How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Doug Your Own Question
Doug
Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 6945
Experience:  Mitsubishi employed and Factory trained ASE certified technician
21364095
Type Your Mitsubishi Question Here...
Doug is online now
A new question is answered every 9 seconds

Mitsubishi Eclipse Spyder GT: Why do I keep throwing a random

Customer Question

Why do I keep throwing a random misfire code?
Submitted: 2 years ago.
Category: Mitsubishi
Customer: replied 2 years ago.
Engine boggs down during misfire
Expert:  Doug replied 2 years ago.
Hi,
Do you ever see any other codes or is it always strictly P0300?
Do you have a scan tool that can display live data?
Customer: replied 2 years ago.
Always strictly p0300 and yes I have a scan tool
Expert:  Doug replied 2 years ago.
Thanks.
Lets run the engine and monitor your long term and short term fuel trims, both at idle and at cruising speed. Let me know what sort of figures you are seeing there.
Customer: replied 2 years ago.
I have already done that at idle st and lt stay right at 0 at cruising speeds the st and lt vary but doesn't go below -8
Expert:  Doug replied 2 years ago.
Thanks, ***** ***** never get anywhere near neutral trim when cruising?
Please pull a spark plug wire out and check it for spark, and tell me as accurately as you can the color and intensity of the spark.
Customer: replied 2 years ago.
Sorry I was thinking about the wrong data.........sorry I have looked at a lot of data the past couple days st and lt fuel trims stay at 0.0% and show no change at all while cruising idling flooring or anything else the fuel trims don't even flicker off of 0.0%
Expert:  Doug replied 2 years ago.
Hmm, that is a much worse situation then. You are absolutely certain they never change off 0%? Thats pretty much PCM territory there and not where you want to be.
Customer: replied 2 years ago.
I'm pretty sure but let me go out to the car and pull the data again and get you some more accurate numbers and give u a definite of what the fuel trims are
Expert:  Doug replied 2 years ago.
Thanks, ***** ***** sure because it will definitely change the direction we go.
Customer: replied 2 years ago.
Would u just like me to give you the values of what it does or would you like me to add videos of what it does?
Expert:  Doug replied 2 years ago.
Just peak values and behavior is acceptable. We are just wanting to see if you are leaning more one direction than they other etc.
Customer: replied 2 years ago.
Ok
Expert:  Doug replied 2 years ago.
Thanks
Customer: replied 2 years ago.
I'll get u the values in about 20 min
Expert:  Doug replied 2 years ago.
No problem.
Customer: replied 2 years ago.
Ok at idle bank 1 st is staying at 4.6% until the misfire kicks in then goes to -4.6% then up to 25% and then slowly fluctuates
Bank 2 st is peaking at 14.1% and fluctuates from 2.2% to the peak
bank 1 lt is staying at 7% and bank 2 lt is staying at -4.5%
Customer: replied 2 years ago.
Cruising is pretty much the same type of activity
Expert:  Doug replied 2 years ago.
Thanks.
That is pretty well all over the place. Lets do this:
Start the engine up and let it idle, monitoring the fuel trims at the same time.
Take a pair of clamping pliers and pinch off each vacuum hose one at a time and see if you can influence the trims (note that the EGR hoses will cause the engine to stumble/stall... don't worry about those).
Then take a can of brake parts cleaner and spray all around the intake/plenum/throttle mounting areas, the hoses, etc and see if you can notice the engine react to it or see the fuel trims adjust.
Customer: replied 2 years ago.
I know for a fact that there are no vaccum leaks I have smoked the entire vacuum system including the intakes
Expert:  Doug replied 2 years ago.
Lets check it out anyway, especially since a smoke test won't show internal leaks (solenoids... the reason for the clamping).
Customer: replied 2 years ago.
ok it did not influence the fuel trims at all
Expert:  Doug replied 2 years ago.
Thanks.
Lets pull a plug wire and check the color/intensity of the spark. Looking also to see if there is any variation there.
Customer: replied 2 years ago.
Does it matter which wire or just pI'll the easiest?
Expert:  Doug replied 2 years ago.
Just the easiest.... since you are seeing random misfire and no specific cylinder, I am suspecting that we are probably having weak spark issues across the board or fluctuating spark intensity. So just pull whichever is easiest (probably #2 or #4) since they all feed off the same coil.
Customer: replied 2 years ago.
Saw no variation in spark I could get the wire about 1/2" to 3/4" away from the distributor cap and still get the arc which I believe at least 1/2" is spec correct? but any more than that and the arc goes away as for color it's pretty much the same color as lighting a really bright white with maybe a tint of pink or a tint of blue to it couldn't tell all that well as the battery was in my way
Expert:  Doug replied 2 years ago.
That really doesn't sounds too bad. Typically we will start seeing yellow or orange in the spark as the coil weakens.
We did have two different software issues to address P0300 on this model, but neither usually had much of a drivability aspect, and more just the fault code itself. That is what makes me more concerned with actual hard problems like spark condition, fuel pressure, etc.
That being said.... do we have the ability to check operating (running) fuel pressure?
Customer: replied 2 years ago.
No with this vehicle there is no way to check fuel pressure without having the adapter to install Which I do not have........let me give you a little bit of background maybe that will help us a little bit more
Customer: replied 2 years ago.
The car ran perfectly fine then I had a cam gear break off which sent the timing belt flying in short all of the intake valves on both heads got bent......I then rebuilt the heads had them decked and the whole 9 yards with them after putting the motor back together I had the random misfire code never really felt much of a drive ability issue afterwards though then about a week after everything was put back together I had an issue where anytime it was put into nuetral it stalled out that turned out to be number 1 cyl spark plug was cracked so I did a full tune up on it and it fixed the whole time I was still throwing the random misfire code then the car was in the yard and it snowed needless to say the car had gotten stuck in the ground so I had a friend pull it when he wrapped the tow strap on it he wrapped it around the rear crossmember that has the wheel speed sensor wires running on it and snatched it a few times and couldn't get it out then he realized it was still in reverse so he took it out of reverse and gave it one more snatched and it came out but when he did he broke the left and right wheel speed sensor wires and it lit up the anti lock brakes light so I took it to work and it was bogging then. I fixed the wires the light went out and it has been bogging ever since however it usually only boggs at more than 75% throttle but it is misfiring as it bucks when going slow if the rpms drop too low. And it has been misfiring since
Expert:  Doug replied 2 years ago.
Thanks.
Was the misfiring present after the engine repairs were made, or not until after the event where it got stuck and had to be towed?
If it was present right after the repairs, do you know how much material was taken off the heads (these can't be resurfaced technically)?
Customer: replied 2 years ago.
It was present right after the repairs and no I do not know exactly how much material was taken off the heads however I have tried different heads on the motor and seems to be exactly the same I mean whether or not they were resurfaced I still have good compression so it shouldn't be an issue at all the only thing that would have changed is compression ratio and that change would have been so miniscule that it wouldn't even register
Expert:  Doug replied 2 years ago.
The odds of trying other heads and them being cut drastically too are pretty thin so that is probably a non issue. The primary problems you run into with cutting too much off the heads are too high of compression or belt shift (from the cam gears being closer to the block). Low compression is never really an issue.
With the direct correlation between the engine repairs and the problem occurring I am at a bit of a loss... I'm not usually one to settle for coincidence, usually there is a connection when problems occur right after repairs etc.
However given what we have checked/found so far, the only thing of consideration I can find is the fuel pressure and there would be really no possible connection there with the repairs.
Would it be possible to borrow/rent a fuel pressure tester from anyone? You would need a "bullet" style test adapter (bolts in between the high pressure line and the rail).
The only other places I can think to go with this would be to check TPS output and make sure it is smooth and linear with no jumps or dead spots, and as a huge long shot check the catalysts for clogging/deterioration (often you will notice a reduction in exhaust pressure at the tail pipe if really bad).
Customer: replied 2 years ago.
Exhaust is not an issue I have a brand new exhaust system on the car I mean brand new from front to back I have already checked the output voltage of the tps and set it........which the output voltage should be from .6v to 1 volt at idle correct? I do not know of anyone who even has the adapter I would need for the fuel pressure I can check my local speed shop but I doubt it
Customer: replied 2 years ago.
And my timing belt is tight and my compression values are 160 across the back 3 cyls and 160 across the front which is a pretty healthy motor
Expert:  Doug replied 2 years ago.
Correct, around 600mV at closed position is right.
Compression is pretty high... was it ~160 on the other heads too? Typical is 100-120 psi. A 25-40% increase in compression is nothing to sneeze at.
Customer: replied 2 years ago.
Look it up on all data the spec for the motor for compression is 174 the min value is 127 and the max difference is 14
Expert:  Doug replied 2 years ago.
Those sound like either 4 cylinder specs of Mivec specs. Official specification from Mitsubishi is 119 psi ideal, minimum 83 psi.
Also, I just checked on Alldata and they are showing 824kPa which is 119 psi.
So I'm not sure where you got that figure from, but it is very incorrect. If you meant "Chilton" or "Haynes" then I would not be surprised... they seem to go out of their way to have incorrect information.
I am stepping out on break (was supposed to stop a half hour ago) but should return in an hour.
Customer: replied 2 years ago.
I'll send you a screen shot of it it's Def on alldata
Customer: replied 2 years ago.
Screen shot is added 1200kpa on alldata site which is 174psi 890kpa min
Expert:  Doug replied 2 years ago.
Yeah that's wrong. I don't know what they did, but it is wrong.
Here is from Alldatapro:

//f01.justanswer.com/ref/http_i.imgur.com/owfsWgA.jpg
And here is direct from Mitsubishi:

//f01.justanswer.com/ref/http_i.imgur.com/5doNM60.jpg