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Hi guys,
Please help me out on what’s possibly going on here. Here’s the situation.
-Car at operating temp
-Restarted after about 30 minutes parked.
-Engine stumbles a bit and idle is rough.
-Short term fuel trim consistently at high negative ~(-10) during idle
-Chirping noises coming out of the exhaust pipe during idleThis will go on for a few minutes but eventually smooths out. The short term fuel trims come back and hovers around -1 to +1.
I’m thinking leaking injectors? What do you guys think?
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That is a possibility. Try starting the car with the pedal
to the floor. This will shut the injectors off. see if it starts better.I’ve been monitoring this situation for a while now.
From looking at live scan data I can see the car runs rich while this is happening. Even if not misfiring, it idles and runs rough in low rpm driving.
Then after a while it all goes back to running fine.
I can see the long fuel trims during idle swing from 0 (running fine, smooth) to -7 (running rough) in a single commute. Then it will swing back from -7 to 0 again on the next commute.
Where should I be looking at as the cause of this? There are no codes, but I dont want to wait until something really expensive breaks to find out what’s wrong.
I’ve cleaned the MAF and IACV. Spark plugs look fine and ignition coils are new. I can view live data and data log too. Please give me some insight on which direction to go here. Thanks.
As College man suggested, you might try starting it with your foot to the floor on the gas. This will turn off the injectors. if it starts better when you do this, it might indicate a leaking injector or some other fuel leak causing it to go rich. You could also check for a leaking injector by hooking up a fuel psi gauge, running the engine, then shutting it down. Crimp off the supply and return lines to the fuel rail after you shut down. Monitor the fuel psi. If it starts to drop then it’s likely you have a leaking injector. You might be able to find the offending cylinder with a power balance test.
It could also be running rich to to a mechanical issue. If there isn’t complete combustion, you will have left over fuel. A compression test will help you find something like that.
It could also be a sensor issue. If you don’t have any check engine light codes, then this might not be the best place to start. You would need to check the coolant temp sensor in particular. If it’s readings are off, then it can upset the fuel mixture. To check it, you would likely need to take the coolant temperature and measure the resistance of the sensor and compare it to spec. I suppose you could also observe the readings on a scan tool and compare them to actual measurements of the coolant temp. This would likely be more efficient.
More info on solving problems like this along with videos on how to do the power balance test here: http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Keep us posted on your findings.
Thanks for the reply Eric and College man,
I forgot to mention it no longer misfires on a warm startup. This happened after I took the spark plugs out to inspect them and put everything back. They looked normal. Slightly brownish all around with 20k miles of use. Weird that this helped somewhat.
I’ve also done a compression test and resulted in around 150psi all around.
I just have a sluggish running car when the fuel trim shows rich. This can happen at any time during the trip and improve at any time too. It runs great when the trim numbers are Long trims are near 0, poor when it gets to -7 or lower.
I’ll look into checking the injectors. Thanks for the advice.
Another questiong guys.
Since my compression test came out 150 148 152 152, do I need to do a leakdown test? Or are the numbers good enough that I don’t need to worry about it?
I’ll be doing the injector leak test Eric mentioned as soon as my fuel pressure gauge gets delivered.
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