1998 Chevy Truck Misfire (Cannot Find Problem ) Help!!

If you mean codes P0147 - O2 sensor heater circuit Malfunction (Bank1 Sensor 3) and P0300 - Random/Multiple cylinder misfire detected

Check the wiring harness where it goes under the vehicle for a spot that has burnt/rubbed through and that is grounding out the 12 volt heater line to the cat. converter sensor. Sounds like the wire is shorting out and cutting power to the ignition causing random power pulses leading to misfires. Shouldn't be to hard to find. Take a dry day and put it up in the air enough so you can get under it. Go along the harness and look for the area that is damaged. Mark it and check the rest of the harness. Repair the bad area. Test vehicle.

Steve W.

Thx Steve, much appreciated, will let you know what happens.

ProTurbo

I had a similar problem a while back, that was caused by a hairline fracture in the distributor cap of my old truck....course, I dunno if yer modern engine there has a distributor cap....I haven't looked under the hatches of many new cars...

-- Lee K. Gleason N5ZMR Control-G Consutlants snipped-for-privacy@houston.rr.com

Change the distrubuor cap and put cilocone on the cap and wires. you can get spray cilocone and spray it on all of it. It sounds like water (dampness) is getting up in your cap and after it runs it drys it out...you can also spray you distrubtor with it too.

Check the distributor cap for cracks or corrosion on the internal contacts. My original cap had aluminum terminals. I began having problems with misfires when damp. When I checked the cap there was a white powder on the terminals (corrosion). After that I always checked at the parts store that the terminals were copper. Never had a problem after that.

R> I have a 1998 4x4 Chevy V6 (a 4.3 I think).

Distributor cap was changed also...

Sorry to all who replied but cap has been changed....

Some are talking about the egr valve (to be cleaned) or oxygen sensor (to replace it)

Need feedback

Thx again

ProTurbo

Check the Travel of your Rocker Arms .. to See if you have a WORN lob on the CAM .

hairline

under the

147 relates to an O2 sensor, and 300 is misfire detected., but I think these are symptoms, not causes. I think if it were me, I would pull every single ground, clean them and the reconnect them. a bad ground will act up more in damp weather than dry,

Whitelightning

What brand distributor cap did you use? The Chevy truck engines are very sensitive WRT distributor cap and rotor selection. If anything other than OEM Delco, change it. Aftermarket caps can and do fail in less than 1 month.

Quite possible.

Check for 12 volts and ground on the O2 heater circuit, if good, then the heater has burned out requiring O2 sensor replacement.

As long as its a quality replacement, it will be fine. You don't actually think GM manufactures those parts do you? On the other side of the coin, the $5.99 special ..........

Whitelightning

It doesn't matter who manufactures for GM, the aftermarket V-6 and V-8 distributor caps are a pattern failure item.

My worst case experience was failure after 5 weeks. Next worse was 13 months, both caps were Echlin premium line. In both cases the [old] OEM cap lasted for over 90K miles. There was a discussion on i-ATN in the last week or so regarding a no start after a tune up, everyone told the OP to swap the cap, the OP claimed it was brand new. A new Delco cap was the fix. Given this, the posters problems warrant checking out who supplied -his- distributor cap.

You Must be a GM/ DELPHIA Worker ???

Do u Enjoy your DELL COMPUTER ?

And I bet you buy most of your tools from HARBOR FREIGHT ( CHINA MADE ) and I am Unpatriotic because I Have a NON GM Vehicle !

Actually, I despise GM with a passion. I'm just a lowly auto mechanic with 35 years of experience.

1 Dell, 3 Apple, 1 Panasonic, 1 HP pocket PC

Mostly Snap-On with a few Mac, Matco and the odd Craftsman.

-WHO- the F&%k are you again?