Misfire Now Kills Truck

[Loomis]

I've had a misfire for awhile now on my 97' tah. It hasn't been driven much at all lately.. Had scan tool put on it long time ago.. had crankcase cam relation code.. replaced both of them.. still had code for a long time after.. started mis firing AFTER them were even replaced.. Had code checked again recently... got a O2 code. Guy forgot what O2 lol. I tried cranking off one of my upstream ones on drivers side.. couldn't get it off for the life of me. I unlplugged it, plugged it back in, tried it some more,finally gave up. Start Her up, misfire is twice as worse now, even killed on me when put into drive. Misfire is WAY worse when put into a gear; but still really noticeable when in park. When I put it in drive the lights were dimming with the idle, oil pressure gauge was fluctuating with it. Why did it get 2x worse? Do you really think it could be a O2? Body has about 168,000. Motor was replaced like 4 years ago I think. I've had a Fuel Pressure regulator put in. A buddy I know thinks it could be the distributor being off when the mechanic put it back in, causing the misfire. But the misfire didn't come about till way after that was replaced. Thanks guys-

 

[Paul Greathouse]

This could be way off base but may be worth a try. A couple years ago my son did some sound system mods in his 93' Z71. Afterward his truck mysteriouly started running rough, the lights would dim and the dash gauges would jump around. Notice the similarities.

I'm better with wrenches than wires, so I was at a disadvantage to begin with. We fought it for a couple weeks, went over the sound system mods again and again but found nothing wrong. So, I took it to the shop that I use when I get in over my head. One of the mechanics went over it for a while and was as stumped as I was, so the owner, who is one the best electrical troubleshooters I know took a look. It was so obvious, it made me and his mechanic both feel silly.

While installing the sound system my son had connected/disconnected some wires at the battery cable connections and had left the ground cable loose. It was just tight enough for the truck to run but run badly. Try checking and cleaning all your battery connections especially the ground cable. Not just at the battery but at the frame too.

Like I said, I may be way off, but it would be a cheap thing to try. You may not have loose connections but you could have corrosion. It sure sound like a grounding problem.

 

[Loomis]

Misfire

Hate to say I found out why the misfire got suddenly worse; Vacuum tube from intake to valve cover was totally unhooked from vavle cover.. cleared code.. came back on. P1345a.. Crank correlation whatever.. misfire seemed WAY better though. I know the tube hasn't been unplugged the last half year causing the misfire. So Its gotta be something else also. Crank, and Cam shaft sensors have been replaced- months ago

 

[tim@sp]

I would say get it on a scanner that can read missfire data... that way you can pin point the missfire... If its a random missfire then you know its a sensor, faulty ground distributor gear ECT. If one cylinder is misfiring then It could be the injector harness plug on the upper intake, or an injector. at that point, pull the spark plug wire that the scanner is telling you that is misfiring and see if it is wet or dry. Dry meens no fuel and wet meens no spark!!

I agree with the grounds, the last tahoe I bought had the motor repalced and they forgot a couple grounds. That took care of most of the issues right there.

Good luck and keep us posted.

 

[tahoeman21]

misfire

Have you checked your fuel injectors?

 

[Loomis]

While back had a fuel injector cleaning. Hooked it up to the machine.. but how I check them?

 

[Loomis]

Hate to say.. idle doesn't seem that bad, but when you bring it past 1,000 RPM its at its worst, then smoothes out above that.

 

[Loomis]

Hey.. I forgot to add in, when Im at a stop.. the truck feels like it wants to keep going, like its working against the brakes. Could the misfire be from it being out of time and running too fast?

 

[41racing]

Has the truck had intake gaskets done just before the miss started. Sounds to me like your cam offset isn't correct. You need a scan tool to check it. It should be 0* +or-3*. Bring the rpm up past 1000 and loosen the dist and turn it until the reading is within spec.

 

[Loomis]

Actually had a different motor put in about 3-4 years ago i believe the guy i bought it from. Wonder how the hell my distrubutor is off?

 

[brodg]

distributor is in wrong timing is too far advanced no vacum in engine hence no brakes. try turning the distributor with the truck running and see if it gets better.

 

[Loomis]

I got brakes, but it just seems to coast right along the speed Im going even if i let off the gas. It remains that speed until I hit the brakes lol. Also got this slop in my rear end. I had it fixed once, but now its back. I think its U-joint related. I take off, and you can feel a loose shifting in the drive line. so annoying.