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diagnostics
Topic Started: Aug 31 2014, 07:49 PM (426 Views)
Geometroconvertible
Fresh Fish
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Can any one help me diagnose my Geo.? I have 1991 metro Lsi convertible 3 cylinder 1.0 manual transmission.
Engine shakes at idle, exhaust makes puffing noise. So far I did compression check and it at 145 psi in all 3 cylinders. I have checked fuel pressure and it at 20 psi but needle quickly jumps between 19 and 21. Spark plug tips are covered in black stuff. I have air filter and it's box off, so there is enough air for the engine. Seems to me its not burning right or not at right time. I only guess that it's running rich, but how I can practically diagnose and verify what's going on ?
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freegeo
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Your compression numbers are a little low but with them all three the same the engine should run fairly smooth.

Sounds like you have a fuel injector that is leaking and causing a rich condition. Check if the spray pattern of the injector looks to be a fine spray or droplets.
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Memphis metro


Check engine light on? Map sensor issue came to my mind. The air filter housing has a iat sensor on it as well. It should be installed.
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myredvert
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myredvert

Quote:
 
So far I did compression check and it at 145 psi in all 3 cylinders.

Spark plug tips are covered in black stuff.
Any codes? [edit] as BR asked? (just saw that.. sorry BR)

I would start with identifying what the "black stuff" is and where it's coming from, as it is very possible that it is also contributing to your low compression. Considering that (if you are @ or below about 2500 feet above sea level and you did the compression check correctly in accordance with the FSM), your compression isn't just "a little low," its at or below Factory Minimum of 156.4

What is your oil consumption like?

All suggestions for little things that may help a little are going to be fair game, as it could be any number of things other than the low compression that is causing it to run rough. G10s with below minimum compression have been known to continue to run relatively smoothly, but it's not a guarantee, and I believe that would also depend on the nature of the compression loss and what other issues it may be causing.

Did you do a "wet" compression test also to get an idea of the loss of compression is more ring or valve related?

Trying some MMO in the oil and/or fuel may help gently remove carbon buildup, or you could also try running the snot of it rpm wise and seeing if that will help clear up some carbon and get some performance/compression back.
Edited by myredvert, Aug 31 2014, 09:08 PM.
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Bad Bent
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Facetious Educated Donkey

Geometroconvertible
Aug 31 2014, 07:49 PM
Engine shakes at idle, exhaust makes puffing noise.
So far I did compression check and it at 145 psi in all 3 cylinders. I have checked fuel pressure and it at 20 psi but needle quickly jumps between 19 and 21. Spark plug tips are covered in black stuff.
I have air filter and it's box off, so there is enough air for the engine.
Seems to me its not burning right or not at right time.
I only guess that it's running rich, but how I can practically diagnose and verify what's going on ?
Engine shake can be worn engine mounts. Have you checked the timing with a timing light? Set it at about 8 deg. BTDC. The distributor bolts will have some back/forth movement in the slots, if not the timing belt may have jumped a tooth.

Did you test the compression according to the instructions at How To Compression Test? Having Wide Open Throttle would change the results.

How old are the plugs, wires, distributor cap and dist. rotor? Check plugs against this chart: http://yorik.biz/gtr/spark_plugs_diagnosis.jpg Clean or replace before installing at 20 ft/lbs torque.

How long has the air cleaner box been off? It should not be run that way. If for a short period it would not make the plugs darken. As BR says it needs the brass looking Intake Air Temp. sensor or else it will sense ambient temp.

My '91 is vacuum advanced and over time the vacuum hoses get clogged so I pull them off at the distributor and spray some Carb. cleaner in the hose while it's running, turn it off, spray more in the hose and let it set a few minutes then start it.

You have some tests and questions to answer for help with the diagnosis. If it is running rich your Fuel Economy will drop. One reason we keep track after each fill up.

myredvert says Marvel Mystery Oil and that reminds me to add some to my fuel at 4 oz. per 10 gallons. :)
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Old Man


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Aug 31 2014, 09:45 PM
myredvert says Marvel Mystery Oil and that reminds me to add some to my fuel at 4 oz. per 10 gallons. :)
I not only do this but I also use 8oz of MOM in the oil at every oil change. (NAPA auto parts $26 per gallon)
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