GearWrench 2756D Spark Tester

[bob_the_builder]

So the check engine light came on my 2004 Silverado - P0300 random miss fire. I picked up a GearWrench 2756D spark tester as that seemed like a good place to start the investigate from what I could find on the net.

Before I try using it I wanted to make sure I was doing everything correctly. Do I just remove the one spark plug wire and connect the tester to it followed by starting the engine? Is there anything else I need to before starting the engine? If I did it this way the truck will only be running on 7 of the 8 cylinders for a short period. Is this a problem?

Bob

 

[Wamsutta]

Yes, you get it set up before you turn the key. Find a good ground for the spark tester and clip it there. If you have a test light, you can use that to find a good ground. Disconnect the boot from the spark plug and connect it to the tester. It should only take you about 10 seconds of running time to determine if you have spark or not. If you have spark, move onto the next cylinder.

 

[bob_the_builder]

Great, thanks for your help. I was thinking about just using a jumper cable to connect the spark tester to the negative terminal on the battery. I read this is a good way to make sure the ground is good.

Bob

 

[shockwave]

Do you have a v6 or v8?

 

[bob_the_builder]

The truck is a v8 6.0L

 

[firebox40dash5]

Make sure you use some hose/boot gripper pliers on the boots, or you'll be ruling out your wires if they haven't been replaced lately. The OE ones have a tenacious grip even just on the terminal, I end up wrecking about 1 in 10 in spite of doing it "right".

 

[bob_the_builder]

What is a good boot puller for a silverado.

 

[shockwave]

Use 45 degree needle nose pliers long for wires and turn them while you pull.

But it would be best to get new wires and make sure intake is not leaking either with scan tool and live data look at your stft on both banks

 

[SO/PW newbie]

Would you want to disable the injector for that cyl so you don't nuke the cat??

 

[rancherbill]

Yes, you get it set up before you turn the key.

Good advice! You might make a shocking discovery.

 

[Skin]

Would you want to disable the injector for that cyl so you don't nuke the cat??

You wont "nuke the cat" doing some quick testing.

Great, thanks for your help. I was thinking about just using a jumper cable to connect the spark tester to the negative terminal on the battery. I read this is a good way to make sure the ground is good.

Bob

Safer to use a good block ground. Misfire counters will give a rough indication of what the problem cylinder is. Even with a P0300 you'll see the counter climbing generally on only 1 cylinder. If you shotgun any parts at it plugs and wires aren't a bad idea however be aware a misfire can be caused by a lot of things.

 

[bob_the_builder]

Sounds like I pull the wire off using a boot puller. Connect up the spark plug tool to a grounding block. Disconnect fuel injector of the cylinder being tested (which consists of just unplugging the wire at the fuel injector, correct?). Start engine, run for a few seconds and check for spark. Seems simple enough.

I have been using a buddies scan tool but I have been looking a purchasing an inexpensive scan tool something like the Launch CReader VI or the OTC 3111. Would either of these show me the misfire counters for each cylinder?

Hopefully not too far off the topic of spark plug testers, am I even on the right track? With a misfire code from what I have read can be caused by a number of things. I was not sure the best place to start so I thought I would start by checking for spark. Just some background, initial code that came up was P0446- Evaporative Emission System Vent Control Circuit. This came up 4 months ago and I replace the Vapor Canister Purge Solenoid as the entire canister was packed with dirt and dust. Last week the P0446 code came back along with P0300 - random misfire and the truck ran very rough (noticeable misfire). Did not have a scan tool so I let the truck sit for a few days and then drove it a little and picked up the scan tool. After letting it sit the truck drove fine with no noticeable misfires as all the shacking was gone. Pulled up the freeze frame data and saw the following:

Short Fuel Trim 1 - Neg 8.6
Long Fuel Trim 1 - Pos 0.8

Short Fuel Trim 2 - Neg 7.0
Long Fuel Trim 2 - Pos 0.8

Short Fuel Trim 3 - Neg 98.4
Long Fuel Trim 3 - Neg 98.4

Short Fuel Trim 4 - Neg 98.4
Long Fuel Trim 4 - neg 98.4

RPM 558
TP (%) - 6.3

With the fuel trims so far negative I am wondering if I have a vacuum leak issue and maybe I should look at that before spark.

Again sorry getting off topic on tools but any insight would be a great help as I am just trying to learn on the fly.

Bob

 

[Skin]

Technically +/- 10% is considered "in spec". Starting at 8% I might look for a problem. Yours are -6.2% and -7.8% so I wouldn't be overly concerned. Likewise that means the computer is taking fuel away so its actually on the rich side, not lean. Just to reiterate, on their own though, the fuel trims look acceptable. Those numbers can change under varying loads and speeds though.

Misfire counters are available in mode 6 which pretty much any $100 scan tool should let you access. Depending on the vehicle there might be a live PID in the vehicle specific data as well IF the scan tool supports it. Generally this is only something found in higher end scan tools.

The code set at idle so if the spark test doesn't yield anything apparent look for an intake leak. You can simply use a water spray bottle, squirt it where the intake meets the block, and listen for changes in the engine sound. Do this when the engine is cold. What ends up happening with intake leaks is they seal up when the engine gets up to operating temp.

Short of that and doing plugs and wires just because, you can either clear it and see if it comes back if you don't have a noticeable misfire, or i'd suggest bringing it to a reputable shop because next would be injector, ignition control, and compression tests.

 

[bob_the_builder]

Skin, thanks for all your helpful insight. Looks like I will be ordering the OTC 3111Pro and start looking further into the truck this week now that I have some more time again.

I was doing some more reading on fuel trim and one question that I could not seem to find an answer on was in freeze frame mode the scanner lists short and long term fuel trim 1,2,3,4 (data above). When I look at the live data on the scan tool I see short and long 1 and 2. I guess the 1 and 2 us for each bank on a v8 buy what does the 3 and 4 data mean in the freeze frame data.

Bob

 

[bob_the_builder]

Just placed an order for the OTC 3111Pro. I should have it in the next week. I will give everyone an update once I get a chance to try it out.

Bob

 

[moto440rider]

Those engines had problem with the Lower intake gaskets sucking in air when they are cold.


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[moto440rider]

Especially to cause the random misfire. The launch shows misfire data live on it. I know I have one. The cr123


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[Wamsutta]

I had a P0300 set on my car one time. The first thing I did was test for spark. Car was running very rich which told me not all the fuel was getting burned up. Car has 3 coil packs with a waste spark system. A spark test told me cylinders 1 & 4 weren't firing. At that point I switched the coil packs around to see if the misfire followed the 1 & 4 coil pack; it did not. At that point the prime suspect was the ignition control module. Sure enough, the driver for the 1 & 4 coil pack was not firing the coil. Replaced ignition control module and all was well.