Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
I have a 1997 Dodge dakota 3.9 litre V6 229k+ miles with new spark plugs, distributor, cap and rotor, spark plugs wires, fuel pump, crank sensor and new upstream and down stream O2 sensors. Replaced the fuel pump when it failed, shortly there after the crank sensor failed and replaced. Now I have 7 DTCs P0300 followed by P0301, P0302, P0303, P0304, P0305 it runs fine at cruising speeds and at idle you can feel the misfires and hear passing through the exhaust. The manufacturer states that there are t different sizes of gas tanks for my truck, standard 15 gal. tank and an optional 22 gal tank, not knowing before hand the size of tank I bought a pump for a 15 gallon tank, now for the main question will that fuel pump cause low fuel psi in turn causing the multiple misfire? Also when I was looking at the 02 sensor readouts from my diagnostic scanner the 02 sensor s are both registering 0.8 mv, would that signify that my catalytic converter is failing or has failed?
Either fuel injectors need to be looked at, test o2 sensors for being stuck rich/lean (make sure it achieves closed loop before tests) or valve adjustment might be needed. As for the fuel pump do the lines hook up with out leaking? Does it fit in the tank properly?
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Ok so every time my Check engine light comes on the primary code is the same P0300 and the cylinders that are misfiring are always different ones. The injectors have been replaced and still comes up as it's misfiring. Still my question hasn't been answered about the fuel pump. Let me try to reword the question on that topic. It turns out that I have a 22 gallon gas tank in my truck. Not sure of the size of tank at time of purchase of new fuel pump I bought a fuel pump for the 15 gallon standard size tank. The gas light comes on at 1/4 tank mark and at 1/8 tank mark on the gage in the instrument cluster it will no longer feed gas to the engine. Will the 15 gallon tank fuel pump over pump gas through the system to cause the misfire issue. This weekend I will check my valve lash and bring that back to spec.
The difference between the two fuel tank sending units is likey shape or size related. They should output the same volume of fuel, (since they are designed to run the same engine, just from a different tank) as long as they are both submerged in gasoline.
However, if you know you have the wrong part for your application, I would recommend changing it for the correct one even if it doesn't fix the problem you are trying to solve now.
Are you able to check fuel pressure at the injectors? Spec is 49.2 psi +/-5psi.
How are the fuel trims at idle, compared to high engine load?
What is the Load Pid doing at WOT under load? (ie Calc. LD / ABS Ld. pids)
Do the IAC counts change from idle to high RPM? if you hold the throttle plate open just a smidge at idle do the misfires go away? This will allow for just a little more air to enter.
First the fuel tank issue the 22 gallon tank must be deeper than the 15 gallon tank so likely the fuel pump is drawing air on the last 1/3 tankful this will cause a lean misfire.
Clear the codes and check for a misfire and fuel trims on a full tank of gas.
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I will look at the fuel time at idle and also under load and post them. I do not have a way to check fuel pressure at the injectors. The misfires go away when just cruising down the road and on an occasion I will feel a misfire. Under a load such as accelerating up hill it will misfire and will be felt.
Im not sure I or we understand the problem fully.
1st this is a consistent misfire at idle and sometimes under high load correct?
2nd we need a graph snap shot with more information than just the single frame relevent info would be ECT, MAP, 02S B1+B2 1&2 (probably only has B1S2 for downstream), RPM , LOAD PID . and maybe more depending on results . however I suspicion this is a compression problem which can be caused by valve lash but at 220+k miles it may be worse i would highly suggest a compression and leak down test....
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