350 Tbi running bad

[87silveradok20]

Ehhhh, yeah a little can be normal to a certain degree in some situations. If the injectors dribbled a little as you shut it off, and the intake is still hot, the fuel drops into the intake then it vaporizes quickly and comes up the TB as steam. Not sure you need to worry about that right now, unless it's just a massive amount.

It's not much. That's probably what it is that makes sense


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[87silveradok20]

A video or sound clip would be helpful. Try to get both the engine and a stand back so we can hear both the carb and the exhaust.


One quick way to tell if the chain has jumped time is, to set your harmonic balancer on the front of the engine to TDC (Top Dead Center) or at ZERO. Pop the distributor cap off and see where the rotor is pointing. If you're on the compression stroke, it should be pointing at #1 on the dizzy cap, if if you're on the exhaust stroke it should be pointing at #6. If the rotor is pointing well behind where it should be, that's a sign the chain has slipped and the cam is in the wrong place which is what drives the distributor.

I'll take a video is the best way to post a video upload it to YouTube then post it?


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[87silveradok20]

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This is the only mark I can find on my harmonic balancer. Does this mark tdc?


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[87silveradok20]

A video or sound clip would be helpful. Try to get both the engine and a stand back so we can hear both the carb and the exhaust.


One quick way to tell if the chain has jumped time is, to set your harmonic balancer on the front of the engine to TDC (Top Dead Center) or at ZERO. Pop the distributor cap off and see where the rotor is pointing. If you're on the compression stroke, it should be pointing at #1 on the dizzy cap, if if you're on the exhaust stroke it should be pointing at #6. If the rotor is pointing well behind where it should be, that's a sign the chain has slipped and the cam is in the wrong place which is what drives the distributor.

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Found tdc and pulled the cap off. This is what I got if I'm not mistaken this means the chain has slipped.



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[87silveradok20]

Here's what it looked like with the cap on

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[Cuba]

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Found tdc and pulled the cap off. This is what I got if I'm not mistaken this means the chain has slipped.



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Yeah, from my info it looks like it did. The rotor should be pointing to more 5 o'clock versus 7 o'clock shown in the photo...

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[HotRodPC]

It's not horribly off to where I'd say definitively that it's off to the point it for sure jumped time. Remember even a loose chain will make it off a bit so if you split the difference of the slop in the chain it may back the rotor up 1/8 inch or so. So if you backed the balancer up a bit, then back to TDC and split the difference in the slop the rotor would be closer to where it's supposed to be. Remember you just turned the engine to TDC, so the chain is tight on one side, and all the slop is on the other side.

If you can get that sound video posted on you tube to let some of us hear it, then I'd feel better saying, yes it sounds like it jumped time.

It would be nice to get some more of the better experienced TBI guys to make a suggestion. @89Suburban @skysurfer @bucket @RetroC10Sport

 

[87silveradok20]

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I spun the motor some more then spun it back to tdc from the other direction and here's what the rotor looked like after that


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[87silveradok20]

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here's the video I took the other day. I'll try to take another one from behind and by the Motor when I have some help.


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[HotRodPC]

So I can't hear that real well, but if all that is backfires, it's consistent backfire for sure. But it doesn't sound like it's both exhaust and intake. Whatever the noise I'm hearing, it sounds like it's coming from the same place everytime. If timing is out, it's going to backfire BOTH intake and exhaust. Not either or. The way that sounded to me, and don't hold me to this cuz I may not have heard it right, but from what I did hear, I'd be thinking a valvetrain problem. Either a burnt valve, or maybe even a flat cam lobe and a valve isn't opening as it should.

Do you have a compression tester? A compression test can also tell alot. Or even a vacuum gauge. Put a vac gauge on. Just T into any vacuum port, (not a ported vacuum) and watch the vac gauge for needle movement. It could be a bouncing needle, it could be an erratic needle and both indicate an internal engine problem which could be valve timing, burnt valve, valve not opening etc. The thing a vac test won't do, is tell you what cylinder is having the problem, it'll just tell you there is a problem. The compression test can tell you which cylinder it is having the issue then you can further inspect that cylinder.


Anyone else have opinions? More heads are better than one. I don't know everything and maybe I'm missing something.

 

[HotRodPC]

Yeah, from my info it looks like it did. The rotor should be pointing to more 5 o'clock versus 7 o'clock shown in the photo...

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This is true, but I'd sure like more confirmation since we don't know for certain where #1 is on the cap. Lots of times when someone drops a dizzy back in, they're not as picky as I am where #1 lands and don't really care where #1 lands. However, I always try to put it back to factory biggest reason being, plug wire lengths and when you have #1 where #3 or #4 or whatever position is, then all your plug wires off and some are to long and some need to be stretched to reach blah blah blah. I'm just not hearing both intake and exhaust backfires in that video.

 

[Cuba]

This is true, but I'd sure like more confirmation since we don't know for certain where #1 is on the cap. Lots of times when someone drops a dizzy back in, they're not as picky as I am where #1 lands and don't really care where #1 lands. However, I always try to put it back to factory biggest reason being, plug wire lengths and when you have #1 where #3 or #4 or whatever position is, then all your plug wires off and some are to long and some need to be stretched to reach blah blah blah. I'm just not hearing both intake and exhaust backfires in that video.

True, not everyone is picky about dizzy placement. And it could be fine the way it is too. I am, though because for me it helps diagnose things a little faster, at least on my vehicles.

I agree with compression testing at least, to check off things of possibility too. It would be nice to avoid having to take front cover off or know for sure if you have to or not.

IDK about the vac test though. When engines are running rough, the needle tends to bounce around too, at least in my experience. Or I'm just not good enough to diagnose with that. *shrugs*

I couldn't tell where the backfires were coming from in the video either, but I believe OP said he'd post another one.

 

[87silveradok20]

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Here's another video. It doesn't appear the backfires are coming through the throttle body now. It did it a few times before but now that I've put the cap back on it hasn't done it. Notice I'm the video the stumble in rpms I was steadily increasing the throttle the whole time.


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[74 Shortbed]

Remember you have to take into consideration initial timing, if it's set at 12* initial timing the rotor will not line up with number one because that would be zero..

 

[Honky Kong jr]

Did the timing chain **** the bed?