Dirty air filter or fuel filter? symptoms? tests?

CSXfan · #1 02-27-2008, 11:45 PM

Hi all,
Sorry for all the posting lately. You guys have been a huge help since I joined.

I'm trying to figure out what's wrong with my '94 Dakota 3.9 4x4 auto. The truck sat for about ayear in a hay field needing a new tranny before I bought it.I can barely maintain speed in 4th gear and acceleration in 4th is impossible. It's getting 12-13mpg. When warming up it backfires/hesitates/bucks under acceleration. 5 minutes after warming up it runs great, but it still has no guts at higher speeds.

Soooo... I changed the dist. cap, rotor, plugs, wires, o2 sensor, coolant temp sensor, thermostat (180*), timing chain, catalytic converter, muffler, PCV valve,crankcase breather filter, and the water pump. I have also cleaned the TB and the IAC solenoid. The timing has also been re-indexed. None of this has made any difference.

All this has lead me to believe that it either has something to do with the fuel pump or maybe the air filter. The fuel pump was replaced with an Airtex electric pump back in Oct 2006. Is Airtex a decent brand? Could a fuel pump go bad that fast? Or maybe it's the fuel filter? How can I test the fuel system?

I don't know when the air filter was last replaced if ever. There is some crud on the filter but I don't know what is normal. Is there a test I can perform to see if a dirty filter is what's causing my problem? I plan on getting a K&N filter in a couple months so I'd rather not buy a new one now if it's not going to help. I'm going to the dealer Friday so I'd like to be a little more educated so they don't try to screw me. If anyone has suggestions, I'd love to hear them. Thanks in advance.

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TheePlaymaker · #2 02-28-2008, 12:20 AM

i would just hold out on the filter and wait till your gonna get the k and n im pretty sure you'd would be able to tell my looking at it if it was teh problem or not it would be pretty obvious

lghtngblt02 · #3 02-28-2008, 12:02 PM

Hey thats why we are on this forum, to talk about our interests and problems. Well after reading your post I noticed you havent replaced the fuel filter. If it has sat for a year its possibly gunked up, I would change the filter and run some sea foam through it. I dont think it would hurt. Filters are relatively cheap.I doubt the pump would be going bad, usually it would not start if that was the case. As for the air filter, like pitkanen44flyerssaid, you should be able to tell if its plugged. It would be super dusty, to the point where just handling it, you would have a decent amount of dirt on yoru hands. If after you replace your fuel filter and its still giving you a problem, it only leaves your exhaust system, by that I mean the CAT could be semi-plugged. By the way, is it spitting any codes out?

Nicegy525 · #4 02-28-2008, 02:16 PM

probably not the air filter. Definitely replace the fuel filter and re-test. If thats not it I would look at the ignition coil. If thats not it, run a compression test to see if you have a dead cylinder.

lghtngblt02 · #5 02-28-2008, 03:23 PM

Hes got a point there, but I would think the ignition coilwould likely act up more when its hot instead of cold though, but its a try

TheePlaymaker · #6 02-29-2008, 12:44 AM

do the first gens have fuel filters because the second gens are built into the tank?

lghtngblt02 · #7 02-29-2008, 08:36 AM

Yeah first gens have an inline filter. The third gens are just like the second gens, like you said, the filter is internal. The fuel filter on the first gens islocated on the inside of the drivers side frame rail, towards the back of the cab. It has some quick clips on it, pretty easy to get off. Just make sure YOU RELEASE THE PRESSURE. There is a schrader valve on the drivers side fuel rail is where you can release the pressure. If you dont do it, you are going to eat fuel, which I heard isnt to nutritional!

Good luck!

CSXfan · #8 02-29-2008, 08:13 PM

Thanks for the replies,
I did a little searching around and I may have found something. I was talking to a former dodge technician and he said that some of the older daks had problems with the PCM regulating the fuel flow at certain temperatures. He said that when the air tempgets under 50* the fuel flow gets messed up.It will run fine for 8 minutes and thenbegin to misfire randomly.After10 minutes of driving it willrun fine again. That sounds exactly like what's happening to mytruck.

It's funning in a really stupid way, I bought my truck and drove it home on the only 60*January day Michiganhas ever had, so the truck ran fine when I wastest driving it. [sm=headbang.gif]