420A Ghost cause of P300 CEL

[dj98eclipse]

Hello dsmtuners,

I am entirely new to the forum and I have a good problem for the detectives on here to see if they can help me out. I have a 1998 Eclipse GS that has a misfire. The code is P0300 Random Misfire and separate codes for misfires on cylinders 1-4. The car definitely does misfire enough that it can be felt/heard by anyone in the car. I have just had the engine rebuilt to stock specifications and all gaskets are new (No oil leaks). The coil pack is new MSD, wires are new MSD, spark plugs are new NGK. All the sensors on the motor have been replaced, the transmission was rebuilt and just about everything else has been either rebuilt or replaced. All of the ignition components were replaced after the misfire started in order to try and fix it, but nothing has changed.

So I guess more to the question and less of the story. I am curious if anyone else has had any issues with the stock computer similar to mine. Also any tips or tricks to diagnosing said misfire would be helpful. I just had the car smog tested (Love California smog requirements) and the car passed all tests with flying colors except the hydrocarbons were just above the limit which caused a fail. Is there any way that a clogged catalytic converter could cause enough backpressure to upset the engine and cause the CEL?

Any help is appreciated!

 

[codym]

Your ignition timing could be off, it would cause the misfires and high hydrocarbons as well. Get a timing light and set your base ignition timing to 5degrees BTDC.


Also verify your plugs were gapped correctly. .044" for N/T's.

A worn out cat could explain the high hydrocarbons, but not the misfire unless there is something clogging it pretty good to affect the exhaust stroke.

 

[dj98eclipse]

Ok I will pull the plugs and check the gap as well as check the timing and see what that does. Thank you!

 

[dj98eclipse]

Your ignition timing could be off, it would cause the misfires and high hydrocarbons as well. Get a timing light and set your base ignition timing to 5degrees BTDC.


Also verify your plugs were gapped correctly. .044" for N/T's.

A worn out cat could explain the high hydrocarbons, but not the misfire unless there is something clogging it pretty good to affect the exhaust stroke.

So I regapped the plugs from .048 to .044. How am I to go about checking the timing on my engine with stock cam gears. How do I set it up with a timing light and check?

 

[PlanZero]

I'm very interested in your findings. I've had a cylinder 3 misfire code for over a year now (it goes off occasionally, but for the most part the cel stays on, blinking at idle- which signifies an active misfire). However, this is my third 420a and if anything she runs better than my previous two.

 

[dj98eclipse]

PlanZero-
Yes, it has been the bane of existence for two local shops and my garage for over a year now. I had an oil eating problem a while back and it ran dry on me one day so the engine was toast. I got it fully rebuilt and when I finally got it back together it had that CEL. It will definitely be interesting to find out what is the cause of it though. I sent it to a third local shop that has a top of the line scanner and a computer reflashing tool to see if they can trace it or set factory defaults and get rid of it. My guess is the PCM because I have checked and rechecked everything else.

codym-
I have ruled out the spark plug gap as a problem and I am having them look at timing this week along with the PCM.

 

[evileclipse909]

You've done the obvious compression test correct? Double and tripple check your timing belt timing as well. Also check your injectors to see if they look clean. And finally I would check for loose or detached grounds.

 

[codym]

So I regapped the plugs from .048 to .044. How am I to go about checking the timing on my engine with stock cam gears. How do I set it up with a timing light and check?

Apologies for taking a while to reply. You don't need aftermarket cam gears to verify base timing, nor do you need a fancy digital timing light, an inductive one will work fine, and will probably confuse you less.

The process is rather simple, hook up the power wire to the battery, the ground somewhere on the chassis that would provide a good ground, and the clamp around Cyl 1 spark plug wire. The light will start flashing, aim that sucker towards your Crank Pulley and look where the line on the pulley crosses the Timing Reference Marks. You want it to be at 5 degrees BTDC at idle.

PlanZero-
Yes, it has been the bane of existence for two local shops and my garage for over a year now. I had an oil eating problem a while back and it ran dry on me one day so the engine was toast. I got it fully rebuilt and when I finally got it back together it had that CEL. It will definitely be interesting to find out what is the cause of it though. I sent it to a third local shop that has a top of the line scanner and a computer reflashing tool to see if they can trace it or set factory defaults and get rid of it. My guess is the PCM because I have checked and rechecked everything else.

codym-
I have ruled out the spark plug gap as a problem and I am having them look at timing this week along with the PCM.

I'd do a compression test, or get one done to rule out the possibility.

 

[honda_burner]

I had the same issues on a 97 talon. CEL would come on and go off for random misfire. I ended up using the engine for another shell I had purchased and upon tear down of the engine to replace the head gasket (for peace of mind), I found that one of the cylinders had burnt valves and was leaking down the intake pretty badly. Car is back together now, and runs like a champ.

 

[wrencher]

The codes you are getting are P0300 P0301 P0304? Not 1 thru 4?
I am just trying to be sure.....
If it is 1/4 I would be concentrating on the ignition system.
Being 1/4 are companion cylinders pair in coil etc.
There could either be a problem with the PCM coil driver circuit or The PCM is mis-precieving there is a misfire.

Over the years (25 years being a tech)I have seen a wide variety of issues causing this.
I limited this list to a few due to the OP stating this is a non-perceivable misfire or no drivability issues.
Because of that I don't think the OP has a run of the mill misfire/SES light problem.

Seen wiring problems to the coils causing odd misfire codes due to connections. Had to rewire completely with new connector terminals & wire to fix.
Have had intermittent issues with coil drivers inside the PCM causing misfire codes. (I'm referring to 420 & like engine based vehicles)

Another issue is specially with a new long block is Crank/Cam correlation. The Chrysler based PCM can be really finicky about this one. So yes the T-belt needs to be dead on. Hopefully its not a strange crank sensor signal issue.
Now unfortunately I would use a digital storage oscilloscope to test for all of the above.

Being that your in Kalifonia I would bet there is an emissions specialty shop that can handle this problem. That is if all your basic checks = plugs, t-belt, wiring all check out....

 

[paack]

I am overwhelmed, I think I will go but a manual for my DSM .

 

[dj98eclipse]

paack - I bought myself the Chilton's manual a while back and it is pretty helpful on the basic stuff. However, all of this problem solving is way far beyond what is included in the manual.

wrencher - I am getting PO300 PO301 PO302 PO303 PO304. I have triple checked the timing belt but I will do it again for good measure. It has been through the best smog shop in town and a couple other shops for diagnosis but it is beyond everyone who has seen it so far. Hence the reason I had to resort to forum help.

honda_burner - I definitely had some bad valve seals due to an earlier problem with a faulty oil pump with 150 psi (Not good). Since then, I have had the engine cleaned up and regasketed top to bottom and no more leaks. Still running rough though.

codym - I will definitely check the timing as soon as I get the car back from the shop. Thanks for the info. I am so used to working on muscle cars that I have no clue as to a lot of stuff on these small FWD cars haha. Never thought about a compression test. I will also try that.

evileclipse909 - I have not yet done a compression test (Don't know why that didn't come to mind first). I have triple checked the timing belt but I will check it again for peace of mind. The car is at the shop right now having the fuel system (injectors, rail, ...) checked because I had a problem previously with the rail getting all rusty inside while the car was torn apart. Making sure that didn't happen again although it would surprise me since the new fuel rail/injectors were installed earlier this year. I have been looking through the wiring, but as far as grounds go, I checked those out first thing when I noticed this problem.


UPDATE: Thanks everyone for the tips. I have been looking at things personally on and off as well as having the car sent to a local shop that deals with mostly imports. One issue I had that the shop found was a faulty EGR solenoid. I went to the local parts store and got a replacement EGR Valve and solenoid setup. I installed it the other day and so far the check engine light hasn't come on yet. However, it doesn't seem to run any better. The car shakes when at partial throttle like it did before so I know that the problem isn't fixed.

 

[GS Dude 52]

I have the same problem with my 96 GS automatic. I have a CEL and only get the P0300 code. It's significant enough that people walking down the sidewalk can hear it when it misfires. Replaced timing belt, exhaust, plugs, wires, throttle position sensor, thermostat, crank position sensor, cleaned the throttle body and everything on it.
Everything I've done helps a little but it still runs terrible. I know my idle air control valve is bad but I don't have the money to fix that when there are other things wrong. I've swapped out the coil pack but that didn't change anything. It really only sputters on acceleration sometimes during a bump, all wires are secure. It's a nightmare but I did buy it for $500. Should I get a new coil? Or computer?