misfire

jlsjoe · September 12, 2006

I have a 1998 Silverado 1/2 T 4WD I drove to work low on gas (I know, a no no) and all seemed fine. 2hrs later I started it and it ran rough and I thought I may be running out of fuel so I put gas in. Started it and it continued to run rough and the SES light began flashing. I drove home 35 mi very slowly and cautiously and the problem continued. Seemed like a severe misfire, I could feel it shake under any load, stronger under heavier load. The SES light flashes while driving and stays on continiously at idle.

Checked air filter, (ok) replaced fuel filter. Problem persists.

OBD = 2 codes, P0301 (misfire cyl 1) P0301 pd ( I assume because the problem continues)

MIL = on

Monitors = 0 Incompete

8 Ready - Misfire, Fuel, Comp, Catylst, Evap, O2 Snsr, O2 Htr, EGR

I cleared the codes and sarted the engine,mis continued and codes returned with the exception of a few of the monitors reported incomplete, I assume because I didn't run it long enough for the test to complete (raw fuel it Cat converter fear).

Replaced plugs with Bosch platinium, old plug were worn but did not appear fouled or wet. Problem persists.

I'm wondering if I should follow with trial and error ie wires, cap, roter etc or does this scream of something specific to anyone? I hate replacing parts and sensors etc only to have the problem continue.

The truck is my work vehicle (cabinet maker), has 148,000 mi, has been well cared for and I don't beat on it. It has been a real horse for me and up to now the only problem I ever had with it was a bad fuel pump. I am the only owner

Thank you!

Joe-

95Sierra2500 · September 13, 2006

Well you definately are detecting a bad misfire on cylinder 1. I'd recommened pulling the plug and seeing what it looks like. It could be that the cylinder is dead due to a bad plug (plug will be wet like it's taking a bath in unburnt fuel), or you may have lost an injector and are getting no fuel to that cylinder. Also, check your gap: you may have chunked a piston, though it's not common on N/A engines.

Haulin' 8.1 · September 13, 2006

Joe the caps on those engines cross the wires so they come out on the same side of the engine they connect to. Eventually the internal insulation fails and they allow crossfiring in the cap. At your mileage I would suggest a new high quality cap and rotor set. This is based on what I do for a living and see most often. Also check the wire to cylinder number 1 very closely for defects and measure it's OHM resistance, it should be under 20,000 OHMs. Get in a dark shop or at night start the engine with the hood up and have someone rev the engine up and down while looking up and down the number 1 wire from plug to cap for spark leakage. Cylinder number 1 on your engine is the front drivers side.

Vernon

jlsjoe · September 13, 2006

Well you definately are detecting a bad misfire on cylinder 1. I'd recommened pulling the plug and seeing what it looks like. It could be that the cylinder is dead due to a bad plug (plug will be wet like it's taking a bath in unburnt fuel), or you may have lost an injector and are getting no fuel to that cylinder. Also, check your gap: you may have chunked a piston, though it's not common on N/A engines.

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The plugs are new and after a couple of short trips(< 2 mi) it is dry. What is the best (easiest?) way to check the injector? The spark plug gap has not changed.

I replaced the plugs with Bosch platninums and have heard different things about them, what is the feeling hear about them?

Thanks.

Joe-

jlsjoe · September 13, 2006

Joe the caps on those engines cross the wires so they come out on the same side of the engine they connect to. Eventually the internal insulation fails and they allow crossfiring in the cap. At your mileage I would suggest a new high quality cap and rotor set. This is based on what I do for a living and see most often. Also check the wire to cylinder number 1 very closely for defects and measure it's OHM resistance, it should be under 20,000 OHMs. Get in a dark shop or at night start the engine with the hood up and have someone rev the engine up and down while looking up and down the number 1 wire from plug to cap for spark leakage. Cylinder number 1 on your engine is the front drivers side.

Vernon

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What would you recommend as a replacement cap/rotor set? I'll checK the wire.

Thanks

Joe-

jlsjoe · September 13, 2006

Joe the caps on those engines cross the wires so they come out on the same side of the engine they connect to. Eventually the internal insulation fails and they allow crossfiring in the cap. At your mileage I would suggest a new high quality cap and rotor set. This is based on what I do for a living and see most often. Also check the wire to cylinder number 1 very closely for defects and measure it's OHM resistance, it should be under 20,000 OHMs. Get in a dark shop or at night start the engine with the hood up and have someone rev the engine up and down while looking up and down the number 1 wire from plug to cap for spark leakage. Cylinder number 1 on your engine is the front drivers side.

Vernon

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I replaced the cap, rotor and wire but still have had no luck...Yet.

Thanks

Joe-

jlsjoe · September 13, 2006

I've also added injector cleaner but am leary to drive it and let the stuff do its thing due to the possibility of ruining the cat convertor or doing other damage. I have read that some vehicles will sense the raw fuel and turn of the fuel to that hole to protect the cat convertor. Is this true and if so would that be a feature on this motor?

KICK · September 13, 2006

I had two bad experiences with Bosch super duper platinum plugs in GM vehicles and won't recommend them to anybody for a GM vehicle.

I'd put in some AC's or Champs and then recheck the engine.

Haulin' 8.1 · September 13, 2006

Hey sorry the parts didn't help. They are the most common cause. You are correct that a severe misfire can melt a catalyst and don't drive it with the CEL flashing if at all possible.

This leaves you with either an incorrect air fuel ratio or low compression on #1. The easiest way to check the injectors is with a scan tool. Other wise you can actually take the upper plenum off and reconnect the injector block and engine harness ground. With the coil disconnected have someone crank the engine with the poppet valves pulled out of the ports. You'll be able to visually see wether they are all working correctly. I know you probably won't try this but I mention it because it is the only way to check them without a scan tool which will fire the injectors individually while you observe the drop in fuel pressure.

Another thing that causes an incorrect air/fuel ratio on those engines is a broken intake gasket at the head suface around the misfiring intake port. Use a can of intake cleaner to spray around the port / intake junction and listen for an obvious change in idle. Also you can check for a leak on the internal side by taking the PCV valve loose and covering the holes in the valve covers where the breather and PCV fit. Hold it for a while then pull one hand off, there should be no suction inside the engine with the PCV laid aside. If there is it's an internal vacuum leak. If you have excessive smoke and pressure suspect worn rings or a defective piston on #1.

As far as compression goes it's usually a busted valve spring on a well maintained engine that causes a sudden low compression misfire. A simple compression check will identify this.

Good luck,

Vernon

95Sierra2500 · September 14, 2006

I had two bad experiences with Bosch super duper platinum plugs in GM vehicles and won't recommend them to anybody for a GM vehicle.

I'd put in some AC's or Champs and then recheck the engine.

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X2. I will not recommend Bosch plugs to anyone for a GM vehicle. Some people can get away with them, but I've seen LT1 TA's, 4.3 Blazers, and 3.8 liter Grand Prixs all have issues with Bosch plugs. Swap 'em for ACs or practically anything else and the problem is gone. Just my personal experience.