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Injector replacement TBI

I want to replace the injectors in 454 GMC. I’m curious about different size injectors. I probably want to lean towards economy. Any suggestion on size?

Don’t try to improve fuel economy because it’s not possible with that vehicle and engine. If you did get lean injectors the engine may not start in cooler weather. My old 74 Suburban used to get 7.6 MPG. I traded it because it took $20 to fill up the 30 gallon tank.

Why do you want to replace the injectors on your 454 of unknown year? Unless your truck is running badly, you would be better off spending the money on gas.

This gets far better mileage than 7.5, I just thought I should replace then
because the last truck I had of that era had dry rotted o-rings. I thought
maybe the same here

And yours was carbureted correct?

42 gallon tank :neutral_face:

  1. It has a miss at an idle…kind of random and varies. I don’t notice it above an idle. I did do a visual on the injectors at idle and they look good

Sounds more like a secondary ignition problem, in my opinion

You could have a misfire, which will be noticeable at idle, but not necessarily at 2500rpm on the freeway

What condition are the plugs, wires, cap and rotor in . . . ?!

For that matter, how old are those components I mentioned?

Your saying it might just need a tune up

If the spray pattern on the injectors looks good, they are most likely fine. Agree with the others, Ignition Make sure all that is up to snuff.

Copy, Thanks

These beg for the typical test for vacuum issues; spraying combustible fluids (starting spray or brake cleaner for example) around the TB base gasket, throttle body shaft bushings etc. Also checking the EGR for operation and carbon fouling. In addition to the ignition areas already pointed out, these are common problem areas from my experience.


I second all the above. And about replacing an injector, I have rebuilt several of the throttle body injectors due to deteriorated components in the pressure regulator but never ran across a failed injector. The deterioration always appeared to be the result of contaminated gasoline. I suspected E-85 ethanol.

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Injectors are rated in pounds of fuel sprayed per hour. The ECM program assumes the injectors installed match that number. If the injectors of incorrect pounds per hour spec are installed, it will confuse the ECM and likely turn on the check engine light, and likely cause the engine to run poorly. There may be different versions of injectors available, but make sure whichever you use matches the manufacturer’s pounds per hour spec for your vehicle.

I used to visually check the spray pattern on my VW Rabbit’s CIS injectors whenever I thought there was something wrong with them. And I’d check they all sprayed the same amount of gas at medium and max flow. I never discovered a problem with the injectors, it was always what was controlling the injectors when there was a fuel problem. On my Rabbit’s CIS system each injector was connected to a flexible hose, so it was easy to pop them out of the engine and put them in four calibrated test tubes to do the test. On your vehicle it might be difficult to visually check the injector spray pattern, but you can do an injector balance test probably, which would show if you have some injectors that are spraying weakly compared to the others. An injector balance test requires a gadget to pulse the injectors while you monitor the rail fuel pressure. The fuel pump has to be disabled during this test.

E85 isn’t even gas is it…grrrr

Sounds like a plan. Thank you

E-85 is 85% ethanol and 15% gasoline but several times cars and trucks with CFI have filled up with fuel and within minutes found the car was running rough and the check engine light came on and in a day or two the engine was flooding with fuel from the throttle body. when dismantled the rubber diaphragm in the throttle body was found partly emulsified. After rebuilding the throttle body, draining and refilling the tank everything returned to normal and I never knew what caused the problem but on my second or third such repair I suspected E-85 and mentioned the possibility to subsequent such customers. I have seen similar damage on motorcycle carburetor diaphragms. And of course old vehicles will have fuel lines turn to mush on 15% ethanol.

E-85 was a great political success. Not much for automobiles though.

Yeah, its garbage. Somebody paid somebody to get that passed.
There are states you can’t hardly find ethanol free, and if you do its a
process to purchase it. Colorado is one

Big Money