i had the same problem with my 97 K2. i replaced all the same parts you have and got nothing. after having to take it to a shop, they found that my catalytic converter was completely clogged. it was glowing red hot after a test drive. they disconnected the pipe and said it ran like a champ. i get the car back tomorrow (monday) and im replacing the cat myself. they told me that my fuel pressure regulator was also bad do to the excessive amounts of back pressure. this is something you can check. not sure that it will fix it, but its something to check. good luck and let me know if this helps.

 

I replaced the original cat and I still am having the same problem, it seems to be getting worse. My CEL is always on, flashes on the freeway and I still can't figure out whats going on. I have also replaced the MAF sensor and ECU any ideas would be very appreciated.

 

sounds like one or both of your o2 sensors is giving you some grief.

 

Thank you for the quick response, just one question; wouldn't a faulty o2 sensor throw a code? If not which one would you say is most likely to be the cause of the problem?

 

It did throw codes:

P0300 - Multiple Random Misfire
P0301 - Misfire cylinder one
P0302 - two
P0303 - three
P0304 - four



All kidding aside, if the computer is detecting too rich or lean a mixture, it will try to adjust ignition timing to keep the engine within stoichiometric balance which could be the reason for the excess carbon buildup under the distro cap (you stated you replaced it already).

That being said, it sounds like the injectors are letting too much fuel through causing an overly-rich mixture which will foul out the plugs and throw the O2 sensors for a loop (plus damage/destroy the cat if left for too long). I would go with bodankie's suggestion of testing the fuel pressure regulator.

Remember, spark, fuel, and air are needed to make your engine run. You've ruled out spark, I can't anticipate any issues with your air (unless your MAF is on the fritz....test it just to be sure), so the next step should be fuel.

Mike (MKIII Emeritus)

 

Check the timing. The belt might have stretched or slipped enough to throw it off.

 

When I took the car to a shop they checked the timing belt and said it was exactly where it should be. To check again what would I do?

Here is a list of what I have replaced as of today:

MAF
ECU
Plugs
Wires
Distributor and Cap
Coil
Cat
Before cat o2 sensor

I bought the after cat o2 sensor but I'm hesitant to put it on. I keep throwing money at this car with absolutely no results.

As a side note I pulled the distributor cap off today and there was a significant amount of buildup on the contact points.

Any other ideas would be greatly appreciated.

 

I would check the cat. I know you said you replaced it, but mine broke apart and threw exactly the same engine codes. also when does the car misfire, under acceleration or at idle?

 

keehn - thank you for the response, what is the best way to test the fuel pressure regulator? Will I be looking for a certain psi?

meadormt - the cat is about 2 months old and was brand new when i put it in, the car was having this problem before I replaced the cat and immediately afterwards. I will check but i do not believe it is the problem. The misfire occurs when its idling, under heavy acceleration and is really bad on the freeway (around 3000 rpm or above the CEL is constantly flashing)

 

Fuel pressure regulators very rarely go bad. You can tell if their bad by taking the hose that goes from the regulator to the intake manifold off. If it sprays gas, its bad.

 

Do I disconnect the hose while the car is off or running?

 

Running, its just a vacuum hose. So if fuel is coming out then its bad. Disconnect it from the intake manifold.

 

No fuel coming out of the fuel pressure regulator. I drove it today and while going up a hill something happened, the car now feels like its running on 3 cylinders.

 

Whats your gas level at? The reason i ask is because i suspect your fuel pump. Since it happened when you were going up hill, the fuel goes to the back of the tank and the fuel pump is at the front. The pump might be getting weak.

 

Turns out it was the Distributor cap I just purchased, there were sparks going everywhere. So solved that issue but I can still feel the car misfire at idle, when I accerlerate it hesitates and like I said before at or above 3000 rpms it gets pretty bad.

I still need to replace the downstream o2 sensor (which I will do tonight) but I have a feeling that isnt the issue. I also have a lifter that sounds like its about gone, could this be causing any issues?

 

the downstream o2 (post cat) does not affect driveability at all, it's only there as a monitor to check catalyst efficiency on obd2 vehicles.

if you were misfiring due to a faulty distributor cap then i suggest that you check and see if the plugs are fouled. a can of seafoam will help to decarbon the combustion chamber if that is the case, or simply a fresh set of plugs.

if it persists, then check your engine vacuum. most guages have indicators on them where the arrow points as to possible issues that could cause the running condition. then just verify them one at a time.

on a side note, a damaged cat will not break a fuel pressure regulator, but a faulty fpr can ruin a new cat. so can prolonged misfires and rich running conditions. and if you smell sulfur (rotten eggs sorta odor), especially after a spirited run, it does not indicate the cat is dying. it's actually working. but this is info for another thread, as i do not wish to hijack this one. (sorry...)

check the simple basics first (properly of course) before guessing by throwing random parts at it. (the dealers do that enough under warranty anyway...)


df

 

Thanks for the info, I won't replace the downstream o2 sensor.

I have replaced the plugs,wires, cap and rotor multiple times because the problem persisted. I replaced the upstream o2 sensor a couple of days ago and I can still feel it misfiring. This car has had this problem since two owners before me and multiple shops have not been able to figure it out (though I don't think that says much).

Where do I begin checking the vacuum? And what do you consider the simple basics?

 

simple basics would be most of what you have replaced already, the 'expected' wear parts. others would be things like the fluid levels and filter conditions/age, as well as age/condition of the battery and cables. and belts. a goofy charging system can really screw up the system, as can excessive resistance in the groung circuit(s).

when i did my engine performance assessments (ep's), everything started with the battery and charging system. if these aren't up to snuff, then don't even bother trying to figure out anything else because the entire electrical system supports the rest of the vehicle systems.

that being said, if battery and charging are good, then check the engine vacuum. tie into the fuel pressure regulator with a 't' fitting to get a reading. the guage should have a guide on the face to point you in the general direction of what to inspect for.

being a random misfire like you describe, though, and the fact that you have thrown lotsa parts at it, i suggest that you take a peak at the crank sensor. do you have extended crank times?? difficult hot restarts?? other goofy driveability issues?? a power graphing meter is a great tool to inspect this component if you can get one to use.

hope this helps.


df

 

had this happen on my mustang ... i would check if the fuel injectors are dirty or clogged

mine was a big leak on the intake manifold ... i used my air compressor to bolt it on when i replaced it and i didn't torque it to specs or sequence.

this is another thing you might try to do .. take your intake manifold out and check for cracks or if its broken.
its easy and you can do it at home

CAUTION: don't forget to use a torque wrench to torque it down
and check the specs and sequence as well (don't do the same mistake i did, it will throw more codes if you didn't) ... also you can replace your intake gasket while your at it.

before you start taking your intake manifold out, i would check the vacuum psi on your vacuum lines, if its too low then its definitely a vacuum leak

also if its not there is a smoke test that you can do at the mechanic shop and it would show where the leak is.

good luck man