cylinder # 6 misfire on a 97' Z71
 

A well cared for 1997 Chevy C1500 5.7 4x4 with 185K miles on it was running great, until first start yesterday morning was very rough and check engine light flashed. Drove to work with engine obviously running rough, check engine light continued flashing. After work, same thing. Stopped at a local Pep Boys with my PB card and a mechanic scanned for the code thrown. He said it was a # 6 cylinder misfire and suggested new plugs. Those old plugs had nearly a 100k miles on em' so I bought & installed new ones. Oh boy were those old ones worn looking! None appeared fouled or unusually black, just very worn looking. Started my truck and still the same roughness. Any advice? New wires? Fuel injector problem? My 17 year old son is very interested in becoming a mechanic and is in his 3rd class of high school auto mechanics and he told me it's most likely the blinker fluid, and if that doesn't fix the problem, perhaps it's the muffler bearing. Hmmm....

It could be a few things...plug wire, cap or rotor, or the Vortec motors are known for the spider injection going bad which will throw that code. Did you notice what the #6 plug looked like? Is it harder to start?

blinker fluid? Muffler bearing????

Damn you're going to need a metric crescent wrench to get at those.

A misfire on #6 Cylinder is DTC P0306 I believe

A P0306 code means that the the car's computer has detected that one of the engine's cylinders is not firing properly. In this case it's cylinder #6

A code P0306 may mean that one or more of the following has happened:

Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer

If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the truck, it may be a good idea to replace them as part of your regular maintenance schedule.

I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs).

In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

update
 

I put new plugs and plug wires and the engine still runs rough - just like that one cylinder isn't firing like the code says. I checked that # 6 plug wire connected to a plug grounded and it has spark at idle. I don't know if there's spart at load though. The oxygen sensor was replaced about 3 years ago. Funny about the metric crescent wrench. My son says he should tell his girlfriend's mother that he'll need to buy one of those the next time she wants him to work on her jap car. Any advice about the next step with this Chevy truck?

If you have spark then I would check compression on that cylinder. If you have good compression then it is probably the injector for that cylinder.

Update
 

This roughness running thing all started one morning so I'm thinking (re-worded HOPING) that it's not a compression problem, since it wasn't a gradual thing. (I was also hoping it would have just been the blinker fluid or that a metric crescent wrench would have fixed the problem). Would a compression thing basically mean the engine needs an overhaul?

If it's a fuel injector problem, does anybody recommend that one injector be taken off and cleaned? Or individually replaced? Or the whole multi port unit replaced? The code thrown was for a misfire on cylinder # 6. I'm wondering about the reliability of this code. Do professional mechanics really trust these codes? If so, would it be advised to focus exclusively on that # 6 cylinder?

Thanks to you all for the great input!

In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced.

There is a diffrent code for a multiple cyl misfire so I would start with just cyl #6

Have you tried checking the injector for the number 6 cyl?

Most fuel injectors will have an electrical resistance of approximately 10 to 18 Ohms;
check the service manual for your vehicle's exact amount.

Injectors can usually be researched online as well for a specific vehicle type to find the correct amount of Ohms.

For this check, you do not need the vehicle running or the ignition to be on. You will be checking Ohms.

First, remove the corresponding electrical connector from the injector you wish to test.

Now you should see two metal prongs (contacts) inside where the connector was. Set your meter to the Ohms (Ω) setting.

Next touch your red meter lead to one injector contact, and the black meter lead to the other contact. Since you are in the Ohms setting, it does not matter which lead goes on either contact. With the meter in the lower Ohms setting, you should get around the same resistance on all your injectors.

If one injector is reading much higher or lower than the rest, it is most likely bad. If you get an open (O.L.) or zero Ohms (shorted), then your injector should be replaced.


You could also check a fuel injector by carefully putting a long screwdriver directly on the injector while the engine is running.

Using a long shank screwdriver, hold the screwdriver handle up to your ear, the shank on the sensor itself, and you should be able to hear a clicking noise. If not, then it is probably either clogged or the circuit inside is open.

If in doubt whether the injector is bad or not, try switching the suspected bad injector with a known working one, say change cyl 6 with cyl 5. Clear the codes, now when the code comes back if it is showing a misfire on cyl 5 now then you know that the injector is bad.

I agree on the compression, but it is such a quick thing to check I always do that first.
For the matter of work involved I would change the whole injection (spider) unit b/c if one has become brittle enough to break then the others aren't far behind. If you haven't already done so recently do the lower intake gaskets as well they are known to fail and leak coolant usually in the front corners where the intake and heads come together.

Hey guys,
My 89 GMC with 5.7, ran like a bag of sh!t all of a sudden, replaced the O2 sensor and it ran PERFECT! And a little why'll ago it started to get a really bad MISS, it was the cap and rotor.

If i was you, id start with a compression test. Id replace the cap and rotor and wires, won't hurt to have new ones.

Hope this helps

O, AND WHAT THE HECK IS BLINKER FLUID!!! OR METRIC CRESCENT WRENCH!!!!???????? Where are these on a truck?? Maybe a Toyota..But a Chevy/GMC! COME ON!!!

Drivelineband did you ever get this resolved?

I am receiving the same error code in my ’97 Suburban 1500 5.7 2x2.
I have changed the plugs, plug wires, rotor and rotor button. After $180, none of these things has helped. I just had a tune-up a year ago with 25,000 miles placed on the vehicle since then. The plug in cyl #6 did look dirty. Actually, no four plugs on that side looked as clean as the ones on the driver side.
What should I try next? I do not smell rotten eggs while the engine is running. I don’t really understand how a Faulty coil (pack) could only miss fire on #6 and fire just fine on the other 7?? I know where that is located and it looks fairly easy to change.
What is involved in replacing the whole injection (spider) unit? I am by far not a mechanic.

Since it happend so quick, I would look at mechanical. Check the valve springs for that cylinder!

The problem was fixed. It was a bad injector. I want to thank the helpful experts on this forum. To the weekend warriers out there like me: replacing an injector on this motor is easy, but getting TO it is intense, and then of course, putting everything back together. My advice would be if you're lucky enough to have a real mechanic friend, invite him over for pizza and beer to help you with this project - otherwise it may easily consume your whole weekend - at least the better part of a day that you could have been out fishing, or perhaps scoring points with your woman by putting her car up on jacks in your garage with the hood open, changing the blinker fluid or muffler bearing with the game or music on the radio.

Sweet man! Thanx for coming on and asking.

Well.....
$678.79 later. My Suburban is now running again. It was the fuel injectors that were bad. The odd thing is that I also had error code P0141 and P0161 (O2 sensor bad). They did not replace those but the error has not returned, yet. Think that was due to the bad injector?
Damn I should have taken the day off and tried to fix it myself!

When the injectors go bad they will either cause a lean or rich mixture. The O2 sensors have a big chance of goin bad when the motor runs rich cause of the unburned fuel creating carbon build up. If you take the O2 sensors off, you can tell alot about how the motor has been running, even if it has a blown head gasket. The coloration shows the evidence. I would replace them anyways.

Wow these are some sharp tools here. Blinker fluid, muffler bearing, metric crescent wrench, please understand that those are all a joke. For the recommendation about checking voltage at the injectors, impossible. The spider injection is one unit under the intake, cannot check voltage. And you're referencing from a ford and not a Chevy and please don't ever diagnose your car with a long screw driver held up to your ear, that's barbaric.
Proper way to diagnose is to first start with checking the plug( cracks or out of gap, possible wrong plug from being a cheap ass), is everything ok? Of so, check wire. Is it arching? Burnt or showing white powder marks on it indicates it vindicating outside the loom. Everything ok? Check coil, you check the coil by checking resistance. Easiest way to check if it's adequate, compare to known good part. Ask your parts store to pull the part and check resistance. Everything ok? Now go to your cap n rotor, any marks indicating false contact? Any condensation? Any white powder or burn marks at the points? Everything ok? Possible distributor or body control module. Don't dare to diagnose the bcm if I have lost you in these basic instructions. Now if anything of these items I asked if they look ok, if they don't, replace and recheck.

Dude it's not a ford!!!! Completely different engines and set ups

I am having the same problem but it keeps melting the wire on cylinder #6 I've been through a box and a half of wires and taken it to 2 shops near my house.