Big6ft6

I"m a visitor on this forum...you guys over here on thrid gen are known across the web as "TBI" gurus, so I thought I'd ask for help.

I've got a new/rebuilt 350 in my 1989 suburban. I Just finished buttoning her up this weekend. Put in oil and coolant...

went to start her and she won't catch. Just spins the motor.

Here are the facts.
1) Starter sounds funny...like it is spinning too easy...I don't get the grrr--rrr-rrr of normal starter, I just get a high-pitched spinning sound. It is turning the engine over....but it just sounds wierd to me. I did drop the starter on the concrete while installing it...but if it is turning the engine over that is all that should matter right?

2) I do have spark...checked against the body of the car while cranking.

3) I do have fuel...it is spraying into the intake from the throttle body.

4) I'm 99% sure my primilinary timing is set correctly. I've got the rotor very close to the #1 contact in the cap when #1 is at TDC. I've messed around moving it a few degrees left and right from there without any change.

5) After I try starting her...if I let it sit for a few minutes...then bump the key she backfires out the exhaust?? It won't back fire while I"m trying to start her...only after I let it sit and try to start it again. Can't figure this one out...makes me super suspicous of the timing. The only way it could back fire is if it is sparking with an exhaust valve open right?

I had my girlfriend crank it over while I watched the timing light, and I couldn't see the timing mark when she flashed, but I couldn't see very well period. But I know for a fact, that my distributor is NOT off 180...

Any ideas?? What is the most typical part of ignition system to fail?

All these parts were on my old engine and it was running when I took it apart.

Thanks all ideas and help!!

kcb37

Does your injectors spray a good cone?
Was your spark blue?
Do you have good fuel pressure?
Have you tried to spray some starting fluid or a little gas in the TBI to see if it will start like that. (little, to much your TBI will burst into flames)
Make sure all your ignition wires are tight, and the connections are clean.

Big6ft6

Thanks for the ideas 37.

after doing some internet research (I mean working hard at work!)

I just was looking at a comp cams cam timing diagram, and I didn't realize that at TDC of the exhuast stroke (TDCE), the valves are essentially closed then as well as at TDC of compression stroke.

I always thought that at TDCE the exhaust valve was wide open.

I was using the "watch the valves" method for finding TDC of compression, and I just watched for when the timing mark came around and both valves looked closed. Now I'm wondering if I wasn't seeing them during the "overlap" at TDCE.

I will now reduce my confidence that my timing is set to 50%, so this will be my first check tonight. If that doesn't work I will start going down your list.

kcb37

You should be able to pull the #1 plug, and put your finger over the plug hole. Rotate the engine. When the pressure blows your finger off, that's compression. Shold be the only upward stroke that you don't have a valve open.

Big6ft6

Alright, well, now I'm 100% sure that my timing is (and was) correct.

So I'm back to square one.

Here is my question now. Could a messed up starter cuase this?

Here is my theory. I dropped my starter while carrying it to install. Something got @#$(*& up becuase the starter sounds really wierd now, more like a high pitched electric motor sound, not like typical cranking sound.

It is turning the motor over, but maybe too slowly?? And by turing to slowly it isn't drawing air into the cylinder fast enough to get a properly mixed charge. And maybe what I'm hearing isn't a "backfire" at all, but actually a single cylinder firing after the excess unburnt gas volitizes enough while sitting between starting attempts to get lit-off by the spark plug?

Thoughts?

I don't have any exhuast hooked up yet, so how would I tell the difference between a cylinder firing and a backfire?

graebz28

iTrader: (5)

I had to have my girlfriend do the same when I was doing my initial start-up. Timing should be around 20 degrees when cranking over. What type of starter?

I would also recommend checking the fuel pressure. Is the motor an exact replacement of what you had before? Same cam?

Big6ft6

The starter is just the stock heavy GM starter.

The engine is a TBI engine bored 40 over, it has a new cam, but supposedly it is a cam that provides a little more torque without needing to get into the computer.

But I didn't have it built, I bought it form the guy who had it built. I have reciepts and cam specs, for it but don't know them off the top of my head what those specs are.

The throttle body is my original (200K mi +) as is the computer etc. It all ran before I took the old engine out.

I don't have anything but the manifolds on for exhaust

Big6ft6

So I just went to the auto store, the starter tested wierd, they didn't say it failed, but it was making grinding noises like a bad bearing.

I just remembered to, when my previous engine died (siezed) I did try once or twice to use the starter to move the rotating assembly around while the engine was still in. It had a hard time maybe that is when I screwed up this starter.

So anywan, as soon as I get home after work.....I'll try the new starter and see what happens.
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20 degrees?? I'm assuming AFTDC? Is this with the ETC wire disconnected or connected?

getsideways

20 deg btdc with wire connected. thats at idle.

Big6ft6

Wow! 20 BTDC? Isn't adavanced timing usually reserved for higher rpms? Or am I backwards? My understanding was at higher RPMs the charge has to be lit-off sooner so the pressure front can "catch-up" to the piston on the power stroke

So should I be playing around with 20 BTDC advanced timing while trying to get this thing to fire off for the first time with the wire disconnected? Then once it is running quickly put it back to 0 BTDC?

I know eventually the static timing is "supposed" to be 0 BTDC with the wire disconnected.

Maybe this will help if the factor seems to think idle is 20 BTDC, I should give it a try?

Big6ft6

o.k.

New update.

Finally got a buddy over to crank the engine while I am under the hood.

At a loss for ideas I pulled a spark plug, but my thumb in the hold and had him crank the engine....nothing.

I'v never done the "finger in spark plug" compression test, but from what I understand, it is pretty obvious amout of pressure.

Now I'm really scared, either the engine builder put the cam in wrong. Or when iwas adjusting the valves, I over tightenen the rocker arms becuase the hydraulic lifters weren't primed, and now with primed lifters the valves aren't seating.

Now I'm worried I've damaged the cam shaft with all the cranking I've been doing if my rocker arms are over-tightened.

Anyone ever experience this?

getsideways

i would go ahead and reset the valves. possible you could have over tightened the rockers. you should definitely get air with your finger in the spark plug hole.

50bmgshooter

iTrader: (4)

like he said
how I would do is
loosen all rocker all the way out then go back one at a time and tighten them down untill you feel a reststance in rotating the push rods after you get them all done check your dist check for compression on #1 with your finger in the plug hole. then try to fire if it fires set valves and close the motor up

Big6ft6

Solution!!

You guys were dead on!!

I over tighitened my valves.

I misunderstood the instructions for adjusting valves, I would spin the pushrods in my fingers, and I would tighten the rocker arm nut until I couldn't spin the pushrod anymore, then I would tighten it another 3/4 turns!

God...I'm an idiot...that doesn't even make any sense, I don't know what I was thinking.

I now readjusted them. This time spinning the pushrod with one greasy finger and tightening until I felt the SLIGHTEST resistance (zero clearance) then I tightened one more half turn. I can easily still spin the pushrod with two fingers easily.

Immediately starter sounds more normal and my engine fired right up. Now I'm only worried that I have damaged my cam with all that cranking on the engine with my valves set so tight.