Author Topic: 1986 k2500 MISFIRING  (Read 2441 times)

Offline suzukiboy14

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1986 k2500 MISFIRING
« on: March 06, 2013, 09:41:12 pm »
Just bought the truck and put long tube headers, and 2.5" duals into flowmasters and dumped, no cats. it was sputtering bad so I had the carb cleaned and rebuilt and tuned by a very reputable engine builder in my area. . It seamed to run better for starting etc but still isn't running right. I put all new spark plugs, wires, rotor, cap, coil, fuel filter. The motor is misfiring really badly. I look under the hood and with the new ceramic coated headers all the tubes from each cylinder look fairly clean and new except 1 of them, cylinder #4 (the second from the front on the passenger side). That pipe coming from the head is Turning rusty and dirty like its not being used. I pulled the plug And it is not black with carbon like the others are so it seams like it is not firing. It has a bit of oil on it, which I believe is normal right?.. Here is the thing, all the plugs are new, wires, rotor, cap, coil is all new..
Does anyone know what could cause this? I thought maybe a broken pushrod not openin the intake valve? Me and a friend tried using a digital compression tester and I think it broke because we tested cylinder 2 And it went up to 85 ish and then started blowing air out. Now it will only read 23 psi and then we tested the bad cylinder #4 and got 23 psi and you can feel air blowing out the Guage so I think it's a broken tester.
Anyways. No idea what is going on here.. Does anyone have Any ideas what I should check next?
Getting frusterated!!

Offline bd

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Re: 1986 k2500 MISFIRING
« Reply #1 on: March 06, 2013, 10:26:58 pm »
Before tearing anything else apart, make sure #4 cylinder is building pressure.  Get your hands on a decent compression gauge and check the compression on all cylinders.  Check the #4 cylinder for spark.  If you have a vacuum gauge, check the intake manifold vacuum.  Report back.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline 454Man

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Re: 1986 k2500 MISFIRING
« Reply #2 on: March 07, 2013, 06:32:05 am »
Sound like the valves may need to be adjusted. #4 valves may be to tight.

Offline Blazin

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Re: 1986 k2500 MISFIRING
« Reply #3 on: March 07, 2013, 07:27:21 am »
If you can get your hands on an infrared thermometer let it run up to temp. Take a reading on all the primary tubes. They should all be fairly close.
I agree on a compression test. Should test them all. They all should be within 10/15 psi of each other.
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Offline suzukiboy14

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Re: 1986 k2500 MISFIRING
« Reply #4 on: April 02, 2013, 09:38:13 am »
turns out it was my plugs, i gapped them to what the book said, but they are the ngk iridium or something like that i believe. anyways i put all my old plugs back in which were AC DELCO or something and the truck fired right up. i set the timing to around 6-8 degrees and now its running really good..
now i have another quesion, my tranny goes into park but it still rolls, a mechanic looked at it biefly and said that it was already adjusted all the way.. its a 700R tranny. i had one given to me but it is out of a 2 wheel drive and mine is 4x4.. he also ave me a TH400 for 2wd.. is there any way i can use these trannies? possily put all the parts from the 700R into my casing or maybe just change tailstock or anthing?
any advise would help,
thanks again for all the help.