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post head rebuild indications of something not quite right; black, sooty spark plugs, poor mpg
Topic Started: Jul 17 2012, 07:39 PM (2,185 Views)
jaevans
Elite Member
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Greetings,

Well, I want to follow up on my recent head rebuild of my 90 Metro (with 94 engine). I could tell fairly quickly that my mileage was going to be lower - 35 MPG on the first tank (versus 45 before) and though I haven't filled up again, I have driven an additional 80 miles and am at about 2/3 a tank remaining. I pulled the spark plugs and all three have a black sooty carbon coating. The engine seems to sound OK but I wonder if my ignition timing is off (I set it for 8 degrees BTDC) or perhaps I am off a tooth on the timing belt. Several rotations of the timing belt before putting the cover back on indicated that the cam sprocket and crank gear marks are right on where they should be. I have no pre-work data on ignition timing before, but once I got the distributor back to where it was before the work was done, the timing indicated it was at 0 degrees. At that time, I adjusted it for 8 degrees.

Any insight?
Edited by jaevans, Jul 17 2012, 07:46 PM.
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idmetro
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How many miles on the engine before the head work? Did you put new plugs in after the work? Did you jumper the diagnostic connector when you set the timing - http://geometroforum.com/topic/2689420/1/
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jaevans
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About 56K miles on the engine before the head work. I did not put new plugs in after the work, but they looked a lot different, normal grayish tan, before. I did jumper the connector when I set the timing and removed it afterward.
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Johnny Mullet
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Fear the Mullet

Did you refresh the bottom end or at least re-ring it? A newly refreshed head will rapidly toast a worn out bottom end.
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jaevans
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No, I did not refresh the bottom at all. A leak down test took over and hour and a half before the kerosene would move an inch and a half.

Rebuild thread is here - http://geometroforum.com/topic/4743355/1/
Edited by jaevans, Jul 17 2012, 08:53 PM.
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Memphis metro


Is the check engine light on? Theres a differance between black sooty plugs and oil fouled plugs. Black sooty plugs usually indicate a rich running condition.
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GeoFlyer
Air Junkie
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I'm of no help to you but I'm interested to see what you find to be the problem! My engine is completely apart and is waiting to go get the "full monty" over at the machine shop. I had a similar overheating issue as you did but it was a leaking radiator cap return valve that started it all off... leading to overheating, steam forming in the engine under full load (without pressure to keep it from happening), resulting in the engine overheating, the thermostat being destroyed, and the head gasket failing. When I finally get it all back together, I'll be watching for the same trouble you've got, so please let me know what you find. Thanks!
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Murf 59
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When I did the engine in the Rocket several years ago. I forgot to make one electrical connection from the back of the TBI to one of the sensors on the fire wall. Sorry but I don't remember which one. But black sooty plugs are showing to rich like the good DR said. So please have a look and make sure everything is just how it should be. I have been working on cars almost 40 years. And still managed to miss something. I hope this helps.
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jaevans
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blue rhino
Jul 17 2012, 09:01 PM
Is the check engine light on? Theres a differance between black sooty plugs and oil fouled plugs. Black sooty plugs usually indicate a rich running condition.
No check engine light but I am not sure it is even functioning. I'll need to remove the cluster to test, but the PO put in a later model cluster from a 94 into the 90's dash cavity, so I am not sure that all the lights would even function. Yes, dry, black, soot basically. I looked for dangling connectors and I think everything is hooked up. It actually seemed to be running better this afternoon, so I cleaned off the spark plugs and will see how they look after my commuter tomorrow. Right now it is at about 1/2 a tank at 138 miles on the top half.
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GeoFlyer
Air Junkie
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Just so you know... the only time I've seen a CEL is when I screwed up the distributor hookup when I first put the G10 engine on my aircraft. Having a giant gap in the throttle body gasket that made the engine rev at "idle" like an impatient muscle car driver at a stoplight didn't make the light go on, nor did losing a hose clamp in flight that resulted in a 5 second flush/drain of all the coolant passages, nor did burning 1.5 quarts of oil in a 30 minute flight. I gotta think that if the check engine light DOES go on, either one of just a few key electrical connectors aren't plugged in, or the emissions system isn't working. I don't know if it indicates anything else. It's definitely NOT a good indicator for stopping something BAD from happening, that's for sure.
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GeoFlyer
Air Junkie
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You're probably all over this but I figure I'll throw my brainstorming input out there: Maybe put the timing at 0 with the jumper and go with completely stock config until you've got this figured out? (and if stock setting doesn't work, maybe the belt is off a tooth?). Can a failing water or air temperature sensor make the engine run rich? I think from reading other posts on sensor trickers that it could. Maybe a harness wire got disturbed and now the the connection is loose? O2 sensor failing? FYI that even with my g10 aircraft engine that burned 1.5 quarts of oil in 30 minutes, the plugs were not covered in carbon, though the cylinder head and exhaust manifold CERTAINLY were, at least a couple of thousandths of an inch thick... the pistons wouldn't come out until I had scraped quite a bit off. But what is the compression on your rebuilt motor? That might help troubleshoot things a bit too. Spark plug gap set right? I'm just "projecting" onto your situation, as I seem to be finding out what NOT to do with a geo engine, one goof-up at a time! :rasp
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allmountain40
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Yes Geoflyer, the IAT sensor and coolant temperature sensors not functioning will make the engine run rich. Jaevans, As Johnny mullet stated a refreshed head will blow out week, worn rings due to the boost in compression. Your leakdown test you did before rebuild is now null and void as you have run the engine with the refreshed head. Reset your timing to factory specs, and do a compression check and go from there. :thumb
Edited by allmountain40, Jul 18 2012, 11:10 PM.
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jaevans
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I find it mildly amusing that many times when folks discuss mileage or performance issues, the first thing suggested is a top and bottom end rebuild. Anyway, there are no indications at all that I have blown the rings as a result of my top end rebuild. There is no oil fouling the spark plugs. The car was running fine prior to the overheating issue which prompted my head replacement and none of the valves were burnt when I inspected them upon removal. Dry compression now is at 120 for each cylinder (yes, I should've done the bottom at the same time, but I wanted to build some level of comfort in doing this work before jumping into all that and the leak down test prior to the engine work indicated that my rings were in decent shape) The overheating issue was the result of a clogged radiator resulting in less than 50% cooling capacity on it.

Yesterday and today has seen much better mileage indicated by the fuel gauge moving a lot less than on the first tank, so I am waiting to see if what the spark plugs look like tonight when I get home. I did reseat all the connectors to the engine and the temp gauge appears to be functioning properly so I doubt the water temp sensor is bad. I may check the air temp sensor to see what it indicates but that may not be needed once I check the spark plugs later.

I do have a 93 XFi that definitely needs a full rebuild at 223K and I will do it right for sure as I love the 50+ mpg that it sees. I wanted to cut my teeth on enough work to test my capabilities, which is another reason why I did the top end on the 90. I will definitely keep you all in the loop and I appreciate the guidance and feedback. I would never attempt any of this without the wonderful support you all provide. I do, however, have to choose my own path once I've digested all the input.

Thanks,
John
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jaevans
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OK, my plan now is to get the MIL (CEL) working as it doesn't illuminate at all when first turning the ignition switch to the first position. Either the bulb is bad or missing (that's what I suspect) or there is a wiring issue. Once I get that working, I should be able to get a lot more info from the DTCs as to what is going on. It should point me in the right direction as to any sensor issues there may be. I just have to remember that the PO put a 94 engine with a different wiring harness and newer cluster in my 90 body so who knows what shortcuts were made. Anyway, more information that the ECM collects is important to diagnosing my issue.

John
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Bad Bent
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Facetious Educated Donkey

jaevans
Jul 18 2012, 08:43 PM
blue rhino
Jul 17 2012, 09:01 PM
Is the check engine light on? Theres a difference between black sooty plugs and oil fouled plugs. Black sooty plugs usually indicate a rich running condition.
No check engine light but I am not sure it is even functioning.
The check engine light will come on as you start the engine. The second key position: right after "accessories." :-/
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