trb108

I have a 87 chevy truck and I bought a new stock GM crate motor to replace the tired one. It has a 350 in it and came factory with the TBI.
When I put the engine in I put on the factory intake and a holley 670 cfm TBI. I have fouled 6 sets of plugs trying to get the engine to run. It floods out when cold starting, and seems to run ok at times when it finally gets hot. I have replaced all the sencors with no avail.
There is no smog on the truck, It has open exhaust and the egr is plugged.
I put a hypertech chip in it years ago. What do I need to do. I put the factory TBI back on it and it runs much better.
Thanks for any help. I was thinking of another computer of possibly finding someone to write me a chip. If no help is available i was gonna carb it and be done.

89fastlookinRS

You should try the 670 tbi with the stock injectors out of the stock tbi. Also with the egr plugged the computer is going to run really rich, so you need to have egr disabled in your prom. Also get a fuel pressure gauge to run with the 670 then you can adjust fuel pressure and know where your at. I would guess 12 psi would be a good starting point.

trb108

The egr is plugged. The only way it will run right now is a 15psi.
How do I disable the prom part
Thanks

89fastlookinRS

www.tbichips.com is a good one to use, it's best to burn your own proms but many of us can't afford it. Just tell him what you have and what you want done and he should be able to handle it. The holley unit should have an adjustable fuel pressure regulator on it. It's that cup looking deal towards the back of the unit. If it can't be adjusted I would run the 670 with stock injectors, that will lean it out from the added air flow and smaller injector flow. The holley's have 85 pph injectors while your stock ones should be 55 pph i believe.

HaulnA$$

Quote:

Also with the egr plugged the computer is going to run really rich, so you need to have egr disabled in your prom.

The computer will not make the car run rich if the EGR is plugged unless the vacuum line at the TB is left open which will cause the computer to see a large vacuum leak and add fuel to compensate. The computer will add timimg when it commands EGR function, which if not present, can cause detonation. However the computer will make the car run rich if larger than stock injectors are used such as those with the Holley TBI and the Injector constant in the prom is not changed accordingly. The computer will use the base injector pulse widths for the size injectors it thinks it has, so if larger injectors are used, the engine runs rich. Lowering the fuel pressure may not help much as it may not be able to be lowered enough. It takes a 20% pressure drop in to cause a 10% flow drop at the injectors. The Holley TBI's typically come with 2 different injector sizes, 65lb./hr (denoted by the yellow plastic under the cap) for the 2" OEM replacements, and 85lb./hr (denoted by the red plastic under the cap) for the Commander System replacements as opposed to 55lb./hr stock for the 350. If you do happen to have the 85lb./hr injectors, the engine will run REALLY rich when you use the Holley. The prom MUST be re-programmed for EGR delete and larger injectors in order for it to run even half decent. You might also check out the prom board for more information and help with chip re-programming.

Low C1500

Don't be fooled by holley::

They rate there injectors @ 22psi, gm rates theres @ 11psi. Also It has be said that the gm injectors are slighlty under-rated. The 85# holley injectors and the 55# gm 350 injectors flow the same @ equal fuel pressure. How else do u think the 670 tb's can just bolt on to a stock motor with no problems.

89fastlookinRS

Sorry, I went off of what a bunch of DIY promers told me on here a while backon the egr thing. Either way, you should get custom tuning done or run the stock injectors in the 670. It really wouldn't be a bad setup with stock injectors, the real big gain that a tbi motor needs is airflow. You'll be gaining a good amount of airflow and it'll gain alittle fuel flow as well with the stock injectors in there, because of the holley running at 15 psi. Which for the most part is more than stock.

HaulnA$$

Low C1500

Youre right. I just checked Holley's website and found out the following:

P.N : Rating:
522-81 : 32 pph @ 12 psi; 45 pph @ 21 psi
522-54 : 45 pph @ 12 psi; 65 pph @ 21 psi
522-80 : 50 pph @ 12 psi, 72 pph @ 21 psi
522-43 : 60 pph @ 12 psi; 85 pph @ 21 psi
522-83 : 65 pph @ 12 psi; 90 pph @ 21 psi

This is good info and might explain why a lot of people have a lot of trouble tuning with Holley TBI's. Since Holley always uses the higher numbers in their catalogs, if you input the published flow rate for your injector constant, you will be way off. Thanks dude!

BlackBird89-350

Now I'm a little confused, let me see if this makes any sence. From what I gather, if your using a GM injector, rated at 11lbs, can you still use your orginal fuel pump and an ajustable fuel pressure valve to make ajustments (say to 12-15psi) to increase the fuel available to your engine instead of having to use the holley and having to get a high pressure fuel pump so that they holley injectors flow like they should as they are rated at 21psi.

In other words, if I have GM 65lb injectors and want to boost the fuel flow, I can just crank up the fuel pressure from 11psi to 12-15lbs to get more fuel. But if I wanted the same 65lbs of fuel with holley, I'd have to either run the Holley 522-54 at 21psi (high pressure fuel pump) or get the holley 522-83 and run them at 12psi (stock fuel pump) to get the same 65lb injector result?

Does this make any sence???

Thanks, I'm just kinda scratching my head here....

Low C1500

The holley injectors don't need to be at higher pressure to run.

Heres a site for flow rate calcs

http://www.csgnetwork.com/fiflowcalc.html

Its been said that the GM 55# are acutally about 62# @ 12 psi, and the 65# are 72# @ 12 psi.