Misfire from 1200 to 2200 RPM? (1 Viewer)

Joined
Aug 19, 2010
Messages
46
Location
San Diego, CA
Hey guys, I'm back again.

I tried to smog my 60 a while back and it failed for high HC. I noticed a misfire from 1200 and up, gets the worst around 2000 to 2200. I'm fairly sure thats what's getting me. I started out by getting a new coil, wires, cap, rotor, plugs and air filter. Checked the timing and its where it should be. I have also replaced half the vacuum lines in the engine bay (didn't buy enough initially and ran out part way through). I have been going through the emissions FSM the last few weeks as time allowed and have had no luck. I was thinking the deceleration fuel shutoff system was the culprit, as pinching the line from the vacuum switch makes no difference in the misfire, but all the components check out fine. I am lost as to what could be causing this misfire. Any ideas?

Kyle
 

inkpot

SILVER Star
Joined
Jan 30, 2003
Messages
13,662
Location
All over Arizona
 
 
 
Howdy! Have you gone thru the valve train? If a a valve is set too tight, or if it is getting sticky/weak return spring, then it may not close tightly for the combustion cycle, especially at higher rpms. That would be a possible source of a miss fire and also raw fuel going into the exhaust stream. John
 
Joined
Nov 26, 2004
Messages
2,465
Location
Texas
 
 
 
I'd be suspicious of your EGR valve not working properly. Search here for stumbling/ hesitation and EGR bypass to troubleshoot it.
 
Joined
Aug 19, 2010
Messages
46
Location
San Diego, CA
Looks to be the EGR system. I tested the vacuum modulator as per the FSM and seems restricted, so I'm gonna get a new one. Pulled the EGR valve off and it had smooth operation. Throwing it all back together, I disconnected the EGR valve from the vacuum modulator and applied vacuum, stumbled like the FSM says it should. Driving it while disconnected, there was a world of difference. Still feels like there is a slight stumble at 2K, but waaay better than it was before. Gonna finish replacing the remaining vacuum lines for good measure and take it back to the smog station. Thanks again for the help guys!

Kyle
 
Joined
Nov 26, 2004
Messages
2,465
Location
Texas
 
 
 
Good to know. Hope you get it figured out! I've had luck spraying Seafoam in the EGR valve to help loosen it up and get rid of carbon build-up.
 
Joined
Dec 14, 2005
Messages
1,430
Location
colorado
 
 
What are you co2, HC readings at cruise? Got a scope to check the secondary coil wave patterns?
EGR is only there to allow some circulation from the exhaust back into the intake in the event cylinder temperatures exceed 2,500 degrees and quenching the production of Nox by reducing the temperature. So EGR would not cause high HC. What is the spark plug gaps?
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top Bottom