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 16 2016, 09:59 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 |
OK, let's go with the assumption that it is some of the injectors that are leaking. I can't imagine all four being messed up at the same time, so with all four plugs being fouled this would clearly point towards the cold start valve (CSV) being the culprit.
I think I can pull it out and check if it is leaking. But could it be the case that the CSV is actually fine, but the thermo-time switch is messed up and keeps the CSV open all the time? I assume I could test this by pulling the plug off the CSV and measuring with an ohm-meter how long the thermo-time switch stays open after starting the engine, right? I would like to not have to worry about changing the oil, then doing diagnostics, only to find that I've been leaking again fuel into the oil so I need to change the oil yet again... So I'd like to isolate the fault as much as I can before changing the oil, i.e., I'd like to test as much as possible without running the engine. But some of the tests (like checking the thermo-time switch, and checking oil pressure) require the engine to run, and from what I've heard I should not run it now until I haven't changed the oil. |
Dave_Darling |
Sep 17 2016, 10:38 AM
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#3
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914 Idiot Group: Members Posts: 14,991 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
I think I can pull it out and check if it is leaking. But could it be the case that the CSV is actually fine, but the thermo-time switch is messed up and keeps the CSV open all the time? The thermo-time switch provides the ground to the CSV. The power to the CSV is supplied by the yellow starter wire. Therefore, the CSV will only open while the starter is cranking. It is possible for the CSV to be leaking, but a shorted TTS is only of concern while you are trying to start the car. You can remove the CSV from the manifold and run the fuel pump to pressurize the system. If the CSV sprays or dribbles, it is bad and is at least one cause of your trouble. If not, then it is not the cause. --DD |
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