TBI Issues, #8 Cylinder Dead

[Jims86]

Thanks guys!
On another note......Faaaaaaahhhhhhck!mFuckfuckfuckfuckfuckfuckfuckfuck!!!!!!
# 8 is dead at low rpm...the cause of my idle problem.

 

[Jims86]

That sux !!! As in compression, or just maybe a spark plug fouled?

That is yet to be determined. I found #8 dead using a bottle of water with a small hole in that cap so I could shoot it at the manifold(ya here that, Dave?) and got pissed, cleaned up my ****, came in the house for a cup of coffee...havent been back out.

 

[Jims86]

Ok, going to see Why the cylinder is dead.
gonna do a compression check, ignition check, and then for the hell of it, going to see if i have leaking valves.

 

[Jims86]

Yeah, plug was fouling out from running rich...had a bad injector O ring. I still have to pull 3 more plugs and check them.

 

[Jims86]

This bitch is fixed! Got a program in her that is supposed to get me 17 mpg too!

 

[Jims86]

Awzum !!! And you're running TBI now right?

Yes.

Uhh BTW Jim. How come this issue, how you detected it, how you diagnosed it, and how you fixed it wasn't in an Engine Performance thread as a write up? You realize a random post about it every 30-40 posts in the Convo thread isn't gonna help anyone in the future with the same type problem. Huh, How Come??? Sup with that???

I will right something up.
But I will elaborate a little here.
the truck was constantly running rich when looking at the Data on my Laptop, except at higher cruise throttle settings.
This got me thinking of the "other than obviouse" differences between carbs, MPFI, and TBI, and where Idle fueling take place.

Carbs-Idle circut uses emulsion tubes, and bypass the throttle blades. Cruise and accel shots happen above the blades.

MPFI(TPI)-All fueling occurs down at the intake valve, downstream of the blades.

TBI- All fueling happens ABOVE the blades.

So,
I knew the spray pattern on the injectors was good, but that was when looking at them, once the truck was warmed up. So when its cold, more fuel is shot into the Throttle Body under the choke tables in the chip.
Bigger than ****, the driver side bore had fuel puddling at the back edge of the throttle plate...this is as bad as an injector on a MPFI car stuck wide open, only, instead of effecting one cylinder, it effects 4 on TBI V8s.
Apparently the throttle shaft twisted somehow, as if the throttle blades were forced shut at some point, Leaving the far other blade on the pass side open a little more than the drivers side.
Using needle nosed pliers, i Opened up the blades, and evened them back out the best I could, and that solved the rich running problem. No more puddling of fuel.

Also, One of the guys on the EFI forum helped me out by altering the program from his Suburban, for use with my HEI large cap distributor, apparently it does make a difference, due to spark latency settings between the small cap and large cap dizzys being different, which may have been the cause of my rough Idle on the TPI when I had it.
The surge is 98% gone...maybe beacause I dont have the throttle blades absolutely perfect, or because The computer needs more time to re learn.
She runs alot better out on the road too.
I know I said 17mpg with the new program, but he is actually getting 19.8 up in Idaho, so, we will see what I get here down at sea level.
****...you might as well move this to the other category.

 

[89Suburban]

Yes.


I will right something up.
But I will elaborate a little here.
the truck was constantly running rich when looking at the Data on my Laptop, except at higher cruise throttle settings.
This got me thinking of the "other than obviouse" differences between carbs, MPFI, and TBI, and where Idle fueling take place.

Carbs-Idle circut uses emulsion tubes, and bypass the throttle blades. Cruise and accel shots happen above the blades.

MPFI(TPI)-All fueling occurs down at the intake valve, downstream of the blades.

TBI- All fueling happens ABOVE the blades.

So,
I knew the spray pattern on the injectors was good, but that was when looking at them, once the truck was warmed up. So when its cold, more fuel is shot into the Throttle Body under the choke tables in the chip.
Bigger than ****, the driver side bore had fuel puddling at the back edge of the throttle plate...this is as bad as an injector on a MPFI car stuck wide open, only, instead of effecting one cylinder, it effects 4 on TBI V8s.
Apparently the throttle shaft twisted somehow, as if the throttle blades were forced shut at some point, Leaving the far other blade on the pass side open a little more than the drivers side.
Using needle nosed pliers, i Opened up the blades, and evened them back out the best I could, and that solved the rich running problem. No more puddling of fuel.

Also, One of the guys on the EFI forum helped me out by altering the program from his Suburban, for use with my HEI large cap distributor, apparently it does make a difference, due to spark latency settings between the small cap and large cap dizzys being different, which may have been the cause of my rough Idle on the TPI when I had it.
The surge is 98% gone...maybe beacause I dont have the throttle blades absolutely perfect, or because The computer needs more time to re learn.
She runs alot better out on the road too.
I know I said 17mpg with the new program, but he is actually getting 19.8 up in Idaho, so, we will see what I get here down at sea level.
****...you might as well move this to the other category.

That is amazing finding those uneven butterflys like that, I love reading this stuff and hope to get this stuff checked out on mine at some point. I really want to get a TBI case from a yard and rebuild it real nice.

 

[89Suburban]

Yes.


I will right something up.
But I will elaborate a little here.
the truck was constantly running rich when looking at the Data on my Laptop, except at higher cruise throttle settings.
This got me thinking of the "other than obviouse" differences between carbs, MPFI, and TBI, and where Idle fueling take place.

Carbs-Idle circut uses emulsion tubes, and bypass the throttle blades. Cruise and accel shots happen above the blades.

MPFI(TPI)-All fueling occurs down at the intake valve, downstream of the blades.

TBI- All fueling happens ABOVE the blades.

So,
I knew the spray pattern on the injectors was good, but that was when looking at them, once the truck was warmed up. So when its cold, more fuel is shot into the Throttle Body under the choke tables in the chip.
Bigger than ****, the driver side bore had fuel puddling at the back edge of the throttle plate...this is as bad as an injector on a MPFI car stuck wide open, only, instead of effecting one cylinder, it effects 4 on TBI V8s.
Apparently the throttle shaft twisted somehow, as if the throttle blades were forced shut at some point, Leaving the far other blade on the pass side open a little more than the drivers side.
Using needle nosed pliers, i Opened up the blades, and evened them back out the best I could, and that solved the rich running problem. No more puddling of fuel.

Also, One of the guys on the EFI forum helped me out by altering the program from his Suburban, for use with my HEI large cap distributor, apparently it does make a difference, due to spark latency settings between the small cap and large cap dizzys being different, which may have been the cause of my rough Idle on the TPI when I had it.
The surge is 98% gone...maybe beacause I dont have the throttle blades absolutely perfect, or because The computer needs more time to re learn.
She runs alot better out on the road too.
I know I said 17mpg with the new program, but he is actually getting 19.8 up in Idaho, so, we will see what I get here down at sea level.
****...you might as well move this to the other category.

I know it's a pain in the ass on your end, but I love reading this TBI stuff, thanks.

 

[Jims86]

That is amazing finding those uneven butterflys like that, I love reading this stuff and hope to get this stuff checked out on mine at some point. I really want to get a TBI case from a yard and rebuild it real nice.

see how much slop is in your throttle blades first, if its bad, have a carburetor or machine shop bush the throttle shaft. Ther are a few guys that have som extras that they are selling here on the forum...Greasedog is one that comes to mind.
If there is nothing wrong with it, dont mess with it.....unless you are an EFI tweeker like me.
Now that she is fixed, I can start learning the tuning nitty gritty!

 

[J Knight]

Wow Jim good find, I would have never EVER suspected that to be causing your motor issues.

 

[89Suburban]

see how much slop is in your throttle blades first, if its bad, have a carburetor or machine shop bush the throttle shaft. Ther are a few guys that have som extras that they are selling here on the forum...Greasedog is one that comes to mind.
If there is nothing wrong with it, dont mess with it.....unless you are an EFI tweeker like me.
Now that she is fixed, I can start learning the tuning nitty gritty!

She's got 190K on her current TBI as far as I know, I am sure it could use some TLC and freshening up, and I like to tinker and learn this stuff.

I have a dial gauge buried in the garage somewhere. Is there a spec for the play in that shaft I can check?

 

[RetroC10Sport]

You will need to get a ALDL cable at some point John.

 

[Jims86]

Wow Jim good find, I would have never EVER suspected that to be causing your motor issues.

Thanks! After looking for vacuum and exaust leaks, was time to think " Outside of the Block"

 

[bucket]

Interesting. Everything I've read says you can change the plugs and swap a small cap dizzy in place of the large cap. I guess you can't go the other way? Or do you think it can cause issues going either way? Large to small, or small to large.

 

[Jims86]

I thought the same thing as well.
Apparently there are differences.
you just need to change the spark latency correction tables to match the large cap HEI, or the timing will be off at various RPMs compared to the small cap.
One of those things that never crosses your mind, especially if the majority of your learning is from old school sources, from a time when vac advance, and centrifugal weights controlled timing.
All of the EFI swaps I have done for others, always had the proper hardware from the donor vehicle, or the vendor they got the parts from. Mine is the only one where I kept the HEI, just because I didnt want to deal with an external coil.