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 23 2016, 10:39 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 |
I see I've ignited quite a few passions with my non-firing spark plugs... (Forgive the bad pun.)
I did more testing today. I discovered that I most certainly have a fuel problem: I checked the oil, and it is 1" above the high mark. This time I am certain that I put in the right amount of oil, 3 quarts exactly, and it was halfway between the high and the low mark. So my plan is to first diagnose where the excess oil (i.e. fuel) comes from, and then deal with the oil getting in the cylinders. A neighbor who is a retired car mechanic and who has worked on Porsches for many years stopped by today. After running the car (poorly) for a couple of minutes we looked at the spark plugs, and he said that one looked like it was looking like it had run ultra rich (lots of soot), and the other three looked like they were slightly wet, but we could not determine if that was gas or oil that was making them wet. (The amount of wetness was slight. Certainly not soaked in oil.) The plan I made with him was to try to diagnose what I can about excess fuel without running the engine, then try it with new spark plugs and see after running it a few minutes if the spark plugs give a more clear indication of what is wrong. In the evening I did a couple more things. I bypassed the cold start valve, as Timothy suggested. I also tried to measure fuel pressure as DD suggested (the bypass of the CSV is actually a T-joint, with the leg of the T being a hook-up for a fuel pressure gauge). I don't know if I did something wrong, or something else is a bigger issue, but I did not get any reading of any fuel pressure from the gauge (stayed flat at zero), with the fuel pump running. I think the problem may be with the gauge, since I could clearly hear the fuel running through the system. I then took out all 4 injectors and tried to see if they leak when there is pressure in the fuel system. They do not. For two of the injectors I even tried to see what happens when grounding the corresponding pin on the ECU connector, and they clearly fired up fuel. I don't know how to tell if their spray pattern was good, but they did roughly what they were supposed to do. So now I have it down to either the CSV being stuck open (now it is bypassed so it won't matter), or the ECU having gone bad and keeping the injectors open all the time. Whatever it is, it is not a minor adjustment -- the FI system puts out a **ton** of fuel (I must have at least an extra 1-2 quarts of oil more than what I started with, and this is only after running the car for perhaps a total of 10 minutes!). I did not dare run it with such a fouled oil. My plan for tomorrow is to change the oil (again!!), and try to run it with new spark plugs and the CSV bypassed. If it still runs rough it means the problem was not the CSV, and it is either the ECU, the AFM, or wrong fuel pressure. I have a spare ECU (which was not tested...) so next step after that is to try the spare ECU. If it behaves the same way I'll do more digging with the fuel pressure gauge and the AFM. I have my work cut out for me... Thanks a lot to all who volunteered opinions. |
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