**FIXED!!**DEFINITELY***Super HIGH idle after multiple parts replacement - TBI 1990 K1500 350engine

[folkenheath]

If your compression varies that much it certainly isn't good for power or efficiency. I can't say if it would cause the TBI to be erratic like that.

My brother and I built a 383 stroker TBI motor about 20 years ago. We used vortec heads, a stroker crank, roller cam, and an aftermarket intake, and a TBI chip from Brian, thing ran great for him, he sold it still running.

If you want a crate engine I would go with a GM over an ATK, but I can get an ATK from my other distributor.

Brian recommends these:

So here is my SBC recommendations for TBI.

1. if you must have EGR for emissions testing then an ATK HP31 or HP05 motor. just deduct about 50hp from the power numbers they advertise for that engine. several sites sell the ATK engines.
2. if you dont need EGR for emissions testing then ATK HP74 or HP90 using vortec heads they are capable of the power numbers advertised if you setup the throttle body and exhaust

from here:

Recommended TBI Engines | TBI

Recommended TBI Engines

harristuning.com

I think I would get the GM unit instead, my distributor has one in stock but they cost more than the ATK because everything is new.

However, I can't say that is your erratic problem.

 

[ZombieK5]

Some good news for a change. I swaped out the new Delphi coil (installed it Spring 2025 new) for a Genuine GM coil. It drove without bogging. Ran a Lil rough but I need to check the timing again, not sure where I left it set.

When I started, after installing new coil, it surged a Lil bit but stopped when I rev'd the engine.

I'll check it out more soon, having a new to me frame from an 86 Blazer delivered.

 

[Wes Harden]

if that is the original chain at 230k something miles, the nylon teeth on the cam gear are little nubs, and the chain is sloppy as hell. I wouldn't go ATK, if I were to use atk I have to disassemble the whole thing down to rings and measure everything, then use ARP every where and new valve springs, maybe even good new SS valves too.
The ECT (engine coolant temp) sensor for ecm has been known to cause weird idle issues. It is the one by the t stat housing, and grounds to the t stat bolt.

 

[ZombieK5]

if that is the original chain at 230 something miles, the nylon teeth on the cam gear are little nubs, and the chain is sloppy as hell. I wouldn't go ATK, if I were to use atk I have to disassemble the whole thing down to rings and measure everything, then use ARP every where and new valve springs, maybe even good new SS valves too.
The ECT (engine coolant temp) sensor for ecm has been known to cause weird idle issues. It is the one by the t stat housing, and grounds to the t stat bolt.

Thanks Wes, the ECT is a new GM part but I will check. I'll unplug it and see how it reacts. I am still planing to get a new fuel pump even though the unit in now is a new Delphi unit installed last Spring. The 10psi has me concerned the TBI isn't getting enough fuel.

We live in bad times when new parts can't be trusted.

Also, I'm not set on ATK, it was just the most economical option. Was also looking at Blueprint engines. Folkenheath pointed me towards a new GM unit but it was a few thousand more.

 

[Wes Harden]

yes 10 psi is to low 12 is gm spec they do well with 14

 

[ZombieK5]

yes 10 psi is to low 12 is gm spec they do well with 14

Agreed. Was looking at pumps. Walbro has one that does 50psi but that seems high. I'd rather not have to put on a regulator.

Carter has one that says it will do 13psi

Carter P90018 Carter Replacement OE Electric Fuel Pumps | Summit Racing

Free Shipping - Carter Replacement OE Electric Fuel Pumps with qualifying orders of $109. Shop Fuel Pumps at Summit Racing.

www.summitracing.com

Any pump recommendations ?

 

[folkenheath]

I have a brand new TBI pump sitting there I pulled off of a new delco sending unit, I needed a 60 psi Walbro)

I'd either run that, or a walbro, I'd have to see if walbro still makes a TBI pressure pump.

 

[ZombieK5]

GOOD NEWS

I removed the coil I installed last April. It was a Delphi unit.

Installed a Genuine GM coil and it now does not bog down. However, I still get some surging. Only thing left unchecked is fuel pump.

Looking for fuel pump recommendations. There is a Delphi unit in the tank now that was Installed new last April.

 

[ZombieK5]

I have a brand new TBI pump sitting there I pulled off of a new delco sending unit, I needed a 60 psi Walbro)

I'd either run that, or a walbro, I'd have to see if walbro still makes a TBI pressure pump.

I am interested if it will work for my setup. Hoping that I don't need a regulator

 

[Wes Harden]

I think the tbi fuel pressure regulator need some checking.
Existing pump may be doing its job.

 

[folkenheath]

It's brand new unused, I'll sell it for half of new cost if you want it. Just let me know.

Do you have a way to see your fuel pressure when you're low on power?

 

[ZombieK5]

It's brand new unused, I'll sell it for half of new cost if you want it. Just let me know.

Do you have a way to see your fuel pressure when you're low on power?

I have a Guage tied into the fuel line immediately before the fuel filter along the frame rail, it never goes over 10psi

 

[ZombieK5]

I think the tbi fuel pressure regulator need some checking.
Existing pump may be doing its job.

Guessing I could tear the TBI apart again. I have another regulator to put in but I can't find the little clear washers that attach where the fuel lines go into the TBI, not the black O-Rings. They come in a kit but the kit is $45. Ughhhh.

 

[Wes Harden]

How are you measuring the fuel pressure? If you were to block/pinch the return to check pressure if it increases to 12-14+ then pump is good and regulator is bad. If it doesn't then pump is bad or has a leak in tank.

 

[ZombieK5]

How are you measuring the fuel pressure? If you were to block/pinch the return to check pressure if it increases to 12-14+ then pump is good and regulator is bad. If it doesn't then pump is bad or has a leak in tank.

I have a pressure gage T'eed into the supply line before the fuel filter.

Ill give that a shot. Unfortunately I have flex steel lines and rigid stainless. I'll look and see if the return line at the tank is rubber.

 

[ZombieK5]

How are you measuring the fuel pressure? If you were to block/pinch the return to check pressure if it increases to 12-14+ then pump is good and regulator is bad. If it doesn't then pump is bad or has a leak in tank.

I just checked and the new fuel lines are solid stainless steel with two flexible stainless steel sections. I can't pinch the return line.

 

[ZombieK5]

NEW UPDATE 6/5/26

OK, replaced the fuel pump with one that folkenheath sent me. Started it and it seemed to be instantly fixed. Put it all back together and fully warmed it up. SAME FRIKIN PROBLEM. It has stopped surging as much but when warm it runs at 1,000rpm. Turn it off then on again and it will idle lower but will slowly rise to 1,000rpm again.

Timing is dead on ball at 0 degrees with advance unplugged. No vacuum leaks.

I haven't check fuel pressure yet. I'll try to get it checked this evening.

I've never thrown in the towel but I am close..
VERY close.

Are there any aftermarket fuel systems for the 1990 TBI 350 engine that will go on the factory style intake manifold?

I'm outta ideas.

 

[Fastereddie]

Just glancing through the last couple posts Seems like low fuel pressure still.

 

[ZombieK5]

Just glancing through the last couple posts Seems like low fuel pressure still.

Gonna hook up pressure gauge later to get a reading but the new pump is supposed to have high psi output.

 

[Fastereddie]

Gonna hook up pressure gauge later to get a reading but the new pump is supposed to have high psi output.

If the regulator is weak it will bypass any good pump