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 21 2016, 03:40 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 |
Timothy, I did your test right now. All 4 injectors behaved exactly the same way: immediately after removing the injector connector the engine would speed up (quite a bit, 3-400 RPM I would guess) and run much better, then a couple of seconds later it would come back to almost exactly the same RPM as before. I had my son hold the throttle pedal steady while I was doing this test, at about 3000 RPM.
Two other strange things. At some point while doing this test I noticed that one of the main hoses had become disconnected from the main FI rubber body -- the hose that goes to the Auxiliary Air Regulator and to the Decel Valve. But even though I had this huge vacuum leak, the engine still ran mostly the same. In fact I reconnected the disconnected hose to the main FI rubber body while the engine was running, and the engine kept running almost the same. Second, I decided to do a strange test: I pulled the AFM plug, and just shorted the two leftmost pins with a wire (so as to get the fuel pump to run). I tried running the engine this way, and again it ran just as before through quite a range of RPM's. Do you think this might indicate that either something is wrong in the AFM or in the wiring harness (at the plug of the AFM?) so that the ECU does not read correctly the AFM signal and thinks the engine runs at full power and needs maximum fuel? (Hence the fouling of the plugs, perhaps running uber-rich?) |
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