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Cylinder not pulling its weight
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KD5NRH
New User
Jan 29, 2016, 5:04 PM
Post #1 of 5
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Cylinder not pulling its weight
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1994 Sunbird LE 2.0L 4 cyl
Was running fine, did a good bit of freeway driving yesterday with no noticeable issues except the occasional random misfire at low RPM. Just enough to put it on my "tune up at some point" list, nowhere near "this is going to get nasty very soon" level. On the way home last night, I stopped for about an hour and a half to visit some friends, got back to the car, it started fine, ran pretty well, (cold weather and enough time to cool off, so a little rough was expected) and the "check oil" light came on. Checked the oil, and it was right at the bottom of the "ok" range on the dipstick. (Nice idea they had there; turn the light on as soon as it's actually low instead of waiting until it's 3 quarts low to say something.) Had some in the trunk, so I got it back up to the top of the range and took off again. No biggie - it's 22 years old and takes just about 3k miles to use a quart, so I guess it's also due for an oil change. Maybe five minutes of 30-45 MPH driving later, I went to get on the highway, and suddenly it got really rough with an obvious power loss. Roadside fiddling determined that pulling the #1 plug wire made no change whatsoever in the idle, so presumably #1 is just dragging now and not contributing at all.
Got enough spark to shock the heck out of me when I pulled the wire, but again, no change at all in the rough idle. Pulling any other wire pretty much kills the engine, regardless of whether #1 is plugged in or not. Replaced the spark plug, then swapped them around to make sure I didn't just have a stroke of really bad luck and put DOA one in there. Some carbon fouling on all the plugs, but not bad considering they were probably in there for 60-100k miles before I got the car.
I can smell a little gas when I pull the plug out, but of course, no way to know for sure whether it's getting a good fuel/air mix that way. Stuck a screwdriver as stethoscope on each of the injectors, but I can't tell any difference between the sound of them...or the sound I got from the screwdriver on the fuel rail itself for that matter. Can't find a 12V check light to see if the module is firing the injector, but I may grab one when I limp it past WalMart on the way home.
This one is the one with a pretty specific coil pack that's $500-700, so no way I'm going to change that as a troubleshooting step on a car that I only paid $500 for. I can go back to Craigslist and find another $500 beater that runs as well as it did for the last month, but if there's a $50-100 option, I'd like to keep it running for a couple months while I save up for something in better shape, and hopefully sell it to some other guy who just needs a beater to get around for a while. (With full disclosure of its remaining problems, of course. Sometimes "It gets down the road right now. No promises about tomorrow." is worth $350 to someone.)
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 29, 2016, 5:24 PM
Post #2 of 5
(1387 views)
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Re: Cylinder not pulling its weight
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So you find no change in leaving #1 plug wire off and new plug made no difference? Now time to compression check this engine fully to diagnose mechanical wear or a fault and where.
Injector may leak down and wash cylinder of oil, foul plug and or not enough compression or who knows yet? Fuel pressure should hold when tested as you noticed fuel odor leaking injector a maybe.
Test lights: Walmart stores vary on what they have. NAPA sells an LED one for within a buck of Wally World ones so you know.
You can get a shock from a wire and it still not fire a plug so a spark tester would help. Wires may jump spark out along one to ground or another plug wire?
If some things test out OK I think I'd put that cylinder on TDC and force air pressure in plug hold to see where it comes out if compression low.
Oil if really only 1 qt or so low shouldn't be a problem. At this age check it manually and frequently if this works out not a lost cause.
If engine messed up enough and proven so and you can drive it, it is still worth bucks if only metal value and can get a price from salvage yards over the phone for a whole car if it comes to that.
Your call always but wouldn't spend way too much on this car unless otherwise in remarkable condition,
T
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kev2
Veteran
Jan 29, 2016, 6:18 PM
Post #3 of 5
(1380 views)
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Re: Cylinder not pulling its weight
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you said good spark So that would suggest fuel - injector ?
then the next would be compression.... before getting a coil or a donor car...
easier said than done swap injector 1--3 maybe see if issue moves to #3
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Discretesignals
Ultimate Carjunky
/ Moderator
Jan 29, 2016, 6:33 PM
Post #4 of 5
(1375 views)
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Re: Cylinder not pulling its weight
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Usually you can kind of tell if you have a compression issue in a cylinder because when you crank the engine, the cranking sound will speed up when the cylinder with low compression comes to TDC on compression. It still would be wise to perform a compression test as the others stated, just to see how the engine is mechanically.
Just because you got a shock doesn't mean it has good spark or good coil output. You really should test spark with an adjustable spark tester. It should be able to at least jump a 3/4 inch air gap. Most waste spark systems will easily jump an inch or more.
You should never remove a plug wire with the engine running and leave it hanging in open air. That will overload the coil or the spark will attempt to find ground through the coil housing instead. The spark needs to find ground, so ground the plug wire if you are going to run the engine to find out which cylinder isn't contributing.
Using a screwdriver to listen to an injector can be misleading sometimes because you can hear the other injectors clicking through the rail making you think it is working. The older Multec injectors where known for shorting, so check the resistance of the suspect injector and compare it to the others. They should all be around 11.8-12.6 ohms.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jan 29, 2016, 6:47 PM)
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KD5NRH
New User
Jan 30, 2016, 3:01 PM
Post #5 of 5
(1344 views)
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Re: Cylinder not pulling its weight
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OK, needed a valve cover gasket anyway, so I figured that would be a good excuse to take a look, especially after the paper test (hold a sheet of paper at the exhaust, and see if it just flutters or if it slaps the pipe indicating a suck during part of the cycle - it slaps hard) strongly suggested a stuck exhaust valve.
Valve cover off, of course, can't see everything with the cam in the way, but on turning the engine, the cam lobes look good, and the valve stems appear to be coming all the way up. Nothing obvious like a broken spring or slipped clip. All poking and gawking shows no obvious difference between the #1 pair and the other three pairs.
Somebody seems to have swiped my multimeter at work, so I'll have to pick one up to check the injector.
Redneck spark test (put a plug in the wire and ground it against the block) gave a strong white spark.
Yes, it's a $500 beater, but I'd like to keep it running for a couple more months while I save up and watch Craigslist for something with a simple, cheap problem. (Missed the shot at a $500 Neon that "Goes just fine but only in second gear. Wife says it has to go away." with a busted shifter bushing. Could have fixed that with a zip tie until the $30 part came in.)
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