Misfire Help???... Im out of ideas!
Thread Starter
Teching In
Joined: Mar 2010
Posts: 49
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From: Connecticut
Misfire Help???... Im out of ideas! I have a 1999 Camaro Z28 LS1. Up until recently the car started to misfire at lower rpm between ~1200-2800 rpm. When ever I would hit the car regardless of what gear I was in, it would stammer and studder and then all of a sudden it will get its power back. This problem happens at random times with no warning or consistency. It occasionally trips an O2 sensor code but only sometimes trips a misfire code.
It showed a random misfire code (or P300). I took it to my mechanic and 7 out of 8 cylinders were misfiring. He recommended we change the spark plugs and see what happens. We did that and the spark plugs showed signs of the engine running lean. But after we changed then, it took about 3 days before it started misfiring again. We hooked up his scan tool and saw that the whole left side, and only the left side of the engine was misfiring (cylinders 1,3,5,7). We checked the fuel pressure and it was at 59-60psi. We changed the fuel filter, and I replaced all the injectors with brand new Ford racing "Red tops" 36lb. We cleaned the Mass Air flow sensor with some brake klean and cleaned the K&N filter. The problem still exists. Any ideas at what could be causing this? Please help me out here!!!
It showed a random misfire code (or P300). I took it to my mechanic and 7 out of 8 cylinders were misfiring. He recommended we change the spark plugs and see what happens. We did that and the spark plugs showed signs of the engine running lean. But after we changed then, it took about 3 days before it started misfiring again. We hooked up his scan tool and saw that the whole left side, and only the left side of the engine was misfiring (cylinders 1,3,5,7). We checked the fuel pressure and it was at 59-60psi. We changed the fuel filter, and I replaced all the injectors with brand new Ford racing "Red tops" 36lb. We cleaned the Mass Air flow sensor with some brake klean and cleaned the K&N filter. The problem still exists. Any ideas at what could be causing this? Please help me out here!!!
I'm guessing you retuned after the injectors? Have you tried the oxygen sensors? If the O2(s) are bad, then it may be causing it to pull or dump lots of fuel, causing the cylinders to misfire. Does your car have longtube headers? If so, trace the bundle of wires I've circled in this picture.
The bundle contains the wire for the Crankshaft Sensor. It runs close to the headers, and the wires can get melted, causing them to ground out and interrupt the crank signal, causing misfiring across all cylinders. I had real bad misfiring for a couple of days, so I moved this bundle away from the headers, and the misfiring stopped. For insurance, I cut a piece of heater hose and wrapped it around the bundle closest to the headers, and have had no problems since.
Also, I don't know what effect brake cleaner would have on the MAF, but I would only recommend cleaning it with MAF Cleaner or Electronics cleaner.
The bundle contains the wire for the Crankshaft Sensor. It runs close to the headers, and the wires can get melted, causing them to ground out and interrupt the crank signal, causing misfiring across all cylinders. I had real bad misfiring for a couple of days, so I moved this bundle away from the headers, and the misfiring stopped. For insurance, I cut a piece of heater hose and wrapped it around the bundle closest to the headers, and have had no problems since.
Also, I don't know what effect brake cleaner would have on the MAF, but I would only recommend cleaning it with MAF Cleaner or Electronics cleaner.
Thread Starter
Teching In
Joined: Mar 2010
Posts: 49
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From: Connecticut
I do have stainless steel kooks long tube headers so I will check those sensors. I have not retuned the car however I am planning on taking to east side performance to have it tuned. The problem however was prevalent prior to putting the injectors in. As far as the
O2 sensors go, I haven't changed them but if the O2 codes trip again I will. I will keep you updated thanks again.
Any my buddy said to check the Air Intake Temp sensor, can that be the problem?
O2 sensors go, I haven't changed them but if the O2 codes trip again I will. I will keep you updated thanks again.
Any my buddy said to check the Air Intake Temp sensor, can that be the problem?
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Keep in mind that until the PCM is scaled to those injectors, it may not run right whether you fix the problem or not. Also the inlet air temp sensor pulls timing, but it can only pull so much timing, not enough to cause the car to misfire. I don't see this being the issue.
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Teching In
Joined: Mar 2010
Posts: 49
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From: Connecticut
I agree completely with that. I will get it tuned ASAP! I also failed to mention that I just replaced the main serpentine belt because it was squealing, could that have been the problem?
whelp if you checked the fuel & spark, and it's showing signs of running lean u may be pulling air into the motor from somewhere after the MAF? Did you check the MAF w/ a voltmeter or just clean it? Sounds like a combo problem...bad MAF + only 1 good 02 sens?
kind of wierd that its just the one side misfiring. i'd change the o2. also, i thought it wasnt a good idea to touch the MAF contacts with fingers or any kind of chemical, like an o2 i thought someone told me it'd go bad that way...anybody else heard that?
I have the same exact problem, word for word, I'm so lost right now its only 1 side of the motor doing it. I replace both 02 sensors and I replaced the maf.....what to check next between us we have replaced almost everything! Could it be the fuel pressure regulator??? Or maybe an evap problem?
Launching!
Joined: Sep 2008
Posts: 234
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From: Ashland,VA
most bank specific random misfires are most always caused by that banks o2 sensor. If you have replaced the sensor then check all the wiring to that sensor. I guess your getting a code for it also???
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Try this...pull the fuel injection rail and check for rust-water inside. I had a similar problem and it was small pieces of rust from the fuel lines collecting in the rails. It would studder and misfire as you give it throttle accelerating at times but ran fine otherwise. My fuel lines were rusted badly inside, had to replace them all to fix the trouble.
Coils? I have seen this problem several times on Tahoe and Suburban.
In those cases it is the coils. Looks like the same problem that's on the 6.5 diesel engine, the driver stops working cause long time heating.
On the trucks we have changed the coils to the new type, and the problems have bean corrected.
I have only seen the problem in early Lm7,Lq9 99 and 00 models.
Newer on the Ls1. but why not..
In those cases it is the coils. Looks like the same problem that's on the 6.5 diesel engine, the driver stops working cause long time heating.
On the trucks we have changed the coils to the new type, and the problems have bean corrected.
I have only seen the problem in early Lm7,Lq9 99 and 00 models.
Newer on the Ls1. but why not..
A lot of websites and people are saying coil packs, I'm going to switch mine around (swap side to side) and see if I have the problem on the opposite side! Then ill let you know what happens