99 Tahoe Really bad miss

[Timberwolf17044]

On my way home last night near the end of a 400 mile trip. Was climbing a steep 3 mile grade towing a 800 lb boat motor and trailer. Engine was running at 3000 rpm. Suddenly started missing really bad. I was able to drive it the remaining 40 miles to home. There was no unusual noise and its not smoking at all. At idle it shakes and carries on like crazy. This vehicle has 197,000 miles on it. I haven't started any diagnoses yet. Any thoughts where to start?

 

[lesterl]

Check into fuel pressure, suspect possibly a leak from possibly FPR? Check condition of plugs.....

How about Cap/ Rotor?

Blown Head Gasket?

Any Codes?

 

[Timberwolf17044]

Ok here is some additional info.

No codes
Don't see any fuel leakage
Replaced plugs, wires and distributor cap.

pulled wire on #2 cylinder no difference in the way the engine runs.

put one of the old plugs into the #2 wire and ran to visually inspect spark and it appears orange. Did the same with other plugs and spark looks white to almost blue. I'm now thinking ignition coil...???

 

[lesterl]

I would suspect #2 wire, plug, or Cap if #2 was orange and others were white.

Fuel leakage would be inside the Intake Plenum, not visible from outside.

 

[Timberwolf17044]

Ok here is an update..

I have now replaced the plugs a second time going to AC Delco Platinum's
Replaced Rotor
Ignition Coil
Cam Sensor
Also checked all cylinders with an inline spark tester and can see no difference with any of them all good spark.
Checked fuel pressure and it reaches 60 PSI with key turned on and drops no lower then 45 even after the key being off several minutes so I don't think I have any fuel leaks.
Whats next?

Also I removed the throttle body to get a somewhat better view inside the plenum and could hear or see no fuel spray. There is alot of varnish deposits inside there. I also did a partial compression test of the #1 & #3 cylinders with a reading of 150 plus on #1 and near 180 on #3. I must add that I was mistaken on the cylinder locations earlier when I had mentioned the #2 cylinder. I'm thinking now I need to do a full compression test just for verification of mechanical integrity?

 

[lesterl]

Lowest cylinder should be within 10% of highest IIRC, so the 150 is pretty awful.... Check compression on all cylinders, on the low ones, put a tablespoonful of oil in the cylinder, and repeat test, if pressure comes up, you have bad / cracked rings, if not suspect valve / head gasket issue.....

 

[Timberwolf17044]

Just an update if anyone is interested turns out it was a bent valve. Any thoughts on how this occurs?

 

[lesterl]

Does it look like it had an impact? Piston have a impact mark on it? Any wild options in engine (Cam/ rockers/ etc?)

 

[Timberwolf17044]

Nope no marks on the piston at all. Just a bent valve. However I am still having issues with it. Brought it home last night after the wrenchie finished up at 11 pm. Still had a slight miss. I was in the shop with the mechanic when he set the valve lash and he DID NOT turn the nuts 360` as per the instructions. I questioned that but he seemed to know what he was doing so I let it go. Today it got the better of me so I removed the valve covers and adjusted the valve lash personally as it is supposed to be, tightened until no up/down movement in the pushrod and then 360` turn after that. It did help alot but I still seem to have a timing issue. I also found that the front screw that holds down the distributor cap wasn't getting tight. Further inspection found the base that the screw screws into is broken. A new screw however did get tight. I realize that there is no timing adjustment on this vehicle but I tried anyhow and what I have found is that I can hardly move the distributor an 1/8" in either direction without adverse effects, excessive hesitation in one direction and excessive misfiring in the other. I also noticed I can turn the rotor at least 1/4" back and forth. The missfire now seems to be at top end or under load although every once in awhile when I start it up it will run for about a minute or less and then just shut off. I'm taking it back to the shop to have them double check the distributor was installed correctly and as per some reading check the cam retard setting I think it is called. I noticed the mechanic had put marks on the distributor and rotor prior to removing it but read somewhere there is a third component to line up? Ok that's a mouthful to say thoughts anyone?

Addon: Rockers and pushrods were all ok.

 

[lesterl]

Have you replaced cap/rotor/plugs/wires recently?

Looks like Cap/wires werent replaced, but you are running some oddball platinums? Go back with OEM plugs (I had a batch of Bosch platinums that were absolute CRAP and replaced them with some NGK's, missfire was gone after that.) Check your gap also on the plugs, dont want anything excessive, probably no wider than 45 thou.....

 

[Timberwolf17044]

Sorry I guess I missed some info, the following were replaced prior to the heads.

Plugs: AC/Delco all gapped .060 as per specs
Wires
Rotor
CMP Sensor
Ignition Coil
Cap

I'm curious how much I should be able to move the rotor if I just take the cap off?

 

[lesterl]

Rotor shouldnt move much in either direction.

Might drop the Gap on the plugs to around .045 Some have had luck with missfires going away with a narrower gap or a hotter coil....

 

[Timberwolf17044]

I understand what your saying but with all these new components I shouldn't have to step away from factory specs. The free play in the rotor bothers me and I know the guy had a time getting the distributor back in place and frustration may have landed it off a tooth in either direction also causing the misfires no?

 

[Timberwolf17044]

Video from this morning starting up cold at 60 degrees F
http://youtu.be/Uz4eaV6Opko

 

[lesterl]

Sounds like ya got an idler or sumtin squeaking.....

 

[Timberwolf17044]

Woo Hoo she's back up and running. Turns out I had the base timing off just a bit. And yep I gots me a squirrel under the hood lol

 

[lesterl]

NICE!!!!!!!!!!!!!!!!!!!