- This topic has 8 replies, 3 voices, and was last updated 9 years, 7 months ago by
.
-
Topic
-
I have been putzing with my mothers 2002 Toyota celica Gt 5 speed with 160k miles ….when I started it it had a P0171 code and a P0302 code. I know the 0171 is for a lean bank 1 to which I changed out the MAF sensor and the 0302 is a misfire on cylinder 2 so I changed out the plugs and coils. Also changed the injectors from looking at long term fuel trim that was also another issue. Now I am stuck with a P0300 which is a random misfire and when this happens I never feel it or notice it but it throws the CEL and Code. can anyone tell me where to look or what to look at for this? Car runs fine, idles nice and smooth. I have read a few possible culprits…1 is the computer is going bad and throwing codes all the time, 2 Is the battery is garbage and part of the reason for the codes also.
Can anyone expand on this further any help or suggestions is greatly appreciated thanks
-
Replies
-
lean code and random misfires indicate fuel starvation. Check your fuel pressure. You could have a clogged filter, faulty pressure regulator, or failing fuel pump.
Sometimes cheap coil packs can cause codes like this because they cause ripples in voltage or resistance that the computer doesn’t like.
Keep in mind that when the computer throws a code it does not definitively mean the part is bad. It only means the computer is having some kind of issue communicating with it.
Normally when you see a misfire on a specific cylinder you would move that coil pack to a different cylinder to see if the trouble code follows it.
Also the lean code could have been caused by the coil pack.
Always make sure you are testing things before you replace them, especially when you are buying parts with someone else’s money. With out testing you can not guarantee that the part was actually at fault and you run the risk of throwing money away.
But I digress.
I would start by checking for vacuum leaks.
Get a can of carb cleaner and (with the engine running) slowly spray it all over the engine vacuum lines, brake booster, intake manifold, injectors, and intake hoses. If you hear the idle suddenly drop then you have a vacuum leak and it needs to be attended to.
If that proves fruitless, try moving the coil to a different cylinder to see if anything changes.
You should probably clean the throttle body too. The most thorough way to do this is to remove it from the engine. Use the throttle body cleaner and a toothbrush.
If none of this changes anything report back and we can move on.
Good luck.The fuel pressure issue could be due to low pressure, but if the engine is not metering air correctly because it is getting misinformation from other components than it would, in turn, not allow correct fuel in.
Checking fuel pressure wouldn’t hurt anything, but I don’t think we are to that point in the diagnosis yet.
I would definitely change the fuel filter if it has never been done though.[quote=”thisisbuod” post=136723]Also the lean code could have been caused by the coil pack.[/quote]
I disagree. Ignition faults normally cause rich conditions due to the unburned fuel in the exhaust stream. Lean conditions with a random misfire usually indicate fuel starvation (due to reduced fuel delivery, usually clogged filter) or vacuum leak (unmetered air entrance diluting the fuel mixture). In 30-some years of working on engines I have never seen an ignition fault cause a lean condition. I start with checking fuel pressure, because it is usually an easier first step than looking for a vacuum leak that may not exist.I will admit that I’m not an engine expert….. yet, but I’ve seen different makes react differently to misfires. My main point though was to test before you replace and follow a logical diag.
Fuel starvation is, pretty much, the definition of “lean,” but the lean issue could be caused because the engine is getting misinformation. I would have gone after the misfire code first because it is a more straight forward code. The lean code is more subjective and has a broader spectrum of causes.
But this is all moot now because, from what I read, the lean code is gone.Just because the lean code is gone right now doesn’t mean the condition doesn’t still exist. Each code has a priority in the computer and a number of faults that must occur before the code is thrown. The computer prioritizes misfires over O2 data, so it is common to see the misfire occur first, then sometime later on a lean or rich code occurs. Chances are the codes are being cleared from the computer before it can re-set the lean code. Random misfire (current code) with history of lean condition still indicates possible fuel starvation to me. We =are= going after the misfire code, using the previous lean code as a clue. The fuel pressure is a valid test for that code, as there is not a fault on an individual cylinder. Once the fuel pressure is confirmed good or bad, we know what direction to take (fuel system vs vacuum leak).
- You must be logged in to reply to this topic.