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Troubleshooting Diagnosing problems done here.

 
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post #1 of 9 (permalink) Old Mar 2nd, 03, 01:37 PM Thread Starter
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Join Date: May 2001
Location: Goose Creek, SC
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I have an 87 Z-28 5.0L that darn near refuses to run. this one has got me and a few other guys stumped. The car idle's very roughly and either backfires or detonates (i don't know what the difference is). Once it is above 2000 RPM's or so, it will run pretty ok. I've checked fuel pressure and timing, and they were all on point. I got a "lean exhaust" trouble code. What could cause an engine to run so badly at lower than 2000 RPM's but almost fine above? When i was checking timing i noted that my spark plug had oil deposits. Could something leaking give me that huge of a problem? This breakdown was not gradual, it was fine one minute, and then has given me hell since. Any ideas?
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post #2 of 9 (permalink) Old Mar 2nd, 03, 06:02 PM
 
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If you are getting a lean exhaust code, does the engine want to surge up and down at idle? When getting a lean exhaust code, it is almost always something to do with a vaccum leak somewhere or fuel pressure. When you checked your fuel pressure, did you see what max pressure was by crimpping off your return line? Check your throttle body gasket too.
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post #3 of 9 (permalink) Old Mar 3rd, 03, 03:51 PM
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If the problem exists when the engine is cold, you can probably rule out O2 sensors for the moment since they are not used when the system is open-loop (such as when cold). I'd check all plugs (sounds like you checked one at least). A lean mixture or cylinder should show on the plug(s). Any chance the oily plug is really just wet with fuel from improper ignition? Compression check is warranted.

-dnult
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post #4 of 9 (permalink) Old Mar 3rd, 03, 04:20 PM
 
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Check the EGR valve,it can stick open or the base gasket can make a vaccum leak.I have fixed a few with this problem [img]graemlins/thumbsup.gif[/img]
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post #5 of 9 (permalink) Old Mar 7th, 03, 02:41 PM Thread Starter
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Well, I've done a compression check on the first three cylinders and found all of them to be low, and have oily plugs. Considering the mileage (190,000) I'm going to break down and rebuild the engine (never rebuilt prior) guess cars can't live forever, huh? lol
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post #6 of 9 (permalink) Old Mar 9th, 03, 07:54 AM
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Did you prop the trottle plates open when doing your test? What pressure did you see. It's more important for the pressures to be balanced between cylinders than to look for a particular pressure. Cams and other peticulars can vary "normal" pressure readings considerably.

Dave
========================
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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post #7 of 9 (permalink) Old Mar 9th, 03, 01:36 PM Thread Starter
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Oh wow...well, they all read 90 (specs at 100-150). I've already started tearing the engine down and i'm almost sure there was oil present in the coolant, what kinda of color would that be? It was very whitish/tanish (orignally green!) One way or another that car is pretty much heading for the scrap yard, so i figure i should at least use it as my "learning" car and see if maybe i can't rebuild it.
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post #8 of 9 (permalink) Old Mar 9th, 03, 03:56 PM
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Oil in the coolant will puddle on top in the radiator. It will tend to be frothy like a milk shake. Brown coolant usually is just overdue for a flush. Rust turns the water brown. There can also be some frothing from bacteria. Oil froth is very easy to spot...it will coat the cap with foam. If your suspecting oil, drain the oil and see if antifreeze comes out from the bottom of the pan.

-dnult

Dave
========================
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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post #9 of 9 (permalink) Old Mar 9th, 03, 06:15 PM
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Not to laugh at the problems of others, but it's kinda funny....another guy in this section can't get his engine to shut off...maybe you two could compare notes and meet somewhwere in the middle!!? Sorry.


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