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350 TBI surging

if it was timed on the exhaust stroke, it might try to run but, would cough and fart and generally only lite for a rpm or 2, not run. now if the timing chain slipped a tooth it would run, have a crappy low end, but the would be way better in the upper rpm. Restabbing the dist, won't help with late cam timing. Advancing the timing will help band aid late timing.
My suggestion would be to turn the crank one way while watching the dist rotor, mark crank position, turn crank the opposite way stop as soon as rotor moves again, and see how the crank moved from your mark. This will give you and idea how sloppy the chain is.
if movement is detected right away then chances are good the chain is in good shape, If the crank moves a lot before rotor does then the chain is stretched and possibly slipped.
 
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Wes Harden said:
if it was timed on the exhaust stroke, it might try to run but, would cough and fart and generally only lite for a rpm or 2, not run. now if the timing chain slipped a tooth it would run, have a crappy low end, but the would be way better in the upper rpm. Restabbing the dist, won't help with late cam timing. Advancing the timing will help band aid late timing.
My suggestion would be to turn the crank one way while watching the dist rotor, mark crank position, turn crank the opposite way stop as soon as rotor moves again, and see how the crank moved from your mark. This will give you and idea how sloppy the chain is.
if movement is detected right away then chances are good the chain is in good shape, If the crank moves a lot before rotor does then the chain is stretched and possibly slipped.
Click to expand...
Kind of sounds like my problem only because it runs better at high rpms and rough at low. And because I have to advance it so much, it would be a pain to take all the accessories off though. I’ll test the chain today. Thanks.
 
When I worked on a lot of g vans, we did water pumps and timing chains from the bottom, we were using a lift so we could stand underneath.
Do so allowed us to leave radiator and shroud in place.
 
Wes Harden said:
When I worked on a lot of g vans, we did water pumps and timing chains from the bottom, we were using a lift so we could stand underneath.
Do so allowed us to leave radiator and shroud in place.
Click to expand...
I’ll have to see if that’s possible for me, I’d love to leave the ac condenser hooked up.
 
1st is the loosen fan nuts, all belts, crank pulley, fan, water pump. Then the balancer and cover. Not sure it can be done with out being able to stand under and reach straight up. I have never tried it not on a lift
 
Wes Harden said:
if it was timed on the exhaust stroke, it might try to run but, would cough and fart and generally only lite for a rpm or 2, not run. now if the timing chain slipped a tooth it would run, have a crappy low end, but the would be way better in the upper rpm. Restabbing the dist, won't help with late cam timing. Advancing the timing will help band aid late timing.
My suggestion would be to turn the crank one way while watching the dist rotor, mark crank position, turn crank the opposite way stop as soon as rotor moves again, and see how the crank moved from your mark. This will give you and idea how sloppy the chain is.
if movement is detected right away then chances are good the chain is in good shape, If the crank moves a lot before rotor does then the chain is stretched and possibly slipped.
Click to expand...
So It wasn’t quite the same test because I can’t really see the rotor moving as I’m turning the crank with one person, but if I rotate the crank a quarter turn clockwise and make a note of how much the rotor turned, and rotate the crank counter clockwise the same amount and check rotor movement I can tell the rotor turned noticeably less on the counter clockwise turn. Note that I’m rotating the crank clockwise a little beforehand to get the chain tight before I do the test.
 
yeah for a g van a helper is definitely handy. but it does sound like there is slop in the chain.
 
Wes Harden said:
yeah for a g van a helper is definitely handy. but it does sound like there is slop in the chain.
Click to expand...
Yeah, not sure if it’s enough to jump a tooth, before I commit to the chain im going to replace the coil. new throttle body gasket and plugs and wires today. It seems to stay running a little better but eventually the idle starts to come down and it gets rough and dies. But I figure the rest of the ignition system is new now might as well replace the coil for $30. We’ll see what happens.
 
Since this is a new to you truck and it has never run for you, I will tell you of my jumped timing chain experience. My co worker and i were driving down 40 mph road near very near lake Havasu, as we came up to a popular cove, people were crossing the road I lifted off the gas and was decelerating. As the people cleared the road my buddy says we're gonna get hit, and I nailed the throttle, but we got hit from behind. Kid in a baja bug no front brakes hit me on passenger rear. After all the official business(one and only time I used channel 9 on a CB) we went on our way. Truck was hard starting at the scene, but i got it running, got to my buddies place had lunch and went out to go back to work, truck wouldn't start, had fuel and spark, only thing left was timing, added some advance and it started. Made it back to work. Quitting time truck won't start, call the wife to pick me up. Next day do some diagnoses, same test I outlined above a bit of slop in chain but not a huge amount. Either way I knew the dist rotor had moved and figured either my hard accell or the hard hit over powered the chain. I had slipped 1 tooth, and was starting to slip a second is when it quit running. I have only seen one other slipped chain and both were the factory nylon coated cam gear had worn
 
Wes Harden said:
Since this is a new to you truck and it has never run for you, I will tell you of my jumped timing chain experience. My co worker and i were driving down 40 mph road near very near lake Havasu, as we came up to a popular cove, people were crossing the road I lifted off the gas and was decelerating. As the people cleared the road my buddy says we're gonna get hit, and I nailed the throttle, but we got hit from behind. Kid in a baja bug no front brakes hit me on passenger rear. After all the official business(one and only time I used channel 9 on a CB) we went on our way. Truck was hard starting at the scene, but i got it running, got to my buddies place had lunch and went out to go back to work, truck wouldn't start, had fuel and spark, only thing left was timing, added some advance and it started. Made it back to work. Quitting time truck won't start, call the wife to pick me up. Next day do some diagnoses, same test I outlined above a bit of slop in chain but not a huge amount. Either way I knew the dist rotor had moved and figured either my hard accell or the hard hit over powered the chain. I had slipped 1 tooth, and was starting to slip a second is when it quit running. I have only seen one other slipped chain and both were the factory nylon coated cam gear had worn
Click to expand...
Thanks for the insight, having no real knowledge of what this motor has been through it’s hard to say whether it’s slipped or not. I’ve always seen that as a rare thing and at 80k miles I wouldn’t expect it but who knows. I just put a new ignition coil in, didn’t seem to do much. I plugged the advance wire back in just for the heck of it and it actually stays running better. Still gets low and shaky and then brings itself back up. It runs long enough so I can look at the timing better, if I set the gun to 25° advanced the mark on the balancer lines up to 0. Is this looking more and more like a slipped chain? Also idle was sitting around 650 but dipping when it would try to die.
 
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Also just noticed thisIMG_8699.jpeg
This is on the passenger side of the engine next to the air cleaner. Was kind of hidden behind wire loom, I’ll replace the top line because it’s spilt on the end. Is there supposed to be a line in that bottom nipple? And if so where does it go?
 
I'll wait for a pro to answer, but I'd guess thats an EGR solenoid, and the open one may be the vent?
 
don't believe that the egr solenoid. The egr solenoid has a round cap snap on, on one end, with a filter under cap. Picture of emissions label ??
 
One thing you might want to check is if your EGR port in the intake manifold is plugged up with carbon. Back when I first bought my TBI square body it had the original engine in it, and when I removed the EGR valve the EGR port in the intake manifold was completely clogged up with carbon to the point where the EGR valve could not even open because the carbon build up stopped the EGR valve from opening.
 
1-ton said:
One thing you might want to check is if your EGR port in the intake manifold is plugged up with carbon. Back when I first bought my TBI square body it had the original engine in it, and when I removed the EGR valve the EGR port in the intake manifold was completely clogged up with carbon to the point where the EGR valve could not even open because the carbon build up stopped the EGR valve from opening.
Click to expand...
Was planning on just replacing the valve anyway so I’ll check it out. Thank you.
 
Be careful replacing those valves. GM used a ton of them, the aftermarket combines many part numbers, a working GM piece that is 30 years old may be better than a new chinese knockoff.

If it moves freely by hand, and holds vacuum, its almost certainly good.
 
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