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Old 05-11-2005, 05:22 PM   #1
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Default Rough running engine

We have an 88 bonneville sse, the trouble is after it has been drove at all in a day after the first time the car wont idle and misses bad and blows lotsa gas out the exhaust, so we checked a few things changed plugs and the center cylinder in the front was soaked with gas but was still firing we grounded the plug to make sure, it seems like there is to much gas but seems like that front center is the only one that looks bad the rest are nice and clean we have changed the coil pack along with the ignition module,0'2 sensor,and cleaned the EGR valve which looked fine to start. We are stuck with it at this time because it runs so bad and wont idle till it has run for about 15 mins then it is fine till you shut it off then same problem all over. would really love some good ideas as to what we can check next. I am new but looks like a good place for info, tyvm
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Old 05-11-2005, 10:19 PM   #2
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It sounds like the injector on the bad cylinder is stuck open. Maybe it frees up after it gets warm or that cylinder has very low compression and improves when warm. You could check the sound of the injector with a mechanics stethyscope or even a long screwdriver held to you ear to see if it sounds like the other "good" ones. A compression test will give you an idea of the general health of the engine. It could be as simple as a bad plug wire too. It takes less energy to fire the plug in the open air than it does under compression.
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Old 05-11-2005, 11:42 PM   #3
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Default ty for reply

tyvm for the reply now that gives us some stuff to look into. didnt even think about injectors and I suppose it could be a bad cylinder like u said after warming up the seals itself..
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Old 05-12-2005, 11:42 AM   #4
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Default center

Are you sure that center cylinder is firing? Remove the plug, attach the wire and ground it against the manifold while someone cranks the engine to see if its sparking.
If so the injector is probably leaking or stuck open.
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Old 05-13-2005, 08:29 PM   #5
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Default rough running engine continued

We have replaced the Injector on the center cylinder that was seeming to dump all the gas and making the plug soaked, well that didnt do it it still runs like crap, so we are wondering after some more checking is could it possibly be the catalytic converter cuz there doesnt seem to be a lot of pressure out the exhaust and there isnt a leak anywhere, after my friend took it for a spin after the injector change there was a loud noise from the catalytic converter sounding like a knocking rod but we scoped the engine and all is quiet in there so sounds like the plate or valve in the converter is blocking maybe then possibly slips outta the way, could the converter cause this trouble with the one cylinder, another we had thought on was could it possibly be the computer doing this. Hoping for many responses tyvm..
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Old 05-13-2005, 10:17 PM   #6
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The converter is a solid honeycomb matrix, no plates or valves that I am aware of. They can become plugged but more common is the heatshield rattles. If plugged, it will usually show up as poor performance and the least load on it is at idle. A simple test to see if the plug is firing when installed in the engine is connect an inductive timing light to the suspect cylinder. If the timing light won't pulse there is no fire. Even better would be a light with built in tach. The plug should fire every engine revolution so the tach should show double the actual engine rpm. The test won't work if the spark is escaping to ground downstream from the inductive pickup.
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Old 05-13-2005, 10:21 PM   #7
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we havce checked the plug for spark by removing and grounding then cranking the engine and plenty of spark, just remember this all goes away after about 5-10 minutes of driving then as soon as motor off and started happens all over again..
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Old 05-14-2005, 01:10 PM   #8
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I don't see any mention that you replaced or swapped the spark plug. I once had a plug that would not fire under 2000 rpm when cold. Also had a SBC that had leaky valve seals, plugs lasted about 1,000 miles before misfires, particularly after starting since the seals would leak while cooling..
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Old 05-14-2005, 03:16 PM   #9
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that was the first thing we did was the plugs since it was soaked figured bad plug but didnt do it..
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Old 05-14-2005, 04:55 PM   #10
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In that case I would pull the new plug shortly after running and see what it looks like: is it gas soaked or oil soaked (shoulld be able to tell by smell). Might have lost an oil seal. Compression test since easy to see (#3 cyl right ?) would also be in order.
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