911 SC Misfiring
12-15-2007, 07:11 PM
#1
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911 SC Misfiring
Hi I recently had a lot of work done by a so-called specialist that included replacing the air box, rebuilding the throttle assembly and replacing spak plugs and leads. I still dont feel the car is as good as it might be. There is a really severe misfire at about 2000rpm which is just about 30pmh, the maximum speed we can drive in towns.
The car is 25 years old, but even so I would appreciate any comments about why the car might misfire. My gut feel says ingnition, but as the fuel side has had so much done on it there may be a problem there.
Do the offical dealers have diagnostic equipment for cars this old.
Thanks
The car is 25 years old, but even so I would appreciate any comments about why the car might misfire. My gut feel says ingnition, but as the fuel side has had so much done on it there may be a problem there.
Do the offical dealers have diagnostic equipment for cars this old.
Thanks
12-15-2007, 10:17 PM
#2
Rennlist Member
Take it back to the specialist and drive the car for him. Your car should be dead smooth through that, and all, rev ranges. The dealer probably does not have CIS gauges any more (fortunately many problems on cars your age can be solved with logic and hand tools), and most dealer mechanics probably don't understand the pre-'90 cars or care much about them...
12-16-2007, 10:03 AM
#3
NASA Racer
Rennlist Member
Rennlist Member
Could be a bunch of things including ignition. Does it misfire under acceleration and/or deceleration? I'd be suspicious about that air box replacement as well as ignition/timing and fuel delivery.
12-17-2007, 02:04 PM
#6
Rennlist Member
No "dwell" on your car (no points). Mixture, if far off enough to cause a severe missfire usually produces other symptoms. Spark plugs can be your culprit; if they're not the correct heat range/type, and they're not gapped properly, they can be a problem. Unfortunately, trying to diagnose this problem on this forum is just about impossible with your limited information. Things that would be helpful:
1. What was the CO% set at?
2. Was an unusual level of HC present?
3. What type of spark plug "leads" were used?
4. What does "rebuilding the throttle assembly" mean?
5. How did the car run before the work was done?
6. Were the injectors tested during airbox replacement?
7. Was the engine removed for airbox replacement?
1. What was the CO% set at?
2. Was an unusual level of HC present?
3. What type of spark plug "leads" were used?
4. What does "rebuilding the throttle assembly" mean?
5. How did the car run before the work was done?
6. Were the injectors tested during airbox replacement?
7. Was the engine removed for airbox replacement?
