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Hello All…. I have a car matter that is driving me a little nutty and am looking for some good advice…
I have a 2001 Mazda Millenia 2.5L and it is throwing engine code P0304 (Cylinder 4 Misfire). I have swapped that plug with another and retested and swapped that wire with another and retested and the same cylinder continues to be misfiring. I did a compression check and that came back good. [.. when starting the engine, the idle goes up as normal and then drops back down to about 800 and then the code comes up… and you can feel the engine is running rough…]
This particular engine does NOT use coil packs, but rather a distributor, so I changed the cap and cleaned all the carbon off the rotor (autozone did not have new on in stock). Still the same problem.
I listened to all the injectors via the screwdriver to the ear method and the tick tick tick-ing of 4 is the same as the others… so it is firing… (though I know it could be clogged)…
Last week, before I tried changing the distributor cap this weekend, I ran it down to a quarter of a tank and put in a bottle of the Lucas fuel treatment and fueled up with 93 and took it on the highway and hit it as best I could…. but still having the problem.
While changing the cap I had the air assembly apart, so I cleaned all of that out, including the MAF. Also I had gotten codes on the VRIS (Vehicle Resonance Induction system), but I tested those and they came back as good…. and if air was a problem I would expect to either get a lean or rich mix code… not a misfire…. Does anyone think the computer could be mistaken in the cylinder is saying is misfiring?
Or does anyone have any other ideas?….. since the only way at these injectors is via removing the plenum, I thinking of purchasing a tool to run the cleaner through the rail and see if that does it…. but want to discuss this with as many pro’s as I can before making any more moves… Thanks for any insight anyone can provide…. I really appreciate it….
Thanks
Matt Montalto
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A couple of possibilities:
There may be a vacuum leak associated with that specific cylinder.
As you state:
“ I listened to all the injectors via the screwdriver to the ear method and the tick tick tick-ing of 4 is the same as the others… so it is firing… (though I know it could be clogged)… ”
It could be clogged or just not delivering the correct amount of fuel to that cylinder.Thanks…. I did do a compression check and it came back good on that cylinder…. did check all my vacuum lines and couldnt find any leaks….. as I mentioned I did have the issue with the VRIS… which is codes 1521 ans 1522 which equated to these 2 little vacuum lines on the back of the engine… and I took them off to test them and they responded correctly…. After testing them I put them back and the codes for them went away…. but after testing a few more times when checking for the misfire code, those 2 have come back… Which, to me is confusing, since I would think an airflow matter would give me a code related to a too rich or too lean mix.
If you’re interested, I followed the testing procedures for these 2 codes that are shown in a video by briansmobile1 (https://www.youtube.com/watch?v=W3gb-ihNN_4)
never the less… I dont think that this could prevent this one particular cylinder from firing entirely? could it…..?.
I spent a lot of time with the engine and a can of carb cleaner and sprayed everywhere I could think inside that engine and was not able to find any vacuum leaks… Looking at the long term fuel trim… I am running at just below 0 so I dont think that there is any vacuum leak at this point…. I ordered the tool and cleaner so I can run some injector cleaner through by doing it directly from the fuel rail, so hopefully that will do the trick…. if not, I will have a least a days worth of work ahead of me to go about removing the upper intake to get down to the fuel rail and injectors
FOLLOW UP….
So… just for anyone interested or dealing with anything similar…..
Ultimately (to make a long story short) I ended up being able to remove the fuel rails without having to take off the upper intake manifold. Once I did, I changed the injector for the #4 cylinder and the misfire code went away.
But wait …. there’s more….
So the … on the topic of the VRIS matter (P5121 and P5122)… I tested all the components of that system as shown in the shop manual and all the components tested good… and in checking all the lines to these components, I flipped over the T connecter it uses and it had a hole melted in it… so I changed that…
But wait …. there’s more…. (after all… this is a Mazda Millenia)…
So after driving the car a few miles or so, the problematic symptom came back…. where the rpm will rev and drop and rev and drop (no code though)…
…. then I pulled off the egr and the iac and throttle body and cleaned all out… then inspected the tps ….. put it all back… same problem….
I, again, pulled off the intake air assembly and tested the IAC continuity wise and it came back within spec
then I did two things at once…. (which I try never to do, but this time I did)… I disconnected the egr vacume line and closed the line to the engine with a screw… and while I was doing this, I used my odbII scanner as a scope and did a throttle sweep while watching the graph… which looked good for the most part… but say maybe one out of 10 sweeps did not look full (but this is a bluetooth scanner that I have seen some connectivity problems with before so I am not convinced that it was totally valid…
after doing this… the car seemed to drive without any issue for a little while… So I tested continuity of the egr (as described in the shop manual) and it seems to be out of spec…
so I thought I had found the problem…. but then the symptom again resurfaced… but much less frequently…. So, since I haven’t yet reconnected that egr vac line, I am inclined to think that the problem may be with the TPS….
Trying to be as certain as possible here since every part on this car seems to be 3 hundred dollars….. Trying not to spend money needlessly, but fixing is usually better that buying something else (cost wise)… as it is I just had to drop 300 this weekend replacing my Honda Odyssey’s fuel pump….
If anyone has any experience with back TPS’s I would love to hear about it… thanks
You did a pretty good cleaning job. But despite the fuel injector is firing that don’t make them mist spray maker.
You might try to clean It in a garage with this tool in the video. I saw a Toyota Corolla 2015 had a misfire always on the same cylinder.
Swapping the coil, changing the spark plug did nothing. Before swapping the injector, a clean have been done and the problem dissapeared and the engine ran smoothly.Thank you Plasmide56 for your response…. Incidentally, I have watched this video before…. any many of his others…. and I have the tool that he demo’s and did use it, but to no avail….. but changing the injector did resolve the misfire issue. So that problem is resolved… I am going to open a new topic I thing on the other issues that are happening now… however, thank you for your reply
Matt
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