Rough idle at start up

Iceman86

Iceman86

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Jun 8, 2014
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Hey guys, new to the forum. I bought a 2001 Ram 2500 Cummins and it idles rough at start up, then smooths out but the check engine light comes on and the tach goes away. Any idea /experience on what it could be? I was thinking a possible ECM issue. Runs and drives fine in all conditions after about 15 seconds.
 
Codes? Probably air in the system for a rough idle at startup. Does it start right away or take a while? Search for losing prime. There is tons of info out there. I don't think the ECM is controlling anything at idle. Possibly a bad ground for the tach going away. Ever get a no bus message on the odometer?
 
I thought it was air as well. Dropped the tank and it did have a crack in the pick up tube, so I fixed that. I do get a cam sensor code, even after just replacing it, and it won't clear with the SOLUS Pro reader. The tach works, but only during the 15 sec or so that it idles rough. Almost sounds like an injector is out. Then it smoothes out and tach stops working and the check engine light comes on(off during rough idle). Also, starts up quickly, even when it was around 55-60 degrees out. I'll check the buss code on the odometer.
 
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Stock filtration and lift pump? Gauges? If you have the stock fuel filter, clean out the housing real well, replace it and make sure the lid is tight with a new 0-ring. If you can, make sure you are getting good pressure. It really sounds like air is getting in somewhere. I'd just get an aftermarket lift pump to replace everything and be done with it. $.02

Whenever you get the "no bus" message, you usually loose other gauges so check them when it happens. I'd still bet on a ground/short for your tach. You can try to tighten up the connector in the fuse box under the hood that contains all the wires going into the cab.
 
does it have an 01 ecm on the truck? if not, it may have an older ecm, looking for the sensor and not finding it. you may try and have the truck reflashed...
 
Thanks for the input guys. Hydroshok, I do have a raptor on it with half inch lines, but I'll go through everything and make sure there is no air getting in there. As far as the check engine light goes, I think I'll have to cover it up for inspection, and figure that out a little later. Damn Germans are strict on that stuff.
 
Did you make sure it is getting good pressure? I finally talked a friend into installing a gauge on his ad150 and it was only making ~10PSI. He went the cheap route and got a $10 oil pressure gauge if money is an issue for you. They work exactly the same so the reading will be accurate.

You can take out the check engine light bulb in about 15min. Pull the bezel off the dash, take out 4 screws and pop the cluster out. Make sure you shine a flashlight in there after you take it out so you know you got the right one.

Loctite 545 is good for connections to make sure it is not sucking air. With my setup sucking through a filter, I had prime issues till I started using the loctite.

Did you try that connector in the fuse box or changing the fuel filter? Do you drain the water? I highly doubt it is water, but you never know. The fuel does come out of the bottom of the filter canister to the pump right? It's been so long since I had a stock fuel system...
 
I like the oil pressure gauge idea, that'd be pretty easy. I have a remote filter/water seperator housing with a manual primer pump after the raptor. I'll try that loctite stuff on those connections. I normally drain my water seperator monthly.
 
Way over done personally...

Park the truck nose down to verify if it starts easy then its truly a air leak. As for finding air leaks just take the truck out and drive it a bit and return back to your shop. If you don't load the fuel system up with fuel you'll get a no leak result. Use a air gun and put a small another of pressure in the fuel tank. If there is any leaks externally the fuel will show up a wet spot. The other spot is the cross over tubes tend to loose o-ring and easy to replace.

As for your error codes you can look up most of them here.
http://articles.mopar1973man.com/2nd-generation-24v-dodge-cummins/59-obdii-error-codes
 
I dont think the rough Idle has anything to do with the fuel system, given that the quits and it instantly runs smooth. I'm leaning toward ECM or wire issue
 
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I double checked all my connections, and inspected the lines from tank to injectors. No leaks, or anything that would suggest air getting in the system. Same symptoms whether the truck is hot or cold, has a full tank, or about empty. Parked it nose down and still had the same issue. I think I'm gonna take it in and have the ECM re-flashed. Hopefully I get an answer as to what it is once Dodge hooks it up.
 
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