88 K5 Chevy 350 brought to TDC but back fires out Throttle Body?

[88Chevyk5]

Okay move the cap counterclockwise in small increments. Truck stopped backfiring but still no run. Could the distributor be bad? I've got a spare motor for parts that came out of my 87 k20 tbi. Ran like a champ so I know everything on it is in working order.

 

[rich weyand]

Wow. If it's backfiring, it has to be getting spark, right? Or it wouldn't fire that either.

If you have a spare distributor laying around, that would certainly be something to try and eliminate the ignition modules, the coil, the cap and rotor, etc.

Also, there are some really cheap ($30) replacement distributors that have good reps.

I'm kinda at a loss here, but trying another distributor seems worthwhile.

 

[88Chevyk5]

Sounds good I'll give it a try. But yeah that's why I'm kind of stumped myself. I hope I'm able to figure it out!

 

[350runner]

Check the wires going to the pickup coil. They could be dry rotted and cracked

Sent from the dust in front of you!

 

[88Chevyk5]

Swapped distributors and checked/swapped wires to pickup coil from other motor. Still nothing. Just cranks now and won't kick.

 

[rich weyand]

Read the whole thread over and I'm not sure you are finding TDC correctly. What concerns me is this line:

"What my father and I did was take the valve cover off and turn the motor over with a bar through the exhaust stroke and just past the intake stroke so the rocker arm on the intake valve was just loose (tdc?). Then I took the distributor out and pointed the rotor towards the number 1 spark plug. I then adjusted the cap so number one on the cap was about where the rotor was pointing."

Just after the intake stroke is not TDC. If you turn the motor over through the exhaust and intake stroke until the intake valve is just closed, you should be about 20* after bottom dead center. You have to keep going through the compression stroke until you can measure through the spark plug hole that the piston is at the top or you can see that the crankshaft pulley keyway is at the 1:30 clock position when looking at the engine from the front.

Once you are in that position, the distributor should come out and go back in so that the rotor is pointing to about 4:30 or 5:00 clock position as viewed looking down on the distributor from the front of the vehicle, the distributor body has the vacuum can pointing at about 7:00 or 7:30 clock position from the same vantage point.

 

[350runner]

Check out this vid Distributor Install on Chevy Small Block: http://youtu.be/hsYDgNoUtBg
Hope it helps

Sent from the dust in front of you!

 

[88Chevyk5]

Read the whole thread over and I'm not sure you are finding TDC correctly. What concerns me is this line:

"What my father and I did was take the valve cover off and turn the motor over with a bar through the exhaust stroke and just past the intake stroke so the rocker arm on the intake valve was just loose (tdc?). Then I took the distributor out and pointed the rotor towards the number 1 spark plug. I then adjusted the cap so number one on the cap was about where the rotor was pointing."

Just after the intake stroke is not TDC. If you turn the motor over through the exhaust and intake stroke until the intake valve is just closed, you should be about 20* after bottom dead center. You have to keep going through the compression stroke until you can measure through the spark plug hole that the piston is at the top or you can see that the crankshaft pulley keyway is at the 1:30 clock position when looking at the engine from the front.

Once you are in that position, the distributor should come out and go back in so that the rotor is pointing to about 4:30 or 5:00 clock position as viewed looking down on the distributor from the front of the vehicle, the distributor body has the vacuum can pointing at about 7:00 or 7:30 clock position from the same vantage point.

That brings up a very good point. I'm surprised I over looked that. I watched the video and that helped me understand as we'll. My father and I will go over it again tonight and make sure it's tdc after the intake stroke. I'll check for the piston, the key way on the pulley, and the yellow mark on the balancer and report back here. thanks for all the help and patience guys!

 

[350runner]

No prob.

Sent from the dust in front of you!

 

[88Chevyk5]

Got it to start! Thanks for all the help guys. Just got to fool around with it now because it doesn't want to idle. Need to change plugs and maybe run some sea foam through it to help clean out any crap in there because it's been sitting for a while.

 

[rich weyand]

Excellent!

No fancy plugs, they're money for nothing. AC Delco R45TS is GM recommended, and I have had no problems running them. They cross-reference to an Autolite 26, which would also be fine and probably a little less prone to fouling, which some people complain about with the AC Delco plugs.

 

[MadOgre]

Okay move the cap counterclockwise in small increments. Truck stopped backfiring but still no run. Could the distributor be bad? I've got a spare motor for parts that came out of my 87 k20 tbi. Ran like a champ so I know everything on it is in working order.

Just try back and forward till it fires. Sometimes a pain in the ass

 

[MadOgre]

Oops I guess I should have read before posting

 

[88Chevyk5]

Sounds good! I'll run out to the store today and grab some plugs. It has a hard time idling. I have to hold the pedal down a touch for it to stay running. Could be tps or throttle body I'm guessing.

 

[HotRodPC]

I know you have it started now but just to add, in most cases, when you're 180 out, you should be getting backfire out both intake and exhaust. Because the timing is so far off when 180 out, some cylinders will be way advanced, some will be very retarded, and this is why you'd end up with both ends backfiring.

Now that you have it started, but not running good, makes me wonder if you haven't just played with it enough moving the dizzy to get it to start and it's running badly because it's jumped time on the chain. You may have just found the right spot to compensate for a tooth or 2 off to get it to start, but it won't continue to run because the timing is off. If you have a timing light, you can compare ignition timing to valve timing use the TDC mark on the balancer in reference to when it's actually firing.