Hey guys, I have a 2002 dodge ram with the 5.9 with mild modifications like tuner, headers, intake, and exhaust. The plenum has been fixed, along with new cap, rotor, plugs, 180 tstat, highflow cat, and o2 sensor. The problem I am having is with cold starts or starts after prolonged sitting, for example after sitting 10 hours during work. When the truck starts up cold MOST OF THE TIME the engine misses, shudders, and sounds like its running on an odd number of cylinders. The exhaust smells like unburnt fuel when this is happening, and I had a buddy tell me I was shooting black smoke when I was showing him my new exhaust (this was a cold start up, however I am unsure if he was just pulling my chains since I have never noticed black smoke myself). I have done a bunch of research and believe I have nailed it down to the ECT. My truck has the one sensor and I decided to test its resistance when the truck is cold and NOT running. I got a cold reading of 12450 ohms, which I believe is high based on what I have read online for other vehicles, but I do not know what in spec resistance is for our particular sensor/sending unit. Could someone hook me up with what in spec resistance should be for our ECT's?

The ECT seems easy enough, but what has me puzzled is that I have read that this particular cold starting phenomenon could be the result of a leaky flow back valve within the fuel pump. People say that priming the fuel pump say 3 or 4 times before starting can diagnose this problem so I tried this and it seemed to help with the cold starting (i tried this 3 times, it very well could have been luck). However would a faulty fuel pump ever make the exhaust smell like unburnt gas?? This is what has me stumped since it seems like this would cause a LACK of fuel to be supplied . Sorry for the long post guys, but thanks ahead of time for any input.

 

Put a gauge on it, and check fuel pressure when cold.

Unburnt fuel in the exhaust is either running rich, or, misfiring cylinders. Black smoke does indicate running rich.... May have a leaky injector, failing ECT, or a number of other problems.... have you done anything with your cat since the plenum fix?

 

I replaced the cat and o2 sensor along with the plenum fix. I forgot to mention that the rough running clears up after a minute or so of idling or driving. It use to throw a cylinder 8 misfire code while it did this before the plenum fix, but after it with the new cat and o2 sensor I haven't seen it since (although it still cold starts like sh*t). So test the fuel pressure while running from a cold start, correct? How expensive is this tool from the local auto store??

Any input on whether my ECT is out of spec??

Thanks so far HeyYou

 

You can download the 01 service manual from the faq section here, it will have wiring diagrams and such, and also should show specs for the temp sensor. (or, I may have found the chart I was looking at online... been a bit ago, just don't remember....)

Fuel pressure gauge can be had for 40 bucks, or, around in that neighborhood, at the parts store. They also rent them, but, I think the deposit is like 150.00...... (seems ridiculous to me, but hey, that's just me.....)

Put the gauge on the engine when it's cold, before you start it. See what the gauge does on initial prime, and see where pressure gets to while cranking. (should be around 49PSI.)

 

Turns out the ECT is within spec and thanks for the link by the way. I will report back with my fuel pressure findings.

 

A little update:

I was unable to rent a fuel pressure gauge, however I managed to chat with a truck mechanic at my work. He said he has seen symptoms like this occur due to the ethanol in todays gas shrinking the seals in the fuel pump. He said adding a lubricative fuel additive may do the trick in freshening the seals and restoring their ability to maintain fuel rail pressure after shutdown. He suggested adding half a quart of ATF fluid into my next tank of gas, however I am a little worried that this may damage my new cat and o2 sensor. Is this safe or is there any other reasonable alternative to using ATF fluid in the fuel system? Does this sound like a proper diagnosis even? Thanks guys

 

Never heard that one.... I can't think that burning ATF would be good for cats, or O2 sensors though.....

 

I have run ATF through the gas before....back in th 70's (BC) before cats....but to cut carbon loose, like we use seafoam today.

Fuel pressure gauge is pretty inexpensive. And very useful.

What brand O2 sensor did you put in?

 

It's an NTK o2 sensor. It seems like the consensus here is to not try this old school method. What about putting some marvel mystery oil in the gas, is that o2/cat safe?

 

There isn't anything you can put in the tank to 'swell seals' that isn't also going to cause numerous other issues. If you have over 100K miles on your truck, it is more than likely time for a new pump in any event. Get the pressure gauge, test things. See what that tells you.