"I have a 1998 dodge dakota 4 cylinder 5 speed. The engine is new with 40 miles on it. The head is totally rebuilt new valves, guides, springs etc., new pistons, new cam, lifters, pushrods, rocker arms, new injectors, new crank sensor, new distributor, new cap, new rotor button, new plug wires, new ignition coil, new timing chain, new timing chain tensioner, This engine is new except for the crank and rods... This engine still does not have any more power then it had before it was rebuilt? I'm lucky if I get 15 miles a gallon! It still cuts out or kinda of like a surge or something when you give it gas to get going? The check engine light works but it is not on! Any ideas what the problem could be? Could it be the oxygen sensors or what?
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That would mean your cat may be bad or even plugged up/old
It could be an O2 problem also or even MAP sensor
Pull the air temp sensor and clean it... it may need replacing they get covered in oil at times.
Just testing sensors doesn't mean everything is ok sensors get lazy and show up as good all the time I say replace all your sensors at the 120 to 150K mark even if still running good
If your cat is not welded in just clamped in take it off and take it for a drive see what happens you may get a dash warning but if it runs way better its the cat
Don't forget to reset the PCM so it starts blank
Also taking it off gives you a chance to inspect it you may find its plugged up good if you cant see inside give it a few good whacks with a hammer then shake it if you hear things rattling inside its toast
The exhaust was tested they don't think it's stopped up because it blows real hard out the exhaust tail pipe.... I had the cat off a few months ago it looked brand new I could see thru every pin hole. The computer is throwing code for a bad cat I just can't see the cat being bad considering how good it flows. I replaced the upstream oxygen sensor but not the down stream I was told the down stream didn't control the engine it was there to tell when the cat was bad
Then I would jump on the down stream O2 $35 I think NTK is best I have Bosch and have no problems but everyone says they are bad but so far my Bosch have been ok for me I think the V8 and V6 don't like the Bosch
You were given BAD information. Change the downstream sensor. This is from the factory manual:
Downstream Sensor: The downstream oxygen sensor (1/2) is also used to determine the correct air-fuel ratio. As the oxygen content changes at the downstream sensor, the PCM calculates how much air-fuel ratio change is required. The PCM then looks at the upstream oxygen sensor voltage and changes fuel delivery until the upstream sensor voltage changes enough to correct the downstream sensor voltage (oxygen content). The downstream oxygen sensor also provides an input to determine catalytic convertor efficiency.
The 2.5 engine has a flaw that's irritating but easily avoided and you listed it the take off from a dead stop to acceleration burp/hiccup the only way to avoid it is feather the clutch and gas it this gets you past the burp/hiccup that's why I'm always fastest off the gun green light.
You may have put the timing chain on wrong or a bad or misaligned distributor.
The 2.5L is a very simple engine
By the way I have talked to many 2.5 owners and everyone has the burp/hiccup problem
Check the intake manifold gasket you should never use a thick gasket only the thin ones why they develop air/vacuum leaks after a few months... use the OEM thin gaskets only