Hey guys, I apologize in advance this is going to be a bit long. I’ve been working on my brothers 2000 4.3 Sierra. It’s had way less power than it should since he’s owned it. It’s gotten to where it will not start when it was cold, he wanted to replace the timing chain and sprockets to make sure that it hadn’t slipped timing or anything, so I did that last week, dropped the pan replaced the oil pump, timing set, new timing cover all of that. When I set it to TDC compression stroke, the arrows on the timing gears were both facing straight up towards the top of the engine, I thought they were supposed to point at each other, bt I don’t know a lot about it and since they were perfectly aligned, I put it back together. It started and ran just like it always did for a day or two and then it just would not start at all, in researching I realized the timing had been wrong, so we pulled it back in the shop and I did the whole job again, I put it on TDC, had the cam gear dot and the balance shaft dot pointing at each other, and then the timing chain gears arrows pointing at eachother, and the distributor pointing at the the little arrow like it’s supposed to and still no start, and still hear compression through the intake tube like it’s out of time. I’m thinking I need to pull the valve covers and check for a broken valve spring or stuck valve or something but I’m curious what you all think since I’m no expert on this stuff, sorry for the long post and thanks in advance - Jordan
4.3 no start
- Thread starter JMF97
- Start date
Cadillacmak
Well-Known Member
Welcome to the forum from Alaska!
Sounds like maybe you got TDC 180 degrees out? That's what I would check for first.
Sounds like maybe you got TDC 180 degrees out? That's what I would check for first.
thank you for the response, I set it to TDC when I tore it down, turned the engine over by hand with a ratchet and felt for compression on the spark plug port. But as I said the arrows were both facing straight up instead of at each other, so I pointed them towards each other, I didn’t really think about it but I guess I might have needed to rotate that around another cycle to get it right
stutaeng
Well-Known Member
Well, if it started and ran fine initially for a few days, then it can't be that the timing was installed wrong. And highly doubtful mechanical timing was wrong to begin with (you mentioned you put it back together the way it was before, right?)
You probably have something else going on. Have you done the basics like checking for fuel pressure with a guage and checking for spark using a spark tester?
You probably have something else going on. Have you done the basics like checking for fuel pressure with a guage and checking for spark using a spark tester?
it started and run for a couple days but then it wouldn’t start at all and was blowing compression through the intake when you’d try to start it, that was when I just put it back together like it had been. But then I redid the job and that’s when I changed the timing, so it’s probably wrong for sure now unfortunately. Just to add, when he bought the truck it didn’t run and someone had the plug wires all switched around, everything that has been worked on has been wrong so that’s why I thought it could be out
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Welcome to the forum from Oregon.
There is absolutely no way that the gear timing marks could be 180 off on one of them and the engine would start and run for a couple days. According to the pic I looked up for a 2000 4.3 "W" engine, this is how the marks should be at TDC. Is it a "W" engine? Look thru this info site and check that you have done the repair correctly: https://charm.li/
There is absolutely no way that the gear timing marks could be 180 off on one of them and the engine would start and run for a couple days. According to the pic I looked up for a 2000 4.3 "W" engine, this is how the marks should be at TDC. Is it a "W" engine? Look thru this info site and check that you have done the repair correctly: https://charm.li/
Notice in the pic, that not only is the dots pointed at each other but the locating pin on the cam gear is at 3 o'clock.
Plus, you said the engine had way less power than it should. Did you check the fuel pressure? Did you check for clogged catalytic converter? Did you check for ..........?
Plus, you said the engine had way less power than it should. Did you check the fuel pressure? Did you check for clogged catalytic converter? Did you check for ..........?
Yes, the dowel pin points at 3 o clock, I took off the chain sprocket and lined up the dots on the cam gear and the balance shaft gear, and then I had the number 1 cylinder up and both arrows pointed at each other on the timing chain sprockets, like your picture. They’re arrows on this truck instead of dots but exactly like that. I checked the cat last year when I did a clutch in the truck because I was worried that was it, but it wasn’t clogged then, fuel pressure is low but that is a new problem, we’re replacing the lines as soon as they come in, but the truck won’t fire with starting fluid either so I don’t think that’s is, could certainly be wrong though
Edit: might be helpful to add, he’s had the truck for probably 4-5 years now, and it’s never had the power it should sometimes it won’t hardly make it to 55mph, I did do a fuel pressure test back then and it was right in the middle of the range of where it was supposed to be don’t hold me to this but I’m thinking it was 60 psi or something like that
Edit: might be helpful to add, he’s had the truck for probably 4-5 years now, and it’s never had the power it should sometimes it won’t hardly make it to 55mph, I did do a fuel pressure test back then and it was right in the middle of the range of where it was supposed to be don’t hold me to this but I’m thinking it was 60 psi or something like that
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What is the fuel pressure now? Does it start or try to start with starting fluid? You need to do a compression test and list all cylinders results here and post pics of the plugs here and correspond the plugs to the correct cylinder hole.
When I tried starting fluid last night it popped back through the intake and blew compression out like it’s out of time. I really don’t think the mechanical timing could be wrong following the steps that were in the video I linked. I don’t have a fuel pressure gauge or a compression gauge I’ll have to rent them from the auto parts store but I can do that for sure. I probably need to pull the cap and double check the distributor, I had a super hard time getting it to line up, I finally got it but the copper tab on the rotor was slightly off center from the arrow cast into the distributor, I’m talking like 1/16th or less from being centered. I figured it was good since when the distributor gear meshes with the cam gear it moves the rotor a significant amount, but I did think that was weird, I don’t know if my description makes sense but I’ll probably pull the cap and double check that
Cadillacmak
Well-Known Member
If it started and ran like that, there is something wrong with the timing chain set. Do you think the factory messed up the markings?
I can’t imagine so, I’d put money on me messing something up before I would the factory making them wrong haha. I’ll check them next time I’m up there I have the old timing set laying on the shop floor. The new timing set were GM parts too by the way, so definitely should be right.
stutaeng
Well-Known Member
Has the distributor been installed correctly? I remember when I did the leaky intake manifold gaskets on my 4.3, I somehow installed the distributor 180 off. I remember there's 2 marks on the harmonic balancer and I guess I kept doing it wrong. The engine would hardly crank, and it sounded like it was "out of time.)
I called my buddy who is a mechanic, and he too couldn't get the darn thing to fire. I had to wait for his older brother, also a mechanic until the following week. He too installed it the way we did, and it didn't fire. He then installed it a different way (180? ...been a long time, don't remember the exact details), and it fired right up.
The timing chains are almost impossible to jump teeth on these engines. If the timing teeth/chain jumped teeth, then you have a way bigger problem. Think piston to valve smashing, bent pushrods and stuff like that.
I called my buddy who is a mechanic, and he too couldn't get the darn thing to fire. I had to wait for his older brother, also a mechanic until the following week. He too installed it the way we did, and it didn't fire. He then installed it a different way (180? ...been a long time, don't remember the exact details), and it fired right up.
The timing chains are almost impossible to jump teeth on these engines. If the timing teeth/chain jumped teeth, then you have a way bigger problem. Think piston to valve smashing, bent pushrods and stuff like that.
If you have all the front engine timing marks right and you have decent enough fuel pressure and the plugs are not trashed, then the problem is likely related to distributor drop or cap/rotor.
I had an awful time getting it lined up because of the shaft from the oil pump, very hard to find it with a screwdriver to turn it, there is an arrow that is molded into the aluminum base of the distributor that the copper part on the rotor is supposed to point at, when I finally got that it was slightly off center, I’m talking like 1/16th or less, which I thought was odd, but when you install the distributor and the gear meshes with the cam gear you know it moves a significant amount like 3/4 of an inch so it being off such a tiny amount didn’t really make sense to me
stutaeng
Well-Known Member
I think you rotate the engine to TDC #1 on the compression stroke, then adjust your rotor pointer backwards a bit (you have to anticipate how much it will mesh and rotate forward) so that it lands on the little pointer on the distributor. At the same time, the oil pump drive has to align with the distributor shaft, so you have to look down and rotate that with a screwdriver ahead of time...
I remember the complication is the harmonic balancer has TWO marks, I can't remember why at the moment. The marks are kinda near each other too.
I remember the complication is the harmonic balancer has TWO marks, I can't remember why at the moment. The marks are kinda near each other too.
Yes that’s how I did it, I think the rotor points back to just ahead of one of the bolt holes for the cap, the factory one has a nice little line to line up the roll pins on the distributor gear, this one is aftermarket and doesn’t have that unfortunately, but I did rotate it back a bit
Edit: I also did the distributor before I had the timing cover and all that on so I could visably see everything lined up, the balancer is like you said two different marks very close together
Edit: I also did the distributor before I had the timing cover and all that on so I could visably see everything lined up, the balancer is like you said two different marks very close together
