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TBI 350 Dies Idling and Wont Run

eclipse85k10

eclipse85k10

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After putting about 8k miles on a fresh long block in my 89 Burb last it died on my when I got to work and would not start again. First I thought it was the Fuel pump and replaced it anyways. Its got plenty of good fuel spray, the throttle body and injectors were rebuilt just before swapping in the rebuilt long block.

I then checked spark and I was getting good spark on all plugs. I tried adjusting timing, it would act like it was trying to start but did not matter how much I advanced or retarded the timing it would not run. The distributor was a few years old before the rebuilt long block so I decided to try a new one anyways knowing the gear can get warped on those. No change.

I then checked the cam timing and for the heck of it replaced the chain, the cam timing was still set on. I have pulled all the push rods to check for any bent ones and they all still look like new. When i crank on it trying to get it to start and adjust the timing it will end up back firing real loud. I'm at a complete loss. I have cranked it with the valve covers off and all the rocker arms are moving like they should so i dont believe its a flattened cam or bad lifter? Stuck valves? Really at a loss, its just been sitting in the shop leaving me stumped for quite a while.
 
It sounds like you fixed it and broke it at the same time. Not sure how you could have done it, but it sure sounds like you are 180 degrees out of time.
That is the classic cause for backfiring and no start.
Any chance you bumped the engine around while the dizzy was out?
Pull the no. 1 plug, and put your finger over the hole while bumping the engine around and watching the rotor. The pressure should blow your finger back when the rotor approaches the no. 1 position.
Otherwise, you still need the basics: Fuel, air, compression, and spark at the right time. If it won't run, one of them is not right.
 
Fordum said:
It sounds like you fixed it and broke it at the same time. Not sure how you could have done it, but it sure sounds like you are 180 degrees out of time.
That is the classic cause for backfiring and no start.
Any chance you bumped the engine around while the dizzy was out?
Pull the no. 1 plug, and put your finger over the hole while bumping the engine around and watching the rotor. The pressure should blow your finger back when the rotor approaches the no. 1 position.
Otherwise, you still need the basics: Fuel, air, compression, and spark at the right time. If it won't run, one of them is not right.
Click to expand...

Ive tried setting the timing with pulling number one and turning the motor over. Also I've manually cranked the motor and set the balancer on the tab. Also just to make sure it's not 180 off I've flipped it so many times. 180 one way it back fires out the exhuast and 180 the other way out the intake.
 
One stuck valve shouldn't prevent it from running--just not run "good"..

I've seen ignition modules go south and still seem to have good spark--they control the injectors too,and that section of the module can go bad,but the ignition side still works OK...(and vice versa )..
If it has a pick up coil those can do weird things too when they fail..
 
diesel4me said:
One stuck valve shouldn't prevent it from running--just not run "good"..

I've seen ignition modules go south and still seem to have good spark--they control the injectors too,and that section of the module can go bad,but the ignition side still works OK...(and vice versa )..
If it has a pick up coil those can do weird things too when they fail..
Click to expand...

Is the ignition module still inside the distributor on a TBI setup or is it one of the modules to the right of the throttle body? I replaced the complete distributor with no change
 
Far as I know the ignition module is inside the distributor,and the "module" on the throttle body is probably the throttle position sensor..

Did you replace the distributor cap & rotor too ?...either of those can carbon track and make the spark jump to ground,or to another cylinder's terminal and cause symptoms like this..
Sometimes a coil shows good spark when you test it by seeing if spark will jump to ground outside of the engine--but not have enough output to fire a spark plug under compression..

Another thing to check is the ground wires for the ECM--often they get corroded and a poor ground can cause all kinds of troubles..
Unfortunately I don't know where those will be located--someone else here will likely know though..

I'm more familiar with old HEI distributors and carbs,never owned a TBI or computer controlled GM truck yet..(and hope not too!)..
I only know a little about any after 1988,just from what I've seen friends have to go thru when they repair newer trucks..

If something like a voltage surge happened,it may have fried the ECM or Prom inside it..seen a few fail after someone did some welding on the vehicle,then it refused to start or run,just backfire and bind up while cranking..
 
Back to basics, firing order, distributor clocked correct, fuel compression. With everything you have replaced, and as many times as the distributor has been out. Time to step back take a deep breath, and then recheck. When you did the timing chain, old marks lined up remove old install new? I ask because I have seen cam timing off by 180 cuase no starts.
 
Also, I've seen top dead center number one cylinder missed a lot of times. Jane to make sure it is on the compression stroke.
 
In his first post he said it had 8k miles on it but died on him at work. So the timing must have been correct to begin with :dunno: So it must be something else that caused the problem in the first place. Although now, it may be out of time as well
 
Might not be any longer. Has changed too many things. What I dont get is, if it has correctly timed spark, fuel and compression, it should be running. So something is missing in the order of things. If it is getting fuel and spark like he posted, means the timing is not where it is supposed to be.

Needs to begin like it is a new engine install now.
 
That was my original thought. I figured the original reason it died was a distributor problem, and then when he replaced it, he fixed the problem, but then broke it when he fixed it by getting it a couple of teeth off.
 
I wonder if the new distributor he tried had a different ignition module and pick-up coil or if he transferred those to the new one. A little far fetched, but could it possibly be a plugged catalytic converter if it even has one?
 
Last edited:
plugged catalytic converter
Click to expand...
Pull the precat o2 sensor and see if it starts. Leave the 02 bung unplugged.
Easy test it will idle with 02 out if cat is blocked.
 
No cat anymore and the distributor was a complete replacement unit. Though I know of new parts to not be any good out of the box. I'm going to try replacing the coil and check out the ecm and maybe look for another one. I'm more familiar with the HEI than this TBI setup. Thought crossed my mine to pull the intake and just though a carb and HEI on it but really rather not.
 
Still could be blocked exhust. Pull o2 easy enough to eliminated constipation
 
Started working on this again recently.

For sure got the distributor gear set right now. Exhuast starts thumping when crank. Like it's on the edge of starting up. New ECM, new plugs , new ESC. Even a little starting fluid sprayed in to the throttle body And nothing.

Decided to try swapping in a known good HEI distributor and no change what so ever.

No cat or blocked exhaust on it. About to start parting this rig out. It's been taking up space in my dad's shop for too long.
 
Just a question, now that you've monkeyed with it a bunch, and knowing at one time it was running, so this can't be the original cause, did you disconnect the bypass wire for the distributor? Brown single wire/connector, somewhere over by the booster on the firewall. Disconnect, start engine (if it will), time to 0*, turn off, reconnect. If it won't start, rotate the distributor. Helps if someone is there to crank it while you rotate.

Unlikely the cause, it takes a lot of rotation to get the timing that far off, but it can't hurt to try. It's free and easy.
 
dyeager535 said:
Just a question, now that you've monkeyed with it a bunch, and knowing at one time it was running, so this can't be the original cause, did you disconnect the bypass wire for the distributor? Brown single wire/connector, somewhere over by the booster on the firewall. Disconnect, start engine (if it will), time to 0*, turn off, reconnect. If it won't start, rotate the distributor. Helps if someone is there to crank it while you rotate.

It's made me wonder if maybe the cam went flat? Never had so much trouble getting a 350 to fire up

Unlikely the cause, it takes a lot of rotation to get the timing that far off, but it can't hurt to try. It's free and easy.
Click to expand...

Up timing wire is unhooked. I've had help cranking. Before we tried the HEI distributor just based on the way it was sounding turning over and adjusting the distributor I could turn it to what sounded like close to right timing but it still would run.
 
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