Last post on Dec 09, 2013 at 4:59 AM
You are in the Chevrolet Suburban & Tahoe
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Chevrolet Suburban, Chevrolet Tahoe, Chevrolet Silverado 2500, Engine, SUV
#58 of 209 Re: rough idle after new plugs and wires [woodyj]
May 20, 2008 (6:49 am)
I have this problem not too long ago on my 99 Suburban after the intake manifold gasket was replaced. I have a good all buddy helped me out on this forum. I bought a non ac delco parts and nothing has change, but when he suggested to replace it with ac delco, the truck ran better. I had a rough engine and showing a code of P0304 misfire on cylinder #4 and a blinking ses light when at a speed of 35 - 45 mph. California vehicle had a special warranty up to 200k mile on their fuel injection system and dealer checked and replaced. Car runs great now.
I did not catch the whole story. Please provide me some symptoms that you are experiencing and what year and type. I will share with you some of my experiences.
#59 of 209 Re: rough idle after new plugs and wires
May 20, 2008 (7:08 am)
Did it give you any codes?
#60 of 209 Suburban K1500 5.3L misfire
Jun 17, 2008 (5:13 pm)
Having a problem with my Suburban, began at a little over 80k miles. SES light activated on interstate at 70mph while towing an empty trailer. Filled up with "better" gas, light out within 50 miles. Light back on within 100 miles, showing a 300 DTC. Cleared code a couple of times, returned as 305 or 300. I figured it was time for a tune-up, replaced plugs and wires. [Note: OEM plugs were DENSO platinum type]. New plugs Iridium, 0.60 gap as specified in manual and engine compartment sticker, new Delco wires. Rough idle still present, 305 code returns after clear.
Have since changed/tried: New fuel filter, swapped coil units beween cylinders, sprayed brake cleaner around intake (as leak detector). No change. Removed and sent injectors for professional cleaning. Still no change. I broke down and took the Burban to the dealership. $184 later, and no diagnosis of the actual problem. They say electronics and fuel system are ok, performed leakdown test, with no issues. Wantd to "disassemble" top of engine suspected "grooved camsaft" or other valve train issue. I declined permission to take the engine apart.
Would be happy for any advice I can get at this point.
#61 of 209 Re: Suburban K1500 5.3L misfire [alanrs]
Jun 18, 2008 (12:35 pm)
Please tell me what year, what code does it have. What state are you in. I had the same problem before and I was showing P0304 cylinder 4 misfire. Let me know. Check compression on each cylinder while the SES light is still on. My Burb did that for 1 year and the problem on mine was the Spyder injectors that was replace for free in the State of California and is waranteed up to 200k mile. A month later it showed up again P0304 and my compression was dead on that cylinder. I ended up getting the engine replaced then sold it due to high gas price in California.
#62 of 209 Re: Suburban K1500 5.3L misfire [elorenzo39]
Jun 18, 2008 (6:15 pm)
I am in Michigan. The code is 305. The engine passed compression and leakdown tests. This is a 2001, injection has fuel rails with individual port injector units, and a plastic composite intake manifold.
#63 of 209 k1500 5.3 mis fire
Jun 19, 2008 (7:55 pm)
Try changing or swapping out number 5 cylinder injector with another known good injector. P0305 code is cylinder 5 mis- firing. Denso plugs are ok for these type of coil/over ignition systems but A/C Delco are the best. What is the fuel pressure? Did you check the TPS sensor?
#64 of 209 Re: k1500 5.3 mis fire [pear69]
Jun 20, 2008 (1:39 pm)
The injectors were removed, tested, cleaned, retested, and yes I re-installed with 2/4 and 3/5 in different locations. Injectors are not the issue. The Denso plugs CAME in the engine FROM GM. I was surprised too...... I replaced with Autolite, only because they were only ones I could find with the specified 0.60 gap in an Iridium type. #3 and #5 coils were also swapped. Tech2 showed no issue with TPS, and I get consistent readings from it on my scan tool as well. Dealer says there is no electrical or fuel issue, and BTW, I measured fuel pressure between 46 and 50 PSI.
The Tech2 showed a misire history stored in the computer that was heavily at cylinder 5 (over 50,000 the day we read it), with way too many (but about 1/10 of cyl 5) on cyl #4. Others showed single digits or zero. I wish I knew of someone with an engine smoker in my area, so I could check the intake gaskets.......
This is perplexing. I love this truck, and am bummed that it is running poorly. Been driving for 40 years, his is the first time I have had any issue like this. I run most of my cars/trucks 150K miles or more with no engine problems.
#65 of 209 k1500 5.3 mis fire
Jun 21, 2008 (9:21 am)
Your fuel pressure should be 55 to 66 psi. Make sure the fuel filter that's attached to the fuel lines is new and installed properly (this filter is directional). If this filter is good then the filter that attaches to the fuel pump (inside of the tank) is probably dirty. This filter ( I believe) is not serviceable. I suggest replacing the fuel pump. When replacing the fuel pump on these chevys it is VERY important to replace the fuel pump chassy harness connector ( this is the electrical connector that plugs into the fuel pump). This connector is a one shot deal -- meaning that it can only be plugged in and out once -- because of a design flaw. Failing to replace this connector will cause the pump to shut off and/or arc creating the potential for a fire. Also, the ground for your fuel pump is connected to the frame close to the fuel tank -- find this (black wire) ground and disconnect it and clean the area around it real good and then reconnect it. This ground corrodes and it is usually better to cut it off and re due the entire connection. This may not be the mis-fire problem but it is important to have the proper fuel pressure before you change everything else (like is seems you have done already). A code 305 is specific to a mis-fire to cylinder 5. Make sure all the wire connections are connected properly. Pull cylinder 5 spark plug and pull another plug that is firing. Is there any difference in the appearance? What do they look like?
I believe you mentioned that you sprayed brake cleaner to look for an intake leak. Try spraying some CRC electrical contact cleaner all around the intake--it is safer. Do this with the engine running at idle -- if the idle changes then (of course) you have an intake leak.
Also, is your coolant low? These engines are famous for the lower intake gaskets to fail. If the coolant is low and there is no outward signes of a coolant leak, then the intake gasket may have failed inside of the engine and coolant can leak into cylinder 5 causing a mis fire. Check your oil to be sure that there is no coolant in the oil. Looking at the plugs will confirm whether or not there is coolant leaking in no. 5 cylinder.
#66 of 209 Re: Suburban K1500 5.3L misfire [alanrs]
Jun 22, 2008 (7:03 am)
One thing that I was told by the GM dealer is that in general misfire trouble code does not indicate fuel delivery problems. It only tells about the quality of the spark, i.e. it measures if correct resistance is present at spark plugs for correct spark. So it means misfire code indicates electrical problems.
Here I explain what happened to my "04 Tahoe 5.3L Flex Fuel engine very soon after I got the car. I have posted about my problems several times in this forum before but this all is very difficult to find I assume. Here are a couple of easy checks.
1. After only about 1200 miles my Tahoe started eating too much gas. This means 18 mpg went down to 13 mpg on highway driving. During the trouble shooting process, which I had to do myself while the dealer did nothing during warranty period, I first changed spark plugs. After that I get misfire trouble codes. As I had only changed the plugs this obviously had to be related to plug change. As a result it ended up being very simple problem. Some of the aluminum metal shields around spark plug booths that my Tahoe engine have were grounding spark to engine ground. For trouble shooting purposes I removed the metal grounding spring from the end of the shields, which allowed me to even see the problem, i.e. when it was dim lighting conditions I could see a spark between some of the shields and engine parts, mostly exhaust manifold.
When spark plug wires get old they can crack and other vice loose isolation properties and start leaking spark to the shield. Because the shield is grounded to the engine with that spring in the end of it the spark has direct contact to ground. This will lead to misfire as the resistance for spark forming changes.
This same problem easily happens when spark plugs are changed. When the plug wires are pulled from the plugs sometimes they are very tight. This can cause the plug connector inside the boot slide out. When this happens the boot does not go over the new spark plug deep enough leading to spark leak around the boot to shield and this was exactly what happened to me. Some of the wire boots did not go on plugs deep enough and spark leak was very bad. This can also happen with new wires as all of them do not have plug connector deep enough inside the boot.
There is very easy way to trouble shoot for this, i.e. remove all aluminum boot shields. They are used only for heat shield purposes so you can take them out and drive a few miles and see if that fixes the problem. I actually took mine out and drove for a week without them. I could smell a little burning rubber but they did not catch fire or anything. Then I went and bought a set of high performance spark plug wires for $5 less than stock wire set from dealer cost, a set that does not require using boot shields and have been trouble free from this problem since. It was not the cause for low fuel mileage though.
If your engine does not have the aluminum heat shields around plug wire boots then above does not apply to you.
2. This happened to me just 2 weeks ago. I was working on the car again for fuel mileage, which has been back to around 17 mpg highway but not 18. I decided to change O2 sensors, the first one in each bank. Went to Auto Zone and they had a Bosch sensor for $65.00. This sensor was of the universal type, i.e. It did not come with wire harness and I had to use the one from old sensor. Further more, the instructions in the package did not explain which wire is the signal so I tried to guess. As we all know Mr. Murphy does not take days off so my guess was wrong, i.e. it is the BLUE wire that is the signal, not white.
But very interesting thing happened while I tried to run the engine with wrong O2 sensor wire as signal wire. I got probably all of the misfire codes the computer can give. And the engine was running VERY ROUGH!
So, your problem could be with oxygen sensor too. It just takes a new sensor to try. There are ways to test a sensor but if you already have 80 000 or so miles on it it might be a good time to change O2 sensors anyway.
#67 of 209 k1500 5.3 mis fire
Jun 22, 2008 (9:04 pm)
Arrie, I agree with your analysis -- however, alanrs seemingly has access to a Tech2 autoscanner. These scanners are what the dealers use and they cost around $8000.00. A bad O2 sensor would have already been indicated. Also, an O2 sensor is nothing more than a fuel delivery device. It measures the amount of oxygen in the exhaust and tells the computer to either richen or lean out the fuel delivery. I agree that with 80,000 miles, changing them is not a bad idea -- but I do not agree that they are causing this mis-fire condition.
This engine has coil over plug wires meaning that they are very short; the reason for this was an attempt to reduce the resistance and arc travel time to the spark plug. It was stated that the wires are A/C Delco ( one of the best ) and they are new. Yes, those heat sheilds can be a problem, but pulling the plug and looking at the condition of that plug will tell you whether or not that particular plug is firing properly -- meaning -- burning all the fuel. It will also tell you whether or not that there is enough fuel getting into that cylinder and also, whether or not there is coolant leaking into the combustion chamber....Low fuel pressure seems to be the problem in this case--but we'll just have to wait and see----