Tbi issues

[biggsteve97]

I have an 87 1/2 ton with a built 350. My issue is I picked up a 454 throttle body with 90 pph injectors and when i installed it tonight the injectors wont fire. I verified power to the injectors and verified fuel to the injectors. That checks good. I was unable to test the throttle position sensor before it got too dark. Any thoughts? Could it be the injectors or the throttle position sensor? Ive had many tbi units and ive never had one that just didnt work.
Posted via Mobile Device

[beamn7]

Pick up a Noid Light from the local auto parts store and check to see if you are getting a signal to the injectors. Doubt it's the TPS since they will idle / run with it unplugged....
I'm with you on this one, never seen one just plain not work....

[burnout2614]

New or used injectors?

[biggsteve97]

Used injectors in a used throttle body. Took apart everything looked good mechanically. No blockages in fuel passages. Press reg diaphram looks good as does the spring. I know its gettin signal because i can put the holley tbi back on and it fires right up. Its weird that neither inj are even trying. Not even a dribble. Ill have to dig more into in the daylight
i
Posted via Mobile Device

[joe231]

I had a used TBI do that to me.
I had to pull the injectors and clean out the bowl where they set.
It had a bunch of crud in there.
Did you pull the injectors?
Posted via Mobile Device

[biggsteve97]

Yep. Pulled both injectors and didnt find anything except fuel in the bowl. I questioned the little strainer in the side of each injector because they look brown instead of white though they were not clogged
Posted via Mobile Device

[joe231]

Weird

Will the injectors swap into your other TBI?

Makes me wonder if both injectors are bad...
Posted via Mobile Device

[biggsteve97]

I wish but no. The holley tbi uses a delphi type injector that is smaller in diameter
Posted via Mobile Device

[joe231]

Well darn!

Lol

You can check the resistance in the injectors. If the coil is open or if there is zero resistance they are most likely bad.
You can also have some one crank the engine while you listen for clicking with a stethoscope, screw driver, or dowel rod..
Posted via Mobile Device

[burnout2614]

You can't see it but the injectors are gummed up inside. Today's gas is absolute junk. Burns ok today but the longer it sits the less potent it becomes. The crap leftover after evaporation is a gummy mess that clogs injectors and carb jets.

[rfmaster]

Take a DVM - measure coil resistance of each injector - it should measure very low resistance around 1.0 to 1.2 Ohms which is normal for TBI injectors. It is very unusual for injector coils to go bad, but it does happen. The other possibility is grud inside injector (once you check coil resistance) or in the TB passages. Very rare, happens when some dumps sugar in the gas tank. I send my injectors to Witchhunter performance for cleaning and testing - takes about 7 to 10 days.

//RF

[rs72z]

Soak them in some seafoam, that should clean them up if they are gummed up and they probably are. Like someone else said, the fuel today will gum up when they set for any length of time.

[biggsteve97]

ok thanks. I will try cleaning the injectors tonight and checking the resistance as well. hopefully they are just gummed up. The inside of the injector pod was real clean for being used in fact the whole throttle body was relatively clean compared to most i have seen that are all black and grimy. there wasnt even that sandy like build up inside that you get from really old gas.

[biggsteve97]

Well i soaked the injectors but it was all to no avail. Found another set of injectors and it fired right up. Runs great, has much better throttle response, power and even sounds meaner. However, that being said i do have an issue now that i have never had before. After the engine is warm and I have driven it atleast 20 mins, if I shut it off it is difficult to restart even if it sits for one minute or 5 mins it doesnt matter. After driving it for over an hour i shut it off the engine and about 2-3 mins later tried to start it and it didnt start. No spit, sputter, nothing it just cranks. Had fuel spraying out of the injectors and had spark. waited about 3-4 more mins and it started but sluggishly. when I revved the engine no black smoke came out so i know its not overfueling but i do not understand what is going on. everything checks out good, and i do mean everything. I did put the holley back on and drove it for 2 days with no issues. i would rather run the 454 tbi but its lookin like im not destined to have that. could it be that i just need to have the chip reburnt to accomidate the different injectors?

[rfmaster]

Originally Posted by biggsteve97

Well i soaked the injectors but it was all to no avail. Found another set of injectors and it fired right up. Runs great, has much better throttle response, power and even sounds meaner. However, that being said i do have an issue now that i have never had before. After the engine is warm and I have driven it atleast 20 mins, if I shut it off it is difficult to restart even if it sits for one minute or 5 mins it doesnt matter. After driving it for over an hour i shut it off the engine and about 2-3 mins later tried to start it and it didnt start. No spit, sputter, nothing it just cranks. Had fuel spraying out of the injectors and had spark. waited about 3-4 more mins and it started but sluggishly. when I revved the engine no black smoke came out so i know its not overfueling but i do not understand what is going on. everything checks out good, and i do mean everything. I did put the holley back on and drove it for 2 days with no issues. i would rather run the 454 tbi but its lookin like im not destined to have that. could it be that i just need to have the chip reburnt to accomidate the different injectors?

Check fuel fuel pressure - it sounds like you have a leaky hose between Fuel Pump outlet and feed through. When fuel is cool the leak is relatively small, but as you drive it circulating fuel warms gas in the tank, softening this fuel hose and consequently increasing in tank leak. Fuel pressure drops off, engine re-starts become impossible.

Connect fuel pressure gauge at inlet port to the TBI and and apply +12 volts (via 10 amp fuse) to a pigtail test plug hanging from the fuel pump relay. With engine off which makes this test easy. A good pump should deliver between 9 and 13 PSI. If fuel pressure is below 9 PSI time to do pump R&R. Use AC Delco pump.

//RF

[biggsteve97]

Well the problem there is these issues only happen with the 454tbi. When i put the holley tbi back on all the issues went away. With the holley fuel pressure is a solid 14 psi with the 454tbi fuel pressure is a solid 12 psi.
Posted via Mobile Device

[rfmaster]

Originally Posted by biggsteve97

Well the problem there is these issues only happen with the 454tbi. When i put the holley tbi back on all the issues went away. With the holley fuel pressure is a solid 14 psi with the 454tbi fuel pressure is a solid 12 psi.
Posted via Mobile Device

Hmmmm. The question do you have 12 PSI when engine is hot (was running for awhile). Another possibility is a flaky ICM in the dizzy or reluctor coil going intermittent after distributor gets hot.

Basically, you'll have to go through a process of elimination to figure out which part goes bad after engine has been running for awhile. Yes, it is tough.

//RF