Missfire under hard acceleration
04-23-2006, 08:53 AM
#1
Missfire under hard acceleration Thought there were some smart people who are reaning this form so here goes:
I did a cam swap and valve springs, push rods, timing chain ect. in March. Car was running fine. Ran about 3 tanks of gas. The other day it sounded like I blew up the motor. It backfired and shut off at around 4000 RPMs Started back up and drove ok untill I hamer down and it backfires and sputters and shuts off sometimes. I have no SES lights. So I am assuming it is a misfire. I checked all the plug wires, valve terain, 4 of the spark plugs, (they were just changed 1000 milse ago). Every thing looks ok. Could I have a bad coil pack or fuel injecter? If so shouldnt I get a SES light? How do you check a coil pack or fuel injector? What the hell is wrong with this car? Please help.
Car has SLP headers and y pipe, MAF, lid, and custom tune by Texas speed. Cam is 228,228 on 112LSA. Cheap Flowmaster exhaust. I aslo get codes for the front 02 sensors the rears are deleted. Thanks for all the input so far. Do mass air flow sensors go bad? Is there a way to test them??
Well I got new 02 sensers. Took a ride with the snap on scanner. No missfires at all. MAF seems to be working fine. No other codes? What the hell is wrong with this thing???? Somebodys got to know???
Take the 2 seconds and disconnect the MAF. Those bitches get dirty and do the same thing you are describing. When mine acted up I was going nuts trying to figure it out.
Easy to check. Disconnect and go for a ride.
I had it disconected and it had a hard time idleing and finaly got to the point where it would idle and I did not even get around the block and seemed to be doing the exact same thing. Should I drive it farther with it disconected?
I did a cam swap and valve springs, push rods, timing chain ect. in March. Car was running fine. Ran about 3 tanks of gas. The other day it sounded like I blew up the motor. It backfired and shut off at around 4000 RPMs Started back up and drove ok untill I hamer down and it backfires and sputters and shuts off sometimes. I have no SES lights. So I am assuming it is a misfire. I checked all the plug wires, valve terain, 4 of the spark plugs, (they were just changed 1000 milse ago). Every thing looks ok. Could I have a bad coil pack or fuel injecter? If so shouldnt I get a SES light? How do you check a coil pack or fuel injector? What the hell is wrong with this car? Please help.
Car has SLP headers and y pipe, MAF, lid, and custom tune by Texas speed. Cam is 228,228 on 112LSA. Cheap Flowmaster exhaust. I aslo get codes for the front 02 sensors the rears are deleted. Thanks for all the input so far. Do mass air flow sensors go bad? Is there a way to test them??
Well I got new 02 sensers. Took a ride with the snap on scanner. No missfires at all. MAF seems to be working fine. No other codes? What the hell is wrong with this thing???? Somebodys got to know???
Take the 2 seconds and disconnect the MAF. Those bitches get dirty and do the same thing you are describing. When mine acted up I was going nuts trying to figure it out.
Easy to check. Disconnect and go for a ride.
I had it disconected and it had a hard time idleing and finaly got to the point where it would idle and I did not even get around the block and seemed to be doing the exact same thing. Should I drive it farther with it disconected?
04-23-2006, 10:23 AM
#2
TECH Regular
iTrader: (1)
Join Date: Aug 2005
Location: Huntingtown, MD
Posts: 465
Likes: 0
Received 0 Likes
on
0 Posts
I Would pull the valve covers off to see if there is a rocker that has come loose or push rod not in place. Happen to me before the rocker came loose and the push rod ended up poping out of the lifter and getting jammed in between the block and the lifter in turn bending the push rod badly.
04-23-2006, 04:14 PM
#3
TECH Fanatic
iTrader: (12)
Join Date: Jan 2004
Location: Houston, TX
Posts: 1,869
Likes: 0
Received 0 Likes
on
0 Posts
A buddy of mine had this problem once in a cammed A4, turned out it was the Crankshaft Position Sensor, no DTCs, log data was perfect until WOT @ 4000rpms or more it would just go BANG and completely shut off. All other putting around town and such was totally fine.
Might not be your problem, but just another place to look... I'd also take a look at the engine grounds
Might not be your problem, but just another place to look... I'd also take a look at the engine grounds
