HELP: my engine rumbles at idle all of a sudden (long problem) - Team Camaro Tech
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post #1 of 11 (permalink) Old Jul 21st, 03, 06:45 AM Thread Starter
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Jim
 
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Ok, I guess I’ll start with a little background.
Vehicle: 86 Chevy Pick-Up
Engine: 4.3L V6 with a 4 barrel carburetor (last year before fuel injection) carb rebuilt 2-1999
Camshaft is #2 at this site installed 1-2000 by me. Engine has 245,000 miles on it, 170psi at all 6 cylinders, manifold vacuum is at 18-20”. I replaced the plugs, wires, cap, rotor, and coil recently. The ignition module was replace in 1997 after it stalled out and wouldn’t start.
The problem:
I took it out for a drive on the highway and tached it up pretty high in 2nd gear. The next red traffic light I came to, the motor began to rumble at idle (in drive) as if I have a vacuum leak. There’s about a million vacuum lines all over this engine, but I could not find any leaks. It idled crappy for a little while, but when I got home, it seemed to have went away. The next morning, it started up as normal, but it would not stay running. It just would not idle, any rpm above idle was fine, but at idle it would rumble. I don’t hear any pinging or knocking, just would just shake the truck. After driving, for a little while the temp will come up to 210, normally it’s lower at like 185. I thought the problem might be the ESC (Electronic Spark Control module) because I’ve had to replace that in 1999 as well, but I disconnected it and jumped terminals A & C at the HEI side and it still had the same idle problem. So yesterday I began doing all the tests, I can get it to idle if I pump the gas and then start it, but if I hit the pedal to a higher rpm and let it down again, it’ll die. The carburetor is squirting fuel with nice streams, and after checking compression and vacuum, I took it for a spin, and this time, it would hardly move. I can get it to rev up in neutral, but when I use Drive or any other gear, the engine will not increase rpm.

So now the problem, has either gotten worse or more problems are showing up. Today I’ll be replacing the pick up coil in the distributor to check that off of this list of possibilities.

Oh here’s a funny thing: early on in the testing, while it was still able to rev up, I was able to pull all three spark wires on the passenger side and it would still run with little to no change in idle. And they were sparking fine, because I got shocked a few times.

Sorry this may have sounded real confusing, but I just tried to get as much info down as possible. Any ideas???

1968 Coupe, 327ci basketcase project
1986 Chevy Stepside, 305ci/300hp
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post #2 of 11 (permalink) Old Jul 21st, 03, 08:14 AM
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I'd be inclined to verify that your timing's advancing correctly with a timing light. If that's o.k., you've got gas, and you can at least get it to run some...so the cam timing's not way off, I'd be inclined to suspect compression issues. With your three plug wires loose (I assume one whole side of the engine), no change in performance, and some overheating, I'd be looking for coolant in the oil, or vice-versa, and poor compression due to a blown head gasket. But you said you'd checked compression.... I'm at a loss...I'd really suspect ignition timing/advance and/or compression. Of course, a jumped tooth or two on the timing chain could be an issue too, but if it's off enough that it's running THAT bad, I'd expect some backfiring, too (as well as compression issues).

Huck<BR>355 SBC powered '87 Chrysler Conquest TSi - 10.3:1, Vortec heads, XE 268H cam, HEI, eq. length shorties, Performer RPM intake, 750 Edelbrock (1407), T-5 and 3.54:1 posi indep. rear
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post #3 of 11 (permalink) Old Jul 21st, 03, 09:00 AM
 
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Sometimes when you really rev up an engine you can pump up the lifters and float the valves. I would pull the valve covers and check to see if all the valves are opening equally. It's possable that by pulling plug wires, you are compensating for a dead cylander. Hope its something simple
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post #4 of 11 (permalink) Old Jul 21st, 03, 11:37 AM Thread Starter
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well all my cylinders were at 170psi, so that's fine. And the timing chain was replaced with a double roller when I put the cam in.
I just replaced my pick up coil and now the damn thing won't even start. I checked the timing with a gun while cranking and it is firing correctly, so the rotor is in the right spot... I spun the distributer a little each way and no start. I'm letting it sit for a while, because maybe I flooded it.

1968 Coupe, 327ci basketcase project
1986 Chevy Stepside, 305ci/300hp
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post #5 of 11 (permalink) Old Jul 21st, 03, 04:22 PM Thread Starter
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now it starts, but can't stay alive....
might be time to retire her and go 350

[ 07-21-2003, 06:49 PM: Message edited by: JIM68 ]

1968 Coupe, 327ci basketcase project
1986 Chevy Stepside, 305ci/300hp
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post #6 of 11 (permalink) Old Jul 22nd, 03, 02:56 AM
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If you pulled 3 wires and the idle stayed the same you found your problem. Probably just bad wires or fouled plugs.

You can check the wires with a multimeter to see if they are open or if resistance changes when you bend the wire. You can also swap wires from side to side to see if the problem follows the wires or stays with the cylinder.

If it stays with the cylinder pull the plug, put the wire back on the plug, ground the side of the plug to the block and crank the engine. If it sparks your problem is with the cylinder (bent valve, head gasket, etc.).

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post #7 of 11 (permalink) Old Jul 22nd, 03, 05:38 AM
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Jim, boy does this sound familiar. I've got an '86 Chev C10 w/ a 350 and I had a very similar problem to yours last year.

I fished for the problem for about two months, turned out to be bad plug wires, they were stock replacements, only six months old! I replaced them with the wires off of the Camaro, and it's been running good ever since.

The strange this was that I tested the plug wires with a meter several times. They tested good. I even wiggled and bent the wires while I was testing them, and it never gave a bad reading!

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post #8 of 11 (permalink) Old Jul 22nd, 03, 05:55 AM Thread Starter
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wow, engines can be fun sometimes...

I'm going to try replacing the HEI ignition module and then take the wires off of my 327.
We got it started and reving last night, but it's not road worthy. When I drive it on the road and then step on the gas, it'll basically want to die out. Reving in neutral is a little better.

1968 Coupe, 327ci basketcase project
1986 Chevy Stepside, 305ci/300hp
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post #9 of 11 (permalink) Old Jul 22nd, 03, 07:22 AM
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I'd change/borrow the whole ign system from the '68. I have seen HEI's well known to burn up a coil/cap/rotor and wires. This would eliminate the ignition, you have gas, air, and now, need to get the right spark at the right time.........

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post #10 of 11 (permalink) Old Jul 22nd, 03, 07:37 AM
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Jim,

Eric's on the right track - you need to find out why those three cylinders aren't doing anything. You're swapping parts willy-nilly, and not isolating your problem. If 3 cylinders are truly not doing much, but the other three are doing o.k., then your pickup and ignition module don't likely have anything to do with it - they don't care what position the distributor's in. And if you just swap those parts out simultaneously with other parts, you don't know what solved your problem (and you're throwing away money).

If you've got three cylinders that are pretty consistently bad, and three that are pretty consistently good, take Eric's advice and swap the wires and see if it follows the wires. Continue following that path.

If it's NOT consistently the same 3 cylinders, but appears to be much more erratic, then you may be on the right track with the ignition module...but slow down, look at what you've got, and take it one step at a time. It'll be much easier to isolate the problem.

Another possibility, if it doesn't seem to follow plugs, wires, compression, or specific cylinders - is the distributor mechanically o.k.?? Is it potentially scattering the ignition because something's loose? And, again, is the ignition advancing correctly? If not, that would certainly allow it to rev somewhat with no load, but not for crap once you put it in gear and try to make it work.

If it's consistently the same cylinders, start with Eric's path first.

Huck<BR>355 SBC powered '87 Chrysler Conquest TSi - 10.3:1, Vortec heads, XE 268H cam, HEI, eq. length shorties, Performer RPM intake, 750 Edelbrock (1407), T-5 and 3.54:1 posi indep. rear
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post #11 of 11 (permalink) Old Jul 22nd, 03, 05:40 PM Thread Starter
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I changed the Ignition module and NO change.

I swaped out the carb and put a holly on that was on the 327, and now it idles fine and revs nice.

right now i have no vacuum advance, i need to figure out how the vacuum hoses get hooked up for this setup.

more on this later..... i need food

Thanks EVERYONE

1968 Coupe, 327ci basketcase project
1986 Chevy Stepside, 305ci/300hp
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