2G Throwing up 2 CEL Codes But Driving Good - Codes P0302 & P0174

[bo0st]

The car is a 98 420a with minor mods I/H/E MSD ignition + wires, pulley, small spray (profile is up to date)

Turned on the car today and got a CEL. Car drove fine so I rolled down to Autozone and got these printed out.

As you can see it says: Troubleshooting P0302

Definition:
Cylinder 2 misfire condition
Probable cause:

1. Ignition system faulty (Don't think it's this as I've replaced both wires + plugs about 1100 miles ago, NGK plugs with MSD wires)
2. Fuel system faulty (I bought a Lucas Fuel System Cleaner for $6.99 today and put it in the gas tank, maybe it'll work?)
3. Vacuum leak (I think this one is the most probable as sometimes the RPM's go up while in Park. sputters to 1100 - 1400 then back down, then back up.. Sounds like it?)
4. Engine mechanical condition

The second one is: Troubleshooting P0174

Definition:
System too lean - cylinders 2 - 3

Probable cause(s) are same as before:

1. Ignition system faulty (Don't think it's this as I've replaced both wires + plugs about 1100 miles ago, NGK plugs with MSD wires)
2. Fuel system faulty (I bought a Lucas Fuel System Cleaner for $6.99 today and put it in the gas tank, maybe it'll work?)
3. Vacuum leak (I think this one is the most probable as sometimes the RPM's go up while in Park. sputters to 1100 - 1400 then back down, then back up.. Sounds like it?)
4. Engine mechanical condition




Once again spark plugs are new NGK (about 1100 miles ago or less) + new MSD ignition Super conductor wires. The car is driving and sounding normal, shifts great, can't really notice anything except the 'CEL' light bright up in my face.

Please help any replies are greatly appreciated!

 

[n0de]

Honestly I would think this has to do with plugs/ignition system but if you think they are alright then I would try clearing the codes and see if they pop up again. If it does pop up again then try and remember the conditions that caused the CEL to turn on, i.e. Under WOT while spraying...

 

[Silver71]

What was the item number for the spark plugs you put in? You most likely know what you're doing, but did you run the right heat?

Did you use any dielectric grease during that install?

If your system is too lean, maybe you have dirty injectors? Maybe you have bad injector seals? I'd def. look for vacuum leaks as well.

Did you do a compression test?

 

[bo0st]

Honestly I would think this has to do with plugs/ignition system but if you think they are alright then I would try clearing the codes and see if they pop up again. If it does pop up again then try and remember the conditions that caused the CEL to turn on, i.e. Under WOT while spraying...

Thanks for the reply. I have cleared the codes earlier today with my CEL scanner. They haven't popped back up yet, but I only pulled in and out of the driveway so I'll give it a few miles or so.

What was the item number for the spark plugs you put in? You most likely know what you're doing, but did you run the right heat?

Did you use any dielectric grease during that install?

If your system is too lean, maybe you have dirty injectors? Maybe you have bad injector seals? I'd def. look for vacuum leaks as well.

Did you do a compression test?

During what install?

NGK BKR7E I believe 2 step colder than stock so that I could spray.

I have put in a bottle of the Deep Clean Fuel System Cleaner by Lucas so I'll see if that helps it clean it out any bit.

Compression tested 4 - 6 months ago, checked out good.

Any other advice guys?

 

[Silver71]

During what install?

During the installation of the new plugs and wires. Just throwing it out there that it is good to use dielectric grease on the spark plug wires (the end that contacts the spark plug).

Have you considered trying Sea Foam? Plenty of info on that out there.

 

[bo0st]

During the installation of the new plugs and wires. Just throwing it out there that it is good to use dielectric grease on the spark plug wires (the end that contacts the spark plug).

Have you considered trying Sea Foam? Plenty of info on that out there.

I have not considered Sea foam as it was never mentioned to me by someone I trust.

The codes were cleared days ago as I mentioned and today only 1 code popped back up, maybe the lucas helped a little?

Code: P0302

Making progress

 

[KewlWinter]

Some of the things that can cause the misfire code are:

1. Faulty crank sensor. Could be cracked, or connector is crudded, or someone has replaced the connector and just twisted the wires together or used butt connectors instead of soldering.
2. Faulty cam sensor. Same as crank sensor for problems.
3. Valve cover leaking oil into the spark plug wells causing intermittent grounding.
4. Vacuum leak due to hose popped off/broken/missing, throttle body leak at shafts, intake manifold gasket.
5. Injector plugs crudded, seals failing, injector failing.
6. Bad plug or wire.
7. Crack in coil housing.

I have personally run into the bad wiring on the crank sensor plug, bad intake manifold gasket (due to improper torque), and oil in the spark plug wells as causes.

Happy troubleshooting!

 

[bo0st]

I think it's something fuel related. It went down in rpms a little more than it 'usually does' but however I was driving more than I normally do. How do I check to make sure it's getting enough fuel?

 

[KewlWinter]

Check the fuel pressure with a gauge. You can get one cheap from Harbor Freight, or invest in a gauge that mounts to the top of your fuel filter. Speaking of fuel filter, when is the last time it was changed? If you havent already, you can also do the fuel pump rewire. The kit is about $15.

 

[bo0st]

Not sure about the last time the fuel filter was changed, but the spark plug from #2 cylinder wasn't looking that good for 1,000 miles. My mechanic said it could've been a million things but I'm going to try to replace them with some new spark plugs tomorrow and see how it goes. Thanks for all the support everyone!