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Hi my name is Keith and i own a 1993 dakota 2wd 3.9l automatic with overdrive. I have owned the truck since feb of this year. When i first got it it seemed great thought i had a steal becuase the truck only had 69k miles (almost at 73k now) about a month after i had it i started to notice a problem with it. It starts fine on a cold start and roars to life ( love the sound of these magnums at a low idle) however after it is warm and shut off for any longer than a few mins and up until it has cooled all the way down it will struggle to start and when i get her going it idles real low and sputters and if i try to floor it and get it above 2k rmps i hear a sort of knocking noise(doesn't sound good at all so i try not to do that) so i just tap the gas to get it up about 200-400 rpms until it returns to a normal idle (this sometimes takes a few minutes) when i first noticed this problem it wasn't so bad but recently has gotten alot worse (i'm scared to go anywhere in my truck right now) things i have replaced since i've had it include fuel filter, distributor cap and rotor, spark plugs, also had a leak in a hose and the flange to the thermostat houseing not only had a small hole rusted in it it didn't even belong on this truck so i replaced all my hoses (excluding the lower radiator hose) and i replaced that flange and the thermostat itself. I was told my problem could be a few different things first one was the fuel pump but then another person told me it wasn't because when the truck is running right it doesn't hesitate. earlier i replaced the fuel filter (thought it could of help although it doesn't seem to have but it never hurts to put something new on there the one on it looked factory) and it was still warm so it struggled to start so i put some gas directly into the throttlebody to get her going and when i put the gas it it bubbled up quick so the throttlebody was REAL hot and when it first started it the throttlebody made a hissing noise so the dude whos house i was at when i replaced the filter told me i should have the throttlebody looked at but i'm only 19 and can't even find a job right now so my pockets are shallow and if i could get enough to take it to a shop chances are i can't afford any parts so i want to try and figure this out without taking to a shop so i can just buy parts and fix it on my own (want to be a mechanic so i try to do as much as possible on my own) the truck also has a freeze plug leak nothing to serious at the moment just don't have time to drop the tranny to get to it i add some water to the radiator every 2 or 3 days seems to leak maybe a quart in that time period and looks like it still has a good amount of antifreeze in it. If anyone can help me i'd be extremly appreciative. i read someone seemed to be having a simmular problem on a 2002 ramvan with the 3.9 in it this was posted on this site.
 

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Welcome to Allpar. Start with diagnosis. You may want a service manual to read about the possible causes of 'Hard starting-hot'. The public library might have a detailed service manual for loan. A main library might even have the factory service manuals.
You may be able to get fault codes from the PCM that would give you a direction to go in.
A fuel rail pressure test when hot would help diagnosis. The ign coil could be another possibility, sometimes these would give a weak yellow spark or no spark at all while hot cranking. Mounted by the right exhaust manifold, these took a beating.
Pay attention to the hot start knocking noise, you may also have carbon build-up issues.
 

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Get the codes for free yourself:
http://www.allpar.com/fix/80s-codes.html
There may be something to point you to what you need to fix.
I suspect there's a sensor or the coil that fails when heat soaked.
 

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Welcome to Allpar.

There could be a couple of causes for this. The knocking noise when you rev it makes me wonder. These engines were known to wear out timing chains by 100K miles or so, and have a redesigned guide/tensioner. If the chain is worn or stretched, fuel injection timing may be off a little.

A common cause of hard hot starting and low idle is the Throttle Position Sensor. These can wear out so that the contact area inside is intermittent. They cost about $20-$30 and are easy to replace. They screw onto the throttle body with 2 screws and have an electrical plug with 3 wires.

Let us know what codes you get.
It was a little hard to read your post without punctuation. I'm sure you are anxious to get the info out and get answers, but if it's a struggle to read, we can miss some of the content, and others just won't read it.
 

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Discussion Starter #5
sorry about the lack of puncuation, yes i was very anxious in posting this. having a rather bad week if you can't tell. Thanks for the imput i will look into it immediatly and come back with the codes.

Also i thought it could of been the ignition coil which i havn't replaced yet and still will, but i'm pretty sure i'm getting a spark. will check the codes now.
 

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Alright so i got the codes and it seems to have spit out a 12(battery died on me when i went to a concert a few weeks ago, friend moved it and left the lights on..) a 51 so accourding to the link valiant posted, my O2 sensor is stuck in lean position possibly due to my MAP sensor being bad going to look into that now. last code obviously a 55. any other imput on this is appreciated!

So at my local autopart store the manifold pressure sensor is $52 plus i have a $10 coupon so gotta see if my mom can't loan me some cash so i can replace this today.
 

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Check the vacuum lines, a poor vacuum signal to the MAP can cause that code. That's even cheaper than the MAP sensor.
 

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Discussion Starter #8
Check the vacuum lines, a poor vacuum signal to the MAP can cause that code. That's even cheaper than the MAP sensor.
Which brings me to my first post when i said i seen someone on this sight with a ramvan with the 3.9l which had simmular if not the same problems. i came across it looking up info about the engine which ultimatly lead me to this sight.

http://www.allpar.com/mopar/39.html

If you scroll down to where it is tittled "common repairs"

It says the 3.9l's were known for vacum leaks at the "belly pan gasket" so could this be my problem and how would i check for this and how can i check my lines.

I'm now hoping it isn't the map sensor because I went down to a neighbors house who owns a 87 dak and lent me his book and i was asking him if he knew where the sensor is located and he didn't know. He also said when replaced it needs to be reset with a computer which i have no idea how to do or if that is even the case.
 

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If the intake belly pan gasket is bad, you'll likely have a rough idle and be using some oil. With the engine off, just take off the air cleaner, hold the throttle open and shine a flashlight down the throttle body bores. If you see oil pooling there, it's being sucked in because of a failed belly pan gasket.

As for needing a computer reset after a MAP replacement, I don't think that is necessary.
 

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Discussion Starter #10
If the intake belly pan gasket is bad, you'll likely have a rough idle and be using some oil. With the engine off, just take off the air cleaner, hold the throttle open and shine a flashlight down the throttle body bores. If you see oil pooling there, it's being sucked in because of a failed belly pan gasket.

As for needing a computer reset after a MAP replacement, I don't think that is necessary.
I looked down my throttle body bores and didn't find a pool of oil but i did notice some black residue not alot just some specks. It was hard to see being it's sunny out so i plan on checking again later when it gets dark and maybe take a pic to put on here.

Also my vacum lines look to be in good condition they are not factory so someone has replaced them in the past. How can i check them to be sure there is not a problem with them.
 

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Discussion Starter #11
About to just get a new ing coil and plug wires (current ones look factory) and start there. I do have my hands on a service manual now so I will be reading into depth about a possible issue.

Is there any reason that my freeze plug leaking will effect the truck in this manner, I do make sure i keep coolant in it and my temp gauge seems to keep steady but it does seem like my truck gets hotter than it should (if you lean on the front fenders after or while it is running they are real hot) and stays hotter longer than it should(have come out to after an hour of it sitting and still feel a good amount of heat from the grill). I've also read about people having a small leak on their freeze plugs and just not fixing it because they're such a pain to get to. but making sure they keep coolant in their radiator.

I definatly want this problem out of my way as soon as possible because for one it's very stressful and even more so because i do not have a job and can't seem to find one. So i have no money and even though my mom would not hesitate to help me out i can't stand asking her for anything.

One more random question. i'm due for an oil change in about 300 miles and thought about changing my differential oil aswell just wasn't sure on how often that should be done. It probably has never been done before by the looks of things i've replaced on it looks like no one cared for this poor truck :(

Plan on keeping it forever as it is my first vehicle maybe one day in the future i can make it into a fun weekend toy.
 

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OK, based on the codes, it's the oxygen sensor. The sensor is ignored for cold starts and the first 2 minutes or so of cold driving, then a bad one can cause hesitation, bucking, poor power and gas mileage and stalling. If the MAP sensor were bad, you'd have problems when cold, also.

The oxygen sensor screws into the exhaust, I think it's in the Y-pipe.
 

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Discussion Starter #13
OK, based on the codes, it's the oxygen sensor. The sensor is ignored for cold starts and the first 2 minutes or so of cold driving, then a bad one can cause hesitation, bucking, poor power and gas mileage and stalling. If the MAP sensor were bad, you'd have problems when cold, also.

The oxygen sensor screws into the exhaust, I think it's in the Y-pipe.
There is one in right before the catalytic converter and one right after. I can't afford to replace both at once so should i do the one before it now and see if it helps? or wait untill i can do both?
 

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So i believe i found the problem. On the idle air control valve there is a little ruber washer that i think dry rotted away so the valve stays open when it should not be.. when the engine runs without the air cleaner after the truck was warmed up shut off and started again later when it struggles it whistles loudly. So i bought a new valve and will change it first thing in the morning. *fingers crosed*

really hope this was my issue the part was $45 and then i can try and save for a new paint job, the current paint job is newer probably done within the last year but it looks like it was done on someones carport, they didn't sand it or even prime it. on the lower rear fender it is starting to peel and the original tan stripe is under it.
 

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When there are two oxygen sensors, the front one is the one that primarily controls the engine mixture. The second one behind the catalytic converter has less effect on the computer as it the primary function of the second one is to ensure the catalytic converter is working. I am surprised there are two on a 1993 model vehicle, I don't recall my 1993 Dakota having two.
 

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1993 would be OBD I and might have right and left O2's, but I don't remember it that way either Mark. I remember one in the left exhaust manifold.
Throttle bodies and AIS ports can make loud hisses and whistles with the air cleaner off. I wouldn't be too concerned as long as everything is clean.
Definitely look into why the O2 sensor is throwing a code. It may not be the O2 sensor itself, but a real problem with the mixture that it is 'sniffing' as it goes past it. It may be way rich or way lean and the O2 sensor may be telling the truth. 'Universal' Bosch O2 sensors can be wrong.
I would avoid buying more parts until this is diagnosed, unless there are obvious visual problems that you see with them. We are still in the process of determining the problem. Are the spark plug tips white or black?
 

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There is no upstream and downstream O2 sensor in the 93. They didn't use downstream until OBDII, which was 1996 model year for most vehicles.
 

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My statement of the two o2 sensors may not be true i read it off another site. i replaced my spark plugs within two weeks of buying the truck i do not rememeber if the tips of the olds ones were black or white i can pull out some of the new ones though.

Drove my truck to the autopart store yeasterday there was a good line so i thought it would struggle to start when i came out but it fired right up. One of those cases of it not wanting to be fixed i guess. have not replaced the iacv yet i looked into it and apparently if i do replace it i need to disconect my fuel rail connecting lines because they are a hinderence. Having never done this before how hard is it to disconect and then reconect those.

I will go look at my spark plugs now and be back in a few minutes with your awnser.
 

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I pulled one of my spark plugs the tip of it seems to be white, so this means it is running lean?'

just so i know so i can get the awnser to this when the next person sees this. i replaced my plugs about 3k miles ago, with them being slightly white at the tip if you suggest for me to replace my o2 sensor should i also get new plugs?

Also what brand of o2 sensor should i purchase, i read on a forum that the boshe have a different case design than the stock o2 sensor so after 10-15k miles it starts to effect engine performance.
 

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Thanks for all the insight so far from everyone by the way. I appreciate the patience i don't know to much about vehicles and even though this whole situation is stressful i am enjoying the learning process.
 
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