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1997 detonation problem; engine detonation
Topic Started: Jul 30 2014, 05:59 PM (1,047 Views)
murray1886
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1997 5 speed: new engine, new head, plugs,wires,cap/rotor, egr cleaned, study vacuum and good even compression, timing is dead on and have tried backing it off just in case, new O2 sensors, fuel filters changed. No codes showing up. Engine fires right up and runs great when cold. When hot, it idles like crap, detonations under load(high speed,hills,etc). I can not figure this thing out. the only thing I've seen that seems out of norm is the center exhaust manifold is running 50 degrees hotter than the other 2. Any advice guys?
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myredvert
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myredvert

Welcome. There's a 1997 Factory Service Manual in the Forum library. :cheers
Geo Metro Forum→The Garage→Factory Repair Manuals/Wiring Diagrams→1997 library

First, check out (link to) 1997 FSM Section 6E2-B, DRIVEABILITY AND EMISSIONS 1.0L and 1.3L "Detonation/Spark Knock" on page 5

I would have said you can ask Geo Glenn to take a look, since he lives in Troy, but he is out on his 2014 West Coast Engine Rebuilding Tour and won't be back for a little while longer I think...

And just out of curiosity, what exactly do you mean by "new" engine? New as in NEW new? Where do you get one of those? And may I ask what the actual "sturdy?" vacuum reading is and what the good even compression numbers are?
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murray1886
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bored 20 over, crank polished, block boiled out, all new internals. re-manufactured head w/stainless steel exhaust valves. compression is 175 +/-1 across all three (thought a little high, but running 93 octane has same result) And a STUDY vacuum, as in no flutter to indicate a valve problem, pulling 20 at idle. I've been through the book. I know my way around engines. I have probably rebuilt 50 in my lifetime and worked as an ASE diesel mechanic 20 years ago. I've never messed with one of these though. Whatever is going on here has me scratching my head.
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myredvert
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myredvert

My questions had nothing to do with me making any assumptions about how well you do or don't know your way around engines, honest. I was simply asking questions to help clarify ambiguous terminology, sorry if they offended you. Also sorry if I offended you by suggesting you run through the FSM diagnostic checks for your symptoms because you hadn't said you already ran through all of them and still can't find the cause.

I honestly was curious because you said "new" engine and I didn't know you could get a new G10 anymore. But I see you meant rebuilt engine. Got it. And you meant steady 20" vacuum. That makes sense now too, thanks. For what it's worth it's great to see someone using a vacuum gauge to help diagnose - you don't see that much anymore even though it can help point towards a lot of things much more specifically than just a compression check alone can.
:cheers
Not that it likely has anything to do with your engine issues, but 175 compression on a G10 isn't high, it's actually a hair on the low side of the middle of the compression range. Spec is 199, minimum is 156.4. But since they are all equal, and with your vacuum indications it doesn't appear to point towards a valve issue.

Since you have been through the book, I'll assume you mean that you have already done the ~20 checks specified for detonation symptoms, to include using a scan tool to check the fuel trim to see if the system is running lean, you verified the plugs are the proper heat range and gapped properly, and that by "dead on" you mean your timing is exactly 5 BTDC with your idle at 850, etc... Other than the FSM checks, I have no educated guesses, sorry, but there are plenty of other folks here who have a lot more experience with these engines and should be able to help you find the cause. Good luck! :thumb
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murray1886
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No, you didn't offend me. Sorry if I came across that way. Attitude is sometimes misrepresented through text I think. I am open to, and appreciate any suggestions anyone has, that's why I'm here, even a correction on my English is appreciated :) I was only trying to give some additional background info to eliminate the obvious... vacuum leaks, improper torqued head bolts, etc. Yes, timing and idle speed are set to specs, I have checked the all sensors including map and TP. I even brought the car to to a shop to run their snap on diagnostic on it, they came up with nothing. The scan tool I have will not show me a fuel trim. It will only read a code. Since I'm not getting an O2 code and the plugs look good, I figured I was running ok. But this is certainly something that has been on my radar. I was sitting here last night thinking how I haven't checked the fuel pressure when the engine is hot and wondering if the pump could be dropping pressure after it warm ups. Seems like the plugs would show a lean condition if this were the case, but perhaps the pump only runs short under max demand?? Any ideas?

What about my center runner on my exhaust running 50 degrees hotter? Is that normal on these engines? Most normally run hotter toward the back.
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freegeo
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Have you checked the spray pattern of the injector? One thought is it is running on the lean side. Running lean and at 5 degrees timing could cause some detonation.

Have you checked out the EGR valve to make sure it is not staying open? Can cause idle problems.

You have a code reader right, not something you can get live data from the computer?
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murray1886
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right, I only have a code reader. I haven't worked much with fuel injection, I'm not sure what the spray pattern should be. The egr seems to be working fine, I can rev the engine and watch it opening and closing, took it completely apart and removed cogs in the intake when I rebuilt the engine, and checked it again when I couldn't resolve this problem. I even blocked it off at one point to eliminate a possible egr opening under load....
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freegeo
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Did you have the head milled or block milled?
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murray1886
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block was straight, since this was a reman head, I'd imagine it was milled.
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arollinstone
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On a Mission from God

Just my two cents Murray, Does your fuel have ethanol ? If so try a higher grade that has none and or throw a little kerosene in the tank till she's broken in.
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socal geo garage
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try e 85 50% for a few 100 miles and see if the ping goes away , then you will know if iits related to your compression, remove the head and gasket match a few ccS more into the combustion chambers.
Edited by socal geo garage, Aug 1 2014, 04:25 PM.
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murray1886
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I'm running 93 octane with octane boost in it now, I've prob put 300 miles on the engine so far. Do you think 50% e 85 will boost the octane?
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socal geo garage
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murray1886
Aug 1 2014, 05:45 PM
I'm running 93 octane with octane boost in it now, I've prob put 300 miles on the engine so far. Do you think 50% e 85 will boost the octane?
its very high something close to 107.
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murray1886
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I did not know that, thank you! I'll give that a shot. If nothing else, one more possibility eliminated.
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Hanuman
"The Almighty Grounds Cleaner"

its very easy to get the timing off one tooth on these cars.

also, the timing marks on my engine were not dead on!
stick a screw driver or pencil in the #1 spark plug hole.
rotate crank until pencil stops coming up, but before it begins to come down, if you over shoot, continue to rotate all the way around and try again.
top dead center is where the pencil stops going up, and sits there for a second before starting to come back down.
while at tdc, move cam to align its mark with mark on valve cover.
install belt and tensioner.
rotate engine 3 revolutions and recheck mark......often.....they dont line up any more! do it again.....

i like to line up the cam mark, then rotate cam reverse of engine rotation about 1 tooth, then install belt as tight as i can, this takes up the "slack that usually results in the belt being off a tooth

also, bosh spark plugs often make these engines run horrible. use ngk.
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