CIS Problem - backfires; low idle; etc.
04-06-2003, 01:52 AM
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CIS Problem - backfires; low idle; etc.
I'd really appreciate some diagnostic suggestions for my '82 SC.
Here are the intermittent symptoms:
1) When cold - backfires; low idle (400rpm); tries to stall
2) All of sudden it starts fine when cold and when it gets warm (above 1st white mark on oil temp guage), it starts losing power; idle goes low.
3) It seems like the frequency valve is not running when I have starting problems.
Here is what has been replaced and done:
1) Thought fuel contamination, so...
Drained fuel tank; replaced fuel filter; used compressed air to clean out the Warm-up regulator (WUR)
When draining fuel (by using fuel pump after shorting fuel relay pins 30 and 87a, and ignition on) - I noticed that the frequency valve was not constantly running. It didn't seem to have a 50% duty cycle.
2) Replaced all 6 fuel injectors. (I had 206K miles on them anyways).
3) Checked continuity on the cold start switch; 15 degree switch; and aux fuel regulator switch.
4) Verified the O2 sensor relay worked. I put 10v on across pins 85 and 86 - it clicked and I measured closed circuits across both 30-87b and 30-87. Could this be intermittent? I tried it several times.
5) I checked ground from the O2 sensor relay. It was good.
6) O2 sensor was replaced 6 months ago. Distributor cap; rotor; air filter replaced 18 months ago.
7) I regapped the plugs and made sure the connectors were on tight. There is continuity across the wires; and no "light show" in the dark when the engine runs.
8) I checked the vacuum lines and all seemed on tight. Air box straps seem tight.
9) Could the Lambda control unit or Oxygen sensor control unit be bad? I checked the wire harness and it seemed firm. Any way to diagnose it?
10) Checked the air flow sensor plate. It seems to move and seat appropriately.
11) I put a dwell meter on the "test connector". It measured 90 degrees. I think this equates to a 100% duty cycle. Of course, this was when the car was idling fine.
12) When it was having idle problems, I tried unplugging the O2 sensor. It didn't make a difference.
13) When running OK, I took off the oil filler cap. This unmetered air resulted in a lower, rougher idle.
I'm running out of ideas. I'll check the fuel pressure next, but the pump seems to be working fine.
Bottom line - help! Do I need to take it to a shop?
Here are the intermittent symptoms:
1) When cold - backfires; low idle (400rpm); tries to stall
2) All of sudden it starts fine when cold and when it gets warm (above 1st white mark on oil temp guage), it starts losing power; idle goes low.
3) It seems like the frequency valve is not running when I have starting problems.
Here is what has been replaced and done:
1) Thought fuel contamination, so...
Drained fuel tank; replaced fuel filter; used compressed air to clean out the Warm-up regulator (WUR)
When draining fuel (by using fuel pump after shorting fuel relay pins 30 and 87a, and ignition on) - I noticed that the frequency valve was not constantly running. It didn't seem to have a 50% duty cycle.
2) Replaced all 6 fuel injectors. (I had 206K miles on them anyways).
3) Checked continuity on the cold start switch; 15 degree switch; and aux fuel regulator switch.
4) Verified the O2 sensor relay worked. I put 10v on across pins 85 and 86 - it clicked and I measured closed circuits across both 30-87b and 30-87. Could this be intermittent? I tried it several times.
5) I checked ground from the O2 sensor relay. It was good.
6) O2 sensor was replaced 6 months ago. Distributor cap; rotor; air filter replaced 18 months ago.
7) I regapped the plugs and made sure the connectors were on tight. There is continuity across the wires; and no "light show" in the dark when the engine runs.
8) I checked the vacuum lines and all seemed on tight. Air box straps seem tight.
9) Could the Lambda control unit or Oxygen sensor control unit be bad? I checked the wire harness and it seemed firm. Any way to diagnose it?
10) Checked the air flow sensor plate. It seems to move and seat appropriately.
11) I put a dwell meter on the "test connector". It measured 90 degrees. I think this equates to a 100% duty cycle. Of course, this was when the car was idling fine.
12) When it was having idle problems, I tried unplugging the O2 sensor. It didn't make a difference.
13) When running OK, I took off the oil filler cap. This unmetered air resulted in a lower, rougher idle.
I'm running out of ideas. I'll check the fuel pressure next, but the pump seems to be working fine.
Bottom line - help! Do I need to take it to a shop?
04-06-2003, 12:53 PM
#2
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Join Date: Jun 2001
Location: Huntington Beach, CA
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I went through the same thing. My car wouldnt idle, it would back fire, and I checked all the things your talking about. I did the fuel filter, plugs etc, etc. It turned out I had a vac leak, well several small ones. i replaced the aftermarket injector O-rings with the green bosch O-rings, I found that the metal vac pipe that plugs into the back of the throttle body was leaking a little, and the vac tube that connects to the WUR was leaking just a little. all these things together turned into a big problem. i squirted carb cleaner around all the vac joints while the idle was running and listened for a difference. It was very frustrating. Good luck
