Tbi backfire through intake

[Road Trip]

UPDATE!!.....
So this afternoon checked egr system out good..... after putting it back together after testing according to book, this is what I got (video).....
Leaking injectors....
But truck running better than it has in at least a year..... was idling great..... everything looked great except injectors....I don't know what I did to cause it to straighten up but it did that's all I know lol......
then.....
I decided to crack open the oil filler cap and it immediately died and can't get a restart yet....

Here's link to video

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Hello Rustjunky67,

In the video you posted in reply #21 those injectors are definitely drooling/showing
a loss of positive fuel control. It's been awhile since I've watched a TBI in person, but
I remember healthy ones looking more like this:

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(credit: screen snap from the TBI video below.)

Check out this video, starting at 0:15. NOTE: There seems to be some visual
wagon-wheel effect due to injector cycling frequency vs video frame rate. That is,
the sound is steady, and I don't think the fuel feed is pulsating when watched
in person?

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So, before we try to troubleshoot the rest of the engine any further, it makes sense
to first regain positive control of the fuel. I looked through a handful of TBI rebuild
threads & a couple of YouTube videos, and for me 'Captkaos' gave a nice blow-by-blow
& sharp photos. (LINK)


If that was my truck, I'd buy the AC/Delco rebuild kit with the following parts in it and
see if a good cleaning & some fresh o-rings might do the trick:
(Please verify that this kit is correct for your truck!)

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(source: Summit has this kit for sale for ~$42: (AC/Delco rebuild kit)

And if you haven't already done so, make sure that you have a known-good
fuel filter installed *before* going through the trouble of rebuilding your
treasure-yard sourced injectors.

****

As for the fact that your truck seems to run for a minute & then die,
another possible explanation would be that the truck will run cold (open loop)
with uncontrolled fuel (drooling) ...but as soon as it goes closed-loop the
rest of the system isn't in a state where it can compensate for that gross
of an error? (Take this with a grain of salt -- I hate to hazard a SWAG like
this in public. :0)

At any rate, I'm not guaranteeing that curing the observed TBI fuel drool will
magically fix all ills with your motor...but if you have been living clean, most
of the time if we fix the obvious, then the exotic symptoms take care of
themselves. Just remember, open loop = linear behavior = the good old
days of working on engines...while closed-loop = non-linear behavior =
how did this over here > goof up that over there?

The good news is that your TBI setup was made to be rebuilt in the field,
instead of just being swapped out and/or requiring a calibrated test stand.

Hope this helps. Happy o-ring renewing --

 

[Schurkey]

If the problem is the spray coming out of the injector, but not leakage or pressure regulator issues, I don't know what fresh gaskets 'n' o-rings, and a regulator diaphragm are going to help.

The issue may be that the injectors are dirty/corroded/eroded. The injectors should be cleaned or perhaps replaced.

This is kinda a chicken-and-egg deal. Do you fix the ESC and battery, or the injectors first?
"I" would lean toward the ESC and battery.

 

[Rustjunky67]

Ok so I got the injector part of the equation figured out at least.....
Upon closer inspection, it appears that the injectors I pulled are specific to a 4.3.....‍‍
At the time I pulled them, I had no idea there were any differences but I did at least look at the numbers and thought they were the same.... so today I cleaned a little better and lo and behold that 6 was actually a 3 ....
5235206 is for v8
5235203 is not
So I guess I'll be testing, possibly reverse flowing, and HOPEFULLY reusing what I had on there to begin with....I really can't afford a new set so it'll be back to the treasure yard with new knowledge if these don't do it....

Just thought I would put my experience wth these to maybe save somebody else the same trouble....

As for the fact that your truck seems to run for a minute & then die,
another possible explanation would be that the truck will run cold (open loop)
with uncontrolled fuel (drooling) ...but as soon as it goes closed-loop the
rest of the system isn't in a state where it can compensate for that gross
of an error? (Take this with a grain of salt -- I hate to hazard a SWAG like
this in public. :0)

The problem is I haven't been able to get it to run long enough to even reach closed loop.....
I feel sure there is something I am just missing that I did or some simple thing that I need to do but don't know about or something really simple....
I mean I've never done any more to an engine than change oil, plugs wires, etc never even taken valve covers off....
And to have redone camshaft lifters, intake etc and to have it fire before I even turned the key fully when I got it back together tells me I at least did some things right..
But I also feel like the "pay your dues" gods are just laughing saying yeah we got him good on that one
One thing about me is I ain't gonna let it beat me and when I'm Victorious I'll be more knowledgeable about a 29 year old vehicle's workings lol.....

 

[Rustjunky67]

I have one more question.....
I have a pile of MAP sensors, ICMs, and TPSs......
Can someone help me out with knowing which part numbers I should/ should not use of these parts? Or where to reference that info....
It is also quite possible that one of these may be leading to some of my troubles.....
I pulled every one I saw without regard to what they were on as I was under the gun as far as closing time when I got them....
Thanks for any help at all in this

 

[Rustjunky67]

I have one more question.....
I have a pile of MAP sensors, ICMs, and TPSs......
Can someone help me out with knowing which part numbers I should/ should not use of these parts? Or where to reference that info....
It is also quite possible that one of these may be leading to some of my troubles.....
I pulled every one I saw without regard to what they were on as I was under the gun as far as closing time when I got them....
Thanks for any help at all in this

I still would like to know if anyone has any info that could help me not waste any more time with wrong parts....
Got my old injectors back in, they're both clicking strong with a DC pulse, but I'm not getting any spray now in the TB.....
ALL SENSORS ARE CONNECTED EXCEPT <ESC MODULE> ......
I wanna know what that one thing is..... the one that fixes it

 

[Schurkey]

Fuel pressure?

 

[Rustjunky67]

Fuel pressure?

14-15 key on....
Pretty much same cranking and running

 

[fancyTBI]

First timer, eh? lol Let the ol' guys tell you about adjusting rocker arms in the freezing cold uphill both ways.
There are a thousand ways to do it, all of them make it easier than all the rest. Personally, I use this method (with 3/4 turn instead of 1/2 on stock-ish motors)

SBC Valve Lash Adjustment on Hydraulic Lifters | 8 Steps

To get the longest life and most performance out of your engine, it's important to have the valve lash set correctly. Here we show you how to set valve lash on a Small Block Chevy using a hydraulic lift camshaft in just eight steps.

www.speedwaymotors.com

The real trick, no matter what method you use to find your cam position, is to find with precision the 'zero lash' adjustment. You have to feel the pushrod, rocker, and lifter pocket by rolling and wiggling the pushrod, and feeling the rocker arm until you know you have no slack, but it's critically important that you do not preload the lifter at all. Then get your 1/2-3/4 turn. Because I'm old, stupid, and never did have enough memory to find my own house on my own block, I clean a shoulder on the rocker arms and use a paint marker to dot the ones I've completed. Then when I'm finished, I roll the motor through 2 more turns to be certain I got them all.

This is how I do it. Good info.

 

[Schurkey]

I still would like to know if anyone has any info that could help me not waste any more time with wrong parts....
Got my old injectors back in, they're both clicking strong with a DC pulse, but I'm not getting any spray now in the TB.....
ALL SENSORS ARE CONNECTED EXCEPT <ESC MODULE> ......
I wanna know what that one thing is..... the one that fixes it

If you supply fuel--aerosol carb spray or a drizzle of gasoline down the two throttle blades--does it run?

 

[Rustjunky67]

Ok so let me back up and punt.....
I know my timing is dead set on zero by timing light.....
All my sensors have tested out with the exception of the esc module, which is unplugged at the moment.....
Est bypass wire connected.....
I can get it to crank and fire.....
I can only get it to crank, fire, and run if I supply some throttle.....
Stays good and smooth as long as it's 800 rpm or higher but as soon as I let off throttle it dies instantly.....
I have constant 15 psi fuel pressure (at least that's what the gauge reads)....
Nice cone spray pattern when throttle is applied but both injectors are also dripping pretty steady the whole time as well.....
She runs smooth with the added throttle, why does she die instantly when it is released??
You can't tell me that with the knowledge and experience here that there isn't somebody who knows exactly what that indicates and what to do to remedy it.....
I know I'm not the first person to encounter these exact symptoms....
Here's a video of the fuel pressure while running (hear how it runs) and a video of the injectors while running.....
Please help a brother out!!

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