99 Tahoe misfiring issue

[Dualstroke]

Hello all, I recently have aquired a misfiring issue or what I believe to be a misfiring issue on my 99 5.7 tahoe.It all started a few weeks back when I was towing one of my enclosed trailers on a 3 1/2 hr trip (one way).I usually use about $150-160 worth of gas on the 7 hr trip.This trip used all of $240 in gas. When I first got there a friend of mine hookep up his nice snap on scanner and codes p0300 and p0174 showed up.One cylinder had over 1400 misfires alone.Unfortunately I can't remember which exact one.Other cylinders on the same side showed some misfires but not nearly as many. Once I got home the symptoms went away(so I thought).Just the other day it did it towing my small boat trailer.I had suspected it was happening only when the truck was working hard but just yesterday and today it has come back without anything in tow. It takes anywhere from 30-60 minutes for it to start acting up.By acting up I mean it is running very rough at idle and is just a dog when accelerating,and using a ton of fuel.I read the codes with my cheap ob2 scanner today and only p0300 showed up.I also noticed today(could be me) but the gas gauge floats back and forth about 1/4 to 3/8 of an inch when running rough.Between searching here and some friends advice it seems as though it could be one of many things. Bad 02 sensor reading improperly and not throwing an 02 code? Bad catylitic converter or converters? Fuel pump? Egr,maf,tps???? I am just not sure where to go next and hoping someone has dealt or heard of similar symptoms. I appreciate any and all help.

 

[Slammed]

P http://www.obd-codes.com/p0300

 

[lesterl]

Check fuel pressure, you might have a bad/ leaking fuel system inside the intake (spider injector or FPR)....

 

[samotahoe]

test maf, does your Tahoe have individual coils?

 

[lesterl]

test maf, does your Tahoe have individual coils?

Not unless he added them, they didnt put individual coils on the 350, waited untill the next body style and put them on the LS series so the 326 had them....

 

[Dualstroke]

Thanks for the info guys. I am still having this problem and to be honest it is driving me crazy. I installed new plugs,wires,cap,rotor,ignition module and nothing changed.Still acts up and only throws a generic p0300 misfire code. Drinking fuel faster than I can put it in. My buddy has the nice scanner but he is 3 1/2 hrs away and no way can I drive this truck on that long of a drive. Guess I am going to have to find a mechanic that can diagnose it correctly and then I will replace the parts. Problem is just cause these mechanics have a scanner doesn't mean they know how to read it or can diagnose it correctly. Unfortunately my dads blue oval has to be my wheels for the weekend trip and not the bow tie

 

[Dualstroke]

Does not have individual coils. MAF has been cleaned and seems to be working correctly.

 

[lesterl]

Have you checked the bleed off of the fuel pressure? Also run it for a few seconds and pull the plugs one at a time and see if one/ some of them are wet with fuel......

 

[ma87k5]

check compression. Bad compression will cause misfire to happen as well.

 

[gary350]

I bought a 99 chevy Tahoe with 95K miles. At 100K miles it started misfiring and gas mileage dropped from 18 to 10 mpg. First thing I did was wait for it to get dark. I raised the hood and started the engine to see if sparks were jumping from the HV ignition coil and HV wires to ground.

Coil was very dirty so I sprayed it clean with carburetor cleaner. I wiped all the HV wires clean with a rag and cleaner. Even though I saw no sparks in the dark the engine seemed to run better the next day.

A few days later the engine is misfiring again. This time I replaced the spark plugs. My Son is an auto mechanic he told me before starting the engine to remove the battery cable at bed time then put the cable back on again the next morning. Removing the battery cable CLEARS all the codes and makes the computer relearn. The engine started hard and ran ruff but it ran better and better the longer it ran. After 75 miles it was running good.

My Son said, reset trip odometer and fill the tank with gas then drive it and check gas mileage. Gas mileage was back to normal and the engine was running good.

 

[Dualstroke]

^^^^^ lol I wish it was that easy.

 

[lesterl]

Pulling the battery on an OBDII system will not clear the codes, I JUST bought a 98 Sierra that the guy tossed the battery several months ago, wired one up, checked codes and got 4 codes (2 were ABS).....

You need to use a scantool to clear codes....

 

[Bigbill]

You need to check fuel pressure you could have a lean miss which could be caused by a restricted fuel filter. It's a cheap check and I had issues when towing our camper in PA it was due to a restricted fuel filter.

 

[Beeker702]

Do a compression test on all the cylinders. Should be around 150 or 10% of each other. If its low then you might have a bad head gasket. You might even have a bad upper intake gasket or a vacuum leak somewhere. Wouldn't even surprise me if someone even tried to turn the distributor and that's causing the problem. Also make sure the wires are on the cap the right way as stupid as it may sound.

Do you have a drill? Take a 1/4 bit and drill a hole about where the two pipes from the manifold meet and drive the truck after the codes are cleared and the hole is drilled. If you have two pipes that go to a flange drill a hole on each pipe before the flange and see what that does. It will be a lil louder but you can have that mig weld after. If it runs better and no codes it's your cats. You might wanna do one pipe at a time if you have two cats so you know which cat it is. And no. Not always will a o2 code will show I've seen it many times before

 

[Suthernrayzd]

I was told that mine of the same year had a misfire issue and that the fuel injectors need replacing. Does your get a nasty stutter going down the road? Mine will stick hard enough to make all the dash panels pop when it sticks so hard, usually after 45 mph, and seems more prominent in humid weather. I'm going to try the spritz bottle trick tonight, but I just had wires, plugs, distributor and all replaced. An old friend says it could be from a solenoid in the transmission for overdrive lockout and that it could be stickin when it slips in an uncontrolled lockout. Says I can unplug the solenoid to see if that's the problem but I also have the horrible gas mileage issue. Any thoughts? 5.7 vortec

 

[gary350]

The shaking problem your having may be the steering bushing.

There is a brass bushing in the steering system that goes bad. At about 45 to 50 mph my front wheels got to shaking so bad it would shake the liquid out of a drink cup. I could drive faster or slower the problem would stop. It finally got so bad the steering wheel would turn 1/8 turn in both directions without moving the wheels. Raise the hood look straight down at the gear box and have someone turn the steering wheel back and forth about 1/4 turn. If your steering arm is moving left/right but the bar it attaches to does not move and front wheels do not move the bushing is bad.

Get the Fork Tool on tool loan at Auto Zone to remove the steering arm. Remove the hex nut hammer the fork in the arm will pop off. Remove nut on other end of arm. Replace bushing and put it back together.

Misfiring is almost always the ignition system. Distributor cap, wires, plugs, coil.

 

[Suthernrayzd]

Right on

Thanks man, ill check all that out, along with the steering issue since I have 23" rims, that bushing is more than likely shot.

 

[Suthernrayzd]

Would the misfire make the truck feel like the drive system locks up hard for a split second then breaks free?

 

[gary350]

Would the misfire make the truck feel like the drive system locks up hard for a split second then breaks free?

Are you driving on the highway in 4 wheel drive?

Some vehicles are designed so the front wheels have a 1% higher gear ratio than the back wheels. In snow and ice and mud this keeps the front wheels all the time pulling harder than the back wheels. But on the dry asphalt highway you get what is called WIND UP. The gears get under tension and soon something has to give so the wheels jerk loose from the road and the whole vehicle jerks and jumps or it strips the gears in the transmission.

Do not highway drive in 4 wheel drive.

 

[Suthernrayzd]

Yeah

No, I don't ride 4wd unless I'm stuck, that happens in 2wd, unless 4wd is not disengaging all the way, but I can definitely hear when it's in 4