91 missing issue??
11-03-2018, 02:48 PM
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91 missing issue??
I have a 91 rs stock 305 tbi. It’s got a bad idle up and downs and sounds like it’s missing on cylinders and backfiring through the tbi and exhaust.. I changed map.. o2.. cap. Wires.. plugs.. throttle position. And fuel pump.. and have looked for leaks.. so I decided to see how the engine would do if I pulled plug wires and pull number 1 and it ran the same. Then Decided to pull number 3 and still ran the same. What is going on!!? Please help!
Last edited by Shane Boswell; 11-03-2018 at 03:40 PM.
11-03-2018, 04:20 PM
#2
Re: 91 missing issue??
Apparently, #1 and #3 are not firing. Perform a cranking compression test of both. (or better yet, do all eight.)
If both #1 and #3 have low/no compression, it's likely you have popped a head gasket. I did that on my engine, between #3 and #5. You could also have leaking valves, broken rings, hole in pistons, etc.--but a popped gasket is the most likely.
Have you checked the rest of the cylinders? For the record, it's better to short the spark than to just pull the wire off. I use a 12-volt test-light probe with the wire connected to ground. Apply a touch of silicone dielectric grease to the pointy probe, and slide it BETWEEN the plug wire and the distributor boot, until the probe touches the metal plug wire end. That will kill the spark to that cylinder, yet does not damage the coil or the plug wire. The test light will not light up.
If both #1 and #3 have low/no compression, it's likely you have popped a head gasket. I did that on my engine, between #3 and #5. You could also have leaking valves, broken rings, hole in pistons, etc.--but a popped gasket is the most likely.
Have you checked the rest of the cylinders? For the record, it's better to short the spark than to just pull the wire off. I use a 12-volt test-light probe with the wire connected to ground. Apply a touch of silicone dielectric grease to the pointy probe, and slide it BETWEEN the plug wire and the distributor boot, until the probe touches the metal plug wire end. That will kill the spark to that cylinder, yet does not damage the coil or the plug wire. The test light will not light up.
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