99 Tahoe rebuilt motor misfire - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Souths79 · 11-25-2011, 07:56 PM

i have had the unfourtunate pleasure of working on a 99 tahoe with a buddy of mine, 350 in it. body has 132k on it. and until the motor started knocking and low oil psi condition it ran perfect. fast forward 6 months. we pulled the motor striped it down and sent it to a well known engine builder got the short block back completely rebuilt and heads freshened up. put the motor back together(bolt heads and intake on and acc junk) got it in the truck again and from the first moment it was fired it had a dead miss. i am a mechanic by trade but this one has me stumped.

Hooked up my MT2500 got the timing set which wasnt but 5 degrees off to begin with and still has a miss on cylinders 5 AND 7. NOW, heres where it gets funny. 5 and 7 miss at idle, above 2k RPM 6 and 8 misfire. you can actually feel the motor smooth out and see it on the scan tool go from misfiring on 5+7 to 6+8. HELP!!

FYI, new plugs etc TWICE to make sure it wasnt that, Fuel Psi 60psi, compression tested great, spark test and injector pulse test ok

Tried not to make this long but more info the better!

70BLAZERX2 · 11-25-2011, 09:42 PM

a valve rocker arm mabye to tight?

dirt on the spyder injector nozzle from cleaning it?

carbon in the egr valve from being apart?

Just the 3 i can think of right now...egr vavle i would check 1st..

loose egr metal tube from intake to manifold..

vacumme leak at brake booster hose to intake

70BLAZERX2 · 11-25-2011, 09:44 PM

bad distributor?

BigBlocksRule · 11-25-2011, 10:00 PM

Bad dizzy cap.

70BLAZERX2 · 11-25-2011, 10:03 PM

if you run a K&N filter ...the oil will foul out the mass air flow meter over time..you need to clean it with the special spray from the parts store..

this could be another cause..try to unplug the iar flow meter and see if it stops...if it does...that may be it...Just guessing here..its hard when its not in front of you

Souths79 · 11-25-2011, 11:50 PM

70blazer: i have rechecked running and not running on the valves before the post. before it was re assembled i made sure to carefully double check the spray nozzles also it stayed in a trash bag in the back of the truck so no weather got to it. also no it does not have a K&N. i believe too that they screw up the MAF. also cleaned that too. no help. 2morrow i will check the o-ring again on the PB Air line. and when i find a distributor i am going to try that if nothing else found

11-25-2011, 07:56 PM	#1
Souths79 Registered User Join Date: Aug 2009 Location: King George, Va Posts: 12	99 Tahoe rebuilt motor misfire i have had the unfourtunate pleasure of working on a 99 tahoe with a buddy of mine, 350 in it. body has 132k on it. and until the motor started knocking and low oil psi condition it ran perfect. fast forward 6 months. we pulled the motor striped it down and sent it to a well known engine builder got the short block back completely rebuilt and heads freshened up. put the motor back together(bolt heads and intake on and acc junk) got it in the truck again and from the first moment it was fired it had a dead miss. i am a mechanic by trade but this one has me stumped. Hooked up my MT2500 got the timing set which wasnt but 5 degrees off to begin with and still has a miss on cylinders 5 AND 7. NOW, heres where it gets funny. 5 and 7 miss at idle, above 2k RPM 6 and 8 misfire. you can actually feel the motor smooth out and see it on the scan tool go from misfiring on 5+7 to 6+8. HELP!! FYI, new plugs etc TWICE to make sure it wasnt that, Fuel Psi 60psi, compression tested great, spark test and injector pulse test ok Tried not to make this long but more info the better!

11-25-2011, 09:42 PM	#2
70BLAZERX2 Registered User Join Date: Jan 2010 Location: GREENEVILLE TENNESSEE Posts: 1,310	Re: 99 Tahoe rebuilt motor misfire a valve rocker arm mabye to tight? dirt on the spyder injector nozzle from cleaning it? carbon in the egr valve from being apart? Just the 3 i can think of right now...egr vavle i would check 1st.. loose egr metal tube from intake to manifold.. vacumme leak at brake booster hose to intake

11-25-2011, 09:44 PM	#3
70BLAZERX2 Registered User Join Date: Jan 2010 Location: GREENEVILLE TENNESSEE Posts: 1,310	Re: 99 Tahoe rebuilt motor misfire bad distributor?

11-25-2011, 10:00 PM	#4
BigBlocksRule Registered User Join Date: Jun 2008 Location: Lubbock, TX Posts: 2,047	Re: 99 Tahoe rebuilt motor misfire Bad dizzy cap.

11-25-2011, 10:03 PM	#5
70BLAZERX2 Registered User Join Date: Jan 2010 Location: GREENEVILLE TENNESSEE Posts: 1,310	Re: 99 Tahoe rebuilt motor misfire if you run a K&N filter ...the oil will foul out the mass air flow meter over time..you need to clean it with the special spray from the parts store.. this could be another cause..try to unplug the iar flow meter and see if it stops...if it does...that may be it...Just guessing here..its hard when its not in front of you

11-25-2011, 11:50 PM	#6
Souths79 Registered User Join Date: Aug 2009 Location: King George, Va Posts: 12	Re: 99 Tahoe rebuilt motor misfire 70blazer: i have rechecked running and not running on the valves before the post. before it was re assembled i made sure to carefully double check the spray nozzles also it stayed in a trash bag in the back of the truck so no weather got to it. also no it does not have a K&N. i believe too that they screw up the MAF. also cleaned that too. no help. 2morrow i will check the o-ring again on the PB Air line. and when i find a distributor i am going to try that if nothing else found



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