What's Causing Misfire and CEL?

[inertian]

2004 PTCruiser Turbo Lite, 114K miles.

Stumped by the cause of a recurring P0302 code (misfire cylinder 2) and CEL light.

Sequence of events:

• Normal cold start
  
• Drive a few minutes and while stopped at first stop sign or red light idle gets rough, CEL flashes,throws code P0302 (via UltraGauge).
  
• CEL light comes on steadily*
  
• Continue to drive without issue - no additional codes or rough idle, just CEL

A few years back I replaced the upper and lower manifold gaskets to address a similar misfire condition. I have also replaced the stock wires with MSDs, fresh Champion copper plugs and most recently, replaced the head gasket due to oil on the spark plug tubes.

My mechanic just scoped the engine, no oil or signs or burnt valves.

We both checked that good spark is getting to the plugs.

Previously we swapped plugs and wires but the problem stays with cylinder 2.

Possible causes:
Burnt valve - scope shows no evidence, and wouldn't the problem be continuous?

Bad valve seats/guides - could be effected by temperature, but no telltale blue smoke at startup

Bad fuel injector - plenty of power and decent mpg, worth it to pull the head and check?

Suggested Actions:
Add fuel system/injector cleaner - done, no change

Replace original coil pack - would think the problem would be worse once the coil pack gets hot vs only when its cold.

Check/replace ECM - replaced original ECM a few years ago when I couldn't disengage the Security system (car wouldn't start or take reprogram)

Other suggestions welcome.

*If I clear codes by disconnecting battery, the CEL may not come on steadily the first time it flashes.

[Handy_Cruiser]

I see just about every likely diagnostic on you list except a dry and wet compression test.

If you haven't already, do a regular dry compression test first. Then squirt some oil in the cylinders and do it again. If you find a weak cylinder during the dry test and there is little or no change during the wet test, then it's likely a valve. If there is a substantial change, then it's likely a broken piston ring, scored or worn cylinder wall or similar.

If no joy, you might try a set of used injectors or just one different injector for cylinder #2. Injectors can be from any PT turbo model except a 2003 GT.

[inertian]

Appreciate the detailed response.

I would've thought a compression test would be the first thing my mechanic did, but I didn't ask and he didn't say so...

How much of a pain is it to get to the injectors? FWIW, I smelled gas in the cabin when I hit the gas hard after I swapped plugs between cylinders to see if the problem followed the plug (it didn't). After my mechanic pulled, regapped (to .040) and reinstalled all the plugs, that smell has not reoccurred.

[Fk5]

Originally Posted by inertian

Appreciate the detailed response.

I would've thought a compression test would be the first thing my mechanic did, but I didn't ask and he didn't say so...

How much of a pain is it to get to the injectors? FWIW, I smelled gas in the cabin when I hit the gas hard after I swapped plugs between cylinders to see if the problem followed the plug (it didn't). After my mechanic pulled, regapped (to .040) and reinstalled all the plugs, that smell has not reoccurred.

Agree on the compression check.

FWIW, I knew you would smell gas, once I heard that the CEL was flashing. That is usually because of a pig rich condition that will ruin the cat in short order. Pull the upper intake and the injectors are right there. You can usually get a better look at the rest too. Get new o-rings and swap injectors (like you did with the plugs) and see if it follows.

I assume you have the aluminium manifold. Usually it happens on cylinder 4 (P304) but here is what happened to my car - lower gasket blew out and blocked the injector port. The fuel would hit the gasket and not be properly ignited in the cylinder. New gasket and it is fine, but without pulling the intake it was undetectable.

[Handy_Cruiser]

I'd do the compression before looking at the injectors.

However, injectors are easy once the top part of the intake is out of the way. Just remove two bolts, disconnect the fuel hose and pull the whole thing out together. Here's some photos from my turbo engine:

[NitroPT]

Disconnecting the battery. this does nothing except making diagnosis delayed or might even add addition problems. You have a Ultra Gauge use it to properly address DTC.


While I admire the effort the mechanic appeared to miss several normal plans of action for a mechanical health checking of the engine.

Scoping is a visual look and not conclusive without other tests. A properly done compression test followed up by a leak down would be more complete.

If the shop you used has an oscilloscope I can almost guarantee that you will either find the source of the problem or narrow the search down considerably.

STOP.. replacing random parts that are not tested to be a problem. This more times then helpful creates addition issues or changes the perimeters how the original problem may have started?

Use your Ultra Gauge and set up the page to watch:
Ignition timing advance
Knock voltage
o2 sensor output

Make note of engine idle speed values, engine cruise speed values both before as soon as the engine light is activated and a DTC generated.

If you have a OBD Diagnostic scanned to connect directly in the diagnostic port and can read your monitors that will also tell you a lot about the state of readiness most having to do with emission control systems which include the ignition and fueling.

Good Luck

[inertian]

Fk5 - have the aluminum manifold, had a similar situation to yours about two years ago, resolved when I replaced the lower gasket. Did the upper gasket at that time as well.

Handy_Cruiser - thanks for the visuals on the injectors.

NitroPT - thanks for the information and setup advice for the UltraGauge. Added Tiiming Advance and O2 Sensor gauges, couldn't find Knock Voltage. Is it listed as something else?

Timing was -3 in Park, 2 in Drive while idling, ran the range up to 60.5, mostly in the 40s while driving.

The 2nd 02 sensor almost always shows a lower value that the first O2 sensor, and seems to lag behind when changing values. Both display 0 when coasting/foot off accelerator, and went as high at .980 when at highway speeds (up to 80 mph).

FWIW, I warmed up the car for a good five minutes or more this morning before driving, no flashing CEL (although it is still on), no additional codes thrown,

Thanks.

[chris15]

Coilpacks are tricky to diagnose, however, in almost every case I've encountered with a coil pack, you'll encounter timing drift on at least a pair of cylinders, if not all of them. The PCM will command, say, 20* of timing advance at a specific load and RPM, and you'll see two (or less) cylinders will check out at 20* of timing advance with a timing light, and the other two will be off, sometimes wildly (in excess of 30-40*) which will cause a misfire condition.

If you haven't done the coilpack, I'd recommend it. It's fairly simple to replace and usually resolves the vast majority of misfire issues (followed mostly by intake manifold gasket leaks and fouled plugs). If that doesn't do it, or if you'd prefer to, you can also move the fuel injector from cylinder to to a different cylinder, clear the code(s) and see if the misfire follows that injector to the new cylinder. Obviously, if that's the case, replace the injector(s).

If you do find the injector(s) is/are problematic, you can also opt to send them for a professional cleaning. This process is usually fairly inexpensive (around $60-$100 for a full set of injectors), and good shops will also flow test the injectors after the cleaning, so you know what you've got.

[NitroPT]

Originally Posted by chris15

Coilpacks are tricky to diagnose,

Not really!
For some reason people forget that this type "coil" are used trouble free on hundreds of thousands of engine not only Chrysler PT cruisers. LOL
It takes about 10 minutes on any oscilloscope!

But I sorta like the rest of your response! sorta!

[chris15]

Originally Posted by NitroPT

Not really!
For some reason people forget that this type "coil" are used trouble free on hundreds of thousands of engine not only Chrysler PT cruisers. LOL
It takes about 10 minutes on any oscilloscope!

But I sorta like the rest of your response! sorta!

Lol, here we go. I’d say that 85-90% of people don’t have an oscilloscope much less a timing light, so that’s where I’m coming from when I mention it’s “tricky”. Glad you’re able to troubleshoot your own ignition coil issues, though.