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Thread: Swapping in a 95 TBI 454, adios 91 TBI 350

  1. #16
    Fuel Injected!
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    Quote Originally Posted by Fast355 View Post
    Not all V6s or small block V8s used the low pressure system. The later model vans and some trucks with the speed governed TBI units built like the 2 ton truck 366/427 TBI units also had high pressure fuel systems.
    I was speaking of pickup's, but everything I had found said that all vans also stayed with the low pressure system, even the rare 96 TBI vortec. I know that non road going TBI switched to high pressure injection in 94. Used to work on boats and some of those ran as high as 60 PSI on the TBI set-ups.
    1995 GMC K2500 SUBURBAN 2001 LB7 DURAMAX/ALLISON swap, mostly stock, tuned by me with EFILive

    1999 Tahoe 2 door 2X4, 5.7l with 0411 swap, and marine intake

  2. #17
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    Quote Originally Posted by THEFERMANATOR View Post
    I was speaking of pickup's, but everything I had found said that all vans also stayed with the low pressure system, even the rare 96 TBI vortec. I know that non road going TBI switched to high pressure injection in 94. Used to work on boats and some of those ran as high as 60 PSI on the TBI set-ups.
    Nope I have played with some that had the 30 psi system. Used the weird TBI with the governor on the side.

  3. #18
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    1995 G30 cutaway van school bus engine.
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  4. #19
    Electronic Ignition!
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    Well, this has been both fun and educational. Joking, not so fun unless fun stands for frustrating. ��

    I went the route of the 454 with factory wiring harness and computer from the donor motor. I have spent lots of time chasing wire and checking diagrams. Suburban runs and drives around the lot but here are the issue I have yet to find the end to.

    Will not come down off high idle. 4 wire iac and the diagrams show all its wires straight from the computer.

    Back fires and wont gain rpm unless the throttle is slow and smooth. I feel once these are fix I may have other things to work through as well.

    Any advice on thing I should be looking into?

  5. #20
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    Quote Originally Posted by THEFERMANATOR View Post
    For the trans, it goes 91-93, then 94+ as far as controls go. Yes the harness changed mid year 93, but the pcs and valve body did not change until 94. So use the correct programming for your trans as 91-93 requires a "cleaning cycle" every 10 seconds to keep the pcs clean and functioning. Every 10 seconds it goes max line pressure to stroke the pcs to clean it. There is an accumulator/buffer circuit built into 91-93 valve bodies to slow line pressure response so the cleaning cycle doesn't damage anything.

    Also of note, all v-6's, small block's, and big block's to 93 ran low pressure injection(8-13 psi), but 94/95 454's ran high pressure tbi(32-38 psi) injection, and the stock injectors in a 95 are actually some of the smallest used, but compensated with higher fuel pressure. So make sure which injectors you're using and use the correct fuel pump capable of supplying the needed pressure(most run the 96/97 vortec pump for overkill, or a tpi pump). Tbi pumps are lucky to hold 13 psi from my experience, 94/95 454's had a different pump(40 psi), tpi's another(50 psi), and 96/97 vortec's used the highest pressure pump(65 psi). Running the wrong combo can lead to some NASTY hiccup's and extreme lean out.
    @Hopper If any of the above statements regarding fuel pressure is true, I'd be questioning if you are running the correct fuel pump. I will say with 100% certainty that your '91 350 uses the lower 8-13 psi fuel pump. You need to determine which injectors you have in your 454 TB and run the correct fuel pump accordingly.

  6. #21
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    I think the iac was stuck. After removing it and shoving my finger in the iac hole in the tbi unit. It came down off high idel but now is running super rich. I don't think the vacuum advance disconnect wire is working for timing it also. The timing isn't changing between connected vs unconnected.

  7. #22
    Electronic Ignition!
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    So I think I'll be taking it to a shop this week unless I can figure out the malfunction. Swapped the 92 ecm with the 91 ecm and right on start up the rpm's dropped down to around 700. Seemed to run super clean for about 10-15 seconds before developing an issue. Obviously, I still have a sensor issue as it make the engine run rough. but runs way better with the SBC ecm. Under closer inspection, the 92 ecm is a ac delco remanufactured replacement. Not sure why and it has a hypertech chip in it. This I knew. This was a running truck that I drove to the shop before removing the drivetrain for the swap. It seemed to have a miss but I chocked that up to the rig sitting for years. bad gas, bad clogged injectors, just a tune up in general. It still ran good with good power. any thoughts? thanks.

  8. #23
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    Quote Originally Posted by stew86MCSS396 View Post
    @Hopper If any of the above statements regarding fuel pressure is true, I'd be questioning if you are running the correct fuel pump. I will say with 100% certainty that your '91 350 uses the lower 8-13 psi fuel pump. You need to determine which injectors you have in your 454 TB and run the correct fuel pump accordingly.
    Have we established that you’re running the correct fuel pump? Here’s an interesting read regarding the IAC…

    http://www.gearhead-efi.com/Fuel-Inj...o-7-4-tbi-swap

  9. #24
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    Quote Originally Posted by stew86MCSS396 View Post
    @Hopper If any of the above statements regarding fuel pressure is true, I'd be questioning if you are running the correct fuel pump. I will say with 100% certainty that your '91 350 uses the lower 8-13 psi fuel pump. You need to determine which injectors you have in your 454 TB and run the correct fuel pump accordingly.
    If everything is straight off a 95 he does have the wrong fuel pump if it is still using the 91 fuel pump. At the most the 91 fuel pump will run 15 spi. The injectors used in the high pressure 454s have the same flow rate as a LB4 4.3 V6 when run at low pressure. Obviously not enough to feed the 454. Luckily a 96 Vortec pump will bolt right onto the TBI sending unit.

  10. #25
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    I have replaced the fuel pump with the mentioned vortec one. i haven't check fuel pressure but i assume with the replacement and the new fuel filter I installed. Lack of fuel isn't the problem unless the computer is having the injector spray enough. They do have a nice even flow with even spray. As I have mentioned in another post. I have no CEL. I don't know if there is a wiring issue which could be but I wonder about the computer as well. The whole computer is a factory replacement according to the sticker on it. the issues I can get passed right now is the trans is in limp mode and the aldl isn't working either. I borrowed a scan tool and it can't connect. i feel this is part of my CEl issue.

  11. #26
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    Have you made sure your ALDL plug is wired correctly? I know early trucks ran the serial data to pin E where the later PCM's ran it to pin M. I ran into this on the 7427 swap I just did where I couldn't communicate with it. Swapped the wire from E to M and it worked perfectly.
    1995 GMC K2500 SUBURBAN 2001 LB7 DURAMAX/ALLISON swap, mostly stock, tuned by me with EFILive

    1999 Tahoe 2 door 2X4, 5.7l with 0411 swap, and marine intake

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