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Old 04-19-2012, 10:11 PM   #1 (permalink)
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TBI 454, need some answers...

My brother-in laws truck (not mine).

91 Chevy 3500, dually, 454 TBI motor. 130,000 miles, about 12,000 on the motor which supposedly is a crate motor.

Here is the problem; and bear with me, Im not an authority on fuel injection.

The engine has been running really rough and missing, especially at lower rpms.

Started running really bad tonight, so I pulled off the air cleaner and I observed that that while the engine is idling and at operating temp, the PS injector is dripping fuel/erratically spraying, and the DS injector is dumping so much fuel into the throttle body that the fuel is running down the inside of the throttlebody in observable streams.

Also, the exhaust is black and smells like unburned fuel.

With the key and engine off, and then turning the key to on, the DS injector sprays a brief bit of fuel. Not the PS side one that I think is clogged.

Which I don't think is right. Keeping in mind that Im no expert and this is the first TBI GM motor I have ever worked on.

So, one injector appears to be plugged and the other is spraying too much fuel?

We checked the codes, only Code 12 comes up (ECU normal mode) and nothing else is coming up.

Im thinking that the fuel pressure regulator could be faulty, or the injectors are ready for replace or rebuild?

Im open to ideas and things to check. Thanks for any help.
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Old 04-19-2012, 10:58 PM   #2 (permalink)
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So, could the o2 sensor be faulty and not throw a comp code?
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Old 04-19-2012, 11:24 PM   #3 (permalink)
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Ok, that makes total sense and kinda what I was thinking.

Finally question, any reason a injector cant be taken apart and cleaned? No stranger to carb disassembly and rebuild, doesn't seem to be any reason in my mind why I couldn't do it....
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Old 04-19-2012, 11:49 PM   #4 (permalink)
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Buddy had this happen to his 5.0 Camaro with TBI. Swapped on a Junkyard TBI unit ($45) ran perfect again. One Injector is clogged forcing more fuel out of the other. Because of the throttle design it will cause one side to run rich, and the other lean.

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Old 04-20-2012, 02:14 AM   #5 (permalink)
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I am no expert, but it sounds like the TBI is old and worn out, however they are even easier to re-build than a carb and you can get a re-build kit at any Orielly's or Autozone, Next you have to address the bleeding down injectors, what IS happening is your injectors are old and cannot handle the pressure anymore, your stock fuel pump's don't push enough PSI to bleed the Injectors and the regulator will bypass the fuel back to the tank anyhow. Grab a new set of injectors off of Summit or Jeg's both carry a Venom series line of injector and they work just fine. Put in a new O2 sensor and check out the map sensor if the truck is old it is time to give it some love. Put it back together and run down the road with no more issues and you will also get back lost fuel mileage that the injectors where bleeding off for some time before they just gave up. I also forgot to mention they will run without a O2 sensor, the computer will attempt to get back to the 14.1 lean condition that it is programmed to run but if it cannot it will close out the loop and run OK, the sensor in that truck is narrow band so it only can sense when it is running correctly.

Last edited by NickDually; 04-20-2012 at 02:34 AM.
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Old 04-20-2012, 04:47 AM   #6 (permalink)
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Quote:
Originally Posted by trkklr77 View Post
depending on where the o2 sensor is and which injector is is dumping fuel it could cause massive confusion with the system.

alot of the o2 are in the exhaust mani. and if the drivers side is running lean do to no flow the comp will try to correct by dumping more fuel in but its only going into the pside cylinders it still reads lean and dumps more fuel in........
You don't know much about TBI, do you?

Aside from the first obvious problem with your theory, which is that the computer can't fuel one injector more than the other, there is the other little detail which also rules out your theory. It's a dual plane system. One injector affects the AFR for both banks of cylinders.


The problem is almost certainly a bad injector.
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Old 04-20-2012, 07:36 AM   #7 (permalink)
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Quote:
Originally Posted by GMCTruxrule View Post
Ok, that makes total sense and kinda what I was thinking.

Finally question, any reason a injector cant be taken apart and cleaned? No stranger to carb disassembly and rebuild, doesn't seem to be any reason in my mind why I couldn't do it....
TBI injectors are sealed units. Damn near impossible to disassemble without destroying. They are to be replaced as complete units which is pretty simple. Just remove the top of throttle body and pull them out. Bear in mind that ONE new TBI injector will cost ~$150. I've got over 260K miles on my TBI injectors WITHOUT ANY MAINTENANCE other than changing the fuel filter (albeit it's NOT 454 TBI, Dahoyle didn't call me out on that for one of my TBI responses on another thread, thnx). Sounds like you may be missing a fuel filter between the fuel pump and the throttle body for both injectors to go south.

And as Dahoyle stated, the TBI injectors are tied together electrically and it really doesn't matter which bank of cylinders the O2 sensor is on.

And for something else to check: make sure that the wires to the injectors aren't shorting to ground somewhere, like being pinched between the air cleaner and the throttle body. And make sure the regulator isn't "sticky" resulting in higher inj pressure (take the top of the throttle body off and make sure valve/spring/diaphram are free).
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Old 04-20-2012, 09:00 AM   #8 (permalink)
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Thanks for all the input guys.

I will check out replacing/rebuilding the injectors today and report back.
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Old 04-20-2012, 10:04 AM   #9 (permalink)
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i've gotten away with pulling both injectors and their screen filters and the orings and leaving them in carb cleaner overnight as a not so quick, but WAY cheaper fix. always recommend going ahead and replacing all of the seals on the unit with a kit that includes all of them and a new regulator diaphragm and the kit comes with the new filter screens for the injectors. if you havent already check the ground on the intake and change the filter on the frame rail and call it a day. also while its apart clean the crud that gets in the crevices of the vac line ports on the front of the tb and around the anvil of the iacv.
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Old 04-20-2012, 12:41 PM   #10 (permalink)
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Originally Posted by trkklr77 View Post
depending on where the o2 sensor is and which injector is is dumping fuel it could cause massive confusion with the system.
The only confusion in this thread is your lack of understanding of EFI systems!

To the OP:
The O2 will not set a specific code, but would not go closed loop if it wern't functioning. If it were dumping tons of fuel it may set a code 45 for overly rich mixture.
Starting with a scanner and watching each device is a cheap way to eliminate what isn't bad. IE: if it goes closed loop the O2 is functioning. Watch TPS, IAC, CTS, and all items shown on scanner as possible problems. Look for BLM counts being close to 128 also.
That said, my educated guess is a fuel issue. Bad injector, clogged fuel filter, and or bad regulator.
Starting with the injectors is a good place. I had a very similar experience with a 305 years ago and it was the injectors.
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Old 04-20-2012, 12:42 PM   #11 (permalink)
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Ok, update:

My BIL took the injectors apart, tried to clean them, took the regulator apart, put everything back together. Nothing has changed. Except now the DS injector is leaking around its o ring from the top.

From reading everything here, and other intardnet forums, Im going to check the MAP sensor and vacuum line, and I told him the injectors and fuel reg need to be replaced.

Also, is it normal for when the key is turned to "on" for only one injector to discharge fuel? And should it discharge so much fuel that it dumps enough gas to cover the throttle blade with about .25" of gas?
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Old 04-20-2012, 01:29 PM   #12 (permalink)
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being a 454 it wouldnt surprise me to dump that much fuel, but not sure on 1 injector. they are however supposed to mist and you have to look really close at a properly working one in order to actually see the spray. highly unlikely that it's a vacuum line causing the issue but the map sensor does do some screwy things on a tbi, but generally will idle fine but when under load will cause it to stumble when they are bad. check that ground to the tstat housing on the intake and make sure the connections to the ring terminal are good and arent pulled out or green from corrosion.
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Last edited by buzzbomber; 04-20-2012 at 01:30 PM.
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Old 04-20-2012, 09:00 PM   #13 (permalink)
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Both injectors should be firing, you should be able to see fuel from both. If not, somthing is wrong, bad wire or injector, plugged filter (small filter in injector housing). Could even be the computer but I doubt it. Switch the injector wires, does the problem move? If not, then the injector is probably bad.

This is going to sound weird, but I have heard of the Pintle binding in the injector. A sharp rap or two with a screwdriver handle should free it, if that's the problem.
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Old 04-20-2012, 09:06 PM   #14 (permalink)
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One injector is odd. Very simple system, I've rebuilt all of mine. I will assume that your BIL THOROUGHLY cleaned the throttle body fuel passages, replaced all the screens, etc. Could be a bad injector if the problem persists.

Good luck, post what you figure out, odd problem
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