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Tbi help

83ChevyK5Blazer

83ChevyK5Blazer

1/2 ton status
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So I got the tbi hooked up in my suburban,

It keeps back firing and popping through the throttle body.

Specs....
Gm goodwrench crate engine
Non tbi heads
Long tube headers
Edelbrock performer intake
Throttle body adapter
One inch spacer

Throttle body is clean and re-gasketed
New injectors
New tps
New iac
New temp sensor
New map sensor
New 3 wire O2 sensor
New distributor.

The coil was with the truck when I got it.

Plug wires are less that a year old and were ran on the engine when it was carbed.

Fuel filter didn't appear to dirty, pump is quiet and primes right up.

Timing is set to 5 degrees tdc with the plug disconnected.

It is popping under wide open throttle and under any load, under load it will die after a pop.

Engine ran really good in the blazer with the quad on it, so I'm not thinking it's a wiped lobe or burnt valve.

What am I missing? I know my setup isn't ideal for tbi but I really need this truck up and running.
 
I’d double check you have the firing order correct, all the vacuum lines and leaks sorted, and that the green three wire terminal is on the MAP sensor and not the throttle position sensor

Recheck the timing. Make sure that you start the truck with the wire disconnected, set timing, shut off, reconnect

Has the damper been changed?
 
Always have to ask that one, so many different timing marks on GM dampers
 
If it’s a new TBI install, it could also act like that with a leaky injector or a bad PROM. The bad prom makes it go into limp home mode which isn’t much more than idle. Make sure your check engine light is is hooked up and working right.
 
Fuel pump pushing 12psi? I did the conversion on my 79 and had the same problem. The O2 sensor was giving me issues along with a vacuum leak. I swapped over the smog sticker and emission setup to the TBI setup (mandatory to register it).

Do you have a laptop you can hook up? There is free software and needed files where you can watch some of the parameters in real time.
 
Sounds like the distributor is in wrong to me. That is not a good thing with a new engine that has a flat tappet cam. Trucks with an old fashion flat tappet cam need to fire up immediately, and brought up to 2000 RPM, in order to break in the camshaft. If you keep cranking the engine over and over again, and backfiring the engine, you will kill the camshaft. It sounds like the distributor is too advanced because it is backfiring out the TBI.
 
Lots of ideas on this, but have you set the timing to zero? That is GM TBI spec, and since what you have is not a TBI engine, it's possible that's just not right for it. Generally too much timing will just retard timing a bunch and make it sluggish, but this having a lot of components non-TBI, who knows.

Buddy threw a GM crate TBI engine in his Suburban awhile back, and with the original high mileage engine, he could bump timing up to ~+4*. Doing the same with the crate motor made it run terrible. It wanted 0*. I didn't think it a bad assumption of his that timing chain slop "allowed" higher timing than spec on the worn out engine in his case.

They aren't designed to kill the engine when timing is off, so that may not be your problem, but it may not be helping, either. Unless you've already tried 0* and it was worse.
 
I just checked the map/tps wiring and they are different plugs so that is good to go.

I timed it a couple days ago and it seemed to run better at 4 degrees than 0 but popped and back fired at both.

I have everything but the pcv and map vacuum capped off at the throttle body and sprayed for leaks a couple days ago also.
 
dyeager535 said:
Lots of ideas on this, but have you set the timing to zero? That is GM TBI spec, and since what you have is not a TBI engine, it's possible that's just not right for it. Generally too much timing will just retard timing a bunch and make it sluggish, but this having a lot of components non-TBI, who knows.

Buddy threw a GM crate TBI engine in his Suburban awhile back, and with the original high mileage engine, he could bump timing up to ~+4*. Doing the same with the crate motor made it run terrible. It wanted 0*. I didn't think it a bad assumption of his that timing chain slop "allowed" higher timing than spec on the worn out engine in his case.

They aren't designed to kill the engine when timing is off, so that may not be your problem, but it may not be helping, either. Unless you've already tried 0* and it was worse.
Click to expand...

It sounds like the timing could be way off, and not just a little off. A few degrees one way or the other from 0-degrees is not going to make the engine backfire out the TBI. Another thing that can cause popping out the TBI is an intake valve staying open during the compression stroke. That could be cause by things like incorrectly adjusted valves, bad valve stem guide, etc, etc.
 
Double check your plug wire routing. You said everything worked before, nothing changed but carb to injection, but that means you had to swap the distributor.

If you have triple checked your plug wire routing, is your idle timing with everything hooked up around 20*?
 
It looks like the number-8 cylinder has a problem with an intake valve not holding compression, which is why it is sending burnt fuel back up the intake manifold, and through the TBI.
 
Since it sounds like the motor sat for a while, especially in a humid environment, I'd seafoam the chit out of it and let it sit for a while. I used to do it to boats that sat for a season or two, you'd be surprised what will come back.
 
Cut the oil filter and inspected it, no signs of a cam lobe lol, but there were a few pieces of metal.....

KIMG0926.jpg

So I readjusted the valves and ran another compression, came up to 100 psi dry, leak down showed no issues.

I replaced the coil and wire since they were old, still popped under high rpm and load.

So I decided to drive it the couple hundred yards to the gas station down the road. It ran like crap so I babied it, then decided to go around the block with gas in the truck.


It cleared out, and doesn't do it now..... :doah:
Might have had bad gas.....
 
That’d be nice.


Not sure on the chunks of mung though
 
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