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1G Rich misfire

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Anthony Boni

5+ Year Contributor
213
23
May 13, 2018
Wrightstown, New_Jersey
Hello all.

Need to pick your brains real quick. At idle I can hear a hollow, misfire sound. Doesn’t affect my AFR, idle is steady.

While cruising, I hear the same hollow misfire sound, my AFR goes rich (12.7:1-12.2:1), and the car stutters for a split second. It’s random while cruising at partial throttle. During heavy acceleration, WOT, or any boost whatsoever, car pulls like a champ. No hesitation, no stuttering whatsoever.

I know most misfires cause a LEAN A/F ratio, but this one goes RICH. Which is why I’m confused.

I don’t want to make assumptions before I hear your guys’ answers, but I have an idea as to what the problem may be. I don’t want to make a recommendation and everyone focus on that one thing, so I’d like to hear some answers before I comment.

Mods:

I’m using FIC 1250cc low-z injectors, BPR7ES plugs gapped to .018”, datalogging with DSMLink V3. I’m also logging fuel pressure through a fuel pressure sensor, and using a fuel lab AFPR. Fuel pressure is rock solid, no spikes/drops throughout the misfire 450HP E85 fuel pump, currently on 93 octane pump.

NGK blue spark plug wires, stock transistor and coil pack. FP76HTA turbo, FP2 cams.

Base timing is set at 5°BTDC, base fuel pressure is set to 43PSI.

I’m currently at work so I can’t post a log from my laptop (posting this thread off my phone).
 
so only misfires in closed loop................tough to do much with so little info but is this a narrowband sim setup or is front factory narrowband still in place?
 
Could be a low-z Injector or plug gap issue. A log would be great.
Starting at the 1145 second point, to 1185 is a good representation of what I am talking about. Smooth, low throttle position, and you can see sudden rich spikes. Battery volts are solid, fuel pressure is solid, MAP sensor isn't acting funny.
 

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so only misfires in closed loop................tough to do much with so little info but is this a narrowband sim setup or is front factory narrowband still in place?
I locked it in open loop and it acts the same. Narrowband simulation. However, because I can feel and hear the misfire I know it's not wideband related.
 
You could be operating the injectors in their non-linear range, you might even have to use an injector low pule-width adder in your injector table.
 
You could be operating the injectors in their non-linear range, you might even have to use an injector low pule-width adder in your injector table.
That’s what I wasn’t going to mention. Low impedance injectors don’t have the greatest idle or part throttle properties. That being said, why would the misfire read rich? That’s where I am confused.
 
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Well because just like an ignition system misfire, you can have a fuel injector misfire where the injector is operating all over the place, so lets just say that you have the injectors set to actually be rich but they are currently running just fine in a lean condition because they aren't open enough due to operating in the no-linear area of that particular injector but yet you think you have it tuned just fine when in reality if the injector were operating right it would be very rich, then you start cruising and running closer to the linear area of the injector and now its actually too rich because the ecu can control it and actually open it in a linear fashion? On another note, if your ignition is acting up you will certainly end up with a rich misfire since the fuel is being injected but not burning.
That’s what I wasn’t going to mention. Low impedance injectors don’t have the greatest idle or part throttle properties. That being said, why would the misfire read rich? That’s where I am confused.
 
Well because just like an ignition system misfire, you can have a fuel injector misfire where the injector is operating all over the place, so lets just say that you have the injectors set to actually be rich but they are currently running just fine in a lean condition because they aren't open enough due to operating in the no-linear area of that particular injector but yet you think you have it tuned just fine when in reality if the injector were operating right it would be very rich, then you start cruising and running closer to the linear area of the injector and now its actually too rich because the ecu can control it and actually open it in a linear fashion? On another note, if your ignition is acting up you will certainly end up with a rich misfire since the fuel is being injected but not burning.
I told my tuner about my symptoms and showed him the log, it stumped him as well. He has some ideas that he bounced off me, but he said he has never seen a rich misfire.

I turned off each injector in link while the car was idling and I didn’t notice anything out of the ordinary from what you would expect when turning off an injector. The car bogged, went lean, then stabilized back at a shaky semi-stoichiometric idle. I wonder if I pulled each individual spark plug if it would go rich like you are saying? Personally, I think it will still read lean. Not only is that fuel not being burned, but the air is not being burned either. This will be a good test tomorrow to see if what you are saying about an ignition misfire has merit.

We were discussing the potential for the injectors to be the culprit, so I’m probably going to order some Hi impedance injectors and go with the hypothesis it’s the low impedance injectors giving me this problem. It’s a pricey experiment, but worst case scenario I have the same problem and better injectors. Oh noooooo.
 
How fresh are the plug wires? I had a set maybe 5 months old, had a misfire I couldn't get rid of, accidentally left a shop towel on the motor and it went away. Was arcing to the hood. Just dumb luck I found it that way. Threw on a crappy Ebay wire set and it went away. Ordered yet another new set of NGK wires and all was fine. Probably not your problem but it was mine.
 
How fresh are the plug wires? I had a set maybe 5 months old, had a misfire I couldn't get rid of, accidentally left a shop towel on the motor and it went away. Was arcing to the hood. Just dumb luck I found it that way. Threw on a crappy Ebay wire set and it went away. Ordered yet another new set of NGK wires and all was fine. Probably not your problem but it was mine.
This is a fresh rebuild with just under 300 miles on it at the moment. Brand new NGK plugs, brand new NGK wires. Compression is 180 across the board as well.
 

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My wires had MINIMAL time on them too. Do the sparkplug test you talled about and see what happens. If it duplicates the problem, good. I was puzzled so I took my hood off and it all went away......just trying to help. Sometimes its the silliest or stupidest thing.
 
My wires had MINIMAL time on them too. Do the sparkplug test you talled about and see what happens. If it duplicates the problem, good. I was puzzled so I took my hood off and it all went away......just trying to help. Sometimes its the silliest or stupidest thing.
I hear ya. Probably scratching my head over here over a spark plug or something LOL.

Anyways, I went ahead and pulled spark from each individual cylinder. The wideband initially went LEAN (about 16:1), as I suspected it would. However, once the spark lead was re introduced, the wideband went RICH (13.3:1). I'm unsure how to explain why that is.

Reviewing the log, I'm not going lean during part throttle or at idle. If I was going lean then going rich, I would chalk this up to an ignition issue. However, my A/F/Rs are stoich, then suddenly spike to rich.
 
Thinking back about my last comment, there is a collection of unburnt fuel in the cylinder you pull ignition from. Once spark is re-introduced, that excess fuel is burnt, resulting in rich AFRs.

Just a guess.
 
Hello all.

Need to pick your brains real quick. At idle I can hear a hollow, misfire sound. Doesn’t affect my AFR, idle is steady.

While cruising, I hear the same hollow misfire sound, my AFR goes rich (12.7:1-12.2:1), and the car stutters for a split second. It’s random while cruising at partial throttle. During heavy acceleration, WOT, or any boost whatsoever, car pulls like a champ. No hesitation, no stuttering whatsoever.

I know most misfires cause a LEAN A/F ratio, but this one goes RICH. Which is why I’m confused.

I don’t want to make assumptions before I hear your guys’ answers, but I have an idea as to what the problem may be. I don’t want to make a recommendation and everyone focus on that one thing, so I’d like to hear some answers before I comment.

Mods:

I’m using FIC 1250cc low-z injectors, BPR7ES plugs gapped to .018”, datalogging with DSMLink V3. I’m also logging fuel pressure through a fuel pressure sensor, and using a fuel lab AFPR. Fuel pressure is rock solid, no spikes/drops throughout the misfire 450HP E85 fuel pump, currently on 93 octane pump.

NGK blue spark plug wires, stock transistor and coil pack. FP76HTA turbo, FP2 cams.

Base timing is set at 5°BTDC, base fuel pressure is set to 43PSI.

I’m currently at work so I can’t post a log from my laptop (posting this thread off my phone).


Pull the vacuum off the egr and block the line or block your egr if you have t already
 
I dont think the injectors are the issue, maybe injector latency could be the problem. You could have one of the injectors that flow a tad bit more than the others. Def could be the problem. No issues with driving or WOT pulls i wouldnt stress on it. Look at your spark plugs and see if theres a difference in the burn.
 
#2 cylinder is running rich compared to the other three. I swapped the #2 injector with #3 injector, and the problem persisted on #2 cylinder. Compression tests show all 4 at 190-195 PSI. It’s a dry foul, not wet at all so I don’t think it’s oil. I also have zero symptoms of burning oil. No blue smoke out of the tailpipe on start up, shut down, in boost, cruising, or heavy vacuum (-25/-26in/Hg) after a pull and staying in gear. BR7ES plugs. These ones were gapped to .022”.

Someone told me #2 and #3 share a coil for ignition? If that’s the case I know it’s not a weak coil pack either. Because #3 cylinder looked just fine. #2 just looks like it’s rich. Which would correlate with why my wideband reads rich and I get a slight misfire. What’s going on?
 

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Only one intake valve is opening or they have mismatched travels? LOL

I am trying to recall my own idle misfire and which way it went.. will have to check some old logs. I believe mine was/is caused by injector latency. I still havent had them tested..
 
Only one intake valve is opening or they have mismatched travels? LOL

I am trying to recall my own idle misfire and which way it went.. will have to check some old logs. I believe mine was/is caused by injector latency. I still havent had them tested..
So I just picked up some FIC 1200cc Hi-Z injectors and a resistor pack delete to see if it’s a latency issue. I doubt it is, because I swapped injectors and the problem persisted on #2 cylinder. That wouldn’t be a bad idea to remove my valve cover and make sure I don’t have a bad lifter or a bent valve or something. Again, doubtful just because it’s not consistent. It’s a random misfire/pop.

I also picked up a custom ISC remote mount to help my idle when I turn on an accessory and when coasting down, because currently both my FIAV and ISC are deleted.

Lastly, I’m wondering if it could be ignition related on #2. I put in new plugs and swapped ignition leads just to see if it’s possibly lead related. I think if it was a coil problem, both #2 and #3 would suffer from a weak coil. But I’m not too sure. I’m thinking on picking up some 8mm wire leads and testing my spark on each cylinder. If I have a weak spark on #2, I’ll have my answer.

I’ll use a dial indicator in the meantime and make sure all of my valves on #2 are opening and have the same amount of travel.
 

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I would surmise weak spark would show as blowout under significant boost, but it may only be weak under shorter pulse times.
Given it appears that #2 is the problem cylinder and you have changed injectors and plugs (could even swap spark leads to quickly validate its not that wire), i would look at the rest that is static. Have you checked the harness for broken or heavily corroded wiring and connectors for broken tabs? Swap ptu?
 
I would surmise weak spark would show as blowout under significant boost, but it may only be weak under shorter pulse times.
Given it appears that #2 is the problem cylinder and you have changed injectors and plugs (could even swap spark leads to quickly validate its not that wire), i would look at the rest that is static. Have you checked the harness for broken or heavily corroded wiring and connectors for broken tabs? Swap ptu?
I have yet to test the harness or swap the PTU. From my understanding, the PTU is a go or no-go. If it is good, it works. If it’s bad, it wouldn’t work. I did change the leads just to make sure it wasn’t a bad lead causing my issues. I’m not entirely sure what to check for when shooting the wires to each injector. I could just shoot #1,3,4 and then compare them to #2.
 
I am just trying to think of everything that so far has remained static. The suggestions I gave to check would be more for detecting lack of spark rather than an abundance of fuel. Something may be instructing the injector in that channel to stay open longer than it should..

(which means wire and ptu are out of consideration)

Grasping at straws but have you looked at the injector drivers on the ecu? Or tried a different CAS? Anything that is used to signal injector timing.
 
I am just trying to think of everything that so far has remained static. The suggestions I gave to check would be more for detecting lack of spark rather than an abundance of fuel. Something may be instructing the injector in that channel to stay open longer than it should..

(which means wire and ptu are out of consideration)

Grasping at straws but have you looked at the injector drivers on the ecu? Or tried a different CAS? Anything that is used to signal injector timing.
I am concerned it may be the ECU, given that nothing we spoke about will garner MORE fuel into the combustion chamber, at least not that I am aware of. I can try a different CAS for the hell of it, I wanted a pretty black top CAS anyways LOL.

I was speaking with my tuner, and he said the black plug is not necessarily a sign of the cylinder running rich, but it could also just indicate poor combustion which opens the door for a variety of different causes.

I’m not electrical savvy, but I did just test for spark on each plug. All I did was yoink out my spark plugs, attach the leads to them and let them dangle out the front of the car while my wife cranked it. It’s hard to say at the moment, but I MIGHT have a weak 2/3 coil. #1 and #4 were producing faint sparks while #2 and #3 struggle bussed to produce much of anything. The battery sounded fairly weak, so what I’m going to do is leave a spark plug installed in #2 cylinder while attaching the lead to another spark plug to see if it produces a strong spark at idle. I’ll do the same to the other 3 cylinders for comparison. I’ll be sure to cut off fuel to each cylinder to keep from washing the walls at idle.
 
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