the parts ( I know it's autozone :/) ...

http://www.autozone.com/autozone/cat...&parentId=59-0

2nd part down is the one I want to purchase...the last part on the page matches the one currently in the truck . I just need to be absolutely sure that this part that I want to use will in fact work . Also could maybe explain to me what the difference is between the parts? I am unclear why one is high altitude and why the other isn't. And why such a huge price diff? Thanks so much crazy ...you have been helpful !

 

Sure NP.
Not to discredit the shop. But quite a bit of times when they can't figure it out they revert back to blaming the computer. If they were 100% sure it is the computer, have them buy it. If it don't work you dont pay for it.

They make different models due to differnt states laws, emission laws ect. To know exactly the part number, we have the factory part manuals in theFAQ in this section.

 

Ok then ...Ill pull out the PCM and take it to the parts store and see if they can get anything out of it ...if not ...then Ill try the new PCm .Thanks man you rock!