Badly fouled spark plugs |
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Badly fouled spark plugs |
andreic |
Sep 15 2016, 08:43 AM
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#1
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Member Group: Members Posts: 172 Joined: 21-December 15 From: Madison, WI Member No.: 19,479 Region Association: Upper MidWest |
Hello,
I have a problem on my newly rebuilt 1.8L engine, with L-Jet. Yesterday as I was driving home the car simply quit about 5 blocks away from home. Until this point it was running very well. I had to have it towed home and now I started trying to diagnose it. So far I've checked that the fuel pump operates when opening the flap in the AFM, so I suspect I got fuel pressure right. The starter spins the engine well. I have strong spark on the main distributor cap wire (coming from the coil), and putting a brand new spark plug into one of the spark plug wires I have spark at that too. (Originally I was too lazy to pull an actual plug from the engine.) But this morning I tried pulling a spark plug from the engine, and it is completely black and covered in carbon. Not wet, just covered in a thick layer of solid black material. I can't check right now whether the spark plug from the engine is fouled badly enough to not give a spark at all, or if it still is OK. (I need to wait for my son to come back in the afternoon to help me, this is a 2-person job.) But assuming the spark plugs are the problem, can somebody offer a guess as to what could have caused the engine to foul the spark plugs so badly and so quickly as to stop the engine while driving? Before that there was no indication something was wrong. Other slightly strange things. a) I've noticed the car burns a lot of gas. I barely get 20 mpg in mixed city/highway driving. b) I have about 600 miles since the rebuild, engine ran well all along. c) The only other issue with the car is that I can not get the idle right: it seems to idle at 1800 rpm most of the time, but if the engine is well warmed up (after about 1/2 hour of driving) or if I hold off the clutch as I come to a stop until the rpm's come down to 900, it'll idle at 900. I've tried two different throttle bodies, thinking it may be the throttle that sticks, but it behaves the same way with both. I started to suspect that the distributor is sticky and does not retard the idle sometimes. Any suggestions, highly appreciated. Thanks, Andrei. |
andreic |
Sep 22 2016, 01:21 PM
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#2
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Member Group: Members Posts: 172 Joined: 21-December 15 From: Madison, WI Member No.: 19,479 Region Association: Upper MidWest |
Hello Len and Timothy,
thanks for your thoughts. Your analysis seems to me to be correct, but I wonder where to go from here. a) How do I figure out if I do indeed have a rich condition? I will try to look at the insides of the AFM later today to see if the arm is stuck. I tried looking into getting a portable air/fuel meter, but everything I've seen seems to require welding a wideband sensor in the exhaust. Are there meters that can just be plugged into the exhaust without permanent modifications? b) What I do not understand about the current story is that if indeed the rings have not seated properly, I would have expected the degradation to be progressive, and to also show up on a compression check. For me everything happened very suddenly, car went from running perfectly to not running at all, and then to smoking to high heaven after the plugs were cleaned. Could it be that the extra rich fuel caused the cylinder walls to glaze, and then this started afterwards letting oil into the combustion chamber? If so, do I understand correctly that I should first fix the rich condition, and then try to seat the rings by driving it at wide open throttle in too high a gear, so as to have low RPM's? c) There is also one thing that puzzles me about the AFM. From looking at the schematics for the AFM it seems to me that between pins 6, 7, and 8 there is basically a potentiometer with total resistance 180 Ohms. So I should measure a resistance of 180 Ohms between pins 6 and 8, and some other resistances X and Y between (6 and 7) and (7 and 8) such that X+Y should be close to 180 Ohms. But when I measure I get X = 120 Ohms, Y = 190 Ohms. This suggests to me that maybe there is some dirt under the washer arm of the potentiometer, with a resistance of about 65 Ohms. (Instead of having X = 55, Y = 125 I get this added resistance of 55+65 = 120, 125+65 = 190.) Is this a cause for concern? How do I clean off the AFM resistor track? Would this be causing the engine to run rich or lean? Thanks a lot. |
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