Question about fuel filter

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Feb 17, 2007
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Clermont, Florida
This is about my 2001 Dodge Dakota. 3.9 liter V6 with a 5 speed manual. 165,200 miles on the odometer now. Old school cast iron Mopar Magnum engine, it has no EGR. I have been trying for about 4 weeks now to fix an odd problem with the idle in my truck. Normally it will start right up and idle at 700 RPM, no matter what the temperature or weather might be. About a month ago it had a no start here at home. Engine cranked and started but had a very low idle and died. I tried it again, it turned over fine but just would not start. I let it sit a few minutes and did get it started but the idle was very low, maybe around 200 or 300 and I had to pump the throttle to keep it going. I held the throttle at about 1200 RPM a minute or so and let off, then the truck idled and drove fine after that. That exact same starting/idling problem has continued up until now, but I only had a no-start that one time. If the truck sits overnight, and I start it in the morning it will idle low, 200 to 300 RPM for a few seconds, run rough and die. If I goose the throttle a bit and hold it upwards of 1000 RPM for maybe 20 or 30 seconds the idle returns to normal and the truck will run just fine all the way to work, which is 20 miles one way. When I leave work in the afternoon, the truck starts, idles and runs fine right away and all the way home. Then the next morning, same thing again with the low rough idle and it dies unless I goose and hold the throttle. I have done a lot of things over the last 3 or 4 weeks trying to fix this problem: New plugs, Autolite 3923's. They are not the OEM spec plug but I have used them nearly all of the time I have owned my truck, and it runs great on them. Gapped at stock gap spec, .040. Cleaned throttle body with throttle body cleaner spray New Autolite Professional plug wires Distributor cap and rotor, Napa Echlin parts New Duralast Gold battery, pro-rated warranty exchange New Throttle Position Sensor, Duralast brand New Idle Air Control Valve, BWD brand from AAP Back in November, long before this cold idle problem ever started I replaced the two mini-cats and main cat with an Eastern Catalytic assembly from Rock Auto. Also in November I replaced both downstream O2's. Upstream O2's have about 50,000 miles on them. All 4 O2's are NTK. I have also sprayed carb cleaner around the engine trying to find any vacuum leaks. The idle never changed no matter where I sprayed the carb cleaner. This past Friday I checked my Intake Air Temperature sensor, it was about 200 ohms out of spec on a hot idle so I replaced it with a BWD sensor from AAP. My scan tool tells me the Engine Coolant Temp sensor is steady at 182 degrees so I believe it is OK. I use a 180 degree t-stat and the colder heat range Autolite 3923 plugs to help avoid preignition ping, which is a common problem on Dodge Magnum engines. I checked the fuel pressure, the engine was cold but I put my fuel pressure gauge on the test port then got it running here at home, at 700 RPM I had 50 psi. I shut the truck off, left the gauge connected and 10 minutes later there was still 40 psi in the fuel rail. I replaced my fuel pump about 40,000 miles and 4 years ago. I used an Airtex pump that I bought from AAP with an online discount code. I have since read about problems with Airtex pumps but never had any problems with mine until now. The pump I bought only had a one year warranty, but Airtex now carries a lifetime warranty. AAP just now told me most likely they will have to go by the original warranty (which expired 3 years ago) or I can try to ask the store manager if he can do some kind of good-faith good customer return on it for a new one. Now to my question. Someone told me last week the fuel pressure can still be within specs whether the engine is running or not but if there is a problem with the fuel filter it can cause this kind of wonky idle problem. The filter is a sock at the bottom of the fuel pump. The same guy also told me the fuel outlet at the top of the pump also works as a filter and can become clogged with dirt/debris which can cause the same problem with normal fuel pressure yet a bad idle on a cold start because the fuel volume is reduced when the filters are dirty. There is no external fuel filter on my truck. Even if I do need a new fuel pump I am not so sure I will go with Airtex again after this problem and reading about other Airtex issues. I am trying to find out if anyone here has seen a similar problem where the car ran fine when warmed up but wold not idle on a cold start due to lower fuel volume, and if so then did/would a new fuel pump solve the problem? Sorry for such a long post here but I figure the info is relevant to help me get some ideas of whether to replace the fuel pump. I appreciate any help.
 
Joined
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NJ, USA
When you replaced the IAC did you clean out the hole that it lives in? If you didn't, a bit of carbon could be your problem.
 

Jimmy9190

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Clermont, Florida
Thanks for the info. IAC orifice is spotless. I had cleaned the TB not long before this problem started and I cleaned the orifice again when I put in the new IAC. I put my scanner tool in the truck tonight so I can check live data tomorrow. I think if the short term fuel trims are too positive while I am driving, maybe from 8% and up it might be an indication the fuel pump volume is weak. One thing I remember is both times when I took out the IAC the plunger was extended all the way out. I wonder if there is a vacuum leak somewhere that I can't find and that is the PCM's way of compensating? Seems to me that if there was a vacuum leak I would have a bad idle all the time, not just when cold started?
 
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Slimy Mudhole
To discard the fuel pump you need to check the fuel volume it delivers; disconnect the hose going to the fuel injectors and put some container activate the fuel pump from the relay for 30s or more and see how much fuel it delivers. A normal flow would be about 1.2 to 2 liters per minute. If you indeed have a bad fuel pump I would expect to see the long term fuel trim (LTFT) above 30 % since the computer compensate the low pressure by opening more time the injectors if you have access to a scanner could be a good idea to check that value But I think your problem could be carbon deposits in the intake valves and manifold, since it only happens when the engine is cold, the carbon deposits prevent the fuel from getting vaporized making a rough start or no start; if your intake manifold is to complicated to remove you could take out a fuel injector to see the intake valves.
 

Jimmy9190

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My truck surprised me this morning. It started up and the rpm dipped down around 500 and came right back up on its own to about 800 then settled at 700. The short term fuel trim was 1.6 to 4.7 on both banks coming to work today. I did not look at any other specs while driving because it was foggy outside and I really needed to concentrate on the traffic. The stft makes me think the fuel pump is ok. I can't help but wonder if a BG intake cleaning might help.
 

Jimmy9190

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Clermont, Florida
Here's an update..My idle was way off on Wednesday morning and again when I left work that afternoon. Not only did it idle low and try to stall out when I first started the engine, it was also idling down very slowly and the idle was erratic as I was slowing down for red lights, stop signs, slowing down in traffic, etc. It was not running at all like it should. This all pointed to a bad IAC so Wednesday night I tried an experiment. I just happened to have on hand an OEM IAC that came with my V8 throttle body when I got it from the junk yard some years ago. I removed the new IAC I had put in just recently then I cleaned up that old OE IAC and put it in. Truck has been starting quick, idling like a new truck and running much better. When I start the engine it idles up around 900 RPM and drops to about 700 normally and on its own. I don't have to goose the throttle or hold it any RPM, it is running like it should now. I also filled up the gas last night and added a bottle of Si-1 for good measure, in case there might be an injector problem. So far my truck is running great, not a single problem since I swapped out the IAC. I guess I could get AAP to warranty the IAC for free or maybe bite the bullet and get another OE IAC from the Dodge Boys but I read that BWD is the OE supplier anyway. The BWD sensor has a Dodge part number on it.
 
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